NASA’s OSIRIS-REx mission will send a spacecraft in September 2016 to the asteroid Bennu in order to extract a sample and bring it back to earth. Bennu is a carbon-rich asteroid that records the earliest history of our Solar System, and by studying a piece of it we could discover the origin of life. Bennu is also one of the most potentially hazardous asteroids. It has a relatively high probability of impacting the Earth late in the 22nd century. OSIRIS-REx will determine Bennu’s physical and chemical properties. This will be critical for future scientists to know when developing an impact mitigation mission.
INSTRUMENT – THERMAL EMISSION SPECTROMETER
To meet mission objectives OSIRIS-REx will have a payload of scientific, navigation, and communication instruments on board. One of which is the OSIRIS-REx Thermal Emission Spectrometer (OTES). Thermal data from OTES will allow scientists to determine the mineral composition and temperature distribution of Bennu for global maps and local candidate sample-site areas. OTES is being developed and built at the School of Earth and Space Exploration at Arizona State University. During several phases of the mission, OTES measures the energy emitted by Bennu over wavelengths of approximately 5 – 50 microns, also called the thermal infrared. At these wavelengths, virtually all minerals have unique spectral signatures that are like fingerprints, which will help the science team to understand what minerals are present on the surface of Bennu and search for minerals of particular interest, such as those that contain water. Additionally, the emitted heat energy (temperature) at these wavelengths can tell the science team about physical properties of the surface, such as the mean particle size.
“Exploded” view of the OTES instrument. From left to right are the sunshade, the telescope, the aft optics plate (the moving mirror assembly is at top, and the beamsplitter is the greenish circle), the electronics board (green card), and the instrument enclosure (with triangular flexure mounts for attaching OTES to the spacecraft)
Once the instrument is built it will need to undergo rigorous testing as NASA’s rules for testing flight instruments and other space hardware are detailed and thorough which they must be. Once the spacecraft leaves Earth, there are no repair calls. Everything has to work perfectly. Testing will include placing OTES in a vacuum chamber space simulation system where it is subjected to the same conditions it will experience during the mission. Aerospace engineers call this process “shake and bake” because it reproduces the vibrations of a rocket launch as well as the extremes of heat and cold that OTES must survive to do its job.
The vacuum chamber space simulation system was provided by LACO Technologies. The space simulation chamber is 60” in diameter and 96” deep. It includes a vibration isolated platen with drilled and tapped holes for instrument mounting. The chamber also comes with full internal shrouds which are cooled with liquid Nitrogen. The system includes a cryogenic vacuum pump for high vacuum and a complete control system for automatic and manual operation. It is designed to replicate the environment that the spacecraft will experience in space with pressures as low as 5 x 10-7 Torr and temperatures as low as -192º C, depending on how much LN2 is run through the shrouds.
As leftover debris from the solar system formation process that began over four billion years ago, asteroids can teach us a lot about the history of the Sun and planets. This is the first U.S. mission to return samples from an asteroid to Earth, addressing multiple NASA Solar System Exploration objectives. Key OSIRIS-REx science objectives include:
- Return and analyze a sample of Bennu
- Document the topography, mineralogy, and chemistry of the sample site
- Globally map the topography, mineralogy, and chemistry of Bennu
- Measure the orbit deviation caused by non-gravitational forces
- Compare observations made at the asteroid to ground-based observations
To get detailed information on the scientific progress made by the OSIRIS-REx team, take a look at their growing list of publications.