Join Donate

Emily LakdawallaFebruary 28, 2019

Fun With a New Data Set: The OSIRIS-REx Earth Flyby

The OSIRIS-REx team recently issued their first data release to the Planetary Data System. This release doesn’t include any closeup pictures of asteroid Bennu, but it does include all the pictures they took during their September 2017 Earth flyby. Looking at familiar targets like Earth and the Moon is helpful for getting into a new data set. This is true for amateurs and professionals both -- read Vicky Hamilton’s article for The Planetary Report on how the Earth flyby helped the science team.

OSIRIS-REx

OSIRIS-REx is a mission to retrieve a sample from near-Earth asteroid 101955 Bennu and return it to Earth in 2023.

It’s a relatively small data release, so I dove straight in. I downloaded everything and converted it from FITS to PNG format using Björn Jónsson’s IMG2PNG software to see what there was. I uploaded all the OSIRIS-REx Earth flyby PNG files here with a little bit of metadata -- browse it for yourself and see what you can find!

What did I find? First of all, there’s a neat set of photos taken with the NavCam of Earth, its size diminishing as OSIRIS-REx flew away from its flyby.

NavCam image animation from OSIRIS-REx’s Earth flyby

NASA / GSFC / UA

NavCam image animation from OSIRIS-REx’s Earth flyby
OSIRIS-REx tested most of its instruments on Earth and the Moon following the 22 September 2017 Earth flyby. This animation includes 29 images of Earth taken between 21:08 and 22:43 on that day as OSIRIS-REx shifted to place the image of Earth in different places on the NavCam detector.

To get a better look at Earth’s rotation and diminution, I aligned all the pictures on one of the cloud features. All we should be seeing in the animation below is Earth rotating and receding. So why does it look like a squishy stress ball?

Squish squash Earth

NASA / GSFC / UA / Emily Lakdawalla

Squish squash Earth
29 images of Earth taken by the NavCam on OSIRIS-REx have been aligned on a cloud feature. Earth's apparent squishiness results from geometric distortion in the camera optics.

It was time for me to read more about OSIRIS-REx’s cameras. OSIRIS-REx has a lot of cameras. For that reason, I made sure that we made a good cheat sheet to accompany the aforementioned Planetary Report article. Take a look and compare the detector sizes and fields of view of the six different cameras.

OSIRIS-REx's instruments

Loren A. Roberts for The Planetary Society

OSIRIS-REx's instruments
OSIRIS-REx’s instrument deck is crowded. Most are science instruments, including OCAMS, OLA, OTES, OVIRS, and REXIS, but TAGCAMS and LIDAR are for navigation purposes.

You can see that there are two main sets of cameras on OSIRIS-REx. First, there are the OCAMS, the science cameras SamCam, MapCam, and PolyCam. They have smaller detectors (1024 by 1024 pixels), which is a common size for space science cameras. Each one has a field of view about 5 times narrower than the next one, providing resolving power 5 times greater. A set of images of the Moon taken 3 days after the Earth flyby shows you how the 3 cameras fields’ of view and resolving power compare to each other.

OSIRIS-REx OCAMS fields of view compared

NASA / GSFC / UA / Emily Lakdawalla

OSIRIS-REx OCAMS fields of view compared
OSIRIS-REx took these 3 images of the Moon with its 3 science cameras within about an hour of each other on 25 September 2017. The pictures illustrate the differences in field of view and resolving power among the cameras. SamCam has a 21 degree field of view; MapCam has a 4 degree field of view; and PolyCam has a 0.82 degree field of view.

The other set of cameras is called TAGCAMS. There are three of them: two NavCams and a StowCam. (One of the NavCams is often called the NFTCam, for “natural feature tracking;” I will have to research more about what that means.) These have larger detectors than the OCAMS and very wide fields of view. They see a lot more area on the sky than any of the science cameras, at slightly higher resolution than SamCam but lower resolution than MapCam or PolyCam.

