OSIRIS-REx Asteroid Sampler Completes 1st Engine Firing for Final Approach to Target Bennu

Illustration of NASA’s OSIRIS-REx spacecraft during a burn of its main engine for arrival at target Asteroid Bennu in Dec. 2018.  Credit: University of Arizona

Ken Kremer  --   SpaceUpClose.com  --   9 October 2018

CAPE CANAVERAL, FL – NASA’s OSIRIS-REx asteroid sampling spacecraft successfully completed the first in a series of critical main engine firings in early October that significantly slowed the probes speed and put it on course for final approach to target Bennu this December.  A second firing is on tap just days away for Oct. 15. 

Engineers commanded OSIRIS-Rex to carry out the firing known as the first Asteroid Approach Maneuver (AAM-1) on Oct. 1.  All appeared to go well but the team need to gather additional and analyze additional telemetry and tracking to confirm a positive outcome.

“New tracking data confirm that the spacecraft completed its first Asteroid Approach Maneuver (AAM-1) on Oct. 1, starting the final approach to Bennu,” officials reported yesterday, Oct. 8.

NASA says the main engine burn slowed the spacecraft as planned – by a speed of 785.831 miles per hour (351.298 meters per second) and consumed 532.4 pounds (241.5 kilograms) of fuel.

The braking maneuver slowed the spacecraft’s speed relative to Bennu from approximately 1,100 mph (491 m/sec) to 313 mph (140 m/sec). 

Three more AAMs are scheduled over the next two months “as the spacecraft prepares to match Bennu’s speed so it can safely navigate around the asteroid.”

The second maneuver known as AAM-2 is slated for early next week on Oct. 15. 

As of today with 53 days left until arrival at Benuu, OSIRIS-Rex is now less than 80,500 km (50,300 miles) distant.

OSIRIS-Rex, which stands for the  Origins, Spectral Interpretation, Resource Identification, Security-Regolith Explorer, has journeyed approximately 1.1 billion miles (1.88 billion km) since its Sept. 8, 2016, launch on a United Launch Alliance Atlas V rocket.

The one way light time for signals is currently 7.2 minutes.

OSIRIS-Rex counts as NASA’s first mission to visit a near-Earth asteroid, survey the surface, collect a sample and deliver it safely back to Earth. 

It is scheduled to arrive at Bennu in about two  months on Dec. 3, 2018. 

On Aug. 17, 2018 NASA’s OSIRIS-REx spacecraft obtained the first images of its target asteroid Bennu from a distance of 1.4 million miles (2.2 million km), or almost six times the distance between the Earth and Moon. This cropped set of five images was obtained by the PolyCam camera over the course of an hour for calibration purposes and in order to assist the mission’s navigation team with optical navigation efforts. Bennu is visible as a moving object against the stars in the constellation Serpens.  Credits: NASA/Goddard/University of Arizona 

The probe has begun science operations and is taking images with the cameras to support navigation and science objectives.

Watch this GIF of Bennu brightening:

Bennu Brightening as OSIRIS-REx Approaches. This processed and cropped set of images shows Bennu (in the center of the frame) from the perspective of the OSIRIS-REx spacecraft as it approaches the asteroid. During the period between August 17 and October 1, 2018 the spacecraft’s PolyCam imager obtained this series of 20 four-second exposures every Monday, Wednesday, and Friday as part of the mission’s optical navigation campaign.   From the first to the last image, the spacecraft’s range to Bennu decreased from 2.2 million km to 192,000 km, and Bennu brightened from approximately magnitude 13 to magnitude 8.8 from the spacecraft’s perspective. Credit: NASA/Goddard/University of Arizona

“From the beginning of the mission’s science operations on Aug. 17 through AAM-1, PolyCam obtained optical navigation images (OpNavs) of Bennu on a Monday, Wednesday and Friday cadence. After AAM-1, PolyCam is taking daily OpNavs as the spacecraft continues to close in on the asteroid,” NASA reported Oct. 8. 

“This last week the spacecraft’s MapCam camera also began taking daily Phase Function images. These images support the mission’s science requirement to measure changes in light reflected from Bennu’s surface as the Sun illuminates the asteroid across a range of angles. These observations provide information on Bennu’s albedo and the way light reflects under various observing conditions.”

OSIRIS-Rex spacecraft in KSC cleanroom prior to launch. Credit: Ken Kremer/kenkremer.com/spaceupclose.com

The asteroid approach maneuvers are designed to fly the spacecraft through a precise corridor during its final slow approach to Bennu.

The final one known as AAM-4 is scheduled for Nov. 12 and target OSIRIS-Rex for arrival on Dec. 3.

“AAM-4 will adjust the spacecraft’s trajectory to arrive at a position 12 miles (20 km) from Bennu on Dec. 3. After arrival, the spacecraft will initiate asteroid proximity operations by performing a series of fly-bys over Bennu’s poles and equator.”

Watch for Ken’s continuing onsite coverage of NASA, SpaceX, ULA, Boeing, Lockheed Martin, Orbital ATK and more space and mission reports direct from the Kennedy Space Center, Cape Canaveral Air Force Station, Florida and Wallops Flight Facility, Virginia.

Stay tuned here for Ken's continuing Earth and Planetary science and human spaceflight news: www.kenkremer.com –www.spaceupclose.com – twitter @ken_kremer – email: ken at kenkremer.com

Dr. Kremer is a research scientist and journalist based in the KSC area.

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