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%3dwh
at%2bis%2baero%2bcapture%26o%3d0%26page%3d1&q=what+is+aero+captur
e&u=http%3a%2f%2ftm.wc.ask.com%2fr%3ft%3dan%26s%3da%26uid%3d280
76a0558076a055%26sid%3d38076a0558076a055%26qid%3d7D3CE1425D8466
4D885B5DA800726D2D%26io%3d4%26sv%3dza5cb0dee%26ask%3dwhat%2b
is%2baero%2bcapture%26uip%3d8076a055%26en%3dte%26eo%3d100%26pt%3dAeronautics%2bSeminars%2b-%2bFall%2b200102%26ac%3d24%26qs%3d0%26pg%3d1%26u%3dhttp%3a%2f%2fwww.its.calt
ech.edu%2f%7ewirz%2fSeminar%2f20012002.htm&s=a&bu=http%3a%2f%2fwww.its.caltech.edu%2f%7ewirz%2fSemin
ar%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.
<http://www.onera.fr/dcsd-en/gyrodynes/>.
Educational Control Products - Control Systems – Control Moment Gyroscope.
<http://www.ecpsystems.com/controls_ctrlgyro.htm/>.
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, <http://science.nasa.gov/ssl/pad/solar/cmes.htm>. 9/30/03.
Crooker, Nancy, Jo Ann Joselyn, Joan Feynman. Coronal Mass Ejections. American
Geophysical Union, 1997. Washington, D.C. 9/30/03.
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
<www.eng.upm.edu.my/~nizam/download/MS4/chapter6-2.pdf>.
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
<http://students.cec.wustl.edu/~sapphire/design/log/sec8adc/8.4.html>.
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.
<http://ieeexplore.ieee.org/iel5/8665/27471/01223522.pdf?isNumber=27471&pro
d=STD&arnumber=1223522&arNumber=1223522&arSt=+695&ared=+699&arAuthor=
+Reyhanoglu%2C+M.>
Sidi, Marcel J. Spacecraft Dynamics and Control. Cambridge: Press Syndicate of the
University of Cambridge, 1997.
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-assistprimer.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, 3rd 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=15
48
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/P175Improvement%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.lexisnexis.com.ezproxy.libraries.psu.edu/universe/document?_m=547c679d94e2e0842768ad0
031002bb9&_docnum=2&wchp=dGLbVlzzSkVb&_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.lexisnexis.com.ezproxy.libraries.psu.edu/universe/document?_m=547c679d94e2e0842768ad0
031002bb9&_docnum=1&wchp=dGLbVlzzSkVb&_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/01032/fullarticle.pdf <September 29, 2003>
NASA Technical Memorandum 110172, A Manual for Pyrotechnic Design,
Development, and Qualification. http://techreports.larc.nasa.gov/ltrs/PDF/NASA-95tm110172.pdf <September 29, 2003>
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.paratechparachutes.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. 119134 (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.”
<http://www.esto.nasa.gov/conference/igarss-2002/01Papers/07100840.PDF>,
accessed 28 Sept, 2003.
Zhitnik, I., A. Ignatiev, V. Korneev, V. Krutov, et al., “Instruments for imaging XUV
spectroscopy of the Sun on board the CORONAS-I satellite.” Proceedings of
SPIE, Vol.3406, pp.1-19 (1998).
Concise Encyclopedia of Aeronautics &Space Systems. Eds. Pellegrin, M., W.M.
Hollister. 1st ed. Pergamon Press, Oxford, 1993.
“The Astro-E Learning Center Glossary”,
<http://agile.gsfc.nasa.gov/docs/astroe_lc/glossary.html>, accessed 23 Sept, 2003
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