Speculation - Larger BFR

[jpfulton314]

I'm curious what discussions, if any, are taking place regarding a follow on to the 9 meter BFR?  As I recall, the first BFR was 12 meters, then it was decided that the costs would be prohibitive, so the decision was made to go with a 9 meter rocket.
Is the plan to go with a larger vehicle in the future, or is SpaceX going to stick with their current design, with an evolution similar to that of the F9?

[spacenut]

Right now, they are sticking to the 9m diameter, developing the Raptor engine, etc.  After this rocket gets operational and makes trips to Mars, then I would speculate a larger rocket, maybe a 15m rocket launched offshore.  That is probably 15-20 years in the future. 

With the current rocket able to get 100 tons to orbit, a lot of 100 ton modules could assemble a large propellant depot or depots.  It can refuel to go to Mars, the moon, and with propellant depots along the way, as Musk said.  They could refuel at Mars, go to Ceres, refuel at Ceres, then on to Jupiter's moons.  From there to Saturn's moons.  A lot can be done with a 9m in space, space ship. 

[Lars-J]

I'm curious what discussions, if any, are taking place regarding a follow on to the 9 meter BFR?  As I recall, the first BFR was 12 meters, then it was decided that the costs would be prohibitive, so the decision was made to go with a 9 meter rocket.
Is the plan to go with a larger vehicle in the future, or is SpaceX going to stick with their current design, with an evolution similar to that of the F9?

This thread should probably be in the BFR section.

[Rocket Surgeon]

I'm curious what discussions, if any, are taking place regarding a follow on to the 9 meter BFR?  As I recall, the first BFR was 12 meters, then it was decided that the costs would be prohibitive, so the decision was made to go with a 9 meter rocket.
Is the plan to go with a larger vehicle in the future, or is SpaceX going to stick with their current design, with an evolution similar to that of the F9?

To be honest, as they improve engine efficiency, I think their main focus won't be an increase in payload, but to use the extra ISP and thrust to make up for a reduced mass fraction. To what end? Increasing the fatigue life of the vehicle components.

I think instead of building bigger, it make more sense to change the design of the BFR so that can lift the same payload, but be reused 1000 times as opposed to 100.

As an example, for the old BFR design, roughly (very roughly) every second of ISP increase in the engines adds an extra tonne of payload to LEO. Now if instead of using that for payload, it would make sense to redesign components that are limiting the fatigue life of the structure of Ship and Boost to increase their life with the added bonus of having real life data to target the mods.

As another example, my current job has me working on a project that only increases the mass of a (non-aerospace  ) vehicle by 9%, but reduces the stress in cracking prone areas by ~3.5, which should theoretically improves the fatigue life by a factor of ~42. This is because fatigue life has a roughly (very roughly) cubic relation to peak stress. Apply the same to the BFS and increasing the ISP by 7 seconds (say from 375s to 382s) gives you roughly 7t extra to play with for the same payload to LEO. I think well designed modifications, especially in new-builds, could definitely improve the fatigue life by a factor of 10+, meaning the Ships could be reused up to 1000 times and the Boosters 10,000.

As a bonus you can use the same tooling to build this new version as well.

[KelvinZero]

I'm curious what discussions, if any, are taking place regarding a follow on to the 9 meter BFR?  As I recall, the first BFR was 12 meters, then it was decided that the costs would be prohibitive, so the decision was made to go with a 9 meter rocket.

Rather than discovering that the 12 meter rocket would be too expensive, the way they phrased it was that they had figured out how to fund this rocket: by sizing it to satisfy all F9 and FH-scale missions while costing less per launch.. a pleasingly down to earth business case.

Im not sure how this is affected by the apparent reduction in mass to LEO.

[rakaydos]

The 9m rocket is also sized for infrastructure in the US- not just the Nova pads, but also legal sound intensity limits from Brownsville.

Any follow-on that's larger, will be strictly limited to sealaunch. That's something we can wait for a market for.

[speedevil]

Assuming the P2P numbers remain similar, this is the best read we have on their estimations of the long term capability of the (presumably) 9m platform.

'Cheaper than an economy flight'.
This is very close to $1M/flight, as a profitable launcher, including a substantial amount of crew handling passengers, and all their liabilities.

Or, $10/kg.

Look around you and try to find a manufactured object at under that price.
The cheapest mass produced cars hover slightly above that.

It puts the cost of even open loop life support at $300/day.

This costs mass into MOI at some $40/kg, $60/kg into LMO, and landed at some $100/kg, using propellant thrown in shaded uninsulated otherwise large balloon tanks or similar, and BFS shuttling back and forward and catching them, with BFS doing almost wholly propulsive retrobraking onto Mars, as no way can it land otherwise with 400 tons.

This is _without_ ISRU, without relying on using BFS over twenty synods, and without any changes to BFS, other than to put a massive tank in the payload bay of some of them.

(1050 tons prop in payload bay loaded in orbit+ 1100 tons of prop and 85 tons of vehicle means you can accelerate to 2000m/s or so, transfer propellant to /from a large tank, and then cancel your outbound vector.)

ISRU helps a lot.