Author Topic: BFR with expendable upper stage  (Read 14109 times)

Offline Michael Bloxham

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BFR with expendable upper stage
« on: 02/13/2018 02:41 AM »
Hey guys,

I'm wondering what the LEO and TMI performance of the BFR would be with an expendable version of the BFS acting as an upper stage? Assume no delta wings, no TPS, and deleted landing engines (so just 4x vacuum Raptors).

The scenario I'm thinking about is if reusable BFS is put in the too-hard basket, or is found suitable for LEO ops only. Or the economics of large-scale fuel manufacturing on Mars doesn't work out (at least for initial missions!)...

The idea of an expendable upper could be quite compelling given the extra TMI performance out of it. With a hammer-head PLF you could fit some very large diameter Mars landers in there, thereby keeping lander density low, easing EDL requirements.

I also found a Reddit thread talking about Falcon Heavy TMI performance with expendable rather than reusable central booster. It implied costs per kg were lower for the expendable case, because of the extra performance.

Cheers,

- Mike

Offline Robotbeat

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Re: BFR with expendable upper stage
« Reply #1 on: 02/13/2018 02:53 AM »
Boo. Theyíll keep trying reusable upper stage until they go bankrupt.
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Offline Michael Bloxham

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Re: BFR with expendable upper stage
« Reply #2 on: 02/13/2018 02:57 AM »
Iím sure theyíll have the reusable upper stage eventually, for LEO and maybe even GEO payloads. What Iím not sure about is the economics for the whole Mars thing.

Offline Prettz

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Re: BFR with expendable upper stage
« Reply #3 on: 02/13/2018 03:00 AM »
If it's expendable they can't afford to launch it in the first place, so what's the point?

Offline Robotbeat

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Re: BFR with expendable upper stage
« Reply #4 on: 02/13/2018 03:06 AM »
Iím sure theyíll have the reusable upper stage eventually, for LEO and maybe even GEO payloads. What Iím not sure about is the economics for the whole Mars thing.
You're confused because you're using direct-launch performance numbers to guide your intution. You basically can't actually direct-launch anything to Mars with a reusable two stage rocket. But that's irrelevant because you refuel the reusable upper stage in orbit. That is way more efficient anyway.

Don't ignore refueling. Refueling changes everything.
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Offline Michael Bloxham

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Re: BFR with expendable upper stage
« Reply #5 on: 02/13/2018 03:17 AM »
Iím not a fan of orbital-refuelling when it comes to Mars missions. With Mars EDL you want a low-density lander, so low surface mass and wide aeroshell diameters. Getting through the bottleneck of EDL is hard. With orbital refuelling, you just end up increasing the density of your payload. It doesnít help you at all. Iím not sure if SpaceX will achieve their EDL goals with BFS.

In a lot of Mars mission studies, the upper stage of the launcher also serves as the TMI stage, so I donít see why I canít assume the same with BFR.

Offline Michael Bloxham

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Re: BFR with expendable upper stage
« Reply #6 on: 02/13/2018 03:20 AM »
If it's expendable they can't afford to launch it in the first place, so what's the point?

If you assume very expensive payloads (as in a Mars mission), then expending the upper stage could make sense, given the increased performance. Youíre still reusing the whole first stage.

Offline RonM

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Re: BFR with expendable upper stage
« Reply #7 on: 02/13/2018 03:25 AM »
Iím not a fan of orbital-refuelling when it comes to Mars missions.

That's the key step in the BFR/BFS architecture. Obviously, Elon Musk likes orbital refueling.

Offline Robotbeat

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Re: BFR with expendable upper stage
« Reply #8 on: 02/13/2018 03:31 AM »
I’m not a fan of orbital-refuelling when it comes to Mars missions. With Mars EDL you want a low-density lander, so low surface mass and wide aeroshell diameters. Getting through the bottleneck of EDL is hard. With orbital refuelling, you just end up increasing the density of your payload. ...
I can't see how you arrive at that conclusion. Nearly all the propellant you're refuelling with orbital refueling is burned doing TMI, so you end up with a low density "payload" (i.e. the entire BFS) with a high effective aeroshell area.

It seems you're not familiar with how BFS is planned to work. Well, you're in for a treat! Here's the 2016 video. BFR/BFS is essentially the same concept, just with a slightly smaller vehicle. Please watch the whole thing.

« Last Edit: 02/13/2018 03:32 AM by Robotbeat »
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Offline Robotbeat

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Re: BFR with expendable upper stage
« Reply #9 on: 02/13/2018 03:33 AM »
If you can't make the reusable upper stage work, then you don't have a Mars lander or aeroshell, either. They're the same vehicle. This is a key innovation in the BFR/ITS architecture. Please watch the above video.
« Last Edit: 02/13/2018 03:34 AM by Robotbeat »
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Offline Michael Bloxham

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Re: BFR with expendable upper stage
« Reply #10 on: 02/13/2018 03:40 AM »
But then you end up with this huge expensive BFS on Mars surface, which you need to refuel to send back. The whole idea of reusing the BFS for Mars relies on huge refuelling infrastructure on Mars. If this ends up being uneconomic, then the benefit of BFS for Mars goes away (still useful for LEO tho). Also, even with successful reuse, youíre still looking at the expense of setting up the fuel manufacturing on Mars in the first place. Youíre also taking the productive asset that is BFS and tying it up with incredibly infrequent Mars missions (one launch every 2.5 years). It might be better to use that asset for LEO work, where it could be flown hundreds of times per year. Thereís always a trade off. Iím suggesting it might make sense to go the expendable route for missions beyond LEO.

Offline AC in NC

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Re: BFR with expendable upper stage
« Reply #11 on: 02/13/2018 03:42 AM »
Pretty sure they know how, by this point, to have run the numbers and decided you're wrong.

Offline Robotbeat

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Re: BFR with expendable upper stage
« Reply #12 on: 02/13/2018 03:46 AM »
Having a big refueling station on Mars isn’t that hard if you can land huge payloads on Mars cheaply. And BFS isn’t very expensive, on the order of $120m, still much cheaper than any comparable expendable lander.

The dream of a Mars City disappears without upper stage reuse and without reusable Mars landers. Full stop.
« Last Edit: 02/13/2018 03:48 AM by Robotbeat »
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Offline Michael Bloxham

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Re: BFR with expendable upper stage
« Reply #13 on: 02/13/2018 03:48 AM »
Pretty sure they know how, by this point, to have run the numbers and decided you're wrong.

Iím sure theyíre still working on their numbers. We havenít even seen their proposal for setting up the fuel manufacturing on Mars surface yet.
« Last Edit: 02/13/2018 03:50 AM by Michael Bloxham »

Offline Michael Bloxham

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Re: BFR with expendable upper stage
« Reply #14 on: 02/13/2018 03:55 AM »
The dream of a Mars City disappears without upper stage reuse and without reusable Mars landers. Full stop.

I disagree. You could build a nice Mars city using expendable landers. Itís down-mass (and volume) that you want. Which fits quite nicely with the idea of using large low-density aeroshells for surface payloads. BFS is volume restricted.

Offline Robotbeat

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Re: BFR with expendable upper stage
« Reply #15 on: 02/13/2018 03:59 AM »
The dream of a Mars City disappears without upper stage reuse and without reusable Mars landers. Full stop.

I disagree. You could build a nice Mars city using expendable landers. It’s down-mass (and volume) that you want. Which fits quite nicely with the idea of using large low-density aeroshells for surface payloads. BFS is volume restricted.
Nope. Can’t afford the downmass with expendable. Cannot and will not happen.

Luckily, there’s no magical law of physics preventing reusable upper stages and landers from happening. We already know it’s possible.
« Last Edit: 02/13/2018 03:59 AM by Robotbeat »
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Offline Michael Bloxham

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Re: BFR with expendable upper stage
« Reply #16 on: 02/13/2018 04:01 AM »
It comes down to the cost of setting up the fuel manufacturing and launch ops infrastructure.

Offline Robotbeat

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Re: BFR with expendable upper stage
« Reply #17 on: 02/13/2018 04:07 AM »
It comes down to the cost of setting up the fuel manufacturing and launch ops infrastructure.
...all of which is cheaper if you have the capability to land large payloads.

Oh, and if you don’t like that BFS is only used once per 26 months (although in several different roles, so effectively reused several times within 26 months), then there are ways to launch several payloads to Mars ballistically, then capture them at Mars and bring them down with a refueled BFS. So the one use per synod is not at all a hard and fast rule.
« Last Edit: 02/13/2018 04:07 AM by Robotbeat »
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Offline Michael Bloxham

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Re: BFR with expendable upper stage
« Reply #18 on: 02/13/2018 04:09 AM »
If you have to do 20+ flights of BFR/BFS to LEO to set up the infrastructure to return one BFS from Mars surface... Maybe it could work out cheaper to just to do one flight of BFR and an expendable BFS derived upper stage with a big dumb lander. The big dumb lander could help you set up the infrastructure more cheaply. Full reusability could come later, if itís desirable at all by that stage. You could just get straight into base-building with a big dumb lander.

