Author Topic: BFR or BFS first or both?  (Read 8560 times)

Online JamesH65

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Re: BFR or BFS first or both?
« Reply #20 on: 01/03/2018 09:59 AM »
The big thing for BFR is the launch cradle.

Yes.

By contrast, for BFS, they would just need some flat concrete to launch and land it, someplace where they'll allow it, and somewhere near an ocean port, something like Landing Zone 1.

I'm expecting the first BFR to have legs, as grasshopper did, until they get its landing accuracy good enough. Seems like a big ask to get the whole cradle thing working right from the initial prototype stage.

Offline Robotbeat

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Re: BFR or BFS first or both?
« Reply #21 on: 01/03/2018 12:49 PM »
The cradle not working out would not be a deal killer in fact I think it's kinda a bad idea as it increases the risk of a mishap destroying the launch facilities.

A botched landing of BFR with a separate landing site you only loose the vehicle but a botch landing with the cradle you damage the launch facilities.

Inclined to agree.

SpaceX /could/ design a level of resilience for a shared launch+landing mount. Perhaps a modular cradle, ready to be swapped out in the event of an unexpectedly crunchy landing. But still, if a tipsy booster bumps the tower then your launch campaign is well and screwed.

Returning to a dedicated landing pad risks so much less, and costs... well, what? 1) a means of transport back to the launch pad, 2) a second booster, for optimal launch cadence.

It seems likely SpaceX will already have both of those.

And a separate landing pad does not necessitate the addition of legs to the booster. It's just another cradle, located safely apart from the tower and GSE. Win-win.
Oh, not this argument again!

You can address this by just making landing reliable and making two pads, which gives you the further advantage of making throughput even higher.
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Offline Dave G

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Re: BFR or BFS first or both?
« Reply #22 on: 01/03/2018 01:51 PM »
I'm expecting the first BFR to have legs, as grasshopper did, until they get its landing accuracy good enough. Seems like a big ask to get the whole cradle thing working right from the initial prototype stage.

To clarify, there were two Grasshopper versions:  v1.0 and v1.1 (a.k.a. F9R Dev1), shown side-by-side below.

Grasshopper v1.0 had metal legs, which were much heavier than the final carbon-fiber legs on Grasshopper v1.1.
Grasshopper v1.0 also used the much shorter F9 v1.0 booster, and lacked grid fins. In other words, Grasshopper v1.0 was just a quick mock-up for SpaceX to get their feet wet on landing a booster.

For BFR tests, if they used metal legs like Grasshopper v1.0, it would make the BFR booster very bottom-heavy, so I'm not sure how useful that would be, especially now that SpaceX has a lot of experience landing boosters.

If they used carbon-fiber legs for early BFR test landings, that would make it less bottom-heavy, but those legs would be HUGE, so the tooling to make them would probably be very expensive.  Also, just designing legs that big may be a significant engineering challenge.

For early BFR booster test landings, it may be cheaper and easier to temporarily place a BFR landing collar on an existing landing pad, like Landing Zone 2.

In addition, they may intentionally destroy some BFR boosters by landing them in the ocean (i.e. without ASDS), like they did on the first few F9R flights.
« Last Edit: 01/03/2018 01:57 PM by Dave G »

Offline speedevil

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Re: BFR or BFS first or both?
« Reply #23 on: 01/03/2018 03:34 PM »
Hmm maybe too much cost to bother. But could a BFS be put up into orbit under it's own power and then a FH send up landing propellent? Im thinking cost of developing the tank might make it a non starter  but throwing it out there.

Yes, it can.
I was in the process of more fully developing this silly idea with actual numbers, but as it's been raised, and I'm not up to it right now:

Assuming the BFR can get to orbit, but cannot land, as it needs ~20 tons more fuel (1000m/s, ISP 365), you can do the very silly thing of making a basically cylindrical tank 3.6m diameter, possibly reusing the F9 tooling, in place of the payload.
This would have along side it basically a matching bottom to the BFR, and some attitude thrusters.

If you are feeling particularly silly, you can then load the second stage from F9H and the vented tank into the BFR, and recover them, for a completely reusable solution.

I will leave sillier solutions such as suborbital refuelling and how many F9Hs you need to get BFS with 150t cargo to mars (about 20 F9H, and 20 BFS, with 2 BFS craft)  alone for now.

This is a theoretically possible thing that can be done, does not involve much new tankage - will involve considerable modifications to cryo load the methane and oxygen on the transporter erector on F9H, some clamps inside BFR, a small robot arm.

As a side-benefit, such a cryogenic methane/oxygen third stage would make small payloads go very, very fast indeed.

