Johnson, Wyatt R. and Longuski, James M. Pitch Control During Autonomous
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Aerobraking
Aerobraking allows a spacecraft to use the planet’s atmosphere to adjust its’ orbit. Rather than using excessive propellant to adjust its’ position, aerobraking can maneuver into an orbit by using solar panels against the friction of the atmosphere.
As the spacecraft enters the planet atmosphere, it will make many “drag passes” to trim its’ orbit into a circular one. Each pass will reduce the altitude of the craft and transform from an elliptical orbit to a more circular one. Small thrusters may be used during these passes to dump any accumulated angular momentum. The number of drag passes for the Mars Odyssey orbit was 380 and took 78 days to complete. During the last few days of aerobraking, the spacecraft will need to fire thrusters to raise the periapsis to achieve the final circular orbit.
Some benefits to aerobraking are the reduced amount of propellant mass needed to place the spacecraft in orbit, which allows a smaller rocket to launch the spacecraft. Aerobraking does require knowledge of the weather, precise navigation, and an accurate knowledge of the forces the structure can handle.
Reference:
Johnson, Wyatt R. and Longuski, James M. Pitch Control During Autonomous Aerobraking for Near-Term Mars Exploration. Journal of Spacecraft and Rockets. Vol. 40, No. 3, 2003.
Hardin, Mary. Mars Global Surveyor Successfully Completes Aerobraking. Jet Propulsion Laboratory, California Institute of Technology. Feb. 4, 1999.
“Surfing High Above Dao Vallis.” SpaceDaily. Oct. 21, 2001. http://www.spacedaily.com/news/aerobraking-01a.html. Accessed: 9/29/2003.
Aero Capture
Aero capture is a process that can be used by satellites or landing craft to enter orbit around a planet without having to do a rocket burn. This is a favorable idea because more weight allocation can be used for payload instead of fuel.
The theory behind aero capture is to use drag from a planets atmosphere to slow an arriving craft into an orbit around the planet as opposed to executing an orbit changing burn upon arrival. The idea has yet to be used on an operational design due mostly to the fact that until recently the technology and materials where unavailable. Now it is because no company wants to risk losing a multi-million dollar craft on an untested theory. (122 words) Text source found on LIAS: AIAA Atmospheric Flight Mechanics Conference, Monterey, CA, Aug. 9-11, 1993, Technical Papers (A93-48301 20-08). Washington, American Institute of Aeronautics and Astronautics, 1993, p. 532-545. Accession Number: A93-48354
Hyperlink to additional web page: http://web.ask.com/redir?bpg=http%3a%2f%2fweb.ask.com%2fweb%3fq %3dwhat%2bis%2baero%2bcapture%26o%3d0%26page %3d1&q=what+is+aero+capture&u=http%3a%2f%2ftm.wc.ask.com%2fr%3ft %3dan%26s%3da%26uid%3d28076a0558076a055%26sid %3d38076a0558076a055%26qid %3d7D3CE1425D84664D885B5DA800726D2D%26io%3d4%26sv %3dza5cb0dee%26ask%3dwhat%2bis%2baero%2bcapture%26uip %3d8076a055%26en%3dte%26eo%3d-100%26pt%3dAeronautics%2bSeminars %2b-%2bFall%2b2001-02%26ac%3d24%26qs%3d0%26pg%3d1%26u%3dhttp %3a%2f%2fwww.its.caltech.edu%2f%7ewirz%2fSeminar%2f2001- 2002.htm&s=a&bu=http%3a%2f%2fwww.its.caltech.edu%2f%7ewirz %2fSeminar%2f2001-2002.htm
Airbags for Landing
Airbags were used to cushion the landing of the Mars Pathfinder lander, and are also being used on the twin MER rovers launched this summer. They were initially developed to avoid contaminating the landing site with rocket propellant exhaust, which would otherwise make scientific obervations questionable. Retro-rockets are still used to slow decent to allow a surface impact at about 20 m/s, but are not fired all the way until touchdown. The airbags are made out of Vectran, which is about twice as strong as Kevlar. In the case of the MER, the airbags are made out of 8 thin layers of Vectran. These airbags are designed to survive impact on a rock sticking up 0.5 meters above the surface of Mars.
References: http://www.jpl.nasa.gov/solar_system/features/airbags.html accessed Sept. 28 http://www.grc.nasa.gov/WWW/PAO/html/marslnpb.htm accessed Sept. 28 http://vesuvius.jsc.nasa.gov/er/seh/pathrove.html accessed Sept. 28
Apogee Kick Motors
An apogee kick motor (AKM) is a rocket motor fired to boost a spacecraft into it’s final orbit. When the spacecraft is launched, it needs to reach a certain speed to be able to orbit the Earth. So, when it gets launched into space, the AKM gives the spacecraft that burst of speed it needs to keep it in orbit. This firing of the AKM is commonly referred to as a “kick in the apogee” or an “apogee kick”. It usually occurs at the apogee of the orbit, but it can also be fired at the perigee. AKM’s can be either solid fuelled (most common) or liquid fuelled rocket engines. They are usually used for satellites in Geostationary Transfer Orbit (GTO) or circular orbits, but can be used for pretty much any orbit. While doing research, I found a webpage that had a list of different types of engines that gives the name of the engine, what the engine is commonly used for, the impulse of that particular engine in kNs, and the fuelled mass of the engine in kg. The webpage is located at http://planet4589.org/space/book/lv/engines/kick/motors.html
References http://my.execpc.com/~culp/space/orbit.html 09-24-03 http://www.faqs.org/faqs/space/launchers/ 09-24-03 http://planet4589.org/space/book/lv/engines/kick.html 09-28-03 http://www.satexpo.it/en/news-new.php/9?c=5001 09-28-03
Control Moment Gyro
A Control Moment Gyro (CMG) is an actuator that consists of a spinner with a sustained kinetic moment modulus (h) and one or two motor-driven tile axes. A CMG can either be considered a generator of torques applied to a satellite or as a generator of kinetic moment exchanged with the satellite momentum. In order to create a kinetic or dynamic moment in a certain direction, it is necessary to combine at least three elementary kinetic moments or gyroscopic torques in variable, non-coplanar directions. One design found to be among the best is to arrange the CMG’s in a tetrahedral for the most efficient and redundant system (being that you only need three for the system to work), allowing for the maximum achievable kinetic moment to be 3.26h, with any value below this, including 0 is achievable.
