Author Topic: F9 - S2 reusable modification as evolution steps to BFS(ITS)  (Read 39388 times)

Offline Ionmars

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If this approach were used to establish a platform for testing BFS, there may be two basic questions. First, how much mass will Falcon 9R block 5 boost to stage separation, and (2) how much volume could be built into a partially-fuelled, empty stage 2-to-orbit vehicle that resembles the BFS. This will tell us how closely this testbed BFS could resemble a final BFS with usable payload that could be launched by an intermediate BFR.

Why launch on F9 if FH is available and could launch it fully fueled?
F9 is less expensive for multiple test flights and is the base case for this thread. I don't know if it would have enough lift for the job. If not, then it will be FH or another approach.
* Mars: a convenient service station for an asteroid-sized spaceship en-route to Ceres. *

Offline Jim

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Anything else? Building integration facilities doesn't seem to be beyond the realm of possibility, as SpaceX needs them anyway for commsats. What particular requirements do NSS payloads have for integration that a commercial bird wouldn't?

just stop.    NSS has their requirements, if others want to play in their sandbox, then they have to play by NSS rules. 

Offline rakaydos

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Anything else? Building integration facilities doesn't seem to be beyond the realm of possibility, as SpaceX needs them anyway for commsats. What particular requirements do NSS payloads have for integration that a commercial bird wouldn't?

just stop.    NSS has their requirements, if others want to play in their sandbox, then they have to play by NSS rules.
There was a recent video of Elon telling the Arkansas govenor that one of the downsides of oldspace is that they will never say no to awful requirements.

Offline JamesH65

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Anything else? Building integration facilities doesn't seem to be beyond the realm of possibility, as SpaceX needs them anyway for commsats. What particular requirements do NSS payloads have for integration that a commercial bird wouldn't?

just stop.    NSS has their requirements, if others want to play in their sandbox, then they have to play by NSS rules.

Would it ever happen that no-one wants to play by those rules any more? Or charges so much money to stick to the rules  that even the NSS thinks they are taking the piss. Would/could the rules be changed?

Not saying they should do one or the other, just commenting that just maybe, over the next few years, rules could change.

Offline Jim

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There was a recent video of Elon telling the Arkansas govenor that one of the downsides of oldspace is that they will never say no to awful requirements.

And that is why it is unlikely that the NSS will use Falcon Heavy

Offline Jim

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Would it ever happen that no-one wants to play by those rules any more? Or charges so much money to stick to the rules  that even the NSS thinks they are taking the piss. Would/could the rules be changed?

Not saying they should do one or the other, just commenting that just maybe, over the next few years, rules could change.

Nope.  The security requirements and associated infrastructure is not going away, along with other infrastructure at DOD launch sites.  And that is what they are DOD launch sites.  Why should they have to move?  They are specifically set up to manage and handle the preparation and launch of NSS assets.


See EPF, TSF and SSF at the Cape.  OMRF, ASO 5m high bay and SSI PPF at VAFB.
« Last Edit: 07/18/2017 02:59 PM by Jim »

Online Basto

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Anything else? Building integration facilities doesn't seem to be beyond the realm of possibility, as SpaceX needs them anyway for commsats. What particular requirements do NSS payloads have for integration that a commercial bird wouldn't?

just stop.    NSS has their requirements, if others want to play in their sandbox, then they have to play by NSS rules.
There was a recent video of Elon telling the Arkansas govenor that one of the downsides of oldspace is that they will never say no to awful requirements.

To be clear this is not an "oldspace" issue. As Jim has said NSS launches from the cape because that is where their infrastructure is.

It would be like if a competitor to Six Flags opened up a theme park 3 states over in the middle of nowhere and expected you to go there because it's cheaper instead of the Six Flags that is down the road.

Offline rakaydos

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There was a recent video of Elon telling the Arkansas govenor that one of the downsides of oldspace is that they will never say no to awful requirements.

And that is why it is unlikely that the NSS will use Falcon Heavy
Out of context, that feels like a beer bet statement. Say, next 3 years, if there is no NSS flights on a falcon heavy, I send you a beer. If there is, I get one.

Offline meekGee

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If the NSS made the rules, the NSS can change the rules - if it wants to.


« Last Edit: 07/19/2017 05:12 AM by meekGee »
ABCD - Always Be Counting Down

Offline mikelepage

One thing I'm curious about - and SpaceX would have data on this now - is to what extent supersonic retro-propulsion reduces peak heating on the returning stage? and to what extent it reduces the need for shielding?

