A list of things SpaceX will unlikely be doing

[hkultala]

Based on opinion.

1) They are not doing SSTO from earth.

BFS lacks the T/W with tanks full and very SERIOUSLY lacks T/W with engines that work well in atmosphere. The first stage is there for a very good purpose.


2) They are not mass-producing many different-sized versions of raptor in parallel. They are now going to the engine with about 170 tonne thrust, with different nozzles for vacuum and atmospheric operation. Initial versions of the same engine size may have lower thrust due lower pressure and later versions may have higher thrust due greater pressure, but they will mass-produce only chamber size, one pump at a time.
 

3) They are not making reusable second stage for Falcon 9/FH. All the extra engineering work not required to service customers who have already signed goes to BFR project.


4) They will not be making BFR/BFS out of cluster of 3.7 meter tanks. These would weight much more etc. Saturn 1 was a quick hack to get Apollo capsule to the orbit as quickly as possible, but a very unoptimal solution.


5) They are not going to do versions of FH with different amount than 27 first stage engines or different tank sizes.


6) They will not be making multi-chamber main engines.


edit: added later

7) Raptor-based upper stage for Falcon 9/FH. They will go all the way into full BFR/BFS.


8 ) They will not drop FH now when it's ready and delay all FH missions ~5 years to move them to BFR/BFS.


9) They will not switch back to 12m BFR/BFS , at least until their Mars colony already exists.

Their facilities can handle 9m but not 12m, their engines are sized for 9m, not 12m. 9m is much better for general purpose usage.


10) They will not use F9 as extra side boosters to BFR/BFS. Way too much complexity, both increasing operating costs and decreasing reliability considrably. And the want to phase out F9 eventually. etc. And no need, the rocket has enough capacity without these.

[Proponent]

Could we add that SpaceX is not developing a Raptor-powered second stage for F9 or FH?

[Semmel]

I hope the list above breathes a bit of realism into people with overenthusiastic needs to speculate. The quality of this site depends on this. There is so much room where speculation is required, but most often a sense of pragmatism would do a lot more as well.

To add:
* No sci fi propulsion like nuclear or enormous solar electric
* No nuclear power for surface operation, at least not initially
* No smaller sized prototypes
* No use of metallic tanks, carbon fibre all the way
* No artificial gravity, at least not initially
* No launch abort system

[DreamyPickle]

I don't like this kind of thread. A few years ago people would have put "no landing at sea" on the list. It's better to just let people speculate.

In particular nuclear is something that people top management at SpaceX have expressed an interest in. Both for surface power and nuclear-thermal propulsion.

[jpo234]

* No sci fi propulsion like nuclear or enormous solar electric
* No nuclear power for surface operation, at least not initially

Gwynne Shotwell recently at MIT:
https://mobile.twitter.com/charlottelowey/status/913145922976190464

[AbuSimbel]

I don't like this kind of thread. A few years ago people would have put "no landing at sea" on the list. It's better to just let people speculate.

In particular nuclear is something that people top management at SpaceX have expressed an interest in. Both for surface power and nuclear-thermal propulsion.

Yeah calm down people. I'm sure Chris has enough space on NSF's servers for these topics that you find pointless. Maybe they're not.

[Darkseraph]

* No sci fi propulsion like nuclear or enormous solar electric
* No nuclear power for surface operation, at least not initially

Gwynne Shotwell recently at MIT:
https://mobile.twitter.com/charlottelowey/status/913145922976190464

They might have been thinking of using said nuclear materials for surface power rather than propulsion. Tom Mueller has made suggestions of it being beneficial for that purpose relative to solar.

[gongora]

I hope the list above breathes a bit of realism into people with overenthusiastic needs to speculate. The quality of this site depends on this. There is so much room where speculation is required, but most often a sense of pragmatism would do a lot more as well.

To add:
* No sci fi propulsion like nuclear or enormous solar electric
* No nuclear power for surface operation, at least not initially
* No smaller sized prototypes
* No use of metallic tanks, carbon fibre all the way
* No artificial gravity, at least not initially
* No launch abort system

This list may be correct for the vehicle just announced but not for their long-term goals.