Offline Steve D

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Re: BFR or BFS first or both?
« Reply #24 on: 01/03/2018 04:18 PM »
Alot of people here seem to have trouble with the basic concept of BFR/BFS. It is much cheaper to fly this huge rocket then to fly ANYTHING else. They will not use falcon/falcon heavy to support BFS. Doing so would cost millions of dollars more then using another BFR/BFS for support. Every Falcon launch still throws millions of dollars of hardware into the ocean. Second stage, interstage and fairings are all lost. BFR loses nothing! Everything is recovered! No lost hardware! Dumping money into falcon or heavy is just wasted.Spacex is moving on from Falcon. Just accept that fact.
Steve

Offline speedevil

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Re: BFR or BFS first or both?
« Reply #25 on: 01/03/2018 05:02 PM »
Alot of people here seem to have trouble with the basic concept of BFR/BFS. It is much cheaper to fly this huge rocket then to fly ANYTHING else. They will not use falcon/falcon heavy to support BFS. Doing so would cost millions of dollars more then using another BFR/BFS for support.
If, and only if BFR is flying at the time you want to do tests with BFS, I wholly agree.

It also only costs many many millions if you expend the second stage.
« Last Edit: 01/03/2018 05:16 PM by speedevil »

Online JamesH65

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Re: BFR or BFS first or both?
« Reply #26 on: 01/03/2018 05:08 PM »
Alot of people here seem to have trouble with the basic concept of BFR/BFS. It is much cheaper to fly this huge rocket then to fly ANYTHING else. They will not use falcon/falcon heavy to support BFS. Doing so would cost millions of dollars more then using another BFR/BFS for support. Every Falcon launch still throws millions of dollars of hardware into the ocean. Second stage, interstage and fairings are all lost. BFR loses nothing! Everything is recovered! No lost hardware! Dumping money into falcon or heavy is just wasted.Spacex is moving on from Falcon. Just accept that fact.
Steve

Really? I not seeing that in the conversation above. AFAICT, most people here are fully versed in the proposed cheapness of the BFR/BFS combination compared with Falcon.

However, what I also see is huge optimism that the BFx combination will be fully working and operational within a 5 year timescale. That is a very short amount of time to develop something like this.

Offline Negan

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Re: BFR or BFS first or both?
« Reply #27 on: 01/03/2018 05:58 PM »
Alot of people here seem to have trouble with the basic concept of BFR/BFS. It is much cheaper to fly this huge rocket then to fly ANYTHING else. They will not use falcon/falcon heavy to support BFS. Doing so would cost millions of dollars more then using another BFR/BFS for support. Every Falcon launch still throws millions of dollars of hardware into the ocean. Second stage, interstage and fairings are all lost. BFR loses nothing! Everything is recovered! No lost hardware! Dumping money into falcon or heavy is just wasted.Spacex is moving on from Falcon. Just accept that fact.
Steve

Really? I not seeing that in the conversation above. AFAICT, most people here are fully versed in the proposed cheapness of the BFR/BFS combination compared with Falcon.

However, what I also see is huge optimism that the BFx combination will be fully working and operational within a 5 year timescale. That is a very short amount of time to develop something like this.

So where do you think they'll be in development in 5 years?

Online JamesH65

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Re: BFR or BFS first or both?
« Reply #28 on: 01/03/2018 06:12 PM »
Prototypes launched, some failures, not yet ready to take over from F9/H. 

Offline Dave G

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Re: BFR or BFS first or both?
« Reply #29 on: 01/03/2018 06:26 PM »
They will not use falcon/falcon heavy to support BFS. Doing so would cost millions of dollars more then using another BFR/BFS for support. Every Falcon launch still throws millions of dollars of hardware into the ocean.
Agreed.

Second stage, interstage and fairings are all lost.
Inter-stage comes back with booster. 

SpaceX has already recovered fairings from the SES-10 launch.  At Stanford, Gwynne said they expect to start reusing previously flown fairings sometime in the first half of 2018.

So only the second stage is lost.

And this is a really important concept: Once SpaceX is reusing fairings, they can take the carbon fiber people that used to manufacture the fairings and use them to build BFR.


Offline Dave G

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Re: BFR or BFS first or both?
« Reply #30 on: 01/03/2018 06:34 PM »
So where do you think they'll be in development in 5 years?
Prototypes launched, some failures, not yet ready to take over from F9/H.
I agree.  Like most things Elon is involved with, BFR will probably be late.

But that's the point: Other SpaceX projects will probably be delayed as well (e.g. Starlink).

So in the end, I suspect BFR will be delayed no more than anything else.

Offline Negan

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Re: BFR or BFS first or both?
« Reply #31 on: 01/03/2018 07:32 PM »
Prototypes launched, some failures, not yet ready to take over from F9/H.

So what kind of failures do you see happening?

Offline speedevil

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Re: BFR or BFS first or both?
« Reply #32 on: 01/03/2018 11:00 PM »
<snip - of F9H-refuelling>
So only the second stage is lost.

The F9 second stage is a cylinder generally 3.6m*15m. A methane/oxygen tank filling much of the rest of the fairing at the same diameter as the second stage is 3.6*10m or so.

The BFS, if the 'crew' compartments are not fitted (or as I have speculated elsewhere are intentionally easily removable) has enough cargo space and downmass capacity and door dimensions to be able to fit these size of cylinders through the ~3.8m opening of the hatch. (measured off the IAC presentations). They are slid directly in, and then tilted for the last portions.
They can then be secured to the side by clamps.

