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I'm pretty sure that at least some large satellites are deployed with their batteries charged so that they can initialize themselves, get their own attitude and position, and possibly establish some communication and even change their orbit without needing time to charge their batteries from the solar panels.

I remember reading that most cubesat launch providers have fairly strict rules about stored energy. Cubesats usually can't contain highly reactive chemicals, very strong and tightly wound springs, or fully charged batteries. Possibly even the real-time clock is not running?

Have I got this basically right?

Sherpa is a really interesting system. It carries a substantial supply of charged batteries. A good discussion of it's structure and operation can be found in this answer.

Here is Sherpa's sequence - I have paraphrased it from that answer and from the linked document therein:

  • Separation from the upper stage
  • Power-up; avionic system initiated & start mission sequence
  • 30 minute coast – no SHERPA activity
  • Start payload deployment sequence
  • 45 minute payload deployment time - detailed position/timing information of each event stored and relayed to ground
  • Continue telemetry to ground until end of battery life approximately 10 hours post SHERPA separation.

Conceivably, Sherpa could pass a little bit of juice (electrical power, not Tang) to some of the cubesats, and even the correct time, position, and attitude of each deployment (but that's really a separate question). However I don't know if the cubesat standard even provides for the necessary electrical connections to do this, or if Sherpa can afford to give away much power.

So, Are cubesats deployed with fully discharged batteries? Even those on Sherpa?

note: Sherpa can host a variety of small satellite shapes and sizes. I'm primarily interested in the batteries of those that meet the cubesat standard, or are at least considered cubesats.

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  • $\begingroup$ fyi ICanHazPDF is a way to request an author of a published paper behind a paywall to e-mail you a personal, individual use copy of their paper. $\endgroup$
    – uhoh
    Jun 13, 2016 at 3:48

2 Answers 2

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All cubesats that I have personal knowledge of (including the Planet Labs fleet) were launched with partially charged batteries, typically at around the 50% level that minimizes degradation in storage.

The launch providers do typically impose fairly strict rules requiring redundant physical interlock switches to prevent any electronics from being energized before deployment, especially for sats going via the ISS.

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  • $\begingroup$ OK, thanks! So at least the launch provider(s) of the launch(es) you describe allow at least stored energy in the batteries of each cubesat. Do you think this applies to the upcoming Falcon-9 / Sherpa mission as well? $\endgroup$
    – uhoh
    Jun 13, 2016 at 2:37
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    $\begingroup$ I would expect so. $\endgroup$
    – pericynthion
    Jun 13, 2016 at 3:03
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Every cubesat I've seen is completely disconnected from the rocket electrically, unlike most satellites. They typically reside inside of a pod of some kind, such as the P-POD. This means there is no method to charge the satellites. In addition, as such a low priority user, they are often loaded into the satellite weeks, or occasionally months ahead of time (For classified launches). Bottom line, it seems unlikely anytime soon that they would be charged at launch. The cubesats that have been launched thus far seem to be able to compensate for this.

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  • $\begingroup$ OK good to know. There exist batteries that can hold a charge for months, so the delay is not by itself proof all cubesats are fully discharged. Aren't there rules, conventions, or specs on stored energy as well? Are electrical contacts excluded by cubesat specs? The question was written carefully to avoid exclusive reference to the past tense alone. $\endgroup$
    – uhoh
    Jun 13, 2016 at 2:21
  • $\begingroup$ Your point about delays is important, considering @pericynthion 's answer that cubes are frequently(?) loaded with batteries partially charged to minimize degradation. A delay of months could have dire consequences for the batteries - at least some types are extremely unhappy sitting at zero. Has there already been a case where the delay was months? $\endgroup$
    – uhoh
    Jun 13, 2016 at 4:28
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    $\begingroup$ Yes, as mentioned the bunch launched with NROL-55 satellite last year were integrated about 6 months in advance. $\endgroup$
    – PearsonArtPhoto ♦
    Jun 13, 2016 at 7:20
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    $\begingroup$ Some of the Planet Labs sats ended up being deployed from ISS almost a year after they were boxed up, after a series of delays both pre-launch and on the station. We were a bit concerned about the battery state of charge but had kept an engineering unit in the same state for the same length of time, for comparison purposes. Luckily it didn't get low enough to be seriously degraded. PearsonArtPhoto is correct that there is no power or data connection between cubesat and launcher. I would expect this to continue to be the case even on SHERPA as it greatly simplifies logistics. $\endgroup$
    – pericynthion
    Jun 13, 2016 at 18:32

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