For simple orientation a sun sensor will give you roll, if your willing to
restrict your launch times...
(My version of sun sensor is wide angle camera with High value ND filter on
it.)
A Horizion sensor pointing forward and a sun sensor to the side will give
you full orientation
again if you are willing to restrict launch times...
On Thu, Dec 27, 2018 at 7:23 PM Henry Spencer <hspencer@xxxxxxxxxxxxx>
wrote:
On Thu, 27 Dec 2018, Ben Brockert wrote:
The star tracker is less useful if it only works when the thing it is
attached to has no roll. Stacking frames is effectively the same as a
longer exposure which, as Henry mentioned earlier in the thread, leads
to star trails rather than brighter stars.
There's one difference between longer exposures and stacking frames: you
can do shift-and-stack operations -- shifting frame N+1 around to look for
the best correlation with frame N, and *then* stacking -- instead of just
stacking. Correlation can work effectively even when the features it's
matching on are buried in background noise, so you don't need to be able
to distinguish the stars clearly in each frame to do shift-and-stack.
This doesn't eliminate the problem, but can reduce it significantly, at
the cost of a lot more CPU cycles (which are not free, especially in a
low-power device with a hard real-time deadline to meet, but are much
cheaper than they used to be).
Dragon has a star tracker and they don’t expose it to space until well
after stage separation, I’d guess to keep the optics clean.
Most likely, yeah. LOX/kerosene rockets -- in fact, most chemical rockets
other than LOX/LH2 -- are notorious for crudding up outer surfaces during
ascent, and staging events are particularly bad for surface contamination.
Apollo's Boost Protective Cover started out as a window shield, although
it was later expanded to help with other issues too.
Henry