Syntin for the second stage of Falcon 9?

[LouScheffer]

Syntin is a synthetic hydrocarbon with slightly better properties than RP-1. It's a little denser and slightly higher ISP.  The main drawback seems to be that it has to be synthesized and is hence expensive.  But it seems like using it in the second stage could help Falcon 9 to GTO significantly.

Assuming current payload to GTO of 4.85t, empty second stage mass of 5t, and propellant load of 90t (200k lbs), and ISP of 340, then the delta-V provided by the second stage is:

340*9.8*ln( (4.85+5+90) / (4.85 + 5)) = 7717 m/sec

Syntin is about 5% denser.  Assuming you cool the LOX, you can get 8-9% denser on that, too. 

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20050203875_2005204553.pdf

So assume you can cram  95t of propellant in the current stage.  The Russian engines got about 8 sec more ISP with syntin.   So now you can loft 6t to GTO...

348*9.8*ln( (6+5+95)/ (6+5)) = 7726 m/s

So how expensive is syntin in industrial quantities? 

EDIT:  Oops, I wrote 940/948 for the ISP where I meant 340/348.  But this was a copying error and the results are correct.

[Proponent]

This is vague, but Bruce Dunn suggested in the mid-1990s that it would cost more than $100/kg.

But the project seems like a lot of work for a slightly greater capacity.

[cartman]

Well if its $100/kg it is $9.5million for 95 tons plus the cost to test and qualify the fuel. Probably not worth it, at least in a launch that costs about $50million

[llanitedave]

Is there any indication that SpaceX has expressed interest in Syntin?

[Lars_J]

Why would it be worth it, if it only provides a slight benefit?

[LouScheffer]

Well if its $100/kg it is $9.5million for 95 tons plus the cost to test and qualify the fuel. Probably not worth it, at least in a launch that costs about $50million

Only half the propellant is Syntin, the rest is LOX, so it adds only 5 million or so.  And there are lots of commercial satellites in the 4.85t < M <6t mass range.  See this recent SeaLaunch example:

http://www.sea-launch.com/missions-q11373-Mission_Overview.aspx

The alternative (from the SpaceX view) would be to use a FH.  If you can compete for these same launches with an F9, it would save a lot of money, even if the fuel was a few million bucks more.

[Elmar Moelzer]

Hmm, pre chilling the RP1 might yield better results (might have other issues though).

[Danderman]

This would work, but:

Sintin is really not available.

and

the engine has to modified to burn Sintin.

As a result, the IRR on learning to burn methane is probably higher.

[cambrianera]

Only half the propellant is Syntin, the rest is LOX, so it adds only 5 million or so.

Actually less than one third; lowest O/F ratio for LOX and RP-1 is around 2.2 (most common around 2.5).

[john smith 19]

Well if its $100/kg it is $9.5million for 95 tons plus the cost to test and qualify the fuel. Probably not worth it, at least in a launch that costs about $50million

Only half the propellant is Syntin, the rest is LOX, so it adds only 5 million or so.  And there are lots of commercial satellites in the 4.85t < M <6t mass range.  See this recent SeaLaunch example:

http://www.sea-launch.com/missions-q11373-Mission_Overview.aspx

The alternative (from the SpaceX view) would be to use a FH.  If you can compete for these same launches with an F9, it would save a lot of money, even if the fuel was a few million bucks more.

Not really. IIRC Robobeat said Spacex are quoting NASA 16 tonnes to LEO and maybe half that to GTO for an expendable mission.

It sounds like Syntin is costing about the same as J10 (the synthetic fuel for cruise missiles) at about $100/lb.

RP1 is somewhere below $1/lb AFAIK. It's said that fuel costs are in the "noise" as far as launch costs are concerned but if that figure is right then Syntin is more expensive than any of the Amines.

The trouble with both  sub cooled propellants and advanced propellants is that they should be designed in before the LV is designed. That increased propellants weight means a) More thrust needed from the engines b)Slower acceleration,  so more stress on the vehicle, which means you either eat into your safety margins or strengthen the vehicle.

