[AR] Re: CubeSat V2
- From: Henry Spencer <hspencer@xxxxxxxxxxxxx>
- To: Arocket List <arocket@xxxxxxxxxxxxx>
- Date: Wed, 21 Aug 2019 20:06:49 -0400 (EDT)
On Sun, 18 Aug 2019, adam paul wrote:
...Henry I know you said that one of the big issues with cubesats is
that 3U just isn't enough space to do anything meaningful.
I think that comment referred to 1U. 3U is still rather cramped, but you
can squeeze a significant range of payloads in there if you work at it.
If you only had to put the payload in that 3u space you could do a lot
more...
Yes, not having to worry about cramming the basic spacecraft systems in
there as well would make a big difference.
the advantage I see of keeping with the cubesat form factor is that it
creates less risk for the customer for using a new standard, as they can
switch back to the cubesat standard during the development process
without too much difficulty.
Well, except then they're back to the rather severe volume/mass
constraints! However, it's not unthinkable to build a 3U-ish payload that
could fly either in the sort of thing you propose, or as the payload half
of a 6U cubesat.
Another advantage of cubesat-ish form factors is that they're familiar and
there is a considerable amount of potentially-useful hardware designed to
fit into them. As I understand it, Nanoracks has had considerable success
using a cubesat form factor for payloads that go *inside* ISS.
...What problems might arise with having
several 'unknown' payloads sharing a common power and data bus?
You definitely want at least switches in between the bus and the payloads,
so that a misbehaving payload (e.g., power bus shorted due to latchup in a
power component) doesn't take the whole thing down. Full isolation, so
that the payloads don't share a ground connection either, is a bit more
work but probably a good idea.
Isolated DC-DC converters, for shipping power across an isolation barrier
(with or without a change of voltage), are already off-the-shelf products.
It's not hard to isolate a serial line or a CAN bus, with off-the-shelf
solutions often available, and modern (twisted-pair) Ethernet has full DC
isolation built in already.
Henry
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