Works Cited: ONERA – DCSD, Satellite attitude control using CMG, presentation.
Coronal mass ejections
Coronal mass ejections (CME’s) are large bubbles of gas that are ejected from the sun over the course of several hours threaded with magnetic field lines. CME’s disrupt the flow of the solar wind from the sun and can produce disturbances that hit the Earth with extreme results. CME’s drive pressure waves into the surrounding corona and solar winds, and when the outward speed is high enough, can produce shock wave disturbances in the solar winds. The ejection masses can range from 1015 to 1016 g., while leading edge speeds of the materials can range from 50km/s to 2000km/s. The geomagnetic storms that result from the CME’s can cause a disruption of satellite operations, communications, navigation, and electric power distribution grids.
References: Coronal Mass Ejections,
Deep Space Network
The NASA Deep Space Network (DSN) is a collection of three antennas that are used in combination with each other to support interplanetary spacecraft missions and radio and radar astronomy observations for the exploration of the solar system and the universe. Each of the antennae facilities is placed at approximately 120 degrees apart around the world to allow for constant observation of spacecraft as the earth rotates. These antennas make it possible for NASA to acquire telemetry data from spacecraft, transmit commands to spacecraft, track spacecraft position and velocity, gather science data, and monitor and control the performance of the network. The antennas are located in California’s Mojave dessert, near Madrid, Spain and near Canberra, Australia.
Resources: Deep Space Network Homepage http://deepspace.jpl.nasa.gov/dsn Accessed on 29 September 2003
A History of the Deep Space Network, 1957-1997 Douglas J. Mudgway The NASA history series Washington, DC: National Aeronautics and Space Administration, Office of External Relations
Earth Sensors
Sensors have been vital to spacecraft and their missions since the inception of the space exploration. Based on the research I have done in the engineering library I have found two important attributes of Earth Sensors and Sensors in general. The first is to assist in spacecraft attitude and control. The second is to observe surfaces of planets whether it is Earth or any other planet.
Earth Sensors are used to help position spacecraft relative to the center of the Earth. For example, Earth sensors are used to position satellites in space such that they are not taking useless pictures of deep space when in fact they are intended to capture images of earth or other orbiting bodies. Secondly, It follows that Earth Sensors are used for geographic purposes. A good example is LANDSAT, which is used by The Corps of Engineers for environmental studies.
In passing I also found that “smart sensors” are taking some of the workload from CPUs and therefore lowering the cost of hardware in spacecraft.
In conclusion we see that Earth Sensors and Sensors in general have many applications to spacecraft design and space mission design. They can give vital position data and succinct information about you terrain and condition the planet which one hopes to visit or Earth. The imperative attributes can help a spacecraft safely land on Earth and in the case of our project, Mars. Using sensors in general can help many of the ERV teams find efficient landing zones on the Martian terrain and save the spacecraft and the personal from a sudden death from a collision.
RESOURCES Nizam. "Earth Sensors." University of Putra, Malaysia. 30 September 2003
Breckenridge, Remote Sensing of Earth from Space: Role of “Smart Sensors.”. Progress in Aeronautics and Astronautics, V. 67. AIAA, 1979.
"Earth Sensors." Attitude Determination & Control. January 1995. Washington University in St. Louis. 30 September 2003
Extremophile Microbes
Extremophile microbes might possibly be able to used in the design of new electronic structures. These electronic structures will be built using modified proteins from the microbes and will be able to create the electronic structures that are on the size of nanometers and can only be seen through an electron microscope. Research and speculation is also being done to try to find if these microbes can be found on the surface of Mars. Researchers say that the conditions on Mars are very suitable for the microbes to grow and live. They would be found underneath the surface of Mars. If these microbes can be found and used the size of electronics on a space craft could be decreased by 10 to 100 times the size. http://www.es.ucl.ac.uk/research/planet/student/work/whiting/main.htm 28 Sep 03 http://amesnews.arc.nasa.gov/releases/2002/02_122AR.html. 28 Sep 03. Fuel Slosh
In space structures, a large percentage of fuel is used to launch the vehicle. Once the fuel tank becomes less full, the remainder of the fuel moves (or sloshes) around inside of the tank. Under both translational and rotational motion, as well as small perturbations, the fuel movement can destabilize the system and controls. The moving fuel interacts with the solid body and most often produces attitude instability. Past space structures did not use liquid fuels and could be approximated as rigid bodies. Present stabilization systems are designed with flexibility taking into account liquid fuel. Pendulum, mass spring, and vibrational models using an infinite number of small masses to represent the moving fluid have been used to study and correct this motion. Methods of correcting the instability caused by fuel slosh include dividing large fuel tanks into small ones, including baffles inside the tank, and thrust maneuvers. These methods do not completely correct the effects of the fuels motion.
References Bryson, Arthur E. Jr. Control of Spacecraft and Aircraft. Princeton, NJ: Princeton University Press, 1994. Reyhanoglu, Mahmut. “Maneuvering Control Problems for a Spacecraft with Unactualted Fuel Slosh Dynamics.” Control Applications. Proceedings of 2003 IEEE Conference. 23-25 June 2003. Vol. 1: 695-699. IEEE Explore. 28 Sept 2003.
