Air launch capability

PistolPete · Nov 2, 2006

<blockquote>In reply to:<hr />If you start calculating ISP of an oxygen augmented ramjet, you see it drop from a highly satisfying 3000 seconds down to about 600 seconds and then tend to forget that 600 seconds of ISP is a great number!<hr /></blockquote> I could have sworn hearing somebody say (maby not on this thread) that jet engines were incredibly inefficient compared to rockets. That just didn't seem right with me. Thanks for clearing that up. <div class="Discussion_UserSignature"> So, again we are defeated. This victory belongs to the farmers, not us.-Kambei Shimada from the movie Seven Samurai </div>

gunsandrockets · Nov 2, 2006

"I could have sworn hearing somebody say (maby not on this thread) that jet engines were incredibly inefficient compared to rockets." They were probably referring to thrust to weight ratio instead of ISP.

bitbanger · Nov 2, 2006

Of course a ramjet is even simpler and lighter than a rocket engine. All it really consists of is a bottle shaped tube, a flame holder, and a conical inlet. Does anyone know what the typical first stage final velocity, altitude, and vector are? I've looked on astronautics with no success. Other sources I've found list velocity and altitude, but omit the vector. It seems to me (and other previous posters) that a ramjet powered first stage is both plausable and viable. Here is an interesting ramjet primer.

mikeemmert · Nov 2, 2006

Thanks, BitBanger. This site is a primer for all kinds of ideas for using ramjets. But in any particular application except maybe AA artillery, the flightpath is very much a part of the engine design. One thing that makes ramjets more suitable to space launch as opposed to, say, fighter planes is that you will be flying the same trajectory or very close to it. NOT an X-wing fighter, not to be launched from a runway, and not for going all the way into orbit. I have an embarrassing confession: none of my back-of-the-envelope oxygen enhanced ramjets have wings. They literally fly like rocks - ballistically. This has been a dream/hobby for me since the mid '80s. Recovery has been an afterthought, that's why I asked about parachutes.

mikeemmert · Nov 2, 2006

<img src="/images/icons/blush.gif" /> Boy, I have really made some bloopers on this thread, haven't I? Double posting, wrong size picture...argghhh!!! So I made me a vow to the moon and the stars I'd search the *****-tonks and bars And kill that man that gimme that awful name. -Johnny Cash

bitbanger · Nov 2, 2006

"the flightpath is very much a part of the engine design" Which I why I'm interested in first stage performance figures. I find it curious that ram/scram jets are always mentioned in association with SSTO's. The first stage of a rocket is the largest/heaviest and provides only about 1/4 to 1/3 of the final velocity. Increasing the efficiency for the first stage would seem to be an ideal first step in reducing cost to orbit. While SSTO would be nice, the cost in mass fraction and the requirement for TPS make it a much longer term solution. The few references I've been able to find on first stage performance indicate that an altitude of 150Kft and speeds of mach 5-6 are reasonable. With further development of ramjets and mass injection at higher altitudes, these numbers should be achievable. The major drawback of a ramjet is that it's performance at low velocities is poor to nonexistent. This means that some form of thrust is required to get the vehicle to operational speeds. On a purely ballistic vehicle, the only real choice is some form of rocket engine. For a winged craft, there are several solutions including jet assist, catapult, rocket assist and combinations of the above. The other advantages of a winged first stage is easier recovery and the fact that your initial thrust to weight ratio can be less than unity. All you need to accomplish is to create enough lift to get off the ground with enough airspeed to keep the ramjets running.

rocketman5000 · Nov 2, 2006

I guess the next question would be is it possible to create an X-Class, or maybe something the size of SS2 that could fly a suborbital trajectory from a horizontal single stage system. Maybe a JATO or something similiar could be used while on the runway to get the spacecraft up to ramjet operational speed. Another possibility of a way to accelerate the craft to operational speed would be a winch system similar to but with much higher output to winches used to launch sailplanes.

