AGRICULTURE
Put to the Test
In just a few years, NASA's Orion spacecraft will travel further into space than anyone has ever been.
This spacecraft will carry up to four astronauts deep into space, where they'll have the opportunity to visit near-earth asteroids, the moon, the moons of Mars and eventually Mars itself. Orion's development, which benefits from more than 50 years of spaceflight research, marks a new era of space exploration, with an aircraft that, according to NASA, “will be the safest, most advanced spacecraft ever built.” Orion is scheduled to take its first manned flight into deep space in 2021.
But before that can happen, researchers and engineers must complete multiple tests to verify the spacecraft is ready for deep space exploration, from making sure it can withstand the harsh environment created during launch to ensuring it can safely re-enter the Earth's atmosphere and land in the Pacific Ocean once a mission is complete.
Orion's Landing and Recovery System is among those systems that must be verified to ensure the spacecraft is ready to take astronauts into space and bring them home safely. The NASA Capsule Parachute Assembly System, or CPAS, is its subsystem. Through CPAS, NASA has put Orion's parachutes to the test for the last five years. The most recent tests, Nos. 12, 13 and 14 were completed earlier this year.
“Our objective is to provide a parachute system that is going to decelerate the Orion capsule to a safe velocity for touchdown in the ocean,” says Charles Williamson, NASA avionics test lead. “We have a whole litany of requirements that we have to meet from the Orion program, and a lot of those requirements were also imposed on the Apollo program. We have some members of the Apollo program on our team so they can pass down their knowledge. One of the biggest requirements is a descent rate that is less than 33 feet per second to ensure crew members are not harmed when they hit the water.”
To determine how fast the test vehicle is falling, the team uses NovAtel's SPAN-SE™ receiver combined with an inertial measurement unit, or IMU. During these drop tests, researchers need to capture vertical velocity data to ensure the test vehicle's descent rate doesn't exceed the 33 feet per second requirement. The SPAN-SE provides the user interface to NovAtel's SPAN technology, and outputs raw measurement data or solution data over several communication protocols or a removable SD card. Combining the SPAN-SE with a SPAN-supported IMU creates a complete INS system.
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 most recent tests
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.
Other tests
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.”
As NASA's avionics test lead, Williamson oversees the design of the CPAS test vehicles avionics system. He collects a variety of data, from navigational to environmental, and is tasked with making sure the avionics work properly and that they can carry out the test procedure.
“The test vehicles are all equipped with sensors and instruments used to determine parachute performance and if we're meeting safety requirements,” he says. “We take humidity, inertial measurements, position, attitude and velocity measurements. We also outfit the vehicles with many types of cameras that are high definition and high speed. We take all data from the sensors and equipment and we use that data to validate the computer models and better predict how the parachute will perform, and make sure we're meeting the safety requirement.”
The team uses NovAtel's SPAN system to measure the test vehicle's attitude and vertical velocity. The team's goal is to observe the capsule dynamics and record how fast the vehicle is falling throughout the test.
The SPAN-SE receiver also offers trajectory estimates, which provides an alternative data set if the avionics system GPS signal is ever lost and there's potential for large data gaps. The IMU could extrapolate from the vehicle's movement and fill in the dots where drop outs occurred. SPAN-SE also offers synchronized position and attitude along with a self-contained recording system.
Heading into space
At the end of this year, Orion will take its first trip to space during the Exploration Flight Test-1 (EFT-1). It won't carry a crew, but will travel 3,600 miles above the Earth for a two-orbit flight, according to NASA. This flight will give engineers the chance to not only verify its design, but to test the systems that are most critical to an astronaut's safety-including launch, re-entry and landing.
During this trip into deep space, Orion will travel 15 times farther than the InternationaSpace Station before it returns to Earth. After circling the Earth twice, Orion will re-enter the atmosphere at speeds close to 20,000 mph and temperatures of up to 4,000 degrees Fahrenheit. The parachute system NASA's team has been testing, with the help of NovAtel's SPAN, will slow Orion down before it lands in the Pacific Ocean.
Orion is scheduled to take a second unmanned trip into space in 2017, and this time the spacecraft will take off from the new Space Launch System, according to NASA. Exploration Mission 1 will test how the SLS rocket and Orion spacecraft work together to prepare for the first crewed flight. That flight, Exploration Mission 2, is scheduled for 2021.
Orion will take us further into space than we've ever been, marking an exciting time in space exploration. But before we get there, multiple tests must be completed to ensure the spacecraft is safe. Safe landing gear is a key component, and NovAtel's plays an important role, providing analysts with velocity data, to help ensure the capsule's descent rate stays where it should.
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