Gravity Assist
Many space missions would not be possible if all the energy needed to reach the final destination came from on-board fuel sources. The spacecraft’s mass would be too large. However, a gravity assist is an orbital maneuver that can rectify this situation. This maneuver is performed by launching at a very specific time in the orbits of the planets involved such that a spacecraft “steals” momentum from a planet and uses it to alter its own orbit. If a spacecraft passes in front of the planet, the spacecraft loses momentum to the planet and will enter a lower orbit in relation to the sun. If a spacecraft passes behind a planet it will gain momentum and enter a higher orbit in relation to the sun. The Galileo mission used gravity assist to gain a total of 11.1 km/s which would have been provided by chemical propellents otherwise.
References JPL. A Quick Gravity Assist Primer. http://saturn.jpl.nasa.gov/mission/gravity-assist- primer.cfm. Accessed 9/30/2003. Sellers, Jerry Jon, et.al. Understanding Space: An Introduction to Astronautics. McGraw Hill: New York, 1994. Hall Thrusters
Hall thrusters are a form of electric propulsion that enables spacecraft to have high specific impulses and high thrust efficiencies. The advantages of a such a system include lower launch mass, longer mission duration times, and larger payloads. They are particularly beneficial to small spacecraft and those spacecraft in small orbits around the Earth. In a Hall thruster, large numbers of ions are accelerated by an applied electric and magnetic fields. “They typically operate at over 50% thrust efficiency, provide an optimal range of specific impulse from 1200-1800 seconds, and thrust to power ratios of 50-70 mN/kW.” [1]
Sources 1. Busek, Co. http://www.busek.com/hall_field.htm. (09/30/03) 2. European Space Agency. Proceedings, 3 rd International Conference on Spacecraft Propulsion. (Cannes, France: October 10 – 13, 2000).
Heat Pipes
According to a NASA related website (see references), a heat pipe is “tubular device in which a working fluid alternately evaporates and condenses, transferring heat from one region of the tube to another without external help.” It was first patented by Gaugler of the General Motors Corporation in 1944. It was developed as a solution to a refrigeration problem. (Faghir, 1995)
A heat pipe consists of a closed container, a wick structure, and a working fluid which is in equilibrium with its own vapor. The heat pipe can be broken down into three parts: the evaporator region (at the location of the heat source), the adiabatic region (the transport region), and the condenser region (at the location of the heat sink).
Heat pipes can be used to transfer heat from a location that is either producing too much heat or a surface that is facing the sun to a location on the craft that requires more heat.
Faghri, Amir. “Heat Pipe Science and Technology.” Taylor & Francis: Washington, D.C.: 1995. www.sti.nasa.gov/tto/spinoff1996/64.html. Date accessed: 9/30/2003
Heat Shields for Planetary re-Entry
In the early days, vehicles (specifically ballistic missiles) were designed with a low ballistic co-efficient, also known as beta. Beta is a function of weight drag and cross section of the vehicle. Given the blunt features of early designs, drag on re-entry was high and consequently the heat generated around the vehicle was minimal. Over the years however, with spacecraft and missile designs turner sleeker and velocities reaching higher values, beta values have also gone up. A direct consequence of this is the value of heat friction and beta going up.
Recent improvisations in thermal shield technologies include Russian and German engineers, experimenting, “with an inflatable reentry vehicle… Just as the shockwave generated by a blunt body can protect a spacecraft by keeping hot gases away from the skin of the vehicle, the shockwave could theoretically protect a vehicle traveling at hypersonic velocity (Mach 6+) for sustained periods of time.” More recently, the EADS Launch Vehicles adapted a new model for the heat shields to Beagle2, the first European attempt to observe Mars. A primary requirement was that the heat shields be able to withstand 1 600°C during the lander's entry into the atmosphere, and able to maintain the temperature inside the probe at less than 125°C at the end of the mission. While Beagle2 is entering into Martian atmosphere, it would be safe to say that Earth re-entering vehicles face same temperature conditions. As a result, designing something that will allow the vehicle to withstand such hostile environment is crucial.
Press Release, HEAT SHIELD FOR MARS PROBE BEAGLE2, THE MARS EXPRESS LANDER, DELIVERED BY EADS LAUNCH VEHICLES. EADS Space Transportation. September 27, 2003. http://www.lanceurs.aeromatra.com/actualites/actu_communique_en.asp? contenu_id=1548 Advanced Re-Entry Vehicles. The U.S Centennial of Flight Commission. September 28, 2003.http://www.centennialofflight.gov/essay/Evolution_of_Technology/advanced_reent ry/Tech20.htm
Launch Vehicle / Spacecraft Interface (Structural)
Composite structures are widely used in aerospace engineering. Many studies have been done on this subject. One subject is the behavior and response of composite structures to high intensity loadings. The high strength to weight ratio of advanced composites is the reason for their use. Understanding of strain rate in various loadings is essential. Finite elements method, finite difference methods, and smooth particle hydrodynamics are used to calculate the various strains. For the LionSat project, the structures will utilize these calculation methods for composite structures.
Some of the space structures are heat pipes for transferring heat from one to other, thermal control coating, solar coatings, struts, tubes, coating surfaces, and various electrical devices.
Applied Aerospace Structures Corp. Sep 30, 2003. http://www.aascworld.com/.
J. K. Chen, D. F. Medina, and F. A. Allahdadi. “Dynamic Damage of Composite Plates to High Intensity Loadings.” Dynamic Response and Behavior of Composites. Ed. C.T. Sun, B.V. Sankar, and Y. D. S. Rajapakse. Low Thrust Propulsion
Low thrust propulsion is a very important part of modern space travel. Especially in long duration mission, using low thrust can improve the accuracy of the trajectory as well as conserve fuel and reduce the mass of the craft due to excess fuel. Two methods that are in use today are electronic propulsion and low-thrust thrusters. The low- thrust thrusters are generally used in nanosatellites, satellites whose mass is less than 10kg, but can be used for fine tuning of trajectories for deep-space space craft. These thrusters are currently being developed to use hydrazine and hydrogen peroxide for the reaction. This combination will allow for much more accuracy than current low-thrust thrusters.
