Author Topic: SpaceX Falcon 9 : Iridium NEXT Flight 4 : December 22/23, 2017 : Discussion  (Read 103361 times)

Offline ugordan

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Edit: or maybe they need the fins to make sure they don't hit the fairing recovery boat with flying booster pieces...

That doesn't make much sense. They can literally move the booster reentry point tens if not hundreds of km away from its ballistic impact point just using a "boostback" burn and for that they only need cold gas thrusters.

Offline quagmire

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Perhaps they’re testing a failure mode - such as the loss of one of the fins. In light of the rampant California fires as mentioned above, I would think that proving adequate control authority with such a failure would be a requirement for RTLS.

Wouldn't they just blow it up in such a case?

Not saying they couldn't test how much control authority they would still have if a fin failed to deploy, but I think such a failure for a RTLS would be an automatic cause for either stopping the maneuvers to get it back to land and let it fall into the ocean or activation of the flight termination system. Don't think VAFB or the Cape would want to take the risk of allowing a booster to return with a failed control system. Drone ship obviously different story.

Offline envy887

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Edit: or maybe they need the fins to make sure they don't hit the fairing recovery boat with flying booster pieces...

That doesn't make much sense. They can literally move the booster reentry point tens if not hundreds of km away from its ballistic impact point just using a "boostback" burn and for that they only need cold gas thrusters.

Good point.

Unless they used the recovery margin on ascent, which is unlikely but possible. Though I'm not sure the booster would be controllable if it wasn't able to do a entry burn.

I don't think they have ever had a crew downrange without grid fins on the booster.

Offline ugordan

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Unless they used the recovery margin on ascent, which is unlikely but possible.

I guess that's a possibility. The press kit for this mission has MECO several seconds later than on earlier Iridium flights and it's closer to, say, Koreasat-5A launch which did not employ a boostback burn.

Offline alang

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The most difficult thing they need to test is the behaviour of a booster shaped like a falcon heavy side booster. Difficult to see how they can do that with a booster with the existing interstage given it has to do the job of stage separation. Cue the Rube Goldberg/Heath Robinson solutions involving discarding the interstage...

Offline envy887

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Unless they used the recovery margin on ascent, which is unlikely but possible.

I guess that's a possibility. The press kit for this mission has MECO several seconds later than on earlier Iridium flights and it's closer to, say, Koreasat-5A launch which did not employ a boostback burn.

Matt Desch says they are doing a "water landing". Which sounds to me like landing, entry, and maybe even boostback burns are planned, like they are testing something related to EDL (as with the soft water landings on early CRS launches) and the fins aren't just for contingency.

Offline russianhalo117

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Unless they used the recovery margin on ascent, which is unlikely but possible.

I guess that's a possibility. The press kit for this mission has MECO several seconds later than on earlier Iridium flights and it's closer to, say, Koreasat-5A launch which did not employ a boostback burn.

Matt Desch says they are doing a "water landing". Which sounds to me like landing, entry, and maybe even boostback burns are planned, like they are testing something related to EDL (as with the soft water landings on early CRS launches) and the fins aren't just for contingency.
If you read today's NSF article fully it indicates that.

Offline ugordan

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Unless they used the recovery margin on ascent, which is unlikely but possible.

I guess that's a possibility. The press kit for this mission has MECO several seconds later than on earlier Iridium flights and it's closer to, say, Koreasat-5A launch which did not employ a boostback burn.

Matt Desch says they are doing a "water landing". Which sounds to me like landing, entry, and maybe even boostback burns are planned, like they are testing something related to EDL (as with the soft water landings on early CRS launches) and the fins aren't just for contingency.

I was indicating that since it's possible they'll skip the boostback burn judging by the 1st stage burn length, my earlier statement that they would be able to significantly redirect the stage away from fairing recovery area loses some credence.

However, my favorite theory is still that the fins are there to explore the limits of lifting entry as all other flights had guidance targets so they might not have explored the entire parameter space.

Offline envy887

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Unless they used the recovery margin on ascent, which is unlikely but possible.

I guess that's a possibility. The press kit for this mission has MECO several seconds later than on earlier Iridium flights and it's closer to, say, Koreasat-5A launch which did not employ a boostback burn.

Matt Desch says they are doing a "water landing". Which sounds to me like landing, entry, and maybe even boostback burns are planned, like they are testing something related to EDL (as with the soft water landings on early CRS launches) and the fins aren't just for contingency.
If you read today's NSF article fully it indicates that.

But unlike Desch's tweet, the article doesn't imply it's sourced directly from SpaceX.