Offline Robotbeat

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Re: BFR with expendable upper stage
« Reply #19 on: 02/13/2018 04:11 AM »
Without upper stage reuse, launch costs will never approach the low levels needed for mass settlement. With partial reuse we can get down to $1000/kg. We might need to get nearly $10/kg (consistent with spaceXís numbers for ITS/BFR) to really make mass settlement feasible. Just not possible without upper stage reuse.
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Offline Robotbeat

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Re: BFR with expendable upper stage
« Reply #20 on: 02/13/2018 04:13 AM »
If you have to do 20+ flights of BFR/BFS to LEO to set up the infrastructure to return one BFS from Mars surface...
No, you just need one booster, one BFS, and maybe another tanker version (which can be used for other tasks) to setup the required infrastructure. The launches themselves are cheap.
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Offline Michael Bloxham

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Re: BFR with expendable upper stage
« Reply #21 on: 02/13/2018 04:17 AM »
Without upper stage reuse, launch costs will never approach the low levels needed for mass settlement. With partial reuse we can get down to $1000/kg. We might need to get nearly $10/kg (consistent with spaceXís numbers for ITS/BFR) to really make mass settlement feasible. Just not possible without upper stage reuse.

You're implying you're not interested in anything less than the economic settlement of Mars being opened up by BFS. I don't see things that way... It could be that BFS will just not be able to make things as easy and as cheaply as Musk envisions. This stuff is hard. So what I'm asking (the performance of a BFR with expendable BFS derived upper stage) is maybe to look at plan B.

Offline Michael Bloxham

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Re: BFR with expendable upper stage
« Reply #22 on: 02/13/2018 04:28 AM »
With Plan B you could concentrate on an exploration phase of Mars, before committing to settlement. You could also look at cooperating more with NASA, and other potential stakeholders. The empty shells of the big dumb landers could also become very useful when you do commit to the base building phase. But anyway... All I want to know is the performance of BFR with an expendable upper stage! :-P

Offline Robotbeat

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Re: BFR with expendable upper stage
« Reply #23 on: 02/13/2018 04:32 AM »
You still donít seem to have a good grasp of the situation, though. Performance to Mars isnít actually lower because of reuse. No significant mass is wasted on the BFS. Everything you might need for reuse is also what you need to land on Mars.

A large expendable Mars lander still needs a huge heatshield. It still needs supersonic retropropulsion. It still needs landing thrusters. It still needs landing legs. You even still need large tanks on your trans Mars insertion stage.

You might save a little bit of IMLEO by staging off pieces (like tanks, heatshield, etc) as they are used, but that also increases complication and costs in its own way. How much did the EDL system for Curiosity cost? I bet itís still about the same as a BFS, even though itís purely expendable and can only land a hundredth of the mass.
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Offline Michael Bloxham

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Re: BFR with expendable upper stage
« Reply #24 on: 02/13/2018 04:41 AM »
Okay, I get it. But there still may be road-stoppers ahead. I'm curious about a Plan B. Okay? :-P

Offline Michael Bloxham

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Re: BFR with expendable upper stage
« Reply #25 on: 02/13/2018 04:46 AM »
One of the potential problems cited with BFS was the high g-loads during Mars EDL. That's because it's still a high-density design even with mostly empty tanks. That could be a problem considering your human cargo - and there's no provision for artificial gravity with BFS. So I was thinking about very low-density high-volume landers to keep g-loads as low as possible. But that question warrants a different thread, and after I'd gotten the answer to this one!

Offline Robotbeat

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Re: BFR with expendable upper stage
« Reply #26 on: 02/13/2018 04:50 AM »
High density design? citation badly needed.

The gee loads are pretty low since the body generates significant lift. The only reason they might look fairly high is the fast transit, which also minimizes microgravity exposure. If you wanted, you could always choose a slower trajectory which would have lower fee loads.
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Offline Michael Bloxham

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Re: BFR with expendable upper stage
« Reply #27 on: 02/13/2018 05:17 AM »
Ah okay. Well how about for a one-off exploration probe to say Titan, for example? How much extra performance could you get out of an expendable upper stage?

Offline Valerij

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Re: BFR with expendable upper stage
« Reply #28 on: 02/13/2018 09:21 AM »
Ah okay. Well how about for a one-off exploration probe to say Titan, for example? How much extra performance could you get out of an expendable upper stage?
Very small. The point is that the efficiency of a two-stage rocket starting from Earth, with the deltaV necessary for a flight to Mars, is very small.
   
For some specific missions, it may be advantageous to use disposable, consumable upper stages on the BFR. First of all, to create a depot of fuel in orbit. It is also possible to deliver the first elements of the fuel complex to Mars. But without refueling this stage on LEO you will not be able to deliver large modules not to the Moon, nor to Mars.
   
You will still need reusable upper stages as tankers for refueling the stage sent to Mars.

Offline DJPledger

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Re: BFR with expendable upper stage
« Reply #29 on: 02/13/2018 09:33 AM »
Expendable US for BFR defeats the objective as BFR is being designed for fully reusability. Expending any BFR hardware will dramatically increase it's cost per launch. Full reusability is what will give BFR extremely low launch costs.

Offline uhuznaa

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Re: BFR with expendable upper stage
« Reply #30 on: 02/13/2018 11:55 AM »
Expendable US for BFR defeats the objective as BFR is being designed for fully reusability. Expending any BFR hardware will dramatically increase it's cost per launch. Full reusability is what will give BFR extremely low launch costs.

"Full reusability" does not necessarily mean to only and always fly reusable second stages on BFR. If what you want to launch is something like a big space station module or some large module to land on the Moon, building a one-off second stage from parts or from a BFS near its end of life would be totally reasonable.

For one-way missions dragging a reusable stage with heat shield, landing engines, legs etc. all the way to the destination and back would be pointless.

Offline Robotbeat

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Re: BFR with expendable upper stage
« Reply #31 on: 02/13/2018 12:44 PM »
Ah okay. Well how about for a one-off exploration probe to say Titan, for example? How much extra performance could you get out of an expendable upper stage?
An expendable kick stage for one-off high energy missions may make sense! But you wouldnít want to do that from LEO. Instead, youíd want to send the BFS (with payload) to a high, elliptic orbit, then the kick stage would start itís burn while already very close to escape velocity at perigee.

Youíd want basically the biggest Star motor in OrbitalATKís catalogue. It, thatíd be one of the cheapest options.
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Offline acsawdey

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Re: BFR with expendable upper stage
« Reply #32 on: 02/13/2018 04:12 PM »
Ah okay. Well how about for a one-off exploration probe to say Titan, for example? How much extra performance could you get out of an expendable upper stage?
An expendable kick stage for one-off high energy missions may make sense! But you wouldnít want to do that from LEO. Instead, youíd want to send the BFS (with payload) to a high, elliptic orbit, then the kick stage would start itís burn while already very close to escape velocity at perigee.

Youíd want basically the biggest Star motor in OrbitalATKís catalogue. It, thatíd be one of the cheapest options.

The step beyond that is a departure stage assembled in orbit (or brought up in a BFS if it can fit). Consists of just a few elements:

* tanks
* BFS-compatible refueling connection
* one Raptor-vac, perhaps with oversize radiatively cooled nozzle extension

Fuel it up (perhaps in a highly elliptical orbit), stick an outer solar system probe on it, and send it on it's way.

Since high chamber pressure isn't all that necessary for vacuum engines, one could also imagine using a low pressure engine that is pressure fed at something like 50 psi so you don't need special tanks. Perhaps Raptor would be affordable enough that it wouldn't be worth bothering.

Online groundbound

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Re: BFR with expendable upper stage
« Reply #33 on: 02/13/2018 05:17 PM »
Ah okay. Well how about for a one-off exploration probe to say Titan, for example? How much extra performance could you get out of an expendable upper stage?
An expendable kick stage for one-off high energy missions may make sense! But you wouldnít want to do that from LEO. Instead, youíd want to send the BFS (with payload) to a high, elliptic orbit, then the kick stage would start itís burn while already very close to escape velocity at perigee.

Youíd want basically the biggest Star motor in OrbitalATKís catalogue. It, thatíd be one of the cheapest options.

The step beyond that is a departure stage assembled in orbit (or brought up in a BFS if it can fit). Consists of just a few elements:

* tanks
* BFS-compatible refueling connection
* one Raptor-vac, perhaps with oversize radiatively cooled nozzle extension

Fuel it up (perhaps in a highly elliptical orbit), stick an outer solar system probe on it, and send it on it's way.

Since high chamber pressure isn't all that necessary for vacuum engines, one could also imagine using a low pressure engine that is pressure fed at something like 50 psi so you don't need special tanks. Perhaps Raptor would be affordable enough that it wouldn't be worth bothering.

