Author Topic: SpaceX Falcon 9 - Iridium NEXT Flight 1 DISCUSSION (Jan. 14 2017)  (Read 286618 times)

Offline matthewkantar

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Wouldn't you want ground confirmation of deployment so as to prevent accidentally deorbiting undeployed but otherwise potentially recoverable sats?

It is simple for the stage to know if the sats have left or not, Would guess when the last one away, the stage deorbits into the Indian ocean at its earliest convenience.

Matthew

Offline mme

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Moved here as it's probably the "more correct" thread...

The boostback burn on this mission just decelerates the stage before reentry.  They still call it "boostback." It's on the timeline at the bottom of the technical webcast and you can see it at about T+4:23 (24:02 into the webcast).
More than decelerating the stage before reentry, it reduced the distance downrange for the landing.  Without it, the rocket would have landed much further out.  It was a partial boostback.  A full boostback would have taken it all the way back to Vandenberg AFB, but they didn't grant permission for that to happen, and they may not have had enough fuel budget for that on this flight anyway.

...
Hmm.. If you're not trying to shorten the downrange landing point, then the way to reduce the entry speed (right after stage separation) is to actually burn "engines up"....  Did they do that?

Ah, ok - a partial boostback makes more sense. 
I choose my words poorly and now that I think about it made some assumptions.  The burn starts at about T+4:21 and appears to last about 40 seconds.  The engines seem to be pointing slightly above the horizon but given the wide angle lens maybe I'm wrong.  I said decelerate because I assumed that it did not entirely reverse the horizontal vector.

I totally should have said "reducing downrange landing distance."
« Last Edit: 01/17/2017 11:07 PM by mme »
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Offline Jim

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I wonder if the loss of tracking during the satellite deployment meant they lost their window for for the deorbit burn. Ie, the d/o burn was to happen x minutes after the last separation, but they didn't regain tracking until x+n minutes when they could confirm deployment, and a d/o burn would have them coming down outside the planned hazard area. So, at that point all they can do is passivate the stage and wait 20 years.

I'm pretty sure the stage computer control the burns. There isn't a need to wait for commands from the ground, so loss of signal wouldn't matter.
Wouldn't you want ground confirmation of deployment so as to prevent accidentally deorbiting undeployed but otherwise potentially recoverable sats?

No, launch vehicles are autonomous and don't receive any ground commands.

The sats would not be recoverable anyways

Offline jcm

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The Jason-3 mission is an example where stage 2 was deorbited on a 3rd burn. Also F9-021/Orbcomm

Good find on Jason-3 -- that one looks like it would have to have 3 burns. F9-021/Orbcomm was launched into its orbit directly on the first burn of the second stage. There should have been no reason to fire that second stage up another two times. Do you have some data on the orbcomm launch that would indicate two more S2 burns?


My bad, there were only two burns for Orbcomm - the second one was a demo burn for GTO missions but it also accomplished the deorbit. Jason 3 does seem to have had 3 burns - MECO-1 at 1851 UTC, MECO-2 at 1937 UTC in
the circular orbit, and MECO-3 at about 2024 UTC for deorbit
-----------------------------

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Online Lars-J

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and the 2nd stage is only good for one re-start,

That's a big assumption, and doesn't fit with what Gwynne said pre-launch (three S2 burns).


A single re-start is what has been demonstrated, AFAIK.

I suppose there was never an announcement by SpaceX of the de-orbit of the 2nd stage.

That appears to be the modus operandi of many posters here. If SpaceX didn't announce it, or - better yet - didn;t show live video of it, obviously it cannot have happened.  ::) ::) C'mon.

Online meekGee

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and the 2nd stage is only good for one re-start,

That's a big assumption, and doesn't fit with what Gwynne said pre-launch (three S2 burns).


A single re-start is what has been demonstrated, AFAIK.

I suppose there was never an announcement by SpaceX of the de-orbit of the 2nd stage.