OSIRIS-REx NavCam field of view compared to OCAMS

NASA / GSFC / UA / Emily Lakdawalla

OSIRIS-REx NavCam field of view compared to OCAMS
OSIRIS-REx's NavCams have a wide field of view (44 by 32 degrees) and large detectors (2592 by 1944 pixels). This is a photo of the Moon taken a few days after OSIRIS-REx's Earth flyby. The squares on the image show the fields of view of the mission's science cameras.

It’s the wide field of view that’s responsible for Earth’s stress-ball-like squishiness in the animation above. There is geometric distortion in the NavCam images, as explained in this paper describing the TAGCAMS instruments. (When data sets get released to the PDS, they also provide documentation, papers about how the instruments work, and this paper is open-access.) Here’s an illustration showing what a NavCam photo of a checkerboard looks like without (left) and with (right) geometric correction. You can see that squares near the center of the uncorrected image appear larger than those nearer the edges, and that the farther you get from the center, the more distorted the squares get.

Correcting optical distortion in OSIRIS-REx TAGCAMS images

Bos et al. 2018

Correcting optical distortion in OSIRIS-REx TAGCAMS images
The left image was taken with an engineering model of an OSIRIS-REx NavCam. On the right, the image has been calibrated, with its optical distortion removed.

By playing with the left image in Photoshop I figured out that I could use the Lens Correction filter and set a custom value of 12.00 in the “Remove Distortion” field o dramatically reduce the distortion. Having done that, I recreated the receding-from-Earth animation, below. It’s not perfect, but it’s pretty good, I think!

Flying away from Earth

NASA / GSFC / UA / Emily Lakdawalla

Flying away from Earth
As OSIRIS-REx departed from its 22 September 2017 Earth flyby, it took a sequence of images of the diminishing, rotating planet with its NavCam.

Björn Jónsson, who’s more skilled than I am at image processing, produced a few really nice views of Earth and the Moon from these data.

OSIRIS-REx MapCam view of Earth, just after flyby

NASA / GSFC / UA / Björn Jónsson

OSIRIS-REx MapCam view of Earth, just after flyby
OSIRIS-REx’s MapCam looked at the Pacific Ocean through color filters just hours after the flyby when Earth filled its field of view. The photo was taken on 23 September 2017 at 00:03 from a range of 179,000 kilometers.
OSIRIS-REx MapCam view of the Moon, 3 days after flyby

NASA / GSFC / UA / Björn Jónsson

OSIRIS-REx MapCam view of the Moon, 3 days after flyby
Color image enlarged by a factor of 2. OSIRIS-REx took this photo on 25 September 2017 from a range of 1,227,000 kilometers.

And here is Jacint Roger Perez' take on some of the MapCam data:

MapCam views of Earth from OSIRIS-REx flyby

NASA / GSFC / UA / Jacint Roger Perez

MapCam views of Earth from OSIRIS-REx flyby
Six days after it flew past Earth, OSIRIS-REx pointed its color MapCam at our home planet.

What can you do with the OSIRIS-REx Earth flyby data? Check them out for yourself!

OSIRIS-REx Earth flyby timeline

Loren Roberts for The Planetary Society

OSIRIS-REx Earth flyby timeline
OSIRIS-REx observed Earth and the Moon with its cameras during four opportunities following its Earth gravity assist (EGA).

Read more: amateur image processing, OSIRIS-REx, Earth, the Moon, explaining image processing

You are here:
Headshot of Emily Lakdawalla (2017, alternate)
Emily Lakdawalla

Senior Editor and Planetary Evangelist for The Planetary Society
Read more articles by Emily Lakdawalla

Comments & Sharing
Bill Nye and people
Let's Change the World

Become a member of The Planetary Society and together we will create the future of space exploration.

Join Today

LightSail
LightSail 2 Sweepstakes

Help power LightSail 2's journey and support the mission by entering to win a complete LightSail swag kit.

Learn More

"We're changing the world. Are you in?"
- CEO Bill Nye

I'm In!