Sponsor: Rich Burns
NASA Goddard Space Flight Center
Lunar ComSat
 
Overview
 
NASA plans to establish a human base on the moon (read the article). The base will most likely be located at the north or south pole of the moon. The primary reasons are that the temperature variations are smaller at the poles, and high amounts of hydrogen have been detected there, which could be used by the base for fuel (read the article).
 
While the base will remain at a fixed location, exploration of the moon will require vehicles to leave the base for extended periods of time. Constant communication between the base and these vehicles, and between Earth and the base, are important requirements.
 
Satellites orbiting the moon can be used to provide a communication link to the lunar base and its vehicles. However, orbits around the moon tend to be unstable because of the gravitational pull of the Earth. Researchers at NASA have identified sets of elliptical lunar orbits that are stable for several years and that can provide coverage of the entire lunar surface.
 
In this project, you will design a Lunar ComSat and a set of orbits around the moon that 2 or more satellites will occupy to provide communication services for the lunar base. The constellation should provide a continuous communication link between Earth and the lunar base, and between the lunar base and other mobile lunar agents. Refer to the paper by Ely (listed at the bottom of this page) for detailed information on the orbits.
 
Requirements
The top level requirements for the mission are summarized below. Your design work should flow directly from these requirements. If any of the requirements are unclear, or if you feel important information is missing, contact the instructor.
  1. 1.    The satellite constellation shall have continuous visibility of the lunar base and Earth.
  2. 2.    The satellites must be capable of receiving / transmitting signals from / to Earth, and from / to the moon.
  3. 3.    The size & mass of the satellite must fit within the limits of conventional launch vehicles.
  4. 4.    The lifetime of the satellite must be at least 10 years.
 
Major Tasks
  1. 1.Identify COTS receivers, transmitters, and other essential hardware for the design.
  2. 2.Simulate the orbits of the spacecraft with disturbance forces from solar pressure, and point-mass models of the Earth, Moon and Sun.
  3. 3.Determine the size and power requirements of the communications system.
  4. 4.Determine the required battery capacity by computing the time-in-shadow and the expected power consumption.
  5. 5.Perform a trade study between conformal solar arrays and normal-pointing solar arrays.
  6. 6.Determine the required solar cell area.
  7. 7.Determine whether the mission lifetime can be achieved without orbital maneuvers
  8. 8.Perform a trade study between different methods of attitude control. Recommend a system based upon your analysis.
  9. 9.Design an attitude control law.
  10. 10.Perform a trade study between 2 and N satellites. Show how the coverage area can be increased with more satellites.
  11. 11.Design a configuration that meets all requirements
 
Expectations
  1. 1.Explain the results of all trade studies.
  2. 2.Demonstrate that the selected orbits provide sufficient visibility of the Earth and lunar base
  3. 3.Show whether the selected orbits will remain stable for the desired mission lifetime.
  4. 4.Demonstrate that the design meets the size and mass requirements of a conventional launch vehicle.
  5. 5.Demonstrate that the power supply is sufficient for the mission.
  6. 6.Demonstrate that the spacecraft and its components will stay within allowable temperature ranges.
  7. 7.Demonstrate that the spacecraft can meet all of the pointing requirements simultaneously.
 
 
Groups
The team will consist of the following groups:
  1. •    Orbital Design
  2. •    Structural Design and Thermal Management
  3. •    Attitude Determination and Control
  4. •    Power and Communications
  5. •    Systems Integration and Management
 
 
References
 
Ely, T. and Lieb, E., “Constellations of Elliptical Inclined Lunar Orbits Providing Polar and Global Coverage”, presented at the AAS/AIAA Astrodynamics Specialists Conference, Lake Tahoe, CA, August 2005, AAS 05-343.
 
 
Links
http://www.google.com/jobs/lunar_job2.html
 
 
 
Mars Lander          Lunar ComSat          Formation Flying          Solar Sail          GPS Bistatic Radar