Mar 98-053 Boosters for Manned Missions to Mars
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MAR 98-053 BOOSTERS FOR MANNED MISSIONS TO MARS, PAST AND PRESENT Greatly expanded version will be made available at: http:// www.webcreations.com/ptm/pubs.htm. Scott Lowther INTRODUCTION A large number of space launch boosters have been proposed throughout the years, many of which were designed for or were applicable to launching components required for manned missions to Mars. In this paper, past and current designs for booster vehicles needed to perform manned Mars missions are examined and compared, with emphasis on current and very recent concepts. Included are such designs as: von Braun’s Ferry Rocket, the Saturn V and various Saturn V derived vehicles, various Nova studies from the 1960’s, the Soviet N-1, the Soviet Energia, various Shuttle Derived Vehicles (such as Shuttle-C, Ares and similar designs), the Evolved Expendable Launch Vehicle, VentureStar, StarBooster 400, StarBooster 1800, VentureStar and Magnum. Vehicle designs are described and shown and capabilities are compared, along with any manned Mars mission modes originally proposed for each booster. The utility of each booster for piloted missions and cargo missions at current technological levels are examined, as are launch site and infrastructure modification requirements. Three baseline Mars missions based on modern technology are also briefly described: a Mars Direct architecture, a JSC baseline Mars Semi-Direct architecture and a stereotypical large on- orbit assembled single vehicle. Each booster is described in relation to these missions. The results are then compared and contrasted. Conclusions are drawn based upon these results, with certain boosters showing a higher level of ability and confidence. Notes on Data Tables Where possible, payloads for the examined boosters have been referenced for the same orbit (typically 407 kilometers and either 28.5 or 51.6 degrees inclination) to permit more direct comparisons. For some vehicles, however, this direct comparison is not possible. For launchers with multiple strap-on boosters, the data for the strap-ons is the cumulative total for all, not for a single strap-on. COMPARISON MISSIONS On-Orbit Assembled From the late 1940’s until the late 1980’s, the main line of thinking for mission modes for manned Mars missions involved some degree of on-orbit assembly. This has ranged everywhere from a few components simply docked together to far more involved orbital construction programs. 529 One essentially stereotypical on-orbit assembled Mars mission was produced by the NASA Lewis Research Center in 1991 for the Space Exploration Initiative. This concept utilized nuclear thermal rocket research then underway at Lewis for lunar logistics support. The main stage of the Mars vehicle used a derivative of the reusable lunar core stage, with additional liquid hydrogen tanks. The Mars vehicle included a space-only mission module and an Apollo capsule-shaped Mars Excursion Module similar to 1960’s designs. Total vehicle length was 105.6 meters, with a mass in Low Earth Orbit of 668,000 kilograms. Heavy lift boosters derived from the Saturn V were the presumed launch system. On-orbit assembled Mars vehicles were the standard NASA and industry design until the early to mid 1990’s, when smaller single-launch vehicles (Mars Direct) and dual launch, on orbit docked (Design Reference Mission) vehicles utilizing Martian resources for propellant became preferred. While the design of such vehicles have been many and varied, on-orbit assembled vehicles that do not make use of Martian resources have tended to be extremely massive. A selection of such designs produced by Boeing for NASA-Marshall in the late 1980’s and early 1990’s showed initial masses on Low Earth Orbit of between 478,000 kilogram (for designs with advanced nuclear propulsion) to 828,000 kilograms (for all-chemical vehicles). Such vehicles have always required heavy lift boosters due to the weights of individual components, and have often had outsized components (fuel tanks, aeroshells, truss structures, etc.) that required large payload fairings. Mars Direct The idea of using Martian resources for rocket fuel (primarily the carbon dioxide in the atmosphere) has been around for several decades, but did not receive a great deal of study until 1990. A group of scientists and engineers at Martin-Marietta proposed a manned Mars mission mode that made maximum use of Martian resources in response to the Space Exploration Initiative. The mission mode became known as “Mars Direct,” primarily due to the use of a single heavy lift launch vehicle to loft components of the mission directly to Mars with no stopover needed in Earth orbit. Two launches of the “Ares” booster would be required for a single manned expedition. The first would send an unmanned