NASA Asteroid Sample Return Mission OSIRIS-REx on Its Way to Bennu

NASA’s first asteroid sample return mission, OSIRIS-REx, successfully lifted off from Cape Canaveral Air Force Station, FL on time at 7:05 pm ET.   Its Atlas V/Centaur rocket performed perfectly, sending the spacecraft on a two-year journey to the asteroid Bennu.  The sample it collects will return to Earth in 2023.

The Origins, Spectral Interpretation, Resource Identification, Security, Regolith Explorer (OSIRIS-REx) needs a gravity-assist from Earth to reach Bennu, which is in an orbit around the Sun similar to Earth’s, but slightly further out (1.2 astronomical units compared to 1.0 for Earth).  The spacecraft is on a trajectory to return to Earth’s vicinity in one year (September 2017), get the boost, and arrive at Bennu in August 2018. 

Bennu (pronounced BEN-yu) is quite small — just 492 meters (1,614 feet) in diameter. The Empire State Building is 443 meters or 1,454 feet high, including antennas, by comparison.  OSIRIS-REx will not go into orbit around Bennu, but fly in formation with it for more than a year to study the surface and determine the best place to obtain a sample.  When ready, it will briefly touch Bennu’s surface.  Using its 3.35 meter (11-foot) Touch-and-Go Sample Acquisition Mechanism (TAGSAM), it will get the sample, move away, and do a check to confirm a sample was obtained.  If not, it can try once more.

The spacecraft must wait until March 2021, when the orbits of Bennu and Earth are correctly aligned, before starting the trip home.  It will take 2.5 years to return to Earth.  The sample will be in a special capsule that will separate from the main spacecraft about four hours before Earth arrival, reenter through Earth’s atmosphere, and land at the Utah Test and Training Center in Tooele County, Utah, in September 2023.  The same type of container was used for the Stardust mission that returned a sample of a comet to Earth in 2006.  The sample will be taken to the Astromaterials Acquisition and Curation Office at NASA’s Johnson Space Center in Texas for analysis.  The main OSIRIS-REx spacecraft will remain in space, orbiting the Sun.

The goal is to bring back at least 60 grams (2 ounces), but perhaps as much as 2 kilograms (4.4. pounds) of asteroid material. 

Bennu was originally designated 1999 RQ36 and received its name after an international student competition. A third grader, Michael Puzio, proposed Bennu, the name of an Egyptian mythological deity linked to rebirth.

The approximately $800 million mission (not including launch) is the third of NASA’s New Frontiers series of Principal Investigator (PI)-led medium-size robotic planetary exploration missions.  The first two were the New Horizons spacecraft that reached Pluto last year after a 10-year journey, and the Juno mission that just arrived at Jupiter.

The PI for OSIRIS-REx is Dante Lauretta, Professor of Planetary Science and Cosmochemistry at the University of Arizona’s Lunar and Planetary Laboratory.  NASA’s Goddard Space Flight Center manages the program.  Lockheed Martin built the spacecraft, TAGSAM, and the return capsule.

OSIRIS-REx Principal Investigator Dante Lauretta.  Photo Credit:  University of Arizona website

In addition to TAGSAM, OSIRIS-REx has several other scientific instruments
including cameras, a laser altimeter, a visible and infrared
spectrometer, a thermal emission spectrometer, and a regolith X-ray
imaging system (REXIS).  REXIS is an MIT-Harvard student experiment to
map elemental abundances on Bennu’s surface.  It also has high- and
low-gain antennas that not only provide communications back to Earth,
but will provide data to measure the mass and gravity field of Bennu,
providing information on the asteroid’s internal structure and refining
measurements of the “Yarkovsky Effect” of how the asteroid’s orbit is affected by surface heating and cooling.

Japan returned the first sample of an asteroid, Itokawa, with its Hayabusa mission in 2010, but only particles were obtained because of a problem with the sample collecting device.  It launched a second mission, Hayabusa2, in 2014 that will return a sample of the asteroid Ryugu to Earth in 2020.   A number of other space missions have studied asteroids and comets, but Hayabusa and Stardust are the only ones so far to bring samples back to Earth for study and the amounts are meager.  OSIRIS-REx is expected to return a larger amount to allow more detailed scientific analysis of these primordial objects, adding to knowledge about the earliest era of solar system formation.