Hypothetical new Falcon 1 type LV

[Stan-1967]

But I understood what you said. That's why S2 is a little bigger than S1 (as you said), and it's less than half the weight of the F9 S2. The diameter is 1.7m.

No, you are still not getting what I mean. The diameter would be 1.7m, but it would contain almost the same amount of propellant as the F9 upper stage. It would be MUCH longer. And due to this non-optimal size, the dry mass of the stage would be the same or likely higher. Therefore no burnout g-load issue.

It will take at least 30 meters of 1.7 meter core to hold around 78,500 kg of fuel, which is what the latest F9 S2 reportedly contains.   The burn time for a Merlin to go through this fuel will be around 295s.  The Merlin 1D at 756 kN cant lift that load of fuel.  Merlin Vac manages because it produces 934 kN.

[Lars-J]

But I understood what you said. That's why S2 is a little bigger than S1 (as you said), and it's less than half the weight of the F9 S2. The diameter is 1.7m.

No, you are still not getting what I mean. The diameter would be 1.7m, but it would contain almost the same amount of propellant as the F9 upper stage. It would be MUCH longer. And due to this non-optimal size, the dry mass of the stage would be the same or likely higher. Therefore no burnout g-load issue.

It will take at least 30 meters of 1.7 meter core to hold around 78,500 kg of fuel, which is what the latest F9 S2 reportedly contains.   The burn time for a Merlin to go through this fuel will be around 295s.  The Merlin 1D at 756 kN cant lift that load of fuel.  Merlin Vac manages because it produces 934 kN.

Yes, so reduce it in size a bit then so it matches the M1D thrust. But I never claimed it was a great design.

[S.Paulissen]

It's not, because it can't make it to orbit, even with no payload.... And still will pull over 10g acceleration at cutoff with 65% throttle with no payload assuming it's mass is nearly a falcon 9 second stage mass.  As mentioned above, falcon 9 fixes this by having excess margin propellant as ballast.  Jim says this all the time, excess performance is transferred to the upper stage and this is largely (but not entirely) why. 

Long story made short, no, acceleration g force concerns were not overblown.

[CuddlyRocket]

Remembering that this is supposed to be a low-cost launcher and its design should therefore be optimised for cost, not performance, I'd suggest the following design parameters: Common propellant for both stages and using existing equipment where possible.

Given the above, how about the following proposal: A 2-stage rocket; both stages keralox with a single M1-D SL engine? The SL version is not as efficient as the Vac in space, but it should be sufficient (it has a vacuum isp of 308 versus 348). It's also lower thrust, which helps with problems of over-acceleration on the second stage (and it can throttle down to 70%).

Anyone care to run the numbers?

Won't work, too much thrust for a merlin on second stage at minimum throttle the upper stage would hit 20gs at burn out.

Shame! By the way, what is the maximum g at burn out one should aim for?

So, either we reduce the thrust of the M1-D SL, which would mean a redesign, or we find a smaller keralox engine. The trouble is, there's not that many about, especially non-Russian ones! Presumably SpaceX still has the plans for its Kestrel engine. I don't know if they could still manufacture it if they were paid to do so, but they might sell the design to someone else so to do. Or someone could bite the bullet and develop a new small keralox engine!

[Modal]

Remembering that this is supposed to be a low-cost launcher and its design should therefore be optimised for cost, not performance, I'd suggest the following design parameters: Common propellant for both stages and using existing equipment where possible.

Given the above, how about the following proposal: A 2-stage rocket; both stages keralox with a single M1-D SL engine? The SL version is not as efficient as the Vac in space, but it should be sufficient (it has a vacuum isp of 308 versus 348). It's also lower thrust, which helps with problems of over-acceleration on the second stage (and it can throttle down to 70%).

Anyone care to run the numbers?

Won't work, too much thrust for a merlin on second stage at minimum throttle the upper stage would hit 20gs at burn out.

Shame! By the way, what is the maximum g at burn out one should aim for?

IIRC, 7g's at a maximum for satellites.

[bstrong]

Or someone could bite the bullet and develop a new small keralox engine!

Like the FRE-1? (thrust: 6,200 lbf, isp: 325 sec)

http://www.fireflyspace.com/vehicles/firefly-a
http://www.fireflyspace.com/news/ournews/first-rocket-engine-test-a-success-for-firefly-space-systems

Edit: actually, those two links disagree on the thrust. the second says 7,000 lbf

[S.Paulissen]

So, it's a kestrel clone, in performance and mode of operation if not design.  The problem with these size of engines (technically just a glorified valve in front of a combustion chamber, not the literal definition of an engine) is that they're too small to lift the size of upper stage needed to best utilize the lift off a Merlin 1d FT.

[JamesH]

So, it's a kestrel clone, in performance and mode of operation if not design.  The problem with these size of engines (technically just a glorified valve in front of a combustion chamber, not the literal definition of an engine) is that they're too small to lift the size of upper stage needed to best utilize the lift off a Merlin 1d FT.

