From runway or launchpad to orbit and back to runway...Why not?

[why06]

Could we develop some special material that froze in space and protected it as it came down? Also some parts of this thread were rather confusing. From what I see and hear it is more than possible to develop the ship right now. What's the biggest problem today with making a multi-stage ship?<font color="purple"></font> <div class="Discussion_UserSignature"> <div>________________________________________ <br /></div><div><ul><li><font color="#008000"><em>your move...</em></font></li></ul></div> </div>

 

[tomnackid]

"From what I see and hear it is more than possible to develop the ship right now. What's the biggest problem today with making a multi-stage ship?"<br />-------------------------------------------------------------------------------------------<br />There are basically three reasons it hasn't been done:<br /><br />1. Money<br />2. Money<br /><br />...what was that third one...oh yes,<br /><br />3. Money

 

[why06]

That's always the problem! <img src="/images/icons/wink.gif" /> <font color="yellow"><br /><br /><br /></font> <div class="Discussion_UserSignature"> <div>________________________________________ <br /></div><div><ul><li><font color="#008000"><em>your move...</em></font></li></ul></div> </div>

 

[rocketman5000]

an RBCC espically the particular engine concepted and designed for the GTX used and aerospike nozzle and would be optiumized to most altitudes over a bell nozzle.

 

[mlorrey]

The Navaho was launched by a liquid fuelled first stage rocket that it was mounted to the dorsal side of. There were several Navaho models, actually. Astronautix.com has some good pages on them. The Navaho was intended as a mach 2.75-3.0 nuclear tipped cruise missile with an intercontinental range. By the time it was perfected, ICBM technology had surpassed its performance. <br /><br />However, knowledge gained about ramjets in the program led to the USAF's development of the Bomarc ramjet propelled surface to air anti-aircraft missile, which was the only SAM the USAF fielded (all others were fielded by the Army) because it was the only one with wings!!! <img src="/images/icons/smile.gif" />

 

[mlorrey]

Okay, for the novices, to answer g_sat's questions:<br /><br />Isp: Specific Impulse - essentially the fuel efficiency of your rocket, tells you how many lb-seconds of thrust you get per pound of propellant. i.e. if you have 100 sec Isp, this means 100 lbs force*sec/lbs fuel. With such a fuel, you can run a 10 lbs thrust rocket engine for ten seconds on one lb of fuel, or a 100 lbs thrust engine for one second, or 1 lbs thrust engine for 100 seconds, all on one lb of propellant.<br /><br />If your Isp is instead 1000 sec, you get 1000 lbs thrust for 1 sec or 100 lbs thrust for 10 secs, or 10 lbs thrust for 100 sec, or 1 lb thrust for 1000 seconds, all from 1 lb of propellant.<br /><br />As you can likely tell, you want your Isp as high as feasible, which is one reason NASA is fixated on liquid hydrogen as a fuel, since it produces about 450 secs Isp when burned with LOX. RP-1 (kerosene) produces 275-325 sec, and the STS SRBs are about 198 sec.<br /><br />Ramjets and turbine engines get thousands of seconds of Isp because their oxygen comes from the air, i.e. it isn't counted as mass the rocket has to carry.<br /><br />Scottb hasn't done the numbers. I have. He's been around a long time, but has a reputation as a curmudgeon who just poo-poohs advanced concepts and innovative thinking.<br /><br />The reason ramjets and scramjets are important is that the high Isp for the portions of the flight regime they work in help to raise the average Isp for the entire trip high enough (by not having to carry so much oxidizer mass, or the airframe mass needed to carry it) that your vehicle's mass fraction (the fraction or percent of lift-off mass that is propellant) requirements to reach orbit in one stage are much lower. <br /><br />If your Isp is over 500-505 secs, you can reach orbit in one stage with a mass fraction of only .78. With an Isp of 1000 sec, your mass fraction can be less than .60, which is well within the range of normal aircraft construction methods, building your TPS into th

 

[mlorrey]

"There are basically three reasons it hasn't been done: <br /><br />1. Money <br />2. Money <br /><br />...what was that third one...oh yes, <br /><br />3. Money "<br /><br />True, however the GTX Reference Vehicle project was estimated under NASA rules to cost $750 million, AFIAKR. Given what we know about NASA costing rules (wrt the SpaceShip1 program), this means if Burt Rutan built a GTX, it would cost about $40-45 million, including the test program.<br /><br />That being said, it would be a higher risk vehicle than SS1.