Similar issues with changing propellants. A 100x fold increase in propellant cost is pretty serious already but the logistics costs around it will cause even more cost and disruption.

The note on the LO2 densification article the OP mentions suggest that it's possible to build an HX with temperature difference across the exchanger of about 1 2/3K. That suggests that using standard boiling point LN2 you could cool any propellant to 79K (provided it's mp > 79k) without the trouble and expense of putting a large, high power vacuum pump on the exhaust to lower the BP of the LN2 (lowering the air pressure in the 2nd stage of the LN2 boiler by about 12 psi buys you about 10k).

Yes it's probably feasible. No it's probably not worthwhile 

[Jim]

Hmm, pre chilling the RP1 might yield better results (might have other issues though).

Heating works better.

[Elmar Moelzer]

Hmm, pre chilling the RP1 might yield better results (might have other issues though).

Heating works better.

I thought of pre chilling the RP1 for increasing the density. Wouldn't heating have the opposite effect?

[cambrianera]

Hmm, pre chilling the RP1 might yield better results (might have other issues though).

Heating works better.

I thought of pre chilling the RP1 for increasing the density. Wouldn't heating have the opposite effect?

We are talking about the second stage, what's important is the specific energy, not the mass density.
Heating increases total energy (and combustion efficiency).
http://forum.nasaspaceflight.com/index.php?topic=5118.msg81521#msg81521
http://forum.nasaspaceflight.com/index.php?topic=5118.msg81574#msg81574
http://forum.nasaspaceflight.com/index.php?topic=5118.msg81581#msg81581

[Dudely]

Man, rockets are hard.

[Elmar Moelzer]

I thought of pre chilling the RP1 for increasing the density. Wouldn't heating have the opposite effect?

We are talking about the second stage, what's important is the specific energy, not the mass density.
Heating increases total energy (and combustion efficiency).

Oh, that makes sense! Thanks!

[Robotbeat]

How much does heating really change the energy, though? Mass ratio is also really important.

[vigleik]

Let me point out a problem with the math in the original post: If you increase the mass of the second stage and the payload the delta v provided by the first stage goes down, and it looks to me like that wasn't taken into account. So the advantage is smaller than implied. (Exact numbers left as an exercise.)

[LouScheffer]

Let me point out a problem with the math in the original post: If you increase the mass of the second stage and the payload the delta v provided by the first stage goes down, and it looks to me like that wasn't taken into account. So the advantage is smaller than implied. (Exact numbers left as an exercise.)

This is certainly true, and it reduces the advantage by about 30%, to about +800kg.  But on the other hand, SpaceX has announced that the regular kerosene powered model can loft 5.3t to GTO, more than the 4.85t previously claimed.  So a Syntin-fueled second stage could still put 6.1t into GTO.  That covers an awful lot of the comsat market.

Of course the FH can do this job easily.  But even if the stages are recoverable, it's still expensive.  Say the engines are $1M each, and can be used 10 times.  Then each use costs $100k.  The 18 extra engines cost at least 1.8 million in wear and tear alone, not to mention recovery and re-stacking.

Furthermore, a 4t comsat could be launched on a recoverable F9.1 mission with Syntin, but would need an expendable or a FH with kerosene.

[Lars_J]

Syntin is not 'KISS'. It only provides a minimal performance boost. Therefore it won't happen.

[Robotbeat]

Syntin is not 'KISS'. It only provides a minimal performance boost. Therefore it won't happen.

Same with subcooling, which Musk suggests is likely?

I have no idea if syntin would be used, but something similar (and much cheaper) may be looked at by SpaceX if they need the performance. Which they probably do in order to reach all their performance goals. Subcooling sounds like a better idea, though, but I wouldn't put it past SpaceX to consider a reformulation of kerosene for the upper stage. A few seconds more Isp, a few percent better density, and you can now afford even upper stage recovery (or at least first stage recovery for an expanded customer list).

Propellant subcooling, carbon-carbon nozzle upper stage, possible other tricks like syntin for upper stage, maybe crossfeed for the Falcon Heavy... Pretty soon you've bought back much of the performance hit of reuse.