Air launch capability

[scottb50]

50,000 feet and mach .80 is not worth all the complication you are proposing. Even with a catapult or rail you would need a lot of propellant in the second stage to get to orbit which means an awful big and heavy first stage.<br /><br />With a rocket powered first stage the second stage could be much smaller and lighter allowing more payload, 400,000 feet and mach 8+ makes a lot more sense than 50,000 feet and mach .80. <div class="Discussion_UserSignature"> </div>

 

[mrmorris]

I'm not particularly interested in air-launch, so haven't participated in this thread. However, I ran across the following document while researching something else. It's a pretty good read, and details the various types of air-launches, pros & cons, engineering concerns, etc. Mind you -- the authors have an agenda -- namely pushing <b>their</b> air-launch proposal, so you have to take some of it with a grain of salt... particularly just how simple and cheap their proposed method would be. Nevertheless, some good info if you're truly interested in air-launch.<br /><br />A Study of Air Launch Methods for RLVs

 

[mrmorris]

For those that haven't read it: "Flight Testing of a New Air Launch Method for Safely Launching Personnel and Cargo into Low Earth orbit" is the t/Space proposal.

 

[rocketman5000]

Interesting, there is a Scaled Composites plane in the opening photo

 

[mrmorris]

RRRiiiggghhhttt... That would be because Scaled Composities is part of the t/Space consortium.

 

[scottb50]

rom what I ubderstabd the T/Space CVX will have a payload of 900kg. and need a 747 to lauch from. While air launch may be perfect for ths class of booster higher payloads are going to require a whole lot bigger carrier. While the 747 isn't the biggest carrier available it's only marginally smaller. <div class="Discussion_UserSignature"> </div>

 

[halman]

Scottb50,<br /><br />If we could get the space shuttle orbiter and 2/3 of the external tank capacity to 50,000 feet, it would probably be able to make it to orbit, based on the fact that it has used 1/2 of the external tanks capacity at the time that the Solid Rocket Boosters seperate, and it has only acheived 1 mile per second, and about 100,000 feet. <div class="Discussion_UserSignature"> The secret to peace of mind is a short attention span. </div>

 

[halman]

Scottb50,<br /><br />The White Knight is the only aircraft that I am aware of that has been built specifically to launch a spacecraft. Rutan is already working on a larger version, and I suspect that eventually we will be seeing carrier aircraft that weigh as much as a 747 with much larger wingspans than a 747. Specialized aircraft are much more efficient at what they are designed for than adapting an off-the-shelf aircraft. There just has not been any money available until now for building such aircraft.<br /><br />By using composite materials, and the engine technologies available today, lifting capacities are going to be much higher than existing aircraft are capable of. All of the giant aircraft that we are familiar with right now are at least 30 year old designs. The biggest ones where built specifically for carrying tanks. Therefore, the airframes are extremely heavy duty, especially as they were required to be able to land on primitive runways. When including the weight of the aircraft, the fuel, and the cargo, 840,000 pounds is lifting off when a war rating C-5 flight is launched. This includes 332,500 pounds of fuel, which is enough to keep the bird in the air for a 2,500 mile journey. By designing a wing for maximum lift, and an acceptable amount of drag, and not hanging a fuselage from it, we can certainly acheive higher take off weights with the same four engines. By adding more engines, we can do even better.<br /><br />If we judge air launching strictly by existing aircraft, it is not a viable option for payloads of any size. But if we allow that specialized aircraft can be built to carry payloads to altitudes of at least 40,000 feet, then we will have to reconsider. Especially if it turns out that we can get a payload of 800,000 pounds to 50,000 feet. <div class="Discussion_UserSignature"> The secret to peace of mind is a short attention span. </div>

 

[mrmorris]

<font color="yellow">"...From what I ubderstabd the T/Space CVX will have a payload..."</font><br /><br />Just replying since it was my post you tagged that to... I have very little interest in the CXV or any air-launched vehicle. I was just providing a link to the document SG mentioned in his reply to *my* post where I supplied a link to a document on air launches & the engineering thereof.

