On the 23th of September, the Capsule and Recovery team launched a modified CanSat rocket, called the V7M, to test multiple new systems for Aether. During this launch day, almost every aspect of project Aether was tested, including the engine, active stabilisation system and the recovery system.
The Capsule and Recovery team handled one of these aspects, namely the high-speed dual-recovery system. This system consists of two parachutes: a small drogue and a larger main parachute. These parachutes are deployed using a combination of a mortar for the drogue chute and a pyrobolt to release the main parachute. The deployment sequence can be seen in the image below. The rocket initially comes nose down with the drogue parachute trailing behind. When the explosive bolt is triggered, the rocket should flip and the main parachute will be pulled out by the drogue.
Parachute deployment sequence for Aether and CanSat V7M
Pyrobolt on testing stand after testing
On Thursday, the pyrobolt and gas-assisted parachute ejection (mortar) were tested. The mortar was successful, firing the drogue parachute into the air as expected. The pyrobolt, unfortunately, did not fire successfully, since the gas produced by the black powder escaped through holes on the side. These holes were meant for the igniter squibs to trigger the bolt. The seal on the holes, however, was not adequate enough to contain the expanding gas and thus it started leaking. On the actual launch day, the pyrobolt, which was upgraded the night before, did fire successfully. With this test completed, all subsystems proved their reliability and the full integration of the CanSat V7M was ready to start.
CanSat V7M fully integrated for launch
The rest of the day was spent integrating the rocket and preparing the system for launch. The CanSat used was the standard model V7, but now upgraded with the new recovery system. At 13:55 the rocket was launched in some of the best conditions we have ever seen during a DARE launch day in the Netherlands. The sky was clear blue, which gave everyone the opportunity the track the full trajectory of the rocket. This later would prove to be vital for the analysis of the launch.
After 12 seconds into the flight, the hatch on the side of the rocket was released exposing the recovery system. One second later the mortar fired, deploying the drogue chute. At this moment, the rocket was perfectly nose-down suspended below the drogue parachute. At 20 seconds into the flight, the pyrobolt fired, pulling out the main parachute as planned. Unfortunately, during the deployment and rotating of the rocket the main parachute snapped off causing the rocket to fall down at terminal velocity.
During the launch, the team could already conclude that the mortar fired successfully, the drogue worked as intended, the pyrobolt fired as planned and the drogue parachute proved capable of pulling out the main parachute. This meant that all the subsystems that the team wanted to test, worked. When reviewing the video footage more problems were discovered.
Main parachute wire after launch
When the hatch was deployed, the wire holding it to the rocket came loose. This was the result of an improper knot being used in the integration and assembly of the system. This happened because of the inexperience with the new system, but had no real consequences on the flight itself. Another detail that was seen on the footage, was the fact that the drogue separated from the main after the pyrobolt was triggered. The force that the drogue exerted on the main was apparently enough to cause this separation. Both parachutes were connected with a single line stitched into the fabric. This connection will be improved upon, in order to ensure that the stitching doesn’t fail on the Aether rocket as it had on the CanSat. The last anomaly was that the main parachute separation was most likely the combination of shock force together with a weakened point in the rope at the knot. The conclusion was drawn after seeing the footage and the remainder of the rocket after touchdown. On the footage, it was clear that the separation occurred the moment the lines got tensioned, exactly when the shock load is at its peak. The remainder of the wire that was recovered, suggested that it broke near the end of the rope where the parachute lines were tied into a knot around the ring.
In the coming period, multiple tests will be performed by the team in order to more thoroughly understand the problem and to improve the reliability of the system. This will all be done to maximise the chances that Aether will have a successful launch and recovery in 2017. Updates on the tests and their results will follow later.