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The (currently unanswered) question How does JAXA's “Int-Ball” manage airflow to optimally navigate inside the ISS? shows a complicated set of twelve ducted airflows for that JAXA aerobotic system aboard the ISS.

Now the first of three AeroBee has arrived at the ISS. These are perhaps the "successors" or next generation of NASA aerobot after the very popular and productive SPHERES.

Question: How do the AstroBees implement attitude control? The figure caption below begins to describe the air system as having two large inputs and twelve outputs, but the details are not shown. For example, which directions do the nozzles point? Which groupings are used for directional propulsion versus rotations, etc.

The number twelve sounds familliar; that's also what is used by the JAXA aerobot discussed in the (currently unanswered) question How does JAXA's “Int-Ball” manage airflow to optimally navigate inside the ISS?.


From the IEEE Spectrum article NASA Launching Astrobee Robots to Space Station:

enter image description here

Astrobee’s components include multiple cameras, a touch screen, laser pointer, and lights. The propulsion system consists of a pair of impellers that pressurize air inside of the robot, which can then be vented through a series of 12 different nozzles spaced around the robot’s body. There’s also a “Terminate Button,” which, if pushed, would instruct Astrobee to seek out and destroy all life aboard the ISS; at least that’s what we assume it would do, but we could be wrong. Image: NASA

The figure caption's reference to "destroy all life" is atypical for the traditionally stoic IEEE Spectrum.

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The paper Astrobee:Developing a Free-flyingRobot for the International Space Station explains the propulsion system rougly in two sentence:

Astrobee’s propulsion system consists of a propulsion module on each of two sides of the free flyer (Figure3). Each module includes a centrifugal fan that pressurizes the module, and nozzles on the x, y, and z axes to allow for six-degree-of-freedom holonomic control. Astrobee will operate in a quiet environment and remain below the ISS noise limits.

With four nozzles per axis, 2 nozzles facing positive and 2 facing negative axial direction, you can induce a linear movement along the axis by activating two nozzles facing the same direction. Inducing a rotation around the axis is accomplished by activating two offset nozzles facing opposite directions. To make "complicated" movements you simply combine several actions from different axis. Additionally I would assume the Astrobees do have reaction wheels for precise movements.

It is a similar system as the JAXA Int-Ball. Astrobees use two fans to power 12 outlets/nozzles instead of the Int-Ball which uses 12 fans fed by 2 inlets.

Fun Fact: the centrifugal fans on the Astrobees need to spin in opposite directions to counter act any torque.

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  • $\begingroup$ With four nozzles per axis, 2 nozzles facing positive and 2 facing negative axial direction, you can induce a linear movement along the axis by activating two nozzles facing the same direction. Inducing a rotation around the axis is accomplished by activating two offset nozzles facing opposite directions. It's the standard functionality of a RCS. To make "complicated" movements you simply combine several actions from different axis. Additionally I would assume the Astrobees do have reaction wheels for precise movements. $\endgroup$ – GittingGud May 2 at 12:13
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    $\begingroup$ @uhoh I've added the explanation to my answer. And I really can't imagine them doing it any different because if they would have implemented some kind of elegant and new control system they would have found a way to reduce all of those nozzles and fans. Those are a lot of components which can fail. $\endgroup$ – GittingGud May 3 at 5:12

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