BFR GTO capability

[speedevil]

At least for this question, it's easy to answer - if you believe the presentation.(*)
That states it can do  3300m/s with a VIP of say 5% of the stage dry mass with 250m/s of landing fuel.

I must have missed it, was that number in the presentation?

Implicitly.
Lunar injection to any orbit which gets you close to the moon from LEO with a hair of margin is 3300m/s.
250m/s of landing fuel is what you get if you integrate gravity losses over the landing burn which begins at 100m/s and lasts 16s.

Well, Musk never explicitly said that it is done without refuelling. Unless we get that information, I would not count on this performance.

No, he did not, but once you go down that rabbithole, the problem gets worse.
The graph of the mission architecture shown specifically did not include refuelling - when the analogous graph from 2017 did.

Given that he then went on to talk about how refuelling helps - without mentioning the moon as an example - the 'least worst' alternative from a determining the ship properties point of view is IMO to assume that it is presumed to be able to do 140t or so payload by 2023.

[DigitalMan]

I think they should build a BFF (otherwise known as a tug) that can depart the BFS with the satellite at some initial orbit and take it to target orbit and come back to the BFS.

edit: Perhaps there is a lot of tech from Dragon that can be a good starting point for this?

[Lars-J]

Taking an 80-90 ton vehicle to GTO seems to be the problem with the 8 ton payload.

SpaceX maybe much better off developing a small reusable space tug for doing the final push.

It would be no stranger than a large truck delivering a small package. In the age of re-usability, you need to step away from the expendable 'payload must fit rocket exactly' mentality.

[vaporcobra]

Taking an 80-90 ton vehicle to GTO seems to be the problem with the 8 ton payload.

SpaceX maybe much better off developing a small reusable space tug for doing the final push.

It would be no stranger than a large truck delivering a small package. In the age of re-usability, you need to step away from the expendable 'payload must fit rocket exactly' mentality.

Precisely this. Along the theme of Musk's clearly overarching statement that they first had to think about the right questions to ask and that BFR in general operates in an unintuitive fashion, it seems logical to conclude that the payload reduction of ~1/3rd indicates that SpaceX is trying to reach beyond the expendable-era instinct that rocket design needs to be centered around single-launch payload to orbit.

If you make a fully reusable LV that can reliably and cheaply get relatively small payloads to LEO (but no further) and requires extensive reliance on tanker refueling or orbital depots, that's certainly one way that development could be hastened. Make BFR just big enough that it is practical as a habitat for dozens of passengers for a dozen or so weeks, but not so big that it becomes an unprecedented engineering challenge, and you seem to wind up with something that looks a lot like BFR 2018.

[docmordrid]

Then he posted an upgrade path from 31 to 42 engines....

[Robotbeat]

Remember, BFR may actually launch from a sea platform, meaning they could launch from the equator. That means GSO is 400m/s closer to LEO than it would be from the Cape. So even with pessimistic dry mass assumptions (100 tons stage burnout before landing), they should be able to put a 10 ton satellite to ~1800m/s-to-go (what SpaceX typically quotes), and a 20 ton satellite to ~2100m/s-to-go (what SpaceX sometimes launches especially heavy satellites to). With better dry mass assumptions(60-65 tons), they could put a 20 ton satellite to 1500m/s-to-go-to-GSO (standard that Ariane quotes).

Without refueling.


...so BFR can most certainly launch significant payloads to GTO in a single launch with recovery. Exactly which GTO energy depends on dry mass, but it most certainly can do many of the GTO energies that F9 launches to.


...and even launching from the Cape with unrealistically high dry mass assumptions, it can do 10 tons to 2200m/s-to-go. So should be quite useful right out the gate.

[meekGee]

Also didn't Shotwell refer to a satellite deployer version not too long ago?

There's a lot of mass savings if it's not a full Mars BFS.

No cabins, seats, windows, lifr support...  minimal  power system...  shorter payload bay (and longer tanks?)

It might be a large truck delivering a small package, but no need to deliver it with an RV...

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ABCD: Always Be Counting Down

[Elmar Moelzer]

Yes, the 85 tonnes are clearly for the passenger BFS.  The cargo version will most likely be significantly lighter. I am sure that the cabin section would have much thicker walls than a simple payload bay. Extrapolating from the mass of the F9 payload fairing, the cargo section of the cargo BFS should be somewhere around 11 tonnes. To get to that number, I assumed a generous 8.5 tonnes for the composite shell and 2.5 tonnes for the TPS, door mechanisms, etc. This does not include the mass of the canards though.

[biosehnsucht]

Ah, I hadn't thought about how the chomper might have changed with those canards on the sides. I wonder if the chomper is out entirely or if it will just have a differently shaped opening and/or doors ?

[meekGee]

Ah, I hadn't thought about how the chomper might have changed with those canards on the sides. I wonder if the chomper is out entirely or if it will just have a differently shaped opening and/or doors ?

I don't see the problem.. the canards are on the centerline, and the chomper door can open just above them.  Or the canards can move down a bit too.  (Clearly the back fins did)

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ABCD: Always Be Counting Down

[Elmar Moelzer]

I think the door was already (just) above the centerline in the 2017 version as well.

[hkultala]

the canards are on the centerline, and the chomper door can open just above them.  Or the canards can move down a bit too.  (Clearly the back fins did)

As they do not have any laminar flow, they are not canards. They are hands.