PistolPete · Nov 2, 2006

The problem with ramjets at high speeds is that they require that the air coming into the inlet be slowed to subsonic velocities. This serves a two-fold purpose: 1) slowing down the air compresses it for combustion, and 2) combustion cannot be achieved at supersonic speeds with hydrocarbons, so the air has to be slowed down in order for the ramjet to work. This actually limits the max speed that a ramjet can achieve to a practical speed of around Mach 3 and a theoretical speed of around Mach 5. Slowing the air coming into the inlet creates a lot of drag and, consequentially, heat. Eventually the inlets develope so much drag that the drag will actually overcome the thrust of the engines and you reach a break-even point. I say that Mach 3 is the highest practical speed because it is the highest speed achieved on a regular basis by production ramjets (SR-71, D-21 drone). Theoretically higher speed can be attained, but higher speeds also require higher thermal insulation which weighs down the craft which means smaller payloads and/or a bigger aerospacecraft and bigger engines and bigger budgets. As for geting a ramjet up to speed for combustion to begin, the American SR-71 and the Russian MiG-25 came up with some unique solutions for this. The SR-71 had a turbojet with a large bypass around it. At high Mach numbers most of the thrust was being provided from the afterburner which was reciving most of it's air from the bypass which was being compressed by the engines inlet cone. In essence turning the bypass and afterburner into a ramjet. The MiG-25's engines have an afterburner that is some 50% larger than it's turbojet. At supersonic speed most of the thrust comes from the afterburners as well, essentially making it a turboramjet. It works somewhat similar to the SR-71's enginse, but has no bypass. Instead the afterburners run off of excess unburnt air coming from the turbojet. Consequentally, it is less efficent. The MiG-31, the big brother of t <div class="Discussion_UserSignature"> So, again we are defeated. This victory belongs to the farmers, not us.-Kambei Shimada from the movie Seven Samurai </div>

propforce · Nov 2, 2006

<blockquote>In reply to:<hr />"...There was the MIPSS system (they need to shoot that name or something)..." I think they did. Does MIPCC sound better? <hr /></blockquote> STOP THAT !!! Newzie, you just made me spill coffee ALL OVER the computer screen. <img src="/images/icons/laugh.gif" /> <div class="Discussion_UserSignature"> </div>

propforce · Nov 2, 2006

<blockquote>In reply to:<hr />The problem with ramjets at high speeds is that they require that the air coming into the inlet be slowed to subsonic velocities. This serves a two-fold purpose: 1) slowing down the air compresses it for combustion, and 2) combustion cannot be achieved at supersonic speeds with hydrocarbons, so the air has to be slowed down in order for the ramjet to work. This actually limits the max speed that a ramjet can achieve to a practical speed of around Mach 3 and a theoretical speed of around Mach 5. Slowing the air coming into the inlet creates a lot of drag and, consequentially, heat. Eventually the inlets develope so much drag that the drag will actually overcome the thrust of the engines and you reach a break-even point. I say that Mach 3 is the highest practical speed because it is the highest speed achieved on a regular basis by production ramjets (SR-71, D-21 drone)......<hr /></blockquote> No, no, no .. .<<shaking my head violently />> A few points, Your #2) "... 2) combustion cannot be achieved at supersonic speeds with hydrocarbons..." is NOT correct. Hydrocarbon fuels combustion has been demonstrated in both subsonic and supersonic combustion speed. I personally have done so at Mach 6 and Mach 8 <img src="/images/icons/cool.gif" />. I also want to introduce the difference between ramjet and scramjet, geometrically wise. A "traditional" ramjet combustor, e.g., D-21, is a "dumped combustor" configuration, or a "sudden expansion". Imagine a cylinder of air duct that is "dumped" into a pelnum, if you will. A "traditional" ramjet also has a "physical" throat and nozzle just like a rocket engine. So a "traditional" ramjet operates like a rocket engine, except that it does not have a turbopump to pressurize the incoming air (oxidizer), but rather uses its inlet shape and aerodynamic principles to "compress" the air through a series of oblique shock wave <div class="Discussion_UserSignature"> </div>

PistolPete · Nov 2, 2006

Thanks for straightening me out on that. I was geting a lot of my info on those jets from books and articles written for the aviation community and I was jumping to a few conclusions about how it would apply to spaceflight. While the aviation and space communities often overlap, they aren't allways trying to reach the same goals and the same audience and don't always put all of the applicable info in their various publications. Also, for some reason (don't ask me why), I just assumed that the D-21 had a simiar top speed to the SR-71. I didn't realize that it had a max cruising speed of Mach 4.5! Wow! I guess I should have looked up all of the facts before I opened my big fat mouth. De de de! <img src="/images/icons/wink.gif" /> <div class="Discussion_UserSignature"> So, again we are defeated. This victory belongs to the farmers, not us.-Kambei Shimada from the movie Seven Samurai </div>

