Author Topic: BFR Private Passenger Moonflight - DISCUSSION THREAD  (Read 103448 times)

Offline TripleSeven

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Re: BFR Private Passenger Moonflight - DISCUSSION THREAD
« Reply #500 on: 09/16/2018 04:17 PM »
this is a completely new vehicle with new shapes, new engines, new everything; almost nothing will come from the 9 or FH and in my view they are still paying off the Falcon "cost".  the level of composite composition of the vehicle is several times higher than anything that has been done in a working vehicle...and all those things have driven a lot of manufactors from airplanes to ships "cost through the roof"
Now, remember the margin.
Many aspects of BFS can fail utterly and it still succeed as a ridiculously capable launcher.

All that needs to work is reliability and reflight cost.
If the dry mass is double the expected, or the heatshield is only good to 5km/s, not 11km/s, or ... almost  nothing changes in the business case.

If the 787 had come in at 100% overweight so it could only carry 50% of designed cargo, and used the same amount of fuel, it would have been laughed out of the industry.

If BFS does the same, it beats every single launcher hollow in almost every single aspect, and the ones it doesn't beat on every single aspect it can beat operationally using propellant transfer far cheaper than they can..

and maybe that is accurate, but I dont think it is; and if any or all those things fail, what will fail along with them is "cost"

because the foundation assumption of all of this is that somehow the BFR/BFS will make the cost that Musk is claiming for it. 

and he may well do it, but all it is right now is a hope

if the B787 met all of its objectives...but the RSM (revenue seat mile) failed...then like the MD 11 its a flop.  nothing else matters

Online Robotbeat

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Re: BFR Private Passenger Moonflight - DISCUSSION THREAD
« Reply #501 on: 09/16/2018 04:56 PM »
"The future hasn't happened yet."

Yes, we know. That's tautological.
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

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Offline garcianc

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Re: BFR Private Passenger Moonflight - DISCUSSION THREAD
« Reply #502 on: 09/16/2018 05:27 PM »
My apologies if I missed this being brought up, and perhaps this is worthy of its own splinter thread.

I would expect that SpaceX would send its own astronauts with this flight. I would guess at least 2, to basically run the mission (housekeeping, comms, etc.).

This leads me to think that there would be plenty of other opportunities to support multiple other mission objectives other than tourism.
I would hope that the announcement covers that and also that, if anyone from NSF is given the opportunity to ask, they would press SpaceX to discuss any such plans.

Offline philw1776

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Re: BFR Private Passenger Moonflight - DISCUSSION THREAD
« Reply #503 on: 09/16/2018 05:37 PM »
I would hope that SpaceX would consider a lifetime NSF member with engineering degrees as possible crew.
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Online Lars-J

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Re: BFR Private Passenger Moonflight - DISCUSSION THREAD
« Reply #504 on: 09/16/2018 06:21 PM »
Triple duty, including exhaust shaping, thermal radiation, and engine shielding... Sounds quite within the realm of possiblity of something Elon & Co would think up.
Hey, totally random thought.. If they did all that, maybe you could do away with any swivel mechanism on the 7 engines? (I think I remember some statement about all engines swivelling though)

Oh, so you think that with this kind of macro-nozzle thing, then none of the engines would have to gimbal? Could the macro-nozzle thing achieve the required control authority on its own, particularly during landing?

NO. It could not. And without individual gimbal you do not have engine out capability at any point in the flight.

Offline CuddlyRocket

Re: BFR Private Passenger Moonflight - DISCUSSION THREAD
« Reply #505 on: 09/16/2018 08:01 PM »
This leads me to think that there would be plenty of other opportunities to support multiple other mission objectives other than tourism.
I would hope that the announcement covers that and also that, if anyone from NSF is given the opportunity to ask, they would press SpaceX to discuss any such plans.

What other mission objectives do you have in mind? Its seems to me that SpaceX will have only two objectives on this flight: 1. Testing hardware, procedures etc, and 2. Earning money. Though I'm sure that if they have the spare capacity they'll consider taking extra cargo and personnel along for the appropriate fee (see 2).