[Lar]

(fan)
I'm not sure I think this thread is a good idea. Let people speculate and if you don't want to read teh thread, don't. Some of the stuff on the combined list (taken from all the posts so far combined) is stuff that I believe SpaceX WILL do, just not at first (nuclear surface power) and some is stuff that they might be forced into rather than give up on BFR/BFS (metallic tanks)

I agree that a lot of the stuff is unlikely but we don't for sure know that it is completely off the table. For example.... Just one size Raptor makes sense to ME but may not be how things go.

(mod) No action at this time but if this thread turns into a speculation bash fest, I'll reconsider. Speculation is OK, within limits.

[speedevil]

1) No SSTO.

SSTO, no. But the stage can do very significant non-orbital hops on its own power.

[jpo234]

* No sci fi propulsion like nuclear or enormous solar electric
* No nuclear power for surface operation, at least not initially

Gwynne Shotwell recently at MIT:
https://mobile.twitter.com/charlottelowey/status/913145922976190464

They might have been thinking of using said nuclear materials for surface power rather than propulsion. Tom Mueller has made suggestions of it being beneficial for that purpose relative to solar.

https://twitter.com/charlottelowey/status/913219813882912768

[Semmel]

I might have overstepped with my post a bit. Sorry about that. I also dont want to stop people from speculation. Just to get some more sense and reflection upon what is actually likely to happen.

Often people speculate because they like a topic, not because its actually based on a need from SpaceX or a hint. Words of a tweet or interview are taken out of context in order to feed a specific speculation. This just decreases the signal to noise on this site. And "dont read it if you dont like it" doesnt help because one has to read it to evaluate if its actually viable or not. I dont want to prejudge people. I take every post seriously. And I do that because here are many more actually well thought through points than anywhere else I know. It does becomes increasingly difficult over time to find the well made points under all the heaps of speculation. And it is tiring, it was especially bad just before the announcement. That was the source of my frustration.

[DJPledger]

Sadly no dev. of an F-1 class engine which they were promising for many years until 2-3 years ago.

Appears SpaceX have no interest in VASIMR so extremely unlikely they will dev. one.

[DJPledger]

* No use of metallic tanks, carbon fibre all the way

Falcon family has metallic tanks. BFR will have CF tanks so no more metallic tanks after Falcon family production stops.

[Jim]

Could we add that SpaceX is not developing a Raptor-powered second stage for F9 or FH?

I am going to post this again.

[Patchouli]

* No sci fi propulsion like nuclear or enormous solar electric
* No nuclear power for surface operation, at least not initially

Gwynne Shotwell recently at MIT:
https://mobile.twitter.com/charlottelowey/status/913145922976190464

Nuclear power would be very useful for early power on a Mars base.
NTR engines would cut the propellant load needed for TMI in half though I think they'll stick with chemical engines here for the near future.
Though they may be more interested in whats called a radio heater unit.

One thing I can say Spacex probably won't do is liquid hydrogen chemical engines as they seem content with hydrocarbon ones.

I can't say no on solar electric and VASIMR as a solar electric tug would drastically reduce the number of launches needed for GTO and cargo missions.

[Robotbeat]

NTR isn't worth it unless 60 day trip times is too long and you want more like 30 or 40.

[Lar]

Surface power on the other hand makes a lot of sense... at some point a solar infrastructure will be bootstrapped, it doesn't make sense not to... but for initial power a small reactor might mass less and be more plug and go...

[Robotbeat]

Surface power on the other hand makes a lot of sense... at some point a solar infrastructure will be bootstrapped, it doesn't make sense not to... but for initial power a small reactor might mass less and be more plug and go...

Initial reactor needs to be like 1 Megawatt, though. Kilopower is only up to 10kW, you'd need 100 of them... & they're expensive. And nothing else is really under development.

[rakaydos]

NTR isn't worth it unless 60 day trip times is too long and you want more like 30 or 40.

I wonder...

Hmm.. Atomic Rockets says Methane is a crappy NTR fuel, because the heat breaks the fuel down into hydrogen (awesome NTR fuel) and elemental carbon (with a tendancy to soot up the engine in a way that O2/methane burning doesnt)

Otherwise, the thought would be a NTR tug designed to fit in a BFR-cargo, and mate with the BFR refueling pipes to run off the BFR's own tanks.

[Lar]

Surface power on the other hand makes a lot of sense... at some point a solar infrastructure will be bootstrapped, it doesn't make sense not to... but for initial power a small reactor might mass less and be more plug and go...