 

[g_sat]

Thank you mlorrey and why06 for the info. <div class="Discussion_UserSignature"> </div>

 

[rocketman5000]

With all this about Isp, what was the average Isp of the GTX concept

 

[mlorrey]

I haven't got it off hand, but page 20 (fig 13) of this document: <br />http://trajectory.grc.nasa.gov/aboutus/papers/NASA-TM-2002-211599.pdf<br />Displays the Isp v Mach Number for the Reference Vehicle trajectory. It appears the average is just under 1000 sec.

 

[scottb50]

Scottb hasn't done the numbers. I have. He's been around a long time, but has a reputation as a curmudgeon who just poo-poohs advanced concepts and innovative thinking... <br /><br />No I don't poo-pooh advanced concepts and inovations, I just don't see the ones being discussed having any relevance. Maybe you could use turbojets and ramjets and scramjets in a first stage to get a rocket above the atmosphere, but it is still a long way's from Mach 12 to Mach 25. The amount of energy to even get to Mach 12, in the atmosphere, which all of the engines proposed would have to do is enormous. The X-43 burns for 7 seconds after being accelerated to Mach 7 by a rocket and has reached mach9.6. I just don't see this as anything that will get payloads into orbit economically to make it worthwhile.<br /><br />It would be great to walk down a jetway and board an aircraft that would taxi to the end of a runway, takeoff and reach orbit, having three or four different types ofengines or three or four that could operate across the range needed to reach orbit is just not possible.<br /><br />Sure Ram-jets and Scram-jets and even turbofans have higher ISP than LOX/LH2 engines, but they don't operate above the atmosphere.<br /><br />SAS: the current NASA spaceflight plan for the future: CEV, CLV, HLV, etc. Scottb is fixated on big phallic ICBM-like rockets because he is inherently conservative and backward looking, which is okay...<br /><br />I,ve never said anything about a big &%$#@!. What I propose is similar to what Elon Musk proposes. A two section Module, LOX in one section, LH2 in the other and an SSME attached at the bottom. Put four of them in an airframe with identical Modules used as SRB housings and carry a second stage piggy back like the Shuttle. The second stage is an identical Module with two RL-60 engines and an attached payload. <div class="Discussion_UserSignature"> </div>

 

[tap_sa]

<font color="yellow">" I just don't see the ones being discussed having any relevance"</font><br /><br />You almost do! <img src="/images/icons/smile.gif" /><br /><br /><br /><font color="yellow">"The amount of energy to even get to Mach 12, in the atmosphere, which all of the engines proposed would have to do is enormous."</font><br /><br />Bingo! It requires a lot of energy and with chemical propellants energy comes from mass, which further means you needa a lot of mass, which further means you need a lot of energy, which ... get the drift? When most of the mass (ie oxidizer) required to release the energy comes from outside the vehicle that's what gives you the Isp in thoudands and relaxed massratio requirements.<br /><br />Tinkering with ye olde rocket equation shows that reducing total dv requirement even a little yields much greater saving in required massratio (given that dv is still much greater than exhaust velocity). Getting to mach 12 with turbo/ram/scramjets with Isp in the thousands would be a boon for the final purely rocket propelled part. Even a plain ramjet that kicks in at about Mach 1 and would do most of propelling up to Mach 5-6 would be magnificent. <br /><br />In fact I find it a bit surprising that there's not first stages with ramjets bolted to the sides like in Bomarc missile. But the reason is that purely rocket propelled booster works, is simpler, and there's no pressing need for the established aerospace industry to push the envelope into more elegant designs. Which approach is better, plain rockets or having airbreathing first stages, there's no clear answer. It depends on the situation, available resources and with what you meter the 'betterness' (R&D costs, operation costs, GLOW etc.etc.)

