Hypothetical new Falcon 1 type LV

[Dante80]

This is a hypothetical exercise for anyone interested (I think it could be fun), I do know that SpaceX is not looking into something like this.

From what we know, development of the Falcon 1 vehicle had a cost somewhat close to $100M. The vehicle itself was retired after 5 launches (the first three unsuccessful). Before cancellation, SpaceX was thinking about producing a slightly larger variant, 1e.

Assuming SpaceX wanted to make something like this again, with their current state of technology and knowledge, how would the end vehicle look like?

Assumptions for the exercise.

1. Using a M1-D FT engine.
2. A second stage using a new variant of the Kestrel engine (what?), or something of similar/close power/thrust.
3. Absolutely no re-usability equipment.
4. Same diameter (1.7m), with the 1e fairing shape.
5. Liberal use of commonalities with F9 FT and 3d printing methods.

What we are looking for.

a. How much would you think it would cost to develop and launch?
b. What could be its capability to LEO, SSO and polar orbits?
c. How would it look like (dimensions, weight)?
d. How would it fare in price against Vega, and the very small launchers under development (XCOR, Electron etc)?
e. Would it eat part of the Falcon 9 market?

[Dante80]

I'm trying to find some sketches for the old Falcon 1 LV for inspiration. Here are some, post others if you have them..C:

[Kansan52]

Wasn't some company already doing that? Designated as a cube launcher if memory serves.

[Dante80]

Wasn't some company already doing that? Designated as a cube launcher if memory serves.

There are a couple out there.

[Kansan52]

Thanks!

[Lars-J]

It would be an interesting exercise, but the first stage would likely need a substantial stretch. M1D FT has roughly twice the thrust that M1A had. 

The question of an upper stage is the toughest nut to crack. Kestrel is long out of production, and M1DVac has a nozzle that is waaaay too large. But I'm sure they could think of something.

And since the F1 tooling is no longer in use, I'm not sure the F1 diameter has to be a constraint. Perhaps a short and stubby F9?  (This would use the F9 FT upper stage as a first stage)

[Dante80]

A stretch would be warranted, yes. Falcon 1e was being designed to be four and a half meters longer than F1, as well as close to 40,000kg at take off.

If we extrapolate, a M1-D FT S1 could be even longer, bringing the total height of the rocket above 30 meters.

Regarding S2, a M1-D vac is overkill, especially since we are brainstorming about an expendable vehicle here  (S2 would have to do less work). That's why I talked about a Kestrel variant. I was thinking of something the size/power of Kestrel2/RD-58MF.

Here is the old upgrade path for Falcon 1. Kestrel 2 was being designed for 330s Isp at the same thrust level.

Regarding diameter, I think that it would be more fun to keep it constant for the exercise.
 

[CameronD]

An interesting idea...

Regarding S2, a M1-D vac is overkill, especially since we are brainstorming about an expendable vehicle here  (S2 would have to do less work). That's why I talked about a Kestrel variant. I was thinking of something the size/power of Kestrel2/RD-58MF.

Maybe something from XCOR with a vacuum-optimised nozzle?

[deltaV]

SpaceX presumably abandoned Falcon 1 because there wasn't enough demand for a launcher that size to justify the fixed costs. Now that Falcon 9 is on the verge of reusing its first stage the business case for an expendable Falcon 1 just got even worse. Why design a launch vehicle that's not worth building?

[Dante80]

SpaceX presumably abandoned Falcon 1 because there wasn't enough demand for a launcher that size to justify the fixed costs. Now that Falcon 9 is on the verge of reusing its first stage the business case for an expendable Falcon 1 just got even worse. Why design a launch vehicle that's not worth building?

Because this is a theoretical exercise and we know for a fact that SpaceX do not want to bring back the Falcon 1.

Maybe something from XCOR with a vacuum-optimised nozzle?

Thats an interesting thought (although I think that SX would use/develop an in-house engine).
Piston fed Kestrel2?

