Thank you Bob... You always have a refreshing, clear, informative response for any inquiry into your systems.
The fact that you recognize a design error publicly reassures us neophytes that new designs are built considering past events. It's always a pleasure hearing one of your explanations. Roger WA1KAT ----- Original Message ----- From: "Robert Bruninga" <bruni...@usna.edu> To: "'Patrick Green'" <pagr...@gmail.com> Cc: <amsat-bb@amsat.org> Sent: Friday, September 04, 2009 9:44 AM Subject: [amsat-bb] Why PCSAT is hard to recover > > Why is pcsat having so much trouble > > carrying its 5 watts then? Even > > when the satellite is in full sun? > > Even on the Z panel? ...what went wrong. > > Error in design. Since it was our first satellite, and the > first time that hamtronics TX and RX were flown in space, we put > in multiple redundancy. Two identical RX=>TNC=>TX systems. We > thought the most important thing was the command link. > > To make sure we could still access both TNC systems even with a > TX or RX failure we added a second UHF RX to both systems. In > additionl we had a relay to CROSS-CONNECT the transmitters. > > THen we made the mistake. We assumed that to recover from an > anomoly, the most important thing was to regain the command > link. Hence, from cold-boot, the spare UHF receivers would both > come on AND the transmitters would be cross-connected. This > assured we could access either TNC even if we had lost one RX or > one TX. > > The mistake was assuming that in such a recovery effort, the > first thing we would then do is TURN OFF the extra receivers and > DISCONNNECT the cross conneced transmitters once we had command. > > Well... DUH.... If the reason the spacecraft crashed back to > defaults was because it was low on power, then the last thing > you want to do is QUADRUPLE the power budget by having the > recovery-defaults turn on double the number of receivers and > double the number of transmitters! > > So we need FOUR times the average power just to get command and > that only happens during mid-day passes during maximum eclipse > periods, and sometimes right at the beginning of full sun > periods in the southern hemisphere. > Our first commmand then IN SEQUENCE is > 1) LOGON > 2) Send command to separate the transmitters > 3) Send command to turn off the two spare UHF reciverss > > If those are successful, AND PCSAT then has a full orbit in full > sun, then we can recover. But the loggon password challenge > from the satellite is the LONGEST packet in the command > sequence, and if is not successful on the FIRST try, then the > battery is exhausted and you loose the pass. > > Bob, Wb4APR > > > > On Sep 3, 2009, at 17:34, "Robert Bruninga" > <bruni...@usna.edu> wrote: > > > > >> To get good coverage you need as many > > >> LEO satellites as possible so they should > > >> each be as small as possible. > > >> Intersatellite linking could be done > > >> via automated ground stations. This > > >> eliminates the need for high-power > > >> transmtters and/or high-gain antennas > > >> on the satellites for interlinkng. > > > > > > Yep, that is what we have been trying to do now for 8 years > with > > > the APRS satellites on 145.825. We just need several of > them in > > > orbit at the same time. We have demonstrated dual-hops > several > > > times whenever two or more of the APRS satellites (and > ARISS) > > > are operational at the same time. If we could get 6 to 10 > of > > > the University cubesats to simply carry the 3.4" square APRS > > > transponder (Byonics TinyTrck-4), then we would have a > > > constellation providing nearly continuous connectivity via > these > > > satellites from any handheld or mobile APRS radio. With 6, > you > > > might have to wait 30 minutes or so to make yoru contacts. > With > > > 10 or so, you might have to wit no more than 5 to 10 minutes > for > > > connectivity. > > > > > > See www.aprs.org/cubesat-comms.html > > > > > >> It's better to put that gain and power > > >> consumption on earth. > > > > > > The advantage of the APRS satellite concept and Packet, is > that > > > we can use a 5 Watt transmitter on the satellite to be able > to > > > hit any mobile or HT using its existing omni antenna because > the > > > packet has a low dutycycle. So running 5 watts on a cubesat > is > > > easy, because the transmitter dutycycle is only on less than > say > > > 5% of the whole-orbit time. (average power 1/4 Watt) > > > > > > Whereas ECHO which is on all the time, has to be set at 1/4 > watt > > > TX power because it is on all the time. > > > > > > Also, EVERY APRS satellite would be on the same frequency > > > 145.825 with no doppler to track, and since every one of > them > > > does the same generic relay, independent of callsign, then > the > > > user on the ground just operates... He does not have to do > > > anything to go from one satellite to another... > > > > > > Bob, WB4APR > > > > > > _______________________________________________ > > > Sent via amsat...@amsat.org. Opinions expressed are those of > the > > > author. > > > Not an AMSAT-NA member? Join now to support the amateur > satellite > > > program! > > > Subscription settings: > http://amsat.org/mailman/listinfo/amsat-bb > > > > _______________________________________________ > Sent via amsat...@amsat.org. Opinions expressed are those of the author. > Not an AMSAT-NA member? Join now to support the amateur satellite program! > Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb > _______________________________________________ Sent via amsat...@amsat.org. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
