The first CPAS development tests focused on one main or one drogue parachute deployed by a static line, but more recent tests have evolved into Cluster Development Tests, or CDTs, that deploy multiple parachutes.
CPAS uses two test vehicles, both utilizing SPAN technology. The first is called a parachute compartment development test vehicle, or PCDTV. When this missile-shaped vehicle drops out of the C-17 aircraft, it falls as fast as possible to test the parachutes' strength. The second option, known as the Parachute Test Vehicle (PVT), was used in January, February and April test launches.
Regardless which vehicle is used, SPAN-SE helps ensure analysts vertical velocity data, and has done so in 15 CPAS test drops since the program began in 2009.
The PTV looks like and weighs about the same as the actual Orion capsule so the team can conduct “apple to apple comparisons,” but that's about where the similarities end, Williamson says. The test vehicle's internal structure is steel and it doesn't come equipped with a heat shield. It is a little shorter than the real Orion so it can fit into the C-17 aircraft, it lands on land rather than in water, and researchers can reuse it for future parachute testing.
Before the parachutes are deployed, the C-17 aircraft flies as high as 35,000 feet-the actual altitude parachutes will deploy from on the real Orion spacecraft. The C-17 aircraft is used to recreate the turbulence as the test vehicle falls through the air, and to see how it reacts to that air turbulence. All CPAS tests are conducted at the U.S. Army's Yuma Proving Ground in Yuma, Arizona.
The tests in January and June, which incorporated a Forward Bay Cover for the first time, proved to be one of the more complex Orion flight-like tests to date. The covers act as a shell that fit over the spacecraft's crew module, protecting Orion during launch, flight and re-entry. When Orion is ready to return from space, the cover must come off before the parachutes can deploy.
Twenty parachutes were deployed during the January test-nine were test technique related, while 11 were Orion system parachutes, according to NASA. This test set out to demonstrate how the full Orion parachute system performs and interacts during an end-to-end test. The test also demonstrated extraction using a modified technique in the reposition and programmer staging.
“When the drogue parachutes are deployed on the Orion capsule, that's where the test sequence begins,” Williamson says. “These parachutes slow the vehicle down to a velocity the main parachutes can handle. At this point, the vehicle is going multiple hundreds of miles an hour. If we just deployed the main parachutes, they would fail. So we slow it down with a smaller set of parachutes first. Once the vehicle is at the right velocity the next step is to deploy the Pilot Parachutes. These smaller parachutes pull the main parachutes out so they can be deployed. That's when the main parachutes will slow down the vehicle to the rate below 33 feet per second.”
Researchers looked at the main parachute's modified reefing stage ratio during this test. The drop test article landed at the speed of 17mph, as measured from a SPAN-SE receiver.
The April 2014 test served as a launch abort simulation. Researchers dropped the test vehicle from a lower altitude-13,000 ft msl-skipping the drogues in the parachute deployment sequence to ensure the main parachutes can inflate and decelerate the vehicle, even if the launch abort system activates on the pad.
Williamson says they got a full data file and early indications show it worked nominally. Test engineers are working with SPAN-SE data within Google Earth, where they are making a 3D plot of the trajectory of the test vehicle from take-off to landing.
A total of 17 development tests will be completed before the team moves on to qualification testing, which is expected to begin in early 2016. The design that was refined and functionally proven will then be tested to qualification requirements levied by the Orion Program. The final CPAS engineering development unit test (EDU) is scheduled for February 2015.
“Now we're working out bugs, failing parts of the parachutes to see how they react,” Williamson says. “In one test we failed one of the three main parachutes to make sure we can still meet the safety of the 33 feet per second descent rate even if one of the main parachutes is missing. When we go into qualification we should have all those tests complete. Then we can focus on the design and proving to the program and safety community that our parachutes meet the design requirement that have been levied upon us.”
The team has tested various failure modes over the years, including a simulated failure involving a skipped second reefing stage on the drogue parachutes resulting in higher parachute loads, and a failure to deploy one of the three pilot parachutes. CPAS also has examined how the wake, or disturbance of airflow behind the vehicle, from the spacecraft affects the parachute system's performance.
“To date we've had great success. Most of our failure cases come out with flying colors,” Williamson says. “We do a lot of prep work. Tests can take 6 months or more to develop before we go out to Arizona. For me success means having a good plan, working that good plan and learning something from it.”