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

ERV to Mars There are three options for re-entry into Mars atmosphere 1.Aerobraking maneuver 2.Aerocapture maneuver 3.Direct re-entry

Aerobraking Maneuver Advantages 1.Uses much less propellant than a purely propulsive maneuver. 1 2.Deceleration is taken over many upper-atmospheric passes which results in lower g-loads on ERV. 3.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 4.History: Has been completed successfully during Magellan mission and Mars Global Surveyor (MGS). 3

Aerobraking Maneuver (cont’d) Disadvantages 1.Depending on needed deceleration the maneuver lasts several days to several months. 4 2.Rarified flow calculations can be difficult at this level.

Aerocapture Maneuver Advantages 1.Similar to aerobraking, aerocapture uses much less propellant than a purely propulsive maneuver. 2.Because the ERV enters farther into the atmosphere than aerobraking, a plane change could be made if needed. 5 3.Maneuver takes much less time than aerobraking.

Aerocapture Maneuver (cont’d) Disadvantages 1.Very intense heating during initial maneuver virtually requires ablative surfaces which are very difficult to model. 6 2.Because of lower altitude, density fluctuations can present a major risk to mission success. 3.G-load during initial maneuver can be high (relative to aerobraking only).

Direct Re-Entry Advantages 1.Very quick and simple compared to aerobraking and aerocapture maneuvers. 2.History: Has been used for past re-entry capsules (i.e., Apollo) Disadvantages 1.Very sensitive to atmospheric changes and trajectory errors. 2.Because of high entry speeds, G-loads could be excessive.

ERV to Earth There are three options for re-entry into Earth atmosphere 1.Aerobraking maneuver 2.Aerocapture maneuver 3.Direct re-entry

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).

References & Notes 1.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.mars.jpl.nasa.gov/mgs/confrm/aerobexp.html 2.Walberg, Gerald. A Survey of Aeroassisted Orbit Transfer, AIAA 9 th 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…” 3.From Ref. #1, gives a detailed analysis of the aerobraking procedure of the MGS. 4.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).

References & Notes (cont’d) 5.From Ref. #2, “Synergetic Plane Change” section. 6.From Ref. #2, “… aerocapture maneuvers produce relatively high values for both the heat-transfer rate and the heating time…”

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