A study of the Earth return aerocapture for a manned Mars mission

The current architecture being considered by NASA for a future manned Mars mission involves the use of an aerocapture procedure at both Mars and Earth arrival. The aerocapture will be used to decelerate and insert the vehicles into the desired orbits at the respective planets. The crew may return to Earth in a large, inflatable habitat known as the Transhab. This Transhab would be complimented with an aeroshell, which will serve the dual purposes of providing protection from the intense heat of high-speed atmospheric flight and offer some lifting ability to the vehicle as well. The aeroshell has been dubbed the "Ellipsled" because of the characteristic shape. This thesis represents a preliminary study of the aerocapture of the Transhab/Ellipsled vehicle upon Earth return. Undershoot and overshoot boundaries have been examined as a function of entry velocity for a variety of constraining factors such as deceleration limits and vehicle ballistic coefficient. The effects of atmospheric dispersions have also been explored. In addition, a simple 180 degree roll maneuver has been implemented in the undershoot trajectories to help target the desired 407 km circular Earth orbit. Results show that the Transhab/Ellipsled vehicle has a nominal entry corridor width of 0.5 - 0.7 degrees for entry speeds ranging from 12.5 km/s to 14.5 km/s. In addition, entry corridor comparisons have been made between the Transhab/Ellipsled and a modified Apollo capsule which is also being considered for the Earth return vehicle. Future studies should focus on refining the heating rate analyses, off-nominal vehicle aerodynamics, winds, horizontal density waves, and changes in the vehicle trim angle of attack. Furthermore, a guidance algorithm should be implemented to optimize the overall trajectory and minimize inclination changes and post-aerocapture delta V needed to circularize the orbit.