Electronic propulsion is also a method of low thrust propulsion. Electronic propulsion can be accomplished in a variety of ways. One method involves ionizing the propellant and expelling it out the back of the craft by an electrostatic field. Another method is to heat the propellant electrically and have it expand out the nozzle. Plasma thrusters offer yet a third alternative. By using electronic energy to create neutralized plasma, it can then be expelled out the craft at very high velocity through a magnetic field. All of these methods prove effective and have ISPs ranging from 1600 to 3000 depending on the specific set up. Due to this fact the thrust is very low.
Sources: Platt, Donald; “A monopropellant milli-Newton thruster system for attitude control of nanosatellites”; Sixteenth Annual AIAA/USU Conference on Small Satellites, Logan, UT, Aug. 12-15, 2002, Logan, UT, Utah State University, 2002.
Racca, Giuseppe; “New Challenges to Trajectory Design by the use of Electric Propulsion and other New Means of Wandering in the Solar System”; Scientific Project Department, European Space Research and Technology Centre, European Space Agency, 2200 AG, Noordwijk, The Netherlands, 17 February 2002.
McConaghy, T. Troy, Theresa J. Debban, Anastassios E. Petropoulos, and James M. Longuski; “Design and Optimization of Low-Thrust Trajectories with Gravity Assists” Purdue University,West Lafayette, Indiana; 3 May–June 2003.
Magnetic Torquers
Magnetic torquers are used in the attitude and control aspects of satellites, often with a gravity gradient boom to control the attitude of a spacecraft. Since they are reasonably reliable, energy efficient, and lightweight, they are often used for smaller, more inexpensive satellites. Magnetic torquers have been unsuccessful when used alone in all three axis stability because the control torque can only be generated perpendicular to the geomagnetic field vector. This results in the system being nonlinear and varying with time. Magnetic torquers can also be used to produce a torque against the geomagnetic field in order to dump angular momentum. Works Consulted
1. “Minimization of reaction wheel momentum storage with magnetic torquers (for spacecraft pointing stability)” Wernli, A; Journal of the Astronautical Sciences, vol. 26, July-Sept. 1978, p. 257-278 2. “Attitude control of Earth-pointing spacecraft using the reaction jets and magnetic torquers” Wang, F., et al.; Spaceflight Mechanics 2002; Proceedings of the AAS/AIAA Space Flight Mechanics Meeting. Vol. 1, San Antonio, TX, Jan. 27-30, 2002, San Diego, CA, Univelt, Incorporated, 2002, p. 339-344 3. “In flight performance of the ZARM magnetic torquers MT80-1/MT140-2 flown on the ABRIXAS mission” Wiegand, Matthias, et al.; Guidance and control 2000; Proceedings of the Annual AAS Rocky Mountain Conference, Breckenridge, CO, Feb. 2-6, 2000 (A00-41276 11-12), San Diego, CA, Univelt, Inc. (Advances in the Astronautical Sciences. Vol. 104), 2000, p. 483-495
Magnetometers
Magnetometers detect mechanical forces or torques on thin films deposited onto microcantilevers. The displacements of these microcantilevers are detected by optical methods. These are important to determine the attitude of a satellite. Cantilevers with low spring constant and high mechanical Q are necessary features for the measurements.
Magnetometers are also important for the detection of magnetic fields. They allow the mapping of the magnetic field, as well as the localization of electrical activity. The ground magnetic field disturbance caused by ionosphere can be detected, and hence, provide valuable information about the ionosphere.
Books Magnetic Compasses and Magnetometers. Hine, Alfred. Engineering Library. QC819.H55 Magnetic Sensors and Magnetometers. Ripka, Pavel. Engineering Library. TA165.M34 2001 Aerospace Database A subfemtotesla multichannel atomic magnetometer. Nature (0028-0836), vol. 422, no. 6932, 10 Apr. 2003, p. 596-599 Pro-Quest New atomic magnetometer achieves subfemtotesla sensitivity. Fitzgerald, Richard.
Mars/Moons Ephemeris Data
Ephemeris data is the computed places of the heavenly bodies for each day of the year, with other numerical data, for the use of the astronomer and navigator. Ephemeris data is the exact location of a celestial body be it a planet, moon, star, comet, or a manmade space vehicle. The location is given in time intervals and is referenced to a point. Attached is the ephemeris data for the planet Mars for the period between September 29, 2003 to October 14, 2003. There is data for the right ascension, azimuthal elevation, and even brightness.
References 1) JPL HORIZONS On-Line Solar System Data and Ephemeris Computation Service http://ssd.jpl.nasa.gov/horizons.html 2) Mahabala's advance ephemeris : daily positions of planets, 1981 to 1990 by Bala, B.
Mars Radiation Environment
Radiation on the Mars surface is much higher than on Earth’s surface, due to the lack of a global magnetic field to shield the planet. Sending spacecraft (especially manned missions) to Mars will involve dealing with this new challenge. Radiation levels are estimated to be about 2.5 times the level of radiation currently encountered on the International Space Station. Currently, NASA’s MARIE (Martian Radiation Environment Experiment) is orbiting the Red Planet to calculate more exact levels of radiation on Mars to aid in future mission planning. MARIE was launched on the 2001 Mars Odyssey Orbiter.
