At NASA, hopes for a new planetary mission to Saturn had been in the works since the early 1980s. Scientists had long sought to visit the second-largest planet in the solar system, with its fascinating system of rings, numerous moons, and unique magnetic field. 11

140 Visiting Saturn 11 The Cassini Mission

s the 1980s drew to a close, the DOE Office of Special Applica- tions had its hands full with space nuclear power system work. Although assembly and testing of four GPHS-RTGs (including Aone spare) for the Galileo and Ulysses missions were complete, other projects filled the time. Ongoing assessment and development of DIPS, begun under SDI, continued on a limited basis under SEI. e SP- 100 space reactor program and TFE verification program were in the midst of ongoing development and testing. DOE also continued supporting DoD in development of a space nuclear thermal propulsion system that had begun under the auspices of SDI.

At NASA, hopes for a new planetary mission to Saturn had been in the works since the early 1980s. Scientists had long sought to visit the second-largest planet in the solar system, with its fascinating system of rings, numerous moons, and unique magnetic field. Flybys of Saturn by the RTG-powered Pioneer 11 spacecraft in 1979 and the Voyager 1 and Voyager 2 spacecraft in 1980 and 1981, respectively, provided information that further piqued that interest. Efforts to acquire a Saturn mission finally came to fruition in 1989 with the authorization of Congressional funding.

Conceived as an international partnership with the ESA and Italian Space Agency, the Cassini-Huygens mission (alternately the Cassini mission) began in 1990 and consisted of an orbiter (Cassini) and a probe (Huygens). e Cassini orbiter was designed to circle the planet and several of its moons over a four-year period. e mission of the Huygens probe was to pass through the atmosphere of Saturn’s largest moon, Titan, and briefly survey its surface during a short-lived mission that was less than one hour. With 12 instruments on the orbiter and six on the probe, the deep space planetary scouts were set up to gather an abundance of information about the planet, its ring system, and its moons.

Because Saturn is almost 10 times farther from the sun than is the Earth, it receives only approximately one percent of the sunlight per square meter as does Earth. us, solar power for the new NASA mission was never really an option—the size and weight of the panels would have made their launch unfeasible.1 erefore, NASA turned to DOE to provide

A seven-year journey to the ringed planet Saturn began with the lifto of a Titan IVB/Centaur carrying the Cassini orbiter and its attached Huygens probe. (Photo: NASA/JPL/KSC)

Photo Credit 141 Visiting Saturn The Cassini Mission

What’s In a Name Powering and Heating Mound, the effort necessitated Cassini the duplication of tooling designs, While Galileo Galilei was the rst to tooling, processing steps, and observe Saturn through a telescope With the experience gained during inspection processes that had been in 1609, limitations of the optics he assembly and testing of the GPHS- successfully used at Mound to used precluded his ability to discern RTGs and RHUs for the Galileo and fabricate flight-certified iridium the planet’s rings. Discovery of the Ulysses missions, it would seem hardware for the Galileo and planet’s rings is attributed to Dutch that repeating the effort for the Ulysses missions. Once operational, scientist Christian Huygens who, Cassini mission would be relatively but before any iridium components with the use of improved optics, straightforward. As time would were produced for mission use, the observed the ring system in 1659. tell, however, that would not be the new manufacturing processes at Huygens also discovered Titan, the case. In preparing for the planned ORNL were subjected to a rigorous planet’s largest moon. Several years 1997 Cassini launch, the DOE space review and demonstration process later, Italian French astronomer nuclear power system group faced to ensure the final product would Jean-Dominique Cassini discovered several challenges in meeting the meet the exacting requirements several additional Saturn moons as needs of NASA. Challenges came for flight-qualified hardware. well as a narrow gap that separates in the form of several firsts for its e process included a series of the ring system into two parts. The Federal contractors. For example, qualification tests and studies gap has since been known as the production of the plutonium followed by a pilot production Cassini Division.1 fuel pellets and subsequent effort to provide assurance that the encapsulation (activities that had ORNL team could reliably produce been performed at SRS for the the iridium components for use in Galileo and Ulysses missions) the Cassini RTGs.2 three GPHS-RTGs for the Cassini were transferred to LANL in 1990. spacecraft to meet its almost 900- Production of iridium cladding and Despite rigorous preparations, watt power requirement, and over frit vent components (called a clad- production of flight quality 100 small one-watt RHUs to keep vent set) in which the fuel pellet hardware wasn’t without its bumps. scientific instruments and other was encapsulated was moved from Although initial production of the equipment warm aboard Cassini Mound Laboratory to ORNL in iridium alloy components started and Huygens during their nearly 1987. Finally, DOE would usher in a in 1989, concerns eventually eight-year journey to Saturn and new transportation system to ship arose related to the metallurgical follow-on missions. the assembled GPHS-RTGs from integrity of the frit vent assemblies. Mound Laboratory to KSC e integrity of the frit vent is in Florida. critical in that it allows the helium gas produced from the decay of At ORNL, the Materials plutnonium-238 to vent from the Engineering Department began fueled clad so as to preclude the a multi-year effort to establish buildup of pressure that could the capability to produce the rupture the cladding. e concerns iridium cladding cups and frit vent resulted in a six-month shutdown assemblies. With assistance from of operations beginning in

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GPHS Fueled Clad September 1992, during which time Frit Vent the ORNL manufacturing processes and product were scrutinized “The vent technology is really pretty and reviewed. After successfully elegant...It’s what’s called a frit. You start demonstrating the rigor of out with...iridium powder. You compress the manufacturing processes, it into a tablet... and... re that at a high production resumed the following temperature to the point where some of year.3 e clad vent set production those individual grains of the power begin campaign would eventually result to fuse together... so what you end up in the production of 425 flight- with is a kind of porous media that you quality sets, over 500 weld shields can pass gas through but you can’t pass (used to protect the fuel pellet particles through... and they sandwich during welding of the iridium [the frit] between...thin layers of... iridium alloy cladding cups), and other metal... and then that assembly gets supporting hardware.4 e flight- welded together and then the whole ready hardware was subsequently assembly gets welded into a capsule.” sent to LANL, where new fuel –Tim George, LANL pellet production and encapsulation operations were being established Iridium and Tungsten to support the Cassini mission.

“Tungsten and iridium are the two Some expected difficulties came highest-melting-point metals on the as a result of the fuel pellet table of elements. The challenge that production transfer. Like any we had was to develop a metal that… good mass-production process, could contain all of the plutonium-238 the goal is to produce widgets and that would… survive both a launch that are identical. e processes pad explosion and a reentry into the by which fuel pellet production earth’s atmosphere… so we had to have operations had been performed a material that was… able to withstand at SRS had been perfected during great temperatures and was also ductile, the work to support Galileo and so when it hit the earth rather than Ulysses. If performed exactly the shatter it would … deform without same way time after time, DOE breaking. It is a very highly specialized Shield cup assemblies (top) and knew what the result would be. metal…” vent cup assemblies with its frit Such is the nature of a rigorous vent (middle) are matched after all manufacturing process. In the –Gordon Michaels, ORNL fabrication steps are completed (bottom). (Photos: ORNL)

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early 1990s, LANL was largely a Production of the heat sources and LANL preparing for production research and development facility; and heater units landed within the and encapsulation of fuel pellets, production operations were not Actinide Ceramics and Fabrication DOE awarded a contract to GE their forte. While researchers and Group of the Nuclear Materials Aerospace in 1991 for production of developers strive for consistency Technology Division at LANL. the thermoelectric generator units and repeatability, there is also Following two years of operational to be used for the Cassini mission. a tendency to experiment and preparations and one year of Although the Cassini GPHS- try to make things better. As a internal and independent readiness RTG program began under GE result, with the transfer of fuel reviews, production of LWRHUs Aerospace, changes at the corporate pellet production operations to and GPHS fueled clads began in level soon followed. In 1993, GE LANL, DOE had to ensure that the 1993. Over the course of three Aerospace was bought by Martin- production process rigor that had years, the LANL teams produced Marietta. Only two short years later, been perfected at SRS was instilled 157 LWRHUs and 216 GPHS fueled Martin-Marietta merged with the in the new fuel pellet production clads for the Cassini mission.6 Lockheed Corporation to become and encapsulation operations to be Lockheed-Martin, which carried performed at LANL.5 With ORNL on board for responsibility for the GPHS-RTGs production of iridium hardware, through the Cassini launch.7

For the GE team and its successors, the scope of work for the Cassini project was relatively straightforward—fabricate, assemble, and test two new electrically-heated thermoelectric generators (ETGs) to be fueled at Mound Laboratory and fabricate the components for a third ETG for long-term storage. Only three new electrically-heated units were needed because one ETG (E-2) and one fueled GPHS-RTG (F-5) that had been assembled as spares for the Galileo and Ulysses missions were still available for use.j In addition to production of the new ETGs, technical expertise and

GPHS plutonium oxide fuel pellets. (Photo: LANL)

j. Converter E-2 had been built and tested in 1983 to support the Galileo and Ulysses missions. Having not been used, it was stored and maintained until its use for the Cassini mission.

