‘All systems go’ for OSIRIS-REx launch in September
Program managers from NASA’s OSIRIS-REx team provided a status update at a public briefing on the agency’s $800 million mission to launch a spacecraft to asteroid Bennu and return with samples in 2023. Dwayne Brown from NASA’s Office of Communications summarized the status by saying, “All systems are go for a launch on Sept. 8 in Florida.”
The spacecraft, which travels under the hefty name of Origins Spectral Interpretation Resource Identification Security REgolith Explorer, will take a gradual approach to its target, a 4.5 billion-year-old, 1,640-foot (500-meter) asteroid, by swinging around the Sun and using the Earth for a gravitational assist in before arriving at its target in 2018.
Once in orbit, the spacecraft will use multiple instruments to study the chemical composition of the asteroid’s surface in the visible, infrared, and X-ray spectral bands for up to two years. Bennu, a carbon-rich asteroid, is expected to include organic material in its makeup that could have had a role in the origins of life on Earth.
According to the mission’s principal investigator, Dante Lauretta from the University of Arizona-Tucson, the samples can help solve the puzzle of “how we are here, why we are here, and how likely it is that this kind of process – the origin and evolution of life – may have happened elsewhere in the Solar System and even throughout the galaxy.”
Bennu is also interesting from a practical point of view. While NASA will be investigating how it formed, companies such as Deep Space Industries and Planetary Resources, which are hoping to mine asteroids, will be interested in learning how well OSIRIS-REx performs proximity operations near the asteroid as well as what there that’s worth mining.
On the “Security” side of the mission, OSIRIS-REx will be studying something called the Yarkovsky effect, where heat from the Sun is radiated into space as the asteroid rotates, acting as a thruster. This effect, if detected, could help better identify how asteroids travel along their orbits, making them easier to detect and track. The “thruster” effect could also be useful should we ever need to change a potentially hazardous asteroid’s orbit.
“The science team took into account three criteria when making that selection: accessibility of the asteroid, size of the asteroid, and composition,” said Christina Richey, NASA’s Deputy Program Scientists, explaining why Bennu was chosen as the mission’s destination.
In the case of accessibility, the target asteroid had to be reached, sampled, and returned from within a few years’ time. In terms of size, the target had to be compatible with operations near the asteroid (orbit) and on it (sampling). Smaller asteroids – less than 656 feet or 200 meters in diameter – spin too quickly for useful operations. Regarding composition, the goal was to find a carbon-rich asteroid from the Solar System’s early formation. Bennu fit all of these categories.
Picking up some dust
Because Bennu’s gravity is much smaller than a planet’s, OSIRIS-REx will be able to do something most NASA orbiters can’t: capture surface samples. Lauretta explained, “We’re seeking samples that date back to the very origin of our solar system.”
Once the orbital survey has been completed around 2020 and scientists have selected the ideal site, the spacecraft will match Bennu’s rate of spin and drop toward the surface at a leisurely quarter mile per hour (10 centimeters per second) before reaching out to touch the surface with something called the Touch-and-Go Sample Acquisition Mechanism or TAGSAM.
TAGSAM is an articulated 11-foot (3.4-meter) pole with a sampling device at the end. When OSIRIS-REx gets close to the surface, the TAGSAM arm will extend, gently touch (“high five”) the surface with a 12-inch (30-centimeter) diameter sample head, and blast the surface with pure nitrogen gas. This will kick up regolith and dust from the surface into the collector. The sample is then brought back aboard the spacecraft.
The minimum sample size for the mission is expected to be around 2 ounces (60 grams), although in testing the sampler typically picked up 5–10 ounces (150–300 grams) of material. The Sample Return Capsule itself can handle up to 4.4 pounds (2 kilograms) of material.
The entire “touch and go” operation will last only about five seconds. After collecting its sample, OSIRIS-REx will go back to orbiting the asteroid. When the time is right, the spacecraft will fire its main engine for its return to Earth. In response to a Spaceflight Insider question, NASA explained that OSIRIS-REx uses a blow-down hydrazine monopropellant propulsion system to maneuver, with its thrusters generating from 0.04 to 45 pounds (0.2 to 200 newtons) of force .
OSIRIS-REx will leave Bennu orbit sometime between March 2021 and April 2022 and return to Earth around Sept. 24, 2023. Once the Sample Return Capsule is jettisoned, the spacecraft will be directed into an orbit around the Sun. The capsule will re-enter the Earth’s atmosphere and land via atmospheric and parachute braking at the Utah Test and Training Range. Samples will then be brought to Johnson Space Center for curation and study.
Part of the samples collected (4 percent) will go to Canada due to their role creating the OSIRIS-REx Laser Altimeter (OLA) instrument. Another half a percent of the sample will go to the Japan Aerospace Exploration Agency (JAXA) as part of NASA’s cooperation on the Hayabusa 2 mission. Seventy-five percent of the samples will be set aside for future researchers “for the science questions we haven’t even thought to ask yet,” according to Gordon Johnston, the OSIRIS-REx Program Executive at NASA Headquarters.
Now fueled and insulated for space at Kennedy Space Center’s Payload Hazardous Support Facility (PHSF), OSIRIS-REx will move out to Cape Canaveral Air Force Station on Aug. 23 and will be encapsulated on Aug. 24 in the fairing of a United Launch Alliance (ULA) Atlas V 411 rocket. The launch vehicle will be moved to the Vertical Launch Facility on Aug. 29 where it will undergo final preparations for flight. Liftoff is targeting 7:05 p.m. EDT (23:05 GMT) Sept. 8.
As for what the future will bring, that will depend on the results OSIRIS-REx gathers from Bennu. When asked why this asteroid was important, Richey said it is a space rock that is primitive and dates back to over four-and-a-half billion years ago.
“It’s carbon-rich, so we know there is potential for organic molecules to be there within that material we bring back,” Richey said. “So it’s important because it helps us understand the formation of our solar system. That’s kind of a big deal.”
Video courtesy of OSIRIS-REx Mission
Bart Leahy is a freelance technical writer living in Orlando, Florida. Leahy's diverse career has included work for The Walt Disney Company, NASA, the Department of Defense, Nissan, a number of commercial space companies, small businesses, nonprofits, as well as the Science Cheerleaders.