new launch vehicle

[larper]

I think we all understood your post. I also think you were just brainstorming and posted something that you really didn't mean to. <br /><br />A ducted SRB obviously makes no sense. If you instead meant a ducted rocket to replace the SRBs, that is something else altogether.<br /><br />He was just being a little flippant. I don't think it was mean spirited in anyway. <div class="Discussion_UserSignature"> <p><strong><font color="#ff0000">Vote </font><font color="#3366ff">Libertarian</font></strong></p> </div>

 

[propforce]

<blockquote><font class="small">In reply to:</font><hr /><p>Thank you both for responding. <br /><br /><< I wonder what adding a duct would do to the performance and cost of an SRB and how that would influence the design of an SRB launched CEV? />> <br /><br />When I read that it clearly implies a ducted rocket, aka, ejector rocket. <br /><br />But I gather from both of your posts that it was not clear to you. <br /><br />For myself, it appeared that he had understood my post and that he was being patronizing and condesending in addition to close minded. <p><hr /></p></p></blockquote><br /><br />Skywalker01,<br /><br />I apologize if my reply offended you. That was not my intent. I've been absent from the board for the last few months therefore you're not used to my weired sense of humor. <img src="/images/icons/smile.gif" /><br /><br />I did know that you meant an ejector rocket and I did follow-up explaining to you that an ejector rocket is not optimum for a vertical launch propulsion system.<br /><br />Below was my post<br /><br /><blockquote><font class="small">In reply to:</font><hr /><p>In reply to:<br />--------------------------------------------------------------------------------<br /><br />I wonder what adding a duct would do to the performance and cost of an SRB and how that would influence the design of an SRB launched CEV? <br />--------------------------------------------------------------------------------<br /><br />Are you adding a duct in front or at the back of SRB? It maybe kinda pretty looking, seeing flame coming out at the inlet of duct. Hmmm... forward thrust - reverse thrust = zero net thrust. A standing rocket? <br /><br />An ejector rocket concept as applied to a SRB for the purpose of launching CEV will only make the SRB less efficient by dragging heavier pipe with only incremental gain of thrust improvement. <br /><br />An ejector rocket concept is only good if you plan to travel within the atmosphere, where you have air for thrust augmentation. It's difficult to ar</p></blockquote> <div class="Discussion_UserSignature"> </div>

 

[craig42]

What do RBCC and TRRC stand for?

 

[tap_sa]

<font color="yellow">"with available technology, the only cost effective option to deliver any kind of payload to LEO is an RBCC scramjet."</font><br /><br />There is a fully working RBCC scramjet engine available somewhere?

 

[tap_sa]

<font color="yellow">"I disagree. If you wait for an increase in market size before designing a better lower cost launch system then you will be waiting a long time.<br /><br />How about designing a better lower cost launch system based on the current market size and letting the lower cost expand the market. "</font><br /><br />You should have read past the first sentence of my post <img src="/images/icons/wink.gif" /> Part of the current model is very expensive launch vehicles which fly mainly because the payload is half-filled with pork barrels. Lower $/lb cost will change the picture and the market, as I said in the second sentence.<br /><br />You hint that perhaps LVs could be a little smaller but fly more often. With that I agree. For instance the future SDHLV will probably be hideously costly to maintain because it needs shuttle-sized assets (buildings, personel, pads etc) and flies maybe once a year. I seriously doubt NASA can cough up the money to build />100t payloads faster than that.

 

[tap_sa]

propforce, I'd like to hear your (and of course other's too) comments (as an 'old guy' who knows his stuff, don't be afraid to patronize <img src="/images/icons/wink.gif" />) about the following;<br /><br />Airbreathing first stage built from ordinary existing turbojets. I've heard about this here and there, but nobody seems to be seriously interested. Everybody is after ramjet/scramjet hypersonic world. But while waiting for them, why not take a few of the best fighter jet engines, bolt them symmetrically, vertical around the stage structure housing fuel tank, and use that to push rocket stage(s) through most of the atmosphere. I'd imagine something like 50,000ft altitude and mach 2 would be reasonable goal? With Isp of a turbojet powered flyback should be relatively easy. I know this might not scale to Saturn V class very well but maybe in smaller league, ~5t LEO payloads?<br /><br />AFAIK best fighter jet engines have T/W over 10, I wonder how hard it would be to raise that at least to 15 or 20 for the stage operation. Is there some 'unnecessary' stuff in them that could be ridden because of the short flight time, 10-20 mins instead of hours. Perhaps mildly cryogenic fuel (methane) could be used, to provide cooling, allowing running the engine safely beyond nominal levels (like SSME doing 109% in every flight).<br /><br />Some may ask how does this differ from airlaunch, except for specialized jet stage instead of maybe tuned 747? Attained final speed might be considerably higher without need for supersonic Concorde/XB-70 II. And conditions during stage sep would be better for ordinary rockets, at least if we take compare to t/Space style airdrop. Jet stage would release the rocket going 'the right way', nose pointing to the way which the rocket would continue thrusting. t/Space drop requires the rocket to turn and begin the flight going 'sideways'. Lateral forces in such maneuver would shred ordinary flimsy liquid rockets, no wonder t/Space is going for pressure fed.

