Wednesday, May 3, 2017

OSIRIS-REx Camera Suite to Unveil the Real Nature of Asteroid Bennu

Artist's rendering of the OSIRIS-REx spacecraft at asteroid Bennu. Image credit: NASA/GSFC

NASA’s OSIRIS-REx spacecraft is on its way to uncover the secrets of an intriguing carbonaceous asteroid named Bennu, which holds many clues about the formation of the sun and planets. With the help of its imaging system, the probe is expected to deliver crucial insights into the real nature of this rocky body, improving our understanding of the evolution of our solar system.

The Origins, Spectral Interpretation, Resource Identification, Security-Regolith Explorer (OSIRIS-REx) spacecraft started its two-year-long journey to Bennu in September 2016. The mission will study the asteroid in detail and is slated to bring back its sample to Earth. The probe will arrive at Bennu in August 2018 while its return is planned for September 2023.

Although OSIRIS-REx is best known for its sample return mission, it will have much work to do when orbiting Bennu. The probe will map the asteroid’s global properties, chemistry, and mineralogy in order to characterize its geologic and dynamic history. It will define the global properties of Bennu and compared it with existing ground-based telescopic data for all asteroids. The spacecraft will also measure the so-called Yarkovsky Effect (the force caused by the emission of heat from a rotating asteroid) and will document the texture, morphology, geochemistry, and spectral properties of the regolith at Bennu’s sampling site.

The OSIRIS-REx Camera Suite (OCAMS) will be crucial to achieve most of the planned objectives at Bennu. It is an imaging system consisting of three cameras, namely: PolyCam (polyfunctional camera), MapCam (mapping camera) and SamCam (sample acquisition camera). OCAMS will be capable of providing global image mapping and sample site imaging and characterization at Bennu.

“The three OCAMS cameras will acquire images essential to support the task of collecting a sample from the surface of Bennu. They can discover any satellites and plumes, document the asteroid’s spin sate, allow the construction of an accurate digital terrain model of the asteroid’s shape and record any surface hazards. They are able to confirm the presence of sampleable regolith on the surface, observe the sampling event itself and image the sample head in order to verify its readiness to be stowed,” Bashar Rizk, OCAMS Instrument Scientist at the University of Arizona, told Astrowatch.net.

The University of Arizona’s camera suite, OCAMS, sits on a test bench that mimics its arrangement on the OSIRIS-REx spacecraft. The three cameras that compose the instrument – MapCam (left), PolyCam and SamCam – are the eyes of NASA’s OSIRIS-REx mission. They will map the asteroid Bennu, help choose a sample site, and ensure that the sample is correctly stowed on the spacecraft. Photo Credit: University of Arizona/Symeon Platts
The University of Arizona’s camera suite, OCAMS, sits on a test bench that mimics its arrangement on the OSIRIS-REx spacecraft. The three cameras that compose the instrument – MapCam (left), PolyCam and SamCam – are the eyes of NASA’s OSIRIS-REx mission. They will map the asteroid Bennu, help choose a sample site, and ensure that the sample is correctly stowed on the spacecraft. Photo Credit: University of Arizona/Symeon Platts

PolyCam is an eight-inch-wide aperture, F/3.15 Ritchey-Chretien telescope. It is designed to image Bennu at high resolution and will be the first camera to acquire the asteroid from about 1.25 million miles (two million kilometers) away. PolyCam is expected to image prospective sample sites and resolve objects 0.8 inch in diameter.

MapCam is a 4.9-inch F/3.3, five-element, radiation-hardened refractive system based on a telephoto lens design. It will map the asteroid in four different colors, revealing the model of asteroid shape and providing high resolution imaging of the sample site. Images acquired by MapCam will be essential for the search for satellites and outgassing plumes around Bennu. It will also serve as a backup for PolyCam for asteroid acquisition and sub-centimeter imaging by reducing the ranges of such observations.

The smallest camera of the OCAMS instrument, SamCam, is a 0.95-inch F/5.5 radiation-hardened refractive system. It is designed to document the sample acquisition event and the touch-and-go (TAG) maneuver. SamCam will image the 15-20 minute sampling event at the highest cadence possible in order to capture the moment of sample acquisition, including the activation of the nitrogen canisters.

“The cameras will view Bennu in great detail and answer several important questions about the asteroid, including the nature of the surface of a carbonaceous microgravity body and what physical forces and energies are important there,” Rizk said.

He noted that Bennu is a sample of early solar system material, a microgravity body with a size scale similar to those of the planetesimals that formed the planets and large asteroids and a carbonaceous object. This asteroid may contain the molecular precursors to the origin of life and the Earth’s oceans.

So far, the OCAMS instrument is working flawlessly. All its imagers have been exercised several times since launch, acquiring thousands of images, mostly of star fields and mostly calibration images.

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