Sources: http://mars.jpl.nasa.gov/odyssey/technology/marie.html accessed 28 September 2003 http://photojournal.jpl.nasa.gov/catalog/PIA04258 accessed 28 September 2003 http://dsc.discovery.com/news/briefs/20020311/radiation.html accessed 28 September 2003
Mars Soil Composition
The composition of the Martian soil is much different from the soil on earth. It is comprised of 5 - 14% iron-oxide from which we can obtain iron and oxygen, useful for many on-site applications. Iron is usually not used for aerospace applications because it is heavy and corrodes easily. Since Mars has 0.38 the gravity of earth, weight is not a problem. Also the iron will not corrode since there is almost no pure oxygen in the Martian atmosphere. Many structures could be built from iron if the iron ore could be refined on Mars.
Other aspects of the Martian surface, useful to us, are the polar ice caps. We could electrolyze this water to make hydrogen. This hydrogen, along with the carbon dioxide from the atmosphere, could be used to make liquid oxygen and methane to be used as propellant for the return trip.
References: http://science.nasa.gov/newhome/headlines/msad03mar99_1.htm (Bringing Mars into the Iron Age) Accessed: September 29, 2003 http://mars.jpl.nasa.gov/MPF/science/lpsc98/1723.pdf
(Minerology, Composition, and Origin of Soil and Dust at the Mars Pathfinder Landing Site) Accessed: September 29, 2003
Micrometeorite Protection
In the space environment, there are pieces of dust and other debris flying around. Any spacecraft in this environment runs the risk of colliding with them. Even though the majority of the micrometeorites are relatively small (in the range of 10-7 to 10-1 m), the relative velocities (on the order of 10 km/s) are so large that the impact can be devastating.
Several steps are taken to protect against impacts with micrometeorites. For smaller particles (diameter < 1x10-4 mm), thermal blankets and structural panels are used to protect the spacecraft from damage. Another strategy is to orient sensitive surfaces away from the incoming debris. Another option is to fly at altitudes/inclinations that would minimize the probability of an impact.
Also, mission planners/engineers need to minimize the amount of debris that their mission could produce, to keep from adding to the amount of orbital debris in space.
Sources
Tribble, Alan C. The Space Environment: Implications for Spacecraft Design. Princeton University Press. Princeton, New Jersey, 1995.
Olson, Michael F. “Payload Accommodations on the ISS Truss Sites”. AIAA Online Journal, 2001-5095.
Kessler, D. J. “Sources of Orbital Debris and the Projected Environment for Future Spacecraft”. Journal of Spacecraft, 18 (4):357, 1981.
Monopropellants
Most current propellants come in a two-stage form, that of the actual propellant and the oxidizer. Monopropellants, however, are single-component sources of propulsion. The fuel and accompanying oxidizer are mixed into one homogenous substance during the manufacturing process. While this simplifies fuel delivery systems to some extent, more specific conditions are usually required for the substance to exothermically decompose. Monopropellants are most often used in attitude control systems on spacecraft. The most popular monopropellant currently in use is Hydrazine. But while it has a high specific impulse (at 205), it is extremely toxic. To this end many companies have turned to developing green fuels, those that provide comparative performance while having a low impact on the environment. One interesting development was the combination of earth fuels to liquid oxygen (LOX). Everything from kerosene and ground up automobile tires was tried. The kerosene/LOX combination was chosen. It is believed that a LOX monopropellant would eliminate half the propellant systems currently in use.
The Cambridge Dictionary of Space Technology Williamson, Mark TL788.w54 in engineering library Page 237
Useful internet links http://www.space-rockets.com/Loxmono.html http://www.18nam.org/Program/Posters/P175-Improvement%20of%20catalysts%20for %20the%20decomposition.pdf http://woodmansee.com/science/rocket/r-other/rb-propellant.html
Multi-Layer Insulation (MLI)
MRIs are used in the aerospace industry to protect components from thermal radiation. This insulation can also be used to keep system in thermal equilibrium by preventing major fluctuation from hot to cold. Multi Layer Insulation is several different materials placed next to each other in order to better insulate the system. These materials can be coatings, films, composites, or other special materials. The combination of these materials creates a more insulated environment than any one of the materials could create on its own.
Sources: Advances in cryogenic engineering. Volume 47B; Cryogenic engineering conference - CEC; Proceedings, Madison, WI, Jul. 16-20, 2001, Melville, NY, American Institute of Physics, 2002, p. 1565-1572 Authors: Ohmori, T; Nakajima, M; Yamamoto, A; Takahashi, K
Staying Cool on the ISS http://science.nasa.gov/headlines/y2001/ast21mar_1.htm Authors: Steve Price, Dr. Tony Phillips, Gil Knier
Nickel-Hydrogen Batteries
The nickel-hydrogen rechargeable battery system combines the technologies of batteries and fuel cells and is used in high reliability aerospace applications. By replacing one of two opposing metal electrodes with hydrogen gas, significant system benefits result. The weight of the replaced metal electrodes is eliminated and the overall system performance is enhanced. The potential for metal-to-metal shorting is also minimized. The lack of ‘wear-out’ mechanism for a gas reaction greatly improves the system cycle life capability. Last, the abuse tolerance, both operational and environmental, is far in excess of any competitive battery. This system is a true hermetically sealed design, which means that it is totally maintenance free and the danger of electrolyte leakage is eliminated. The system can withstand a wide temperature range and per unit weight offers more than twice the power of the nickel-cadmium battery system. Whether the batteries are used in LEO or GEO satellites, they operate in Earth-like conditions. In GEO, arrays of solar cells power the spacecraft and recharge the batteries while in sunlight, and the batteries are used when in the Earth’s shadow. In LEO the batteries are more active. They power the satellite for 30 minutes and spend 60 minutes being recharged by solar cells. Programs that have, are, or will use the nickel-hydrogen battery system include an HBO satellite, military satellites, the Hubble space telescope, and the International Space Station.