Offline russianhalo117

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Unless they used the recovery margin on ascent, which is unlikely but possible.

I guess that's a possibility. The press kit for this mission has MECO several seconds later than on earlier Iridium flights and it's closer to, say, Koreasat-5A launch which did not employ a boostback burn.

Matt Desch says they are doing a "water landing". Which sounds to me like landing, entry, and maybe even boostback burns are planned, like they are testing something related to EDL (as with the soft water landings on early CRS launches) and the fins aren't just for contingency.
If you read today's NSF article fully it indicates that.

But unlike Desch's tweet, the article doesn't imply it's sourced directly from SpaceX.
Article info generally comes out of L2 and from SpaceX sources.

Offline WheelsStop

From the update thread (https://forum.nasaspaceflight.com/index.php?topic=44273.msg1762722#msg1762722) there's something different with airspace restrictions this time around.  There's a flight restriction up as an eastern extension of W-537.  Is this launch taking a more easterly track than the other Iridium launches?

I think it's too close in-shore, but given the other discussion here, I'm tempted to speculate that they're going to drop the first stage in that vicinity and want a little extra space.  Perhaps as a lead up to an RTLS?  Again, total speculation.

Offline Brunberg

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I think the boosters are recovered from the ocean no matter what.

Offline joek

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From the update thread (https://forum.nasaspaceflight.com/index.php?topic=44273.msg1762722#msg1762722) there's something different with airspace restrictions this time around.  There's a flight restriction up as an eastern extension of W-537.  Is this launch taking a more easterly track than the other Iridium launches?

Maybe a bit.  Most recent launch license LLS 17-096B (Rev 2) update (sec. 2 pg. 2):
Quote
Revision 2 - Issued October 6, 2017
1. Paragraph (3)(c) changed from "On a flight azimuth .of 179.2 degrees" to "On a flight azimuth between 175 and 180 degrees".
Or could be the current publicly accessible license is not up to date (would not be unusual).
« Last Edit: 12/22/2017 06:54 PM by joek »

Offline ChrisGebhardt

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Regarding the grid fins left on expendable booster,
100% speculation:

There were no attempts so far of RTLS landings in VAFB. My guess - the reason is the place is much more dangerous with wildfires than Florida.
Therefore it seems reasonable that VAFB put a requirement - like *N successful demonstrations* of pinpoint accuracy in stage return.
I may be wrong, but it seems to me, that a malfunction resulting in just inaccurate landing - this mishap is much more dangerous in VAFB - it can result if forest fire.

If my guess is right, and there is indeed such a requirement - then this expendable flight still gives an opportunity to demonstrate the required accurate landing (at predefined spot in ocean) and add another *one* towards that *N*.

There's a lot of assumption here.

1. Wildfires have nothing to do with Falcon 9 landings. Florida is extremely prone to fires in winter and spring outside the state's rainy season.  There's no correlation as you're implying.
2. If Vandenberg officials were that concerned over the potential of a rocket to start a fire they wouldn't be able to handle, they would:
     a. not have approved SpaceX building the landing pad
     b. not let anyone launch from Vandenberg because of the risk of failure and associated fire risk to a failing rocket (whether launching or landing)
     c. not let SpaceX static fire (which has started at least one fire just this year)
3. Assuming your point, however, how are the 20 successful, pin-point landings to date not enough to prove the system?
4. Vandenberg is not the licensing authority for landings.  They don't get that much of a say over "now you have to do x number of things before we're happy."
5. There is no difference - from the Falcon 9's landing systems - to an RTLS landing at CCAFS v. Vandenberg.
« Last Edit: 12/22/2017 06:55 PM by ChrisGebhardt »

Offline philw1776

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I think the boosters are recovered from the ocean no matter what.

I doubt that as no reports of large ship with crane ship activity near impact points.
No NSF guys reporting ship coming back with large shrouded object, etc.
« Last Edit: 12/22/2017 06:57 PM by philw1776 »
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Offline Herb Schaltegger

I think the boosters are recovered from the ocean no matter what.

I doubt that as no reports of large ship with crane ship activity near impact points.
No NSF guys reporting ship coming back with large shrouded object, etc.
Further, we’ve seen videos of what happens to a first stage once it tumbles over. Not a lot left typically but fragments. ;)
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Offline whatever11235

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Was that boostback burn after stage separation?

Offline HVM

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Online Lar

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no word on fairing but they never say. Much less public info about fairings than about the S1 landings when those were under development...
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Offline ngilmore

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View of launch from Los Angeles.

If I'd known it was going to be this spectacular, I would have had a better camera ready.

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