A Small Re-Entry Capsule - BREM-SAT 2

Following the successful end of the first BREM-SAT mission, BREM-SAT 2 will return back to Earth with a deployable heat-shield and a small solid rocket motor after its mission. A parachute and a small radio beacon are then used to find the satellite with the scientific data of its re-entry and the material samples of a microgravity solidification experiment. Most subsystems are taken from the flight-proven first BREM-SAT mission with minor adaptations to the new mission profile. Attitude control, power supply and onboard data handling will essentially remain unchanged, whereas the structural design incorporates most of the changes. The results given in this paper focus on the heatshield design, the flight dynamics, and the thermal loads associated with the re-entry. The heat-shield used for BREM-SAT 2 is a so-called parashield which resembles a reinforced umbrella and increases the satellites front area by a factor of 12. The initial diameter of 0.65 m during launch and orbital flight changes to 2.24 m when deployed. This shifts the peak of the deceleration loads to an altitude of 70 km; in contrast, the peak-load altitude of a standard reentry capsule is about 40 km. Part of the heat flux is absorbed by the flow due to the blunt cone design, and the temperature is significantly lowered by the large emission area on the front and the back of the heat-shield. Lower temperatures allow the use of conventional, off-the-shelf available materials, like the silicon fabric of the heat-shield originally used for high temperature insulation in terrestrial applications. In additional to the advantages in thermal design, a deployable heat-shield allows the integration of a solar array on the back side of the stowed shield. The shield offers additional safety to the design, because the satellite will not survive the re-entry temperatures when it is not deployed. Alternatively, it may be used to lower the orbit until the retro impulse will guide the satellite into a pre-determined landing area. The free-fall speed in the lower atmosphere is low enough to use a conventional parachute. The mechanical design of the deployable heat-shield is necessarily more complex, and the materials used are pushed to their limits by both mechanical stresses and thermal loads. Finite analysis shows that the design is capable to carry the static loads, and where struts must be strengthened to provide a larger margin of safety. The mechanical design is in fact limited to small (and light-weight) satellites due to the mechanical loads. A successful flight experiment will expand the applications of small and low-cost satellites