In-flight Abort System
When things go wrong during ascend, the crew needs to be able to remove themselves from a failing rocket. Launch escape systems have to operate at the highest dynamic pressures and the toughest conditions. This blog post is on how the design of the parachute system is influenced by the inclusion of a launch escape system. From the Apollo design report it can be seen that the launch escape system introduces an expansion of the envelope
In the envelope, one can see the envelope of the drogue and main parachute. In the envelope, there is an additional area named the high altitude aborts. For these aborts, a higher dynamic pressure can be seen. The dynamic pressure increases from 100 PSF (4.8kPa) to 204 PSF (9.8 kPa). The low altitude aborts, or pad boards, tend to be less intense for the parachute system and more demanding for the rockets. These rockets are tasked with the separation between the capsule and the rocket. Most crewed systems have been put through their passes and have been tested for abort scenarios. One notable example was the SpaceX in-flight abort test done in 2019.
Testing the abort system
Crewed missions often test their abort system on the ground or in flight. Several examples are the crew dragon in-flight abort test and the boeing pad abort test.
CrewDragon in-flight abort test
On the 19th of January 2020, SpaceX performed their in-flight abort test of the Dragon 2 capsule. The abort test was the final test before the crewed flight later that year. The mission demonstrated the ability of the Draco thrusters to push away the crewed capsule in the event of a failure with the Falcon 9. For the test, the Falcon's main engines were shut down, leading to an abort decision of the capsule.
What made this test interesting was the fact that the parachutes deployed while the rocket was ascending. The exact moment of flight termination was at Max Q, in other words, the most stressful moment for the rocket. As with more SpaceX (and other commercial tests), not much data is available showing the actual numbers of dynamic pressure at parachute inflation or how close the results are with the predicted results. The only thing known is that SpaceX considers the test to be a success and that the capsule was recovered safely.
In terms of parachutes, the two drogue parachutes reefed in two stages performed well, followed by the cluster of four main parachutes. The upward-looking camera nicely shows the inflation of both parachute systems and the dancing of the cluster. It can be seen that one of the drogue parachutes are fluttering quite a bit after inflation, possible due to the high dynamic pressure it experiences. Flutter in parachutes can be caused by a parachute not being in equilibrium or due to the body (in this case, the dragon2 capsule). This leads to a constant over and under-inflation of the canopy. Later on, the drogues inflate stability and the four main parachutes are deployed. These inflate nice and slow, as desired. Later on, two main parachutes can be seen almost entangling with each other.
Starliner Pad abort test
On the 4th of November 2019, Boeing performed the pad abort test of the CST-100 starliner. The abort was initiated by the boosters launching the capsule to about 1.3 km where the drogue parachutes were deployed. The boosted part of the flight took about 17 seconds and the parachutes were extracted at 20 seconds. When the three main parachutes were supposed to be extracted, only two appeared. This was due to a faulty connection between the pilot and main parachute. NASA/Boeing still considered the test to be a success as Starliner was designed to operate with only two of the three main parachutes inflated.