 

[mlorrey]

Scottb, if you have ever actually done the numbers yourself, and knew what you were doing, you'd have to come to the same conclusion I have. I started out being a proponent of BDBs, primarily of my 1.5 stage version of the Spencer Launcher, but I've put a lot of time into studying the airbreathing propulsion issue and found that the numbers work.<br /><br />Disparaging the concept just because X-43A only accelerated a little bit for a few seconds is dishonest. HyperX was never meant as a launch vehicle, it was only built to demonstrate positive supersonic combustion, and THAT IS IT. It held a small tank of gaseous hydrogen as fuel, which I've told you before, several times, and which you've ignored. A proper RBCC launcher would still be mostly liquid fuel, which HyperX wasn't. That you continue to argue as if HyperX was a launcher exposes that you are being dishonest, or just ignorant.<br /><br />You've also ignored that RBCC engines CAN, in fact operate above the atmosphere, because they are also rocket engines, in addition to being ramjets and scramjets. Your stubborn refusal to admit this also exposes your dishonesty.<br /><br />You are also being dishonest by claiming I am speaking of turbine engines. That being said, there is no reason why the first stage of a multi-stage launcher could not be turbine engine based. Many first stages only carry a rocket to mach 2-3 anyways (like the SRBs), so building such boosters around turbine engines would go a long way toward making them recoverable and reusable. This hasn't always been feasible, given the low T/W of turbine engines, but newest models range from 12-15, rather than the 5-10 range of older models. With this T/W, turbine engines gain the advantage over rocket engines with their high Isp, high throttlability, and high reusability. If you ever actually did the numbers, you'd agree with me. Of course you never do, which is why you're just being curmudgeonly.

 

[scottb50]

You've also ignored that RBCC engines CAN, in fact operate above the atmosphere, because they are also rocket engines, in addition to being ramjets and scramjets. Your stubborn refusal to admit this also exposes your dishonesty. ...<br /><br />Where did I say that?<br /><br />A proper RBCC launcher would still be mostly liquid fuel, which HyperX wasn't. That you continue to argue as if HyperX was a launcher exposes that you are being dishonest, or just ignorant....<br /><br />Any reference I have made has been using the concept in a launch vehicle, where did I claim the x-43A was anything other than a test article?<br /><br />You are also being dishonest by claiming I am speaking of turbine engines. That being said, there is no reason why the first stage of a multi-stage launcher could not be turbine engine based.....<br /><br />Once again I am only trying to point out how hard it would be to build a runway launched vehicle that would put a substantial payload into orbit. <div class="Discussion_UserSignature"> </div>

 

[mlorrey]

"Where did I say that?"<br /><br />Now I know you are a troll. Immediately above you said: "Sure Ram-jets and Scram-jets and even turbofans have higher ISP than LOX/LH2 engines, but they don't operate above the atmosphere."<br /><br />What do you think an RBCC is? What the hell do you think we've been talking about all this time? <br /><br />"The X-43 burns for 7 seconds after being accelerated to Mach 7 by a rocket and has reached mach9.6. I just don't see this as anything that will get payloads into orbit economically to make it worthwhile. "<br />^^^^^^^ is where you claim the X-43 is something other than a test article. Saying the X-43 is not "anything that will get payloads into orbit" is an assertion that the X-43 is a launch vehicle.<br /><br />Your claim that it is hard to build a runway launched vehilce that would put a substantial payload into orbit is also bogus. I've demonstrated with my X-106 proposal, that according to the math, a vehicle under 99,000 lbs GLOW, with wings, could launch from a runway, put two people and 500 lbs of payload into orbit, reenter, and be reused.<br /><br />The fact is that I started the 106 concept as a lark, a thought experiment of "what I would do" if I wanted to build a runway launched space plane as a private project, using proven and/or off the shelf technology in as many places as possible, to do my best at it to prove that it wouldn't work. It turned out my original premise was wrong: it will work. Before that, I was a BDB supporter and pretty critical of the spaceplane crowd.<br />

 

