<div dir="ltr"><div><div><div><div><div>Phil writes:<br>>
Most LEO AMSAT satellites eventually succumb to battery wearout because<br>> of the constant day/night cycles (typically 14).
<br><br></div>Well, many, but not all, succumb to battery failures.<br><br>In particular, UO-11 (and most of the Microsats) flew with batteries that Larry Kayser,<br></div>VE3LK, now a silent key, selected and "matched" from a large set of commercial grade <br>batteries. UO-11 was launched in 1984(!) after a rather hasty development effort. <br>However, those batteries have survived many tens of thousands of charge discharge <br>cycles. UO-11 is still heard when the watchdog timer switches the transmitter "ON". <br></div><div><br></div>Unfortunately, I cannot find the low level details describing exactly how Larry did <br>his battery matching. I am pretty sure that if his process could be re-discovered that <br>people would line up to have a battery pack for their satellite that was likely to last a <br>long time. I'm also pretty sure it's more tedious than complicated because he didn't <br>have all that much time before the launch in order to develop and execute his matching <br>process.<br></div></div><div><div><div><br></div><div>Anyway, if anybody know *ANY* of the details of Larry's battery matching, please <br>share them. I'd like to reproduce his results one day.<br><br></div><div>Douglas KA2UPW/5<br></div><div><br></div><div><br></div></div></div></div><div class="gmail_extra"><br><div class="gmail_quote">On Tue, Apr 24, 2018 at 12:00 AM, Phil Karn via Ground-Station <span dir="ltr"><<a href="mailto:ground-station@lists.openresearch.institute" target="_blank">ground-station@lists.openresearch.institute</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><span class="">On 4/23/18 21:34, Mark Whittington via Ground-Station wrote:<br>
<br>
> On the open research side of things, testing mechanical components to<br>
> failure and publishing the results sounds like fun. Are there other<br>
> general categories of parts that would be useful to characterize in<br>
> similar ways?<br>
<br>
</span>The AMSAT practice and experience has been to just fly good commercial<br>
grade parts but only after all the standard pre-launch tests, primarily<br>
thermal vacuum and vibration (or "shake and bake"). After a while you<br>
begin to see patterns in what works and what doesn't. I think<br>
electrolytic capacitors can be problematic, and so can crystals (which<br>
may not oscillate at low temperature). Connectors should be minimized or<br>
eliminated.<br>
<br>
Jan King, W3GEY, has said for a long time that if you survive the<br>
launch, space (especially low earth orbit) is actually a pretty benign<br>
environment. There's no gravity, no vibration, no rain and no hams<br>
tinkering with the hardware. There will be day/night thermal cycling,<br>
but if you do your thermal design properly this is a manageable problem.<br>
<br>
Even radiation is fairly benign in LEO, though it does get much worse as<br>
you go up. The inner Van Allen belt around 1/2 - 1 earth radii is full<br>
of energetic protons and is best avoided. Nevertheless, AMSAT Oscar 10<br>
got into an elliptical orbit with a perigee around 4000 km, and despite<br>
using 16kx1 MOSTEK dynamic RAM, about the most rad-sensitive stuff out<br>
there, it survived about 3 years before succumbing to total dose. It had<br>
mechanical shielding and used ECC ram with scrubbing, and we could see<br>
the error counts go up on each perigee pass.<br>
<br>
Most LEO AMSAT satellites eventually succumb to battery wearout because<br>
of the constant day/night cycles (typically 14). One (Oscar-7, launched<br>
1974) actually came back years later when the batteries finally went<br>
open-circuit and let the electronics run when the panels were in sunlight.<br>
<br>
More recently, many of our satellites have worked fine right up to<br>
orbital decay. AO-13 was in a resonant orbit that took the perigee into<br>
the atmosphere after about 8 years. Our most common LEO destination used<br>
to be 850-1400 km, which is very long lived, but more recent LEO<br>
opportunities are in the 400-600 km range (particularly 400 km, since<br>
some are launched from the ISS and that's where it flies). Orbital<br>
lifetimes here are much more limited; ARISSat-1, deployed from the ISS<br>
in August 2011, decayed in early January 2012. So again, it's common for<br>
these satellites to operate right up until they decay. And that's<br>
actually OK with me, because space debris is becoming a real problem and<br>
we're much less likely to encounter pushback when we go into the lower<br>
orbits.<br>
<br>
Phil<br>
<br>______________________________<wbr>_________________<br>
Ground-Station mailing list<br>
Ground-Station@lists.<wbr>openresearch.institute<br>
<a href="http://lists.openresearch.institute/mailman/listinfo/ground-station" rel="noreferrer" target="_blank">http://lists.openresearch.<wbr>institute/mailman/listinfo/<wbr>ground-station</a><br>
<br></blockquote></div><br></div>