Initial reactor needs to be like 1 Megawatt, though. Kilopower is only up to 10kW, you'd need 100 of them... & they're expensive. And nothing else is really under development.

I remember a rumor going round that SpaceX had talked to some marine reactor company, and add that to Gwynne saying they were seeking nuclear material and you get something bigger than 10kW I think.

[rakaydos]

Surface power on the other hand makes a lot of sense... at some point a solar infrastructure will be bootstrapped, it doesn't make sense not to... but for initial power a small reactor might mass less and be more plug and go...

Initial reactor needs to be like 1 Megawatt, though. Kilopower is only up to 10kW, you'd need 100 of them... & they're expensive. And nothing else is really under development.

I remember a rumor going round that SpaceX had talked to some marine reactor company, and add that to Gwynne saying they were seeking nuclear material and you get something bigger than 10kW I think.

The 10 kw Kilopower is 2 tons. (https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20160012354.pdf page 4)
How strong is the BFS's crane? how much bigger can a reactor get, before it has to stay on the spaceship?

[JamesH65]

Surface power on the other hand makes a lot of sense... at some point a solar infrastructure will be bootstrapped, it doesn't make sense not to... but for initial power a small reactor might mass less and be more plug and go...

Initial reactor needs to be like 1 Megawatt, though. Kilopower is only up to 10kW, you'd need 100 of them... & they're expensive. And nothing else is really under development.

I remember a rumor going round that SpaceX had talked to some marine reactor company, and add that to Gwynne saying they were seeking nuclear material and you get something bigger than 10kW I think.

The 10 kw Kilopower is 2 tons. (https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20160012354.pdf page 4)
How strong is the BFS's crane? how much bigger can a reactor get, before it has to stay on the spaceship?

I think we can guarantee that the crane in the BFS will be big enough to handle all possible/known requirements.

[CuddlyRocket]

How strong is the BFS's crane? how much bigger can a reactor get, before it has to stay on the spaceship?

Depends where that spaceship is: a crane's capacity is determined by the weight its load-bearing structures can sustain - and that weight includes the weight of its cable etc., all of which depends on gravitational strength.

I think we can guarantee that the crane in the BFS will be big enough to handle all possible/known requirements.

Certainly. Although you could have two cranes (at each end of the loading hatch) to allow for faster loading/unloading and some redundancy, which can work together for really heavy objects.

[docmordrid]

Alternative unloading plan: the early ships unload the parts for  mobile elevators which then have the capability to unload much heavier items, de-crew more elegantly etc. Crop of the Moon Base Alpha image,

[Dalhousie]

Surface power on the other hand makes a lot of sense... at some point a solar infrastructure will be bootstrapped, it doesn't make sense not to... but for initial power a small reactor might mass less and be more plug and go...

Initial reactor needs to be like 1 Megawatt, though. Kilopower is only up to 10kW, you'd need 100 of them... & they're expensive. And nothing else is really under development.

I remember a rumor going round that SpaceX had talked to some marine reactor company, and add that to Gwynne saying they were seeking nuclear material and you get something bigger than 10kW I think.

Ship reactors are cooled by seawater.  You would need a new cooling system.  Rule of thumb for thermal output of marine reactors is, I think, 5 X 10 electrical capacity. So 5-10 MW radiators.

[Lar]

Alternative unloading plan: the early ships unload the parts for  mobile elevators which then have the capability to unload much heavier items, de-crew more elegantly etc. Crop of the Moon Base Alpha image,

Agree.  A mass optimization would be to (eventually) remove the crane (just leave the mounts so it can be put back) from ships that are on the Earth-Luna run as they don't need it... but leave it in for ships that venture elsewhere, especially new places.... But I bet SpaceX doesn't bother with that mass optimization.

[envy887]

Surface power on the other hand makes a lot of sense... at some point a solar infrastructure will be bootstrapped, it doesn't make sense not to... but for initial power a small reactor might mass less and be more plug and go...

Initial reactor needs to be like 1 Megawatt, though. Kilopower is only up to 10kW, you'd need 100 of them... & they're expensive. And nothing else is really under development.

I remember a rumor going round that SpaceX had talked to some marine reactor company, and add that to Gwynne saying they were seeking nuclear material and you get something bigger than 10kW I think.

