PCSAT(NO-44) バッテリー
● (No.776) PCSAT(NO-44) バッテリー (2013年2月3日) ---------------------------------------------- Subject: [amsat-bb] PCSAT batteries! From: Robert Bruninga Date: Sat, 2 Feb 2013 11:14:30 -0500 我々はバッテリーを衛星の中間に設置した。(取り付けていない)太陽電池パネル (衛星の側に取り付けていない状態)では、+90℃〜-100℃まで完全に耐性がある。 太陽電池パネルは アルミニウムフレームに取り付けられていて、衛星は約 1RPM (1分間に1回転)なので、パネル上でも (1軌道あたり)約10℃以上の温度変化は生 じない。 そして、衛星上のこの 10℃の変動は、バッテリーでは1軌道あたり、および 1日 あたり、約 +/- 1℃の変化しか与えない。しかし、Sun/Orbit ベータアングルと 共に、長期間の変化が存在する。 PCsat の平均温度は約 10℃である。 全蝕期間(高ベータアングル)で、低くても 0℃、全日照の時で 1週間ほどは高くても 40℃である。この周期は約 2ヶ月ごと にやってくる。 現在 PCsat の内部は、快適な 25℃である。 我々 PCSAT(現在12才)の問題は、管制局との接触を回復するために予備の送受信 機をオンにする ｢故障検出モードからの再起動｣ を設計する我々自身の致命的な 欠陥である。今にして思えば馬鹿なことだった... 特にその理由が低電力による ことならば。 高ベータアングル(最大の太陽エネルギーを入手可能)の時、我々はいつでも臨時 の送受信機をオンオフをすることができるが、それは 蝕に入り消える(軌道ごと に充電するには不十分な時間)前の 15分間だけである。 しかし年に 2/3回は全ての予備機をオフにするコマンドを送信できて、それらが 保たれるような全日照期間に入る。しかし全日照の時はまた、最も悪いサンアン グル(最少の平均電力)でもあるので、コマンドが通るかどうかは不確かである。 http://www.findu.com/cgi-bin/pcsat.cgi?absolute=1 を見よ。 (下段に生パケットがある｡) 消える前の 9分間に、その日の試行が成功した結果 を見ることができる。毎回リセットされて 001 から始まるテレメトリ シリアル ナンバーを見よ。例えば 2013年2月2日14:29:24z にそれが起きたことがわかる。 -----Original Message----- Subject: [amsat-bb] PCSAT batteries! From: Robert Bruninga Date: Sat, 2 Feb 2013 11:14:30 -0500 We placed the batteries in the middle of the satellite. It is quite immune to the +90C and -100C possible fluctuations on (unattached) solar panels (if they were not attached to the sides of the satellite). Since the solar panels are attached to the aluminum frame and the satellite rotates at about 1 RPM, we don't see any temperature variations even on the panels of more than about 10C (per orbit). And then these 10C fluctuations on the sides only penetrate to about a +/- 1 degree variation at the batteries per orbit and per day. Though there is a long term variation with the Sun／Orbit beta angle. The average temperature of PCsat is around 10C, getting as low as 0C during full eclipse seasons (High Beta angles) and as high as 40C for a weak or so when it is in full sun. This cycle moves over a 2 month or so cycle. Right now, PCsat inside is a nice comfortable 25C. Our problems with PCSAT (now 12 years old) is our own fatal flaw of designing it with a reboot-after-fault-detection mode of turning on backup transmitters and backup receivers to regain contact with the command station. Now with 20/20 hindsight, that was dumb... especially if the reason it faulted is due to low power! We can get in and turn off the extra XMTRS and RCVRS any time we want during high beta angles (maximum peak solar power available), but then there is only 15 minutes left before it goes back into eclipse and dies (not enough time to charge each orbit). But then 2 or 3 times a year, it enters full sun periods when, if we can get the command in, then we can send those commands to turn off all the spares and they will hold... BUT this time of full sun, is also the time of the worst sun angle (least average power), and so it is iffy if we can get the command in. See http://pcsat.aprs.org (raw packets at the bottom) and you will see that today's attempt resulted in achieving 9 minutes of operation before it died. See the telemetery serial numbers starting at 001 each time it resets. That occurred at 2013-02-02-14:29:24z Hope that helps Bob, WB4APR [Supplement] Subject: [amsat-bb] PCSAT normal(?) operations resume From: Robert Bruninga Date: Tue, 5 Feb 2013 11:31:30 -0500 PCSAT (NO44) is again returned to users (but not usable until a few weeks when sun angles get better). The Transponder on ISS is also operational now. The variation of power available to PCSAT is inversely proportional to the "sun-to-orbitplane-angle" (viewable in Instantrack with the "E" and "D" keys. It is currently above 78 degrees. Once it went above about 65 degrees