Author Topic: IFT-2 Pacific Recovery  (Read 8865 times)

Offline Yeknom-Ecaps

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IFT-2 Pacific Recovery
« on: 11/07/2023 02:51 pm »
Is there a document/write-up that describes how the IFT-2 recovery in the Pacific Ocean will be performed (where/when/how)?

Thanks.

Online DanClemmensen

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Re: IFT-2 Pacific Recovery
« Reply #1 on: 11/07/2023 02:59 pm »
Is there a document/write-up that describes how the IFT-2 recovery in the Pacific Ocean will be performed (where/when/how)?

Thanks.
I think the Pacific splashdown is supposed to be identical to the one proposed for IFT-1. It is documented extensively in the WR. If all goes as planned, the SS will deliberately hit the water belly-down with enough force to break the LCH4 downcomer inside the LOX tank mixing the fuel and oxidant and causing an explosion that will sink the SS even if it would otherwise stay afloat. Nothing to recover. SpaceX assets will then do a search for any messy bits that might still be afloat. This picture:
    https://commons.wikimedia.org/wiki/File:Starship_internal_structure.jpg
If from this document:
    https://www.faa.gov/media/27271
« Last Edit: 11/07/2023 03:02 pm by DanClemmensen »

Offline Slothman

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Re: IFT-2 Pacific Recovery
« Reply #2 on: 11/07/2023 03:06 pm »
Also, https://www.spacex.com/launches/mission/?missionId=starship-flight-2 has the flight plan. No "recovery" planned.

Offline Nomadd

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Re: IFT-2 Pacific Recovery
« Reply #3 on: 11/07/2023 03:38 pm »
 Maybe they'll do a simulated landing a few hundred feet up to test everything out, then cut the engines. I can't see them wasting the opportunity to check precision if everything else goes ok.
Those who danced were thought to be quite insane by those who couldn't hear the music.

Offline alugobi

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Re: IFT-2 Pacific Recovery
« Reply #4 on: 11/07/2023 04:10 pm »
My guess:  it will already be in pieces by the time it hits the water.  The tilework doesn't look like it has yet matured.

Offline eriblo

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Re: IFT-2 Pacific Recovery
« Reply #5 on: 11/07/2023 04:24 pm »
My guess:  it will already be in pieces by the time it hits the water.  The tilework doesn't look like it has yet matured.
That is certainly a possible outcome but it is not relevant to any recovery plans - it is generally prudent to have a plan for the case when everything goes according to plan  ;)

Offline StevenOBrien

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Re: IFT-2 Pacific Recovery
« Reply #6 on: 11/07/2023 04:50 pm »
If it's following the same plan as IFT-1, it's expected that Starship will explode on impact with the water and sink if it survives re-entry.

There's a lot of detailed information about this in the Written Re-evaluation for IFT-1: https://www.faa.gov/media/27271

Online DanClemmensen

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Re: IFT-2 Pacific Recovery
« Reply #7 on: 11/07/2023 05:24 pm »
Maybe they'll do a simulated landing a few hundred feet up to test everything out, then cut the engines. I can't see them wasting the opportunity to check precision if everything else goes ok.
The WR specifically states that the plan is to hit the water at terminal velocity for a belly-first SS, specifically to assure that it breaks up. They would need to amend the WR to do what you propose, I think.

Offline KilroySmith

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Re: IFT-2 Pacific Recovery
« Reply #8 on: 11/07/2023 07:12 pm »
The WR specifically states that the plan is to hit the water at terminal velocity for a belly-first SS, specifically to assure that it breaks up. They would need to amend the WR to do what you propose, I think.
Probably a reasonable approach at this stage - it seems like so long ago, but they have done significant experiments landing a SS already....

