DanRyanIrish

> > * spice module can be moved to `sunkit-instruments` > > We should ask if the spice team want it in their spice package. That would be even better....

Hi @ebuchlin. This is a confusing place to have this conversation, which is my fault. Apologies. I did not mean that functionality should be moved from `ndcube` to `sospice`. I...

@Cadair, as requested, an explainer on the API/behaviour has been added to the PR description.

@Cadair, except for narrative docs, I think this PR now addresses all but one minor comment of yours. Unless you'd like to look at it again, I will merge it...

Thanks for the review @Cadair. I've addressed your comments with a couple exceptions where I ask for further clarifications.

Thanks so much for raising this issue @mwcraig.

Superpixelling is now possible with ndcube v 2.1.1 via the `NDCube.rebin` method. (sunpy/ndcube#450). So it seems the only outstanding item is better fitting support in astropy.

Yes, in principle that's right. If it turns out it doesn't work as expected, we should look into that.

@andyto1234 Did this resolve your issue?

I approve of the principle of this PR. I think that this is a case of the FITS standard being insufficient, rather than solar physicists not adhering to that standard....