Author Topic: Cargo BFS with Dragon crew.  (Read 10271 times)

Offline Negan

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Re: Cargo BFS with Dragon crew.
« Reply #60 on: 10/12/2017 06:45 PM »
I'm not sure landing the BFS itself on the Moon is a good idea since it will have a lot of mass that won't do any good on the moon, e.g. airframe, heat shield, Earth return fuel, tanks, second stage engines. Why waste the fuel needed to get all that mass to a soft landing on the Moon, and then lift it back off?

A separate lander with enough structure, engines, and fuel to go up and down and support the crew on the surface sounds more sensible to me. Perhaps a two part lander with living quarters that could remain on the Moon for later incorporation into a larger lunar habitat, and a much lighter launcher just to get the people back to the orbiting BFS. Maybe that could be left in lunar orbit for the next flight to be refueled and reused.

Back on topic for a moment: I remain doubtful NASA is going to accept the BFR without an escape system for a very long time, however, there are so few crewed flights, why should SpaceX bother?

A related question though is if there will be enough (or any) non-NASA crewed flights that would justify designing and building a crewed version of the BFS. My personal guess is that for a long time the answer will be no.

Also it would be interesting to know what the implications will be to landing and launching BFR off an unprepared surface.
« Last Edit: 10/12/2017 07:19 PM by Negan »

Offline RDoc

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Re: Cargo BFS with Dragon crew.
« Reply #61 on: 10/12/2017 07:21 PM »
Fuel is cheap. Vehicles are expensive. Human rated in-space vehicles are really expensive.
Actually, fuel on the surface of the Moon is extremely expensive. If the goal is to actually put hardware mass on the Moon and do something with it, carrying a hundred tons of useless stuff along for the ride doesn't sound like a good idea.
« Last Edit: 10/12/2017 07:41 PM by RDoc »

Offline CuddlyRocket

Re: Cargo BFS with Dragon crew.
« Reply #62 on: 10/12/2017 08:19 PM »
Fuel is cheap. Vehicles are expensive. Human rated in-space vehicles are really expensive.
Actually, fuel on the surface of the Moon is extremely expensive. If the goal is to actually put hardware mass on the Moon and do something with it, carrying a hundred tons of useless stuff along for the ride doesn't sound like a good idea.
I'm sure SpaceX will do the appropriate engineering trades. But it's important to remember that SpaceX optimises for cost. If it turns out cheaper to carry a hundred tons of useless stuff along for the ride then that's what they will do. People will other ideas are welcome to build their own rocket.

SpaceX's approach is designed to work through the cost of development and manufacture of the spacecraft being amortised over a much greater number of flights. Thus each flight becomes so relatively cheap that even if you need more flights to accomplish a given task (such as landing a particular tonnage of hardware on the Moon) it's still cheaper overall.

Online guckyfan

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Re: Cargo BFS with Dragon crew.
« Reply #63 on: 10/13/2017 07:24 AM »

I'm sure SpaceX will do the appropriate engineering trades. But it's important to remember that SpaceX optimises for cost. If it turns out cheaper to carry a hundred tons of useless stuff along for the ride then that's what they will do. People will other ideas are welcome to build their own rocket.

Or purchase cargo capacity to the moon and produce propellant to sell to SpaceX. SpaceX would buy it if cheaper than bringing their own propellant. But the propellant would have to be delivered to where SpaceX needs it.

Offline CuddlyRocket

Re: Cargo BFS with Dragon crew.
« Reply #64 on: 10/13/2017 08:40 PM »
Or purchase cargo capacity to the moon and produce propellant to sell to SpaceX. SpaceX would buy it if cheaper than bringing their own propellant. But the propellant would have to be delivered to where SpaceX needs it.

I doubt that lunar-produced propellant would be cheaper to SpaceX than propellant sourced on Earth. The advantage of such propellant is that it enables a greater payload mass to the Moon, so the comparison would be between the additional income to SpaceX from that greater payload against the additional propellant expense to SpaceX. And the former depends on demand - if no-one needs the additional payload capability, they won't pay for it!