I've actually wondered if someone might come up with a kick stage / tug hybrid that used methalox boost and solar electric return. Cycle time might be a year or more until it could get back to some earth orbit where BFS could refuel it, but that roughly matches the target market -- outer planet exploration missions.


Offline Ludus

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Re: BFR with expendable upper stage
« Reply #34 on: 02/13/2018 06:40 PM »
But then you end up with this huge expensive BFS on Mars surface, which you need to refuel to send back. The whole idea of reusing the BFS for Mars relies on huge refuelling infrastructure on Mars. If this ends up being uneconomic, then the benefit of BFS for Mars goes away (still useful for LEO tho). Also, even with successful reuse, youíre still looking at the expense of setting up the fuel manufacturing on Mars in the first place. Youíre also taking the productive asset that is BFS and tying it up with incredibly infrequent Mars missions (one launch every 2.5 years). It might be better to use that asset for LEO work, where it could be flown hundreds of times per year. Thereís always a trade off. Iím suggesting it might make sense to go the expendable route for missions beyond LEO.

If you like the frugality of using the BFS hundreds of times near earth, do that first. Once youíve amortized and depreciated your BFS so it has little book value, send it to Mars and treat it as expendable.

Offline TrevorMonty

Re: BFR with expendable upper stage
« Reply #35 on: 02/13/2018 07:26 PM »
An expendable 3rd stage would be better option for BFR. This could be fully fuelled 100t 1xRaptor stage + payload, delivered to LEO inside BFR 2nd stage. Shouldn't cost much more than F9 2nd stage, ideally have life of few days so it can deliver payloads direct to anywhere in cis lunar space.

Why initially expendable could turn into reuseable OTV that returns to LEO for BFR delivered payload and fuel. Much like what ULA plan to do with ACES.

The long life and refuelling capabilities this OTV needs are also required by BFR, so good test bed.

In expendable mode can deliver about 40t to  LLO or 30t when reusable. 30t to LLO in single launch using fully reuseable vehicles    would make for cheap lunar missions.
« Last Edit: 02/13/2018 07:37 PM by TrevorMonty »

Offline spacenut

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Re: BFR with expendable upper stage
« Reply #36 on: 02/13/2018 09:02 PM »
Musk mentioned it would take 6 tanker launches to completely fill the BFS or second stage for transport to Mars.  He is also sending two cargo ships to Mars 2 years prior to the human trip.  These would have the equipment to make Methane and LOX for refueling the human lander for return to earth.  He also said for a base, it would probably take 10 cargo flights to Mars with all the equipment and food for one human ship.  He also said the trip will be during the time when Mars is closest to earth and only require about a 2 month trip, so no real worries about zero g for humans for two months.  The stay on Mars would be about 2 years for the crew, to then return or continue to stay longer, eventually setting up the colony.  SEP tugs could also bring cargo via slow route on a continuous basis. 

Offline AC in NC

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Re: BFR with expendable upper stage
« Reply #37 on: 02/13/2018 09:44 PM »
This is Plan B:

The Hunt for Red October (1990)
Quotes
Captain Ramius: When he reached the New World, Cortez burned his ships. As a result his men were well motivated.

Offline AC in NC

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Re: BFR with expendable upper stage
« Reply #38 on: 02/13/2018 09:51 PM »
Ah okay. Well how about for a one-off exploration probe to say Titan, for example? How much extra performance could you get out of an expendable upper stage?

Why?

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Re: BFR with expendable upper stage
« Reply #39 on: 02/13/2018 10:32 PM »
Ah okay. Well how about for a one-off exploration probe to say Titan, for example? How much extra performance could you get out of an expendable upper stage?

Why?

Because BFS has a dry mass that cripples it for launching things to extreme energy trajectories. I buy that it is useful to Mars and maybe a little beyond. More than that and the final boost stage needs to go on a diet.

Offline AC in NC

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Re: BFR with expendable upper stage
« Reply #40 on: 02/13/2018 10:48 PM »
Because BFS has a dry mass that cripples it for launching things to extreme energy trajectories. I buy that it is useful to Mars and maybe a little beyond. More than that and the final boost stage needs to go on a diet.
I can grant that and will.  It's beyond my direct knowledge.  But I don't think that means anything close to what the OP is wedded to.

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Re: BFR with expendable upper stage
« Reply #41 on: 02/13/2018 11:21 PM »
This is one of those "I figured out something SpaceX didn't" threads in which OP takes on all comers and keeps mutating the idea, or the assumptions, to try to keep it alive.

Ultimately, boring.

Locked. Use the report to mod function. to appeal the decision, if you must.
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"We're a little bit like the dog who caught the bus" - Musk after CRS-8 S1 successfully landed on ASDS OCISLY

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Re: BFR with expendable upper stage
« Reply #42 on: 02/14/2018 02:43 PM »
Based on a request from a respected elder member of the forums, reopening, let's see how it goes.
"I think it would be great to be born on Earth and to die on Mars. Just hopefully not at the point of impact." -Elon Musk
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Offline Robotbeat

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Re: BFR with expendable upper stage
« Reply #43 on: 02/14/2018 02:49 PM »
Ah okay. Well how about for a one-off exploration probe to say Titan, for example? How much extra performance could you get out of an expendable upper stage?

Why?

Because BFS has a dry mass that cripples it for launching things to extreme energy trajectories. I buy that it is useful to Mars and maybe a little beyond. More than that and the final boost stage needs to go on a diet.
I think I agree with this. Even with launch costs of like, say, $3-5m for BFR, for very high energy trajectories that need a lot of refueling, a $10m solid kick stage could be cheaper. Also, some trajectories would be super hard to recover the BFS from, and you don't want to expend a BFS or send it on a 5 year mission just for a small outer planets orbiter or something.
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Offline John Alan

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Re: BFR with expendable upper stage
« Reply #44 on: 02/14/2018 03:51 PM »
My opinion...Once BFS comes on line...
The need for (like said above) a solid or IMHO Hypergolic (or hybrid with both working together) kick booster will better serve the needs of high energy missions...  ;)

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Re: BFR with expendable upper stage
« Reply #45 on: 02/14/2018 04:46 PM »
My view: The base BFS system can do a lot. It should (and will) be built first. As experience is gained, optimizations for certain types of missions will be found. These may be in the form of third stages carried in the cargo bay, or they may be in the form of on orbit vehicles like tugs, or in the form of specialty BFS (the tanker mk II is likely to be something weird looking, not sharing the OML of the rest of the BFS variants) . All of this specialization starts from the base BFS, not the other way round.

(the basic Model T was done first, and then Ford and others (aftermarket) elaborated it into trucks, buses, racing vehicles, the model TT heavy truck/bus chassis,  even tractors.. (that last was a rather poor idea but it WAS tried) )

Eventually we move from "missions" to "cargo runs" at least in the inner system, and missions don't always (or even usually) originate on earth, they start with cargo taken somewhere. Lewis and Clark didn't start from NYC.
« Last Edit: 02/14/2018 04:47 PM by Lar »
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"We're a little bit like the dog who caught the bus" - Musk after CRS-8 S1 successfully landed on ASDS OCISLY

Offline AC in NC

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Re: BFR with expendable upper stage
« Reply #46 on: 02/14/2018 05:40 PM »
It seems to me that many alternatives and requirements are being conflated here.  I would very much appreciate if we could differentiate what we are talking about.

BFR with ExUS to me says the part bolted on BFR.  I just don't ever see this being expendable.  I can't imagine the cost/benefit ever working out vs. working within the limitations of what you've already got with some other approach (refueling, on-orbit assembly, etc..).  There are just too many options with planned marginal launch cost.

BFS-Cargo taking up some payload with an expendable stage is a different matter.

Offline Michael Bloxham

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Re: BFR with expendable upper stage
« Reply #47 on: 02/14/2018 05:59 PM »
What about for a BFS that has come to the end of its service life. Say itís done 4 round trips to Mars - the TPS has worn out. So itís stripped down and launched as an expendable...?

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Re: BFR with expendable upper stage
« Reply #48 on: 02/14/2018 06:05 PM »
Expendable US for BFR defeats the objective as BFR is being designed for fully reusability. Expending any BFR hardware will dramatically increase it's cost per launch. Full reusability is what will give BFR extremely low launch costs.

"Full reusability" does not necessarily mean to only and always fly reusable second stages on BFR. If what you want to launch is something like a big space station module or some large module to land on the Moon, building a one-off second stage from parts or from a BFS near its end of life would be totally reasonable.

For one-way missions dragging a reusable stage with heat shield, landing engines, legs etc. all the way to the destination and back would be pointless.

Exactly! I could also imagine SpaceX wanting to retire their Block 1ís & 2ís this way, once they start flying Block 3ís & 4ís. Even 747ís retire eventually ;-)

Offline 1

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Re: BFR with expendable upper stage
« Reply #49 on: 02/14/2018 06:39 PM »
What about for a BFS that has come to the end of its service life. Say itís done 4 round trips to Mars - the TPS has worn out. So itís stripped down and launched as an expendable...?