Sources: Goddard Space Flight Center 21st annual Battery Workshop (1988 NASA Goddard Space Flight Center) p. 277, 278, 281, 282, 340 NAS 1.55:3237 Microform 2nd floor Paterno – U.S. Documents
Design News, March 03, 2003, Features; Pg. 86 Hard Charger; Michelle Manzo Leads NASA Efforts To Advance Battery Technology, Jon Titus; Contributing Editor http://80-web.lexis-nexis.com.ezproxy.libraries.psu.edu/universe/document? _m=547c679d94e2e0842768ad0031002bb9&_docnum=2&wchp=dGLbVlz- zSkVb&_md5=5bd9f838da9d4f0639714a0e92604122
Aviation Week & Space Technology, July 21, 2003, IN ORBIT; Vol. 159, No. 3; Pg. 17 Boeing/Loral Team Gets $ 145-Million Contract for ISS Batteries Edited by Frank Morring, Jr. http://80-web.lexis-nexis.com.ezproxy.libraries.psu.edu/universe/document? _m=547c679d94e2e0842768ad0031002bb9&_docnum=1&wchp=dGLbVlz- zSkVb&_md5=78181eddfca74a1b131af03573dcfa21 http://micro.magnet.fsu.edu/electromag/electricity/batteries/nickelhydrogen.html
Planetary Protection
There are two main principles of the concept of planetary protection. First, harmful cross-contamination of planets and celestial bodies needs to be avoided at all costs. If there were any dangerous materials that explorers, whether they be robotic or human, were exposed to in the investigation of a celestial body then that must be taken care of immediately before returning to earth. NASA and COSPAR are trying to create policies on planetary protection protocol that can be internationally agreed upon. Experts are meeting to discuss ethical issues and assess the risk and impact of importation of alien life to a planet.
The second main principle is that the standards that are developed need to meet NASA’s and COSPAR’s technical and scientific concerns, satisfaction, and approval. The public must also be reassured that appropriate safeguards are being taken every step of the way through space exploration.
Sources: “Planetary Protection Implementation on Future Mars Lander Missions,” a NASA conference publication by, R. Howell and D.L. DeVincenzi http://astrobiology.arc.nasa.gov/roadmap/objectives/o17_planetary_protection.html
Pyrotechnic Bolts
Pyrotechnic bolts are fastening devices with one special characteristic. They are filled with an explosive that, upon detonation, causes the fastener to loosen. Pyrotechnic bolts have various uses on the Space Shuttle. Before the launch, the Space Shuttle is held on the launch pad by these bolts. Upon launch the explosive is actuated causing the nuts on the bolts to fracture and instantaneously freeing the Space Shuttle. These nuts are created by drilling small holes into the top each nut and filling them with a pyrotechnic devise. Upon detonation of the devises, the nut is split. The timing of these explosions is very precise ensuring an instantaneous releasing of all of the bolts.
References NASA, NASA explores, Bolting it Down. http://media.nasa explores.com/lessons/01- 032/fullarticle.pdf
NASA Technical Memorandum 110172, A Manual for Pyrotechnic Design, Development, and Qualification . http://techreports.larc.nasa.gov/ltrs/PDF/NASA-95- tm110172.pdf
Radio Isotope Generators Radio Isotope Generators have been in existence for the past 30 years. They can provide continuous power for twenty or more years. They are used frequently in regions of space where the use of solar power is not feasible. 44 RTGs have been used aboard 25 missions – and they have never been the cause of a failure. RTGs convert heat from the natural decay of radioisotope materials into electricity. RTGs contain a supply of plutonium-138 which decays over time. There is also a set of solid-state thermocouplers which convert the heat given off by the plutonium into energy. http://www.ne.doe.gov/pdf/mmrtg.pdf http://www.ne.doe.gov/pdf/stirling.pdf Radiation hardening (electronics)
Radiation hardening of electronics is a topic which is often confused with radiation tolerance. A radiation tolerant electronic device is a device that exhibits some degree of radiation survivability. It’s purely by chance that the device can survive some exposure to radiation. A radiation hardened electronic device has been specifically designed to meet certain radiation level requirements. In the aerospace industry electronic systems are constructed with Radiation Hardness Assured (RHA) devices that are fabrication process monitored, electrical designed, and layout controlled to ensure radiation hardness. Only through the application of all three categories of design and manufacturing techniques could a device be known as radiation hardened. Junction isolation, dielectric isolation, silicon-on sapphire devices, and silicon-on-insulator devices are four basic ways to harden a device. All of the methods listed above isolate each electronic device from surrounding components to eliminate the possibility of latchup and reduce the possibility of a Single Event Upset (SEU).
For more information on SEU follow the NASA ASIC Guide link.
For a brief description of latchup follow the MRC Microelectronics link.
References:
MRC Microelectronics (http://www.mrcmicroe.com/Radiation_Hardening.htm) Sept 28, 2003
The NASA ASIC Guide: Assuring ASICS for Space Section 3 Chapter 4 (http://nppp.jpl.nasa.gov/asic/Sect.3.4.html) Sept 28, 2003
Emerging Radiation Hardness Assurance (RHA) issues (http://radhome.gsfc.nasa.gov/radhome/papers/RHA98.pdf) Sept 28, 2003
Rate Gyro
A rate gyro is designed for a single-degree-of-freedom. The gyro uses Coriolis effect of sensor element to sense the speed of rotation. Some of its uses are for: automotive yaw rate sensors, global positioning, and fluxgate compass compensation. The rate gyro can be place in a few components to the space shuttle also, such as: the orbiter rate gyro and the solid rocket booster rate gyro. For the orbiter rate gyro it is used in the flight control system during launch, landing and aborts as final feedback to final rate errors tat are used to augment stability and then displayed to the commander of the flight. It senses roll rates, pitch rates, and yaw rates. The SRB rate gyro is mainly used during the first stage of launch as feed back to find rate errors from ignition to just about three seconds before SRB separation.