Online guckyfan

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Re: Cargo BFS with Dragon crew.
« Reply #65 on: 10/13/2017 10:05 PM »
Or purchase cargo capacity to the moon and produce propellant to sell to SpaceX. SpaceX would buy it if cheaper than bringing their own propellant. But the propellant would have to be delivered to where SpaceX needs it.

I doubt that lunar-produced propellant would be cheaper to SpaceX than propellant sourced on Earth. The advantage of such propellant is that it enables a greater payload mass to the Moon, so the comparison would be between the additional income to SpaceX from that greater payload against the additional propellant expense to SpaceX. And the former depends on demand - if no-one needs the additional payload capability, they won't pay for it!

The mission profile proposed by Elon Musk was refuelling from a tanker in Earth Moon transfer. this would enable them to fly the full payload to the moon if not back. So anyone producing propellant on the moon would compete with the cost of that tanker. Or there is something on the moon valuable enough to justify large return payloads that need more propellant.

Offline CuddlyRocket

Re: Cargo BFS with Dragon crew.
« Reply #66 on: 10/15/2017 11:28 AM »
Or purchase cargo capacity to the moon and produce propellant to sell to SpaceX. SpaceX would buy it if cheaper than bringing their own propellant. But the propellant would have to be delivered to where SpaceX needs it.

I doubt that lunar-produced propellant would be cheaper to SpaceX than propellant sourced on Earth. The advantage of such propellant is that it enables a greater payload mass to the Moon, so the comparison would be between the additional income to SpaceX from that greater payload against the additional propellant expense to SpaceX. And the former depends on demand - if no-one needs the additional payload capability, they won't pay for it!

The mission profile proposed by Elon Musk was refuelling from a tanker in Earth Moon transfer. this would enable them to fly the full payload to the moon if not back. So anyone producing propellant on the moon would compete with the cost of that tanker. Or there is something on the moon valuable enough to justify large return payloads that need more propellant.

Propellant availability on the Moon enables you to send more payload to the Moon. Without such propellant availability, the BFS has to carry sufficient propellant to enable it to return. If propellant is available on the Moon, the BFS doesn't have to carry that amount of return propellant and additional payload can be carried instead.

Online guckyfan

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Re: Cargo BFS with Dragon crew.
« Reply #67 on: 10/15/2017 01:15 PM »
Propellant availability on the Moon enables you to send more payload to the Moon. Without such propellant availability, the BFS has to carry sufficient propellant to enable it to return. If propellant is available on the Moon, the BFS doesn't have to carry that amount of return propellant and additional payload can be carried instead.

My understanding was that the additional tanker enables BFS to land its full 150t LEO payload on the Moon. To land more it would require adding payload in orbit. I am not sure this would make sense.

Offline envy887

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Re: Cargo BFS with Dragon crew.
« Reply #68 on: 10/15/2017 10:35 PM »
The mission profile proposed by Elon Musk was refuelling from a tanker in Earth Moon transfer. this would enable them to fly the full payload to the moon if not back. So anyone producing propellant on the moon would compete with the cost of that tanker. Or there is something on the moon valuable enough to justify large return payloads that need more propellant.
Musk proposed refueling in elliptical Earth orbit before TLI. BFS needs to be about 500 m/s above LEO in order to land 150 tonnes on the Moon and return empty. It can return with cargo if it lands less.

Offline CuddlyRocket

Re: Cargo BFS with Dragon crew.
« Reply #69 on: 10/15/2017 11:15 PM »
Propellant availability on the Moon enables you to send more payload to the Moon. Without such propellant availability, the BFS has to carry sufficient propellant to enable it to return. If propellant is available on the Moon, the BFS doesn't have to carry that amount of return propellant and additional payload can be carried instead.

