WASHINGTON, May 10, 2021 /PRNewswire/ -- After nearly five
years in space, NASA's Origins, Spectral Interpretation, Resource
Identification, Security, Regolith Explorer (OSIRIS-REx) spacecraft
is on its way back to Earth with an abundance of rocks and dust
from the near-Earth asteroid Bennu.
On Monday, May 10, at 4:23 p.m. EDT the spacecraft fired its main
engines full throttle for seven minutes – its most significant
maneuver since it arrived at Bennu in 2018. This burn thrust the
spacecraft away from the asteroid at 600 miles per hour (nearly
1,000 kilometers per hour), setting it on a 2.5-year cruise towards
Earth.
After releasing the sample capsule, OSIRIS-REx will have
completed its primary mission. It will fire its engines to fly by
Earth safely, putting it on a trajectory to circle the sun inside
of Venus' orbit.
After orbiting the Sun twice, the OSIRIS-REx spacecraft is due
to reach Earth Sept. 24, 2023. Upon
return, the capsule containing pieces of Bennu will separate from
the rest of the spacecraft and enter Earth's atmosphere. The
capsule will parachute to the Utah Test and Training Range in
Utah's West Desert, where
scientists will be waiting to retrieve it.
"OSIRIS-REx's many accomplishments demonstrated the daring and
innovate way in which exploration unfolds in real time," said
Thomas Zurbuchen, associate
administrator for science at NASA Headquarters. "The team rose to
the challenge, and now we have a primordial piece of our solar
system headed back to Earth where many generations of researchers
can unlock its secrets."
To realize the mission's multi-year plan, a dozen navigation
engineers made calculations and wrote computer code to instruct the
spacecraft when and how to push itself away from Bennu. After
departing from Bennu, getting the sample to Earth safely is the
team's next critical goal. This includes planning future maneuvers
to keep the spacecraft on course throughout its journey.
"Our whole mindset has been, 'Where are we in space relative to
Bennu?'" said Mike Moreau,
OSIRIS-REx deputy project manager at NASA's Goddard Space Flight
Center in Greenbelt, Maryland.
"Now our mindset has shifted to 'Where is the spacecraft in
relation to Earth?'"
The navigation cameras that helped orient the spacecraft in
relation to Bennu were turned off April
9, after snapping their last images of the asteroid. With
Bennu in the rearview mirror, engineers are using NASA's Deep
Space Network of global spacecraft communications facilities
to steer the OSIRIS-REx by sending it radio signals. By
measuring the frequency of the waves returned from the spacecraft
transponder, engineers can tell how fast OSIRIS-REx is moving.
Engineers measure how long it takes for radio signals to get from
the spacecraft back to Earth in order to determine its
location.
Exceeding Mission Expectations
The May 10 departure date was
precisely timed based on the alignment of Bennu with
Earth. The goal of the return maneuver is to get the
spacecraft within about 6,000 miles (approximately 10,000
kilometers) of Earth in September
2023. Although OSIRIS-REx still has plenty of fuel
remaining, the team is trying to preserve as much as possible for a
potential extended mission to another asteroid after returning the
sample capsule to Earth. The team will investigate the feasibility
of such a mission this summer.
The spacecraft's course will be determined mainly by the
Sun's gravity, but engineers will need to occasionally make small
course adjustments via engine burns.
"We need to do regular corrections to bring the trajectory
increasingly closer to Earth's atmosphere for the sample release,
and to account for small errors that might have accumulated since
the last burn," said Peter
Antreasian, OSIRIS-REx navigation lead at KinetX Aerospace,
which is based in Simi Valley,
California.
The team will perform course adjustments a few weeks prior to
Earth re-entry in order to precisely target the location and angle
for the sample capsule's release into Earth's atmosphere. Coming in
too low could cause the capsule to bounce out of the atmosphere
like a pebble skipping off a lake; too high and the capsule could
burn up due to friction and heat from the atmosphere. If OSIRIS-REx
fails to release the capsule, the team has a backup plan to divert
it away from Earth and try again in 2025.
"There's a lot of emotion within the team about departure,"
Moreau said. "I think everyone has a great sense of accomplishment,
because we faced all these daunting tasks and were able to
accomplish all the objectives thrown at us. But there's also some
nostalgia and disappointment that this part of the mission is
coming to an end."
OSIRIS-REx exceeded many expectations. Most recently, in the
midst of a global pandemic, the team flawlessly executed the most
mission's critical operation, collecting more than 2 ounces (60
grams) of soil from Bennu's surface.
Leading up to sample collection, a number of surprises kept the
team on its toes. For example, a week after the spacecraft entered
its first orbit around Bennu, on Dec. 31,
2018, the team realized that the asteroid was releasing
small pieces of rock into space.
"We had to scramble to verify that the small particles being
ejected from the surface did not present a hazard to the
spacecraft," Moreau said.
Upon arrival at the asteroid, team members also were astonished
to find that Bennu is littered with boulders.
"We really had this idea that we were arriving on an asteroid
with open real estate," said Heather
Enos, OSIRIS-REx deputy principal investigator, based at the
University of Arizona, Tucson. "The reality was a big shocker."
To overcome the extreme and unexpected ruggedness of Bennu's
surface, engineers had to quickly develop a more accurate
navigation technique to target smaller-than-expected sites for
sample collection.
The OSIRIS-REx mission was instrumental in both confirming and
refuting several scientific findings. Among those confirmed was a
technique that used observations from Earth to predict that the
minerals on the asteroid would be carbon-rich and show signs of
ancient water. One finding that proved unsuccessful was that Bennu
would have a smooth surface, which scientists predicted by
measuring how much heat radiated off its surface.
Scientists will use the information gleaned from Bennu to refine
theoretical models and improve future predictions.
"This mission emphasizes why we have to do science and
exploration in multiple ways – both from Earth and from up-close in
space – because assumptions and models are just that," Enos
said.
Goddard provides overall mission management, systems
engineering, and the safety and mission assurance for OSIRIS-REx.
Dante Lauretta of the University of Arizona, Tucson, is the principal investigator. The
university leads the science team and the mission's science
observation planning and data processing. Lockheed Martin Space in
Littleton, Colorado, built the
spacecraft and provides flight operations. Goddard and KinetX
Aerospace are responsible for navigating the OSIRIS-REx spacecraft.
OSIRIS-REx is the third mission in NASA's New Frontiers Program,
managed by NASA's Marshall Space Flight Center in Huntsville, Alabama, for the agency's Science
Mission Directorate Washington.
For more information about OSIRIS-REx, visit:
http://www.nasa.gov/osiris-rex
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SOURCE NASA