Sources: Title: The Dictionary of Space Technology, second edition. Author: Joseph A. Angelo, Jr. Copy write: 1999 Publisher: Facts on File, Inc.
Reaction Wheels
Reaction wheels are based on the principle of Newton’s third law of motion: for every action there is an equal and opposite reaction. Reaction wheels are on board satellites to control their attitude. These devices are comprised of a motor, flywheel, bearings, and a PC circuit board to process commands. They are also encased in an aluminum casing to protect them from radiation and vibrations due to takeoff. The reaction wheels are oriented such that when the flywheels spin, their torque vectors are oriented in a three dimensional, right handed, coordinate system. When a command is given, one or more of the flywheels spin in either direction. According to Newton the torque created by the spinning flywheel must have an equal and opposite reaction. Accordingly, the satellite spins in the opposite direction, changing the attitude of the space craft. http://www.algor.com/news_pub/cust_app/goddard/goddard.asp accessed 28 Sep 03 http://www.sti.nasa.gov/tto/spinoff1997/t3.html accessed 29 Sep 03
Reentry Parachutes
Knacke defines a parachute recovery system as a device that “uses aerodynamic drag to decelerate people and equipment” moving through a fluid (air, or Martian atmosphere) in his book Parachute Recovery Systems. This system must bring an object from a higher velocity to a lower velocity. This lower velocity is called many things: impact velocity, rate of descent, or landing velocity. A reentry parachute system must meet some or all of the following requirements: personnel are uninjured and ready for activity; equipment and vehicles are undamaged and ready for use or refurbishment; ordnance must impact at a pre-selected angle and velocity. A parachute recovery system is usually used in conjunction with a heat shield and airbrake system to decelerate the payload prior to parachute deployment. Parachutes have several parts, including: drogue chute to slow the vehicle before main chute, the primary (main) chute (sometimes several), an extraction bridle to deploy the chutes, a reefing unit to cut the reefing line that keeps the parachute bundled tightly when not in use, risers to keep the lines from contacting the payload and becoming tangled, and a disconnect to release the parachute either just before impact or afterwards. NASA’s Wallops Flight Facility publishes a Sounding Rocket Handbook that discusses parachute recovery systems in more detail. There are also dozens of handbooks, design books, and information sources available at www.paratech- parachutes.com/references/ref-papers.html. Sources in the engineering library on reentry parachutes are located under the call number TL752; there are multiple books currently available on this topic at the engineering library. Parachute Recovery Systems. Knacke, T.W. Call Number TL752.K53
Sounding Rocket Handbook. Available www.wff.nasa.gov/pages/documentation.html Accessed 9/29/03
Additional Sources. Available www.paratech-parachutes.com/references/ref-papers.html Accessed 9/29/03
Single Event Upset
A Single Event Upset (SEU) is a phenomenon that occurs in near to earth orbit spacecraft and satellites. In general, a Single Event Upset occurs when an energized particle goes through a transistor substrate. This energized particle is usually, but is not limited to a cosmic ray or proton. This results in electrical signals traveling within the transistor. The upset can also occur in digital, analog, and optical components of electrical devices. In regards to space, an SEU occurs while the spacecraft is passing through the Van Allen Belts. The upset is especially common in spacecraft that are passing through the northern and southern auroral zones and the south Atlantic anomaly. In order to find out more information on specific SEU occurrences in space, one should visit the following websites:
Reports-Sept. 29,2003 http://www.gsfc.nasa.gov/ftp/pub/pao/releases/1999/tsr3.htm http://nssdc.gsfc.nasa.gov/space/model/sun/creme.html http://klabs.org/richcontent/fpga_content/Act_1/rh1020_clk_upset_White_paper.PDF Background Information- Sept. 29,2003 http://landsat7.usgs.gov/investigations/seus/ http://nepp.nasa.gov/index_nasa.cfm/767/
Solid Rocket Motors
Solid rocket motors (SRMs), used to provide very high power at relatively low weight, come in a wide variety of sizes and capabilities. Inherent to each are the four main elements, namely the case, propellant, igniter, and nozzle. The case is almost invariably made of a graphite-epoxy composite shell (see the Delta II GEMs & the Pegasus boosters). The propellant in an SRM is a solid, lending the motor both its name and its characteristic low weight. A major safety flaw and control problem inherent in the design lies in the fact that once ignited, SRMs fire until they exhaust the available fuel, with no possible means to shut them down. Of course, this makes them totally unsuitable for any sort of periodic thrust, such as altitude adjustment, and limits them to initial boost out of a gravity well. As a final note, solid rocket motors have been used to assist in both ground-launches, such as the STS, and in aircraft-launches, like the Pegasus launch vehicle. Overall, they form a powerful, if inflexible, means of propulsion. http://mars.jpl.nasa.gov/mer/mission/launch_srm.html Accessed: 29Sep03 http://science.ksc.nasa.gov/shuttle/technology/sts-newsref/srb.html Accessed: 29Sep03 http://spaceflight.nasa.gov/shuttle/reference/shutref/srb/srb.html Accessed: 29Sep03 http://www.thiokol.com/orion.html Accessed: 29Sep03
Spacecraft Charging
Spacecraft charging is a phenomena associated with the buildup of charge on exposed external surfaces of spacecraft. The surface charging occurs through spacecraft interactions with geomagnetic substorm plasma. The particle energies of the plasma ranges from 1 to 50 keV. The charging can happen in two ways, absolute and differential. Absolute charging occurs when the entire spacecraft has a potential relative to the plasma around it. Differential charging occurs when different parts of the spacecraft are charged to different potentials relative to each other. Effects that can be attributed to spacecraft charging include operational anomalies, physical spacecraft damage, and degradation of spacecraft surface material thermal and electric properties. http://trs.nis.nasa.gov/archieve/00000292/01/rpl375.pdf http://etdo.msfc.nasa.gov/technology/docs/systems/system_see_ISC.pdf
Spectrometers on Spacecraft
Spectrometers are remote sensing instruments that measure the amount of light emitted from an object as a function of energy, wavelength, or frequency. They analyze the physical condition of the light-emitting object (i.e. temperature, density, composition, and motion). Spectrometers are used for space-based remote sensing to observe conditions on Earth (air temperature, humidity), as well as to study the Sun (solar cycle) and interstellar medium (origins). To this end, they serve as instrumentation aboard spacecraft. The type of spectrometer is selected on the basis of the phenomena being studied, the observational requirements, and the feasibility of extracting the desired information from the measurements. Spectrometers are used for their reliability, as they show quick operation, an absence of moving parts and mechanical failure, and a high degree of optimization. In terms of impact upon their operational platforms, their weight and cost are taken into account in the design and budget of the spacecraft. In addition, certain spectrometers rely on the spacecraft’s data processing capabilities.
