Quote from: Sam Ho on 01/23/2017 03:55 am Furthermore, it can't deploy its solar panels while attached, so it's going to run out of power quickly. Is that always true? I would think that once the fairing is gone, for some birds deployment is at least possible... (might not be a good idea)
Furthermore, it can't deploy its solar panels while attached, so it's going to run out of power quickly.
Quote from: Lar on 01/23/2017 04:27 pmQuote from: Sam Ho on 01/23/2017 03:55 am Furthermore, it can't deploy its solar panels while attached, so it's going to run out of power quickly. Is that always true? I would think that once the fairing is gone, for some birds deployment is at least possible... (might not be a good idea)I imagine that at least for some satellites, their folded panels may have one fold "out" such that it could get a low level of solar power generation (as if it was mostly but not entirely shaded by another vehicle, in this case itself). However, it's possible that nobody designs them such that the panels are "connected" to generate power until after deployment ... but I don't know of any reason why they couldn't be.
The engineer says "SpaceX sends a signal" to simplify things for the public? Wouldn't it be simpler to say: "the second stage is programmed to release the space craft automatically?" Why would she say something that is completely false?Matthew
I believe people are misinterpreting the quote to assume that there is some ground control. SpaceX (the upper stage) is sending a signal to the Iridium dispenser. That's all.
The quote is: Quote from: WHAP on 01/22/2017 04:05 pmI believe people are misinterpreting the quote to assume that there is some ground control. SpaceX (the upper stage) is sending a signal to the Iridium dispenser. That's all.But it is unsourced. The claim "SpaceX" means "the upper stage" is strained. Get a reliable quote from someone who actually knows, or I will go with what the engineer for SpaceX said. Matthew
Iridium Communications Inc. (Nasdaq:IRDM) and SpaceX today announced the successful completion of dispenser qualification testing for the Iridium NEXT constellation. The dispenser is the mission-unique assembly that holds the satellites during launch and manages the perfectly timed separation of each satellite from the rocket, placing each of the satellites into its proper orbit.
Speaking from a satellite commanding background, the time it would take for a commanding system to issue, transcode and send the commands would easily take a couple hundred milliseconds at a minimum to transmit and receive/process. Even more if you are going off a relay sat. I'm not sure how precise the release has to be, but I think by far the trust is in the flying hardware.
Quote from: jjyach on 01/24/2017 03:14 amSpeaking from a satellite commanding background, the time it would take for a commanding system to issue, transcode and send the commands would easily take a couple hundred milliseconds at a minimum to transmit and receive/process. Even more if you are going off a relay sat. I'm not sure how precise the release has to be, but I think by far the trust is in the flying hardware.It most likely is, but it is also quite easy to precisely compensate for communication delays, come on this is trivial on a realtime OS
What is the lifetime of the second stage in LEO? Does anyone know? Because if the LEO deployment orbit is wrong, it can be preferable to not deploy, but wait for further instructions from home.So there's plenty reason to do it, and we don't know what capabilities the second stage has. It may have internally the ability to accommodate a receiver that's simply not installed, for example.
Quote from: meekGee on 01/24/2017 07:46 pmWhat is the lifetime of the second stage in LEO? Does anyone know? Because if the LEO deployment orbit is wrong, it can be preferable to not deploy, but wait for further instructions from home.So there's plenty reason to do it, and we don't know what capabilities the second stage has. It may have internally the ability to accommodate a receiver that's simply not installed, for example.That's what we do with spacecraft where they safe themselves. They get in a sun pointed direction and await recovery commands from the ground when bad things happen. The stage in theory may be able to do it, but I don't know how long it holds it's power. Then in that case it would take a new uplink of commands for the future, but not doing instantaneous commands. You have to remember too that when commanding that there is not a 100% guarantee that all commands transmitted get received. Sometimes you need re-transmits in a group and thats why commands are sent in loads with checksums.