propforce · Nov 2, 2006

No problem Pete. <img src="/images/icons/smile.gif" /> I admire your reading during your spare time in betwen running in 110 degree heat with a fully-loaded gear, drink your own urine and get to shoot a M-16 at bad guys <img src="/images/icons/cool.gif" />. I just sit in my air-conditioned office with feet up on my desk and complaint about life is too boring <img src="/images/icons/tongue.gif" />. I want to work for you when you become a colonel one day. What do you think a shoulder-launch ramjet that blows bad guys RPG away at a distant far from they can even see me, eh? You think we can use one of these babies today? <div class="Discussion_UserSignature"> </div>

PistolPete · Nov 2, 2006

I've heard of jet engines being used to blow away snow from streets and runways. Perhaps we could use them to blow away IEDs from a distance. It wouldn't be terribly efficent, but it sure would be fun. <img src="/images/icons/laugh.gif" /> <div class="Discussion_UserSignature"> So, again we are defeated. This victory belongs to the farmers, not us.-Kambei Shimada from the movie Seven Samurai </div>

josh_simonson · Nov 2, 2006

I think between the Barret 50BMG, Javelin, XM29 and XM982 that capability is or soon will be available, no ramjet needed - 20+ miles for the XM982 is plenty of range.

josh_simonson · Nov 2, 2006

>I've heard of jet engines being used to blow away snow from streets and runways. Perhaps we could use them to blow away IEDs from a distance. It wouldn't be terribly efficent, but it sure would be fun. Or coerce the local cell phone companies to make every phone in the country ring randomly once/day to keep the insurgents on their toes.

PistolPete · Nov 2, 2006

Who needs to coerce the cell phone companies? The Army has the equipment to do that now. <img src="/images/icons/wink.gif" /> <div class="Discussion_UserSignature"> So, again we are defeated. This victory belongs to the farmers, not us.-Kambei Shimada from the movie Seven Samurai </div>

mikeemmert · Nov 3, 2006

Hello, propforce; I read your link on the Advanced Strategic Air Launched Missile and quickly figured out why they kept it below mach 4.5. It's the same reason they did not let Bomarc or Talos fly faster. ASALM was supposed to attack enemy AWACS aircraft. To do this, it would need a guidance system. Above mach 4.5, a sheath of plasma envelopes the missile and electromagnetic radiation of all kinds (except gamma rays) cannot penetrate it. So you cannot have infrared, radar, or even a command guidance system. As you have noted, you can get a ramjet up to mach 5.5, mach 6, or even mach 8. But you have to fly blind. Astronauts are used to this on re-entry.<blockquote>In reply to:<hr />The problem with both ramjet and scramjet, for the purpose of space access, is that BOTH needs to stay LOW in the atmosphere so they can have air to compress in order to gain any kind of useful thrust!<hr /></blockquote>That's where the idea for injecting liquid oxygen into the air inlet came from.<blockquote>In reply to:<hr />I also want to introduce the difference between ramjet and scramjet, geometrically wise. A "traditional" ramjet combustor, e.g., D-21, is a "dumped combustor" configuration, or a "sudden expansion". Imagine a cylinder of air duct that is "dumped" into a pelnum, if you will. A "traditional" ramjet also has a "physical" throat and nozzle just like a rocket engine. So a "traditional" ramjet operates like a rocket engine, except that it does not have a turbopump to pressurize the incoming air (oxidizer), but rather uses its inlet shape and aerodynamic principles to "compress" the air through a series of oblique shock waves (hence the beauty and the skill of a inlet design).<hr /></blockquote>Note that injecting liquid oxygen into a mach 4.5+ airstream will also compress the air, the LOX woud act like a brick wall under those circumstances, and not only that, it will quench the plas