So is the Lamborghini a Ferrari clone?  Same performance, same mode of operation. Not really a clone I would say.

[CuddlyRocket]

Or someone could bite the bullet and develop a new small keralox engine!

Like the FRE-1? (thrust: 6,200 lbf, isp: 325 sec)

http://www.fireflyspace.com/vehicles/firefly-a
http://www.fireflyspace.com/news/ournews/first-rocket-engine-test-a-success-for-firefly-space-systems

Edit: actually, those two links disagree on the thrust. the second says 7,000 lbf

So, it's a kestrel clone, in performance and mode of operation if not design.  The problem with these size of engines (technically just a glorified valve in front of a combustion chamber, not the literal definition of an engine) is that they're too small to lift the size of upper stage needed to best utilize the lift off a Merlin 1d FT.

By the look of it, these engines are designed to be clustered (not necessarily in an aerospike) so it depends on how many will fit under the 2nd stage. At least there should be no problems with excessive acceleration!

[swervin]

In light of all experience gained at SpX for recovery, and the proposed S2 recovery for F9 via the ‘party baloon’ concept, any thoughts on utilizing a similar system to make any part of this theoretical LV recoverable? Yes, margins are beyond thin or non-existent for mass/space, and SpX isn’t furthering the dev of this rocket, but hey, this is a theoretical topic anyway!

Also, non-theoretical: did SpX ever make a 6th F1 core? What happened to all the tooling and already built Kestrel engines?

Hope y’all don’t get mad at an old topic resurfacing... 😳

Cheers,
Splinter

[IanThePineapple]

Yes, there is a sixth F1 core and an F1 fuel tank sitting in SpaceX's junkyard in Hawthorne

[swervin]

Thx, Ian! I didn’t realize they had a ‘junkyard’ at Hawthorne. Anyone have a sat pic of it! I don’t see it on google maps...

[IanThePineapple]

There was a post on /r/SpaceX about it a few months back, just search "junkyard" on the subreddit

[Elthiryel]

Yep, it can be found on reddit.

https://www.reddit.com/r/spacex/comments/61pizd/looking_through_the_spacex_junkyard_on_google/
https://imgur.com/a/QZ7Wi

/u/randomstonerfromaus:

For those that are not aware, this is at the SpaceX Wilkie facility which is an annex of Hawthorne which IIRC is tasked with R&D. Here it is on maps. The legs are located on the East side of the building, about half way up. The junkyard is above the North East corner of the building.

[Giovanni DS]

Wouldn't make more sense to base this hypothetical new small launcher on Raptor? They would need an engine for the 2nd stage but It would be in a very different performance class compared to Falcon1 while still having a similar level of complexity.

[speedevil]

Wouldn't make more sense to base this hypothetical new small launcher on Raptor? They would need an engine for the 2nd stage but It would be in a very different performance class compared to Falcon1 while still having a similar level of complexity.

A launcher with a 170 ton engine is not most peoples idea of a small launcher.

[rakaydos]

Wouldn't make more sense to base this hypothetical new small launcher on Raptor? They would need an engine for the 2nd stage but It would be in a very different performance class compared to Falcon1 while still having a similar level of complexity.

Upper stage would be a cluster of the Gas Methalox RCS they are developing for BFB landing control- the number I remember is 10 tons of thrust each, and it's effectively the same propellant on both stages and as their larger launcher.

A single raptor booster might be small enough for parachute recovery, too.

[Lars-J]

Wouldn't make more sense to base this hypothetical new small launcher on Raptor? They would need an engine for the 2nd stage but It would be in a very different performance class compared to Falcon1 while still having a similar level of complexity.

A launcher with a 170 ton engine is not most peoples idea of a small launcher.

Falcon 1 doesn't fit that criteria for some people either.    Is your goal to just create a hypothetical smallest launcher, or is it to create a hypothetical small launcher that would actually be more compatible with SpaceX efforts going forward? If the latter you base it on Raptor, and it is would still be a very "small" launcher in SpaceX's lineup.

[speedevil]

Falcon 1 doesn't fit that criteria for some people either.    Is your goal to just create a hypothetical smallest launcher, or is it to create a hypothetical small launcher that would actually be more compatible with SpaceX efforts going forward? If the latter you base it on Raptor, and it is would still be a very "small" launcher in SpaceX's lineup.

Hmm.

If we're going 'going forward',, I propose a F9S2 methalox sized S1, with a smaller metholox stage on top.

Perhaps 9 tons to LEO, or if you stick it in BFR, as a third stage, you get about 45 tons to mars orbit. Add aerobraking hardware, which is conveniently already available, extend the duration a lot, and for one launch, not seven, you get 30 tons in low mars orbit, or perhaps making some assumptions, 20 tons to the moon. (with a second stage/lander).