Talk-Polywell.org

". . .powered by RD-191, arguably the world’s best “clean” engine that uses kerosene and oxygen as fuel."

I'm really curious what is "clean" about kerosene. Is this as compared to solid boosters that fill the air with toxins? And is anyone familiar with the details of how this is "best"? Does it produce higher Isp's and have lower weight and higher reliability than the SpaceX thrusters like the Merlin? Anyone know what an Angara launch costs?

http://rt.com/news/216663-angara-heavy-booster-launch/

GIThruster wrote:I'm really curious what is "clean" about kerosene. Is this as compared to solid boosters that fill the air with toxins

Oh no, much worse than that...

The new rockets are to replace the Proton-class launchers, which use hypergolic N2O4 and UDMH

Dinitrogen tetroxide and unsymmetrical dimethylhydrazine are nasty toxic, and the spent stages are dropped on areas of land where... nobody important lives. Well, anymore.

This has left quite mess over the decades.

zapkitty wrote:. . .Dinitrogen tetroxide and unsymmetrical dimethylhydrazine are nasty toxic, and the spent stages are dropped on areas of land where... nobody important lives. Well, anymore.

This has left quite mess over the decades.

Do you rattle off stuff like this all the time? You must be fun at Christmas parties. That's better than Calvin's transmogrifier.

GIThruster wrote:Do you rattle off stuff like this all the time? You must be fun at Christmas parties.

Just a rocket fan... there's an Elton John-based parody waiting there

But I spelled them out to emphasize just what the Soviets did to themselves with the stuff and why having tons of metal tankage crashing down and spilling kerosene everywhere is considered an "Eco-friendly" improvement over the former status quo.

Kerosine as a rocket fuel (burned with liquid oxygen oxidizer) is useful because it is only mildly toxic. Almost everyone has used it or something similar in some form for cattle spraying, dipping, hand cleaning, lamps, diesels, barn heaters, etc. It is intermediate in ISP. Perhaps ISPs of ~ 300-to 350 is reasonable. This is a little better than solids, much better (I think) than mono propellents like hydrazine, poorer than methane and hydrogen is the best. The problem with liquid hydrogen is that it is much lighter than water, so it takes larger and more insulated tanks to hold enough of it. This adds weight to the rocket which partially offsets its performance advantage. Kerosine is more dense so smaller tanks for the same mass of fuel. It is liquid at room temperature, is relatively safe against fire and explosions (all bets are off in the presence of concentrated oxygen), And it is cheap to make and store.
Space X Falcon 9 uses kerosine for the first stage.

Dan Tibbets

GIThruster wrote:". . .powered by RD-191, arguably the world’s best “clean” engine that uses kerosene and oxygen as fuel."

Does it produce higher Isp's and have lower weight and higher reliability than the SpaceX thrusters like the Merlin?

Vacuum thrust-to-weight seems to be just shy of 100, versus ~150-160 (insufficient data) for the Merlin and 145 for the NK-33. Reliability... it's a new engine, so I'm not sure. But probably better than the half-century-old surplus NK-33s Orbital was trying to use...

Isp? Any Russian high-pressure staged combustion engine absolutely flattens the Merlin. Comparing first stage configurations in the interest of fairness, the RD-191's sea level Isp appears to be the same as the Merlin 1D's vacuum performance. In fact the RD-191's vacuum performance is only a few seconds lower than the Merlin 1D's performance in upper stage configuration (much larger nozzle, useless at sea level). The NK-33 doesn't match the RD-191, but still beats the Merlin (first stage config) by 15-20 seconds.

The larger, older RD-180 used by the Atlas V has a slightly lower T/W than the RD-191, but its Isp seems to be slightly better...

...and of course the American-made RS-68A used by the Delta IV gets 412 seconds in vacuum, which is horrible for a hydrogen engine (in addition to being a gas-generator engine like the Merlin, it has a fuel system design flaw they haven't bothered to fix) but stomps all over any kerosene engine ever made (though the low fuel density means big tanks and a vacuum T/W below 50). So technically, the Merlin 1D is the second least efficient liquid-fueled main engine currently in use on any U.S. launch vehicle, beating only the ultra-reliable RS-27A on the Delta II. Its T/W is good, but its biggest advantage is probably its low cost.

I am pretty sure the T/W for the Merlin 1D is the highest out there so far (150:1), no?

If you want best possible ISP, staged combustion and high chamber pressure are favored. If you want low cost and rock solid reliability, gas generator or expander cycle and lower chamber pressure are preferred. It's an engineering trade off.

hanelyp wrote:If you want best possible ISP, staged combustion and high chamber pressure are favored. If you want low cost and rock solid reliability, gas generator or expander cycle and lower chamber pressure are preferred. It's an engineering trade off.

I am curious to see how the Raptor will perform in this regard. It is methane too, so higher ISP just from that.