Online Asteroza

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Re: IFT-2 Pacific Recovery
« Reply #9 on: 11/07/2023 10:03 pm »
Maybe they'll do a simulated landing a few hundred feet up to test everything out, then cut the engines. I can't see them wasting the opportunity to check precision if everything else goes ok.
The WR specifically states that the plan is to hit the water at terminal velocity for a belly-first SS, specifically to assure that it breaks up. They would need to amend the WR to do what you propose, I think.

Shame they don't just do a simulated landing in mid air, then drop, but I guess they can't guarantee a bellyflop impact?

Online DanClemmensen

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Re: IFT-2 Pacific Recovery
« Reply #10 on: 11/07/2023 10:17 pm »
Maybe they'll do a simulated landing a few hundred feet up to test everything out, then cut the engines. I can't see them wasting the opportunity to check precision if everything else goes ok.
The WR specifically states that the plan is to hit the water at terminal velocity for a belly-first SS, specifically to assure that it breaks up. They would need to amend the WR to do what you propose, I think.

Shame they don't just do a simulated landing in mid air, then drop, but I guess they can't guarantee a bellyflop impact?
Please read the WR. It specifies "terminal velocity", which it very carefully defines as the velocity it reaches when falling from the top of the atmosphere, not from some intermediate stopping point. I strongly suspect the bulk of the WR was written by SpaceX and submitted as a draft to the FAA, who then took a look at it and decided it was reasonable. SpaceX could have chosen your alternative, but they did not. "terminal velocity" was specifically chosen to ensure the breakup and explosion of the SS when it hits the water. All of this happened prior to IFT-1, and I think quite a bit before then. There is even a diagram illustrating why the CH4 downcomer will break inside the Oxygen tank. Attempting to change this agreed-upon plan at this late date would be a very bad idea.

Online Echo_Jex

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Re: IFT-2 Pacific Recovery
« Reply #11 on: 11/07/2023 10:25 pm »
Maybe they'll do a simulated landing a few hundred feet up to test everything out, then cut the engines. I can't see them wasting the opportunity to check precision if everything else goes ok.
The WR specifically states that the plan is to hit the water at terminal velocity for a belly-first SS, specifically to assure that it breaks up. They would need to amend the WR to do what you propose, I think.

Speaking of SS re-entry, I know SX website makes it crystal clear their intentions, but the WR also says that the 'first' SS will belly flop at terminal velocity after the cruise period, and that the 2nd and 3rd flight SS are not configured to survive re-entry and are planned to tumble and break apart.
So is S25 going to be treated like the 'first' flight profile since it IS configured to survive re-entry, or like the '2nd' flight profile since it is IFT-2?

As a side thought here very much my own ponder, maybe when the license gets modified to allow for a second launch attempt, it may have other amendments? I doubt it'll be a simple white out the date and flight number, print and sign, but zero real bearing on how modified Modified can get.

Offline lrk

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Re: IFT-2 Pacific Recovery
« Reply #12 on: 11/07/2023 10:57 pm »
S25 is still using hydraulic TVC.  The hydraulic system might not be capable of surviving an hour+ in space, so they can't attempt a landing.

Another, slightly more conspiratorial theory: they are going to attempt a landing, but they expect that it will fail and end up with a terminal velocity impact.  But saying they expect a terminal velocity impact won't trigger an FAA investigation.

Offline eriblo

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Re: IFT-2 Pacific Recovery
« Reply #13 on: 11/08/2023 12:06 am »
Starship does not have to fall from the edge of space to reach terminal velocity, 1-2 km is enough.

The reason not to attempt a simulated landing before resuming the belly flop on the first and presumably the second flight could be that the hardware/software is not ready or that some part of the test profile precludes it. For example, the WR talks about venting all but 14 t of propellant for ballasting reasons. This is still more than needed for landing but it might involve half empty tanks at unsuitable conditions.

Offline alugobi

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Re: IFT-2 Pacific Recovery
« Reply #14 on: 11/08/2023 12:21 am »
Or, they may not have confidence in the installed generation of engines to restart as commanded.

