Any new advance in Propulsion for rockets

[caper]

Any new advance in Propulsion for rockets such that the weight can be reduced e.g. I read something about pulse propulsion being more powerful than convential. If so we could use them also for planes. Am I right. Please post your comments.<br /><br />Caper the Red

 

[shuttle_rtf]

Pulse Denotion Engines? Could be an interesting thread!

 

[space_dreamer]

Yes it would!<br /><br />I read an article in popular science about Pulse Detonation Engines about a year ago <br /><br />General Electric – Hybrid PDE prototype by 2005<br /><br />Pratt & Whitney – Pure PDE missile prototype by 2005<br /><br />I haven’t heard anything this year thought.<br /><br />

 

[space_dreamer]

here is a link to the article <br /><br />http://www.popsci.com/popsci/aviation/article/0,12543,473272-1,00.html<br /><br />This links prity cool as well!<br /><br />http://www.grc.nasa.gov/WWW/AERO/base/psbase.htm

 

[yurkin]

Pulse detonation jet engines can’t really be used for a rocket. Their advantage is greater efficiency but they are not as fast as a conventional rocket or a scramjet.<br /><br />It’s interesting to note that pulse-det engines are not a new idea. The Germans used many of them back in world war two.<br />

 

[CalliArcale]

I don't think caper's referring to the air-breathing pulse-jet concept, such as the V-1 "buzz bomb" used. (It was called a buzz bomb because of the characteristic sound of its then-novel jet engine.) What he's referring to is the Project Orion concept, which was not airbreathing at all. The idea was to drop nuclear bombs out the back of a rocket so they'd detonate immediately behind it. The resulting shockwave would push the spacecraft forward. Obviously you'd need a LOT of nuclear bombs, however, which does present a bit of a logistical challenge. I believe a subscale version was tested using dynamite. It's crude, but it could work.<br /><br />The VASIMR engine shown in the intial post is not a pulse-propulsion concept, but another nuclear propulsion concept. VASIMR, like ion drives, is not a high-thrust engine. You definintely could not use it to lift off of the ground. However, it (theoretically) has extremely high specific impulse and should have better thrust than an ion drive, which means you could use it to get to Mars a hell of a lot faster, which would be invaluable for manned missions. High specific impulse means that it can afford to keep thrusting for a very long time without running out of propellant. The high-thrust Shuttle SRBs, for instance, can only burn for a couple of minutes before exhausting their propellant. But the low-thrust VASIMR could theoretically burn for days or even weeks!<br /><br />VASIMR has never been built. It is currently in funding limbo, along with many other worthy concepts, such as the well-established but never-used aerospike engine (a chemical rocket with no engine bell).<br /><br />High-thrust non-pulse nuclear propulsion concepts also include NERVA (which got as far as a subscale static test firing) and GCNR (a more powerful extention of NERVA that, like VASIMR, exists only on paper). These use a nuclear reactor to heat a propellant, thereby forcing it to exit the engine and produce thrust. <div class="Discussion_UserSignature"> <p> </p><p><font color="#666699"><em>"People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff."</em>  -- The Tenth Doctor, "Blink"</font></p> </div>

 

[najab]

Actually, the pulse-detonation engine they are talking about isn't Orion - it's not the buzz bomb either, but it's fairly close. Take a buzz-bomb, seal the air intake and inject fuel <b>and</b> oxygen into the combustion chamber. That's the principle of the PDE.

 

[najab]

Oh, and do it 30 or 40 thousand times per second, rather than a couple hundred.

 

[space_dreamer]

Exactly najaB <br /><br />I would be very interested to know what progress has been made.<br />

 

[siarad]

I well remember those buzz bombs. By the time the siren went we could only jump out of bed & watch them.

 

[scottb50]

I think hybrid engines offer a lot of possibilities. I would think it would be rather easy to convert an SRM. Carry LOX in a jacket around the motor segments and use engine heat to vaporize the LOX. With a more efficient nozzle and higher internal pressure <br /><br />Other than nozzle steering you would only need a few parts and could have multiple redundancy. <div class="Discussion_UserSignature"> </div>

 

[najab]

I seem to remember 800-900s, but that's just off the top of my head.

 

[najab]

Still looking, but I found one paper that indicated 5000s on the high end of the operating range.

 

[najab]

This site lists it at between 1000 (high thrust mode) and 30000 (high efficiency mode) seconds.

