In her tweet ISS expedition 59/60/61 astronaut Christina Koch shows two SPHERES doing something.

What are they doing exactly? Why do they appear to be connected?

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Had a blast cheering on the students from the SPHERES Zero Robotics Middle School Summer Program during their competition today! The SPHERES team tests algorithms developed by students and selects the best designs for the competition to operate the robots onboard @Space_Station.

  • $\begingroup$ if you're wondering about the cool patterns on the SPHERES, see @tristan's answer. $\endgroup$
    – uhoh
    Commented Sep 3, 2019 at 23:34
  • 3
    $\begingroup$ For future reference: space.stackexchange.com/a/17915/31521. This appears to be two identical hooks interlocking. One purpose for the SPHERES is testing docking GN&C code. Linking together like this requires a similar amount of precision. $\endgroup$ Commented Sep 4, 2019 at 4:22
  • 3
    $\begingroup$ It looks like they're going to arm wrestle ;) $\endgroup$
    – amI
    Commented Sep 4, 2019 at 6:23

1 Answer 1


This student competition involved writing code to command the SPHERES. The scenario and requirements were presented as follows:

The Red SPHERES Satellite is in trouble.

Increasing numbers of satellites are being deployed to Low Earth Orbit (LEO) to study Earth’s atmosphere, climate, land, oceans, and weather. To protect the success of this important research the SPHERES program is working with space agencies internationally to identify and remove space debris from LEO. Recently the SPHERES program deployed ECO-SPHERES as a part of its Evade, Capture, de-Orbit (ECO) initiative to remove debris. The ECO-SPHERES design includes a hook for the SPHERES to use to tow any type of cargo.

By its very nature, capturing and removing junk puts expensive debris removal satellites in harm’s way. Any clean-up method is prone to damage. As you heard in the transmission above, one of our SPHERES Satellites has been damaged by debris and we need to retrieve it. The mission ahead of us, however, is dangerous. We must deploy another ECO-SPHERES to traverse the crowded LEO and, instead of moving debris, it needs to hook onto the damaged red SPHERES Satellite and bring it back to safety.

Program your satellite to avoid debris while trying to locate the red SPHERES. Use expert geometry to latch onto the damaged satellite, and bring it back to safety, taking into account the momentum of your precious cargo as to not further damage it.

Good luck to all participating space engineers.

(Emphasis mine)

The entries were down-selected by being tested in simulations and the finalists got to test their code out in the ISS SPHERES.

That's really neat.

Diagram of the hooks attached to the SPHERES.

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While researching this I learned that the SPHERES have been retired in favor of the ASTROBEEs.

Source: Zero Robotics Middle School Summer Program 2019


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