For multiple DARE flagship projects such as Aether, Stratos III and Stratos IV the recovery system makes use of a Hemisflo ribbon drogue parachute. This parachute is selected for its high supersonic capabilities, up to Mach 3.
Within the Parachute Research Group (PRG) multiple tests are performed on all recovery systems to see if hardware complies with all requirements of a project. When looking at a parachute deployment and flight, the two most critical items are the dynamic pressure and the supersonic regimes encountered.
Dynamic pressure scales with air density and velocity. Therefore, deployments at a higher altitude at high velocities as in the flagship missions can have the same dynamic pressure as deployments close to the ground at lower velocities. To test our parachutes up to high dynamic pressures, the Parachute Investigation Project (PIP) was created. This test launcher aims at deploying a test parachute very close to the ground, picking up speed between apogee and parachute deployment. The expected dynamic pressures run up to 8 kPa which is similar to a deployment on Stratos. Thus, the dynamic pressure aspect of the Hemisflo ribbon drogue parachute deployment is testable.
The supersonic flight aspect that the parachute needs to be able to handle, is more difficult to test. Large enough supersonic wind tunnels exist but are very expensive. Next to this, there are still slight differences in loads and behaviour between deployment in flight or in a wind tunnel. Therefore, a supersonic flight test would be necessary to validate the supersonic performance of this parachute.
In the above-mentioned DARE flagship missions, a supersonic deployment of the drogue parachutes is possible. However, the primary goal of the recovery system is to retrieve the payload safely, not to test its own parachutes. Thus, we aim to create as ‘soft’ conditions as possible during parachute deployment to ensure the highest chance of success.
Inspired by SUPERMAX, flown on MAXUS, the launch of a module specifically for testing our drogue parachute would offer a perfect solution. This led to the proposition of a new mission to fly on the REXUS sounding rocket; the Supersonic Parachute Experiment Aboard REXUS (SPEAR).