 

[propforce]

You also don't get much heat at all with a SRM. The unburned propellant act as insulator to the outer liner.<br /><br />Hybrid motors (LOX with solid grain fuel such as HTPB) does not get you a higher Isp, but provide safety & control, however; at the expense of more hardware, e.g., LOX tank, pressurization tank, valves, regulator, lines, software, interface electronics, etc. <div class="Discussion_UserSignature"> </div>

 

[scottb50]

If you are going to inject it into the core of a solid engine, like the SS1 motor, you need to get the pressure and temperature up, the best way is to cool the solid motor core while raising the temperature, and pressure of the LOX at the same time, no pumps needed and it cools the motor body, allowing higher teperatures at less stress as well as increased efficiency and payloads.<br /><br />You want high pressure Oxygen for a hybrid engine, the SS1 loses thrust as the oxidizer starts coming out liquid. <br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /> <div class="Discussion_UserSignature"> </div>

 

[propforce]

Scottb50,<br /><br />Not worth it in the case of a hybrid SRM for reasons of cost, and thrust-to-weight ratio. <div class="Discussion_UserSignature"> </div>

 

[scottb50]

Looking at the way the SS1 motor operates, it is a lot more efficient at the beginning when the pressurized Nitrous Oxide is being injected, and the efficiency falls off when the pressure drops and residual liquid is being delivered. The same holds true with Oxygen. For a hybrid engine you would have to have O2 under pressure constantly to provide enough flow to efficiently oxidize the fuel. SS-1 does it by pressurizing the Nitros tank, most liquid engines do the same thing using turbopumps, though the RL-10's use Helium pressurization to provide flow, just like the SS1 hybrid. The point is not heating the fuel, it is increasing the pressure to allow gaseous Oxygen to be injected into the core of a solid motor.<br /><br />There are two main ways to increase pressure, physically pump the fluid to the desired pressure or heat it, which also increases pressure. Using the waste heat of the solid motor core to heat, as well as cooling it to reduce structural requirements, and thus pressurizing the oxidizer allows more efficient use of the oxidizer as well as eliminating pumps other extraneous systems.<br /><br />If the core of a SRB could be all fuel and the material to hold it together, the SRB currently has 16% fuel, .17% catalyst, 14% bonding and other agents and 69.83% Oxidizer, it would be possible to have an engine that could not only reach orbit but operate as a re-startable upper stage, if you inject Oxygen into a central core, just like the SS-1 type engine does. An existing SRB core could hold three times the fuel, or a 4 foot diameter solid core could provide thrust comparable to an SRB. <br /><br />As for thrust to weight the fuel composition, distribution and internal design of the fuel itself can be easily modified to give the efficiency needed. Obviously, you would have less ISP than a liquid design, because of the different binding and extraneous agents required in a solid design, but it would be butt simple, easily built and provide a lot of power.<br /><</safety_wrapper> <div class="Discussion_UserSignature"> </div>

 

[propforce]

Scottb50,<br /><br />Solid motors (SRM) and hybrids such as the SS1 work on self-pressurizing principle, not dependent on pump or pressure-fed. For SRM, chamber pressure and thrust profile is controlled by grain patterns, burn rate and chamber-to-nozzle throat area ratio. A much faster burn rate with a too small of throat area is key to explosion of SRM motorcase. A hybrid motor work on the similar principle except for the oxidizer is injected. Similarily, you would not be increasing the chamber pressure of a hybrid rocket motor with a high oxidizer injection pressure.<br /><br /><blockquote><font class="small">In reply to:</font><hr /><p>Carry LOX in a jacket around the motor segments and use engine heat to vaporize the LOX. With a more efficient nozzle and higher internal pressure <p><hr /></p></p></blockquote><br />One only needs to take a look at a SRM/ hybrid motor schematic to realize that your proposed concept does not work, with all due respect <img src="/images/icons/smile.gif" />. The propellant grains, either fuel/oxidizer/binder combination or just fuel/binder, act as "thermal insulator" preventing heat to reach the outer LOX cooling jacket. In addition, you would increase the system complexity, manufacturing difficulty, and potentially a critically-1 catastrophic failure mode into a system ---- a significant reduction of reliability.<br /><br />It is far more reliable, cheaper, lighter, and simpler with a helium/ nitrogen pressurized LOX tank to provide the pressure. One can control the pressure with a use of regulartor to throttle the pressure throughout the mission as required. <br /><br /><blockquote><font class="small">In reply to:</font><hr /><p>most liquid engines do the same thing using turbopumps, though the RL-10's use Helium pressurization to provide flow, just like the SS1 hybrid. The point is not heating the fuel, it is increasing the pressure to allow gaseous Oxygen to be injected into the core of a solid motor. <p><hr /></p></p></blockquote><br /><br />Just a point <div class="Discussion_UserSignature"> </div>