You're probably better off landing it one last time and using it as a permanent habitat module on Mars; or even just for spare parts. I think one of Robobeat's previous points is worth exploring in greater detail.

A large expendable Mars lander still needs a huge heatshield. It still needs supersonic retropropulsion. It still needs landing thrusters. It still needs landing legs. You even still need large tanks on your trans Mars insertion stage.

Let's look at a breakdown of a couple recent missions. From wiki:

Mars Science Laboratory:
 -Cruise Stage: 539kg
 -Curiosity Rover: 889 kg
 -Entry-Decent-Landing system: 2401 kg
 
 -Total mass: 3893 kg

Mars Exploration Rovers:
 -Instruments: 5 kg
 -Propellant: 50 kg
 -Heat Shield: 78 kg
 -Rover: 185 kg
 -Cruise Stage: 193 kg
 -Backshell / Parachute: 209 kg
 -Lander: 348 kg
 
 -Total Mass: 1,063 kg

Schiaparelli:
 -rear heat shield: 20 kg
 -hydrazine: 45 kg
 -main heat shield: 80 kg
 -lander: 280 kg
 
 -Total Mass: 577 kg


Even for a relatively "simple" missions, it's clear that incorporating EDL gear comes at great cost to your mission payload, for lack of a better phrase. At best, if you abandon BFS's built-in EDL capabilityes, one half if your total payload will be "useful". At worst, perhaps one fifth. Expending BFS would need to result in at least twice as much payload as a refeuled BFS. Likely better to use an end-of-life BFS as payload.
   

Offline Norm38

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Re: BFR with expendable upper stage
« Reply #50 on: 02/19/2018 02:39 AM »
One of the main concerns made by the OP on the first page is large scale fuel production on Mars.  But there's no avoiding that. ISRU is needed to get crew back. We certainly won't be landing return fuel with expendables.
So there's little point coming up with Plan Bs for that. There is no plan B to large scale ISRU.

Offline AC in NC

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Re: BFR with expendable upper stage
« Reply #51 on: 02/19/2018 02:46 AM »
One of the main concerns made by the OP on the first page is large scale fuel production on Mars.  But there's no avoiding that. ISRU is needed to get crew back. We certainly won't be landing return fuel with expendables.
So there's little point coming up with Plan Bs for that. There is no plan B to large scale ISRU.

Pretty sure the OP wasn't interested in returning crew with that wide diameter low density lander.

Offline Norm38

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Re: BFR with expendable upper stage
« Reply #52 on: 02/19/2018 12:22 PM »
Is there a payload that needs that new lander?  Without crew, all we need for science is some orbiters and Curiosity sized rovers.

Also, I'm not worried about the first few BFS not coming back. It's not a waste, they're prototypes and SpaceX likes to iterate. The first few BFS build up the base. They're the ISRU plant, tanks, supplies, shelter. That's 4 ships right there that don't need return fuel, but do need to be the full configuration to test everything out. Using a new expendable lander configuration doesn't get us anywhere.
« Last Edit: 02/19/2018 02:21 PM by Norm38 »

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Re: BFR with expendable upper stage
« Reply #53 on: 02/24/2018 12:11 PM »
A striped down version of BFR described by the OP (no heat shield, extra raptor engines removed) makes perfect sense as a lunar lander to me. You could use it as the BFS prototype, then rather than dispose of it after testing launch it as the first BFS orbital flight, then use early full up cargo BFRs to demonstrate in orbit refueling to send it to the moon.

That way you turn early test flights and equipment to deliver new operational capabilities!
And this is a good reminder that just because one of your fellow space enthusiasts occasionally voices doubts about the SpaceX schedule announcements or is cautious about believing SpaceX has licked a problem before actually seeing proof that's true, it doesn't mean they hate SpaceX.

Offline Hotblack Desiato

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Re: BFR with expendable upper stage
« Reply #54 on: 03/20/2018 07:17 AM »
In my opinion, there is only one business case for an expendable upper stage for BFR:

A customer needs to get a massive monolithic payload into LEO (ballpark >300t), and is willing to pay for expending the stage. then a traditional upper stage makes sense.

But these customers will be very rare, especially since the BFR can already do monolithic payloads with 130-150t, and even if a 300t payload can't be split up in 2x150t, maybe it can be done at 3x150t.

So, SpaceX may not develop that stage because it's useless, and SpaceX already indicated that BFR will not be their biggest system. And suddenly, SX can do 300t reusable.

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Re: BFR with expendable upper stage
« Reply #55 on: 03/20/2018 01:27 PM »
I wonder... there's been talk in other threads about a design for an orbital tug with a single raptor-vac and BFS-style refuelig pipes. Could a variant tug of this sort put itself into orbit "expendably" as a replacement second stage, under a fairing, and be fueled up in orbit for orbital operations?

Offline Slarty1080

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Re: BFR with expendable upper stage
« Reply #56 on: 03/20/2018 02:26 PM »
In my opinion, there is only one business case for an expendable upper stage for BFR:

A customer needs to get a massive monolithic payload into LEO (ballpark >300t), and is willing to pay for expending the stage. then a traditional upper stage makes sense.

But these customers will be very rare, especially since the BFR can already do monolithic payloads with 130-150t, and even if a 300t payload can't be split up in 2x150t, maybe it can be done at 3x150t.

So, SpaceX may not develop that stage because it's useless, and SpaceX already indicated that BFR will not be their biggest system. And suddenly, SX can do 300t reusable.

I think this has been asked before, but it is relevant here, so I will ask again, why are SpaceX building the BFS before the BFR? Seems to me that a BFR might be of great use on its own with the ability to launch 140mt to LEO (with a disposable adaptor and shroud attached).
 
If BFR could be launched repeatedly, rapidly and cheaply it could eat the space launch market alive, earning a lot of money to fund BFS development. But developing BFS first means itís going to sit around until BFR is ready to launch it, which seems a waste. Obviously SpaceX must have thought about this a lot more carefully than me; I'm just interested in their reasoning.


 
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Offline RonM

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Re: BFR with expendable upper stage
« Reply #57 on: 03/20/2018 02:33 PM »
In my opinion, there is only one business case for an expendable upper stage for BFR:

A customer needs to get a massive monolithic payload into LEO (ballpark >300t), and is willing to pay for expending the stage. then a traditional upper stage makes sense.

But these customers will be very rare, especially since the BFR can already do monolithic payloads with 130-150t, and even if a 300t payload can't be split up in 2x150t, maybe it can be done at 3x150t.

So, SpaceX may not develop that stage because it's useless, and SpaceX already indicated that BFR will not be their biggest system. And suddenly, SX can do 300t reusable.

I think this has been asked before, but it is relevant here, so I will ask again, why are SpaceX building the BFS before the BFR? Seems to me that a BFR might be of great use on its own with the ability to launch 140mt to LEO (with a disposable adaptor and shroud attached).
 
If BFR could be launched repeatedly, rapidly and cheaply it could eat the space launch market alive, earning a lot of money to fund BFS development. But developing BFS first means itís going to sit around until BFR is ready to launch it, which seems a waste. Obviously SpaceX must have thought about this a lot more carefully than me; I'm just interested in their reasoning.

BFS is more of a technical challenge than BFR. If SpaceX can't get BFS to work the way they want then there is no need to build BFR.

Offline envy887

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Re: BFR with expendable upper stage
« Reply #58 on: 03/20/2018 02:45 PM »
In my opinion, there is only one business case for an expendable upper stage for BFR:

A customer needs to get a massive monolithic payload into LEO (ballpark >300t), and is willing to pay for expending the stage. then a traditional upper stage makes sense.

But these customers will be very rare, especially since the BFR can already do monolithic payloads with 130-150t, and even if a 300t payload can't be split up in 2x150t, maybe it can be done at 3x150t.

So, SpaceX may not develop that stage because it's useless, and SpaceX already indicated that BFR will not be their biggest system. And suddenly, SX can do 300t reusable.

I think this has been asked before, but it is relevant here, so I will ask again, why are SpaceX building the BFS before the BFR? Seems to me that a BFR might be of great use on its own with the ability to launch 140mt to LEO (with a disposable adaptor and shroud attached).
 
If BFR could be launched repeatedly, rapidly and cheaply it could eat the space launch market alive, earning a lot of money to fund BFS development. But developing BFS first means itís going to sit around until BFR is ready to launch it, which seems a waste. Obviously SpaceX must have thought about this a lot more carefully than me; I'm just interested in their reasoning.

BFR (the booster) can't launch 140 tonnes to orbit without an upper stage (like BFS). It could maybe launch 30 tonnes, but it would be expendable itself, and be far more expensive than a FH launch of the same mass.

BFR (the booster) with an expendable upper stage like the Falcon 9 upper stage could launch perhaps 100 tonnes to orbit, with a booster landing. However, this would require a lot of pad configuration for a system not intended to be operational for long.