propforce · Nov 3, 2006

Howdy Mike, <blockquote>In reply to:<hr />As you have noted, you can get a ramjet up to mach 5.5, mach 6, or even mach 8. But you have to fly blind. <hr /></blockquote> Don't know much about plasma waves and electromagnetic radiation, etc., there are much smarter people than I in this area. But from our discussion with various "airframers", this has not been an issue. We discussed various mission scenario, including for ISR, for Mach 6, 8 and higher and these "...sheath of plasma envelopes the missile and electromagnetic radiation of all kinds ..." issues have never come up. As far as ASALM, the article said that it uses "inertial guidance" system, effectively flying blind, as do most ELV rockets fly today, e.g., Atlas & Delta, etc. <blockquote>In reply to:<hr />Note that injecting liquid oxygen into a mach 4.5+ airstream will also compress the air, the LOX woud act like a brick wall under those circumstances, and not only that, it will quench the plasma. It will accomplish cooling two ways, one evaporative and the other by production of nitric oxide, which takes energy. It takes a lot of head-scratching calculations to model that, but I think it would be well worth it.<hr /></blockquote> There has been a lot of work done on MIPCC by NASA-Glenn Research Center (GRC) since the '60s. You are correct in that "... injecting liquid oxygen into a mach 4.5+ airstream will also compress the air...", otherwise known in aerodynamics as "constant area with mass injection". BTW, you can inject other fluids and they work just as well, such as water, etc. This approach is mostly used to help turbojet engines to operate at high altitudes, where air density is thin, by providing a higher density air for compression and provide a higher oxidizer content for combustion. The problem is, this approach is self-defeating for using <div class="Discussion_UserSignature"> </div>

vulture2 · Nov 3, 2006

I have not been able to find any information on actual LOX injection in turbojets, particularly in flight tests. Has this been tried at all, other than on paper? It would seem to be a relatively low cost modification, if an existing engine can be used.

mikeemmert · Nov 3, 2006

I'll be de-sequencing some of your quotes, I think you'll see why, somehow I don't think you'll get upset (some might).<blockquote>In reply to:<hr />The problem is, this approach is self-defeating for using scramjets and will dramatically reduces its Isp benefits. Isp, as you know, is defined as the thrust engine produced divided by the propellant mass flow rate. If LOX is used to augment the thrust, by increasing inlet air density, then it should be book-kept as a part of propellant used for propulsion.<hr /></blockquote>And if you check an earlier post I made in this thread, that is exactly how I bookkeep it. The design turns out to be a winner, anyway. ISP = pounds of thrust/pound of fuel burned per second; pounds cancel and the unit is seconds. ISP is a convenient mathematical tool to incorporate into an exponential equation. Try this: take some ISP, say, 350 seconds; hold the thrust steady by throtleing down and run the simulation for 350 seconds. Then divide the remaining mass by the initial mass. The ratio expressed = 1/e (e=Euler's number, 2.7182818456). Magic! I mathematically proved that this isEuler's number a few years ago, but I lost the paper in the Homeless War. If you want to retain thrust at very high altitude, there's no choice but oxygen injection. Now, reduction from an ISP of 3000 seconds to about, say, 500 sounds dramatic at first. But if we could increase an SSME's ISP from 453 seconds to 500, this would be seen as a dramatic improvement. In fact it would be just that, leading to a large increase in payload with the same size rocket. Here's another part of the bookkeeping you might want to consider. I noticed early these things needed high acceleration. So as ISP starts going down, throttle needs to be turned down. Since airflow is the same at the same speed & altitude, all of the reduction in oxygen content comes from what is sprayed into the inlet.

propforce · Nov 6, 2006

Hi there Mike, Sorry for the late reply. In general I don't disagree with your stated MIPCC benefit, the details of pros/ cons would have to be worked out in some number crunching. There's some benefit of using scramjet for space launch, but that benefit is not obvious at this point as compared with the traditional solid/ liquid rocket engine systems at this tiime. The main problem is that the state-of-art of scramjet propulsion system is still under development and its capability is not fully well-understood. It is clear, IMO, that its ultimate benefit for space launch would be in use as a part of resusable first stage system for a TSTO type mission. Here's a bit of nit-pick <blockquote>In reply to:<hr />ISP = pounds of thrust/pound of fuel burnedper second; pounds cancel and the unit is seconds...<hr /></blockquote> Technically, Isp = pounds of thrust/ pound of propellant that is; fuel + oxidizer, per second. The propellants do not need to be "burned" in order to be book-kept as "consumed". For example, in a traditional liquid rocket engines, there are fuels injected for film cooling purpose and not burned, but we book-keep them as a part of consumable in Isp calculation. <blockquote>In reply to:<hr />Now, reduction from an ISP of 3000 seconds to about, say, 500 sounds dramatic at first. But if we could increase an SSME's ISP from 453 seconds to 500, this would be seen as a dramatic improvement. In fact it would be just that, leading to a large increase in payload with the same size rocket<hr /></blockquote> I know what you're saying but it's still an apple and orange comparison. The reason is that you forget to take the propulsion system thrust-to-weight, T/W, in to consideration. If you consider the weight of a scramjet engine needed for a given thrust level produced, y <div class="Discussion_UserSignature"> </div>

