article image

OSIRIS-REx mission is one step closer to grabbing asteroid dirt

Amy Tyndall, News reporter
Jul 1, 2015, 19:22 UTC

Sen—The construction of one of the instruments for NASA's mission to return a sample from an asteroid has been completed.

The mission, called OSIRIS-REx—which stands for Origins-Spectral Interpretation Resource Identification Security Regolith Explorer—seeks to help answer a question that has been asked since humans first became aware: How did we come to be?

The target for the mission is asteroid 1999 RQ36, also known as Bennu. Bennu is classed as a Potentially Hazardous Object (PHO), with a one-in-1,800 chance of impacting the Earth in the year 2182, and measuring 575 meters (one-third of a mile) in diameter.

The spacecraft, which is slated to launch in late 2016, is currently being assembled. On board will be five instruments. Construction of the OSIRIS-REx Thermal Emission Spectrometer (OTES) has been completed, bringing NASA's OSIRIS-REx mission one step closer to its target of landing on asteroid Bennu in 2018.

Asteroids are building blocks left over from the formation of the Solar System, meaning that the study of such primal rocky bodies may help us uncover exactly how the planets formed, and perhaps even reveal organic molecules that explain the origin of life itself. As such, Bennu was chosen as the target for OSIRIS-Rex in the belief that it remains relatively unchanged since its formation.

By sending a package of instruments to Bennu, OSIRIS-REx will carry out several mission goals, once it arrives in orbit in 2018, that relate to studying the asteroid from both a historical perspective and its label as a PHO. Its larger properties have already been well-studied and characterised by both ground- and space-based telescopes, which allows the team to launch with a smaller mission risk and higher certainty of the presence of loose rock and dirt (regolith) that can be collected and brought back to Earth for further analysis.

Initially, the spacecraft will spend one year in orbit to map the global spectral, thermal and geological properties of Bennu at altitudes ranging between 0.7 and five kilometers.

The development of OTES has been led by Instrument Scientist Philip Christensen of the Arizona State University (ASU). The spectrometer has been designed to observe the surface of the asteroid in the infrared regime (from 5—50 microns).

OTES has been in development over the past few years, and has undergone rugged testing to mimic life in space: bombarded with solar radiation, exposed to extremes of temperature, and put under a range of pressures from Earth-like to pure vacuum. OTES has now been delivered to the Lockheed Martin Space Systems facility in Littleton, Colorado, for its installation onto the spacecraft.

"We're extremely pleased to have built this outstanding instrument here at ASU," said Christensen in a statement. "Our weeks of testing and calibration have shown that OTES is of exceptional quality and sensitivity."


OTES in one of the clean rooms at ASU. Left: Instrument scientist Philip Christensen. Rear: opto-mechanical engineer Bill O'Donnell. Right: project engineer Greg Mehall. Image credit: Charles Leight/ASU News

Every mineral possesses its own unique infrared "fingerprint", which will allow scientists to distinguish between them based on the infrared emission detected by OTES from the ground below. OTES will also detect thermal emissions every two seconds at these infrared wavelengths, with an accuracy of 0.1°C, to reveal physical properties, such as the average particle size. These two analyses combined will allow the team to see what the surface is made up of and what its temperature distribution is, both on a global scale and in the candidate sampling locations.

Such global and local maps will provide scientists with an overall context within which to place the regolith, which will be collected from the surface from October 2019 using the Touch-And-Go Sample Acquisition Mechanism (TAGSAM) instrument.

The TAGSAM consists of a robotic arm with a sampler head. OSIRIS-REx will approach a pre-determined location on the surface of Bennu at a speed of 10 cm/s (0.22 mph) and graze the surface for just five seconds. As it does so, it will release a burst of nitrogen gas, causing loose material to be stirred up and directed into a collector on the sampler head which will analyse its texture, morphology, geochemstry and spectral properties down to the submillimeter scale.

The TAGSAM will contain enough nitrogen for three attempts at sample collection, and the team hope to pick up at least 60 grams of rubble and dirt. The sample will then be brought back to Earth in a Sample Return Capsule (SRC), touching down in 2023 for further, more precise analyses that cannot be performed by the spacecraft.

OSIRIS-REx will also search for plumes, similar to those found on Comet67P/Churyumov-Gerasimenko, and measure the "Yarkovsky Effect", which describes how Sunlight exerts a force on the object. 

The other instruments that will be installed onto the spacecraft are: the OSIRIS-REx Camera Suite (OCAMS), the OSIRIS REx Visible-Infrared Spectrometer (OVIRS), the OSIRIS-REx Laser Altimeter (OLA), and a student experiment called the Regolith X-ray Imaging Spectrometer (REXIS).

OSIRIS-REx will launch from Cape Canaveral, Florida, on board an Atlas V rocket. The launch window for the mission opens on Sep. 3, 2016, and will last for 39 days. 

The OSIRIS-REx team is led by Dr Michael Drake, Director of the University of Arizona's Lunar and Planetary Laboratory, and is made up of scientists from the University of Arizona, Arizona State University, KinetX, the Canadian Space Agency, NASA Johnson Space Center, NASA Ames Research Center, NASA Langley Research Center, and other members from across academia. The mission will be managed by the NASA Goddard Space Flight Center in Greenbelt, Maryland, while Lockheed Martin is responsible for construction of the spacecraft itself.

The OSIRIS-REx mission aims to study near-Earth asteroid Bennu and return a sample of rock from its surface. Video credit: NASA