If you can fly your first stages back, the Specific Impulse of their fuel becomes almost secondary.

Skipjack wrote:

hanelyp wrote:If you want best possible ISP, staged combustion and high chamber pressure are favored. If you want low cost and rock solid reliability, gas generator or expander cycle and lower chamber pressure are preferred. It's an engineering trade off.

I am curious to see how the Raptor will perform in this regard. It is methane too, so higher ISP just from that.

Raptor should be a very good performer, correcting for fuel. It's a full-flow gas-gas staged combustion design, which is closed-cycle (so no gas generator losses) and can get extremely high pressure more easily and robustly than a conventional staged combustion engine. It's pretty much as far towards the performance end of the design space as a chemical rocket can get (again, correcting for fuel - and while hydrolox is the king of Isp, it isn't optimal for first-stage performance, so if you want a single propellant combo for your vehicle, especially a cheap one, methane is a likelier choice). Though SpaceX may not take full advantage of the performance potential, as this cycle offers plenty of room to trade performance for robustness (you may be sure they have not forgotten the lesson of the RS-25, which took 30 years to get anywhere near the original maintainability projections).

KitemanSA wrote:If you can fly your first stages back, the Specific Impulse of their fuel becomes almost secondary.

On the contrary. Hardware procurement is far from the only cost that scales with the size of the vehicle. And flyback and landing maneuvers increase the impulse requirement on the stage (or else load more delta-V onto the upper stage, or both), so high Isp gives a larger advantage to a reusable than to an expendable.

93143 wrote:

KitemanSA wrote:If you can fly your first stages back, the Specific Impulse of their fuel becomes almost secondary.

On the contrary. Hardware procurement is far from the only cost that scales with the size of the vehicle. And flyback and landing maneuvers increase the impulse requirement on the stage (or else load more delta-V onto the upper stage, or both), so high Isp gives a larger advantage to a reusable than to an expendable.

Speaking of the "Delta", the zeroth stage (6 small solids) had very low SI but were reasonably cheap. Imagine the F9H with 4 extra strap on F9Cores feeding the F9Htri-core's engines and then flying back. It really wouldn't matter if the SI was 450 or 350 if it were cheap enough. With cheap reusables go with 3 or 4 or 5 reusable stages.

zapkitty wrote:

GIThruster wrote:I'm really curious what is "clean" about kerosene. Is this as compared to solid boosters that fill the air with toxins

Oh no, much worse than that...

The new rockets are to replace the Proton-class launchers, which use hypergolic N2O4 and UDMH

Dinitrogen tetroxide and unsymmetrical dimethylhydrazine are nasty toxic, and the spent stages are dropped on areas of land where... nobody important lives. Well, anymore.

This has left quite mess over the decades.

Whoa.. they use hypergolic fuels in the boost stage? That IS unclean

ohiovr wrote:Whoa.. they use hypergolic fuels in the boost stage? That IS unclean

Pork staging. Totally not kosher.

KitemanSA wrote:

93143 wrote:

KitemanSA wrote:If you can fly your first stages back, the Specific Impulse of their fuel becomes almost secondary.

On the contrary. Hardware procurement is far from the only cost that scales with the size of the vehicle. And flyback and landing maneuvers increase the impulse requirement on the stage (or else load more delta-V onto the upper stage, or both), so high Isp gives a larger advantage to a reusable than to an expendable.

Speaking of the "Delta", the zeroth stage (6 small solids) had very low SI but were reasonably cheap.

Cheap, reliable, lots of thrust in a small package, and as expendable as they come. Also compact enough that sticking a bunch of them around the core doesn't result in structural issues with the stack:

Imagine the F9H with 4 extra strap on F9Cores feeding the F9Htri-core's engines and then flying back. It really wouldn't matter if the SI was 450 or 350 if it were cheap enough. With cheap reusables go with 3 or 4 or 5 reusable stages.

Mitigating the manufacturing costs doesn't get rid of all the other costs associated with launch vehicles, and all of those also scale with the size and number of stages. In fact, post-flight servicing/refurbishment is a whole new cost that expendables flat-out don't have, and it scales with size and number too, probably more than manufacturing cost does. So to first order, your scheme doesn't scale any better for reusable stages than it does for expendables.

Then consider that the reusability requires those stages to put out more impulse in order to do the same job, meaning either they have to be bigger or more numerous (= more expensive to have, use, and refurbish) or the Isp has to be better. Or both. In fact, your scheme would result in the main boosters and especially the core ending up much faster and further downrange by the time they had to drop off and go back, making the problem worse.

You can't just assume reusable = free and throw ganged cores at the problem. Or more sequential stages for that matter; each unique stage you add requires its own DDT&E and special manufacturing and handling treatment, which could rapidly eat up the advantage of reusability.