BFR (the booster) with a large expendable Raptor upper stage (similar to New Glenn's 2nd stage) could launch perhaps 200 tonnes with booster reuse. But the expended upper stage would be quite expensive, and the overall utility of the system is questionable compared to the fully reusable BFR/BFS. There are no customers with 200 tonne payloads willing to pay that much, and FH can meet all existing payload requirements at a lower price.

The only system that is a notable improvement over F9/FH is one that is fully reusable.

Offline speedevil

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Re: BFR with expendable upper stage
« Reply #59 on: 03/20/2018 03:13 PM »
If BFR could be launched repeatedly, rapidly and cheaply it could eat the space launch market alive, earning a lot of money to fund BFS development. But developing BFS first means itís going to sit around until BFR is ready to launch it, which seems a waste. Obviously SpaceX must have thought about this a lot more carefully than me; I'm just interested in their reasoning.

The above assumes implicitly several things that may not be true.
* F9/H is not already capable of eating the market alive, especially with reduced costs with block 5, and reusability of fairings and other components.
The initial figure given way back when was that S1 was 60% of the stage cost, making S2 somewhere in the range of 20 million dollars without the fairing.

I am unsure if they have published more recently than that on the cost of S2s.
It's not unreasonable to suspect it might be considerably lower.

* There is no value in repeated F9/H launches that may transfer over to BFS/R operations.
At least some aspects - payload preparation, launch licences, ... are going to be similar, and these set a limiting cadence to BFR/S operations.
* BFS can't do anything without BFR.
Depending on questionable assumptions, it is at least somewhat plausible that BFS-SSTO can launch a large fraction of satellites, with the aid of in-orbit refuelling. BFS - without BFR eats the launch market.

* There is no 'political' value for SpaceX in delaying the apparent likely launch date of BFR/S.
Developing BFS up until they believe it is orbital-capable can be undersold as 'just tests', leading others to be able to insist to themselves it's not happening, and that full up-launches, for which they need to develop BFR anyway is still some years off.
Why they might be doing this is unclear. It could be for example that they want others considering entering the market to do so now, in the knowledge that they can kill them in several years, rather than to invent plans which might actually work in the face of BFR (I don't believe this one).

* More money would help the development effort.
At some point, if you've got a good team that works well together, and enough equipment, adding more people and equipment may not actually make stuff go faster - at least in a sustainable manner.
Being able to go out and buy subassemblies may mean you'd later need to develop that again internally, and face requalifying the systems they interact with.

* The architecture we saw at IAC2017 is still accurate.
Some of the speculation I did in the above mentioned thread was of a BFS-in-air refuelling. This is at least somewhat plausible, and would enable much, much greater capability for BFS without BFR.


Do I believe all of the above are false - no.
Do I know which - if any are actually true - no.

« Last Edit: 03/20/2018 03:39 PM by speedevil »

Offline Slarty1080

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Re: BFR with expendable upper stage
« Reply #60 on: 03/20/2018 06:12 PM »
If BFR could be launched repeatedly, rapidly and cheaply it could eat the space launch market alive, earning a lot of money to fund BFS development. But developing BFS first means itís going to sit around until BFR is ready to launch it, which seems a waste. Obviously SpaceX must have thought about this a lot more carefully than me; I'm just interested in their reasoning.

The above assumes implicitly several things that may not be true.
* F9/H is not already capable of eating the market alive, especially with reduced costs with block 5, and reusability of fairings and other components.
The initial figure given way back when was that S1 was 60% of the stage cost, making S2 somewhere in the range of 20 million dollars without the fairing.

I am unsure if they have published more recently than that on the cost of S2s.
It's not unreasonable to suspect it might be considerably lower.

* There is no value in repeated F9/H launches that may transfer over to BFS/R operations.
At least some aspects - payload preparation, launch licences, ... are going to be similar, and these set a limiting cadence to BFR/S operations.

* BFS can't do anything without BFR.
Depending on questionable assumptions, it is at least somewhat plausible that BFS-SSTO can launch a large fraction of satellites, with the aid of in-orbit refuelling. BFS - without BFR eats the launch market.

* There is no 'political' value for SpaceX in delaying the apparent likely launch date of BFR/S.
Developing BFS up until they believe it is orbital-capable can be undersold as 'just tests', leading others to be able to insist to themselves it's not happening, and that full up-launches, for which they need to develop BFR anyway is still some years off.
Why they might be doing this is unclear. It could be for example that they want others considering entering the market to do so now, in the knowledge that they can kill them in several years, rather than to invent plans which might actually work in the face of BFR (I don't believe this one).

* More money would help the development effort.
At some point, if you've got a good team that works well together, and enough equipment, adding more people and equipment may not actually make stuff go faster - at least in a sustainable manner.
Being able to go out and buy subassemblies may mean you'd later need to develop that again internally, and face requalifying the systems they interact with.

* The architecture we saw at IAC2017 is still accurate.
Some of the speculation I did in the above mentioned thread was of a BFS-in-air refuelling. This is at least somewhat plausible, and would enable much, much greater capability for BFS without BFR.

Do I believe all of the above are false - no.
Do I know which - if any are actually true - no.

that was an interesting thread.
People were talking about what BFS might be able to do on its own. BFR must be much more capable than BFS as it doesn't have all the cargo decks etc.

Also it mentioned that the IAC2017 architecture is no longer accurate (extra engine added to BFS):
https://www.reddit.com/r/space/comments/76e79c/i_am_elon_musk_ask_me_anything_about_bfr/dodcg22/
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Offline envy887

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Re: BFR with expendable upper stage
« Reply #61 on: 03/20/2018 06:28 PM »

Offline JamesH65

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Re: BFR with expendable upper stage
« Reply #62 on: 03/21/2018 03:52 PM »
How can BFR refer to two distinct things?

Surely BFB and BFS as individual items, BFR (or even BFx) should refer to the whole stack?

Offline speedevil

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Re: BFR with expendable upper stage
« Reply #63 on: 03/21/2018 03:56 PM »
How can BFR refer to two distinct things?

Surely BFB and BFS as individual items, BFR (or even BFx) should refer to the whole stack?

Yes, it should.
It would be very nice if it did, however Elon does not use these terms precisely, and there is no better one that has come up.
Unfortunately, BFR is ambiguous, and may refer to both, or only the booster.
I tend to - when I remember use BFR (the booster) the first time in a post, then BFR/BFS.

Offline envy887

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Re: BFR with expendable upper stage
« Reply #64 on: 03/21/2018 04:37 PM »
How can BFR refer to two distinct things?

Surely BFB and BFS as individual items, BFR (or even BFx) should refer to the whole stack?

We're talking about SpaceX. Consistent naming convention is not their strong suit, unfortunately.

Offline alexterrell

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Re: BFR with expendable upper stage
« Reply #65 on: 03/21/2018 05:19 PM »
In my opinion, there is only one business case for an expendable upper stage for BFR:

A customer needs to get a massive monolithic payload into LEO (ballpark >300t), and is willing to pay for expending the stage. then a traditional upper stage makes sense.

But these customers will be very rare, especially since the BFR can already do monolithic payloads with 130-150t, and even if a 300t payload can't be split up in 2x150t, maybe it can be done at 3x150t.

So, SpaceX may not develop that stage because it's useless, and SpaceX already indicated that BFR will not be their biggest system. And suddenly, SX can do 300t reusable.
If the customer wanted an all in one starter moonbase, they could launch a BFS without the wings and TPS, land it on the moon, and it stays there?

But I'm not really sure the benefits - saving 20-30 tons isn't really worth it. I suppose the Raptor engines could be unbolted and returned at some point in the future.

The only other monolithic payloads are pressure domes. The mass of these increases in proportion to the volume. If someone wants a 200m diameter pressure vessel to make a base, that could need 200 tons. But it would also be too large for the lunar lander.

So we're back to standard BFS, and the only issue I can see with that is the apparently small door - when many payloads launched these days are 5m in diameter.
« Last Edit: 03/21/2018 05:20 PM by alexterrell »

Offline TrevorMonty

Re: BFR with expendable upper stage
« Reply #66 on: 03/21/2018 05:33 PM »
A single raptor expendable US could be useful for BLEO missions, especially if is refuelled by single tanker launch. Spacex take on ULA DL. Should be good for about 50t, with 150t topup.

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Re: BFR with expendable upper stage
« Reply #67 on: 03/21/2018 06:52 PM »
A single raptor expendable US could be useful for BLEO missions, especially if is refuelled by single tanker launch. Spacex take on ULA DL. Should be good for about 50t, with 150t topup.

Yup. As much as the BFR architecture is being sold as "do anything, just refuel more," its biggest weakness is sending a few tonnes to very high delta-V trajectories. Something with much much less dry mass would be better.

I think the other weakness that has been minimized by a little Elon slight of hand is that the economics of reusability really only apply for earth orbit. Send a BFS beyond Mars orbit and you have basically expended it. By the time it comes back it will be obsolete.

