On September 8, NASA launched OSIRIS-Rex (Origins, Spectral Interpretation, Resource Identification, Security-Regolith Explorer). The probe will spend two years in space, chasing down an asteroid known as Bennu. Discoveries from the mission could help scientists understand clues to the origins of life.
NASA Tech Briefs: Why did you choose to target Bennu?
Jason Dworkin: There are about 700,000 asteroids. Of those, there are 5,000 or so that are near-Earth asteroids that we could have a chance of getting to. There are only 120 or so that are larger than 200 meters — a critical size. Below 200 meters, the asteroids tend to spin very fast, where a day can even be as short as a minute. Maneuvering a spacecraft around an object spinning at one revolution per minute is a huge challenge and risk. That left us with five asteroids that have spectra indicating the presence of an ancient, unaltered, carbon-rich material. Of those, Bennu was the object that was best characterized, with extensive ground and space-based observations, from radar down to infrared.
NTB: How does the spacecraft select the sample?
Dworkin: The spacecraft slowly descends with the Touch-And-Go Sample Acquisition Mechanism (TACSAM) arm — a 10’-long “pogo stick” with an air filter on the end. We slowly descend at less than 10 centimeters per second. We touch the surface for no more than 5 seconds. During that contact, a power valve releases a jet of nitrogen gas from a canister. The gas goes through a ring on the sampler of the TACSAM head, stirring up, mixing, and mobilizing the stones, rocks, and dust from the surface. The regolith gets thrown into the air-filter-like device and locked inside a check valve. Then, we fire our thrusters and move to a safe distance, measure how much material we have, take images, and stow the sample in the sample return capsule (SRC).
NTB: What other instruments are onboard?
Dworkin: We have a suite of cameras from the University of Arizona called OCAMS (OSIRIS-REx CAMera Suite). Arizona State University’s OTES (OSIRIS-REx Thermal Emission Spectrometer) will give us thermal information from the asteroid as well as grain size. We also have the OVIRS (OSIRIS-REx Visible and Infrared Spectrometer) instrument from NASA Goddard, which will give us mineralogy and organic information. The Canadian Space Agency (CSA)-contributed TSA instrument called OLA, or OSIRIS-REx Laser Altimeter, provides our range to the asteroid and helps us figure out the topography of the surface. An X-ray imaging spectrometer, built by students at Harvard and the Massachusetts Institute of Technology (MIT), will help us understand the elemental composition of the top layer of the regolith.
NTB: What will we learn from this mission?
Dworkin: We’ll be getting progressively closer to the asteroid to learn more about the asteroid’s shape and spectra so we can pick the safest and most interesting site to sample from, and bring that sample back in September of 2023. The sample will contain clues to the formation of the solar system, and possibly the formation of life on Earth, Mars, Europa, or elsewhere.
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