Online DanClemmensen

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Re: IFT-2 Pacific Recovery
« Reply #15 on: 11/08/2023 01:12 am »
Or, they may not have confidence in the installed generation of engines to restart as commanded.
Remember that they proposed this protocol long before IFT-1 (I seem to recall that the protocol was in the PEA, which was out for public review about a year ago.) It does not reflect their current level of confidence. It reflects the confidence they had a year ago.

Offline alugobi

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Re: IFT-2 Pacific Recovery
« Reply #16 on: 11/08/2023 01:16 am »
Or, they may not have confidence in the installed generation of engines to restart as commanded.
Remember that they proposed this protocol long before IFT-1 (I seem to recall that the protocol was in the PEA, which was out for public review about a year ago.) It does not reflect their current level of confidence. It reflects the confidence they had a year ago.
I didn't remember that.  Fair point.

Nevertheless, were they to front this protocol today, I think they'd have the same reservations about the engines currently installed.

Offline Slothman

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Re: IFT-2 Pacific Recovery
« Reply #17 on: 11/08/2023 01:35 am »
Hypothetically, if the engines don't restart for a high altitude simulated landing (high enough to reach terminal velocity again, I'm sure someone can calculate that based on gravity, aur density and surface area), starship just stays in belly flop configuration (or ruds in mid air in the attempt).

Worst case, the engines light, starship goes vertical but then the engines somehow lose the ability to kick it back to horizontal. Would RCS/flaps have enough authority to bring it horizontal, even if it takes longer than desirable for a nominal belly flop?

I say hypothetically because of course they won't change their announced flight profile and add unnecessary uncertainty/ifs/risks.

Online edzieba

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Re: IFT-2 Pacific Recovery
« Reply #18 on: 11/08/2023 11:59 am »
Worst case, the engines light, starship goes vertical but then the engines somehow lose the ability to kick it back to horizontal.
No, worst case is engines ignite, Starship remains horizontal under positive thrust (IIP starts moving and Starship accelerates towards the edge of its cleared airspace), and the FTS system does not fire or is ineffective resulting in Starship heading towards Kauai effectively uncontrolled.
"Vehicle out of control under thrust with FTS ineffective" is sadly a demonstrably possible outcome, so precluding it by not even attempting engine relight is prudent. Once it has been demonstrated that Starship can remain within a designated corridor for entry and descent, and SpaceX can recover telemetry for the vehicle and confirm no avionics issues as a result of entry (thermal damage to engine bay avionics has killed more than one vehicle, so whether by local fires or by radiant heat from entry plasma this is a non-zero possibility), then it is reasonable to start experimenting with the terminal EDL stages after entry.

Offline eriblo

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Re: IFT-2 Pacific Recovery
« Reply #19 on: 11/08/2023 12:55 pm »
Worst case, the engines light, starship goes vertical but then the engines somehow lose the ability to kick it back to horizontal.
No, worst case is engines ignite, Starship remains horizontal under positive thrust (IIP starts moving and Starship accelerates towards the edge of its cleared airspace), and the FTS system does not fire or is ineffective resulting in Starship heading towards Kauai effectively uncontrolled.
"Vehicle out of control under thrust with FTS ineffective" is sadly a demonstrably possible outcome, so precluding it by not even attempting engine relight is prudent. Once it has been demonstrated that Starship can remain within a designated corridor for entry and descent, and SpaceX can recover telemetry for the vehicle and confirm no avionics issues as a result of entry (thermal damage to engine bay avionics has killed more than one vehicle, so whether by local fires or by radiant heat from entry plasma this is a non-zero possibility), then it is reasonable to start experimenting with the terminal EDL stages after entry.
It is easy to make sure that the vehicle does not have enough propellant to get out of the exclusion zone before attempting a (simulated or real) landing burn.

