A&AE 450 – Senior Design

1. A&AE 450 – Senior Design Jeremy Davis Group A – Aerodynamics Preliminary Design Analysis January 23, 2001

2. ERV to Mars • There are three options for re-entry into Mars atmosphere • Aerobraking maneuver • Aerocapture maneuver • Direct re-entry

3. Aerobraking Maneuver • Advantages • Uses much less propellant than a purely propulsive maneuver.1 • Deceleration is taken over many upper-atmospheric passes which results in lower g-loads on ERV. • With each atmospheric pass, orbiter can analyze drag data and plan small burns accordingly which leaves virtually no risk of mission failure during maneuver.2 • History: Has been completed successfully during Magellan mission and Mars Global Surveyor (MGS).3

4. Aerobraking Maneuver (cont’d) • Disadvantages • Depending on needed deceleration the maneuver lasts several days to several months.4 • Rarified flow calculations can be difficult at this level.

5. Aerocapture Maneuver • Advantages • Similar to aerobraking, aerocapture uses much less propellant than a purely propulsive maneuver. • Because the ERV enters farther into the atmosphere than aerobraking, a plane change could be made if needed.5 • Maneuver takes much less time than aerobraking.

6. Aerocapture Maneuver (cont’d) • Disadvantages • Very intense heating during initial maneuver virtually requires ablative surfaces which are very difficult to model.6 • Because of lower altitude, density fluctuations can present a major risk to mission success. • G-load during initial maneuver can be high (relative to aerobraking only).

7. Direct Re-Entry • Advantages • Very quick and simple compared to aerobraking and aerocapture maneuvers. • History: Has been used for past re-entry capsules (i.e., Apollo) • Disadvantages • Very sensitive to atmospheric changes and trajectory errors. • Because of high entry speeds, G-loads could be excessive.

11. ERV to Earth • There are three options for re-entry into Earth atmosphere • Aerobraking maneuver • Aerocapture maneuver • Direct re-entry

12. Maneuver Differences for Earth • In the case of an aerobraking maneuver, spending weeks in orbit around Earth could be unappealing to astronauts and would put unnecessary constraints on food requirements. • Aerocapture maneuver could enable a Space Shuttle rendezvous for re-entry. • Aerocapture could be too risky for manned space flight (further analysis intended).

16. References & Notes • NASA, JPL. mars.jpl.nasa.gov/mgs/confrm/aerobexp.html gives a comparison between Mars Global Surveyor, which used aerobraking, and Mars Observer (both of similar payload masses) showing Mars Observer’s launch mass 2.4 times that of MGS. • Walberg, Gerald. A Survey of Aeroassisted Orbit Transfer, AIAA 9th Atmospheric Flight Mechanics Conference, San Diego, Calif., 1982, mentions multi-pass aerobraking maneuvers are possible to be made “fail-safe” and that “…tracking data obtained during the early high-altitude orbits can be used to provide estimates of atmospheric density…” • From Ref. #1, gives a detailed analysis of the aerobraking procedure of the MGS. • From Ref. #1, the MGS aerobraking procedure was designed to last 4 months, due to a small error, it lasted 17 months. Magellan mission to Venus had a 44 day aerobraking procedure (from Ref. #2).

17. References & Notes (cont’d) • From Ref. #2, “Synergetic Plane Change” section. • From Ref. #2, “… aerocapture maneuvers produce relatively high values for both the heat-transfer rate and the heating time…”

18. Relevant Experience • Courses Taken • A&AE 439 • A&AE 490 ( Research of Satellite Fuel Tanks in Zero-G Environment, with Prof. Collicott) • Currently taking A&AE 519 (Hypersonics) • Computer Skills • MATLAB, FORTRAN & Surface Evolver