BFR GTO capability

[Alvian@IDN]

Considering BFR will be replacing all of the Falcons, GTO market will be still one of the important market for BFR, even though GEO market now decrease & LEO smallsats increase.

Did BFS has a capabilities to do a second burn, deploy a satellite in GTO (like Falcon 9 S2), but it will do a retrograde burn (maybe in periapsis to lower the apoapsis to below the Karman line) ?

Maybe considering to ask Elon Musk in his upcoming Reddit AMA.

[Nomadd]

 Are you asking if a spaceship designed to land on Mars can do a burn a few hours after it's launched?

[JonathanD]

If it can't do a second burn to get to GTO, Mars EDL will be a very brief experiment in lithobraking.

[su27k]

Yeah, of course it can do a 2nd burn. The real question is does it need orbital refueling before it does GTO burn. The 2017 version doesn't, but with the lower Isp engine and potentially higher dry mass, not sure if the 2018 version can still do single launch GTO mission.

[JonathanD]

Yeah, of course it can do a 2nd burn. The real question is does it need orbital refueling before it does GTO burn. The 2017 version doesn't, but with the lower Isp engine and potentially higher dry mass, not sure if the 2018 version can still do single launch GTO mission.

On-orbit refueling for a GTO mission would be crazy.  I have to think they'd throw on some vacuum raptors if they had to.

[su27k]

On-orbit refueling for a GTO mission would be crazy.  I have to think they'd throw on some vacuum raptors if they had to.

It's not that crazy if you have a full and rapid reusable launch vehicle. The delta-v to GTO is substantial, it's only 700m/s or so lower than TLI, it's a big ask to require your reusable 2nd stage to do single launch to GTO when the first stage does RTLS, I think the total delta-v required for the 2nd stage would be similar to SSTO.

[Semmel]

My question exactly in the engineering thread.  GTO performance is the only relevant performance number early on. We have the thrust per engine, we have the ISP of the sea level engines and we have the payload to LEO. We have an approximation of the fuel volume, one can derive the mass from that. We don't have the dry mass (85 mT is not relevant for Sat delivery)  but maybe the above info is enough to get an estimate?

[hkultala]

Yeah, of course it can do a 2nd burn. The real question is does it need orbital refueling before it does GTO burn. The 2017 version doesn't, but with the lower Isp engine and potentially higher dry mass, not sure if the 2018 version can still do single launch GTO mission.

If the craft weights about 90 tonnes and can lift 110 tonnes to LEO, it means i could lift a 8-tonne satellite plus 102 tonnes of fuel to orbit.

Unfortunately it does not have extra tanks for this fuel and it it wants to have this fuel available in main tanks, it has to leave this fuel unused in the main tanks, burning less than "optimal for maximum payload" for the main burn to LEO, meaning the mass to LEO drops a bit.

This means that in practice, without extra tanks, with the 8-tonne satellite, it could lift slightly smaller amount of fuel to LEO, maybe like 90 tonnes.

LEO to GTO is about 2.5km/s.

90+90+8 = 188 tonnes initial mass, 98 tonnes final mass, 357 second specific impulse gives about 2.28 km/s delta-v after LEO.

So, GTO not achievable with these numbers with 8-tonne satellite.

But, if the satellite launcher version of BFS is only 80 tonnes instead of 90 tonnes, and it can lift slightly more to LEO (100 tonnes of fuel + 8-tonne satellite), then we get about 2.65 km/s delta-v after LEO, enough for GTO.

So, close call. I think they are nailing the details in such way that it will work for the biggest common GTO satellites, as GTO satellites are important source of income.

[speedevil]

So, close call. I think they are nailing the details in such way that it will work for the biggest common GTO satellites, as GTO satellites are important source of income.

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.

You have 820m/s left over after GTO, meaning you can lift a VIP-mass sat to GTO+300m/s or so - doing part of its insertion burn - and then return to earth after doing a 300m/s burn to lower perigee again, with some margin.

Or, lift a ~20 ton satellite to GTO.
The point in the last post about the tanks not being big enough is wrong(*) as it must be able to do 3300m/s after LEO.