This of course assumes that F9 second stage recovery doesn't happen in the imagined way.

There are many ways for BFR+BFS to come into being.

The above monstrosity only has a point if BFR is delayed behind BFR sufficiently that BFS testing possibilities are exhausted, and a narrow 5- 20 ton delta-v range exists between SSTO and SSTO+landing.

Other scenarios I prefer might occur, such as BFR following on rapidly enough the above is irrelevant, or even BFR first or if BFS-SSTO works reusably with small payload.


Online Ronsmytheiii

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Re: BFR or BFS first or both?
« Reply #33 on: 01/04/2018 04:25 PM »
Minor question, instead of BFS for the spacecraft and BFR for the booster, why not use orbiter for the former and booster for the latter? That way it distinguishes the booster from the overall system, BFR.
« Last Edit: 01/04/2018 04:26 PM by Ronsmytheiii »
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Offline speedevil

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Re: BFR or BFS first or both?
« Reply #34 on: 01/04/2018 04:38 PM »
Minor question, instead of BFS for the spacecraft and BFR for the booster, why not use orbiter for the former and booster for the latter? That way it distinguishes the booster from the overall system, BFR.
Because inventing our own names for things that spacex has named never generally ends well.

Offline Dave G

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Re: BFR or BFS first or both?
« Reply #35 on: 01/04/2018 04:48 PM »
Minor question, instead of BFS for the spacecraft and BFR for the booster, why not use orbiter for the former and booster for the latter? That way it distinguishes the booster from the overall system, BFR.

Elon has been using the terms "BFR" and "BFS" since at least 2015, probably earlier. 

We know this from his GQ magazine interview:
Quote from: Elon Musk's GQ interview
The rocket that they are working on is referred to internally by the code name BFR. And it doesn't stand for some arcane, smarty-pants science term. It stands for Big frakking Rocket.

I ask Musk whether he really calls it that; his answer is both delightfully nerdy, and not.

"Well, there's two parts of itóthere's a booster rocket and there's a spaceship... So, technically, it would be the BFR and the BFS." As in "Big frakking Spaceship."

Online FutureSpaceTourist

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Re: BFR or BFS first or both?
« Reply #36 on: 02/06/2018 06:22 AM »
From the transcript of Elonís pre-FH demo launch press conference:

Quote
And then the ship, which is the hardest part, just by far the hardest part of the vehicle, of the BFR system, or interplanetary transport system. Because the ship has to have a heatshield that's capable of re-entering from very high velocities. From velocities way higher than... Basically interplanetary velocities, as opposed to orbital velocities. It's got to control itself through a wide regime, from everything from vacuum, to rarefied gas. Everything from thin atmosphere to thick atmosphere. Hypersonic, supersonic, transonic, subsonic. Different types of atmosphere, from different planets. And then land on unimproved terrain, and be able to take off from unimproved terrain. That's a pretty ridiculous set of requirements for the ship. That's why we're focusing on the ship first, because it's kind of the hard part.

Quote
So our focus is on the ship, and we expect to hopefully do short flights on the ship, with the ship next year. You know, aspirational.

Offline Giovanni DS

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Re: BFR or BFS first or both?
« Reply #37 on: 02/06/2018 06:46 AM »
Personally I see BFR landing on the launch pad as the weakest link. This landing concept is the one thing I would remove from the architecture and return to the proven F9 concept.

Even if you achieve a 95% perfect landing rate (to be demonstrated) then you are going to destroy or severely damage the pad one out 20 launches, the required launch rate would make this a real risk considering they have one pad usable for this.

This is why BFR should be first, to retire this risk.

Offline Cheapchips

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Re: BFR or BFS first or both?
« Reply #38 on: 02/06/2018 06:55 AM »

They don't have to land back at the launch pad.  A dedicated landing pad+cradle near the launch site would work for test/maturity phase.

Offline meberbs

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Re: BFR or BFS first or both?
« Reply #39 on: 02/06/2018 07:16 AM »
Personally I see BFR landing on the launch pad as the weakest link. This landing concept is the one thing I would remove from the architecture and return to the proven F9 concept.

Even if you achieve a 95% perfect landing rate (to be demonstrated) then you are going to destroy or severely damage the pad one out 20 launches, the required launch rate would make this a real risk considering they have one pad usable for this.

This is why BFR should be first, to retire this risk.
As Musk was quoted above there are a lot more really hard parts on the ship than the single one you pointed out on the booster. Plus the ship testing already starts giving them experience landing using Raptors. The requirements listed for the ship are absolute requirements, or the architecture simply will not work. On the other hand, the cradle landing can be simply worked around if it is too hard by landing on a pad 100 meters away and getting transported back.

The first thing you ever want to test is the dealbreakers if at all possible. Also, discussion is kind of moot, because it has now been stated from multiple sources both that the ship will be first, and exactly why.

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