mikeemmert · Nov 6, 2006

<blockquote>In reply to:<hr />The propellants do not need to be "burned" in order to be book-kept as "consumed". For example, in a traditional liquid rocket engines, there are fuels injected for film cooling purpose and not burned, but we book-keep them as a part of consumable in Isp calculation.<hr /></blockquote>I was figuring on running the fuel/oxidizer pumps from the onboard oxygen tanks. That would also have to be figured in. The V-2 used hydrogen peroxide to run the fuel pumps and that had to be calculated in with the consumables, too. That's kind of inefficient, but the V-2 worked. Now, here's a source of lowered ISP; there seems to be a problem igniting hydrogen in a supersonic airstream. One solution would be to vaporize the hydrogen and heat it to ignition temperature with a preburner using the onboard oxygen supply. That would absolutely assure combustion. But it would cost ISP. It's a compromise. What the hell, you can afford some ISP lowering devices. An ISP of about 1180 gets 50% of the launch weight into orbital delta v.<blockquote>In reply to:<hr />I know what you're saying but it's still an apple and orange comparison. The reason is that you forget to take the propulsion system thrust-to-weight, T/W, in to consideration.<hr /></blockquote>Well, actually I didn't forget. You design the engine to withstand maximum combustion chamber pressure. Without MIPCC, then if you are running at a higher altitude or lower speed, then you have lower thrust, but the engine still weighs the same. Thus a lower thrust/weight ratio. MIPCC keeps the chamber pressure pretty much constant. Ramjets have been built with T/W ratios that were quite high. But the few that have reached production, Talos, Bomarc, a few others, were launched from the ground and ignited in the thick lower atmosphere. Thus they had to have robust engines. Bomarcs particularly cruised with a low T/W ration b

rocketman5000 · Nov 7, 2006

some engines have to dump the fuel used to run the turbopumps right? Since after it is expanded in the turbine it is running at a lower pressure than the combustion chamber...

scottb50 · Nov 7, 2006

As I understand it all the fuel and oxygen on board is available to the SSME. What is used to cool the nozzle is ducted to the fuel pre-burners while the Low-pressure pumps use hot gas from either the fuel or oxidizer hot gas maifolds. Exhaust from the L-P pumps goes to the respective H-P turbo-pumps. Eventually all of it ends up at the injector though. The advantage is both the fuel and oxidizer are at higher temperatures and pressure by the time they reach the injector allowing a higher power output. <div class="Discussion_UserSignature"> </div>

halman · Nov 7, 2006

mikeemmert, Not being as fanatical about aerospace as I was when I was younger, these discussions of ram and scramjet applications don't really hold my attention, in part because I don't see how they would benefit a two-stage-to-orbit system. If we use the atmosphere for providing oxidizer as well as lift, we can obtain huge savings over vertically launched vehicles. Turbofan engines powering a wing are extremely efficient for the purpose of getting the wing and the orbiter up to 50,000 feet, without having to go supersonic. Launching the orbiter from 50,000 feet means that it will only be in atmospehere for about 2 or 3 minutes after seperation, so any use of engines other than pure rocket are only adding complexity and weight, in my opinion. Probably where the greatest challenge lies is in getting a vehicle weighing around 2 million pounds into the air in the first place. Turbofan engines are not very efficient at low speeds and low altitudes, so using a different energy source for the initial acceleration is indicated. However, this leads to dealing with another major challenge, and that is developing an undercarriage which could support 2 million pounds without adding tremedous weight to the wing. By using a catapult pushing a cradle that the wind/orbiter stack is laying on, these two problems can be addressed in a beneficial way. The catapult should be able to accelerate the combined vehicle to about 300 miles per hour, which should be fast enough that the wing will be stable and have adequate lift. And this can be done without using large amounts of fuel for the wing's engines. <div class="Discussion_UserSignature"> The secret to peace of mind is a short attention span. </div>

Air launch capability

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