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support were also to be provided silicon-germanium unicouples were for the ETG converter units, one in areas such as safety assessment subjected to a rigorous review by qualification unit, and for spares. preparation, shipment of the DOE to ensure the final product Once completed, the assembled assembled RTGs to KSC, and would be ready for use in its space qualification and ETG converter integration of the assembled RTGs application. After two and one-half units were shipped to Mound for into the Cassini spacecraft. years of preparations, during which subsequent fueling and testing. several manufacturing issues had One of the major tasks facing been addressed, silicon-germanium In Ohio, workers at the Mound GE and its successors was the unicouple production was deemed Laboratory had begun receiving need to re-establish the capability ready to proceed in May 1993.7 the LANL-produced fueled clads to produce silicon-germanium in 1996.k e fueled clads were thermoelectric materials and the Over the course of the Cassini subsequently assembled into GPHS production processes for the silicon production campaign, 2,000 modules, the basic heat source germanium unicouples used in the individual silicon-germanium building block of the GPHS-RTG. GPHS-RTG. Due to the lack of a unicouples, requiring tens Mound workers assembled and follow-on mission after Galileo of thousands of individual inspected 72 GPHS modules in and Ulysses, the thermoelectric manufacturing steps, were produced all, 18 modules for each RTG. production and manufacturing processes had been shut down in the mid-1980s.7

Re-establishing the capability was not a trivial exercise—raw materials and equipment had to be identified and procured, equipment had to be installed and proper operation verified, and the workers who would be performing the manufacturing processes, as well as those who would provide for independent inspection, had to be trained and qualified. Just like fuel pellet production at LANL and iridium component production at ORNL, the manufacturing processes used to produce new

Mound technicians moving a GPHS-RTG in the vibration test cell using a crane on wheels. (Photo: Mound Museum Association) k. Following assembly and testing of the GPHS-RTGs for the Cassini mission, RTG operations performed at Mound were subsequently transferred to ANL-W, as discussed in Chapter 10, Infrastructure.

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to unfold. at task involved the Over the course of the Cassini production analysis and assessment of risks associated with the plutonium that campaign, 2,000 individual silicon-germanium was contained in the three GPHS- unicouples, requiring tens of thousands of RTGs aboard the spacecraft. individual manufacturing steps, were produced... e three GPHS-RTGs planned for use on Cassini held a combined mass of 72 pounds, or 400,000 Fueling of the E-2, E-6, and E-7 which consisted of three new 9904 curies, of plutonium oxide fuel. In ETG converter units was completed shipping packages and two new addition to the RTGs, the mission in 1996, resulting in GPHS- semi-trailers, had been transferred planned to use 117 LWRHUs, RTGs F-2, F-6, and F-7. After to Mound from its production each producing approximately one fueling, the RTGs were subjected location at Hanford in early 1997. watt of heat. e LWRHUs were to a series of tests, including With the new equipment came dispersed on both the Cassini and vibration and thermal vacuum the responsibility for operations Huygans spacecraft to keep the tests, and magnetic field and mass and maintenance. e new RTG instruments and other spacecraft properties measurements, to transportation systems would see equipment warm in space. It was determine acceptable operational their maiden voyage later that year the largest quantity of nuclear performance for the planned when the three Cassini RTGs were material ever planned for launch mission. With an average power transferred from Mound to KSC with a NASA spacecraft. As for output of approximately 296 in anticipation of an October 1997 the Cassini payload, with a mass of We (beginning of mission), the launch.9 slightly more than 12,500 pounds combined power output of the (5,670 kilograms), it was the largest three units exceeded the mission- Facing Opposition interplanetary spacecraft-probe required minimum of 826 We. NASA had planned to launch. GPHS-RTG unit F-5, which had Unlike Galileo and Ulysses, which While LANL and Mound were were ferried to space aboard the served as the spare unit for the fabricating fuel pellets and Galileo and Ulysses missions, was space shuttle, NASA planned assembling thermoelectric to use a Titan IV-B rocket and once again placed in the same converters, NASA and its capacity for the Cassini mission. Centaur upper-stage launch international partners were vehicle to lift Cassini from its Upon completion of testing in building the Cassini spacecraft early 1997, the RTGs were placed launch pad at Cape Canaveral. and Huygens probe and the 19 e Titan IV-B/Centaur rocket in storage until the time for their scientific instruments that would shipment to KSC.8 was 180 feet tall and used two be located on the deep-space large solid-fuel rocket boosters sojourners. Behind the scenes, the Shipment of the GPHS-RTGs to and a two-stage liquid-fuel agencies were heading up another core to perform its designed KSC brought a new opportunity task that would eventually take for the RTG team at Mound. A task. At launch, the system held center stage as preparations for approximately two million pounds new RTG transportation system, the Cassini mission continued

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(907,185 kilograms) of propellant.10 e safety analyses referred to upon which launch approval would Hypothetical accidents involving by Huntress in his decision were either be granted or denied by the a launch vehicle failure and other those being performed by DOE White House. e analysis and scenarios such as spacecraft re- and, eventually, the INSRP for review process utilized for Cassini entry were the focus of the safety the Cassini mission. Similar to continued a system of checks and and risk analyses performed by NASA, DOE was responsible balances, rigor, and independence DOE and NASA. to prepare a separate and more that had been used for all launches detailed Safety Analysis Report involving a nuclear power source By the summer of 1995, NASA in which the risks associated with dating back to 1961.13 had completed an evaluation accidents that could adversely of the potential environmental affect the plutonium fuel in the In keeping with the Presidential impacts associated with the RTGs were formally assessed directive14 governing the approval planned Saturn mission in its final and documented. e Cassini to launch a nuclear power system EIS.11 NASA considered several INSRP prepared an independent into space, approval authority alternatives to the planned 1997 review of the DOE Safety Analysis resided with Dr. John H. Gibbons, launch, including multi-year Report and prepared yet a third Director of the White House launch deferrals and mission evaluation that provided the basis Office of Science and Technology cancellation. However, in October 1995, the agency announced its intent to proceed with the Cassini mission as planned. In its formal decision, Wesley Huntress, Associate Administrator for Space Science, noted “I am confident that reasonable means to avoid or minimize environmental harm from the Cassini mission have been adopted; or, if not already adopted, will be adopted, upon conclusion of the safety analyses.” Following completion of a supplemental environmental evaluation prepared to reflect the results of the safety analyses, the agency stood by its earlier decision.12

Operators remove an empty 9904 shipping package from an RTG transportation system trailer during training (circa 2005). The same system was used to move the Cassini GPHS RTGs from Mound Laboratory to KSC in 1997. (Photo: INL RPS Program)

147 Visiting Saturn The Cassini Mission

Policy. After a careful review of re-entry at that speed, the ability of and DOE steadfastly continued the assessments, Gibbons noted the GPHS to contain its plutonium their own public education and that “NASA and its interagency fuel could be severely challenged. outreach efforts. ey sought to partners have done an extremely e risks and consequences of such reassure the public of the safety of thorough job of evaluating and accidents, presented by DOE and launching Cassini and its nuclear documenting the safety of the NASA, were questioned amidst the power system and assuage them Cassini mission.” Regarding skepticism and distrust.16 of all fears. At the core of their mission risk versus scientific assurance and confidence was benefit, Gibbons concluded that With this and other concerns at the the design of the plutonium heat “the important benefits of this core of the anti-Cassini sentiment, sources and the safety testing to scientific mission outweigh the local and national newsprint which they had been subjected; potential risks.”15 picked up the debate. Headlines such testing proved their ability to withstand myriad energetic accidents, including explosions, The risks and consequences of such accidents, high-velocity impacts, projectile presented by DOE and NASA, were questioned as impacts, fires, and re-entry heat. Every facet of the heat sources, skepticism and distrust ran high. from its ceramic fuel form to the iridium that encapsulated the fuel and the graphite components Not everyone was as confident in included “Critics Warn of Nuclear surrounding the clad fuel, were the safety analysis prepared for the Mayhem for NASA Launch”17 specifically designed and selected mission. For example, the “STOP and “Saturn Mission’s Use of to ensure that minimal, if any, CASSINI!” movement, initiated in Plutonium Provokes Warnings of plutonium would be released in the the mid-1990s, was one of several Danger.”18 In addition to print and event of an accident. groups that opposed the launch of other media, some groups had any nuclear material into space.16 also capitalized on the worldwide is was the message of Beverly From their perspective, the release web, the computer-based network Cook, Director of Space Nuclear of any plutonium resulting from through which information could programs in DOE. Having several any accident was unacceptable. Of be rapidly and broadly distributed. years of experience in nuclear particular concern was the planned As its users would soon discover, reactor design and safety, and use of several gravitational assist the relatively young web allowed responsibility for the safety of the maneuvers to increase the speed information to be directly Cassini mission for DOE, Cook of the spacecraft to shorten its disseminated without the filtering had an excellent grasp of the travel time to Saturn. Following or constraints imposed by other technical details pertaining to the two gravitational assists at Venus, media outlets such as newsprint, GPHS-RTG nuclear power system. the spacecraft would be traveling television, and radio.19 By 1997, she had become the de to Earth for a third gravitational facto spokesperson for DOE and assist. If a computation error or As anti-Cassini and anti-nuclear NASA on the topic of nuclear other mishap led to inadvertent sentiment continued in the months safety as it pertained to the Cassini leading up to the launch, NASA