Earth Return Vehicle directly to Mars, with its fuel tanks virtually dry. Once there, the Earth Return Vehicle would begin processing the local carbon dioxide with onboard chemical reactors and a small supply of liquid hydrogen. Sufficient fuel and oxidizer can be produced to allow the two-stage Earth Return Vehicle to launch directly back to Earth. The piloted mission would be launched to Mars on the next available window, after the ERV has completed its fueling. This mission would contain a single habitation module with a pressurized rover and four crew. The habitation module would, it was planned, be landed within walking or driving distance of the ERV. The crew would spend in excess of one Earth year on the surface of Mars; at the end of which time they would board the ERV and return home. The mission would leave behind the habitation module and all its provisions, to serve as a basis for future explorations. The ERV had a mass of 28,600 kilograms; the habitation module massed 25,200 kilograms. These masses do not include the masses for the required aeroshells, parachutes and lander stages. 530 While the Mars Direct concept is generally regarded as overly optimistic, some of the basic premises have been incorporated into current NASA thinking. The current Design Reference Mission uses In Situ propellant production to fuel the ascent stage used to boost the crew from the Martian surface to the orbiting Earth return vehicle. The habitation module will also be left behind. Design Reference Mission NASA’s current studies for a manned mission to Mars revolve around the Design Reference Mission. This is an ongoing study to design low cost and reliable Mars mission using available or near term technology. As of this writing, the current NASA Design Reference Mission involves the use of six launches of a Magnum class booster. Each launch would orbit a Mars- bound spacecraft or its trans-Mars injection stage; the payload and stage would be docked in LEO, and then sent to Mars.. The current baseline for the trans-Mars injection stage is a nuclear thermal rocket (NTR) system with three engines using liquid hydrogen as the reaction mass. Trans Mars Injections stage has a dry mass of 27,000 kilograms and a propellant loading of 50,000 kilograms. The three payloads to be sent to Mars are the Earth return vehicle (71,400 kilograms, to be left in Mars orbit, with 147,500 kilograms launched from Earth), the ascent stage (66,000 kilograms, to be landed on Mars, with 134,700 kilograms launched from Earth) and the piloted TransHab (60,800 kilograms, to be landed on Mars, with 137,500 kilograms launched from Earth). Total payload to be launched into Earth orbit (407 kilometers by 51.6 degrees) is 419,700 kilograms. The Design Reference Mission follows a mission similar to that proposed for Mars Direct, in that the Earth return vehicle and the ascent stage are sent to Mars unmanned and several years before the manned stage. The ascent stage would use an ISRU plant to produce the fuel required to make the ascent from the Martian surface to the orbiting Earth return vehicle; the Earth return vehicle would be fully fueled prior to launch from Earth. WERNHER VON BRAUN’S “FERRY ROCKET” The first truly large space launch vehicle ever designed at any level of practical detail was Wernher von Braun’s “Ferry Rocket.” This vehicle, which first appeared in von Braun’s 1948 book “Das Marsprojekt,” had it’s origins with the A-4, A-9 and A-10 rockets of World War Two. The Ferry Rocket was designed to fulfill three main missions: launching components for a space station, a lunar mission and a Mars mission. The Ferry Rocket’s design had elements that, seen from a vantage point fifty years further on, seem both quaint and oddly futuristic. The Ferry Rocket was intentionally designed to not break new ground, technologically; everything about it was meant to be possible using early 1950’s technology. Propulsion for the giant three stage vehicle was to be provided by no less than 51 rocket engines in the first stage, 22 in the second and 5 in the winged third stage. These engines burned the propellant combination of hydrazine and nitric acid; while thoroughly toxic, this fuel combination did at least have the advantage of being hypergolic, thus reducing problems of ignition. These propellants were also non-cryogenic. The rocket engines on the first two stages were to be packed so closely together that instead of having circular cross-section bell nozzles they had hexagonal cross section nozzles, a practice virtually unknown in the world of rocketry. 532 The third stage of the ferry rocket was winged and manned, and used conventional tricycle landing gear for a return to a runway. In this respect it was similar to the current Space Shuttle. However, it was to be made of primarily stainless steel, and had a small, hockey-puck shaped cargo bay.