[S.Paulissen]

I don't think that they would constrain themselves to the given constraints that you provided. 

I suspect that they would have instead made a two stage rocket, with a single merlin 1d that amounts to being something near a shrunken F9 second stage and a triple sized falcon1 second stage.

Given that Merlin1D FT has about 756kN (77000 kg) of thrust at sea level, or enough to lift a vehicle with a 74000kg GLOM with a liftoff acceleration of about 0.05g, well in the range of other SpaceX launches (maybe even a little high).

The current F9-SII has a dry mass of about 4000kg and a propellant capacity of about 100000kg  naturally this cannot be lifted by a single merlin at take-off so it needs to be shrunk with each 1m of length subtracting about 220kg of dry mass and losing 20000kg of propellant.  Thus the stage could drop about 53000kg of propellant and 625kg of dry mass to have a first stage GLOW of ~44000kg leaving about 27500kg of mass for the second stage and payload.

I don't think there is a lot of performance to be wrung out of the kestrel engine design because it's pressure fed, thus any increase in performance would be at the cost of increased tank mass to contain additional tank pressure needed to get ISP.   I based it largely off of a stretched version of the falcon 1 second stage, including a diameter reduction after the second stage (yup, this would be an awkward looking bird, like some old-timey ICBM based stacks).  It would carry about 24250kg of propellant and have a dry mass of 1800 kg; because of this I used a triple sized Kestrel 2 engine that gets the same 317s ISP.  The relatively low mass fraction is required for the tanks to achieve the ~150PSI tank pressure needed to feed the 135PSI chamber pressure.  Tankage mass increases three fold for the same volume.  This is partially offset (compared to the merlin stage) by kestrel 2 only weighing 200kg (triple sized kestrel) compared to 490kg for merlin.

This stack can push 700kg to 28 degrees LEO (9.9km/s dV) and leaves a LOT of room for optimization and mass fraction gains.  Keep in mind this is a back of the envelope quality estimation of performance at best (as expected playing lego-rockets)

[Gliderflyer]

Maybe something from XCOR with a vacuum-optimised nozzle?

According to Wikipedia, the Kestrel had 6900 pounds of thrust, so a couple of 5K18s (Lynx engine) should be in the ballpark.

[Dante80]

I don't think that they would constrain themselves to the given constraints that you provided. 

I suspect that they would have instead made a two stage rocket, with a single merlin 1d that amounts to being something near a shrunken F9 second stage and a triple sized falcon1 second stage.

But what you wrote is inside the constraints I gave (save for the different diameter of the 2nd stage).

Very cool post btw, thanks for that. What would the total height of the rocket be in your example?

[Stan-1967]

I have wondered the same thing.  I posted this a few weeks back:
http://forum.nasaspaceflight.com/index.php?topic=38149.msg1463029#msg1463029

I was thinking of something in the class of a "Rutherford" electric pump fed engine with better ISP than a Kestrel.  I concluded that re-doing Kestrel would not be worth it.  I think the Rutherford engine is still pretty small, and I'm not sure of the mass estimates for the battery scaling issues if making a larger S2 engine.

I have been meaning to go back and see if I can make some WAGS on reasonable dimensions and mass for S1 and S2.   The exercise was academic, as no market emerged for this class of launcher, nor has it yet emerged.  It's just interesting because I think it makes an impressive rocket against the small launchers out there like VEGA or LauncherOne.   

1.  Use same S1 structure as F1-e, but stretch the tank to max fineness ratio
2.  Purchase used Merlin 1D FT engines from returned cores
3.  3-D print my upper stage engine if I can't buy it somewhere else.
4.  Build in-house only what is necessary.  Outsource the rest.   Too small a market to take on lots of fixed costs.