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mission. She had a knack for Against the backdrop of protests, use of space nuclear power systems conveying technical information NASA and DOE continued their and for gaining the attention using every-day concepts and, as work for a safe and successful of members of Congress, who a mother who planned to have her launch while the anti-Cassini subsequently sought additional daughter observe the launch, she protestors fought to keep that analysis from NASA and DOE.16 could connect with the public on a day from coming. On October 3, personal level. rough interviews, 1997, Gibbons granted approval In the years following the Cassini communication forums, and for the Cassini launch. Mission launch, DOE embarked on a safety airtime on the likes of CNN, Good proponents were elated. Although improvement program whereby Morning America, and C-Span, the anti-Cassini campaign had the GPHS aeroshell design was Cook, along with others from the failed to stop the launch, their modified to improve its overall agencies, sought to educate and efforts were later credited by some strength and survivability against remove the fear of the unknown.5 for getting NASA to reconsider its more-severe impact and re-entry

Artist’s concept of Cassini spacecraft, showing one of its three RTGs, as it passes by Saturn. (Image: NASA)

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events. e program resulted in altitude of 727 miles and received a As for the three GPHS-RTGs development of a Step-1 design, gravity assist that boosted it onward aboard the Cassini spacecraft – which was subsequently used in to Jupiter at a speed of 42,000 miles they performed splendidly. ey the Pluto-New Horizons mission per hour, where it would receive its have provided a consistent, steady launched in 2006 (discussed in final assist on its way to Saturn.21 source of power to the instruments Chapter 12). A Step-2 design, and other systems and are expected which further increased the At the end of its seven-year to continue to do so as long as the survivability of the aeroshell against journey through space, the Cassini Cassini mission continues. impact and re-entry, was used in spacecraft entered orbit at Saturn the multi-mission radioisotope on July 1, 2004. As of July 2014, the thermoelectric generator spacecraft had returned hundreds (MMRTG), which was launched of gigabytes of scientific data from aboard the MSL in 2011 (discussed which over 3,000 scientific reports in Chapter 13). In both cases, were written. Over 300,000 images the quantity of ablative material of the Saturn system had been (i.e., FWPF) for the aeroshell was taken during over 200 orbits. Over increased.20 130 close flybys of Saturn’s moons were completed, and seven new Saturn at Last moons were discovered. Among its countless accomplishments On October 15, 1997, the Cassini- were the first complete view of the Huygens spacecraft was launched hexagon-shaped north pole, the at 4:43 a.m. Eastern Daylight Time discovery of giant hurricanes at against a black backdrop of the both of Saturn’s poles, and intensive early morning sky. e ground lit study of the planet’s ring system. up like daytime as the Titan rocket As for the ESA/Italian Space lifted the spacecraft to begin its Agency Huygens probe, it was the seven-year, 2.2 billion-mile journey first man-made object to land on to Saturn. e launch went off a moon (Titan) in the outer solar as planned, and there were no system, having provided data and explosions or other problems. images during its descent and short 30-minute battery-powered life. After traveling to Venus, where it With three years remaining in its received two gravitational assists, final mission, time will tell what additional discoveries Cassini will the Cassini-Huygens spacecraft 22 was on a trajectory that returned make. it near Earth. On August 17, 1999, the spacecraft passed Earth at an

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Saturn and its rings. Images such as this are possible by the electrical power provided by RTGs. (Photo: NASA)

151 After years of sending mechanical ambassadors to neighboring planets and the far reaches of the solar system, Pluto remained a distant, icy, and largely unknown orb.

152 To Pluto and Beyond 12 New Horizons

fter years of sending mechanical ambassadors to neighboring planets and the far reaches of the solar system, Pluto remained a distant, icy, and largely unknown orb. Although missions to the distant body had often been envisioned, none had ever become a A 1, 2 reality. However, that would soon change.

Planning the Trip

In January 2001, NASA issued an Announcement of Opportunity in which proposals were solicited for a mission to Pluto and the neighboring Kuiper belt, a large band of icy objects that includes Pluto. e primary goals of the mission focused on the geology, morphology, and surface composition of Pluto and its largest moon, Charon. e mission also sought to study the Plutonian atmosphere due to the possibility of its freezing as Pluto continued to move further from the sun during its 248- year orbit.1

e following months were filled with proposal development and a downselect process, after which only two proposals would have their mission concepts refined. In November 2001, the evaluation process concluded when NASA selected the New Horizons proposal for its Pluto mission. Dr. S. Alan Stern of the Southwest Research Institute served as principle investigator for the mission in partnership with the Applied Physics Laboratory of Johns Hopkins University and others. e mission name, New Horizons, symbolized the new scientific horizons of exploring Pluto and the Kuiper belt, and the new programmatic horizon of having an outer-planet mission led by a principle investigator rather than a Federal agency.1 As the project unfolded, New Horizons would take on an even broader meaning for the larger project team. With a $500 million contract and a launch date of January 2006, the groundwork was laid to finally reach Pluto and the Kuiper belt, one of the highest-priority solar-system-exploration missions identified by the broader planetary science community.3

Artist’s concept of Pluto and its moon Charon. (Image: NASA.gov)

Photo Credit 153 To Pluto and Beyond New Horizons

e space probe designed for the comedy series from the 1950s, and the spacecraft approached its historic journey to Pluto was built LORRI and REX, each instrument target.4 e instruments and the by the Applied Physics Laboratory brought a unique capability to the data-transmission systems that and designed to carry a suite of mission. Alice was designed to would someday send images back seven scientific instruments. e gather data on the composition to Earth needed power from a instruments themselves were of the atmosphere. Ralph would source other than solar due to the designed and built by Stern and map surface compositions of the immense distance from the sun. others. With names like “Alice” Pluto-Charon system. LORRI, a at power would be provided by a and “Ralph,” reminiscent of the long-range imaging device, would GPHS-RTG, the same technology Kramdens of e Honeymooners take pictures of the surface as that had been successfully used on several previous NASA missions.

An RTG Fast-Track

As in the past, the RTG would be assembled, tested, and delivered by DOE and its contractors. e generator would be built by Lockheed-Martin at its facilities near Valley Forge, Pennsylvania, and LANL would provide the encapsulated fuel. ORNL would provide materials expertise. SNL would later support the safety analysis prepared by Lockheed- Martin. RTG assembly and testing, historically performed at Mound, would take place at ANL-W, its first such effort since receiving the mission in 2002.

With New Horizons planned to launch in January 2006, DOE and its new ANL-W team, under the leadership of Stephen Johnson, had three years to fuel, test, and

Artist’s concept of the New Horizons spacecraft and science instruments. The GPHS-RTG, shown in the left side of the image, is mechanically attached to the spacecraft. (Image: NASA)

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deliver an RTG. Under normal To support the move, DOE had unique construction challenges, circumstances, such a schedule set an aggressive schedule to particularly when pouring concrete would have been considered have everything out of Mound in sub freezing temperatures. While manageable. But three years to by the end of September 2003. construction crews use special relocate a program (following its On the other end of the move, means to keep equipment from transfer from Mound in 2002), it was decided that the new freezing and ensure proper concrete including the construction of a ANL-W RTG facility needed to curing, sometimes things can still new facility and standing-up a be operational by the middle of go awry. Johnson recalled one new operation, was a tall order. 2004 to allow sufficient time to such episode: ere was little, if any, room for assemble and test the GPHS-RTG errors. Such a move would require for New Horizons. With teams “Our first day pouring concrete… more than a can-do attitude. It in place, expectations defined, started on a Saturday and it was necessitated a will-do attitude in and a schedule before them, the about 9 degrees outside…We had the which failure was not considered real work began in January 2003. forms up. We had tubing running an option. And that’s the attitude Between January and September through it outside the forms and we that DOE and Johnson brought to 2003, 28 semi-trailers carrying had vibrational thumpers so that the table. over 300 tons of equipment we could pour the concrete without was transferred from Mound to it freezing. But the pneumatic lines Johnson realized early on that Idaho. At the same time, Merrick to the thumpers actually froze first. the chances for project success Engineering and other members And we were pouring I think 10 or could be greatly improved with of Johnson’s team worked on the 12 cement trucks of concrete that the help of Mound workers who design for the RTG facility. day and we did that for quite a few had hands-on RTG experience. days and it was a challenge. I always After much discussion and A Building Takes Shape think of that experience when people negotiation, eight Mound workers say, we can’t get that done. We only agreed to hire on with Johnson e ANL-W RTG facility ended up have this amount of time. I’m like, and help with the move. By the being a 10,000-square foot annex you know, you can get just about time the RTG was assembled anything done if you’re organized to an existing building. e facility 6 three years later, only one of the was designed to withstand the and you don’t give up.” workers remained with the Idaho hazards posed by extreme winds, team; however, their dedication earthquakes, and other natural e design and construction crews and contribution to the success events, thereby providing maximum were as dedicated as the men to the relocation effort, and the protection for the valuable space and women who moved the RTG RPS program as a whole, was batteries that would eventually be operation. Construction of the considered invaluable. It was assembled and stored in the facility.5 Space and Security Power Systems that kind of dedication that had Excavation and construction of the Facility (SSPSF), as it would later be permeated the DOE RPS program building foundation were completed called, was completed in July 2004 and their customer at NASA for between August and November in a period of approximately 13 decades and would continue to 2003. Facility construction began months and at a cost of slightly less prevail in the years to come. in January 2004, in the middle of than $5 million. the Idaho winter, which can pose