References: Dementiev, B.V., V.V. Ivanov, S.G. Kuklin, et al., “Infrared spectroradiometric system ISTOK-1 of the “Mir” orbital station.” Proceedings of SPIE, Vol. 3406, pp. 119- 134 (1998). Green, J.C. “The Cosmic Origins Spectrograph.” Proceedings of SPIE, Vol. 4498, pp. 229-238 (2001). Peri, F., J.B. Hartley, J.L. Duda. “The Future of Instrument Technology for Space-based Remote Sensing for NASA’s Earth Science Enterprise.”
Star Trackers
NASA and others interested in astronomy have need of star trackers. Yet many of the current cutting edge technology fail to meet the next-generation spacecraft needs. To design more efficient instruments, the Air Force has begun working on an intelligent star tracking system called IntelliStar which uses new optics housing and smart active pixels. The system should be lighter in weight that current systems with greater speed, and better power usage and radiation tolerance.
One specific use of Star Trackers is a NASA project to measure differential star rotation by examining the rotational periods individual sunspots. This should provide information on the degree of subsurface fluid shear. By analyzing sequences of densely packed echelle spectra of AB Doradus spanning deconvolution. The current research has shown differences between the rotation rates of individual spots and the theoretical data are much greater than the observational errors. The smaller spots show a greater scatter than the larger ones, which leads researchers to believe that buffeting by turbulent supergranular flows could be responsible.
Sun Sensor/Attitude Control Sources
Three sources were found that give background information on sun sensors and attitude control. The first is a textbook titled "Spacecraft Dynamics and Control". The book is entirely dedicated towards giving the reader an overview of its title subject, and includes background on sun sensors and how they are used in attitude control. The back of the book also contains pictures, and descriptions of some common commercially used sun sensors. The second source is from the Journal of Astronautical Sciences, and contains a precise overview in attitude determination, aptly described by its title: "Attitude Determination Using Vector Observations: A Fast Optimal Matrix Algorithm". The third source gives an overview of some of the many representations used in attitude dynamics. The title of the source is "A Survey of Attitude Representations," and is a good reference for the relations between different attitude notations.
Markley, F.L (1993). “Attitude Determination Using Vector Observations and Singular Value Decomposition.” Journal of the Astronautical Sciences. 261-280.
Shuster, Malcolm D (1993). “A Survey of Attitude Representations.” Journal of the Astronautical Sciences. 439-517
Sidi, Marcel J (1997). Spacecraft Dynamics and Control: A Practical Engineering Approach
Viking Missions
In the summer of 1975 NASA launched the Viking Mission to learn more about Mars. Twin spacecraft, each composed of an orbiter and a lander, were sent to the Red planet to obtain high resolution images of the surface, characterize the structure and composition of the atmosphere and surface, and search for evidence of life. The spacecraft were launched on August 20, 1975 and September 9, 1975 and took approximately 10 months to reach Mars. The results from the Viking experiments give our most complete view of Mars to date.
What They Did
The orbiter's initial job was to survey the planet for a suitable landing site. After the lander detached to go to the surface, the orbiter's instruments studied the planet and its atmosphere and the orbiter acted as a radio relay station for transmitting lander data. The orbiters imaged the entire surface of Mars at a resolution of 150 to 300 meters, and selected areas at 8 meters. The lowest periapsis altitude for both Orbiters was 300 km.
The Viking Landers transmitted images of the surface, took surface samples and analyzed them for composition and signs of life, studied atmospheric composition and meteorology, and deployed seismometers.
Phases of Deployment
For launch, the Viking orbiters were attached to their lander pods and were positioned inside the nose cones of Titan Centaur launch vehicles. The landers were folded up inside their pods, which were designed to isolate the landers from biological contamination while on Earth.
After entering the Martian atmosphere, the lander released its parachute. When the parachute was deployed, the lander pod was at an altitude of about 6 km (4.0 mi) and traveling at a velocity of 900 kph (600 mph). Soon after, the lower half of the heat shield fell away and the lander's legs unfolded. At an altitude of about 1.5 km (5000 ft) the pod separated from the parachute and using three retro-engines to control its descent, landed safely on the surface of Mars. Just before it touched down on the Martian surface, the lander's terminal descent propulsion system (three retro-engines) had slowed the craft down so that velocity at landing was about of 2 mps (7 mph). Seconds after the lander reached the surface it began transmitting images back to the orbiter for relay to Earth.
Sources: http://pds.jpl.nasa.gov/planets/welcome/viking.htm, accessed on 9/28/03 http://nssdc.gsfc.nasa.gov/planetary/viking.html, accessed on 9/28/03