Author Topic: BFS Design Requirements  (Read 20181 times)

Offline speedevil

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Re: BFS Design Requirements
« Reply #40 on: 02/20/2018 02:10 PM »
They did a FOD ingestion test during Merlin dev that consisted of dropping a #10 nut into the turbopump inlet, supposedly it ate the nut and kept running fine. Haven't hear of a similar test during Raptor dev, but it would probably be good to have some FOD tolerance.

In order to be properly comparable to airliner engines, it should be able to ingest a canada goose.

Offline acsawdey

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Re: BFS Design Requirements
« Reply #41 on: 02/20/2018 03:31 PM »
But they have 38 engines per BFR/BFS, all of which will be tested. During development, testing will probably include individual engine FOD and RUD containment tests as well. I think it will be done similar to turbine engine development.

John

Do you expect that they will do tests analogous to the blade-out test that is done on commercial turbofans, i.e. intentionally cause a turbopump failure to test the engine controller shutdown response and the containment system? I seem to recall hearing that spacex has already done a "nut ingestion" test.

They did a FOD ingestion test during Merlin dev that consisted of dropping a #10 nut into the turbopump inlet, supposedly it ate the nut and kept running fine. Haven't hear of a similar test during Raptor dev, but it would probably be good to have some FOD tolerance.

Yes, the point would be to make sure that the combination of the control system and the containment system can handle events like the loss of a pump vane or a chunk of the turbine disk and get things shut down without damaging adjacent components.

If there are Canada Geese in the LOX tank I think SpaceX has bigger quality control issues. That said, maximum reported flight altitude for a Canada Goose is 9 km, at which point either Falcon or BFR would be moving at a good clip -- better make sure fairings and windows are bird-strike proof.

Offline IRobot

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Re: BFS Design Requirements
« Reply #42 on: 02/20/2018 03:33 PM »
They did a FOD ingestion test during Merlin dev that consisted of dropping a #10 nut into the turbopump inlet, supposedly it ate the nut and kept running fine. Haven't hear of a similar test during Raptor dev, but it would probably be good to have some FOD tolerance.

In order to be properly comparable to airliner engines, it should be able to ingest a canada goose.
If you can think of a way that a canada goose can avoid hitting the top of the rocket, somehow do a 180 turn and enter the turbopump at high speeds... they test for the faults they can think of. There is no air intake in front, so the airline test makes no sense.

Offline speedevil

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Re: BFS Design Requirements
« Reply #43 on: 02/20/2018 03:38 PM »
In order to be properly comparable to airliner engines, it should be able to ingest a canada goose.
If you can think of a way that a canada goose can avoid hitting the top of the rocket, somehow do a 180 turn and enter the turbopump at high speeds... they test for the faults they can think of. There is no air intake in front, so the airline test makes no sense.

It seems I need to add more smilies to my posts.
It was an attempted joke at inappropriate safety standards.
Though airframe birdstrikes are a moderate issue.

Online niwax

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Re: BFS Design Requirements
« Reply #44 on: 02/20/2018 08:32 PM »
They did a FOD ingestion test during Merlin dev that consisted of dropping a #10 nut into the turbopump inlet, supposedly it ate the nut and kept running fine. Haven't hear of a similar test during Raptor dev, but it would probably be good to have some FOD tolerance.

In order to be properly comparable to airliner engines, it should be able to ingest a canada goose.
If you can think of a way that a canada goose can avoid hitting the top of the rocket, somehow do a 180 turn and enter the turbopump at high speeds... they test for the faults they can think of. There is no air intake in front, so the airline test makes no sense.

Maybe if it nests inside the tank
Which booster has the most soot? SpaceX booster launch history!

Offline biosehnsucht

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Re: BFS Design Requirements
« Reply #45 on: 02/20/2018 11:58 PM »
Perhaps try ingesting a COPV? Surely an albatross is as good as a goose?

Offline Lar

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Re: BFS Design Requirements
« Reply #46 on: 02/21/2018 12:46 AM »
Can we do a 180 on the thread humor level before the great post ingester in the sky throws an impeller from too much deletion?

Oh never mind. Carry on.
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Offline Patchouli

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Re: BFS Design Requirements
« Reply #47 on: 02/21/2018 03:33 AM »
I think they should purposefully test a Raptor for hard start next to another running engine to see if they can prevent a domino effect failure like what happened on the N1.
« Last Edit: 02/21/2018 03:35 AM by Patchouli »

Offline Lars-J

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Re: BFS Design Requirements
« Reply #48 on: 02/21/2018 03:58 AM »
I think they should purposefully test a Raptor for hard start next to another running engine to see if they can prevent a domino effect failure like what happened on the N1.

With FH flying, can't the N1 ghost be laid to rest? C'mon.

Offline Patchouli

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Re: BFS Design Requirements
« Reply #49 on: 02/21/2018 04:08 AM »
FH is a different beast it has three cores with much simpler plumbing and GG cycle engines .
The FAA would never allow BFS for P2P unless they can demonstrate it can land after a catastrophic engine failure plus there is no launch escape system which means fault tolerance is your only safety net.
« Last Edit: 02/21/2018 04:51 AM by Patchouli »

Online docmordrid

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Re: BFS Design Requirements
« Reply #50 on: 02/21/2018 11:07 PM »
There's no LAS on an airliner either, and AIUI Raptor engines have integrated frag shields which mimic the effect of Octaweb cells - so it should  have engine-out.
DM

Offline tchernik

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Re: BFS Design Requirements
« Reply #51 on: 03/05/2018 09:12 PM »
I have a question that may fit within this thread: what are the design requirements for automated cargo delivery to the Moon?, both with BFS return and expendable missions.

