posted June 30, 2014
Usually, scientists and engineers work very hard to keep spacecraft from colliding. In April, however, a team of researchers deliberately sent a projectile flying into their “spacecraft” just to see what would happen.
DebriSat, as the unfortunate object was dubbed, was part of an experiment to help researchers study what happens when objects impact each other in space.
“The test used one of the most powerful light gas guns in the world to accelerate a soup-can-sized projectile to just shy of orbital velocity to collide with the targets, including a realistic satellite mock-up,” said Marlon Sorge, the technical lead for the project at Aerospace. “Nothing like this has really been done for debris in 20 years.”
The study of space debris is growing in importance. As more and more objects get launched into space, there are more items that must be tracked to avoid collisions. And if collisions do occur, they create even more debris that must be tracked.
The goal of this project, started several years ago, is to understand what happens during collisions and to be able to accurately model how the debris spreads. It was an ambitious undertaking that required the expertise of a number of different organizations: The Aerospace Corporation, the Space and Missile Systems Center, the NASA Orbital Debris Program Office, the University of Florida, and the Arnold Engineering and Development Complex.
One area in which Aerospace was able to provide expertise was the design of the test satellite. The researchers wanted to approximate a real satellite as closely as possible, while not incurring the costs associated with a real satellite.
Aerospace’s Engineering and Technology Group has experts in satellite subsystems who were able to help with the design of DebriSat. The final product, which had to be small enough to fit inside the testing facility, was about 56 kg and half a meter in each direction.
The projectile also needed to be realistic. An experiment like this had been done 20 years prior using a solid aluminum sphere as a projectile. However, a satellite is much more likely to be struck by another satellite or piece of debris, not a solid object.
The researchers were limited in what they could use, since the projectile must endure extreme acceleration. They chose to employ a hollow cylinder about the size of a soup can. The cylinder, made of aluminum and nylon, would break up when it collided with DebriSat.
Now, in order to make the projectile and the target collide at the appropriate speed, a proper testing facility was needed.
“There is a facility called the G-Range at the Arnold Engineering and Development Complex in Tennessee that has the only light gas gun, certainly in the United States, and probably in the world, that’s capable of doing this,” Sorge said.
A light gas gun uses an explosive and a piston to force a light gas, in this case hydrogen, down a barrel to propel the projectile at great speeds.
The G-Range gun would be used to fire the projectile at DebriSat, causing the mock satellite to break up and spread debris all over the soft catch foam the team would set up. The team could then assess what type of debris landed where.
As part of the preparation for the test, the gun needed to be fired in a pre-test. Since the gun was going to be fired anyway, the team decided to take advantage of it. Aerospace scientist Patti Sheaffer coordinated the fabrication of an object they called DebrisLV, which resembled a simplified upper stage. They used DebrisLV as a target for the pre-test two weeks before the real test.
“It ended up becoming … a really useful second target,” Sorge said.
In order to collect as much data as possible, the team employed lots of instruments for the test, such as high-speed color and black and white cameras, a high-speed infrared camera, an infrared hyperspectral system, a mass spectrometer, a nanosecond spectrometer, a borescope, and a gas collector. Gouri Radhakrishnan and Paul Adams from Technology and Laboratory Operations were key contributors in the area of data collection.
All the instruments were set up, the foam was placed, the gun was tested. Years of preparation culminated in a very brief moment as the gun actually fired.
“You’re standing up there, they kind of count down, you feel the building shake, you hear … the whooshing of the gun going off, and it’s done,” Sorge said.
Both the pre-test and the actual test were a success, spreading debris all over the place and generally making a big mess for the team to clean up.
“We then spent the next two days — all of the next two days — with well over a dozen people I think, working to collect all the debris,” Sorge said.
The team had to gather all the debris, keep track of where it came from, and send it off to the University of Florida, where it would be analyzed. They discovered that packing it was quite a chore, since there were fragile parts, and wires sticking all over the place. They ended up with about 20 pallets of debris from each test.
“It was a huge effort,” Sorge said.
Now that DebriSat has been turned into pieces of scrap, the next step is to analyze all the data. Given the amount of data collected, that could take some serious time.
“The next year or two is just going to be processing all this stuff,” Sorge said.
But the results should be worth the wait. As Sorge said, “the test series is the most complex and thorough one of its kind ever conducted.”
It promises to contribute valuable data to the ongoing space debris issue.