If the exhaust plume from the engine is creating a tear-drop-shaped protective interface around the returning stage, does this help to protect the stage? and/or create additional deceleration over & above the thrust itself in the same way a drogue chute does?

Basically I'm wondering to what extent the requirement for S2 shielding can be removed by just changing the reentry procedure (timing/throttling of reentry/landing burns).

Online livingjw

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One thing I'm curious about - and SpaceX would have data on this now - is to what extent supersonic retro-propulsion reduces peak heating on the returning stage? and to what extent it reduces the need for shielding?

If the exhaust plume from the engine is creating a tear-drop-shaped protective interface around the returning stage, does this help to protect the stage? and/or create additional deceleration over & above the thrust itself in the same way a drogue chute does?

Basically I'm wondering to what extent the requirement for S2 shielding can be removed by just changing the reentry procedure (timing/throttling of reentry/landing burns).

Supersonic retro-propulsion will not be used, a heat shield will be. The only reason supersonic retro-propulsion is used for the booster is to keep it from exceeding about Mach 3.5. Much faster and the booster would get to hot. Reentry from orbit is 7 times faster than that and must use the atmosphere to slow down. Not enough propellant to do anything else. For landing it will either be parachutes or subsonic retro propulsion (the landing burn).

Studies have been done which show that a rocket firing from the center does not increase drag, but that drag can be increased if rockets are fired from around the perimeter. I cannot remember if heating was reduced. I will see if I can't dig up the study.

John
« Last Edit: 07/19/2017 11:47 AM by livingjw »

Offline Req

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Studies have been done which show that a rocket firing from the center does not increase drag, but that drag can be increased if rockets are fired from around the perimeter. I cannot remember if heating was reduced. I will see if I can't dig up the study.

John

Online livingjw

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Thanks. That is what I was thinking of. After reading it, I saw no good reason to use retro-propulsion on Mars except for the actual landing. Aero-braking with low ballistic coefficient and some L/D will get you slowed down and ready for  the landing burn.

John
« Last Edit: 07/19/2017 04:18 PM by livingjw »

Online Lars-J

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Studies have been done which show that a rocket firing from the center does not increase drag, but that drag can be increased if rockets are fired from around the perimeter. I cannot remember if heating was reduced. I will see if I can't dig up the study.

No, no, no. People keep misunderstanding this. This observed effect was only at low throttle levels. It does not mean that braking is impossible with a center mounted engine. Surely you have observed the F9 braking burns?
« Last Edit: 07/19/2017 04:31 PM by Lars-J »

Offline envy887

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Studies have been done which show that a rocket firing from the center does not increase drag, but that drag can be increased if rockets are fired from around the perimeter. I cannot remember if heating was reduced. I will see if I can't dig up the study.

No, no, no. People keep misunderstanding this. This observed effect was only at low throttle levels. It does not mean that braking is impossible with a center mounted engine. Surely you have observed the F9 braking burns?

Those do not rely to any significant extent on drag. Drag is most important in the hypersonic and high supersonic phases of entry.

Offline envy887

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One thing I'm curious about - and SpaceX would have data on this now - is to what extent supersonic retro-propulsion reduces peak heating on the returning stage? and to what extent it reduces the need for shielding?

If the exhaust plume from the engine is creating a tear-drop-shaped protective interface around the returning stage, does this help to protect the stage? and/or create additional deceleration over & above the thrust itself in the same way a drogue chute does?

Basically I'm wondering to what extent the requirement for S2 shielding can be removed by just changing the reentry procedure (timing/throttling of reentry/landing burns).

Stage 2 entry is at too high a velocity for the stage to do this. Firing the engine backwards decreases drag and decreases heating, but means it takes much longer to decelerate.

For example, at 5 g deceleration (50 m/s^2) it takes ~132 seconds to go from orbital velocity (~7790 m/s) to Mach 3.5 (~1190 m/s) where the heating rate is more acceptable. The MVac burns 103 kg/s at minimum throttle, so running it for 132 seconds requires ~13,700 kg of fuel... all of which has to be put in orbit in lieu of payload. That's a major issue when F9 can launch ~18,000 kg with booster reuse and most LEO payloads are 9,000 kg or more.

The problem with reduced drag is that it cannot dive deeper into the atmosphere and decelerate faster, at least not without significantly increased heating, which is what you're trying to avoid in the first place. A 20 g dive would cut the fuel requirements to ~3,400 kg, but greatly increase the TPS requirements. At that point, it's much simpler to use a fully orbital velocity capable TPS and skip the retro-propulsion at entry.