155 To Pluto and Beyond New Horizons

While facility construction had ever assembled or handled each containing four fueled clads. was progressing, other project an RTG, were trained, and the e fueled clad consists of the activities were focused on ensuring newly installed equipment was plutonium oxide fuel pellets, clad the people and paper were tested to ensure proper operation. in iridium metal. Of the 72 fueled ready for eventual operations. Following a thorough review of the clads needed for the RTG, 20 new Procedures were written to provide facility, equipment, personnel, and ones were provided by LANL. instructions for all aspects of procedures by DOE, ANL-W got Safety and security issues at the operations, such as ventilation the green light from DOE to begin LANL site during 2004 resulted systems, glovebox atmospheres, operations in October 2004. in a prolonged shutdown of and RTG assembly and testing. operations, precluding their ability e procedures were validated, Repurposing an RTG to provide the full complement of a process by which the entire heat sources. Fortunately, DOE procedure is performed step-by- didn’t have to look far to find 52 e New Horizons mission called 6,7 step but without nuclear material, for a single GPHS-RTG, the same other fueled clads. to ensure that RTG assembly and power system that had been testing was done right the first used on the Cassini, Ulysses, and Back in 2002, when DOE relocated time. Operators, quality assurance Galileo missions. e GPHS-RTG its heat source material from staff, and engineers, none of whom utilized 18 heat source modules, Mound in the wake of anticipated security upgrades, one of the items transferred to ANL-W was a fueled GPHS-RTG. e RTG, referred to as F-5, was assembled in the mid- 1980s and served as a spare unit for the Galileo, Ulysses, and Cassini missions. While never used, DOE continued to maintain the flight- qualified status of the power system, keeping it for a time when its use might be needed. at day had finally arrived.8

Use of the heat sources from the F-5 generator posed some unique, but not insurmountable, challenges to the builders of the New Horizons RTG. First, because the plutonium oxide fuel in F-5 was approximately 20 years old, it had lower thermal

Equipment set up to pour concrete for the walls of the new SSPSF. (Photo: INL RPS Program)

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wattage per mass of fuel than the RTG were based on the original NASA Mission new fuel present in the LANL design, referred to as Step-0. GPHS-RTGs fueled clads. To ensure the New The GPHS-RTGs that have been Horizons RTG would meet mission Because the modules had since assembled and own on NASA power requirements, engineers been redesigned to improve their missions are:9 had to determine and then select ability to withstand re-entry the F-5 heat sources with the heating in the event of a high- Galileo: F-1, F-4 highest thermal wattage for use altitude accident, the older Step-0 with the new heat sources that modules would not be used in the Ulysses F-3 been supplied by LANL. Second, New Horizons RTG. Consequently, Cassini F-2, F-6, F-7 the GPHS modules used in the F-5 the F-5 unit was disassembled in an inert chamber in SSPSF in Spare F-5 May 2005 to recover the fueled (subsequently GPHS modules. Once recovered, disassembled the modules were disassembled to for New Horizons) remove the graphite impact shells containing the clad plutonium New Horizons F-8 oxide fuel pellets. e graphite impact shells containing the fueled clads were then assembled into new Step-1 GPHS modules for use assembled into the F-8 converter in a new GPHS-RTG generator assembly. (later named F-8).8 By early September 2005, assembly e unfueled RTG power converter of F-8 had been completed, assembly, which was fabricated and marking the eighth flight-qualified tested by Lockheed-Martin Space GPHS-RTG built by DOE and the Power Group, was received by the first RTG assembled in Idaho. e Idaho team in June 2005. e new RTG was assembled using five fueled clads had been shipped from GPHS modules containing new Ribbon-cutting at the newly-completed LANL earlier in the year. Assembly fuel and 13 modules containing Space and Security Power Systems of the GPHS modules occurred fuel from F-5. e 18 combined Facility. Pictured from left to right are in an inert argon atmosphere in modules contained 24 pounds (11 John Sackett, Associate Laboratory the Module Assembly Glovebox. kilograms) of plutonium oxide fuel Director for ANL-W; William Magwood, Following assembly, the modules and had a thermal power of almost DOE Assistant Secretary for the Oce were transferred to the Inert 4,000 watts. e RTG was expected of Nuclear Energy, Science, and Atmosphere Assembly Chamber, to deliver approximately 200 We Technology; Kyle McSlarrow, DOE where they were stacked and by the time the New Horizons Deputy Secretary; and Congressman Mike Simpson, Idaho. (Photo: INL RPS Program)

157 To Pluto and Beyond New Horizons

was unusually compressed and had By early September 2005, assembly of F-8 to be completed in less than two- and-one-half years. From the safety had been completed, marking the eighth flight perspective, the New Horizons qualified GPHS-RTG built by DOE and the first RTG INSRP raised questions about the integrity of the GPHS fuel pellets assembled in Idaho. after being encapsulated for 20 years. In response, Lyle Rutger (the DOE Nuclear Launch Safety program manager) pointed to the spacecraft reached Pluto, exceeding To Pluto via Florida rigorous safety testing under which the minimum mission power the GPHS components had been requirement of 191 We. Other Following assembly and testing subjected and a detailed inspection mission requirements such as RTG of F-8, the RTG was transported process that the fueled clads mass were also met or exceeded. to the RTG facility at KSC. e had been subjected to following RTG was subsequently subjected their removal from the original Following assembly, F-8 was to a hot-fit check during which it RTG qualification unit. After subjected to a variety of tests to was fully integrated with the New thorough analyses, evaluation, and ensure it would properly operate Horizons spacecraft, just as it discussions, the Office of Science in space. Mass properties testing would be in space, to ensure that and Technology Policy eventually determined the RTG center of all systems checked out acceptably. granted approval for Pluto-New gravity, which was used by NASA Following successful completion Horizons to launch with the in their planning for control of the of the hot-fit check, the RTG F-8 generator. spacecraft once in space. ermal was returned to storage at KSC vacuum testing determined the where it awaited the day of its final Conversely, NASA was addressing RTG power performance in a integration with the spacecraft. concerns with the rocket propellant high-vacuum condition, similar tank on the New Horizons launch to the environment in space. As with previous missions that vehicle. A qualification tank similar Vibration testing was performed used a nuclear power source, New to the one on the launch vehicle had using a shaker table to subject the Horizons was subjected to rigorous failed during testing in September RTG to forces similar to those nuclear safety assessments that 2005, just months before the associated with launch. Radiation included an EIS required by the planned launch date. With the measurements and radiography National Environmental Policy Act, mission potentially at stake, of the assembled RTG were also and a safety analysis report and NASA performed a comprehensive performed. Testing of the RTG safety evaluation report prepared review, investigation, and was successfully completed by for the Presidential Nuclear Launch evaluation that, along with the the end of October. All assembly 10 Approval Process. e assessments technical input and experience of and testing operations were served to ensure that accidents and many involved in the program, led reviewed by DOE, and F-8 was consequences had been adequately to the decision to proceed with the finally accepted for flight use in 11 evaluated and analyzed. However, launch during the planned January December 2005.5 the launch approval process for 2006 launch window.12 the Pluto-New Horizons mission

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transferred RTG operations from Mound to the new SSPSF, and assembled and tested their first RTG in Idaho. And another RTG- powered spacecraft was on its way to deep space.

The F-8 GPHS-RTG during assembly in the Inert Atmosphere Assembly Chamber. (Photo: INL)

Just days before the planned launch finally begun its 10-year journey date of January 17, the RTG was to Pluto. moved to the Vertical Integration Facility at Cape Canaveral Air For everyone involved, there was Force Station, Florida, where it was an indescribable feeling of awe and integrated with the New Horizons a deep sense of accomplishment spacecraft for the final time. On as the rocket arched ever-higher January 19, 2006, at 2 p.m. Eastern over the Atlantic Ocean. NASA Standard Time, a Lockheed-Martin had overcome several hurdles, Atlas V 551 launch vehicle lifted off including questions about the from Space Launch Complex 41 at structural integrity of a fuel tank.l Cape Canaveral Air Force Station. e DOE team had built a new e New Horizons spacecraft had RTG assembly and test facility, l. e decision process undertaken by NASA that led to acceptance of the fuel tank for the New Horizons mission provides an excellent example of balancing an equipment qualification process founded upon thorough technical investigation, evaluation, and review, with the application of sound engineering judgment.

159 To Pluto and Beyond New Horizons

Asteroid 5886 Rutger

Asteroid 5886 Rutger (formerly 1975 LR) was named after Lyle Rutger in recognition of his role as the DOE Nuclear Launch Approval program manager for the Pluto- New Horizons mission. The name was given by Dr. Alan Stern of the Southwest Research Institute, and principle investigator for the New Horizons mission.

The New Horizons spacecraft launches from Complex 41 at Cape Canaveral Air Force Station on January 19, 2006. (Photo: NASA.gov)

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161 ...the new MSL rover represented a significant leap in exploration capability on another world.

