SpaceX Unveils Heavy-Lift Vehicle Plan

[DeltaV]

SpaceX Unveils Heavy-Lift Vehicle Plan

[WizWom]

Actually, nuclear-Ionic should give much faster mission times to mars. even 1/1000g would have more delta-V at 60,000 ISP than 5g at 700 ISP.

But Nuclear thermal is attractive for ground launch.

[IntLibber]

Yeah, that XX rocket really is a biggie eh? Would that be a Nova class or beyond Nova?

Anybody who doubted Elon's determination to settle Mars before should be convinced by now. I volunteer to take a one way trip to Mars.

BTW: here are the PPT files that detailed the heavy lift plan:

http://commercialspace.pbworks.com/f/Sp ... small.pptx

http://commercialspace.pbworks.com/f/Ma ... small.pptx

[GIThruster]

Am I the only person who notes Elon wants USG to fund development of a NFR while he's building chemical?

Elon is right! NASA ought to be building the TRITON! Let PI build better chemical rockets while freeing NASA to design something next gen.

If we're stuck with rockets, then USG needs to spend the money to build a TRITON:

http://www.engineeringatboeing.com/data ... 4-3863.pdf

[93143]

TRITON is too heavy. And the power generation capability is far too small for primary propulsion, which means you're stuck with the ~900 second NTR mode to send you to Mars.

Now, a Dumbo-type NTR is another story...

Yeah, that XX rocket really is a biggie eh? Would that be a Nova class or beyond Nova?

No. Even Godzilla VII wasn't really Nova-class. The Saturn C8 was supposed to be 210 mT, and looking over the history I kinda feel like the lower bound should be 200 mT. Lots of 'Nova' designs were 400 mT or higher... Sea Dragon is a Nova-class MCDB...

[GIThruster]

No, the NTR thumbnail study you note has bogus numbers. It uses Isp numbers for the chemical side of the comparison that are higher than the SSME, and 800 sec for the NTR side when the prediction is 900 sec. (With better materials, much higher than 900 is possible.)

I think he's just showing how to do a comparison, rather than proposing this is a valid one. That's Goff, isn't it? He writes in other places how the NTR is his favorite choice for launch.

[WizWom]

No, the NTR thumbnail study you note has bogus numbers. It uses Isp numbers for the chemical side of the comparison that are higher than the SSME, and 800 sec for the NTR side when the prediction is 900 sec. (With better materials, much higher than 900 is possible.)

I think he's just showing how to do a comparison, rather than proposing this is a valid one. That's Goff, isn't it? He writes in other places how the NTR is his favorite choice for launch.

I should also be noted that a rocket typically sacrifices T/W ratio to increase specific impulse; I suspect a heavier working fluid would increase the T/W ratio considerably.

[93143]

That's Kirk Sorensen. He seems to be a bit closed-minded on the subject of nuclear propulsion (he thinks Polywell is fantasy, for one thing - heck, he thinks Dumbo is fantasy), but that analysis isn't too far off.

(And he has successfully demonstrated that a NERVA-type NTR is worthless for launch - you need a T/W above 10 or so for a positive payload.)

The chemical engine he cites in that example weighs the same as an RL-10A4-2 and has the same specific impulse as an RL-10B-2. This is a slightly over-optimistic set of specs, but not preposterous.

The T/W ratio he uses for the NTR is also too low. But for TRITON, not by much. Same with the specific impulse. (He has some harsh words for the designers who think they can get above 900 seconds with "imaginary Russian fuel elements"...)

Yes, a heavier working fluid would certainly increase thrust. But the specific impulse comes down proportionally, and the effect of Isp is much greater than the effect of T/W (the only reason T/W is so important in the example is that it is so incredibly low). Double the thrust and you've reduced the Isp to below that of the chemical engine - and your T/W is still ten times as bad...

The LOX augmentation mode changes things, but mostly by improving the initial T/W at the cost of Isp (like using a heavier working fluid, but with extra power from combustion). TRITON might be worth the development cost (I'd say it probably would be; I'm not as pessimistic as Sorensen on the subject of NTR), but it's not what I'd call a game-changer. I'd like to see more work on the Dumbo-type design myself - imagine that with LOX augmentation...

[IntLibber]

That's Kirk Sorensen. He seems to be a bit closed-minded on the subject of nuclear propulsion (he thinks Polywell is fantasy, for one thing - heck, he thinks Dumbo is fantasy), but that analysis isn't too far off.

(And he has successfully demonstrated that a NERVA-type NTR is worthless for launch - you need a T/W above 10 or so for a positive payload.)

The chemical engine he cites in that example weighs the same as an RL-10A4-2 and has the same specific impulse as an RL-10B-2. This is a slightly over-optimistic set of specs, but not preposterous.

