David, et all,
(I don't think this is to far off topic for Arocket, since propulsion for
home built satellites is a concern :)
As far as I could tell, the POD designs varied considerably. The original
P-Pod was a single 3-U sized box, that weighed considerably more than
the satellite it contained. It had a swing open door at the business
end, with a spring pusher plate at the other. (There was a hole in
the plate that you could put a 'trunk' down inside the spring for a
little extra room). of the 4 rails, or "double tracks" running up
the sides of the box, one was spring loaded to push in, to clamp the
sat in place. The door released this mechanism so the sat was free
to slide out when the door opened.
It seemed to me that a better system would be two adjacent rails clamping
to be more secure across the sat, but whatever.
You can stack multiple sats in the 3U space, hence the use of 1, 1.5, and
2 U sats.
Other designs, from other manufacturers, had assorted improvements,
lighter weight, deployment sensor switches etc. The one we eventually
flew on was capable of flying a 12U Cubesat. It had dividers to allow
6U or 3U holes. I imagine smaller sats were accompanied by spacers if
additional small sats were not available.
I have seen (and probably possess somewhere) the notional specifications
on the 6U and 12U standards. The problem I saw was that above 6U the
clamping rails did not supply enough support, so they were suggesting
T-Rails. I Did not confirm the engineering behind this, but it appeared
that a 12U would not really be that common in design. My personal
CubeSat Design can be easily changed from 3U down to 1U or up to 6U.
(It is open source, if I get around to finishing the final report)
The Tip-off Rates for deployment is specified to be between 1 and 2 m/s
but didn't give angular rates. I find this suspect, since we didn't
give them a mass, and they don't really know how well we fit. We were
snug in two orientations on the Shake and Vibe Test 3U test pod. We
were concerned enough that we brought along a slightly larger fit
check unit to the final integration. The flight pod was significantly
larger and we had no problems. I would suggest a more positive separation
scheme. perhaps pull the rails away and gently nudge with a servo ?
I would strongly suggest a custom pod available to the customer for
shake, vibe, and G loading tests. I believe it could be considerably
lighter. If you have the capability of live downlink video, a view of
the payload would solve any lingering questions of who did what in
the event of a failure.
An additional comment on the Cubesat Standard, It is nominal to have
at least two, serial connected, normally closed, switches on the
end posts of each sat. They inhibit all power when depressed and
only power the satellite after it is released. The sat also needs a
timer to inhibit operation after the power is applied. This time
varies. Some rules say 30 min, some 60 min. A Last minute requirement from
our launcher was 10 hrs, then the FCC said never. (we negotiated)
On our sat, we used parallel and serial switches for redundancy.
all four end postes had switches. Since the Sat had redundant systems,
both ends were fully populated. On smaller sats, two of the posts
need springs for separation.
And charge maintenance ? baw-Ha. We said goodbye two months out, and then
had weeks of launch delay. If someone was just launching us alone, I
would imagine showing up with the sat, the week of the launch !
yea, that would be great. :-)
-Gar.
PS. For orbital trim burns, maybe use the RCS system after a few orbits ?