162 Roving Mars 13 Return to the Red Planet

ith the announcement of its intent to continue an ongoing Mars Exploration Program and the launch of the Mars rovers Spirit and Opportunity, 2003 gave birth to a new chapter in Wthe decades-old exploration effort of the red planet. Explora- tion of Mars dates back to the 1960s, when the first Mariner fly-bys re- turned images of a moon-like surface, likely disappointing to those who had hoped for an Earth-like environment teeming with life. Exploration contin- ued in the 1970s. e successful touchdown of the Viking 1 and Viking 2 or- biter-landers in 1976, planned to coincide with the Bicentennial celebration of the nation, continued the quest to learn more about this distant cousin of Earth. e multi-year life of those first man-made robotic explorers to set foot on the Martian surface was sustained through the use of the SNAP-19 RTG. Nearly 30 years later, the SNAP-19 technology would beget a new RPS to sustain the next generation of robotic explorers on Mars.1,2

A New Mission to Mars

In March 2004, NASA announced its intent to solicit proposals for instrumentation and science investigations to be part of Mars Science Laboratory (MSL), a mission planned for launch in 2009. Later that year, the eight proposals that had been selected to be part of the rover-based mobile laboratory were announced. e suite of scientific capabilities included high-tech cameras to collect pictures of the planet while on the surface (as well as during spacecraft descent and landing) x-ray spectrometer and fluorescence instruments for chemical analysis of rock and soil samples, and instruments to analyze the makeup of the Mars atmosphere. With instruments and investigators from organizations like the Russian Federal Space Agency, the Spanish Ministry of Education and Science, and the Canadian Space Agency, MSL was a melting pot of scientific capability reflecting ongoing partnerships among international space organizations.3,4

In addition to the broad suite of investigative capabilities that would make up MSL, the planned rover would be the largest NASA ever landed on a planet. Significantly larger than the small rover Sojourner, which landed on Mars on July 4, 1997, and four times larger than the Mars exploration

NASA’s Mars exploration rover Opportunity caught its own silhouette in this late- afternoon image taken by the rover’s rear hazard avoidance camera. (Photo: NASA/ JPL-Caltech)

Photo Credit 163 Roving Mars Return to the Red Planet

rovers Spirit and Opportunity, would also allow operation of which landed on January 4, systems, instrumentation, and 2004 and January 25, 2004, science investigations day and respectively, the new MSL rover night, thereby avoiding downtimes represented a significant leap in when the sun wasn’t shining, and exploration capability on another offering the use of reject heat for world. Although solar power was thermal control. e preference for considered for the MSL mission, an RPS culminated in the MMRTG nuclear-based power would allow that had been under development the fullest set of mission objectives by DOE since June 2003.5 to be met, including the maximum latitudinal range over which the Multi-purposing an RPS MSL could be landed. An RPS A MMRTG concept under consideration by DOE and NASA was confirmed in 2001 when the two agencies convened a joint agency team to ensure the convergence of RPS supply and demand for missions in the 2004 to 2011 timeframe. e team, led by John Casani of NASA, was tasked to provide a provisioning strategy to guide RPS-related decisions and support integrated planning between the agencies.6

Front and center is the ight spare for the rst Mars rover, Sojourner, which landed on Mars in 1997 as part of the Mars Pathnder Project. On the left is a Mars exploration rover project test rover that is a working sibling to Spirit and Opportunity, which landed on Mars in 2004. On the right is an MSL test rover the size of that project’s Mars rover, Curiosity, which landed on Mars in August 2012. (Photo: NASA/JPL- Caltech)

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e joint agency effort continued Was production capability available Faster, Better, Cheaper the practice of cooperation in for various RPS components? With Under the leadership of Daniel matters involving space-based termination of silicon-germanium Goldin, NASA Administrator from RPS development and supply thermoelectric production 1992-2001, NASA began an initiative that was embodied in the 1991 following the Cassini mission, centered on doing things faster, Memorandum of Understanding the RPS program faced a finite better, and cheaper. The initiative in which the authorities and inventory of some materials unless was part of an aggressive e ort to responsibilities for each agency had production was restarted. address perceptions that the agency been formally defined.7 was bureaucratically bloated and In a pre-decisional report, the in pursuit of missions that were In the process of developing a team recommended development too expensive, took too long to strategy, a small set of questions of an RPS capable of operating in develop, and ew too infrequently. were deemed fundamental to both the vacuum of deep space Workforce reductions, increased establishing a framework for future and in a planetary atmosphere, productivity, and reduced costs planning—would potential missions such as on the surface of Mars. e ensued. Relative to space missions, operate in the vacuum of space or team also recommended a two- spacecraft became smaller, with in a planetary atmosphere or both? path development strategy with a lower power needs; gone were the How much electrical power would Stirling convertor (already under days of MHW missions like Voyager the potential missions require? development at the time) and a and Galileo. The initiative provided While the GPHS-RTG supplied new MMRTG as its foundation. an impetus for DOE and NASA to a large amount of power (greater Development of a new RTG was pursue development of a Stirling than 300 We) in the vacuum of put forward to serve as a hedge radioisotope generator and the space during the most recent against the technical immaturity MMRTG. space exploration missions, lower of the Stirling technology at the power levels were anticipated for time. Embodied in the strategy future missions. e maturity and recommendations, and the level of various RPS technologies, underlying evaluation, was a stretched back to the SNAP-19 important to deliverability and comprehensive snapshot of the RTG. With a proven track record of the safety- and launch-approval state of RPS development for use RTG operation in the atmosphere processes, also required careful by decision-makers from both of Mars and the vacuum of consideration. agencies. space, Teledyne’s experience was instrumental in creation of the new How much plutonium-238 would An MMRTG Takes Shape multi-purpose RTG.8,9,10,11 be available? Domestic production of the heat source isotope had Development of the new RTG As development of the new RTG stopped with the shutdown of SRS began in 2003 when DOE awarded progressed, it was only a matter of production reactors in the early a contract to the Rocketdyne time before it was connected to a 1990s, and the finite domestic division of Boeing. Rocketdyne NASA mission. at connection inventory of the heat source had partnered with TES, whose occurred in 2004 when DOE and material was being augmented with thermoelectric experience NASA linked the generator to the a finite supply from Russia. upcoming Mars rover mission

165 Roving Mars Return to the Red Planet

via a supplement to the 1991 system integrator for MMRTG as intended. e engineering unit Memorandum of Understanding development activities. Fabrication was subjected to a full battery of between the agencies.12 of the power conversion system performance and environmental and the lead telluride-TAGS tests. As design and development e ensuing years were filled thermoelectrics took place at progressed, a qualification unit with design, engineering, Teledyne facilities in Hunt Valley, was then built to test the new fabrication, and testing activities Maryland. e initial design gave RTG under thermal conditions as the Rocketdyne-Teledyne birth to an engineering unit that similar to those that would be team transformed concept into was used to check every part of experienced once the unit was product. Mission requirements the new power system for proper fueled with a nuclear heat source. and limitations, such as power fit, function, and operation. Due to schedule constraints and levels, weights, and heat loads, Like a master watchmaker, the limited availability of fueled clads, were translated into an initial Rocketdyne-Teledyne team the qualification unit was never MMRTG design. From their brought the various pieces and fueled but was fully tested as an facilities in Canoga Park, components together to ensure the electrically-heated unit, and was California, Rocketdyne served as assembled product would operate also used by the JPL for integration and testing exercises with the rover. Finally, the first of two flight units, F1, was built and prepared for shipment to INL, where it would be fueled and run through another battery of tests.

In designing an RTG that can operate in a planetary atmosphere, designers must consider the possibility of adverse reactions between compounds in the atmosphere and the thermoelectric materials. ermoelectrics undergo a steady, but small and predictable, degradation in their conversion efficiency over their operating life. Such degradation is taken into account by power system designers to ensure adequate power levels will be available for the life of the mission. However, the reaction The MMRTG shown with its eight GPHS modules, thermocouples, housing, and heat rejection ns. (Image: INL RPS Program)

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equipment and the tanks that Like a master watchmaker, the Rocketdyne- held the hydrazine propellant for the spacecraft. Overheating of Teledyne team brought the various pieces and filled hydrazine tanks creates an explosion hazard. To address the components together to ensure the assembled concern, JPL engineers devised product would operate as intended. a simple set of jumper tube assemblies that mated the cooling tubes on the MMRTG housing to a of thermoelectric materials with 120 watts was converted to useable chiller system located outside the atmospheric compounds, such electricity. e residual unused launch vehicle, thereby providing as oxygen or the carbon dioxide heat had to be properly managed to a means to remove heat from the present in the atmosphere of Mars, ensure long-term efficient operation MMRTG following its integration can accelerate that degradation. To of the RTG and the surrounding with the rover. When integration avoid this problem in the MMRTG, spacecraft. rough the use of a of the cruise-stage system was the thermoelectric modules were heat rejection system, designers complete, the temporary jumpers located in a completely sealed employed various methods to were disconnected. While seemingly enclosure that was filled with dissipate the excess heat during all simple, the installation, operation, argon gas prior to closure. e phases of the mission, including and removal of the jumper tubes inert argon gas wouldn’t react with cruise, entry/descent/landing, required the coordination of the thermoelectric components and surface operations on Mars. personnel from at least nine and because the thermoelectric In addition, a heat exchanger on separate organizations. at modules were completely sealed, the rover was located to partially close-knit coordination was but they were isolated from any cover the MMRTG, capture some a microcosm of the coordination interaction with the atmosphere of its excess heat, and route the required among the multiple of Mars.13 heat through a fluid loop to provide organizations involved with the for thermal management of rover multitude of tasks associated with 14, 15 In addition to materials and hardware during operation on Mars. the MSL mission. chemistry challenges, engineers faced thermal challenges when A cruise-stage heat rejection As development of the MMRTG designing an RPS. Given the system also provided for heat proceeded under the Rocketdyne- relatively low efficiency (