[spacelifejunkie]

mlorrey, I usually like to just read and learn from reading your posts as well as others' and then ask the occasional question and hope for a reply. I respect your opinion and would like to hear what you think of the following proposal.<br /><br />"If your Isp is over 500-505 secs, you can reach orbit in one stage with a mass fraction of only .78. With an Isp of 1000 sec, your mass fraction can be less than .60, which is well within the range of normal aircraft construction methods..."<br /><br />What about pulsed detonation engines, Isp and mass fractions? They have a lot of flexibility. Such as...<br />1. Completely throttleable, unlike rockets.<br />2. They use much less fuel due to detonation compared to combustion.<br />3. Very simple overall design with just a few moving parts. <br />4. A smaller LOX tank could be carried along for above atmospheric flight.<br />5. The engine is scalable, i.e. more detonation tubes, higher detonation frequency, etc. Overall maximum thrust is an issue I think but how big of a problem?<br /><br />I can't do all the math so I'm looking for someone to help me out. I think GE and P & W are taking the lead on this technology and I would love to see it mature soon. Also, if PDE's are incapable of SSTO what about dropping from altitude? Can PDE's offer enough advantages to be competitive with all the other proposals on this thread?<br /><br />SLJ

 

[mlorrey]

The T/W ratio for pulse detonation engines is dismally poor, so for getting to orbit, they are a bad idea. For travelling around in space, as an alternative to regular constant deflagration (i.e. rocket engines) combustion, they have merit. If further research can get the thrust of these engines improved significantly, I'm interested, but they just can't compete at this point. The best choice, given todays propulsion and materials technology, is ramjets with rockets, or a combined cycle ram-rocket engine. Scramjets are almost ready for prime time, but the velocity range they help in (mach 8-14) airbreathing hypersonic propulsion is just a bit too high for our materials technology to build vehicles for.<br /><br />PDEs have a T/W ratio worse than turbine engines. This needs to be gotten up to 40-50 to be worthwhile.<br /><br />One limiting factor with PDEs is that the bigger you make them, the lower their pulse frequency, which detracts from the lbf-sec, since less time is spent in actual combustion, so both thrust and Isp suffer. This may place a tight physical limit on the scalability of PDE.<br /><br />Just clustering more detonation tubes does not mean scalability. You do gain a bit from multiple tubes helping each others ignitions through harmonic design, but if you always use the same amount of engine mass to produce the same amount of thrust, and that T/W is terrible, then you are scaling a little crap into a huge pile of crap.<br /><br />Ultimately, your T/W needs to scale with the Isp advantage. Even if your PDE engine has twice the Isp, if its T/W is half or less than what you were using before, then you don't gain anything.

 

[rocketman5000]

I disagree with your last statement. If the Isp doubles from say 500 to 1000 seconds your final mass fraction would change from 20% to 40%. but since the engine is not 100% of the final mass it would give you an advantage in getting to orbit.<br /><br />That is assuming it can produce enough thrust to get off the ground in the firstplace. Think vasimr or ion thrusters. On thing about horizontal takeoff is you don't need an engine that can lift you off vertically at take off, but only one that can over come drag. If you could get enough lift to get into the upper atmosphere (think waverider, high lift to drag ratios like the U-2 or something similiar) where drag diminishes you could possibly achieve orbit on an engine that has less than ideal T/W but a high Isp<br /><br />however, information on PDE's has tappered off as of late. Are they still being pursued?

 

[mlorrey]

True, but you have to have a decent T/W to begin with for the entire vehicle to get within the 20% dry mass margin. Even with ramjets and scramjets, which have a T/W ranging from 20-50, their Isp in the thousands helps them overcome their T/W ratio and improve the mass fraction a bit. For instance:<br /><br />a) 400 sec avg eff. Isp, LH2/LOX, T/W: 50<br />b) 1000 sec avg eff. Isp, Scramjet. LH2/air/LOX T/W: 30<br />c) 2000 sec avg eff. Isp, PDE LH2/air/LOX, T/W: 2<br />d) 300 sec avg eff Isp, Kerosene/LOX, T/W: 100<br />e) 700 sec avg eff. Isp, RBCC, kerosene/air/lox T/W: 50<br /><br />Which is the system that will get you to orbit in one stage? Which is the worst? What is more, the multi-thousand second Isp performance of PDE only occurs when the PDE is air breathing. When you are using liquid oxidizer in your PDE, its Isp drops back down to normal peak Isp for the fuel/ox combination.<br /><br />The highest performing rocket engines are not deflagration combustion, they are constant detonation engines, with exhaust gasses exiting the nozzle at supersonic velocity. For this reason, a high performance rocket engine will always have a higher T/W than a PDE using the same fuel, because the high performance rocket engine is under constant detonation, while the PDE is only detonating for a small fraction of the time.<br /><br />I've read a number of papers of experiments with them over the past several years. Apparently, there is also a speed limitation, generally mach 3-4, at which point their Isp drops to little more than ramjet levels. There are apparently some interesting concepts with using them in bypass air vents of turbofan engines, but one of the main reasons they have low T/W is that the detonation pulsing causes premature metal fatigue, so det tubes need to be much thicker, as does the rest of the structure around it.<br /><br />I imagine the vibration would be hell in a manned vehicle.

