TRACE is designed as a free flight experiment to test and evaluate the use of transpirative heat shields on a sounding rocket. The key to a successful experiment is to ensure the flight envelope allows for sufficient heating of the experiment surfaces. The concept of a free-flying experiment as a testbed for such a transpiration cooling experiment was laid out in the bachelor thesis “Design of a free-flight experiment to be carried on the REXUS mission” by Clemens Weitzel. It showed that high speeds in dense atmosphere allow such a free flight experiment within the flight envelope of a REXUS mission. Nevertheless, extensive aerodynamic optimizations of the re-entry vehicle are necessary.
Our proposed re-entry vehicle consists of a 15° cone with a rounded nose and an aerodynamically optimized boat tail. The experiment is designed to fit in the nose cone of a REXUS rocket and to be ejected after the rocket is despun. It will be passively aerodynamically stabilized.
The experiment itself consists of two reference surfaces and two transpiration cooling tiles. The forward cone will be split into four quadrants. Two opposing quadrants will house the transpiration cooling experiment with the two other opposing quadrants acting as reference surfaces. The entire forward cone surface will be made of PEEK, a high-temperature resistant thermoplastic polymer with the required properties to ensure sufficient heating of the reference surfaces. The transpiration cooling elements will be manufactured out of PEEK with a porous structure. They will be cooled cooling gas from inside the capsule. Besides the cooling system, the nose cone houses a set of temperature and heat flux sensors, as well as electronics for data logging, avionics, and system control.
For our mission goal, a full recovery of the TRACE free flying unit can be achieved by using a two-stage parachute system consisting of a drogue and main parachute. The experiment recovery starts at an altitude of 8000m. During the first stage, the boattail is ejected and the drogue parachute deployed. The parachute decelerates the experiment from supersonic to subsonic velocities. In the second stage, the main parachute is opened which slows down the TRACE free flying unit to a lower terminal velocity for landing. To facilitate the staging, the experiment has multiple points of separation.
Besides data storage, the TRACE free flying also contains an Iridium satellite communication module, a GNSS module, and a power management system to help with locating it after landing. It has enough power for at least 5 hours of transmission. The following graphic shows the estimated velocity on the re-entry trajectory.