[Craftyatom]

Math time, boys.  Using specs on the F9 1.1 FT from SF101 (which are admittedly estimations):

fully-fueled first stage weighs about 431,700kg and is 94.9% propellant
First stage is 41.2m tall (without interstage) and 3.66m in diameter for a volume of 433 m^3 (this is not actual tank volume, but works fine for estimations)
Density of first stage is 997kg/m^3

A single Merlin 1D Full Thrust has a thrust of 756kN at sea level
A TWR of 1.1 should be completely sufficient
Which means that the engine can lift just over 70,000kg at liftoff

Based on earlier statistics and a diameter of 1.7m (as per Falcon 1), the F1SSTO, or "Fisto", is 31 meters tall, has no second stage, burns for 236 seconds (281kgprop/s), and assuming it reaches vacuum after the normal F9 burn time of 162 seconds, has a delta-v of... 8771m/s.  Not quite enough, given that the Falcon 9 uses 10304 to get its max payload to LEO using the same calculation scheme.

One day, Fisto...  One day.

[Nomadd]

 It did surprise me that a rocket with close to the same payload as the Pegasus at 1/5th the price didn't have much of a a market. But, customers like Orbcomm or Iridium can do a lot better with a reusable F9, so maybe SpaceX thought it was a dead end. It's not likely a single engine rocket could return to the launch site.

[sdsds]

If the premise is that SpaceX will not be doing this, it would be interesting to think about a startup that purchased M1D engines from SpaceX and licensed the technology required for the remainder of an F1e-like vehicle.

In particular I think SpaceX might license Kestrel2 technology. With M1D having maybe twice the thrust of M1A, perhaps the second stage could be powered by dual Kestrel2 engines? How badly would that "blow" the diameter of the vehicle?

[Dante80]

It's just interesting because I think it makes an impressive rocket against the small launchers out there like VEGA or LauncherOne.   

That was pretty much the same reason for me posting this thread. C:

If the premise is that SpaceX will not be doing this, it would be interesting to think about a startup that purchased M1D engines from SpaceX and licensed the technology required for the remainder of an F1e-like vehicle.

In particular I think SpaceX might license Kestrel2 technology. With M1D having maybe twice the thrust of M1A, perhaps the second stage could be powered by dual Kestrel2 engines? How badly would that "blow" the diameter of the vehicle?

Here is an old diagram about Falcon 5 using 2 uprated Kestrel engines for S2. The diameter was the same as Falcon 9.

Btw, keeping the same diameter as Falcon 1 would match the F9 FT thinness ratio at about 32 meters total height.

Assuming a 31kN Kestrel 2 with 330s Isp (as it was being designed), I think that you could keep S2 having a solitary engine and still be good for the job if the first stage with the new Merlin did more of the job (the rocket is expendable, so recovery operations are not a factor for S1-S2 SEP. Only maximum g-load is). Maybe a bigger niobium or carbon-carbon nozzle extension could do the job?

[Dante80]

A couple of F1-F1e sketches.

[S.Paulissen]

I don't think that they would constrain themselves to the given constraints that you provided. 

I suspect that they would have instead made a two stage rocket, with a single merlin 1d that amounts to being something near a shrunken F9 second stage and a triple sized falcon1 second stage.

But what you wrote is inside the constraints I gave (save for the different diameter of the 2nd stage).

Very cool post btw, thanks for that. What would the total height of the rocket be in your example?

My lift off height is estimated at about 25m.  4.5m are from fairing, 10.0m are from the first stage, and 7.5m are from the stretched second stage plus 3m of interstage.

I arrived at 10m for the first stage by losing 2m from the vacuum nozzle of the existing second stage as well as a 2.5m shrink of the tank to fit the proposed propellant 14.3m-2-2.5=~10m giving a little extra leeway for size.  I kept the interstage length constant (about three meters) as expansion ratio (and hence nozzle length) the same.  The upper stage tank is about 7.5m (3x Falcon 1) long plus the 3m of kestrel.  However the 3m of kestrel overlap with the already accounted for interstage length.