That's what we do with spacecraft where they safe themselves. They get in a sun pointed direction and await recovery commands from the ground when bad things happen. The stage in theory may be able to do it, but I don't know how long it holds it's power. Then in that case it would take a new uplink of commands for the future, but not doing instantaneous commands. You have to remember too that when commanding that there is not a 100% guarantee that all commands transmitted get received. Sometimes you need re-transmits in a group and thats why commands are sent in loads with checksums.
Quote from: biosehnsucht on 01/23/2017 09:52 pmQuote from: Lar on 01/23/2017 04:27 pmQuote from: Sam Ho on 01/23/2017 03:55 am Furthermore, it can't deploy its solar panels while attached, so it's going to run out of power quickly. Is that always true? I would think that once the fairing is gone, for some birds deployment is at least possible... (might not be a good idea)I imagine that at least for some satellites, their folded panels may have one fold "out" such that it could get a low level of solar power generation (as if it was mostly but not entirely shaded by another vehicle, in this case itself). However, it's possible that nobody designs them such that the panels are "connected" to generate power until after deployment ... but I don't know of any reason why they couldn't be.OR, that could be a good way to throw the 2nd stage off course.
Quote from: CyndyC on 01/23/2017 10:21 pmQuote from: biosehnsucht on 01/23/2017 09:52 pmQuote from: Lar on 01/23/2017 04:27 pmQuote from: Sam Ho on 01/23/2017 03:55 am Furthermore, it can't deploy its solar panels while attached, so it's going to run out of power quickly. Is that always true? I would think that once the fairing is gone, for some birds deployment is at least possible... (might not be a good idea)I imagine that at least for some satellites, their folded panels may have one fold "out" such that it could get a low level of solar power generation (as if it was mostly but not entirely shaded by another vehicle, in this case itself). However, it's possible that nobody designs them such that the panels are "connected" to generate power until after deployment ... but I don't know of any reason why they couldn't be.OR, that could be a good way to throw the 2nd stage off course.I'm not sure why it would? I'm not saying it folds out part of the solar panel array, merely that when folded up for launch, that one segment of the power generating side of the array is exposed (the 'front' of the panel is out, instead of the back)
If it moved the center of mass away from the main axis that might mess up the final burn
Quote from: biosehnsucht on 01/25/2017 07:28 pmQuote from: CyndyC on 01/23/2017 10:21 pmQuote from: biosehnsucht on 01/23/2017 09:52 pmQuote from: Lar on 01/23/2017 04:27 pmQuote from: Sam Ho on 01/23/2017 03:55 am Furthermore, it can't deploy its solar panels while attached, so it's going to run out of power quickly. Is that always true? I would think that once the fairing is gone, for some birds deployment is at least possible... (might not be a good idea)I imagine that at least for some satellites, their folded panels may have one fold "out" such that it could get a low level of solar power generation (as if it was mostly but not entirely shaded by another vehicle, in this case itself). However, it's possible that nobody designs them such that the panels are "connected" to generate power until after deployment ... but I don't know of any reason why they couldn't be.OR, that could be a good way to throw the 2nd stage off course.I'm not sure why it would? I'm not saying it folds out part of the solar panel array, merely that when folded up for launch, that one segment of the power generating side of the array is exposed (the 'front' of the panel is out, instead of the back)I'm pretty sure the Law of Conservation of Momentum guarantees that unfolding a solar panel array can't change the course of the second stage. If it moved the center of mass away from the main axis that might mess up the final burn, though. And I suppose it adds a risk that the unfolded array might not be strong enough to survive the final burn.
Coming back to the subject of this thread, the Iridium NEXT solar panels are folded against the sloped sides of the spacecraft for launch, between the body of the satellite and the dispenser.
Quote from: Greg Hullender on 01/26/2017 02:04 pmIf it moved the center of mass away from the main axis that might mess up the final burnThat is how it would mess it up.