Online edzieba

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Re: IFT-2 Pacific Recovery
« Reply #20 on: 11/08/2023 01:03 pm »
Worst case, the engines light, starship goes vertical but then the engines somehow lose the ability to kick it back to horizontal.
No, worst case is engines ignite, Starship remains horizontal under positive thrust (IIP starts moving and Starship accelerates towards the edge of its cleared airspace), and the FTS system does not fire or is ineffective resulting in Starship heading towards Kauai effectively uncontrolled.
"Vehicle out of control under thrust with FTS ineffective" is sadly a demonstrably possible outcome, so precluding it by not even attempting engine relight is prudent. Once it has been demonstrated that Starship can remain within a designated corridor for entry and descent, and SpaceX can recover telemetry for the vehicle and confirm no avionics issues as a result of entry (thermal damage to engine bay avionics has killed more than one vehicle, so whether by local fires or by radiant heat from entry plasma this is a non-zero possibility), then it is reasonable to start experimenting with the terminal EDL stages after entry.
It is easy to make sure that the vehicle does not have enough propellant to get out of the exclusion zone before attempting a (simulated or real) landing burn.
Only by either shaving your propellant margins to near zero, or greatly expanding the exclusion zone (and thus moving its target centre out of the range of the tracking assets you are trying to drop it next to). Remember that prior to entry, one of the passive safety measures is to inject into the desired suborbital trajectory and then safe the vehicle, with no deorbit burn. That means if you aim for an absolute-minimum prop load for the flip & burn, you must accomplish that through propellant management during ascent, whilst still hitting the desired suborbital trajectory (not running short or running long). If you instead remove the propellant mass at entry constraint, you can more easily target the desired suborbital trajectory with generous propellant margins for any engine-outs during ascent.

Offline eriblo

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Re: IFT-2 Pacific Recovery
« Reply #21 on: 11/08/2023 01:23 pm »
Worst case, the engines light, starship goes vertical but then the engines somehow lose the ability to kick it back to horizontal.
No, worst case is engines ignite, Starship remains horizontal under positive thrust (IIP starts moving and Starship accelerates towards the edge of its cleared airspace), and the FTS system does not fire or is ineffective resulting in Starship heading towards Kauai effectively uncontrolled.
"Vehicle out of control under thrust with FTS ineffective" is sadly a demonstrably possible outcome, so precluding it by not even attempting engine relight is prudent. Once it has been demonstrated that Starship can remain within a designated corridor for entry and descent, and SpaceX can recover telemetry for the vehicle and confirm no avionics issues as a result of entry (thermal damage to engine bay avionics has killed more than one vehicle, so whether by local fires or by radiant heat from entry plasma this is a non-zero possibility), then it is reasonable to start experimenting with the terminal EDL stages after entry.
It is easy to make sure that the vehicle does not have enough propellant to get out of the exclusion zone before attempting a (simulated or real) landing burn.
Only by either shaving your propellant margins to near zero, or greatly expanding the exclusion zone (and thus moving its target centre out of the range of the tracking assets you are trying to drop it next to). Remember that prior to entry, one of the passive safety measures is to inject into the desired suborbital trajectory and then safe the vehicle, with no deorbit burn. That means if you aim for an absolute-minimum prop load for the flip & burn, you must accomplish that through propellant management during ascent, whilst still hitting the desired suborbital trajectory (not running short or running long). If you instead remove the propellant mass at entry constraint, you can more easily target the desired suborbital trajectory with generous propellant margins for any engine-outs during ascent.
I am not sure I get what you are saying. The dv to get out of the exclusion zone is higher than that required for landing unless you start the simulated landing burn much higher or closer to the edge than what you would plan for. If the ascent is nominal there sould be plenty of excess propellant (no payload) but we already know they will be venting it during the coast phase...