167 Roving Mars Return to the Red Planet

Evolution of the GPHS plutonium-238 fuel pellets had approval of the MSL and its nuclear Module been prepared and readied for power source. e process included encapsulation. Assembled fueled evaluation of the new Step-2 GPHS The module identied as Current clads were shipped from LANL to aeroshell design that was to be was Step-0, the rst-generation INL where they were assembled showcased in the MMRTG. e design used in the Galileo, Ulysses, into GPHS modules, the building MSL mission would also mark and Cassini missions. Following the blocks of the MMRTG heat source. the first time that SNL was solely launch of Cassini, DOE undertook responsible for producing a Safety a two-phase e ort to enhance At SNL in New Mexico, a DOE Analysis Report for a space nuclear the GPHS aeroshell relative to safety assessment team began an mission. e SNL launch safety postulated launch and re-entry assembly process of a different team was first assembled in late accidents. In the Step-1 module sort—the thorough and exhaustive 2005 and had to produce a full used in Pluto-New Horizons, the process of preparing the analyses and comprehensive assessment by graphite impact shell openings and reports that would ultimately late 2008 to support a Fall 2009 are separated by 0.1 inch and the provide the basis for launch launch.5, 16, 17, 18, 19 openings are fully encased in the aeroshell material. In the Step-2 design, the module is lengthened 0.2 inches in the vertical direction. Each change also resulted in a small increase in module weight (Step-0 was 3.1 pounds [1.4 Step-0 (Galileo, Ulysses, Cassini) kilograms]; Step-1 was 3.3 pounds [1.5 kilograms]; Step-2 is 3.5 pounds [1.6 kilograms]). Because Insulation 0.185 CBCF of the increased length, 2.09 Aeroshell Step-1 (Pluto New Horizons) the Step-2 design Graphite could not be used in impact shell the GPHS-RTG without Insulation signicant changes to Fuel capsule 0.185 CBCF Step-2 the convertor and 2.09 Aeroshell Current (MSL) heat source structural Graphite support system therein. impact shell (Image: INL RPS Program) 0.100 Insulation Fuel capsule 0.285 CBCF 2.29 Aeroshell Graphite impact shell 0.100 *All dimensions Fuel capsule are in inches

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Assembly, Testing, including weight and center of As DOE and its contractors and Bumps gravity, were determined for use continued down the path to deliver with similar properties for the the MMRTG for the planned 2009 e first MMRTG flight unit, F1, spacecraft. launch, NASA found itself hitting was received at INL in August 2008. some technical bumps along By the end of October of that year, By May 2009, all testing had been its path to Mars. By early 2008, INL engineers, quality inspectors, successfully completed. e problems with the material to be and technicians fueled the new six-year development and testing used for the heat shield had been generator. Fueling of the generator effort marked the first time in identified during testing.20 was performed in the Inert almost 20 years that an RTG had In the months that followed, other Atmosphere Assembly Chamber been taken from concept to flight technical challenges continued at the SSPSF, where the Step-2 unit, the last time being the to arise, and the viability of the GPHS modules were assembled GPHS-RTG. As the new power planned 2009 launch date became into a stack of eight and then placed system for NASA missions increasingly questionable.21 In inside the generator housing. Once requiring power beyond the December 2008, NASA finally fueled, the housing was closed and capabilities afforded by solar or postponed the MSL launch to the MMRTG was prepared for its chemical, the assembled MMRTG the next available window, which next round of testing. weighed approximately 99 pounds would occur in late 2011. “We (45 kilograms) and measured will not lessen our standards for In the months that followed, the 1.9 feet (0.6 meters) long and testing the mission’s complex fueled MMRTG was subjected to 1.9 feet (0.6 meters) wide at the flight systems, so we are choosing the normal suite of tests to ensure cooling fin tips. At its heart, the the more responsible option of the unit was ready for operation eight GPHS modules contained changing the launch date,” noted in space and on the surface of approximately 11 pounds Doug McCuistion, director of Mars. A shaker table simulated (5 kilograms) of plutonium oxide the Mars Exploration Program at conditions, such as vibration, fuel. e plutonium oxide from NASA Headquarters.22 In making that would be experienced during which the fuel pellets were the postponement decision, NASA launch and passage through processed had been purchased had taken the technical high the atmospheres of Earth and from Russia, making the MMRTG ground and kept its eyes on the Mars. Inside a thermal vacuum the first DOE RPS to be fueled Mars prize. chamber, the electrical output of entirely of non-domestic material. the unit was monitored to verify e power conversion system acceptable performance in vacuum utilized 768 lead-telluride/TAGS conditions that mimicked those thermocouples to convert the of outer space. e magnetic and 2,000 watts of thermal power into radiation fields associated with the approximately 110 watts of MMRTG, important to the NASA useable electricity.11 engineers designing the spacecraft electrical and data systems, were also mapped. Mass properties,

169 Roving Mars Return to the Red Planet

MMRTG assembly inside the SSPSF Inert Atmosphere Assembly Chamber. Clockwise beginning at top left: 1) Fueled GPHS modules being stacked. 2) The stack of eight GPHS modules ready for installation in the MMRTG housing. 3) The heated GPHS modules glow red inside the insulated MMRTG housing. 4) MMRTG assembly complete. (Photo: INL RPS Program)

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A Journey Begins until it was ready for transfer to adjustments to the rover KSC. roughout the testing, one power budget.23 With a revised schedule and unexpected performance condition funding in place, the spacecraft arose. In late 2009, the measured After two years of storage and and rover Curiosity (and the power output of the MMRTG monitoring, a small team of INL science instrument and launch was found to be less than power workers, along with a cadre of vehicle) were made mission-ready predictions that had been made security personnel, accompanied during the following two years. prior to fueling of the unit. Upon the MMRTG on its 2,500-mile At INL, the MMRTG was placed investigation, the discrepancy (4,000 km) voyage to KSC in June in a storage configuration to was determined to be caused by 2011, five months ahead of the preserve the unit and minimize an error in a computer model MSL launch date. After safely degradation of its thermoelectric that was developed to predict arriving at KSC, the precious elements, and engineers continued MMRTG power performance. cargo was moved into the RTG monitoring the electrical output Although the error was remedied, Facility, which would be its home and other conditions of the unit the slightly lower power output of until launch. the MMRTG did necessitate some During the second half of 2011, DOE and its contractors continued to maintain a watchful eye over the MMRTG as NASA completed their preparations for MSL launch. In one of the final activities to ensure the MMRTG was ready, it was connected to and fully integrated with the rover Curiosity. In one final hot-fit check, the rover and generator were run through a series of tests to ensure the electrical output and heat rejection system operated properly. It would be the last such test until November, when the MMRTG was relocated to the KSC Vertical Integration Facility, where it would be connected to the rover for the last time in preparation for launch. MMRTG being integrated to the Curiosity rover for testing in the Payload Hazardous Servicing Facility at KSC. (Photo: NASA)

171 Roving Mars Return to the Red Planet

On November 26, 2011, seven- and-a-half years after the MSL On November 26, 2011, seven-and-a-half years was announced, an Atlas V 551 rocket lifted off from Space Launch after the MSL was announced, an Atlas V 551 Complex 41 at Cape Canaveral rocket lifted off from Space Launch Complex 41 at Air Force Station. While many watched from a designated viewing Cape Canaveral Air Force Station. location at KSC, many others simply lined the byways and highways around KSC and Cape Canaveral to catch a glimpse of the continuous status of the launch via On August 5, 2012, many of the launch. At liftoff, a white cloud of the internet, allowing listeners to same individuals who had gathered steam erupted beneath the launch catch each phase of progress. MSL to watch the launch gathered again vehicle and the vehicle slowly had begun its eight-and-one-half to witness the landing of MSL. rose above the pad. As seconds month journey to Mars. In its “Seven Minutes of Terror” became minutes, NASA provided animated video, NASA/JPL provided a blazing description of the end of the voyage as the spacecraft ripped through the Mars atmosphere. With a seven-minute delay between the landing of Curiosity on Mars and receipt of the radio signal from the Mars Orbiter, people everywhere anxiously awaited for the first indication of success. e words announced by NASA/JPL commentator Al Chen, “Touchdown confirmed. We’re safe on Mars,” led to an eruption of cheers and hugs, not only in the offices of NASA and JPL but across the country. With the safe landing of Curiosity and the generation of images that shortly followed, American pride beamed as MSL began its new journey on Mars.

NASA’s MSL spacecraft, sealed inside its payload fairing atop a United Launch Alliance Atlas V rocket, clears the tower at Space Launch Complex 41 at Cape Canaveral Air Force Station in Florida. The spacecraft’s payload included the car-sized rover, Curiosity. (Photo: United Launch Alliance)

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During the months that followed, MSL gathered countless images and collected numerous samples of the atmosphere, soils, and rocks. Man’s understanding of Mars continued to expand as data and information were transmitted from the mobile laboratory to its users back on Earth. And that understanding is expected to continue to expand for years to come as an MMRTG quietly powers the distant laboratory.

NASA’s Curiosity rover used the navigation camera (NavCam) on its mast to catch this look-back eastward at wheel tracks from driving. The MMRTG appears in center of the bottom photo. (Photo: NASA/JPL-Caltech/Malin Space Science Systems)

173 The march...gave rise to an industry focused on harnessing the energy of the atom for use in exploring and conquering the final frontier.