I understand an orbit-refueled BFS is designed to be capable of doing a landing and return mission to the Moon without human intervention, given it can do landing and return with its own reserves of fuel. The cargo is less, but it can do a full Apollo-like mission profile.

The same mission profile on Mars would probably require people in situ, to ensure the ISRU fuel production and transfer works OK.

If BFS can deliver cargo to the lunar surface on automated mode, how such delivery of cargo to the surface would be performed?

BFS is a very tall vehicle, with the Raptors and the fuel tanks between the payload and the lunar surface. Elon Musk presentations and some media show BFS lowering stuff with cranes on the Moon, but they don't seem very automated.

If they actually aren't, that requires people in place to do the placement of the cargo. Is that the way this is supposed to happen?

Or if they are automatic, is anyone developing such cranes?

Offline speedevil

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Re: BFS Design Requirements
« Reply #52 on: 03/05/2018 09:21 PM »
Or if they are automatic, is anyone developing such cranes?

For the case of the moon, common industrial cranes are typically slow enough that a couple of seconds teleoperation delay is quite managable by a skilled operator.

Especially as there is no pressing need for speed, and having the crane go at a maximum speed that is safe enough that the several people watching it do its job can stop it in an emergency is a complete solution to the problem.

Mars teleoperation is slow enough that you actually need to solve this problem in an automated manner.
The very most basic 'put that load over there' operations are quite simple to automate, especially at slow speed, more will require some thought.

Offline envy887

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Re: BFS Design Requirements
« Reply #53 on: 03/11/2018 01:38 AM »
I think they should purposefully test a Raptor for hard start next to another running engine to see if they can prevent a domino effect failure like what happened on the N1.

If they want to fly passengers P2P they will likely have to show that the engine casing contains a RUD, just like airliner engines are tested for turbine/compressor blade containment.

Online docmordrid

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Re: BFS Design Requirements
« Reply #54 on: 03/11/2018 02:06 AM »
I think they should purposefully test a Raptor for hard start next to another running engine to see if they can prevent a domino effect failure like what happened on the N1.

If they want to fly passengers P2P they will likely have to show that the engine casing contains a RUD, just like airliner engines are tested for turbine/compressor blade containment.

AIUI Raptor has a frag containment shield, but instead of being an external Octaweb cell it's integral.
« Last Edit: 03/11/2018 02:10 AM by docmordrid »
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Offline alang

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Re: BFS Design Requirements
« Reply #55 on: 03/11/2018 07:47 AM »
With respect to unimproved terrain:
As I recall the Harrier was quoted to be able to operate from forest clearings which suggests some terrain improvement but how much?
I suspect that there's been a lot of military engineering research in this area for lightweight surface improvement even if it's beyond my search skills.
I can see that 'refractory glass cloth' is used in welding applications but only up to 1000 degrees C. Also, the mechanical effect of the blast force would need to be managed and it would  need to be anchored. It wouldn't have to survive very long though.
I mention glass because an  in situ resource is likely to be silica and such a material could have other uses if it could be manufactured locally.

Offline Archibald

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Re: BFS Design Requirements
« Reply #56 on: 03/11/2018 07:57 AM »
I think they should purposefully test a Raptor for hard start next to another running engine to see if they can prevent a domino effect failure like what happened on the N1.

With FH flying, can't the N1 ghost be laid to rest? C'mon.

A reasonable case could be make that Elon Musk is a little more mentally balanced and under far less pressure than the unfortunate Vasily Mishin... https://en.wikipedia.org/wiki/Vasily_Mishin
« Last Edit: 03/11/2018 02:07 PM by Archibald »
...you have been found guilty by the elders of the forum of a (imaginary) vendetta against Saint Elon - BLAAASPHEMER !

Offline speedevil

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Re: BFS Design Requirements
« Reply #57 on: 03/11/2018 07:54 PM »
I can see that 'refractory glass cloth' is used in welding applications but only up to 1000 degrees C. Also, the mechanical effect of the blast force would need to be managed and it would  need to be anchored.

A related topic might be how rich can you operate a Raptor before it goes out.

Might jet impingement at 2km/s not 4km/s be easier on the surface?

If the vacuum raptors could be operated at 30% throttle very off-mixture, that may create a very different impingement pattern on the surface, at a much lower peak pressure than one sea-level raptor in the middle. (or the cluster of three)

Offline envy887

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Re: BFS Design Requirements
« Reply #58 on: 03/11/2018 11:37 PM »
I can see that 'refractory glass cloth' is used in welding applications but only up to 1000 degrees C. Also, the mechanical effect of the blast force would need to be managed and it would  need to be anchored.

A related topic might be how rich can you operate a Raptor before it goes out.

Might jet impingement at 2km/s not 4km/s be easier on the surface?

If the vacuum raptors could be operated at 30% throttle very off-mixture, that may create a very different impingement pattern on the surface, at a much lower peak pressure than one sea-level raptor in the middle. (or the cluster of three)

I would be rather surprised if the normal exhaust of the landing engines was anywhere near 1270 K. The SSME exhaust was about half that. The nozzle expands and accelerates the exhaust gas, and the energy to do that comes from the heat in the gas itself. An ideal nozzle would expand it all the way to the condensation point.

Offline Robotbeat

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Re: BFS Design Requirements
« Reply #59 on: 03/11/2018 11:56 PM »
There's no LAS on an airliner either
Airliners are 10,000x safer than rockets, so adding a "LAS" would only decrease safety.
Bingo.
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