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13 June 2011
Q: How do you test a parachute designed to enter a planet's atmosphere at high speed?
A: By entering a planet's atmosphere at high speed.
In conjunction with the European Space Agency (ESA), students from the Cambridge University Spaceflight team have recently tested parachutes for the ExoMars lander, a European-led robotic mission to Mars currently under development by NASA and the ESA, by re-entering Earth's atmosphere at 450mph.
"Six Minutes of Terror" is how engineers describe the process of Entry, Descent, and Landing (EDL) on Mars. It is perhaps the most challenging part of any mars lander mission, a complex ballet of heat shields, parachutes, retro-rockets and airbags, all having to assemble themselves mid-air; a failure in any one part would lead to almost certain mission failure. Simulating this is no easy task, a parachute is a complex, fabric structure opening into a fluid flow and so real hardware testing is essential. However, Mars has an atmosphere more than one hundred times thinner than Earth's, and re-creating these high velocity, low density flows in a wind tunnel is a hugely expensive, if not impossible, task. The Spaceflight team's testing method has not only been successful but is an extremely cost effective way to test parachutes in a Mars-like environment.
Using their experience with high altitude scientific balloons and instrumentation, the CU Spaceflight team built a balloon-lofted vehicle, packed with a test parachute. This was taken to the top of the atmosphere, where the air is a similar density to the surface of Mars. They then instructed the vehicle to free-fall for an amount of time calculated to let it accelerate to Mach 0.8 (Mach 0.8 is 80% of the speed of sound), where it deployed the parachute and monitored its inflation using a suite of instrumentation including accelerometers, gyroscopes and a high speed camera.
The CU Spaceflight team Iain Waugh, Ed Moore, Fergus Noble, Dan Strange, and Jon Cormack are giving a talk about testing the parachutes on Friday 17th June at 1pm in LT0.
The slow motion video below shows the parachute dynamics during one of the low-speed system development tests. At 24km, the vehicle cuts away from the balloon, and a rope from the balloon immediately pulls the parachute out of the deployment bag. Because the vehicle is going so slowly, and the air is so thin, the parachute takes a few seconds to inflate (the video is 10x slower than real-life) and the vehicle tumbles. In the high-speed parachute test, the parachute was deployed at Mach 0.8 and was fully inflated in 1/20th of a second.
The team recently presented their work at the 21st AIAA Aerodynamic Decelerator Systems Conference in Dublin, where it took first place in the Best Student Paper competition.
The paper can be downloaded here: http://www.cuspaceflight.co.uk/CUSF_AIAA_2011.pdf
Cambridge University Spaceflight is a student-run society formed in 2006 to experiment with low-cost spaceflight www.cuspaceflight.co.uk
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