174 Into the Future 14 Powering New Missions

or over six decades, U.S. space nuclear power systems have continued a steady technological march forward. at march has encompassed radioisotope power systems and space nuclear Freactors, static and dynamic power conversion systems, and passive and active heat rejection concepts. e march has been conducted in support of civilian and military missions, across numerous presidential administrations, and amidst the ebb and flow of congressional support. It gave rise to an industry focused on harnessing the energy of the atom for use in exploring and conquering the final frontier.

e march gave us the RTG which, with its incredible simplicity and reliability, has powered missions in the orbit of Earth and on the moon, to the sun and most of the planets in the solar system, and even beyond our solar system. And yet the RTG is but one system in a suite of space nuclear power technologies, which include dynamic RPS and space nuclear reactors, that might one day power new and ever larger missions in the decades to come.

As our survey of space nuclear power through the decades comes to a close, it is worthwhile to reflect upon the accomplishments and successes, and even the failures, of the past 30 years, the main period covered by this book. It is also instructive to note trends and lessons that might serve to guide future space nuclear system development and use. For these efforts, founded upon the labor and work of countless individuals, provide the firm technical foundation, experience base, and resources necessary to power new missions for decades to come.

Three (More) Decades of Power

For the quiet technology of the RTG, the highlight of the last three decades was the successful development and use of two new systems: the GPHS- RTG and MMRTG. e GPHS-RTG became a true workhorse for NASA, having powered four separate missions (Galileo, Ulysses, Cassini, and New Horizons) with a combined seven individual RTGs. With the retirement of the GPHS-RTG following the New Horizons launch in 2006, DOE delivered the first-ever MMRTG, which has successfully powered the rover Curiosity since its landing on Mars in August 2012. As of 2014, all RTGs have provided reliable and consistent power that has enabled the collection

In this concept image, a resource prospector carrying a Regolith and Environment Science and Oxygen and Lunar Volatiles Extraction payload roves on the lunar surface. (Image: NASA)

Photo Credit 175 Into the Future Powering New Missions

Radioisotope Power of countless images and data that telluride-TAGS material used in Systems: Providing have greatly expanded and enriched the MMRTG. In addition, the Power Where the Sun mankind’s understanding and skutterudites appear to have Don’t Shine knowledge of the solar system. a lower degradation rate than the MMRTG thermoelectric “…one of the captions or slogans I kind At the heart of both RTG designs materials, which would further of wanted to use for the program was is the GPHS, which has been improve lifetime efficiency. Future ‘we give them power where the sun successfully used for over 30 years. plans include development of don’t shine...’”1 In addition to its modularity, the the manufacturing capability for Richard R. Furlong GPHS met another goal of its the skutterudite thermoelectric DOE (retired) designers, which was to eliminate materials, thermoelectric couples, the need for costly mission- and modules for possible use in an The unique characteristics of specific flight requalification. On enhanced MMRTG, or eMMRTG.2 these power systems make them the power conversion side of RTG especially suited for environments technology, the silicon-germanium In addition to RTGs, the where large solar arrays are not thermoelectric material and compact LWRHU saw use in practical, and at long distances from unicouple, first used in the MHW several NASA missions as DOE the sun. To date, DOE has provided RTG of the 1970s, continued and its contractors delivered radioisotope power systems for use to see use in the GPHS-RTG. over 250 heater units for use on 24 missions, and a space nuclear Similarly, the lead-telluride/TAGS aboard the Galileo and Cassini reactor power system used on one thermoelectric materials used in spacecraft as well as on the Mars mission, that provided some or all the SNAP-19/Pioneer RTGs of rovers Pathfinder, Spirit, and of the spacecraft on-board electrical the early 1970s were used, with Opportunity. e small size of the power (excluding the three failed minor changes, in the MMRTG. heater units, coupled with their missions/launches). In addition, With their very high reliability simplicity, continue to make them RHUs have been provided for nine and performance record, both a very effective means to maintain missions for thermal heating of thermoelectric materials have desired thermal environments for critical spacecraft and/or rover been in use for several decades. spacecraft instruments and other components. These nuclear power Such success, however, is not electronic devices. systems have enabled many space deterring ongoing research into and planetary exploration missions new materials that hold the hope rough the course of preparing in places scientists would otherwise for improved power conversion and delivering the RTGs and have not been able to study. performance. LWRHUs, DOE transferred RTG assembly and test operations from One such thermoelectric material Mound to INL. e birthplace of is a family of cobalt arsenide the RTG (Mound) was subsequently compounds called skutterudites. shut down in 2004 after 50 years of Early testing conducted by JPL and notable service in RTG technology. TES indicate the possibility for conversion efficiency approximately 25 percent higher than the lead-

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In addition to the infrastructure oxide per year. DOE will continue met through the purchase of change, DOE and NASA initiated to draw upon its existing nuclear Russian fuel material. a Plutonium-238 Supply Project infrastructure, including two in 2013 to restart production of nuclear reactors (High Flux Isotope As 2014 came to a close, DOE the heat source isotope following Reactor at ONRL and Advanced and NASA were looking ahead a 25-year hiatus. In a break from Test Reactor at INL) and a modified to a Mars 2020 mission as the previous funding arrangements, chemical processing facility at next opportunity to assemble NASA will fund DOE to establish ORNL. Such efforts will bring to a and test an MMRTG. As in the and maintain the capability to close the long-standing need for a past, responsibility for delivery of produce approximately 3.3 pounds long-term domestic plutonium-238 the MMRTG will reside with the (1.5 kilograms) of plutonium-238 supply, which had been temporarily Space and Defense Power Systems group within DOE-NE. With its infrastructure in place and a future supply of plutonium-238 assured, DOE appears to be well-positioned to deliver RTGs for future NASA missions.

Dynamic Radioisotope Power System Advancements

While RTGs remained the mainstay of space nuclear power systems for NASA missions, DOE and NASA continued efforts to develop dynamic RPSs. Most notably over the last three decades was the effort to develop Stirling power conversion technology. Initiated under the SRG-110 project and continued under the ASRG project, significant advancements were made in two different Stirling convertor concepts during a cumulative 12-year effort. Development of the ASRG included the use of the Advanced Stirling

The reactor pool at the High Flux Isotope Reactor. (Photo: ORNL Flickr)

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Convertor (ASC). Several different be scalable over a broad range of from high-temperature refractory series of ASCs were developed as power levels (10 to 1,000 kWe) and metal alloys were demonstrated. the technology matured towards could be adapted to the needs of Fabrication and testing of a qualification and flight hardware. multiple users. Scalability was to prototypic control rod drive Although advancements were made be achieved through the design assembly in high-temperature in all areas of Stirling convertor and use of modular components vacuum conditions were completed. technology, budget conditions and such as the power conversion Advancements were also made in the need for additional technology system. e scalability concept silicon-germanium thermoelectric development led to termination of the ASRG project.3 In spite of the obstacles, the effort to develop Space Nuclear Reactors— Power and Propulsion the SP-100 space reactor power system made significant progress. For space nuclear reactor technology, the last three decades were marked by two major periods of concept development and was of particular benefit due to the power conversion modules and the technology advancement work. e absence of a specific mission. While electromagnetic pumps to be used first period originated under the DOE, DoD, and NASA had a golden in the power conversion system. auspices of SDI and included the opportunity to develop the space At the time of its termination, the SP-100, TOPAZ, and Timberwind/ reactor power system, division program was considered to be SNTP programs. e second period over technology (thermionic versus within one year of demonstrating originated a decade later under NSI thermoelectric), ongoing funding the ability to fabricate all of the and gave rise to the Prometheus/ shortfalls, and the lure of foreign key components required for JIMO project. A third effort, albeit power conversion technology a flight-ready power system. much smaller, was conducted under worked against the program. With the extensive hardware, the auspices of SEI but was limited documentation, and records- to evaluation and assessment of In spite of the obstacles, the effort retention effort undertaken by space reactor power and propulsion to develop the SP-100 space reactor DOE following termination of the technologies. power system made significant SP-100 program, a solid technology progress. e program completed base was established from which e SP-100 program was a detailed reactor power system future space reactor power system by far the largest and most design, including the criticality technology efforts might build. successful domestic space reactor experiments and hydraulic flow development program undertaken testing necessary to demonstrate In the area of nuclear thermal since the Rover/NERVA program the design. Uranium nitride fuel propulsion, the sole technology was terminated in 1973. From pin fabrication processes were development effort consisted the onset, the program focused re-established and techniques for of the classified Timberwind on developing a 100-kWe space fabricating the reactor vessel and program was initiated under the reactor power system that would its internal structural components auspices of SDIO and the DOE