*) The outlined moon mission needs a dry weight of 60 tons or so, if it has 1100 tons initial mass. Which is ... ambitious.
So, either it's awesomer that we thought, or something has to give. Either a tanker, or the vehicle has to grow/be respecced.
This obviously means basing numbers on it is problematic.

If you assume '100t+ to LEO' includes ~150 tons, then all the problems with the presentation go away.

If, on the other hand, you assume they are implicitly assuming a refueling for the moon mission, 100+ to LEO may be the 'worst case best case' that they are aiming at.
100 tons would be more-or-less the point at which they can do all current F9 GTO payloads without retanking.

[Semmel]

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?

[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.

[Alvian@IDN]

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, lower the periapsis so it will  burn up, so it won't ended being a GTO space junk.

But this maybe will increase the spacecraft price (if the kick stage manufactured by satellite maker), or considered as "wasteful" by SpaceX, who're at that time didn't even know about "expendable" thing thanks to BFR.

[speedevil]

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.

[Alvian@IDN]

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.

[matthewkantar]

Refueling for a GEO mission is acceptable if you take ten eight ton sats with you, drop them where they need to be, pick up five dead GEO sats and then return to LEO, tank up again and return to the launch site.

edited to add a missing "if"

[wannamoonbase]

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.

[Cheapchips]

Longer term, shouldn't they be retanking and providing customers with larger satellite options?  Or would a bigger tug still be the way to go?

[Elmar Moelzer]

If the craft weights about 90 tonnes

Where is that assumption coming from? The cargo version should have a significantly lower dry mass than the 85 ton passenger version. I would assume a cargo version to be at most 65 tonnes.

[RedLineTrain]

SpaceX is already launching 7+ ton birds to GTO-2200 rather than GTO-1800.  I would imagine the theme could be expanded upon for BFR.

[Semmel]

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.

[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.

[Robotbeat]

....
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. ...

...except BFS reaching GTO on its own is not a major challenge even without vacuum Raptors. Seriously, it's not. At least not to the kind of GTO energies that Falcon 9 often sends satellites.

[Lars-J]

....
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. ...

...except BFS reaching GTO on its own is not a major challenge even without vacuum Raptors. Seriously, it's not. At least not to the kind of GTO energies that Falcon 9 often sends satellites.

Yeah, if BFS can do a lunar free return trajectory without any propellant transfer, it will have no issue doing a less demanding GTO trajectory with any current satellite payload. No problem.

[niwax]

....
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. ...

...except BFS reaching GTO on its own is not a major challenge even without vacuum Raptors. Seriously, it's not. At least not to the kind of GTO energies that Falcon 9 often sends satellites.

Yeah, if BFS can do a lunar free return trajectory without any propellant transfer, it will have no issue doing a less demanding GTO trajectory with any current satellite payload. No problem.

Crazy idea: Use a moon slingshot for GEO insertion. BFS returns on its free return trajectory while the satellite gets injected into a 36000x385000 transfer orbit which should for only 600m/s dv from deployment to GEO

[Ultrafamicom]

I think a slide in 2017IAC presentation suggests BFR Recoverable can deliver 20t to GTO1800 without refuelling? Assume 2018ver has simmilar size with 110t LEO capacity，by using RVac for BFS，some 30t can be gained, so it may still have 10t capacity after upgrading. Given its fully reusable nature, It should easily beat NG dual manifest at cost even with single manifest only.

Before the RVac arrived, just use ASDS instead of RTLS, maybe with even better performance.

[cybertrn]

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.

What is the estimate of dry mass BFS? Space Shuttle external tank (46.88 m length, 8.4 m diameter, Al-Li alloy) has weight 30 tonnes. Add 14 tonnes for 7 engines and 11 tonnes for cargo section = 55 tonnes. So, if passenger BFS (dry mass 85 tonnes) can SSTO with zero payload, cargo BFS can deliver 30t payload to LEO without BFB. Not so bad! In other words, we can say that
BFR=BFS+kick stage; BFS+BFB = BFR Heavy. I think this is main use case for BFS  - SSTO with reusable kick stage. Huge buster and BFS refuelling needed only for especial cases.