Offline WindyCity

Re: BFR Private Passenger Moonflight - DISCUSSION THREAD
« Reply #506 on: 09/16/2018 08:16 PM »

the F9 booster would come completely apart had it to reenter from orbital velocities  as I suspect they have found out the second stage would as well

I don't recollect if this idea has been brought up before, so I apologize if I'm repeating it. Could a BFS returning from BEO get refueled in earth orbit before reentering the atmosphere and landing retropropulsively? I suppose the question is whether it would take more fuel to go into orbit than it would to power a landing with fuel reserves left over after Mars or lunar departure. SpaceX has experience with retropropulsion, and perhaps applying the techniques it has learned with F9 to slowing down the interplanetary vehicle would make more sense than equipping it with extra-robust shielding.

Offline TripleSeven

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Re: BFR Private Passenger Moonflight - DISCUSSION THREAD
« Reply #507 on: 09/16/2018 08:39 PM »

the F9 booster would come completely apart had it to reenter from orbital velocities  as I suspect they have found out the second stage would as well

I don't recollect if this idea has been brought up before, so I apologize if I'm repeating it. Could a BFS returning from BEO get refueled in earth orbit before reentering the atmosphere and landing retropropulsively? I suppose the question is whether it would take more fuel to go into orbit than it would to power a landing with fuel reserves left over after Mars or lunar departure. SpaceX has experience with retropropulsion, and perhaps applying the techniques it has learned with F9 to slowing down the interplanetary vehicle would make more sense than equipping it with extra-robust shielding.

good question.  If a BFS was returning from BEO and could enter earth orbit at an altitude that could be reached by a tanker then without a doubt; if the basic refueling system works then it could easily be refueled for a propulsive landing

what would be interesting to explore...from a fuel etc viewpoint what would be the affect on fuel etc of using the atmosphere to "aerobrake" into some high eccentric orbit (ie one with a high point and a low point but a very high point) do a few more aerobrakes (maybe with some propulsive burn) to circularize and then refuel for a landing. 

it would take some serious orbital mechanics work to figure out the pros and cons of that.

direct entry is always less expensive on fuel than any orbital manuevers (to then land) but you dont have the same heat issues.

good question.

Offline RobLynn

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Re: BFR Private Passenger Moonflight - DISCUSSION THREAD
« Reply #508 on: 09/16/2018 08:40 PM »
the parallel-looking gaps between the petals would in general imply only a small amount of radial movement to close up the gaps (maintaining same cone angle), assuming no petal overlap is created by mechanism.

If they are a nozzle extension of some sort could they be set up to fold into a lobed cone shape around the engine bells to be more conformal to the bells than a simple cone would be?  Use of 2 petals per engine suggests that this could be part of the solution.  Could they be designed to work as Expansion-deflection nozzles?  The ring of raptors being gimballed outwards to each fire against the 2 deflector petals for just that engine, mostly independent of other engines (so that only 2 engines need be fired at once).  Middle engine could/would be shut down for this.

I like the idea that they might also shield non-firing engine nozzles from debris during a Mars or Lunar landing.
I'm a "glass is twice as big as it needs to be" kinda guy

Offline envy887

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Re: BFR Private Passenger Moonflight - DISCUSSION THREAD
« Reply #509 on: 09/16/2018 08:40 PM »

the F9 booster would come completely apart had it to reenter from orbital velocities  as I suspect they have found out the second stage would as well

I don't recollect if this idea has been brought up before, so I apologize if I'm repeating it. Could a BFS returning from BEO get refueled in earth orbit before reentering the atmosphere and landing retropropulsively? I suppose the question is whether it would take more fuel to go into orbit than it would to power a landing with fuel reserves left over after Mars or lunar departure. SpaceX has experience with retropropulsion, and perhaps applying the techniques it has learned with F9 to slowing down the interplanetary vehicle would make more sense than equipping it with extra-robust shielding.
It takes about 10 times more fuel to land than it does to aerobrake into LEO and circularize. Refueling on the way down is definitely a way to increase payload, at the cost of some more operational complexity.

