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Hot Rod Job For SpaceShipOne
rwven writes "MSNBC is reporting that the engine on SpaceShipOne has been modified to provide more thrust, for a longer amount of time. Mainly, the Nitrous Oxide tank has increased in size to lengthen the amount of time before the dropoff of thrust when it goes from a liquid to a gas. Also reporting is Space.com."
Look at the cutaway - it really is a "hot rod." It appears the n2o tank is, like, six feet in diameter and right behind the crew with the engine right behind that. Yeesh, it's almost like one of those jet powered dragsters with wings - and some brave soul is gonna take it into space? I guess the next evolution will be nothing more than a good flight suit, an engine, and some carbon fiber bungee cords...
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Yeah. It's an easy fuel/oxidizer combo, but not very scalable. The specific impulse is just too low, and the nitrous tank too heavy. I do find it funny that they described hybrid rocket engines as not being "conventional rockets" ;)
And before some of the posters here start going off on a "Specific impulse isn't everything!" line, I'll add: It's not everything, but it is *incredibly* important. And if you can't have lightweight tanks to compensate for your loss of specific impulse (which you can't with nitrous), you're not going to scale. Plus, using a carrier launch, you're not going to handle the spiralling mass increase very well.
In short, this type of design, while great for getting the X-prize (it's very simple - self pressurizing, no liquid/liquid combustion, etc), would never scale to orbit. I'd like to see a good tow-launch LOX/subcooled propane rocket; that should be scalable and yet still take advantage of air breathing power to get to altitude, and wouldn't have to deal with LH.
What everyone hopes for are some of the things that are on the horizon, that have high ISP without the various tank mass or cryogenic limitations. For example, alane (stabilized aluminum hydride) hybrid boosters, which have an ISP that even with a weaker oxidizer like H2O2, nears LOX/LH's isp, and a very high density. Everyone in rocketry would like such a panacea; however, for now, everyone has different opinions on what is the best way to go.
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I wonder how much testing this new engine config has received? I don't believe it has gotten any flight time- it would have to be all ground tests.
Seems kind of concerning to me. When I finish working on my car, it sure as hell might crank up and idle okay in the garage but it is usually hit or miss the first time I take it on a road test. Obviously, these guys are better rocket scientists than I am a car mechanic, but you get the point...
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Modifications in design invalidate the hardware test, and put it up there in the "risky" category again... esp. with the modification being an increase in the amount of fuel hangin' around. I hope they had this intent in the first phase (we start with this size tank, and move up to this one later)...
meh
Well, the fact ( from personal usage ) is that Nitrous injection via a plate between the fuel injection and the manifold has been around 1983. I also saw a mazda with a rotary motor having water injection and was told that it had No2. Seen Honda's that are pulling clean 13's (seconds) with No2 since late 80's. Had a Cosworth motor that could redline at 11K, that I ran No2 ( very light system due to fears ) to help me out of curves.
I can not recall the exact engine ( air ), but the year is 1944, the p-38 lightning ( Britains order) and the engine for the Huricane had No2 systems installed, tested, and aproved for usage ( if used I have no details ).
Onepoint
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You are right about one thing, they seem to have chosen the lowest-possible performance design on all counts:
1. Solid fuel = makes the whole fuel tank a propulsion chamber = large thick heavy wall -- compared to liquid fuel, where the pressure wall is just the little combustion chamber in the engine.
2. Pressure fed oxidizer = thick walled heavy tank - compared to pump-fed design.
3. There are fuels with much higher energy contents than HTPB/NOX.
But then, you don't know what they did to the HTPB, but they did do something, otherwise the thing wouldn't burn fast enough to push a shopping cart, lest a space rocket. Whatever they did, maybe it had an effect on Isp as well.
Secondly, you don't know what that N2O tank is made of. It could be some super-strong composite, rather than fiberglass/metal.
And of course, they use high-altitude air-launch, which improves the mass ratio required for orbit.
Overall, it looks like the engine takes up only a small portion of RubberRocketOne, compared to any old booster. So there is room to improve the mass ratio right there by putting in a biger engine.
I'd kinda like to see some calculations, but without knowing the weight of the ship and the material of the nitrous tank it would be difficult to calculate anything interesting.
> Whatever they did, maybe it had an effect on Isp as well.
http://www.astronautix.com/stages/spaipone.htm
Nope. Besides, the N2O is as much of a problem as the fuel. It's a worse oxidizer than nitric acid and peroxide, which are both worse oxidizers than LOX (which is a worse oxidizer than FLOX, and especially than LF2, but few use the former and noone uses the latter)
> Secondly, you don't know what that N2O tank is made of.
Irrelevant. Because whatever it's made of, you could make a non-pressurized tank in a turbopump-fed rocket far lighter using the same material. Pressurized tanks have to be built a lot thicker than nonpressurized tanks, whatever you build them out of.
> And of course, the use high-altitude air-launch, which improves the mass ratio required for orbit
Not if they have to scale their craft up. With an ISP and tanks like this, they'd require a carrier craft that makes the An-255 look like a moquito by comparison. You'd be lucky to get such a huge carrier to lift it's own weight, since you'd need so much structural reinforcement.
> Overall, it looks like the engine takes up only a small portion of RubberRocketOne
But a major portion of its mass - and this will only get far worse due to the low ISP (btw, I assume you mean "tank" and "fuel/oxidizer").
I was watching this thing on TV about some guy named Hitler. Someone should stop him!