[Lar]

Welcome to the forums. There is a thread about BFS SSTO.

[Elmar Moelzer]

What is the estimate of dry mass BFS? Space Shuttle external tank (46.88 m length, 8.4 m diameter, Al-Li alloy) has weight 30 tonnes. Add 14 tonnes for 7 engines and 11 tonnes for cargo section = 55 tonnes. So, if passenger BFS (dry mass 85 tonnes) can SSTO with zero payload, cargo BFS can deliver 30t payload to LEO without BFB. Not so bad! In other words, we can say that
BFR=BFS+kick stage; BFS+BFB = BFR Heavy. I think this is main use case for BFS  - SSTO with reusable kick stage. Huge buster and BFS refuelling needed only for especial cases.

That was the same dry mass estimate I made for a very optimized cargo BFS in another thread. Problem is that the 2018 BFS got quite a bit heavier and has no vac engines. I would assume around 5 tonnes of cargo as SSTO (still useful).

[niwax]

What is the estimate of dry mass BFS? Space Shuttle external tank (46.88 m length, 8.4 m diameter, Al-Li alloy) has weight 30 tonnes. Add 14 tonnes for 7 engines and 11 tonnes for cargo section = 55 tonnes. So, if passenger BFS (dry mass 85 tonnes) can SSTO with zero payload, cargo BFS can deliver 30t payload to LEO without BFB. Not so bad! In other words, we can say that
BFR=BFS+kick stage; BFS+BFB = BFR Heavy. I think this is main use case for BFS  - SSTO with reusable kick stage. Huge buster and BFS refuelling needed only for especial cases.

That was the same dry mass estimate I made for a very optimized cargo BFS in another thread. Problem is that the 2018 BFS got quite a bit heavier and has no vac engines. I would assume around 5 tonnes of cargo as SSTO (still useful).

I think any estimate on SSTO cargo is going to be very rough since a 1% difference in dry mass to orbit is still going to be more than most smallsat launchers manage at all

[hkultala]

What is the estimate of dry mass BFS? Space Shuttle external tank (46.88 m length, 8.4 m diameter, Al-Li alloy) has weight 30 tonnes. Add 14 tonnes for 7 engines and 11 tonnes for cargo section = 55 tonnes.

You are totally forgetting the legs and their actuators.

Falcon 9 legs weight about 2 tonnes together, and falcon 9 1st stage landing weight is about 10 times less than BFS landing weight. And because they do not act as aerodynamic controls, they don't need as heavy actuators.

So BFS legs will weight MANY tonnes. Probably more than 10.

You are also forgetting the weight of the heat shielding.

Orbiter had almost 9 tonnes of heat shielding. SpaceX uses more advanced heat shield technology, but they also want to
1) be able to re-enter from higher velocity
2) have much less maintainance for the heat shield, meaning higher margins.

So, true empty mass probably much more than your 55 tonnes.

So, if passenger BFS (dry mass 85 tonnes) can SSTO with zero payload

Assumption without ANYTHING backing it up. It's extremely unlikely that it can.

, cargo BFS can deliver 30t payload to LEO without BFB. Not so bad! In other words, we can say that
BFR=BFS+kick stage; BFS+BFB = BFR Heavy. I think this is main use case for BFS  - SSTO with reusable kick stage. Huge buster and BFS refuelling needed only for especial cases.

So, you have incorrect input numbers AND condition that is extremely unlikely as your inputs.

The end result is then also total garbage.


The real question is that can the cargo version reach LEO without any payload. Probably they will engineer it so that it (barely) can, to make testing much easier. it's much easier to fly to (very low) orbit, stay there for 24h hours and come back to launch site than launch to 90% of orbital velocity and come back - somewhere at wrong place.

[envy887]

The real question is that can the cargo version reach LEO without any payload. Probably they will engineer it so that it (barely) can, to make testing much easier. it's much easier to fly to (very low) orbit, stay there for 24h hours and come back to launch site than launch to 90% of orbital velocity and come back - somewhere at wrong place.

They don't need to reach orbital velocity to test orbital heat load at entry, since heat load is a function of both entry angle and velocity.