was our last successful commanding. Recovery did not work this period. But we learned enough to be more successful in the Fall. A "sun-to-orbitplane-angle" means PCsat’s orbit is now over the day/night terminator meaning it is in full sun (no eclipses) with solar power coming in on the (weaker) side panels and little if any on the +Z face (best panel). Attitude is maintained by alignment with the Earth’s magnetic field. It’s the best time for a recovery (no eclipses to cause a reset), but the worst time for commanding. It is too weak to respond to the needed logon and 3 additional commands. Though it will be strong again as the sun angle improves (lower). Then it will have better sun on the +Z face for commanding, but then it will be doing Eclipses. And even though we can then command it to turn off unnecessary loads, it does not have enough time before the next eclipse to charge up enough to survive the next eclipse. What we did (re)learn is a condensed command method where we can put all 3 PCSAT low-power commands in a single packet (using the TNC’s ^V pass character). That way, we only need a successful logon to complete the Restoration. 1) The CONNECT ACK. 2) The password challenge, 3) Then the command prompt. Then we can hit it with the full low-power command set and disconnect all in one packet which cancels the need for PCSAT to respond to each command separately. On the FIRST day available in full sun(our best shot), I not only got logged on, but completed all 3 requried functions. Then signals sounded so good, I got greedy and put in the another three (which also improves power budget, but not as much as the first three). Yep, I gambled and lost. It died on the last one! The next day I got all 3 in, and it died on the 3rdcommand due to a user packet I think. Days since, I have been unable to logon. Hence, end of this attempt period. In most attempts in the past (after successful logon) we would send one command at a time to give it a few seconds rest between each one. But these 3 commands then required 3 ACKS and 3 RESPONSES in addition to the 3 required to get logged. Those extra 6 packets kill it, especially if there was a user packet in there. Next time all we need are the 3 loggon responses. Also, next time, we will give users advance warning to QRT all transmissions when we are trying to command. Each one of their packets robs us of power we need to complete the command. I failed to warn everyone this time, and so we had some interference. As sun angle improves, You may continue to experiment with PCSAT during MIDDAY passes. That is when it is strongest (in the Northern Hemisphere), but do limit yourself to only attended operations so humans can actually contact humans, or if you are doing an unattended test, keep your transmissions to once every 2 minutes. That should let you get one good successful packet per pass. Which is the mission of PCSAT. See the downlink on http://pcsat.aprs.org There you can see the telemetry packets (list at the bottom of page) right now are rarely getting above 001 meaning typically a minute or so of life before it gets overloaded and resets back to 000. It is easy to visualize the relationship of the sun angle to the orbit plane and to see how that affects power budget given that our best panel (out of 5) is on the +Z face and that is magnetically aligned to point towards magnetic South. There is NO panel on the -Z which is why PCsat is rarely usable in the Southern Hemisphere (not planned, but just a result of it crashing in every eclipse). Just thought you would like to know what is going on with one of the oldest student projects in space that is still "semi-operational" for users. Bob, Wb4APR US Naval Academy Satellite Lab
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