Improving Delta V and ISP

[spacy600]

"We have identified the causes of a hybrid's poor delta V performance as its low propellant mass fraction and its high propellant residuals. A pump-fed, high oxidizer to fuel ratio (O/F), and high bulk density propellant combination can improve a hybrid's propellant mass fraction and reduce its residuals so that its performance is equal to solids and most liquid fueled rockets. Further, we have discovered that despite its slightly lower specific impulse, cryogenic Nitrous Oxide provides the highest delta V capability for such a hybrid. "<br />http://tinyurl.com/2su276<br /><br />Is this correct?

 

[spacy600]

Can you explain why, In layman's terms please.<br /><br />He talks of less weight, more common materials. <br />I am looking at this from a business point of view.<br /><br />Thanks

 

[propforce]

<font color="yellow">Can you explain why, In layman's terms please.</font><br /><br />Shuttle_Guy summarizes well in one sentence ---- /> less structural weight, therefore more efficient.<br /><br />By using a "cryo" nitrous oxide (actually "cryo" anything), it reduces the density, hence volume, of the its oxidizer tank. <br /><br />A smaller volume tank means either a smaller diameter, or a shorter, rocket. It reduces the cost of fabricating the rocket. If you keep the same size tank, then you can load MORE propellant, therefore can burn the rocket LONGER, thus the claimed higher delta-vee.<br /><br />But its Isp does suffer a little bit because the oxidizer comes into the combustion at lower temperature (at "cryo" temperature), the combustion must first "raise" the cryo to a high enough temperature before this oxidizer is ready to "react" with fuel. At the end, you do get a slightly lower combustion temperature, so a lower Isp. This is a chemistry thing.<br /> <br />In the case of a first stage launch vehicle, the benefit of denser propellant out-weighs the benefit of a slightly lower Isp. Thereby making it a more efficient stage.<br /><br />This is NOT NEW, by the way. It's the same argument why LOX/ RP-1 is a better propellant combination for a first stage than a LOX/LH2. Compare Atlas V and Delta IV and see how "small & short" the Atals V first stage is?<br /> <div class="Discussion_UserSignature"> </div>

 

[spacy600]

ok, thanks, that makes sense.<br /><br />But it brings up more questions<br /><br />1 Why is he patenting it, will they issue him one<br /><br />2 what about all that stuff about smaller slivers <br />higher ratio of oxidizer to fuel.<br /><br />3 can a hybrid rocket get to LEO, with a useful payload?<br /><br />Thanks

 

[propforce]

<font color="yellow">1 Why is he patenting it, will they issue him one </font><br /><br />Who knows... people patent ideas for all reasons. When comes to patents, you don't have to prove that your idea will work, you just need to prove that (in this case) nobody else has patent the idea of "cryo" nitrous oxide in a hybrid rocket.<br /><br />If I can patent my "secret sauce" for fried chicken, I can certainly patent my rocket propellant design.<br /><br /><font color="yellow">2 what about all that stuff about smaller slivers higher ratio of oxidizer to fuel. </font><br /><br />By "biasing" O/F ratio higher, you "tilt" the argument toward your claim because you can pack MORE oxidizer in the same size tank, thereby produces a higher benefit of higher delta-vee. <br /><br />You can also plot the TOTAL propellant weight (on the Y axis) vs. propellant O/F ratio (on X axis) for any propellant combination. You'll find the curve is a "U" shape. What you want is the bottom of that "U" because it represents the minimum propellant weight, hence the minimum vehicle weight, for your rocket.<br /><br /><font color="yellow">3 can a hybrid rocket get to LEO, with a useful payload?</font> <br /><br />A hybrid rocket can certainly be used as a first stage of a vehicle to get useful payload to LEO. The benefit of a hybrid is mainly of 1) Safety (as compared to a solid propellant rocket), 2) Control & Throttle (by adjusting the oxidizer flowrate), 3) Higher Isp (than solids) that can approach a LOX/RP-1 liquid rockets, and 4) Simple to make (as compared to liquid rockets). <br /><br />The difficulties (technical challenge) of a hybrid rocket is making the combustion efficient (when compare to solid or liquid rockets). It will still be longer and heavier than a solid rocket, and operationally is almost as complex as liquid rocket, but not as good of a performer. There's no military value (where major R&D money comes from) as solids are predominately favo <div class="Discussion_UserSignature"> </div>

 

[spacy600]

Very informative, thank you.<br /><br />"So the argument against a hybrid is why bother?"<br /><br />Are they less expensive than other rockets?<br />environmentally benign? less toxic?<br />cheaper and easier ground handling?<br /><br />Thanks <br />

 

[josh_simonson]

Particularly if it's a pump-fed hybrid, why bother? Adding a turbopump eliminates the reliability considerations of the hybrid engine. <br /><br />There is more to the cryogenic NO than simply less volume, the tank is at much lower pressure, hence it doesn't have to be as strong. <br /><br />Still, if you're building a pump fed cryogenically fueled rocket, it might as well be RP-1/LOX and skip the high-pressure fuel tank too. A pump-fed hybrid is the worst of both worlds.

 

[propforce]

<font color="yellow">There is more to the cryogenic NO than simply less volume, the tank is at much lower pressure, hence it doesn't have to be as strong. </font><br /><br />Well I guess someone needs to crank some numbers, eh? <img src="/images/icons/smile.gif" /><br /><br />The difference is not much with a pump-fed system. You'll find that ground handling & launch environment will drive its minimum tank wall thickness. <div class="Discussion_UserSignature"> </div>

 

[vulture2]

Let's not forget that in a reusable system such as Spaceship 1, the hybrid requires replacement of the fuel segment and nozzle with each launch. Compare that with the first large reusable liquid, the XLR-99 which powered the X-15, which could run one hour between overhauls and required relatively little maintenance between flights. [Ironically Reaction Motors was bought, and ultimately shut down, by ... Thiokol] <br /><br />Rutan favored the hybrid in the SpaceShip 1 and 2 because of its perceived safety advantages, but all new systems have failures. In the long run overall cost of operation for a reusable launch vehicle may favor the all-liquid approach.

 

[josh_simonson]

Certainly nobody is favoring solid fueled cars, planes or jets, and they're doing gymnastics to try to cook biowaste down into liquid fuels rather than gasses like methane. The solid grains won't scale well either - for big ones you'll need huge expensive cranes to move them, with liquid fuels all you need to move it about is a tube and a pump, and the capacity scales as the square of the diameter of your tubing... <br /><br />The difference in program cost between GEM type booster motors and SRBs demonstrate the poor scaling involved in using solid fuels.

 

[vulture2]

SOLID FUEL CARS!!??? What a concept.