A orbital heatshield can also be easily uprated for entries from GTO, which are much more difficult with retro-propulsion.

Offline Peter.Colin

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One thing I'm curious about - and SpaceX would have data on this now - is to what extent supersonic retro-propulsion reduces peak heating on the returning stage? and to what extent it reduces the need for shielding?

If the exhaust plume from the engine is creating a tear-drop-shaped protective interface around the returning stage, does this help to protect the stage? and/or create additional deceleration over & above the thrust itself in the same way a drogue chute does?

Basically I'm wondering to what extent the requirement for S2 shielding can be removed by just changing the reentry procedure (timing/throttling of reentry/landing burns).

Supersonic retro-propulsion will not be used, a heat shield will be. The only reason supersonic retro-propulsion is used for the booster is to keep it from exceeding about Mach 3.5. Much faster and the booster would get to hot. Reentry from orbit is 7 times faster than that and must use the atmosphere to slow down. Not enough propellant to do anything else. For landing it will either be parachutes or subsonic retro propulsion (the landing burn).

Studies have been done which show that a rocket firing from the center does not increase drag, but that drag can be increased if rockets are fired from around the perimeter. I cannot remember if heating was reduced. I will see if I can't dig up the study.

John

I think the S2 of a regular Falcon 9 could land without shielding, if the payload is replaced with an extra fuel tank, that can optionally be jetisonned.
It takes far less amount of fuel to decelerate from very high speed than to accelerate, because the S2 gets a lot lighter when burning fuel.

For the Falcon Heavy the second stage without shielding could be a little longer, and it would have enough fuel for a small usefull payload, a few deceleration burns and a landing burn.

If you would want to maximize the payload of a fully reusable Falcon Heavy, with a cylindrical S2.
Refueling in orbit definitely helps.
A Raptor engine also, as does landing in a landing cradle.

Heat shielding seems difficult for a cylindrical S2 because of the engine weight at the back end, that makes it unstable, you would have to ad steering fins etc.




« Last Edit: 07/19/2017 08:42 PM by Peter.Colin »

Online Lars-J

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Studies have been done which show that a rocket firing from the center does not increase drag, but that drag can be increased if rockets are fired from around the perimeter. I cannot remember if heating was reduced. I will see if I can't dig up the study.

No, no, no. People keep misunderstanding this. This observed effect was only at low throttle levels. It does not mean that braking is impossible with a center mounted engine. Surely you have observed the F9 braking burns?

Those do not rely to any significant extent on drag. Drag is most important in the hypersonic and high supersonic phases of entry.

Right. But the problem is that some people interpreted the paper on drag reduction using a central thruster as proof that retro propulsion at supersonic speeds is impossible with a central thruster. ("you'll never get thrust, only reduce drag!")
« Last Edit: 07/19/2017 06:06 PM by Lars-J »

Offline envy887

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Studies have been done which show that a rocket firing from the center does not increase drag, but that drag can be increased if rockets are fired from around the perimeter. I cannot remember if heating was reduced. I will see if I can't dig up the study.

No, no, no. People keep misunderstanding this. This observed effect was only at low throttle levels. It does not mean that braking is impossible with a center mounted engine. Surely you have observed the F9 braking burns?

Those do not rely to any significant extent on drag. Drag is most important in the hypersonic and high supersonic phases of entry.

Right. But the problem is that some people interpreted the paper on drag reduction using a central thruster as proof that retro propulsion at supersonic speeds is impossible with a central thruster. ("you'll never get thrust, only reduce drag!")

Why wouldn't you get thrust? That defies conservation of momentum. I've never seen this claim before.

Online livingjw

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Studies have been done which show that a rocket firing from the center does not increase drag, but that drag can be increased if rockets are fired from around the perimeter. I cannot remember if heating was reduced. I will see if I can't dig up the study.

No, no, no. People keep misunderstanding this. This observed effect was only at low throttle levels. It does not mean that braking is impossible with a center mounted engine. Surely you have observed the F9 braking burns?

Those do not rely to any significant extent on drag. Drag is most important in the hypersonic and high supersonic phases of entry.

Right. But the problem is that some people interpreted the paper on drag reduction using a central thruster as proof that retro propulsion at supersonic speeds is impossible with a central thruster. ("you'll never get thrust, only reduce drag!")

Of course you can use retro-propulsion to slow down, but why would you want to? A heat shield is much much lighter way to slow down in an atmosphere at high speed. S2 will be using aerodynamic drag to slow down until just before landing.

John

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