 

[barrykirk]

That doesn't sound quite right.<br /><br />Now I'm just working from memory and I'm probably way off on this ( Shuttle_guy ) please let me know if i'm even in the ballpark.<br /><br />I was under the impression that the shuttle main fuel tank had about 8 minutes of fuel and the SRB's burned for about 2 minutes.<br /><br />Now, Max-Q which is highly supersonic occurs long burn SRB burnout.<br /><br />So, the main fuel tanks would be about 3/4 full at SRB burnout.<br /><br />100,000 feet and 1 mile / second figure is substantially higher and faster than a 747 could ever achieve.

 

[scottb50]

The SRB'S burn-out and Mach 4.5 and 150,000 feet, it would take a lot more ET propellant to get from M .80 and 50,000 feet to orbit than what it does from SRB burn-out.<br /><br />I would think air launches might be acceptable for payloads under 2000 pounds. Launch vehicles with that capability, Atlas E, M-352, LLV-1, Conestoga, are in the 200,000 pound launch weight area. <div class="Discussion_UserSignature"> </div>

 

[propforce]

<blockquote><font class="small">In reply to:</font><hr /><p>"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." <br /><br />I do not know any rocket engine that dumps the fuel used to cool the chamber. It is normally burned in the combustion chamber. <p><hr /></p></p></blockquote><br /><br />Sorry for the late replay, SG.<br /><br />Perhaps you know this better by the name of "BLC" (boundary layer cooling" as in the SSME. <br /><br />This "... fuels injected for film cooling purpose and not burned..." is a standard practice for MOST liquid rocket engines. It's not often talked about other than the folks who deal with the combustion issues in details. <br /><br />How it works is this, on the outer ring of injector elements, there's a slot (or holes - called the <font color="yellow">BLC holes</font>in SSME on the injector primary face plate) just for the fuel to be injected along the wall of combustion chamber. This introduce a layer of fuel as "coolant" to reduce the heat transfer and to protect the structural integrity of combuster wall. Since it introduces as a layer of "film" to keep the "boundary layer" cool, it's often call as "film cooling" or "boundary layer cooling", e.g., BLC. <br /><br />This "film cooling" is very important when it comes to ACS/ RCS thrusters as the ones on the Shuttle (and on satellites, etc.), since these thrusters are not "regeneratively cooled" as big liquid rocket engines, the amount of fuel used for "film cooling" is significant and they take a hit on the Isp as a result.<br /><br />In the case of SSME, there are other places in the combustor that uses extra hydrogen for cooling purpose and not for combustion. The BLC is one, another is on the face of injector element. Hydrogen provides "transpirartional cooling" to the injector face sheet so the combustion flame front does not burn out the iinjector. On <div class="Discussion_UserSignature"> </div>

 

[propforce]

<blockquote><font class="small">In reply to:</font><hr /><p> From Rocketman<br />"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... "<br /><br />ah yes, some of the the expander cycle engines do dump the fuel used for cooling the chamber. That is why that use of the expander cycle has a lower Isp lower than the pre burner cycle, gas generator cycle engines as well as the expander cycle engines that do not dump the fuel used as coolant. <p><hr /></p></p></blockquote><br /><br />Geez whiz, SG. You know how I hate to disagree with you, especially in a public forum, but I must correct you on this one <img src="/images/icons/smile.gif" /><br /><br />Expander cycle engines, such as the RL-10, do NOT <i>"... dump the fuel used for cooling the chamber..."</i>.<br /><br />In fact, that's how the expander cycle engines work. They "pick up" the heat from cooling the chamber and use it to drive turbopump, then return the fuels back to the injector and "dump" them into the combustion chamber to burn with oxygen. <br /><br />Expander cycle engines may have a lower chamber pressure (hence a lower thrust) than both the pre-burner and GG cycle engines, but because they're largely for <i>SPACE ENGINES</i>, they have <font color="yellow">higher</font>Isp than previous 2 cycles of engines.<br /> <br />GG cycle engine, such as the J-2, RS-68, RS-27, MA-5, F-1 etc., <i>"... dump the fuel used for powering the turbopumps...".</i>, that's why they generally have a lower Isp than the pre-burner cycle (or staged combustion cycle) engines such as the SSME, RD-0120, RD-180, etc. , being both cycle of engines are mostly used as booster stage engines. <br /><br />Now don't put me in this position again ! <img src="/images/icons/wink.gif" /> <br /><br /><br /><br /><br />Edit: change from "...GG cycle engine, such as the J-2, RS-68, RS-27, MA-5, F-1 etc., <i>"... dump the fuel used for cooli</i> <div class="Discussion_UserSignature"> </div>