The T/W ratio he uses for the NTR is also too low. But for TRITON, not by much. Same with the specific impulse. (He has some harsh words for the designers who think they can get above 900 seconds with "imaginary Russian fuel elements"...)

Yes, a heavier working fluid would certainly increase thrust. But the specific impulse comes down proportionally, and the effect of Isp is much greater than the effect of T/W (the only reason T/W is so important in the example is that it is so incredibly low). Double the thrust and you've reduced the Isp to below that of the chemical engine - and your T/W is still ten times as bad...

The LOX augmentation mode changes things, but mostly by improving the initial T/W at the cost of Isp (like using a heavier working fluid, but with extra power from combustion). TRITON might be worth the development cost (I'd say it probably would be; I'm not as pessimistic as Sorensen on the subject of NTR), but it's not what I'd call a game-changer. I'd like to see more work on the Dumbo-type design myself - imagine that with LOX augmentation...

The main problem with Kirk's analysis is he uses TRITON numbers for an SSTO, when TRITON was never intended for any part of a launch vehicle, it is strictly for interplanetary use and to provide power at destinations. So his whole argument falls apart on that alone.

For a launch vehicle, it is perfectly ok to do LOX augmentation at the cost of Isp, as long as you keep average Isp above 650 sec or so the LV works just fine with a fuel fraction of .78.

NERVA was likewise never intended for a first stage of anything. It is very useful as a second stage propulsion system.

[93143]

Did you even read the link?

[EDIT: Wrong link. This one's better.]

The analysis I actually linked to was for an in-space EDS supplying ~4 km/s of delta-V. The conclusion was that despite the much higher Isp of the nuclear option (and its much higher development cost), the comparison with chemical was roughly a wash. (Yes, this assumes a significantly worse T/W than NERVA, and lower Isp too, on top of an unrealistically light chemical engine...)

The SSTO analysis showed a graph of payload fraction vs. engine T/W for four different values of Isp. It doesn't look good for NERVA types... especially when you consider the fact that he's not taking into account mass penalties for reusability of the stage, or loss of performance due to underexpansion at sea level...

LOX augmentation seems like it would help a fair bit, but I'm too lazy to try to run any numbers right now... I believe I also owe some guy who calls himself mlorrey a parametric analysis of Polywell all-rocket SSTO performance; that too will have to wait until I can get a couple of more important tasks out of the way...

Also, what does it matter that NERVA wasn't designed as a first-stage engine? It's not like they wouldn't have tripled the T/W if they could have... the poor T/W is inherent in the design.

[WizWom]

This one's better.

The sad thing is the Merlin-1C has a T/W of 96, which would mean the NTR would have to REALLY get it's act in gear.
The F-1 had a T/W of 82; the SSME's was 73. Engine design is VERY important for getting a good T/W.

The SSTO analysis showed a graph of payload fraction vs. engine T/W for four different values of Isp. It doesn't look good for NERVA types....

Except... he's using a payload fraction of 35%. Which is a CRAZY mass fraction. The Falcon 1 has a payload mass fraction of 2%. The Space shuttle has a PMF of 1%.

So, since he can't manage a SIMPLE LOOKUP, I'd call him an anti-nuke loon who's trying to look impressive.

Also, as he points out, LH2 is a poor fuel choice for a NTR to orbit, because of the crazy low density of LH2. Better is getting 80% the thrust with liquid NH4.

The problem with an NTR at this point is they don't want to play with pure. If they played with tiny cores of pure U235 or PU239, they could make a VERY small core, massing in at a few tens of kg. Even with shielding, it would be just a few hundred kg over a chemical burn rocket of similar thrust.

[93143]

The SSTO analysis showed a graph of payload fraction vs. engine T/W for four different values of Isp. It doesn't look good for NERVA types....

Except... he's using a payload fraction of 35%. Which is a CRAZY mass fraction. The Falcon 1 has a payload mass fraction of 2%. The Space shuttle has a PMF of 1%.

...you didn't read the link either.

35% is the non-propellant fraction required given the Isp of 900 seconds.

The payload fraction is what's left after you subtract the engines, tankage, and structure from the non-propellant fraction. There's a graph most of the way down the article - take a look.

So, since he can't manage a SIMPLE LOOKUP, I'd call him an anti-nuke loon who's trying to look impressive.

...he's also the webmaster for energyfromthorium.com...


Back on topic, it appears NASA and Congress aren't the only ones who think having a >100 mT HLV would be helpful...

[djolds1]

Yeah, that XX rocket really is a biggie eh? Would that be a Nova class or beyond Nova?

Nova, if you upgrade Falcon XX to a 3-core XX-Heavy.

[kunkmiester]

Those powerpoint links aren't working for me. says there's no such file.

[Betruger]

They were removed from that website. Someone uploaded them in the NSF thread on this topic.
http://forum.nasaspaceflight.com/index. ... #msg625850