Offline envy887

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Re: BFR Private Passenger Moonflight - DISCUSSION THREAD
« Reply #510 on: 09/16/2018 08:44 PM »

the F9 booster would come completely apart had it to reenter from orbital velocities  as I suspect they have found out the second stage would as well

I don't recollect if this idea has been brought up before, so I apologize if I'm repeating it. Could a BFS returning from BEO get refueled in earth orbit before reentering the atmosphere and landing retropropulsively? I suppose the question is whether it would take more fuel to go into orbit than it would to power a landing with fuel reserves left over after Mars or lunar departure. SpaceX has experience with retropropulsion, and perhaps applying the techniques it has learned with F9 to slowing down the interplanetary vehicle would make more sense than equipping it with extra-robust shielding.

good question.  If a BFS was returning from BEO and could enter earth orbit at an altitude that could be reached by a tanker then without a doubt; if the basic refueling system works then it could easily be refueled for a propulsive landing

what would be interesting to explore...from a fuel etc viewpoint what would be the affect on fuel etc of using the atmosphere to "aerobrake" into some high eccentric orbit (ie one with a high point and a low point but a very high point) do a few more aerobrakes (maybe with some propulsive burn) to circularize and then refuel for a landing. 

it would take some serious orbital mechanics work to figure out the pros and cons of that.

direct entry is always less expensive on fuel than any orbital manuevers (to then land) but you dont have the same heat issues.

good question.

Direct entry with a propulsive landing is always more expensive (in terms of propellant used) compared to aerocapture and circularization.

It's about 600 m/s to land vs about 60 m/s to circularize in LEO.

Offline Rocket Science

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Re: BFR Private Passenger Moonflight - DISCUSSION THREAD
« Reply #511 on: 09/16/2018 09:01 PM »
I would hope that SpaceX would consider a lifetime NSF member with engineering degrees as possible crew.
Or perhaps as a "biological specimen" for test flights...
https://getyarn.io/yarn-clip/2c13dde1-6649-47a7-909e-b124b6b93052
« Last Edit: 09/16/2018 09:05 PM by Rocket Science »
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Offline ThomasGadd

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Re: BFR Private Passenger Moonflight - DISCUSSION THREAD
« Reply #512 on: 09/16/2018 09:09 PM »
I've known the SSME could operate SL to vacuum with no problems recently I read on how it did it.
The nozzle was the ideal vacuum shape so it would operate over a wider pressure range at the cost to efficiency.
Carrying engines BFS couldn't use seemed wasteful......


Offline WindyCity

Re: BFR Private Passenger Moonflight - DISCUSSION THREAD
« Reply #513 on: 09/16/2018 09:14 PM »

what would be interesting to explore...from a fuel etc viewpoint what would be the affect on fuel etc of using the atmosphere to "aerobrake" into some high eccentric orbit (ie one with a high point and a low point but a very high point) do a few more aerobrakes (maybe with some propulsive burn) to circularize and then refuel for a landing. 

Is it reasonable to think that the shielding necessary for aerobraking maneuvers and refueling would be less massive and complex than what would be required for direct entry from BEO? If true, could that translate into a capacity to return larger payloads to earth?

Offline speedevil

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Re: BFR Private Passenger Moonflight - DISCUSSION THREAD
« Reply #514 on: 09/16/2018 09:24 PM »
Is it reasonable to think that the shielding necessary for aerobraking maneuvers and refueling would be less massive and complex than what would be required for direct entry from BEO? If true, could that translate into a capacity to return larger payloads to earth?

You can also do entry like Mars Global Surveyor or similar.
Instead of entering low earth orbit, you enter a very eccentric earth orbit, which may take a kilometer a second or so of propellant, and then gradually brake into orbit very slowly. MGS did it over several months, but that would be a _lot_ of passes through the radiation belts.

And yes, it is plausible that taking this kilometer a second or so off aerodynamically can enable you to return much heavier masses.
At the least, you save the 20t or so of landing fuel, at most, you can end up with 500 tons or more of payload. (that has to be returned in parts.

- see 35:40 or so.
This is the entry into Mars. Note that until 3.5km/s horizontal speed, the ship is having to aerodynamically force itself down to keep in the atmosphere longer.
If you spin round the other way, you pop out.

The higher speed at earth entry - >10km/s may mean that even with very light passes taking off 1km/s per pass, there is some heatshield wear.