That appears to be the modus operandi of many posters here. If SpaceX didn't announce it, or - better yet - didn;t show live video of it, obviously it cannot have happened.  ::) ::) C'mon.
Yeah, but why would it have been left in orbit?  Previous stages have been deorbited.  I'm waiting for more information...
ABCD - Always Be Counting Down

Offline dglow

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Is there a chance that the reversion to likely "warmer" LOX in the wake of the AMOS 6 incident took away the margin needed for de-orbit?

Wait, is that right? I understood the revision to be the addition of a fourth COPV, allowing for warmer helium.

Offline deruch

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Is there a chance that the reversion to likely "warmer" LOX in the wake of the AMOS 6 incident took away the margin needed for de-orbit?

Wait, is that right? I understood the revision to be the addition of a fourth COPV, allowing for warmer helium.
The LOX was also loaded earlier and slower, ergo it had more time to warm up in the tanks than it would have in the fast loading sequence.  i.e. At launch the LOX was warmer than before.  I haven't seen anything about whether or not they have also somewhat raised the loading temp of the subcooled LOX so that they weren't as close to the freezing point.
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Offline Danderman

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That appears to be the modus operandi of many posters here. If SpaceX didn't announce it, or - better yet - didn;t show live video of it, obviously it cannot have happened.  ::) ::) C'mon.

I am reacting here to the revelation that there is an extra object in orbit along with the 10 payloads. Perhaps it is not the 2nd stage.

Offline su27k

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...or simply deorbit burn was done and that stage will be up for days/weeks, not years...

Unlikely given this: http://forum.nasaspaceflight.com/index.php?topic=41751.msg1628106#msg1628106, seems to me the plan is to bring it down in a few hours...

On the other hand, if there is a restart anomaly I assume we'd have heard it by now, it will have consequences to follow on schedule and customers, kinda hard to hide it after they informed EchoStar/NASA/SES/Spaceflight Industries...

Offline Danderman

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Unlikely given this: http://forum.nasaspaceflight.com/index.php?topic=41751.msg1628106#msg1628106, seems to me the plan is to bring it down in a few hours...


You are suggesting that the plan is to bring down the stage a few days after launch?

Online Johnnyhinbos

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Is there a chance that the reversion to likely "warmer" LOX in the wake of the AMOS 6 incident took away the margin needed for de-orbit?

Wait, is that right? I understood the revision to be the addition of a fourth COPV, allowing for warmer helium.
The LOX was also loaded earlier and slower, ergo it had more time to warm up in the tanks than it would have in the fast loading sequence.  i.e. At launch the LOX was warmer than before.  I haven't seen anything about whether or not they have also somewhat raised the loading temp of the subcooled LOX so that they weren't as close to the freezing point.
This topic has been hashed before. I believe the following to be true...

- addition of fourth COPV to 2nd stage as a stop gap until reengineering of design.
- return to the original (slower) loading protocols for subcooled props. Still subcooled, just not the rapid fill they were toying with.
- still has same amount of prop at launch time, no performance hit there (with the small exception of the weight and displaced LOX caused by 4th COPV.
- same performance because LOX lost from warming is added during this slower process.)
- real hit is not to performance but from loss of ability to recycle count and try again (if the launch window allows). This is because too much subcooled LOX is required for topping off and so not enough in the GSE for a second try.
« Last Edit: 01/18/2017 10:41 AM by Johnnyhinbos »
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Offline ugordan

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This topic has been hashed before. I believe the following to be true...

- return to the original (slower) loading protocols for subcooled props. Still subcooled, just not the rapid fill they were toying with.

There was never an "original" loading protocol for subcooled prop to return to AFAIK, the first subcooled flight (OG-2) used the rapid load and all the previous v1.1 ones were normal LOX load. They weren't "toying" with it, rapid load was their operational procedure for v1.2 boosters.

- still has same amount of prop at launch time

No, it doesn't because warmer LOX at liftoff means less dense LOX means less total mass in kg of propellant loaded onto the vehicle means less total impulse by the vehicle.

