Who needs batteries anyway?

Jan King with Oscar7 on the 'shake table'

Oscar7 it's fair to say is an old bird..... a very old bird.  Launched November 1974, the satellite operated for about six and a half years, before the NASA supplied battery * failed short-circuit.  The satellite remained dead in earth orbit until June 2002 when the failed battery went open-circuit, rare for Ni-Cd's, and so oscar7 became quite a usable 'daylight only' satellite.  In fact, it's term of operation since the battery failed now exceeds it's 'first' lifespan as a battery carrying satellite.    This fact was noted recently on the EU-AMSAT yahoo forum by Thomas Frey HB9SKA. 

Compared to today's amateur satellites, Oscar7 was built in a far more simple manner and had no IHU, which of course begs the question, would an IHU equipped bird have lasted so long?  The answer is most likely no.  The loss of the battery in some ways saved Oscar7 and showed that the electronics can greatly outlive the 'wet chemistry' based batteries on which satellites depend.

When LA2QAA and myself were decoding telemetry from the bird a few years ago, the performance in sunlight was reasonably good, so long as stupid inconsiderate users were not hitting the transponder with the sort of high power  levels that even AMSAT seem to be supporting these days. AO7 has an incredibly sensitive receiver on board, so 5 watts on the uplink works fine, so long as you are not stone deaf. LA2QAA makes do with less power than that.

Some day, satellite builders may wake up to the fact that batteries are a real liability and in many cases are the reasons for the failure of otherwise perfectly viable satellites.  Oscar7 has gone downhill further through continuing gradual degradation of the solar panel cover slides by radiation. Modern materials could increase the life of solar panels over that enjoyed by Oscar7. In the meantine, batteries have only improved a little.  The battery of any satellite in LEO has a very hard life indeed.  Perhaps it's time to consider the unthinkable and build at least a couple of linear LEO's without batteries or IHU's .   However boring that idea may be to the satellite builders, it could result in a couple of very long-lived linear birds that could provide a lot of opportunities for satellite fans.

* That troublesome NASA battery used on Oscar7

The prismatic battery pack flown on Oscar7 was a flight spare from a NASA project. At the time of launch, it had already undergone very many charge-discharge cycles.

Much has been said on the various BB's about Oscar7 telemetry with people recording meaningless information from the bird when the telemetry system decides to send info.  In short, a telemetry frame that does not end with the numbers 649, 650 or 651 is not worth decoding.

Here's what a good data frame might look like.

Hi Hi
 100  176  164  178
 280  262  200  254
 375  358  331  354
 453  454  461  459
 541  501  552  529
 600  600  601  651

More often you will just see the line numbers with 'empty values' and no correct last number.  Why is that last number so important?  Well Oscar7 used a single A/D converter that was supplied with a precise reference voltage. That reference voltage is what is sent as the last entry in the telemetry, so if it is not 649,650 or 651, then the associated information is meaningless.

 73 Al

GM1SXX