Exactly like a skydiver has hands and legs.

[kevinof]

Do the canards (aka Hands) fold back into the fuselage? If so how does this work on the chomper - it would impact the space reserved for the payload. Even without folding there would be motors/pumps inboard.

[speedevil]

Do the canards (aka Hands) fold back into the fuselage? If so how does this work on the chomper - it would impact the space reserved for the payload. Even without folding there would be motors/pumps inboard.

The canards are way up front - if you (for example) fill the payload bay with a domed cylindrical closely fitting station component, the canards are several meters forward of it, as the nose narrows a lot before you reach them.

[jpo234]

Then he posted an upgrade path from 31 to 42 engines....

As mentioned before, this was almost certainly a reference to the "Hitchhikers guide to the Galaxy" . The Mars space ship will be called the "Heart of Gold", after all.

[meekGee]

the canards are on the centerline, and the chomper door can open just above them.  Or the canards can move down a bit too.  (Clearly the back fins did)

As they do not have any laminar flow, they are not canards. They are hands.

Exactly like a skydiver has hands and legs.

Yup..  I was corrected above that the correct term  is attached flow..  Apparently the boundary layer is not laminar even under normal flight.

I like fore and aft brakerons.

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ABCD: Always Be Counting Down

[CuddlyRocket]

I think they should build a BFF (otherwise known as a tug) that can depart the BFS with the satellite at some initial orbit and take it to target orbit and come back to the BFS.

If the BFS can do the mission itself then that's probably optimal. Otherwise a tug would seem the only solution if you want the business. One thing to take into account is that with a tug you may be able to launch two (or more) satellites into GTO with one launch of the BFS (one tug or two?). Also, a tug might be useful for more missions than GTO satellite launching. I expect this will be one of those times for some cost optimisation calculations.

NB. The tug doesn't have to come back to the same BFS. It could be picked up by a later launch (though this may coincidentally be the same actual craft).

Perhaps there is a lot of tech from Dragon that can be a good starting point for this?

Possibly. But SpaceX shouldn't limit itself to its own technology. There may be solutions developed elsewhere that can be utilised without all the development costs.

[su27k]

If the BFS can do the mission itself then that's probably optimal. Otherwise a tug would seem the only solution if you want the business. One thing to take into account is that with a tug you may be able to launch two (or more) satellites into GTO with one launch of the BFS (one tug or two?). Also, a tug might be useful for more missions than GTO satellite launching. I expect this will be one of those times for some cost optimisation calculations.

NB. The tug doesn't have to come back to the same BFS. It could be picked up by a later launch (though this may coincidentally be the same actual craft).

I don't see a tug anytime soon, especially given the much reduced GTO market. Just use orbital refueling as BFS is designed to do, there's nothing wrong with it. It would take a few more hours but a GTO mission on Proton would take 7+ hours anyway, so it's nothing new. SpaceX can offer a better GTO injection performance to offset the perceived risk.

[speedevil]

If the BFS can do the mission itself then that's probably optimal. Otherwise a tug would seem the only solution if you want the business. One thing to take into account is that with a tug you may be able to launch two (or more) satellites into GTO with one launch of the BFS (one tug or two?). Also, a tug might be useful for more missions than GTO satellite launching. I expect this will be one of those times for some cost optimisation calculations.

NB. The tug doesn't have to come back to the same BFS. It could be picked up by a later launch (though this may coincidentally be the same actual craft).

I don't see a tug anytime soon, especially given the much reduced GTO market. Just use orbital refueling as BFS is designed to do, there's nothing wrong with it. It would take a few more hours but a GTO mission on Proton would take 7+ hours anyway, so it's nothing new. SpaceX can offer a better GTO injection performance to offset the perceived risk.

Or several more retankings, and you get to go along with your satellite to actually deploy it in orbit and bring it back if it doesn't start up.

[Lobo]

OR, simply put the small kick/third stage installed with satellite. Deployed earlier in LEO
After spacecraft deployed, that third stage do a retrograde burn, so it won't ended being a GTO space junk.

Indeed.
Something looking very like a F9S2 would be quite adequate to get from a LEO vehicle with 100 tons payload to GTO with a 20 ton payload, and then back to its original orbit empty, so it could be picked up and reused.
A very much more modest kick stage would be just fine if you just want it to get the payload to GTO and  burn up.

SpaceX (of course in BFR's early days) could use the remaining of Merlin 1D vac in storage for that kick stage, like NASA do with RS-25 

I'm still waiting for Elon's AMA though, we will see what he thinks about this.

The problem with a F9US is that you now have a 3rd propellant to handle as well as additional hoses and umbilicals that would need to get through the BFR shell on the pad, as the payload and F9US would be "encapsulated" in BFR.  I think this would add a lot of additional complexities to the pad layout that they'll want to avoid.

Which means if you want to go with a kick stage, go with a hypergolic or solid one, that doesn't need umbilicals on the pad after it's encapsulated with the payload.    Like the IUS that was used on the Shuttle for Galileo. 

Although I think they'll probably find a way to make BFS get to GTO on it's own.  It might not be until after Vacuum Raptor is developed.  Remember, F9 isn't going away any time soon.  And they just recently rebuilt Pad 40 at the Cape and BFR can't launch from there.  So that pad will be launching F9 for some time on the East Coast, even if they were to have 39A launch BFR. 
Once BFR is able to launch those sats to GTO, then F9 can start being phased out.