 

[rocketman5000]

I hadn't thought about the fatigue of the detonations on the tubes. It would be a nonsymetrical stress cycle every time there was a combustion event. Operating at frequency of 40 or 50hz would quickly add up the cycle life.<br /><br />wouldn't it also be possible to have the motor be continuous burning in the LH2/LOX configuration?

 

[mlorrey]

That is essentially what an SSME does: its turbopumps are so powerful so that the fuel and oxidizer combines and combusts at supersonic velocities. It isn't quite up to the speed that is seen in some PDEs, with shock wave velocities as high as mach 5, which is why PDEs have higher Isp. The faster the shock wave, the more powerful it is and therefore the more rugged your detonation tube and exhaust nozzle need to be. Ruggedness means mass, ergo lower T/W ratios in exchange for higher Isp. <br /><br />What I'd like to see is a large piston pump able to deliver large quantities of fuel and air in pulses, rather than just little bitty injectors into small tubes. This might be an effective means of starting these going with significant thrust from 0 velocity.

 

[rocketman5000]

not neccessarily the the strength of the shockwave but the number of cycles that the tube would see.

 

[mlorrey]

shock strength is an issue. It dictates dynamic pressure of the pulse, and like any gun maker designing a gun barrel, both specified pressure limits and number of rounds fired dictate the thickness of the material used, and what strength material is required, how it is machined, forged, treated, etc. That is essentially what a PDE is: a gun firing blanks.

 

[spacelifejunkie]

Excellent info, thanks. I always thought the main limitations were noise, vibrations and material fatigue. Those are all big mountains to climb in and of themselves but the T/W is a real issue. I am anxious to see how GE and P&W are doing with their research. This is the last I heard...<br /><br />"The vehicle Dean plans to use to reach his goal looms over the rest of the test cell, looking for all the world like a chunk of water main. The GE research group calls it simply "the big rig"—a heavily instrumented length of pipe roughly 16 inches in diameter. The one part of the test cell that's off-limits to visitors is the area just in front of the big rig's mouth—the only place that would give a view down its throat, presumably revealing details that GE would prefer to keep to itself. Those details, one guesses, have something to do with what Dean refers to as "valveless" operations, which could be the key to generating detonation frequencies as high as hundreds or even thousands of cycles per second in a single tube. <br /><br />Dean is reserved on this subject, noting in a later e-mail that he's "not ready to say much about this." But Maclin, GE's marketing manager, is more expansive. "We're looking at an order of magnitude higher frequency than anybody else in the industry," Maclin says. "I like to think of it as an aerodynamic valve as opposed to mechanical valves, and that's what allows us to get to the much higher frequency, because there's a limit to what you can do with mechanical valving." In such a design, the air-fuel mixture and timing would be controlled by aerodynamic forces created by the shape of the detonation chamber itself. This "aerodynamic valve," Maclin says, would "allow air in before detonation, but the pressure from detonation will be high enough to prevent the second charge of air and fuel from entering until the detonation wave moves downstream." <br /><br />When asked what kind of results he's getting so far with the big rig, Dean again s

 

[mlorrey]

Sounds like they've made some advances. I hadn't seen this article, but you'd expect to see some working prototypes being flight tested by now.<br /><br />I suspect the 'aerodynamic valve' is a convergent-divergent venturi choke, that, like that of a rocket nozzle, holds a shock wave, only this time it uses a shock wave at the throat to prevent premixed air and fuel from entering the detonation zone. If it is, this means the PDE is speed limited in airbreathing mode.