 

[propforce]

Hi Mike,<br /><br /><blockquote><font class="small">In reply to:</font><hr /><p>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. <p><hr /></p></p></blockquote><br />Hydrogen peroxide (H2O2) as a "monopropellant" works. All you need in the combustion chamber is a silver-screen as catalyst and it will undergo rapid "exo-thermo-decomposition" and produces O2 and H2O (steam) as product. There're rocket engines that uses solely H2O2 as a "mono-propellant" system, BTW.<br /><br /><blockquote><font class="small">In reply to:</font><hr /><p>...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<p><hr /></p></p></blockquote><br /><br />Actually there's little to no difficulties in getting hydrogen to light in a supersonic airstream, my friend.<img src="/images/icons/smile.gif" /> There is a problem, however; to get hydrogen to mix with air in a supersonic airstream and, if you don't get good mixing, you won't get a good combustion efficiency and thrust. <br /><br />To appreciate the difficulties to mix hydrogn, or any fuel, in a supersonic airstream, let's try this. Imagine you're back in high school and driving down the highway with your buddy driving his car next to you. Assuming you both are going 80 mph per hour (make sure no cops are around) and you try to squirt some water to reach your buddy. Notice how water quickly get swept by the air stream and it "bends" to the side quickly, even splash back on your own car door in the rear? Well... that's at 80 mph, now imagine how strong the air flow is at 750 mph!! <br /><br />Secondly, you'll have a much more difficulties to light liquid hydrocarbon (HC) fuel in a supersonic stream than you would with gaseous H <div class="Discussion_UserSignature"> </div>

 

[propforce]

<blockquote><font class="small">In reply to:</font><hr /><p>Well actually I said some of them do ("ah yes, some of the the expander cycle engines do dump the fuel used for cooling the chamber.") Was I totally incorrect?....I think I was. <p><hr /></p></p></blockquote><br /><br />I think you were partially correct.<img src="/images/icons/wink.gif" /><br /><br />The expander cycle engines that I know of, e.g., the RL-10 and other "on-paper" design concepts take ALL the fuel used for cooling the combustor to drive the turbopumps, then return all the fuel back to the main injector. We called this cycle as a "closed" expander cycle.<br /><br />There is a derived concept, called "expander bleed" cycle or "open expander cycle" that takes only a partial fuel used to cool the chamber to drive the turbopumps. At the end, the remaining fuel has too low of energy that they did not have enough pressure to be re-injected back into chamber. One concept, the Rocketdyne's MB-XX engines, reinject these "tired" fuel in the nozzle instead. This is similar to the way F-1 engine re-inject the "tired" GG exhaust into the nozzle. Note the "wrap-around" duct on the F-1 engine nozzle. <div class="Discussion_UserSignature"> </div>

 

[mikeemmert]

<blockquote><font class="small">In reply to:</font><hr /><p>...imagine how strong the air flow is at 750 mph!!<p><hr /></p></p></blockquote>I think I can imagine it, especially since the cramjet runs between 900 and 12,000 mph. (I'm one of those believers in the metric system, that's where I did my crude preliminary calculations). BTW, one good thing about MIPCC in the cramjet is that while the launch plane is travelling mach 0.85, you can get the air inlet speed to over mach 1 by spraying cold LOX into it. The <i>local</i> speed of sound goes over mach one, the launch plane doesn't have to take the stress of supersonic flight.<blockquote><font class="small">In reply to:</font><hr /><p>The challenge now is, as state-of-art, on how to get HC fuel energized prior to injection into a scramjet combustor therefore accelerate its reaction kinetics.<p><hr /></p></p></blockquote>Hydrogen is the only fuel that will work. The last time I read anything about a hydrocarbon-fueled scramjet was in <i>Scientific American</i> this summer. The author proposed cooling the engine by decomposing the hydrocarbon fuel, pointing out that this absorbs 5 times as much energy as simple vaporization. But this would create gunky carbon deposits in the cooling channels. I've messed around with decarbonizing enough two-stroke engines to wonder about this idea. This scramjet was for quick-reaction military surveillance systems so I think it was a disposable. I don't like that idea.<blockquote><font class="small">In reply to:</font><hr /><p>... you'll have a much more difficulties to light liquid hydrocarbon (HC) fuel in a supersonic stream than you would with gaseous H2. The problem is 2 fold, first of all notice I said "..gaseous H2..", that's because by the time the liquid H2, LH2, gets to the fuel injectors, it has been used (typically) to cool the combustor wall and has "vaporized" to the gas phase (technically a "super-critical" phase since under high pressure) as GH2.<p><hr /></p></p></blockquote>Now, here's a proble

