Aerodynamic Investigation of NASA Crew Exploration Vehicle Forward Bay Cover Separation Characteristics

Abstract

The Constellation Program’s Orion Crew Exploration Vehicle (CEV) is the spacecraft that will carry America’s next generation of astronauts back to the moon and perhaps one day beyond. Orion employs a system of parachutes to safely return the astronaut crew to Earth. Prior to main parachute deployment, the Forward Bay Cover (FBC), which covers the stowed parachutes, must be quickly jettisoned. Successful jettison is critical to the safety of the astronauts and is of concern because of near re-contacts experienced during the Apollo program. The FBC will be jettisoned into a highly unsteady region of re-circulating flow, tending to push the FBC towards the CEV. This investigation conducted an extensive series of wind tunnel tests to define these characteristics and found a maximum negative average FBC drag coefficient of -0.0664. However, it was also found that oscillations in the flow could result in a negative drag coefficient as large as -0.491. The negative drag region was identified as a major concern for potential FBC re-contact. The FBC time-averaged forces and moments reach their maximum magnitude at 1.2 CEV heat shield diameters of aft separation distance. Increasing Mach number tended to reduce force and moment coefficient magnitude while increasing FBC rotation angle tended to increase these characteristics. The average uncertainty in the data analyzed was 0.0205, and the greatest data uncertainty tended to occur near the boundary of the re-circulation region and in the pitching moment and lift coefficient. Accounting for the drag due to the jettison velocity but neglecting the impulse necessary for inertial acceleration, a “worst case” required impulse of 19,000 lb-s was projected at 10,000 ft and a 38 fps jettison velocity to ensure the FBC clears the re-circulation region, ensuring flight safety and mission success. NASA Johnson Space Center sponsored the investigation.