NASA’s first asteroid sample return mission took a step closer to reality on Wednesday, as the OSIRIS-REx project was cleared for development and testing. Scheduled to launch in 2016, the mission passed a series of detailed project assessments and now goes on to the development phase. The Origins-Spectral Interpretation Resource Identification Security REgolith Explorer (OSIRIS-REx) is intended to rendezvous with the asteroid Bennu (1999 RQ36) in 2018, carry out an extensive survey, and return a 2-ounce (60 gm) sample of its surface to Earth in 2023.
The choice of Bennu as a target wasn't just drawn out of a hat. Bennu is a B-type asteroid, meaning that it's carbonaceous rather than composed of stone or a mix of iron and nickel. It’s rich in volatiles and may contain water and organic molecules that could provide clues as to the origin of life on Earth. Out of over 500,000 asteroids known, Bennu is one of only five B-types that is of suitable size and orbit for rendezvous and sample return. In addition, if pure science isn't enough, Bennu is also one of the most likely asteroids to hit Earth in the next few centuries, so taking a close look has an element of self-interest.
OSIRIS-REx’s mission objective is to carry out the most detailed study so far of an asteroid. In addition to returning a sample of the dust and other small particles that make up the regolith that coats Bennu, OSIRIS-REx will also study its chemistry, mineralogy and topography, compare telescope-based data with on-the-spot observations, and make a precise determination of the asteroid’s orbit.
The latter is of particular importance because NASA wants to study the Yarkovsky effect. It’s been known since 1902 that heating of an asteroid by the Sun and then re-radiating that heat affects the object’s orbit. As the asteroid turns, the face heated by the Sun turns into darkness and radiates heat. The escaping radiation produces a tiny thrust that over the course of centuries can significantly change its orbit. Considering current concerns over protecting Earth from wayward asteroids, this effect could be of great importance in assessing possible threats.
OSIRIS-REx is about 2 meters (6.6 ft) on each side and is powered by lithium-ion batteries using active solar arrays covering 8.5 square meters (91 sq ft). There are a battery of instruments for studying Bennu, but the star is the Sample Return Capsule (SRC) for bringing back samples to Earth. It’s the same as that used in the Stardust mission, that returned samples of a comet’s tail in 2006.
The samples will be collected using the Touch-And-Go Sample Acquisition Mechanism (TAGSAM). This consists of a simple sampler head attached to an articulated arm developed for the Stardust mission. During sample collection, OSIRIS-REx comes within 25 meters (82 ft) of Bennu and the arm extends. As the cylindrical head briefly touches the asteroid, nitrogen is blasted into the head for five seconds, blowing a sample into the outer wall of the cylinder for collection. If the first attempt isn’t successful, there’s enough nitrogen onboard for three tries. Once collected. the sample is visually verified, then the head is placed inside the SRC. When OSIRIS-REx next approaches Earth, the SRC is jettisoned for reentry and recovery.
The principal investigator for the mission is the University of Arizona, and the spacecraft is being built by Lockheed Martin Space Systems in Denver. The mission itself will be under the control of NASA's Goddard Space Flight Center in Greenbelt, Maryland.
The video below outlines the OSIRIS-REx mission.