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Office of Defense Programs but developed by DOE-NR. e project importance or priority, they may transitioned to the purview of was terminated after three years serve to guide future development the Air Force and DOE-NE as the due, in part, to the significant costs and planning efforts. SNTP program. e Timberwind anticipated for development of the Need for Long-Term Commitment effort focused on a high-power space reactor power system. particle bed reactor propulsion e need for long-term commit- concept with development of the While the large space reactor ment may be the biggest challenge PBR fuel particle and fuel element programs of SP-100 and facing DOE, NASA, and DoD in as primary objectives. Although Prometheus have long since developing future space reactor the same objectives were carried passed, current space reactor power systems. As shown by histor- into the SNTP program, the desire development efforts are focused ical space reactor programs such as for nuclear thermal propulsion on smaller system concepts such Rover/NERVA (17 years of devel- eventually succumbed to other as a Kilopower Fission Power opment upon its termination) and mission needs and the SNTP system that is scalable from 1 kWe SP-100 (10 years of development 4 was terminated. to 10 kWe. In addition to the upon its termination), it’s clear that ongoing space reactor technology space reactor development requires As the SDI-based efforts came to development efforts, NASA and a significant investment in time as a close toward the end of the Cold DOE initiated a Nuclear Power well as money. Closely related is War, SEI came on the horizon Assessment study in 2014 that the need for a development effort in 1989 and provided a brief includes an evaluation of two focused on the advancement of three-year impetus under which potential NASA missions identified technology that typically requires DOE and NASA developed and in the 2011 Decadal study, Vision long lead times, such as nuclear fuel evaluated several space reactor and Voyages for Planetary Science and materials qualification. ere 5 propulsion system concepts to in the Decade 2013–2022, and the is simply no way to fast track the support a manned mission to technology needed to accomplish development and deployment of Mars, and various space reactor those missions. e study was such systems. erefore, there must power system concepts for manned completed in early 2015 and be long-term commitment to any Lunar outposts. Due to the limited provides information useful for such development program, not funding associated with SEI, work the future development of space just among the partner agencies but was directed at detailed evaluation nuclear power systems. also by Congress through which the of technology and assessments of funding necessary for such develop- potential reactor system concepts Lessons, Trends, and ment will come. for both power and propulsion. Take-aways Technology Decisions in the Face of Limited Resources Ten years later, in 2002, NSI Emerging from the provided one last effort to develop accomplishments, successes, and e major space reactor develop- nuclear electric propulsion. failures of space nuclear power ment efforts conducted over the Under the Prometheus/JIMO system development and use last 30 years have shown that a project, NASA sought to develop a over the last three decades are broad variety of technologies can be nuclear electric propulsion system a variety of lessons and trends. combined to develop a multitude of powered by a space reactor concept While presented in no order of system concepts meeting the needs

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of a particular mission. e vast majority of system concepts are In the long-run, system development efforts may typically eliminated from further consideration following an appro- actually be hampered when development work is priate screening process, leaving a spread among too many technologies. small subset for final consideration by decision makers. Although competing technologies may offer launched, the most recent being the need to re-establish production a hoped-for level of performance, New Horizons with its GPHS-RTG processes, including equipment technology decisions must ulti- (2006) and MSL with its MMRTG and facility setup and worker mately be driven by clear mission (2011). With the cancellation of training, typically against an requirements and sound systems the ASRG project in 2013, the next aggressive mission schedule. engineering and acquisition pro- launch for which a space nuclear cesses. In the long-run, system power system (MMRTG) will be Secondly, less frequent missions development efforts may actually be utilized is planned for 2020. Almost can also present challenges in hampered when development work 10 years will have lapsed since the retaining knowledgeable and is spread among too many technol- last MMRTG was assembled and trained workers, including those ogies. John Warren of DOE/NASA tested. In the past, DOE has felt the associated with thermoelectric, provided a relevant perspective consequences of mission cancella- heat source, and RTG assembly when reflecting upon the various tion in two notable ways. and testing operations, as well space reactor programs conducted as support personnel (engineers through the 1980s and 1990s: “We First, mission delays and lulls, such and quality). Managers are often had so many concepts competing as occurred following the Galileo faced with the need to find interim with one another. And the problem and Ulysses RTG production work and worker qualification and is we had limited resources—by activities, led to decisions to training is often allowed to lapse. that I mean funds and people—and terminate thermoelectric material we still have limited resources, and Need for Robust Infrastructure production and defer processing I think the strategy has to be pick 6 equipment maintenance. In both one and get it going.” e advent of the DOE Office instances, significant effort and of Environmental Management Downward Trend in Frequency of cost were required to re-establish program in the late 1980s and the Missions Utilizing RTGs operations at new locations and de-emphasis on nuclear research with new contractors. Although and development through much of e frequency of missions requir- maintaining a base level of the 1990s resulted in a significant ing RTGs has decreased significant- operations between missions is reduction in the number of facilities ly over the past 30 years. During desirable for worker proficiency available to support space nuclear the first 20 years of RTG use and productivity, and equipment reactor system development. For (1961–1981), 22 separate launches operability, limited funding and example, nuclear reactors once carrying 38 RTGs were complet- other factors may preclude such available for materials and com- ed. However, since the launch of activities. When a definitive NASA ponent testing in support of the Galileo in 1989, only five space- mission was eventually announced SP-100 program, such as EBR-II craft and eight RTGs have been (i.e., Cassini), DOE was faced with

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and FFTF, were shut-down and dis- Clearly, the development of RTG is their high cost—it has proven mantled. Other facilities that were technology benefited from well- difficult to maintain support when available to support ground testing defined missions where power development costs begin to greatly and flight qualification of space levels were established early on and outpace cost estimates, particularly reactors, such as PRTR at Hanford, typically unchanged, giving power when such trends recur. As such, it have also been dismantled. Future system developers a fixed target in is clear that being tied to a specific space reactor development efforts terms of application, schedule, and mission brought no more success should therefore include a thorough funding. Most importantly, RTG to the space reactor development inventory of existing DOE facilities missions rarely disappeared—when programs of the last 30 years against expected testing and devel- NASA said an RTG was needed by than most of those conducted opment needs to ensure any gaps a given date, DOE delivered. previously. are included in long-term system development plans and budgets. For decades, the space nuclear power system While the RTG operations infrastructure saw perturbations community has operated under the premise that through the same period, it development efforts are best supported and remained intact as DOE relocated operations and activities to new justified when tied to a specific mission. sites. As demonstrated by the operating experience with the SRS PuFF facility, the need to maintain By contrast, space reactor In the absence of a clear and plutonium-238 processing facilities development programs over the long-term mission, space reactor and equipment will continue to last 30 years have experienced a system development could require special attention. different outcome. Missions came benefit greatly from ongoing and missions went, generally in the technology advancement between Need for a Clear Mission— context of a broader “initiative.” large mission-driven system Maybe Not When the need went away, support development efforts. In addition For decades, the space nuclear eventually dried up, and when to advancing various sub-system power system community has support dried up, the technology components, such as fuel or power operated under the premise that development effort soon ended. conversion technology, such efforts development efforts are best sup- In essence, development efforts could reduce the overall mission ported and justified when tied to a were hampered by the lack of cost and schedule when a specific specific mission. e premise was clear, enduring mission needs need arises in the future. strongly underscored in the 1983 and associated requirements. National Research Council report e same pattern displayed itself Alternatively, future space reactor that maintained the importance of in the SP-100, Timberwind/ development programs might matching research and develop- SNTP, TOPAZ, and Prometheus adopt a pattern of development ment to a firm requirement, or at programs. Another factor that similar to that of RTGs—start least the emergence thereof.7 has adversely affected space small and grow gradually. e reactor development programs advancement of RTG technology

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occurred largely over a period of 20 Into the Future As long as dreams and desires to years, during which power levels explore the “final frontier” remain, gradually grew from 2.7 We to 300 From the underlying science and the power in the atom will continue We through an ongoing evolution engineering by which electrical to lend itself as a means through of several RTG designs. Starting power is generated from the atom which they might be fulfilled. with a much smaller system may to the reliability and longevity for And with six decades of experience offer advantages such as relatively unattended operation of power at its back, DOE remains well- low cost, shorter development systems for years and decades, the poised to carry space nuclear times, and simpler technology. history of space nuclear power technology boldly and successfully However, such advantages would and the systems developed to into the future. have to be carefully weighed date is truly fascinating. Equally against technology breakpoint fascinating is the development and factors such as the operational advancement of nuclear-based aspects of heat generation versus propulsion systems. But integral to propulsion, and power conversion the story of the technology are the breakpoints. countless men and women whose Nuclear Safety and Response knowledge, skill, ingenuity, and Preparedness determination brought concepts to reality and paved a way for the use Nuclear safety will remain a sig- of such systems in the future. nificant emphasis for all future space nuclear power system uses. After 60 years of invention, at emphasis will continue to be development, and use, space driven by rigorous launch approval nuclear power systems continue processes and supported by the to provide a unique niche that ongoing enhancement of knowl- solar and chemical systems cannot edge pertaining to potential launch fill. e power in the atom has, accident environments and an ever figuratively, taken mankind to improving ability to model the con- every planet in the solar system sequences of potential accidents. (except Mercury) and beyond. It Coupled with the strong empha- has powered rovers on Mars and sis on safety will be the ongoing orbiters around Saturn and enabled need for well-planned emergency surveys of the sun. Such systems response that can be quickly and have allowed mankind to extend decisively executed if the need our reach to destinations within arises. Such response must include the solar system and beyond that provisions for timely and frequent would otherwise remain unknown. communication with a concerned And yet the door to space public. exploration remains barely ajar.

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NASA’s Spitzer Space Telescope observed a fledgling solar system, like the one depicted in this artist’s concept, and discovered deep within it enough water vapor to fill the oceans on Earth five times. (Photo: NASA/JPL-Caltech)

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