BFR GTO capability

[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.