My understanding was that the additional tanker enables BFS to land its full 150t LEO payload on the Moon. To land more it would require adding payload in orbit. I am not sure this would make sense.

I suspect you're going to need more than one tanker flight! The BFS propellant load is more than 1,000t and a tanker can't get much more than 150t of spare propellant into LEO, let alone the high elliptical orbit it is proposed the BFS is in before TLI. You'll probably have to have multiple tanker flights to refuel the tankers that meet the BFS in its high elliptical orbit!

Elon was a bit vague on payload to the Moon. I was assuming that a fully refueled BFS wouldn't be able to carry its own return propellant and a full 150t cargo. It's possible I'm wrong about that!

Online guckyfan

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Re: Cargo BFS with Dragon crew.
« Reply #70 on: 10/16/2017 06:36 AM »

I suspect you're going to need more than one tanker flight! The BFS propellant load is more than 1,000t and a tanker can't get much more than 150t of spare propellant into LEO, let alone the high elliptical orbit it is proposed the BFS is in before TLI. You'll probably have to have multiple tanker flights to refuel the tankers that meet the BFS in its high elliptical orbit!

Elon was a bit vague on payload to the Moon. I was assuming that a fully refueled BFS wouldn't be able to carry its own return propellant and a full 150t cargo. It's possible I'm wrong about that!

I understand they send a fully refueled tanker from LEO to that highly elliptical orbit along with the ship. So one tanker leaving LEO but a number of tanker flights to refuel it. That's what I refered to and Elon mentioned.

Offline RDoc

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Re: Cargo BFS with Dragon crew.
« Reply #71 on: 10/24/2017 12:32 AM »
I must say that NASA might be better employed figuring out things like a lunar lander/ascender system and orbital fuel depot than messing around with the SLS. Private companies can come up with good business cases for heavy lift to LEO, but none, apart from NASA, for Lunar specific work.

Offline RDoc

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Re: Cargo BFS with Dragon crew.
« Reply #72 on: 10/24/2017 01:05 AM »
AIUI NASA only has to man-rate it to put their own people on it. If SpaceX want to put there own people on it, it doesn’t matter one lick what NASA thinks about having or not having LAS. FAA will only become interested if it hosts paying customers. If internal employees only, the FAA’s only concern is safety of the public.
That may well be true, but if NASA can't send its people, who's going to pay for the flights? SpaceX doesn't have either the money or the motivation I wouldn't think.

I could imagine some cludge involving launching the BFS unmanned, then a F9 with a Dragon to carry up the crew for an in orbit transfer, but not more than a few times. If this kind of thing were to be more than a flag waving stunt, it would seem a lot more efficient and safe to design and build an escape system for the BFS.

There may well be a good argument for the proposals with a Dragon in the BFS nose with a way to blow the nose apart to release it in an emergency. After ascent, the crew could access the rest of the BFS volume.

Offline KelvinZero

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Re: Cargo BFS with Dragon crew.
« Reply #73 on: 10/24/2017 07:27 AM »
There may well be a good argument for the proposals with a Dragon in the BFS nose with a way to blow the nose apart to release it in an emergency. After ascent, the crew could access the rest of the BFS volume.
I tried to start a discussion about that earlier. What would a well designed, non-kludge solution look like.

The nose, with some sort of ejectable nose cone, is no doubt the least controversial for LAS. It is a pity though if you are going to carry a Dragon all that way and not be able to use it for escape during reentry. Reentry may very likely be more dangerous than launch. There are more variables that you will have no control over, such as weather and micrometeoroid damage from months in space.

(An ACRV would just be an easy bonus, pretty much for any configuration)

Offline RDoc

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Re: Cargo BFS with Dragon crew.
« Reply #74 on: 10/24/2017 06:58 PM »
There may well be a good argument for the proposals with a Dragon in the BFS nose with a way to blow the nose apart to release it in an emergency. After ascent, the crew could access the rest of the BFS volume.
I tried to start a discussion about that earlier. What would a well designed, non-kludge solution look like.