Offline envy887

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Re: BFR with expendable upper stage
« Reply #68 on: 03/21/2018 07:12 PM »
A single raptor expendable US could be useful for BLEO missions, especially if is refuelled by single tanker launch. Spacex take on ULA DL. Should be good for about 50t, with 150t topup.

Yup. As much as the BFR architecture is being sold as "do anything, just refuel more," its biggest weakness is sending a few tonnes to very high delta-V trajectories. Something with much much less dry mass would be better.

I think the other weakness that has been minimized by a little Elon slight of hand is that the economics of reusability really only apply for earth orbit. Send a BFS beyond Mars orbit and you have basically expended it. By the time it comes back it will be obsolete.

If there is a demand for very high energy trajectories, it might be worthwhile to develop another stage. But BFS is designed to minimize costs to LEO, GTO, the Moon, and Mars - not high energy trajectories.

For the very low number of high energy payloads, the cost of expending a BFS (especially a flight proven one) is not a major barrier. Europa Clipper, for example, is expected to use SLS Block 1B, at around a billion dollars for the launch. A fully refueled, stripped down, and expended BFS would be a about a quarter of that and offer a much larger mass or a higher C3.

Alternately, there are several ways to put a payload on Earth escape trajectory without having the BFS itself escape, including lunar gravity assists and aerobraking.

Offline speedevil

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Re: BFR with expendable upper stage
« Reply #69 on: 03/21/2018 07:17 PM »
A single raptor expendable US could be useful for BLEO missions, especially if is refuelled by single tanker launch. Spacex take on ULA DL. Should be good for about 50t, with 150t topup.

Yup. As much as the BFR architecture is being sold as "do anything, just refuel more," its biggest weakness is sending a few tonnes to very high delta-V trajectories. Something with much much less dry mass would be better.
Depends how much you believe fuel is cheap.

Refuel in LEO, and you can throw some tens of tons to 6km/s over LEO (ending up in an orbit you have barely enough fuel to burn back to an earth capture orbit some hours later).
Start out in GTO, (requiring twelve launches, filling two upper stages in LEO), and it's more like 8.5.



Offline envy887

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Re: BFR with expendable upper stage
« Reply #70 on: 03/21/2018 07:40 PM »
A single raptor expendable US could be useful for BLEO missions, especially if is refuelled by single tanker launch. Spacex take on ULA DL. Should be good for about 50t, with 150t topup.

Yup. As much as the BFR architecture is being sold as "do anything, just refuel more," its biggest weakness is sending a few tonnes to very high delta-V trajectories. Something with much much less dry mass would be better.
Depends how much you believe fuel is cheap.

Refuel in LEO, and you can throw some tens of tons to 6km/s over LEO (ending up in an orbit you have barely enough fuel to burn back to an earth capture orbit some hours later).
Start out in GTO, (requiring twelve launches, filling two upper stages in LEO), and it's more like 8.5.

Or fully refuel in LEO, burn to elliptical Earth orbit (e.g. GTO or similar) with a ~120 km perigee, wait one orbit, do the escape burn just before perigee, then sep the payload and do a sideways burn to drop to 70 km where there is enough atmosphere to slow back down and not escape. This gets 15 tonnes to about LEO+8500 m/s (almost enough for solar escape) without the BFS ever getting any further away than GEO.
« Last Edit: 03/21/2018 07:40 PM by envy887 »

Offline philw1776

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Re: BFR with expendable upper stage
« Reply #71 on: 03/21/2018 07:43 PM »
A single raptor expendable US could be useful for BLEO missions, especially if is refuelled by single tanker launch. Spacex take on ULA DL. Should be good for about 50t, with 150t topup.

If SpaceX were to develop a single Raptor expendable US for BLEO, make it in the profile for launch on the F9 or FH.
A Europa or Titan mission would see that F9 Raptor US refueled in LEO by a BFS and the refueled US would outperform the SLS at a fraction of the cost.

Heading into Kerbal territory, the BFS could add on side strapped propellant tanks (crossfeed zombie rises again) for a real high C3 launch.

If you're gonna do expendable, do an inexpensive Falcon class launched Raptor expendable enhanced by LEO refueling.
« Last Edit: 03/21/2018 07:45 PM by philw1776 »
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Offline acsawdey

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Re: BFR with expendable upper stage
« Reply #72 on: 03/21/2018 07:50 PM »
A single raptor expendable US could be useful for BLEO missions, especially if is refuelled by single tanker launch. Spacex take on ULA DL. Should be good for about 50t, with 150t topup.

If SpaceX were to develop a single Raptor expendable US for BLEO, make it in the profile for launch on the F9 or FH.
A Europa or Titan mission would see that F9 Raptor US refueled in LEO by a BFS and the refueled US would outperform the SLS at a fraction of the cost.

Heading into Kerbal territory, the BFS could add on side strapped propellant tanks (crossfeed zombie rises again) for a real high C3 launch.

If you're gonna do expendable, do an inexpensive Falcon class launched Raptor expendable enhanced by LEO refueling.

If you have BFR/BFS, why bother making a stage that can launch with F9S1? Why not just bring it up as BFS cargo unfueled, then refuel it and send it on it's way. Then you don't need aerodynamics at all and it can just be a bundle of tanks and struts with a raptor at the back, payload at the front, and a BFS compatible fueling port.

Offline Robotbeat

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Re: BFR with expendable upper stage
« Reply #73 on: 03/21/2018 11:18 PM »
How can BFR refer to two distinct things?

Surely BFB and BFS as individual items, BFR (or even BFx) should refer to the whole stack?

Yes, it should.
It would be very nice if it did, however Elon does not use these terms precisely, and there is no better one that has come up.
Unfortunately, BFR is ambiguous, and may refer to both, or only the booster.
I tend to - when I remember use BFR (the booster) the first time in a post, then BFR/BFS.
I donít believe this is correct. You remember incorrectly. BFR has consistently referred to the stack, with BFB now being used for the booster, and BFS always for the spaceship.
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Offline QuantumG

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Re: BFR with expendable upper stage
« Reply #74 on: 03/21/2018 11:33 PM »
I donít believe this is correct. You remember incorrectly. BFR has consistently referred to the stack, with BFB now being used for the booster, and BFS always for the spaceship.

Hey, where's the first use of BFB? I didn't see it in the 2007 IAC, was it in there?
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Offline RonM

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Re: BFR with expendable upper stage
« Reply #75 on: 03/21/2018 11:51 PM »
I donít believe this is correct. You remember incorrectly. BFR has consistently referred to the stack, with BFB now being used for the booster, and BFS always for the spaceship.

Hey, where's the first use of BFB? I didn't see it in the 2007 IAC, was it in there?

On this site, I think this week.

Offline Robotbeat

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Re: BFR with expendable upper stage
« Reply #76 on: 03/22/2018 01:15 AM »
I don’t believe this is correct. You remember incorrectly. BFR has consistently referred to the stack, with BFB now being used for the booster, and BFS always for the spaceship.

Hey, where's the first use of BFB? I didn't see it in the 2007 IAC, was it in there?

On this site, I think this week.
No, earlier and by SpaceX, I believe. Definitely not this week.

EDIT: Here’s a post by Waitbutwhy using BFB in 2016. Not SpaceX, but did get correspondence (and maybe approval?) with Elon: https://waitbutwhy.com/2016/09/spacexs-big-fking-rocket-the-full-story.html

...and I do believe there is a more recent use of SpaceX themselves using it. Elon, I think.
« Last Edit: 03/22/2018 01:18 AM by Robotbeat »
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Offline QuantumG

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Re: BFR with expendable upper stage
« Reply #77 on: 03/22/2018 02:35 AM »
...and I do believe there is a more recent use of SpaceX themselves using it. Elon, I think.

If you can de-vague that I'll consider it canon (until Elon just makes up some other words), but I think most of us have been using BFS/BFR.
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Offline Robotbeat

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Re: BFR with expendable upper stage
« Reply #78 on: 03/22/2018 03:47 AM »
...and I do believe there is a more recent use of SpaceX themselves using it. Elon, I think.

If you can de-vague that I'll consider it canon (until Elon just makes up some other words), but I think most of us have been using BFS/BFR.
I think Musk said it in some video since the start of the year, but I am a little too intimidated to look through all of them. It also may have been Shotwell.

But i strongly disagree that /most/ people were calling just the /booster/ "BFR." I think most were referring to it by "booster."

BFB is definitely superior and clearer terminology than calling BFR just a piece of BFR. Like, that makes no sense. BFR is clearly the whole rocket, not just the booster.
« Last Edit: 03/22/2018 03:49 AM by Robotbeat »
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Offline Robotbeat

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Re: BFR with expendable upper stage
« Reply #79 on: 03/22/2018 03:57 AM »
Or it could also be "BRB"...

...QuantumG is right that Elon sure likes to mess with terminology.

But can we all just call it: BFS + BFB = BFR for now??