Offline Slothman

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Re: IFT-2 Pacific Recovery
« Reply #22 on: 11/08/2023 07:11 pm »
Worst case, the engines light, starship goes vertical but then the engines somehow lose the ability to kick it back to horizontal.
No, worst case is engines ignite, Starship remains horizontal under positive thrust (IIP starts moving and Starship accelerates towards the edge of its cleared airspace), and the FTS system does not fire or is ineffective resulting in Starship heading towards Kauai effectively uncontrolled.
"Vehicle out of control under thrust with FTS ineffective" is sadly a demonstrably possible outcome, so precluding it by not even attempting engine relight is prudent. Once it has been demonstrated that Starship can remain within a designated corridor for entry and descent, and SpaceX can recover telemetry for the vehicle and confirm no avionics issues as a result of entry (thermal damage to engine bay avionics has killed more than one vehicle, so whether by local fires or by radiant heat from entry plasma this is a non-zero possibility), then it is reasonable to start experimenting with the terminal EDL stages after entry.

So.. rotate the potential horizontal thrust vector... Away from hawaii? There really is not much to hit anywhere close to the designated splashdown zone, especially north of it as far as I know.

Online edzieba

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Re: IFT-2 Pacific Recovery
« Reply #23 on: 11/08/2023 07:45 pm »
Worst case, the engines light, starship goes vertical but then the engines somehow lose the ability to kick it back to horizontal.
No, worst case is engines ignite, Starship remains horizontal under positive thrust (IIP starts moving and Starship accelerates towards the edge of its cleared airspace), and the FTS system does not fire or is ineffective resulting in Starship heading towards Kauai effectively uncontrolled.
"Vehicle out of control under thrust with FTS ineffective" is sadly a demonstrably possible outcome, so precluding it by not even attempting engine relight is prudent. Once it has been demonstrated that Starship can remain within a designated corridor for entry and descent, and SpaceX can recover telemetry for the vehicle and confirm no avionics issues as a result of entry (thermal damage to engine bay avionics has killed more than one vehicle, so whether by local fires or by radiant heat from entry plasma this is a non-zero possibility), then it is reasonable to start experimenting with the terminal EDL stages after entry.

So.. rotate the potential horizontal thrust vector... Away from hawaii? There really is not much to hit anywhere close to the designated splashdown zone, especially north of it as far as I know.
If your proposed solution for a "vehicle is not under control" scenario requires the vehicle to be under control, that doesn't really work.

Offline aperh1988

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Re: IFT-2 Pacific Recovery
« Reply #24 on: 11/08/2023 08:03 pm »
Worst case, the engines light, starship goes vertical but then the engines somehow lose the ability to kick it back to horizontal.
No, worst case is engines ignite, Starship remains horizontal under positive thrust (IIP starts moving and Starship accelerates towards the edge of its cleared airspace), and the FTS system does not fire or is ineffective resulting in Starship heading towards Kauai effectively uncontrolled.
"Vehicle out of control under thrust with FTS ineffective" is sadly a demonstrably possible outcome, so precluding it by not even attempting engine relight is prudent. Once it has been demonstrated that Starship can remain within a designated corridor for entry and descent, and SpaceX can recover telemetry for the vehicle and confirm no avionics issues as a result of entry (thermal damage to engine bay avionics has killed more than one vehicle, so whether by local fires or by radiant heat from entry plasma this is a non-zero possibility), then it is reasonable to start experimenting with the terminal EDL stages after entry.

So.. rotate the potential horizontal thrust vector... Away from hawaii? There really is not much to hit anywhere close to the designated splashdown zone, especially north of it as far as I know.
If your proposed solution for a "vehicle is not under control" scenario requires the vehicle to be under control, that doesn't really work.

I think what Slothman is saying is while the vehicle is still under control (because attempting to go vertical requires vehicle to be under control) the rotation to vertical should be attempted towards a vector pointing away from the island such that if a control failure develops the vehicle is already pointing away.

