# Offset of the DART roll out solar arrays [duplicate]

Looking at images of the DART space craft with the solar cells fully extended, the solar cells on each side of the craft are offset from one another, instead of being inline, as the picture below shows.

Why are the solar cells offset? Is it because of a mass distribution issue, or issues relating to possible rotation of the craft as the cells are rolled out, or something else?

• From a symmetry standpoint, one could argue they aren't offset. Commented Dec 14, 2021 at 12:26
• I've flagged with the following message: "Each question now has votes to close as a duplicate of the other. Both of these answers are guesses, the answer to the other question seems more authoritative, but instead of duping this could be a good candidate for merging."
– uhoh
Commented Jan 31, 2022 at 11:15
• @uhoh: I have no issues with merging. If someone can do, let it be done.
– Fred
Commented Feb 1, 2022 at 4:26

A guess rather than an answer.

I suspect it is because attaching the solar arrays at the middle of each face will create a conflict with the High-Gain Antenna (either accomodation or pointing masking).

This can be inferred for example from this picture taken from NASA Gallery (Dart gets its 2nd wing)

I don't know for sure, but I think it's because the panels start rolled up into a cylinder on each side, like this:

O$$\square$$O

If the cylinders were attached to the rectangular box in the center of opposite faces, like O-$$\square$$-O , then the first turn (the right-angle junction between the $$-$$ and the O) would be quite sharp, so it might break the panel components, and it folds in the opposite direction from the rest of the unwinding.

If instead you attach the cylinders at the corners the way DART has done, like O_$$\square\bar{}\!$$O , then the attachment point is already properly oriented, and the initial curvature is the gentlest possible.

The result, as Jörg said, is symmetrical: ___$$\square\bar{}\!\bar{}\!\bar{}$$ is symmetric under rotation, just not reflection. $$-\square-$$ is symmetric under both (or would be, if I could get the vertical spacing right in my $$\LaTeX$$ ascii art). If you mean why use ___$$\square\bar{}\!\bar{}\!\bar{}$$ rather than $$\bar{}\!\bar{}\!\bar{}\square\bar{}\!\bar{}\!\bar{}$$ (symmetric under reflection but not rotation), it's because in the way they did it, the center of mass stays near the geometric center of the spacecraft. If they attached both wings to one face, the center of mass would move toward that panel as the booms unrolled, which would make maneuver control trickier.

• Your last example was what I meant. The center of mass idea is interesting. Thanks.
– Fred
Commented Dec 15, 2021 at 0:28
• I think sharp argument does not make sense as rolling out happens by rollers attached at the end points away from satellite. Rather reasons might be center of mass combined with the fact that this orientation would help to close the solar panel to satellite body attachment like a “lid” closer to satellite body and fit inside fairing ! Commented Dec 15, 2021 at 5:02
• If symmetry is an issue (for flight control), they could keep the solar arrays attachments as they are but rotate the deployed arrays by 45° (S/C seen as a losange rather than a square in the direction of flight). Commented Dec 15, 2021 at 11:43