EDIT: here's the evidence of Musk calling it BRB:
https://www.reddit.com/r/SpaceXLounge/comments/7vl7j4/qa_elon_musk_discusses_the_launch_and_flight_of/
« Last Edit: 03/22/2018 04:00 AM by Robotbeat »
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Offline speedevil

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Re: BFR with expendable upper stage
« Reply #80 on: 03/22/2018 04:13 AM »
Or it could also be "BRB"...

...QuantumG is right that Elon sure likes to mess with terminology.

But can we all just call it: BFS + BFB = BFR for now??

EDIT: here's the evidence of Musk calling it BRB:
https://www.reddit.com/r/SpaceXLounge/comments/7vl7j4/qa_elon_musk_discusses_the_launch_and_flight_of/

The only thing he is consistent with is inconsistency.
I think trying to come to a firm conclusion of what the booster is 'really' called, is basically pointless.
Even forgetting the whole "big freaking rocket"/falcon/you know what really/F(unvoiced)/ ... thing he's got going on.

It's probably written down somewhere, but he says whatever amuses him at the moment, and assuming that the components change name every time he comes up with something else off the cuff is just as confusing.
It'll probably all be finally answered when there is a BFR user guide.


Offline QuantumG

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Re: BFR with expendable upper stage
« Reply #81 on: 03/22/2018 04:14 AM »
BRB
I hear those things are awfully loud. It glides as softly as a cloud. What's it called? Monowhale!

Offline Nomadd

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Re: BFR with expendable upper stage
« Reply #82 on: 03/22/2018 04:24 AM »
Stop making such a BFD out of the name.

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Re: BFR with expendable upper stage
« Reply #83 on: 03/22/2018 07:05 PM »
Hey, where's the first use of BFB? I didn't see it in the 2007 IAC, was it in there?
I am pretty sure it wasn't at the 2007 IAC, that was well before the first Falcon XX renders... :)
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Offline docmordrid

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Re: BFR with expendable upper stage
« Reply #84 on: 03/23/2018 12:59 AM »
Just to end this Musk used the term  "BF Booster," BFB, in the 2017 Reddit AMA. IMO the first use is irrelevant, this is recent. He also said it'll be a full size vehicle.

Quote
Will be starting with a full-scale Ship doing short hops of a few hundred kilometers altitude and lateral distance. Those are fairly easy on the vehicle, as no heat shield is needed, we can have a large amount of reserve propellant and don't need the high area ratio, deep space Raptor engines.

Next step will be doing orbital velocity Ship flights, which will need all of the above. Worth noting that BFS is capable of reaching orbit by itself with low payload, but having the BF Booster increases payload by more than an order of magnitude. Earth is the wrong planet for single stage to orbit. No problemo on Mars.
« Last Edit: 03/23/2018 01:04 AM by docmordrid »
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Offline TomH

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Re: BFR with expendable upper stage
« Reply #85 on: 03/23/2018 11:11 PM »
Alright, if you really want a disposable upper stage for BFR, there does exist one single scenario in which it could possibly make sense. It's never going to happen, and rockets are not legos, but here is the single way it could be made to happen.

SLS is going to be surpassed by BFR/BFS' capacity, but the entrenched interests may still insist that the pork keeps flowing to those states and districts. It obviously will look more and more like a waste of money. After EM-1 flies, the stream of new funding continues to EUS, tower renovations, RS-25E, then Dark Knight boosters. More money after more money, after more money, and all that still doesn't come close to BFR/S capacity.

If the powers that be simply refuse to let go of SLS, how can they make the thing productive, yet avoid all those costs?

I broached this in another thread after the 12 m ITS was revealed. With the BFR/S now at 9m, the idea might be slightly more reasonable. If NASA were to put J-2X engines on the SLS core, strengthen the core, forget EUS and Dark Knights, then pay Space X to put this thing on top of BFR  with BFR as a booster, you'd have an immensely capable disposable upper stage. You could still put iCPS on top of that if you wanted to. Let it launch from LC 39A. No transporter, no tower mods, no RS-25E, no Dark Knights. BFR does RTLS, NASA pays SpaceX, pork still flows to the same places (except Utah), the ultimate SLS expenditure is lower, the capability is higher, and everybody can say NASA is doing something.

I know, lots of issues exist, it's never going to happen, but if you absolutely demand an expendable US for BFB, this is a way that it could be done.
« Last Edit: 03/23/2018 11:14 PM by TomH »

Offline Hotblack Desiato

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Re: BFR with expendable upper stage
« Reply #86 on: 03/24/2018 10:01 PM »
A single raptor expendable US could be useful for BLEO missions, especially if is refuelled by single tanker launch. Spacex take on ULA DL. Should be good for about 50t, with 150t topup.

If SpaceX were to develop a single Raptor expendable US for BLEO, make it in the profile for launch on the F9 or FH.
A Europa or Titan mission would see that F9 Raptor US refueled in LEO by a BFS and the refueled US would outperform the SLS at a fraction of the cost.

Heading into Kerbal territory, the BFS could add on side strapped propellant tanks (crossfeed zombie rises again) for a real high C3 launch.

If you're gonna do expendable, do an inexpensive Falcon class launched Raptor expendable enhanced by LEO refueling.

You could go even more kerbal.

Use BFB (if that is the name that should be used) to push a single or dual raptor US with a really heavy payload into LEO. That US should have the same refuelling mounts as the BFS. Launch some tankers, refuel it, and load fuel into the payload (many interplanetary probes consist of a large portion of fuel, that should be tankable aswell).

Then, I don't see any obstacles why the interplanetary probe shouldn't be at a mass of 200t or even more (with an extra several hundred tons of fuel).

Offline Bob Shaw

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Re: BFR with expendable upper stage
« Reply #87 on: 03/24/2018 11:02 PM »
Alright, if you really want a disposable upper stage for BFR, there does exist one single scenario in which it could possibly make sense. It's never going to happen, and rockets are not legos, but here is the single way it could be made to happen.


'Rockets are not legos' is an out-of-date notion which was never really true...

Look at F9H - three F9s bolted together in the best Kerbal tradition. Or Aries 1. Or SLS - STS components bolted onto tankage, with a stretched pre-existing upper stage. Or Orion plus an ATV. Or Energia plus the still=flying boosters. Or the second lives of the Soviet Luna stages, or the NI third stage. Or Saturn 1B's second stage, AKS the Saturn V third stage and, in passing, a space station.

Rockets and spacecraft regularly get put together using pre-existing components, some major and some minor.
« Last Edit: 03/24/2018 11:02 PM by Bob Shaw »

Offline Robotbeat

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Re: BFR with expendable upper stage
« Reply #88 on: 03/25/2018 02:23 AM »
Actually, FH kinda illustrates why rockets aren't legos: the core had to be significantly strengthened. Legos are supposed to be interchangeable.

(I swear to Goddard, Lar, you better not change that to "elements".)
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Offline john smith 19

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Re: BFR with expendable upper stage
« Reply #89 on: 03/25/2018 08:03 AM »
'Rockets are not legos' is an out-of-date notion which was never really true...
Except among people who build actual rockets, when it is. :(

Quote from: Bob Shaw
Look at F9H - three F9s bolted together in the best Kerbal tradition.
Except Musk said the core FH booster is not a stock F9 first stage. It's a special build. Extra strong to resist the side loads. It'll be interesting to see what effect that will have on payload, but we won't know till they manage a successful recovery of an FH core.
Quote from: Bob Shaw
Or Aries 1.
Whose only flight (as Ares 1-x) was a 4 segment SRB witha dummy 5th segment and a completely dummy US? The one with the serious vibration issues, but they were "probably" due to it not being a real full 5 segment SRB?
Quote from: Bob Shaw
Or SLS - STS components bolted onto tankage, with a stretched pre-existing upper stage.
For very loose value of "Shuttle derived." IE with the entire tank structure built to hold the SRB design, as mandated by the SRB mfg. "Lego" implies all are existing stages. What you're talking about is (loosely) called "coach building."
Quote from: Bob Shaw
Or Orion plus an ATV.
Again. Not an ATV. New build hardware loosely based on the ATV.
Quote from: Bob Shaw
Rockets and spacecraft regularly get put together using pre-existing components, some major and some minor.
Actually the best examples would probably be the Centaur and Agena US's that were "re-hosted" on various buses (Agena launched 300+ times, yet is barely remembered today  :( )

So vehicles are put together with some pre existing components and the rest is heavily bespoke to fit them. Both their strengths and their weaknesses (which for solid fuel SRB's are substantial).
Which of course raises the question "At what point do the (supposed) benefits of using this existing stage get outweighed by the PITAness of fitting all the other bits around it?"

