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Emily Lakdawalla • Apr 20, 2018

OSIRIS-REx shows us space isn't entirely empty

It's no secret that I love pictures of spacecraft taken in space. So even though OSIRIS-REx's StowCam viewpoint doesn't change much at all from one month to another, I still thrill at seeing a new-to-me picture of the mission's sample return capsule. Cool! But wait, what's that black dot near the top?

The OSIRIS-REx Sample Return Capsule imaged by Stowcam on March 2, 2017
The OSIRIS-REx Sample Return Capsule imaged by Stowcam on March 2, 2017 This image of the OSIRIS-REx Sample Return Capsule (SRC) was taken on March 2, 2017, by the spacecraft’s StowCam imager as part of a visual checkout of the SRC conducted six months after launch. A small, dark spot is visible on the surface of the SRC that was not present during the checkout images taken after launch in 2016. Subsequent analysis has shown that this spot is an indentation approximately 2 mm across – the size of a poppy seed – that may have been caused by a particle hitting the SRC during flight. The SRC is the capsule on the spacecraft that will securely stow the sample of asteroid Bennu once it is collected, and it will ultimately detach from the spacecraft and land under parachutes in the Utah desert in 2023. The indentation visible in the image is located on the SRC’s ablative heat shield, which was designed to withstand being hit by particles and the high-speed entry into the Earth’s atmosphere. After further investigation, it was determined that the indentation will not affect the SRC’s performance.Image: NASA / GSFC / Lockheed Martin / U. Arizona

Yep, the capsule heat shield -- which is designed to withstand a fiery entry into Earth's atmosphere at mission end -- already has a little ding from a high-speed encounter with a teeny weeny particle somewhere out there in empty space. It didn't escape my attention that this photo was released more than a year after it was acquired. "After further investigation," heh. I'll bet those three words elide an awful lot of emails and meetings. Joking aside, I'm very happy to hear that this little dot is of no concern.

Here, you can compare it to the image of the spacecraft taken right after launch:

First light for OSIRIS-REx StowCam
First light for OSIRIS-REx StowCam On September 22, 2016, two weeks after launch, the OSIRIS-REx spacecraft switched on the Touch and Go Camera System (TAGCAMS) to demonstrate proper operation in space. This image of the spacecraft was captured by the StowCam portion of the system when it was 6.17 million kilometers away from Earth and traveling at a speed of 30 kilometers per second around the Sun. Visible in the lower left hand side of the image is the radiator and sun shade for another instrument (SamCam) onboard the spacecraft. Featured prominently in the center of the image is the Sample Return Capsule (SRC), showing that our asteroid sample’s ride back to Earth in 2023 is in perfect condition. In the upper left and upper right portions of the image are views of deep space. No stars are visible due to the bright illumination provided by the sun.Image: NASA / MSSS / UA

I'll make the comparison even easier with a flicker gif. The black spot isn't the only thing that changes. I'm pretty sure the shifting white lines have to do with reflections from thermal blanketing and other shiny hardware.

Teeny impact on the OSIRIS-REx sample return capsule heat shield
Teeny impact on the OSIRIS-REx sample return capsule heat shield A comparison of two images taken by StowCam on September 22, 2016 and March 2, 2017 shows the mark of a tiny impactor having struck the sample return capsule's heat shield some time in the intervening six months. A detail is shown inset at upper left.Image: NASA / GSFC / Lockheed Martin / U. Arizona / Emily Lakdawalla

For context, here's an artist's concept of the spacecraft.

Diagram of the OSIRIS-REx spacecraft instrument deck
Diagram of the OSIRIS-REx spacecraft instrument deck Image: NASA / GSFC / Lockheed Martin

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