This fall NASA Reduced Gravity Office flew the “OSIRIS-REx Low-Gravity Regolith Sampling Tests” on NASA’s C-9 aircraft, called the “Weightless Wonder.” Each of the five flights included five test chambers and several OSIRIS-REx team members to run the tests. They were able to accomplish highly successful tests of sampling mechanisms and have some amazing fun too!
Science Team members, Dante Lauretta, Bill Boynton, Beau Bierhaus and Scott Messenger and Lockheed Martin engineers, Joe Vellinga, David Wurts, Kevin Payne, James Harris and Tony Siderius donned flight suits and boarded the C-9 to conduct the tests on October 16, 17 and 18, 2012. Flyers Lauretta, Boynton, Messenger and Vellinga also provided ground support and OSIRIS-REx Science Team Member Keiko Nakamura-Messenger supplied ground support for the flights.
Lockheed Martin is developing the Touch-And-Go-Sample-Acquisition-Mechanism (TAGSAM) to retrieve a sample from the OSIRIS-REx mission’s target asteroid 1999 RQ36. Previous testing has demonstrated the technology in relevant environments including ground-based testing in ambient, vacuum, hot and cold environments and in low-gravity in 2007, 2009 and May 2012. In previous tests the flights included other experiments, which required periods of positive and negative g. Negative g levitates the regolith, spoiling the TAGSAM tests. To avoid this drawback, the October 2012 flights were dedicated to OSIRIS-REx with the pilots carefully targeting low positive g without creating negative g.
The C-9 low-gravity tests provided data to correlate with the ground tests. “We need to test the methods in low-gravity because these better duplicate the conditions at the asteroid where gravity is close to zero. We expect that in the asteroid micro-gravity TAGSAM will collect a lot more material than in Earth’s gravity. These flights are important to confirm this hypothesis,” said Boynton.
The flights tested five sampler head-regolith configurations per flight to determine how well the sample collection mechanism would work on different surfaces in low gravity. Using a range of simulated regoliths (the loose material lying over harder rock on an asteroid), the team conducted tests of two collection mechanisms: gas fluidization, where compressed nitrogen gas is released to force regolith into the collector, and contact surface sampling with specially designed pads of various materials designed to collect small grains from the asteroid surface by direct contact.
The OSIRIS-REx team took one flight on the first day and two flights on each of the next two days. Each flight lasted less than two hours from take-off to landing. “We had a total of seven on the team. For each flight, two remained on the ground to prepare for the next flight and review the results of the previous tests while the others flew and conducted the sampling tests. Because we had such a short time (14 seconds) to perform the sample collection, we made detailed preparations, practiced and had specific assignments for each of the team members including documenting the tests on video. And it all went off perfectly,” explained Boynton.
TAGSAM collected hundreds of grams in each test and over 1,000 grams during four of the tests. The surface contact pads collected small surface grains in each trial.
This NASA diagram shows a typical zero-g maneuver. However, the maneuver can be modified to provide any level of g-force less than one g. The OSIRIS-REx experiment required low-gravity (very low amounts of positive G force). Some typical g-levels used on different tests and the corresponding time for each maneuver are:
Negative-g: (-0.1 g): approximately 15 seconds
Zero-g: Approximately 25 seconds
Lunar-g: (one-sixth g): Approximately 40 seconds
Martian-g: (one-third g): Approximately 30 seconds
After the flights, Boynton was in little doubt that the TAGSAM design is robust. “We were reasonably confident that these tests would work, but we were really pleased that they went better than we ever could have imagined. The mission science requirement is to collect over 60 grams of material from the top few centimeters of the regolith. TAGSAM seems capable of collecting far in excess of this amount. After these tests, we’re very confident that the TAGSAM bulk and surface sampling pads will work as planned when we get to the asteroid.”
Next steps include more thorough evaluation of the test results to completely understand how the bulk sampling and contact pad designs are working. The next low gravity tests are not currently planned until the spring of 2014 – much to the disappointment of would-be flyers on the OSIRIS-REx team.
“This was a great experience: all the sample collecting worked really well and we had a bit of time at the end to play in low-gravity. Rigorous science play – what could be better? I’m ready and willing to go again anytime,” promised Boynton.