But IRL sticking (more or less) any stage to any stage is nonsense.
« Last Edit: 03/25/2018 08:03 AM by john smith 19 »
BFS. The worlds first Methane fueled FFORSC engined CFRP structured A380 sized aerospaceplane tail sitter capable of flying in Earth and Mars atmospheres. BFR. The worlds biggest Methane fueled FFORSC engined CFRP structured booster for BFS. First flight to Mars by end of 2022. Forward looking statements. T&C apply. Believe no one. Run your own numbers. So, you are going to Mars to start a better life? Picture it in your mind. Now say what it is out loud.

Offline RyanC

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Re: BFR with expendable upper stage
« Reply #90 on: 03/25/2018 01:41 PM »
There's no reason to develop an expendable upper stage -- just wait until the first three BFS built reaches their (realistic) lifetime limit -- while they may have designed it for airline operations with hundreds of flights, they'll retire the first couple built early:

first one likely goes to a museum near Hawthorne after an intensive study through non destructive methods.

second probably is torn apart in a hangar near the launch site and everything studied.

that leaves the third -- you can just strip off all the extraneous stuff you don't need anymore and expend it to orbit.

Because those first BFS are going to be not as good as the later "Mark II BFS".

Think the difference between Columbia and the second round of shuttles, which were 3600 (Discovery) to 3963 (Endeavour) kg lighter than Columbia.

« Last Edit: 03/25/2018 01:41 PM by RyanC »

Offline john smith 19

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Re: BFR with expendable upper stage
« Reply #91 on: 03/25/2018 09:17 PM »
There's no reason to develop an expendable upper stage -- just wait until the first three BFS built reaches their (realistic) lifetime limit -- while they may have designed it for airline operations with hundreds of flights, they'll retire the first couple built early:
An expendable BFS is basically a BFS - all the human support parts and recovery systems and Mars flight systems

Ideally that means the wings (never coming back), most (all?) of the TPS, radiators, PV arrays for Mars, although how much of that would have been installed for a regular cargo BFS is debatable.
BFS. The worlds first Methane fueled FFORSC engined CFRP structured A380 sized aerospaceplane tail sitter capable of flying in Earth and Mars atmospheres. BFR. The worlds biggest Methane fueled FFORSC engined CFRP structured booster for BFS. First flight to Mars by end of 2022. Forward looking statements. T&C apply. Believe no one. Run your own numbers. So, you are going to Mars to start a better life? Picture it in your mind. Now say what it is out loud.

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Re: BFR with expendable upper stage
« Reply #92 on: 04/12/2018 10:13 PM »
Why couldn't SpaceX have an expendable upper stage by leaving off the winglets, landing legs, sea level Raptors, heat shielding, and docking/refueling equipment?  Then it is just an upper stage with a capability of probably 200 tons to LEO or a huge 3rd stage/deep space probe. 

SpaceX would probably only do this if NASA needed something that large or a huge Bigelow module.  Mostly just a specialty stage used only once a year or so.  It would probably still be less than SLS in a cost/kg. 
« Last Edit: 04/12/2018 10:16 PM by spacenut »

Offline AC in NC

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Re: BFR with expendable upper stage
« Reply #93 on: 04/12/2018 11:02 PM »
Why couldn't SpaceX have an expendable upper stage by leaving off the winglets, landing legs, sea level Raptors, heat shielding, and docking/refueling equipment?  Then it is just an upper stage with a capability of probably 200 tons to LEO or a huge 3rd stage/deep space probe.

Of course they could.  But it just doesn't make a lot of sense vs. the alternative(s).

Offline whitelancer64

Re: BFR with expendable upper stage
« Reply #94 on: 04/12/2018 11:02 PM »
Why couldn't SpaceX have an expendable upper stage by leaving off the winglets, landing legs, sea level Raptors, heat shielding, and docking/refueling equipment?  Then it is just an upper stage with a capability of probably 200 tons to LEO or a huge 3rd stage/deep space probe. 

SpaceX would probably only do this if NASA needed something that large or a huge Bigelow module.  Mostly just a specialty stage used only once a year or so.  It would probably still be less than SLS in a cost/kg.

They could do that, but it would mean reworking most of the BFS design to build it. It would effectively be something they'd have to design and build from scratch.
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Offline yokem55

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Re: BFR with expendable upper stage
« Reply #95 on: 04/13/2018 12:17 AM »
Why couldn't SpaceX have an expendable upper stage by leaving off the winglets, landing legs, sea level Raptors, heat shielding, and docking/refueling equipment?  Then it is just an upper stage with a capability of probably 200 tons to LEO or a huge 3rd stage/deep space probe. 

SpaceX would probably only do this if NASA needed something that large or a huge Bigelow module.  Mostly just a specialty stage used only once a year or so.  It would probably still be less than SLS in a cost/kg.

They could do that, but it would mean reworking most of the BFS design to build it. It would effectively be something they'd have to design and build from scratch.
How much of a redesign is it to take things off or strip down an existing design? I suppose they might want to design/build a 9m fairing and payload interface. But otherwise, how much different is it when you are just taking away peices of an existing design?

Offline AncientU

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Re: BFR with expendable upper stage
« Reply #96 on: 04/13/2018 12:24 AM »
Why couldn't SpaceX have an expendable upper stage by leaving off the winglets, landing legs, sea level Raptors, heat shielding, and docking/refueling equipment?  Then it is just an upper stage with a capability of probably 200 tons to LEO or a huge 3rd stage/deep space probe. 

SpaceX would probably only do this if NASA needed something that large or a huge Bigelow module.  Mostly just a specialty stage used only once a year or so.  It would probably still be less than SLS in a cost/kg.

They could do that, but it would mean reworking most of the BFS design to build it. It would effectively be something they'd have to design and build from scratch.

Not hardly 'from scratch.'  They would have tankage, though shorter tanks probably would be used.  No inner/landing tanks, no shielding, many fewer engines (maybe 1-2), but same vacuum engine(s).  A large fairing would be a challenge, but no new technology.  Avionics, etc simple derivation from what they've done.

Say someone needed to loft something massing a hundred tonnes and fluffy in mid-2020s or beyond like UVOIR, or 15 tonnes destined for Jovian system...  the cost for this stage would be a pittance compared to these multi-billion dollar payloads.
« Last Edit: 04/13/2018 12:25 AM by AncientU »
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Offline speedevil

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Re: BFR with expendable upper stage
« Reply #97 on: 04/13/2018 12:32 AM »
Say someone needed to loft something massing a hundred tonnes and fluffy in mid-2020s or beyond like UVOIR, or 15 tonnes destined for Jovian system...  the cost for this stage would be a pittance compared to these multi-billion dollar payloads.
15 tons to Jupiter - the upper stage also needs to be cheaper than refuelling.

Offline guckyfan

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Re: BFR with expendable upper stage
« Reply #98 on: 04/13/2018 07:45 AM »
I wonder if it would be possible to get rid of the whole cargo bay outer hull once in orbit. Like shedding the fairing. It would make the T/W ratio a lot better and increase available delta-v for very high energy trajectories to the outer solar system.

Offline speedevil

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Re: BFR with expendable upper stage
« Reply #99 on: 04/13/2018 08:05 AM »
I wonder if it would be possible to get rid of the whole cargo bay outer hull once in orbit. Like shedding the fairing. It would make the T/W ratio a lot better and increase available delta-v for very high energy trajectories to the outer solar system.

If you've got a winding machine and raptors, it's likely going to be cheaper just to stick one raptor (or perhaps even one methalox GOX 1 ton thruster) on a five hundred ton capacity tank you take up empty, tank that full, and then kick it off.

Five tons, not 60 dead-weight.

Refuelling also is great.
If you start out refuelled in GTO, burn till near empty towards earth, you can release the payload just before perigee, do a light and very, very hot aerobrake, then moderate burn so a tanker can catch you, and get around 50 tons to 10km/s over LEO.

Without such exotics, you can throw 600 tons at Mars from a fully refuelled BFS in LEO, that then burns back to recover.

Offline Hotblack Desiato

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Re: BFR with expendable upper stage
« Reply #100 on: 04/13/2018 09:26 AM »
Just a funny idea:

How about going the ACES-route with a quasi-expendable upper stage?

The use-case would be: heavy payload needs to go to a destination in the solar-system that will take up to a decade to go to (some outer planets), a location where you don't want to send a BFS to, since that would mean expending the BFS.

BFR + US + payload launches (no sealevel-engines, only a thin heatshield or no heatshield at all, but long term flight hardware, no life support, regular fairing, expendable or not etc). In LEO, tankers start refuelling the US, and then the US departs to whereever the payload has to go (or if the payload is even heavier, after refuelling, go to a highly elliptical orbit, like that refuelling-trajectory announced for moon-landings).

Advantage of that system: it has every benefit from LEO-refuelling, and yet there is no BFS that will likely never return to earth anyways.

The US even could return to earth, perform aerocapturing but then remains in orbit.

Or it could serve as a fuel depot somewhere.

alternatives to that: 2-3 BFS + a few tankers launch to a highly elliptical orbit, one contains a kickstage, the other one contains the payload, and that gets refuelled. BFS + tankers then return home, payload + kickstage goes off into deep space.

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