That being said, it wouldn’t mitigate the risk of the vehicle pointing towards the island due to some aerodynamic buffeting or whatever once control is lost. Or other scenarios such as control is lost with thrust positive before attempt to go vertical and vehicle ends up pointing towards land because *waves hands* reasons.
« Last Edit: 11/08/2023 08:13 pm by aperh1988 »

Offline tgr9898

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Re: IFT-2 Pacific Recovery
« Reply #25 on: 11/09/2023 01:36 am »
Worst case, the engines light, starship goes vertical but then the engines somehow lose the ability to kick it back to horizontal.
No, worst case is engines ignite, Starship remains horizontal under positive thrust (IIP starts moving and Starship accelerates towards the edge of its cleared airspace), and the FTS system does not fire or is ineffective resulting in Starship heading towards Kauai effectively uncontrolled.
"Vehicle out of control under thrust with FTS ineffective" is sadly a demonstrably possible outcome, so precluding it by not even attempting engine relight is prudent. Once it has been demonstrated that Starship can remain within a designated corridor for entry and descent, and SpaceX can recover telemetry for the vehicle and confirm no avionics issues as a result of entry (thermal damage to engine bay avionics has killed more than one vehicle, so whether by local fires or by radiant heat from entry plasma this is a non-zero possibility), then it is reasonable to start experimenting with the terminal EDL stages after entry.

So.. rotate the potential horizontal thrust vector... Away from hawaii? There really is not much to hit anywhere close to the designated splashdown zone, especially north of it as far as I know.
If your proposed solution for a "vehicle is not under control" scenario requires the vehicle to be under control, that doesn't really work.

I think what Slothman is saying is while the vehicle is still under control (because attempting to go vertical requires vehicle to be under control) the rotation to vertical should be attempted towards a vector pointing away from the island such that if a control failure develops the vehicle is already pointing away.

That being said, it wouldn’t mitigate the risk of the vehicle pointing towards the island due to some aerodynamic buffeting or whatever once control is lost. Or other scenarios such as control is lost with thrust positive before attempt to go vertical and vehicle ends up pointing towards land because *waves hands* reasons.

In a hardware-rich environment like the Starship development environment, I think they're more inclined to focus on the hot staging test, separation, and the Starship startup.  If they can achieve all that, the best bet is to leave Sir Issac Newton in the driver's seat for the rest of the flight - he's an excellent driver, BTW - and prep for the next test campaign since newer hardware is sitting at Boca Chica

Offline CorvusCorax

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Re: IFT-2 Pacific Recovery
« Reply #26 on: 11/10/2023 07:45 am »

In a hardware-rich environment like the Starship development environment, I think they're more inclined to focus on the hot staging test, separation, and the Starship startup.  If they can achieve all that, the best bet is to leave Sir Issac Newton in the driver's seat for the rest of the flight - he's an excellent driver, BTW - and prep for the next test campaign since newer hardware is sitting at Boca Chica

In theory I agree. I practice, Starship hardware rich development is currently hampered by slow regulatory progress, which forces SpaceX to advance in much slower, larger steps instead of many small ones when it comes to flight tests. The result of this is only every nth Starship or booster actually gets launched, while the in-betweens get built, used for ground tests, then scrapped.

Offline Barley

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Re: IFT-2 Pacific Recovery
« Reply #27 on: 11/10/2023 03:43 pm »
So.. rotate the potential horizontal thrust vector... Away from hawaii? There really is not much to hit anywhere close to the designated splashdown zone, especially north of it as far as I know.
If your proposed solution for a "vehicle is not under control" scenario requires the vehicle to be under control, that doesn't really work.
You can't design the hardware so it is intrinsically incapable of harm in all phases of flight.  The stack on the pad could hit Hawaii -- as an orbital rocket it could hit anywhere on the planet.  This is of course why there is an independent flight termination system.  This could be extended to any phase of flight if the game is worth the candle.

"Under control" is not a binary condition.  It is possible to not have enough control to simulate a landing but have enough control to miss Hawaii.  It doesn't take much control to miss Hawaii.  You can design different parts of the system with different complexity and robustness. 

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