Ship reactors are cooled by seawater.  You would need a new cooling system.  Rule of thumb for thermal output of marine reactors is, I think, 5 X 10 electrical capacity. So 5-10 MW radiators.

How about a ground-coupled heat exchanger? Does the temperature, thermal capacity, and conductivity of the near subsurface at Mars support dumping that kind of heat with a small-ish HX?

[ValmirGP]

* No use of metallic tanks, carbon fibre all the way

Falcon family has metallic tanks. BFR will have CF tanks so no more metallic tanks after Falcon family production stops.

Highly speculative question. Could it be that from these assertions it would be also feasible/desirable to convert F9/FH tanks to CF too?

[Jim]

Highly speculative question. Could it be that from these assertions it would be also feasible/desirable to convert F9/FH tanks to CF too?

No, since they are going to be retired
 

[Lar]

How about a ground-coupled heat exchanger? Does the temperature, thermal capacity, and conductivity of the near subsurface at Mars support dumping that kind of heat with a small-ish HX?

There is a whole Power on Mars[1] thread that went through a lot of this. One important thing to rememeber is that on Mars, heat is not a thing to be shed. Rather it is a useful byproduct that can be used for many things.. process heat for the Sabatier, greenhouse heating, liquefaction of ice mined and a scad of other things. Might take several heat exchanger loops before you have water that is highly unlikely to have radioactive traces in it high enough to be worrisome. But you also don't really care if the heat exchangers are leaking heat to the atmosphere....

1 - https://forum.nasaspaceflight.com/index.php?topic=39785

[hkultala]

Added few more.. also edited these to the first message

8 ) They will not drop FH now when it's ready and delay all FH missions ~5 years to move them to BFR/BFS.


9) They will not switch back to 12m BFR/BFS , at least until their Mars colony already exists.

Their facilities can handle 9m but not 12m, their engines are sized for 9m, not 12m. 9m is much better for general purpose usag.

[JasonAW3]

Highly speculative question. Could it be that from these assertions it would be also feasible/desirable to convert F9/FH tanks to CF too?

No, since they are going to be retired

Eh, you never know, the F9's could still be pretty useful as strap-ons for a BFR Super Heavy design.  (Yes, I realize that the BFR booster would need to be beefed up for something like that, but it would be possible).

[envy887]

Highly speculative question. Could it be that from these assertions it would be also feasible/desirable to convert F9/FH tanks to CF too?

No, since they are going to be retired

Eh, you never know, the F9's could still be pretty useful as strap-ons for a BFR Super Heavy design.  (Yes, I realize that the BFR booster would need to be beefed up for something like that, but it would be possible).

And that would be inefficient and expensive. If the 9m BFR works great and there is demand for an even heavier LV, building a 12m or 15m version would be far more effective.

Falcon will be done once DoD switches to BFR.

[philw1776]

Highly speculative question. Could it be that from these assertions it would be also feasible/desirable to convert F9/FH tanks to CF too?

No, since they are going to be retired

Eh, you never know, the F9's could still be pretty useful as strap-ons for a BFR Super Heavy design.  (Yes, I realize that the BFR booster would need to be beefed up for something like that, but it would be possible).

Not only bad design but totally against SpaceX's cost philosophy.  Now you have 2 completely different propellant families, adding cost, and the F9 is NOT designed clean sheet, ground up to be rapid, inexpensive launch & re-launch servicable.  A Kerbal lego rocket fantasy out of whack with engineering reality.

[hektor]

At some point there were discussion the Falcon 9 would lift off from ASDS and land back on launch site to save on trips by the ASDS. Can we consider now that this is something Space-X will not do ?

[nacnud]

Depends where that spaceship is: a crane's capacity is determined by the weight its load-bearing structures can sustain - and that weight includes the weight of its cable etc., all of which depends on gravitational strength.

The crane could be very light, a dyneema rope strong enough to lift 2 tonnes in lunar gravity masses less than half kilo per 100m

http://www.samsonrope.com/Pages/Product.aspx?ProductID=872

[envy887]

At some point there were discussion the Falcon 9 would lift off from ASDS and land back on launch site to save on trips by the ASDS. Can we consider now that this is something Space-X will not do ?

They are probably saving that for BFR and even then it's well down the road.