- same performance because LOX lost from warming is added during this slower process.)

It's not a about LOX volume but LOX mass.

- real hit is not to performance but from loss of ability to recycle count and try again (if the launch window allows). This is because too much subcooled LOX is required for topping off and so not enough in the GSE for a second try.

The hit to performance is real because of warmer LOX, heavier 2nd stage due to an extra COPV and the entailing LOX volume displacement it also carries.

If neither of this carried a performance hit, SpaceX obviously wouldn't have pushed the margins on this so much. In fact, sacrificing their recycle options in the process of introducing subcooled prop. They literally had just minutes to recycle even with rapid load, the less subcooled prop doesn't make much difference to that.
« Last Edit: 01/18/2017 10:59 AM by ugordan »

Offline deruch

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Is there a chance that the reversion to likely "warmer" LOX in the wake of the AMOS 6 incident took away the margin needed for de-orbit?

Wait, is that right? I understood the revision to be the addition of a fourth COPV, allowing for warmer helium.
The LOX was also loaded earlier and slower, ergo it had more time to warm up in the tanks than it would have in the fast loading sequence.  i.e. At launch the LOX was warmer than before.  I haven't seen anything about whether or not they have also somewhat raised the loading temp of the subcooled LOX so that they weren't as close to the freezing point.
This topic has been hashed before. I believe the following to be true...

- still has same amount of prop at launch time, no performance hit there (with the small exception of the weight and displaced LOX caused by 4th COPV.
Warmer LOX is less dense and therefore there should be some volume lost due to underfill to allow expansion as it warms.  Of course, this depends on whether and how large a gap they are allowing above the LOX, etc. 

Somewhat OT for this thread.

edit: ninja'd by ugordan
« Last Edit: 01/18/2017 10:58 AM by deruch »
Shouldn't reality posts be in "Advanced concepts"?  --Nomadd

Online Johnnyhinbos

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Expansion is vented. Loss volume replaced by GSE supplied LOX. Density remains at subcooled LOX. SpaceX overtly stated they are returning to original slower subcooled prop loading.

Main hit is quantity of subcooled LOX in GSE.

Honestly, these things have been discussed ad nauseam.
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Online FutureSpaceTourist

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Interesting background interview with Iridium CEO on working with SpaceX:

Quote
http://video.cnbc.com/gallery/?video=3000584939 Can't believe I still need to defend @SpaceX.  When engines light, they are 96.6%. Expect that to climb further.

https://twitter.com/iridiumboss/status/821704969409720320

Offline mn

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So we know the 2nd launch needs to be a minimum of 3 months after the first for insurance reasons. To verify that there are no issues with the SC before you launch more. At the same time waiting is lost revenue for Iridium.

Is it possible for SpaceX/Iridium to decide to assume the risk on their own (or spacex taking on the risk to make up for delays) and launch earlier?

Do we have any idea what is the revenue value of launching the next batch in February instead of April? (especially considering that it's not a new service just an upgrade to existing service).

The range doesn't seem that crowded, I would imagine they could launch if they wanted to.

Not suggesting this is going to happen, just throwing it out there out of curiosity, if anyone knows what the numbers are and what would be the hypothetical cost/benefit.

Offline MKremer

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So we know the 2nd launch needs to be a minimum of 3 months after the first for insurance reasons. To verify that there are no issues with the SC before you launch more. At the same time waiting is lost revenue for Iridium.
Iridium will have known that for years and planned for it, at least to the extent that even a several month delay between launches shouldn't cause any sort of financial crisis. The new sats will complement the old in the existing network until the new one is complete.

Offline Moonwatcher

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Holy moly!!

https://www.flickr.com/photos/spacex

Photos now they've got the reel of film back from the ASDS:

Hey Chris, do you reely think they're still using film...?  ::)

Offline guckyfan

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Hey Chris, do you reely think they're still using film...?  ::)

No, he just wants to confuse those under 30 years of age.  ;D

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