Author Topic: SpaceX Falcon 9 - Iridium NEXT Flight 1 DISCUSSION (Jan. 14 2017)  (Read 287122 times)

Offline biosehnsucht

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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.

Offline CyndyC

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.
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Online matthewkantar

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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

Offline douglas100

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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

WHAP already answered that.
http://forum.nasaspaceflight.com/index.php?topic=35112.msg1633847#msg1633847
Douglas Clark

Offline envy887

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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

Probably just to mess with the type of people who would worry about whether it's commanded or automated.

Or maybe she isn't used to talking to 100,000 people on a live webcast and didn't get her phrasing quite right.

Or perhaps she not an expert in that area and went with an apparently common misconception. Systems engineers work on all kinds of things entirely unrelated to upper stagecommunications or deployment.

Picking apart an off the cuff statement word by word isn't a great idea.

Online matthewkantar

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The quote is:
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.

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

Offline llanitedave

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The quote is:
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.

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

You can "go with" whomever you like, but that will have no effect on what SpaceX does.
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Offline jjyach

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If this helps at all.

Quote
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.

http://investor.iridium.com/releasedetail.cfm?releaseid=857729

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.

Offline Lar

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That settles it I think... the argument is stale and boring so...
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Offline manoweb

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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.

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

Offline meekGee

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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.

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

When it comes to the deployment of these 10 satellites, which were deployed on time, I think there's exactly zero reason for it to be commanded from the ground.  That's just asking for trouble.

In general, short-lived launch sequence don't leave enough time to "think about it and decide what to do".

But - that's different than saying that the second stage can't and shouldn't be able to listen to the ground.

Is SpaceX thinking about direct-GEO, for example? If so, then there are hours to take corrective action in case of an anomaly.

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.

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Offline jjyach

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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.

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.

Offline meekGee

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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.

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.
Yes - I was talking about uploading a new sequence, not about "flying it with a joystick".
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Offline Jim

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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.

Launch vehicles are not spacecraft.  Some spacecraft don't even require computers to control them (see lunar Prospector).

There is no safe mode for launch vehicles.  They try complete the existing program

As stated before the stages timeline is in minutes.  It doesn't have a receiver for commands from orbital altitudes. The software is not set up for receiving commands.
« Last Edit: 01/25/2017 07:37 PM by Jim »

Offline biosehnsucht

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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)

Offline Greg Hullender

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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.

Offline Jim

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If it moved the center of mass away from the main axis that might mess up the final burn

That is how it would mess it up.

Offline Sam Ho

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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.

Yes, moving the center of mass would do it, and even if you don't move the center of mass, you are changing the moment of inertia, which has a good chance of destabilizing the control loop.  In any case, aside from payloads where the upper stage (Agena, HAPS) was designed to be part of the satellite, there isn't any reason to remain attached to the upper stage.  The upper stage is programmed for the target orbit.  If it didn't make it there, it's out of propellant or has had some other failure (propulsion, guidance) that prevented getting to the target orbit.  Either way, it's pretty much dead weight.

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.

Offline JBF

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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.

The sloped sides are correct, but that puts them not between the satellites and the dispenser but between the satellites
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Offline Jcc

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If it moved the center of mass away from the main axis that might mess up the final burn

That is how it would mess it up.

If S2 needs a power source for longer endurance, why not attach solar panels to the surface if the stage, like on the trunk of Dragon2?

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