OSIRIS-REx to include planetary defense science, student experiment
When NASA’s OSIRIS-REx spacecraft launches on Sept. 8, it will include five instruments for examining the 1,640-foot (500-meter) diameter asteroid Bennu, including an X-ray spectrometer built by students at Harvard University and Massachusetts Institute of Technology.
What’s in a name?
OSIRIS-REx is named after an ancient Egyptian deity. As the NASA mission website explains it:
The mythology of the Egyptian god Osiris loosely parallels the OSIRIS-REx mission. Osiris, in his original form, was believed to have spread an understanding of agriculture throughout the Nile Delta, hence bringing life to the ancient world. Likewise, OSIRIS-REx seeks to return samples of an asteroid that may contain organics that led to the origin of life on Earth. Osiris also had a dual role as the god of the Underworld, which mirrors the destruction that large asteroid impacts have created.
The name itself is a lengthy acronym for a complex spacecraft and mission: Origins Spectral Interpretation Resource Identification Security REgolith Explorer.
Among the mission objectives in store for OSIRIS-REx are collecting and returning a surface sample from the asteroid; defining the properties of a primitive, carbon-rich asteroid and comparing them with ground-based observations; and mapping the general properties of the asteroid, including chemistry and mineralogy as well as the texture, morphology, geochemistry, and spectral properties of the asteroid’s regolith or surface material.
One mission objective will investigate a property that could be useful for deflecting an asteroid for planetary defense. OSIRIS-REx will measure the Yarkovsky Effect – a force caused by a rotating asteroid emitting heat, potentially changing its orbit over time.
In an asteroid deflection scenario, heat could be generated by exploding a nuclear warhead near the asteroid or firing a high-powered laser at it, theoretically heating the surface and deflecting it into a safer orbit. This investigation will lay the groundwork for determining if such a deflection is possible.
Instruments of investigation
To do all this scientific heavy-lifting, OSIRIS-REx will carry multiple instruments, including a suite of three cameras: PolyCam, MapCam, and SamCam. These cameras will “see” asteroid Bennu as the spacecraft approaches it; provide global image mapping and sample site imaging: and record the entire sampling event during the touch-and-go (TAG) maneuver for retrieving the surface sample.
The OSIRIS-REx Thermal Emission Spectrometer (OTES) will collect infrared spectral data from Bennu at wavelengths between 5 and 50 microns to obtain mineral and temperature information on the asteroid’s surface. OTES will be recording the unique infrared signatures of minerals, enabling scientists to determine which minerals are present on the surface. The infrared data will also enable the investigators to determine the physical properties of the surface, such as the average particle size.
Another spectrometer with an acronym-within-an-acronym name is the OSIRIS-REx Visible and Infrared Spectrometer or OVIRS, which will measure visible and infrared light from Bennu. This instrument will study the asteroid in the blue to near-infrared wavelengths: 0.4 to 4.3 microns.
Elemental observations: the student REXIS instrument
The student experiment Regolith X-ray Imaging Spectrometer or REXIS will go beyond the mineral level of observation to determine which individual elements are present on Bennu and how abundant they are.
Observing the asteroid through a set of four charge-coupled devices (CCDs) sensitive only to X-rays, REXIS will be able to identify the fluorescing signatures of electrons from individual elements on the surface. Like minerals, which are combinations of elements, individual atoms re-emit X-rays at specific frequencies. This type of observation is possible because the Sun emits high-energy X-rays into space; these X-rays are absorbed by the lower layers of Earth’s atmosphere, so they present no danger to people on Earth. Bennu, lacking an atmosphere or magnetic field, takes those X-rays straight on.
According to a recent NASA release, REXIS was selected as a Student Collaboration Experiment for the OSIRIS-REx mission. It has been built by a team from MIT and Harvard, and the students will perform data analysis of REXIS as part of their coursework.
“This has been an amazing experience for the students,” said Rebecca Masterson, REXIS co-principal investigator and instrument manager at MIT. “They get to see how a mission evolves and what it takes to get to the point of launch. They’re getting to see how an idea goes from conception to completion and actually play a role in its success.”
Richard Binzel, Professor of Planetary Science and Joint Professor of Aerospace Engineering at MIT, told Spaceflight Insider: “OSIRIS-REx issued a Call for Proposals for a student instrument in March of 2010. That call was answered by MIT Professors Richard Binzel and David Miller working with Harvard Professor Jonathan Grindlay.”
When asked about student input into the initial design, Binzel explained, “Although we had an initial design, that design had to be verified to be sure it would make it through the rigors of launch and survive the temperature extremes experienced in space. So it was the students and their analyses that turned the initial design into the real REXIS.”
These students have gained valuable hands-on experience with developing hardware.
Goddard Space Flight Center is in charge of overall mission management, systems engineering and safety and mission assurance for OSIRIS-REx. The mission’s principal investigator is Dante Lauretta from the University of Arizona. The spacecraft was built by Lockheed Martin Space Systems in Denver. OSIRIS-REx is the third mission in NASA’s New Frontiers Program, which is managed by Marshall Space Flight Center in Huntsville, Alabama, for NASA’s Science Mission Directorate.
Scott Bellamy, Mission Manager for the Discovery and New Frontiers Program, told Spaceflight Insider: “All is going great with Assembly, Test, and Launch Operations. We encapsulate on August 24th for launch on Sept. 8th.”
The mission is scheduled to launch from Cape Canaveral Air Force Station aboard a United Launch Alliance Atlas V 411 on Sept. 8. It will orbit the Sun for a year before passing by the Earth in a gravity-assist maneuver to rendezvous with Bennu in August 2018. Spending more than a year studying the asteroid from orbit, OSIRIS-REx will then perform a “touch-and-go” maneuver to land and scoop up a sample of regolith, sending it Earthward in March 2021. The sample capsule is expected to return to Earth and reenter the atmosphere in September 2023.
Video courtesy of NASA Goddard
Bart Leahy is a freelance technical writer living in Orlando, Florida. Leahy's diverse career has included work for The Walt Disney Company, NASA, the Department of Defense, Nissan, a number of commercial space companies, small businesses, nonprofits, as well as the Science Cheerleaders.