 

[rocketman5000]

The major problem with burning any fuel in a super sonic stream is as Propforce pointed out getting the fuel to mix. Supersonic flow is inherently stable and does not mix well. Von Schlerin photographs show mixing angles of less than 7 degrees, hence the long length of combustion chambers. Hydrogen burns much more readily since it can combust with a very large band of concentrations. Hydrogen at STP can sustain a flame from from 5% to 95% concentrations. Therefore much less mixing is required to be able to ignite.

 

[holmec]

Yes they did.<br /><br />The Air Force has a simple idea of launching a rocket out the back of one of their unmodified cargo planes like C-17 with AirLaunch LLC. I wonder how big of a rocket and payload you could possibly make for the C-5.<br /><br />Also if your going with just spiting out rockets rather than droping them. You could possibly modify a 747 to spit one out the back...maybe at an angle. <br /><br />Or push the rocket out the front of the 747 on a rail. This would be good because you do not have to compromise or modify any of the structural integrity of the plane. Just give it a funny looking nose. <div class="Discussion_UserSignature"> <p> </p><p><font color="#0000ff"><em>"SCE to AUX" - John Aaron, curiosity pays off</em></font></p> </div>

 

[mrmorris]

<font color="yellow">"Or push the rocket out the front of the 747 on a rail. This would be good because..."</font><br /><br />Have you considered the aerodynamic aspects of a large cavernous space with a hole in the <b>front</b> with an airstream of several hundred miles an hour coming straight into it?

 

[propforce]

<font color="yellow">Have you considered the aerodynamic aspects of a large cavernous space with a hole in the front with an airstream of several hundred miles an hour coming straight into it? </font><br /><br />Too funny.... <br /><br /><br /> <div class="Discussion_UserSignature"> </div>

 

[propforce]

<br /><blockquote><font class="small">In reply to:</font><hr /><p>The last time I read anything about a hydrocarbon-fueled scramjet was in Scientific American this summer. The author proposed cooling the engine by decomposing the hydrocarbon fuel, pointing out that this absorbs 5 times as much energy as simple vaporization. But this would create gunky carbon deposits in the cooling channels. <p><hr /></p></p></blockquote><br /><br /><i>THIS summer?</i> <img src="/images/icons/shocked.gif" /> Good Lord, we did this 15+ years ago! We looked into this "endothermic" fuel that you read, it starts out as methycyclohexane but as it absorb heat, it decomposes to aromatic compounds such as benzene and toluene. Not exactly good stuff for supersonic combustion. <br /><br />Since then there has been lots of work done on raising HC fuel cooling capability. Note that we are not changing the composition of fuels, but merely conduct investigations to find out its upper temperature limits. The results are very pleasantly suprising good. AFRL did lots of good work in this area.<br /><br /><blockquote><font class="small">In reply to:</font><hr /><p>Now, here's a problem; I don't think, especially in a large engine (because of the square/cube law) that you can get enough heat transferred through the combustion chamber walls to sufficiently heat the fuel. The engine would be overcooled. It takes 14 calories to heat a gram of hydrogen 1 degree Centigrade (or Kelvin). That's a lot. That's 14 times as much as water, which is an excellent coolant, hydrogen's 14 times better. I think the fuel would need further heating beyond what heat it picks up doing it's job cooling. Thus the need for a little extra oxygen and burning a little hydrogen before injecting it into the airstream.<p><hr /></p></p></blockquote><br /><br />Oh you'd be suprised how much fuel needed to cool a scramjet. As a matter of fact, a common problem in scramjet design is that you'll need MORE fuel for cooling than the amount of fuel needed for combu <div class="Discussion_UserSignature"> </div>

 

[propforce]

