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At one point there were formal specifications for cubesat dimensions. I know it's a bit larger than precisely $10m \times 10n \times 10$ centimeters, where $m=1, 2$ and $n=1, 2, 3$ but I am not sure how much.

The reason I've asked is that I was looking at this photo from the JLP/Caltech page Arcsecond Space Telescope Enabling Research in Astrophysics (ASTERIA); Mission Information:

enter image description here

The article continues:

ASTERIA is a 6U CubeSat (roughly 10 x 20 x 30 cm, 12 kg) that will operate in low-Earth orbit. The payload consists of a lens and baffle assembly, a CMOS imager, and a two-axis piezoelectric positioning stage on which the focal plane is mounted. A set of commercial reaction wheels provides coarse attitude control. Fine pointing control is achieved by tracking a set of guide stars on the CMOS sensor and moving the piezoelectric stage to compensate for residual pointing errors. Precision thermal control is achieved by isolating the payload from the spacecraft bus, passively cooling the detector, and using trim heaters to perform small temperature corrections over the course of an observation.

In May 2017, the flight spacecraft was delivered for integration into the Nanoracks Cubesat Deployer. ASTERIA is currently scheduled to launch to the International Space Station (ISS) with the SpaceX Falcon-9 Crew Resupply Services – 12 (CRS-12) mission in August 2017. Deployment from ISS is planned for October 2017 to begin the 90-day ASTERIA technology demonstration mission.

So if JPL calls it a cubesat, and it will be accommodated by the "Nanoracks Cubesat Deployer" then by gosh it certainly sounds like it's a cubesat!

But, when I look at the photo, there is an optical table breadboard with its grid of holes. These are traditionally either 25.0mm or 25.4mm spacing (you can order either one). While the camera is at an oblique angle, the satellite appears fairly parallel to the grid in both directions. From that I can estimate a size, and it does not appear to me to have a footprint anywhere near 20 x 30 cm, nor a height of 10 cm.

Question: so I'd like to ask; What are the absolute maximum dimensions of a proper 6U cubesat? Does ASTERIA comply?

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    $\begingroup$ @uhoh Are you counting the unfolded solar panels in your estimate? 8 visible rows of breadboard holes suggests 20cm, consistent with the description. $\endgroup$
    – Quentin Clarkson
    Aug 14 '17 at 12:51
  • $\begingroup$ @QuentinClarkson No I'm not counting the solar panels. Let's wait, but I definitely get at least 9 if not more, and if you do it again, carefully, you will too. $\endgroup$
    – uhoh
    Aug 14 '17 at 13:51
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There are a number of definitions out there as to what a cubesat is. 4 inches and 10 cm are the two most common size constraints for a 1U, but there are others out there. The best definition, in my opinion, comes from Cal Poly, as they are responsible for launching many cubesats. The dimensions that they list are 100 x 226.3 x 386.0, which I assume is mm. The reason why a larger cubesat is allowed more space is that the main body of the spacecraft is limited to 10 cm, but there are poles and other things that have to extend a bit beyond the base frame.

Keep in mind that those dimensions are for when it is in the container. You can have deployable items, like antennas and solar panels, that extend further than that after deployment.

I can only assume that Asteria complies with those dimensions, but I don't have any way to verify that.

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  • $\begingroup$ OK that's an 8.7U volumetrically (humor) and already a lot closer to what I've been estimating. Thanks! $\endgroup$
    – uhoh
    Aug 14 '17 at 13:52
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As another example, I've just found that the stowed dimensions of the MarCO 6U cubesats are actually 36.6 x 24.3 x 11.8 cm when writing the question How can the two MarCO cubesats remain reliably close to InSight during their six month trip to Mars?.

So it seems that a "U" turns out to be closer to 12 than to 10 cm on a side in practice, and may have some flexibility depending on the targeted deploy service.

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