The nose, with some sort of ejectable nose cone, is no doubt the least controversial for LAS. It is a pity though if you are going to carry a Dragon all that way and not be able to use it for escape during reentry. Reentry may very likely be more dangerous than launch. There are more variables that you will have no control over, such as weather and micrometeoroid damage from months in space.

(An ACRV would just be an easy bonus, pretty much for any configuration)
Why wouldn't the Dragon in the nose be usable for an emergency reentry lifeboat?

Offline KelvinZero

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Re: Cargo BFS with Dragon crew.
« Reply #75 on: 10/24/2017 11:35 PM »
Why wouldn't the Dragon in the nose be usable for an emergency reentry lifeboat?
The problem of being sideways to the plasma is fairly obvious. There are lots of solutions of course, right up to designing a whole new Dragon 3.0 that is fully integrated with the nose cone and halfway to a Dream Chaser... though that is cheating a bit.

Im open to a Dragon on the nose that can be used during launch and reentry. Outline it for me. If people get enthusiastic maybe they will start playing around with models to show how the BFS, BFS nose cone and Dragon all fit together.

Online Lars-J

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Re: Cargo BFS with Dragon crew.
« Reply #76 on: 10/25/2017 12:20 AM »
Im open to a Dragon on the nose that can be used during launch and reentry. Outline it for me. If people get enthusiastic maybe they will start playing around with models to show how the BFS, BFS nose cone and Dragon all fit together.

Who is 'they'?

Offline Patchouli

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Re: Cargo BFS with Dragon crew.
« Reply #77 on: 10/25/2017 12:54 AM »

The problem of being sideways to the plasma is fairly obvious. There are lots of solutions of course, right up to designing a whole new Dragon 3.0 that is fully integrated with the nose cone and halfway to a Dream Chaser... though that is cheating a bit.

Im open to a Dragon on the nose that can be used during launch and reentry. Outline it for me. If people get enthusiastic maybe they will start playing around with models to show how the BFS, BFS nose cone and Dragon all fit together.

They'd have to pretty much go to something along the lines of Winged Gemini if they were to keep any of the original internal structure and systems.

I guess a side benefit Musk won't have to eat his words when he called Boeing's landing mode crude after power landings were taken off the board.
« Last Edit: 10/25/2017 01:01 AM by Patchouli »

Offline RDoc

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Re: Cargo BFS with Dragon crew.
« Reply #78 on: 10/25/2017 01:11 AM »
Why wouldn't the Dragon in the nose be usable for an emergency reentry lifeboat?
The problem of being sideways to the plasma is fairly obvious. There are lots of solutions of course, right up to designing a whole new Dragon 3.0 that is fully integrated with the nose cone and halfway to a Dream Chaser... though that is cheating a bit.

Im open to a Dragon on the nose that can be used during launch and reentry. Outline it for me. If people get enthusiastic maybe they will start playing around with models to show how the BFS, BFS nose cone and Dragon all fit together.
I'm assuming the lifeboat would be used if something disastrous happened in orbit, not while actually reentering! I'm pretty doubtful that would be possible with anything like current technology.

Realistically, I suspect that literally putting a Dragon inside the BFS is unlikely, an integrated design likely makes a lot more sense, but the development time and cost sounds pretty serious.

Offline KelvinZero

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Re: Cargo BFS with Dragon crew.
« Reply #79 on: 10/25/2017 08:50 AM »
I'm assuming the lifeboat would be used if something disastrous happened in orbit, not while actually reentering! I'm pretty doubtful that would be possible with anything like current technology.
It is almost certainly doable. Just very likely so expensive and such a radical redesign that it never happens, for sure.

My position is that first you brainstorm what it might look like. There is not much cost in that. Just thinking about it will not will force Elon Musk into a pointless multibillion dollar dead end.

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