OSIRIS-REx Spacecraft Takes a Selfie in Space
The "proud parents" of the UA's mission team talk about their excitement after a flawless launch sequence, jitters prior to powering up the spacecraft's instruments for the first time in space, and what it takes to talk to a robotic probe hurtling around the sun millions of miles away.
Two weeks after launch, the OSIRIS-REx spacecraft found itself 3.9 million miles — about 16 times the Earth-moon distance — away from Earth, hurtling around the sun at 19 miles per second. Last week for the first time, engineers and scientists turned on the spacecraft's instruments.
The performance of the University of Arizona-led asteroid-sampling spacecraft mission so far has team members gleaming with smiles often seen from new parents.
"We launched within 180 milliseconds of our opening launch window, and that set the tone for the performance of this mission," said Dante Lauretta, professor in the UA's Lunar and Planetary Laboratory and OSIRIS-REx principal investigator. "We didn't work any anomalies during the countdown; launch was absolutely flawless; the spacecraft separated from the rocket with no issues; we got the spacecraft stabilized and powered on, and it was talking to two Deep Space Network antennas immediately."
Since then, OSIRIS-REx extended its solar panels into cruise configuration to harvest power from the sun and embarked on its journey to asteroid Bennu, periodically performing what engineers call "routine momentum dumps" — short firings of thrusters to compensate for momentum induced by the spacecraft's reaction wheels, which are used to control the attitude of the spacecraft.
Then, last week, came the moment of truth — a moment both eagerly awaited and dreaded by the mission's team members. OSIRIS-REx was about to switch on its instruments, for the first time not in the controlled environment of a testing chamber, hooked up to monitoring equipment and under the watchful eyes of engineers.
This time, it would be in the cold emptiness of deep space.
Like a Newborn's First Breaths
"Launch is like birth," said Bashar Rizk, senior staff scientist for OCAMS, the OSIRIS-REx Camera Suite, the "eyes" of the spacecraft. "It's like watching the newborn take its first breaths. During the instrument checkout, we exercised every piece of copper in all cameras, the circuits, the detectors, the focus mechanism, everything."
All of the spacecraft's instruments powered up as expected and all were able to acquire data and downlink to Earth, Lauretta reported, after passing through the processing pipeline and finally onto the mission's science processing servers.
"Our feeling going into the instrument checkout was very nervous," said Sara Knutson, a senior operations engineer and alumna of the UA College of Engineering who is responsible for science operations planning and making sure the instruments function as they should to achieve the mission's science goals.
"The spacecraft is millions of miles away, and there is nothing I can do if (an instrument) doesn't turn on."
But nervousness quickly gave way to excitement, and "there were a lot of 'proud parents' in the crowd and a sense of elation," said Knutson, who was at Lockheed Martin's headquarters in Littleton, Colorado, where the spacecraft was built, monitoring the downlink.
"We powered the instruments on in series — first MapCam, then SamCam, followed by PolyCam — and when the first of 150 images came down at 11 a.m. on Monday, Sept. 19, there was cheering and clapping."
Developed and built at the UA, the three cameras make up OCAMS, an instrument designed to support the mission to the asteroid through all of its phases, from approach to sample collection.
Similar to a scout's spyglass, PolyCam will be the first to spot the asteroid from a million miles away. Once closer, it will help identify dangerous areas on the asteroid's surface by spotting and mapping large boulders and rocks, and characterize a dozen prospective sample sites in detail. The medium-resolution Mapping Camera, or MapCam, will search for potential hazards to the spacecraft once it gets to the asteroid, such as small rocks trapped in orbit, or outgassing plumes. MapCam will map the entire surface of Bennu from a safe distance of three miles. Once a suitable sampling site has been identified, the Sampling Camera, or SamCam, will continuously document the spacecraft's final trip onto the asteroid's surface and the sampling sequence.
In addition to OCAMS, which will peer out into the void of space and won't see much other than stars until OSIRIS-REx approaches Bennu, StowCam, a small camera mounted next to the probe's sampling capsule, also opened its shutter for the first time last week, taking the first selfie of OSIRIS-REx in space.
According to Knutson, many considerations and precautions go into acquiring images through the spacecraft's instruments, with the process involving 30 to 40 people in some way. Every command to the spacecraft is carefully planned on the ground and translated into computer code, which is then checked multiple times to ensure that no maneuver is initiated that may put the spacecraft or any of its instruments in danger.
'Things Heat Up Very Fast'
The biggest risk, according to Bradley Williams, OCAMS systems engineer and also a graduate of the College of Engineering, is direct sunlight, with visible light being the least of concerns. Much more dangerous are wavelengths that we on Earth don't have to worry too much about because our atmosphere filters much of them out before they reach the ground. But in space, there is constant radiation danger and "things heat up very fast," and pointing OSIRIS-REx's cameras directly at the sun would "fry the image detectors, like a magnifying glass on an ant," Williams said.
"Once we get to Bennu, we'll be facing essentially a black chunk of coal, which gets very hot, relatively speaking," he said. "You have to design your instruments and check them so that you can find out their temperature performance and tolerance. Everything we want to take pictures of has to be lit by something, either the sun or by starlight, and we have to look at the exposure times necessary to capture the images we need. All these things go into taking an image."
At the UA's Drake Building, which serves as the OSIRIS-REx Science Processing and Operations Center, team members such as Knutson and Williams are responsible for writing what they call the command products — instructions that the science instruments can understand and execute.
"We write those line by line with code," Knutson said, "then we do a variety of testing on simulation testbeds on the ground, and then everything is radiated through Lockheed Martin, from there using the pipeline of the Flight LAN at NASA's Jet Propulsion Laboratory, which monitors everything that is going to the Deep Space Network to be sent to the spacecraft.”
Last week, it took 10 seconds for the data to arrive at the spacecraft, and 10 seconds for its responses to come down, Knutson said.
"In contrast, when we are at Bennu, it will take 13 minutes to get it all up there, and another 13 minutes for the spacecraft's response to come back to us," she said.
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University of Arizona in the News