Offline Rocket Science

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Re: BFR Private Passenger Moonflight - DISCUSSION THREAD
« Reply #515 on: 09/16/2018 09:25 PM »
I've known the SSME could operate SL to vacuum with no problems recently I read on how it did it.
The nozzle was the ideal vacuum shape so it would operate over a wider pressure range at the cost to efficiency.
Carrying engines BFS couldn't use seemed wasteful......
It was a compromise nozzle...
http://www.rocket-propulsion.info/resources/articles/NozzleDesign.pdf
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Offline speedevil

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Re: BFR Private Passenger Moonflight - DISCUSSION THREAD
« Reply #516 on: 09/16/2018 09:34 PM »
t to efficiency.
Carrying engines BFS couldn't use seemed wasteful......
The vacuum engines on BFS (2017) only can't be used under 5km or so (ideally).

There is no reason to ever use them at this time in a nominal flight, so they never 'can't be used'.

Staging happens basically in complete vacuum, and the sea-level engines would likely be used at least for the first few seconds of second stage flight, as all seven engines burning at this time has a point.

There is almost no penalty between having seven vacuum raptors in this case, and four plus three sea-level ones.

There is no benefit in a nominal landing of lighting all the engines.
It is only in the case of abort, which is at best questionable with seven engines and SSTO, which is again questionable it becomes useful to light the vacuum raptors near the ground ever.


Online meekGee

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Re: BFR Private Passenger Moonflight - DISCUSSION THREAD
« Reply #517 on: 09/16/2018 10:19 PM »
the parallel-looking gaps between the petals would in general imply only a small amount of radial movement to close up the gaps (maintaining same cone angle), assuming no petal overlap is created by mechanism.

If they are a nozzle extension of some sort could they be set up to fold into a lobed cone shape around the engine bells to be more conformal to the bells than a simple cone would be?  Use of 2 petals per engine suggests that this could be part of the solution.  Could they be designed to work as Expansion-deflection nozzles?  The ring of raptors being gimballed outwards to each fire against the 2 deflector petals for just that engine, mostly independent of other engines (so that only 2 engines need be fired at once).  Middle engine could/would be shut down for this.

I like the idea that they might also shield non-firing engine nozzles from debris during a Mars or Lunar landing.

Yeah the parallel gaps threw me for a loop for a while, but if you think about a motion that's a little bit inwards (closing the gaps) and otherwise axially aft, you get pretty much the macro-nozzle.

I even tried at one time (in my head) and even-odd arrangement, where the odds ones extend twice as far as the even ones, and everything shrinks inwards.  This is how desperate I got   :)

Static radiators would also be beneficial.  You need to press the tanks, and that's a great way to grab heat from the engines.

Oh Monday, deliver us.

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Offline JonathanD

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Re: BFR Private Passenger Moonflight - DISCUSSION THREAD
« Reply #518 on: 09/16/2018 11:14 PM »
Oh Monday, deliver us.

I expect an update, I do not expect all these details to be explained, especially if there is not a Q&A session.  If there is a Q&A session, and all the pre-approved questions start with "How do you feel now that..." I'm going to freak :p

Offline speedevil

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Re: BFR Private Passenger Moonflight - DISCUSSION THREAD
« Reply #519 on: 09/16/2018 11:26 PM »
Oh Monday, deliver us.

I expect an update, I do not expect all these details to be explained, especially if there is not a Q&A session.  If there is a Q&A session, and all the pre-approved questions start with "How do you feel now that..." I'm going to freak :p

If this is indeed the 'big news' this year, then if it follows the pattern of IAC2017, useful technical info came out after.
For example, the reddit AMA.

Even 'big picture' is valulable - the 'party line' since IAC2017 has been unchanged, even in the face of changes we know have happened not being reflected in graphics or presentation.

Any announcement of tourism, for example that goes beyond the bare facts must give us interesting insight into the capabilities.
For example, if we're told that it can go round the moon with no tanker, that tells us interesting things about the planned dry weight.
More explanation of P2P would also be very revealing about operations costs.

I would of course like testing schedules of BFS and BFR, ISPs and thrust, and if the Mars plans have changed meaningfully.

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