<blockquote><font class="small">In reply to:</font><hr /><p>The major problem with burning any fuel in a super sonic stream is as Propforce pointed out getting the fuel to mix. Supersonic flow is inherently stable and does not mix well. Von Schlerin photographs show mixing angles of less than 7 degrees, hence the long length of combustion chambers. Hydrogen burns much more readily since it can combust with a very large band of concentrations. Hydrogen at STP can sustain a flame from from 5% to 95% concentrations. Therefore much less mixing is required to be able to ignite. <p><hr /></p></p></blockquote><br /><br />Good stuff. I can see you understand supersonic mixing and combustion issues <img src="/images/icons/smile.gif" /> <div class="Discussion_UserSignature"> </div>

 

[rocketman5000]

I loved compressible flow in college, alas I was only able to take 2 semesters of it. If I ever wen't back to school for anything beyond an MBA I that would be my focus of study.

 

[mikeemmert]

<blockquote><font class="small">In reply to:</font><hr /><p>Keep in mind this is the case for a "prolong" flight as one would with a real system, not the so-called "X" vehicle that only fly for seconds as oppose to tens of minutes or hours.<p><hr /></p></p></blockquote>The Concorde was missing important parts.<br /><br />Customers!<br /><br />I think hypersonic airliners are a little beyond the scope of this thread...I've changed the subject line, that might have been the source of the confusion.<br /><br />The thread title is "air launch capability". Now, there's a problem there. The subject matter is too large. The thread title did not say "rocket", but some posters have assumed that that was what the thread was all about. For instance, halman proposed an absolutely gigantic plane that would have to have a different launch gear than the landing gear. That's legitimate, since he's thinking of doing something like launching a fully loaded Delta IV or Atlas V from it. And that's certainly one way to do it.<br /><br />I saw "air launch capability" and reflected about how helpless ramjets are on a runway and all that free oxygen you can get from the air. Thus the idea to launch a plane from another plane. propforce is thinking in terms of a quick-reaction military surveillance system, thus a very small vehicle that doesn't need augmentation with oxygen and, because of the square-cube law, has a large surface area to absorb heat and must travel for hours (unlike a space-launch vehicle with it's high acceleration).<br /><br />What is launched from the air launch capability determines the direction of the conversation. Thus this is five or six threads in one. All are legitimate.<br /><br />I started on this thread because I saw a picture of the Boeing blended wing-body plane in, of all places, Free Space. It looked to me like it would be a great launch plane. For what? Why, for a cramjet, of course; I've been sitting on that idea for a long time, it wants to come out.<br /><br />I fee

 

[halman]

mikeemmert,<br /><br />There is a very good reason why air launch capability is important. According to Arthur C. Clarke, in the "The Promise Of Space", a vertically climbing rocket loses 20 feet per second of velocity every second. That is 1,200 feet per second every minute of vertical climb. But a rocket launched from sea level has to climb more or less vertically, at least for a minute or more, so that it can get above the thickest part of the atmosphere, which is the first 5 miles or so. But a rocket capable of several g's of acceleration has to throttle back right after take off, to avoid the dreaded 'max Q' regime. And vertical velocity adds nothing to the critical component of acheiving orbit, velocity relative to the center of the planet. After climbing out of the dense, lower atmosphere, a rocket then turns until it is pointing at the horizon, and begins to add velocity where it counts. Of course, this is an oversimplification of the trajectory that modern rockets fly, but I believe that it is fundamentally sound.<br /><br />What I would like to find out, since I know practically nothing of math, is what a vehicle, capable of 2 gravities of acceleration if traveling vertically, were to be launched at a 15 degree angle above the horizontal, at full thrust, off the back of a carrier vehicle, at 50,000 feet of altitude, would do in terms of reaching orbit. It would not lose any altitude, as a vehicle dropped by its carrier would, because it would be powering itself off of the back of the carrier vehicle at full power, and would be able to overcome gravity losses through thrust, without using aerodynamic lift. Where would it encounter max Q, and at what velocity? Would it have to increase the angle of climb above the horizon, or could it stay at 15 degrees? I realize that it would be experiencing high acceleration near the end of the burn, but I imagine that it would be very brief. I stipulate a 15 degree angle at seperation because that seems like a s <div class="Discussion_UserSignature"> The secret to peace of mind is a short attention span. </div>