[Ground-station] Yes, you can buy a cubesat, but...

[Phil Karn]

On 4/23/18 21:34, Mark Whittington via Ground-Station wrote:

> On the open research side of things, testing mechanical components to
> failure and publishing the results sounds like fun.  Are there other
> general categories of parts that would be useful to characterize in
> similar ways?

The AMSAT practice and experience has been to just fly good commercial
grade parts but only after all the standard pre-launch tests, primarily
thermal vacuum and vibration (or "shake and bake"). After a while you
begin to see patterns in what works and what doesn't. I think
electrolytic capacitors can be problematic, and so can crystals (which
may not oscillate at low temperature). Connectors should be minimized or
eliminated.

Jan King, W3GEY, has said for a long time that if you survive the
launch, space (especially low earth orbit) is actually a pretty benign
environment. There's no gravity, no vibration, no rain and no hams
tinkering with the hardware. There will be day/night thermal cycling,
but if you do your thermal design properly this is a manageable problem.

Even radiation is fairly benign in LEO, though it does get much worse as
you go up. The inner Van Allen belt around 1/2 - 1 earth radii is full
of energetic protons and is best avoided. Nevertheless, AMSAT Oscar 10
got into an elliptical orbit with a perigee around 4000 km, and despite
using 16kx1 MOSTEK dynamic RAM, about the most rad-sensitive stuff out
there, it survived about 3 years before succumbing to total dose. It had
mechanical shielding and used ECC ram with scrubbing, and we could see
the error counts go up on each perigee pass.

Most LEO AMSAT satellites eventually succumb to battery wearout because
of the constant day/night cycles (typically 14). One (Oscar-7, launched
1974) actually came back years later when the batteries finally went
open-circuit and let the electronics run when the panels were in sunlight.

More recently, many of our satellites have worked fine right up to
orbital decay. AO-13 was in a resonant orbit that took the perigee into
the atmosphere after about 8 years. Our most common LEO destination used
to be 850-1400 km, which is very long lived, but more recent LEO
opportunities are in the 400-600 km range (particularly 400 km, since
some are launched from the ISS and that's where it flies). Orbital
lifetimes here are much more limited; ARISSat-1, deployed from the ISS
in August 2011, decayed in early January 2012. So again, it's common for
these satellites to operate right up until they decay. And that's
actually OK with me, because space debris is becoming a real problem and
we're much less likely to encounter pushback when we go into the lower
orbits.

Phil
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