The image below is from Spaceflight Now's Fresh batteries, experiments on the way to the International Space Station

In the photo there appears to be a giant reentrant "hole" in the side of the HTV spacecraft with some heavy equipment that is equipped with the standard grapple thing for the ISS' robotic arm.

During launch I can't see how this opening could be exposed to the atmosphere. I would expect it to be covered since all that insulation would probably rip off in supersonic atmospheric flight, but in the image it looks flush with the lower part of the spacecraft painted white, so I'd like to understand how this is covered for launch.

click for larger view

Spaceflight Now Japan’s eighth HTV supply ship

Japan’s eighth HTV supply ship is seen during launch preparations at the Tanegashima Space Center. Credit: JAXA

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    $\begingroup$ What do you mean by "reentrant" here? $\endgroup$ Commented Sep 25, 2019 at 0:42
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    $\begingroup$ @RussellBorogove en.wikipedia.org/wiki/Concave_polygon (but in 3D) the surface I'm seeing is an insulation-covered cylinder with a rectangular cut-out in the side. I think this is standard usage of "reentrant" when describing the shapes of 3D solids or 3D surfaces. $\endgroup$
    – uhoh
    Commented Sep 25, 2019 at 0:48
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    $\begingroup$ Huh, I hadn't encountered that usage before. $\endgroup$ Commented Sep 25, 2019 at 0:49
  • $\begingroup$ @RussellBorogove "recessed" might be a better choice, but here are some random examples of uses of "reentrant" referring to a concave area of a 3D surface: 1, 2, 3 $\endgroup$
    – uhoh
    Commented Sep 25, 2019 at 0:55
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    $\begingroup$ The external cargo is mounted on a pallet that slides into that hole. The SSRMS grapples the pallet and pulls it out. It's a slick design like all the JAXA ISS stuff. $\endgroup$ Commented Sep 25, 2019 at 1:43

1 Answer 1


It's all covered by a payload fairing that isn't flush with the body of the spacecraft. A picture is worth a thousand words:

enter image description here


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