And I don't really see how any of this relates to BFR's GTO payload. The delta-v from staging to GTO is similar to surface to LEO, but operating only in vacuum increases I_sp  quite a bit.

SpaceX hasn't said anything about reaching GTO with the new version without refueling, and they haven't given us enough information to calculate if it can, even by making reasonable inferences.

So this thread is 100% pure speculation.

[speedevil]

SpaceX hasn't said anything about reaching GTO with the new version without refueling, and they haven't given us enough information to calculate if it can, even by making reasonable inferences.

So this thread is 100% pure speculation.

As mentioned early on in the thread, if you believe the mission to 3300m/s from LEO (the moon) will happen without refueling, as that was not mentioned, it can trivially do GTO (2500m/s) or 'GTO' - 1800m/s or so.
(Or GEO, and not return).
We do not need any more information to calculate.
(and yes, many doubt the implied ~60 ton dry weight in a condition to take VIPs)

[cybertrn]

So, if passenger BFS (dry mass 85 tonnes) can SSTO with zero payload

Assumption without ANYTHING backing it up. It's extremely unlikely that it can.

This isn't assumption, this is widely known statement from Musk's AMA-2017. Simple calculation for BFS2018:

   dV    = 9,81 m/sec² * 356 sec * ln( 1185t / 85t) = 9201 m/sec
   TWR =  7 * 2,095 kN / 9,81 m/sec² / 1185 t  = 1,26
All Raptor2018 SL numbers - ISP =356 sec, thrust at sea level = 2,095 kN from this thread.

SpaceX hasn't said anything about reaching GTO with the new version without refueling, and they haven't given us enough information to calculate if it can, even by making reasonable inferences.

So this thread is 100% pure speculation.

As mentioned early on in the thread, if you believe the mission to 3300m/s from LEO (the moon) will happen without refueling, as that was not mentioned, it can trivially do GTO (2500m/s) or 'GTO' - 1800m/s or so.
(Or GEO, and not return).
We do not need any more information to calculate.
(and yes, many doubt the implied ~60 ton dry weight in a condition to take VIPs)

So, if you believe the VIP mission without refuelling => you need ~60 ton dry mass => you can do 85 - 60 = 25 tons SSTO to LEO or ~ 10 tons to GTO with Raptor2018Vac kick stage. Calculation for last number:
  exp( 2500m/s /( 9,81m/s²*375s) = 1,97 = 25t / (M_kickstage - M_payload) -> M_payload = 12,67t - M_kickstage

Congratulation, you have perfect Shuttle 2.0 without expendable parts with refuelling ability and optional booster for huge payload...

[hkultala]

So, if passenger BFS (dry mass 85 tonnes) can SSTO with zero payload

Assumption without ANYTHING backing it up. It's extremely unlikely that it can.

This isn't assumption, this is widely known statement from Musk's AMA-2017.

No' it's not. You are interpreting things wrongly. Reading nonexistent things from between the lines.

Worth noting that BFS is capable of reaching orbit by itself with low payload

He did not say WHICH version of BFR is SSTO-capable. It's very probably the cargo/satellite launcher version.

And after this statement the capacity oif BFR has dropped considerably. Because of 1) lower isp of the engines 2) probably also because of increased mass.

Simple calculation for BFS2018:

   dV    = 9,81 m/sec² * 356 sec * ln( 1185t / 85t) = 9201 m/sec
   TWR =  7 * 2,095 kN / 9,81 m/sec² / 1185 t  = 1,26
All Raptor2018 SL numbers - ISP =356 sec, thrust at sea level = 2,095 kN from this thread.

.. and sea level isp of 336 secs. The average isp might be something like 351 secs, giving only 9.06 km/s.

Also the craft was changed considerably for the 2018 version, growing in size. It might have also gained some weight (this would be a very logical explanation for the quite big payload drop, the sea level engines alone should not explain it), I would except the weight of the passenger version to be more like 90-100 tonnes than 85 tonnes. 90 tonnes would mean something like 8.88 km/s.

[Semmel]

...

You forgot to account for the landing fuel. Also, you forgot to account for the fact that 356s is the ISP of sea level Raptors in vacuum. Doesnt look good for your payload to LEO.