 

[scottb50]

Airbreathing first stage built from ordinary existing turbojets...<br /><br />Look at the Pegesus as an example. The amount of payload reaching orbit is pretty limited. The only way to increase it would be a larger vehicle, which would quickly overtake the capability of any aircraft. I would also question getting to Mach 2 with any payload externally attached. <br /><br />Even if you airlaunch the most important requirement for reaching orbit is speed, not altitude. Starting at even Mach 2 doesn't reduce the propellant required to get to orbital velocity. The Shuttle reaches Mach 1 in a little more than a minute so for all practical purposes an airlaunch would eliminate roughly 1/2 the mass of the SRB's and less than 10% of the mass of the propellant, so it would still take a very large vehicle to reach orbital velocity.<br /><br />Ramjet/scramjets would be useless until enough speed was attained to start them. They would also require larger first stages, to compensate for the added mass. For something usable for just a very few minutes the added thrust they could provide would be minimal, you would still need rocket engines which would be much lighter and simpler.<br /><br />One possibility would be a dual cycle engine. A rocket engine that would use a high speed compressor to force air into the motor through about 50,000 feet or so. Since LOX is the heaviest component of the propellant reducing the amount needed might help. The problem would be needing additional turbopumps, to compress the air and whether the added weight would be offset by the LOX savings.<br /><br /> <div class="Discussion_UserSignature"> </div>

 

[tap_sa]

<font color="yellow">"Look at the Pegesus as an example. The amount of payload reaching orbit is pretty limited. The only way to increase it would be a larger vehicle, which would quickly overtake the capability of any aircraft. I would also question getting to Mach 2 with any payload externally attached."</font><br /><br />Pegasus is all solids rocket so it's payload isn't that good no matter what you do. And it's airlaunched from an airplane. I didn't mean any sort of winged craft but a stage where rocket engines are partially or fully replaced with turbojets. Current turbojets lack in T/W but they have ten times the specific impulse.<br /><br />Your shuttle-example shows that even mach 1 means a lot, one SRB + 10% of ET is nearly 700t!

 

[skywalker01]

<< I apologize if my reply offended you. That was not my intent.>><br /><br />Thank you Sir.<br />And you have my apologises for my being a grumpy old fart and jumpimg the gun.<br /><br />And also thank you for the information on ejector design. It is one of those areas of rocket design that I have never had the time to learn about as much as I wanted so that I could actually apply it to a design example to see how it would size up.<br />My closest encouter with ejector rockets before this was the strutjet, aka, RBCC, which includes rockets in the ramjet/scramjet flow path. But in that case I was sizing a vehicle based on propulsion system data provided by Aerojet and the vehicle was flying a constant Q flight profile.<br /><br />Regarding the ratio of primary to secondary air flow of 1:4. How quickly does the performance boost from the ejector effect drop off as you move away from that condition? Is it fairly flat curve or steep? If you have are report numbers or links on this subject that you could recommend I would appreciate it. <br /><br />In spite of what they say about old dogs not learning new tricks, this old dog very much likes to learn.<br /><br />Thanks again.

 

[propforce]

<blockquote><font class="small">In reply to:</font><hr /><p>......why not take a few of the best fighter jet engines, bolt them symmetrically, vertical around the stage structure housing fuel tank, and use that to push rocket stage(s) through most of the atmosphere. I'd imagine something like 50,000ft altitude and mach 2 would be reasonable goal? With Isp of a turbojet powered flyback should be relatively easy. I know this might not scale to Saturn V class very well but maybe in smaller league, ~5t LEO payloads? <p><hr /></p></p></blockquote><br /><br />One major issue with using turbojets for a vertical launch is the relative low thrust of turbojet engines. Take for example the most powerful turbojet engine to date, the GE90-115B being used for the 777, rated at 115,000 lbf. One would need 8 of them just to come close to the equivalent thrust of a RD-180 for lift-off. <br /><br />The engine thrust-to-weight (T/W) is also low as compared to liquid rocket engines which has a T/W from 60 and up. The RD-180 has a T/W of 72 whereas the GE90 has a T/W of 6.3, just to give you a comparison.<br /><br />Therefore using jet engine for a vertical take-off would not be a preferred design. However; using them for horizontal take-off, and/or as a fly-back engine for a vertical take-off vehicle is certainly a viable idea.<br /><br />Studies have been done on attaching jet engines on a 1st stage booster, using liquid rocket engines for take-off, then using jet engines for fly back to launch site after stage separation. But since they were done by 'traditional launch vehicle design houses' who were not very familiar with how to integrate jet engines and wings with rockets, I am sure there was a certain bias against the concept. A first stage VTHL using rocket for VT and jet engines for flyback HL can still be a viable option for a reusable routine launch vehicle. The first stage will just get much bigger than a traditional rocket, as one pays the penalty for the fly-back option. The question <div class="Discussion_UserSignature"> </div>

 

[skywalker01]

RBCC -- Rocket Based Combined Cycle<br /><br />Its a propulsion concept designed by Aerojet that has multiple small rocket motors in the flow path of a ramjet/scramjet. Since the rocket motors are within the flow path of the ramjet/scramjet the rockets are effectively ducted, i.e., have an ejector effect, which increases the effective performance of the rocket motors.<br /><br />The basic flight profile for a straight RBCC powered HTOHL vehicle is to use the ducted rocket for the take-off roll and to accelerate up to ramjet speed (somewhere between Mach .8 and Mach 1.2). At that point the rocket motors are shut down and the vehicle continues to accelerate on the ramjet up to about Mach 4 or 5 at which point the scramjet takes over and accelerates the vehicle up to somewhere between Mach 8 and Mach 12. As the scramjet thrust starts falling off in the Mach 8 to 12 range the ducted rocket motors are started up again to maintain the thrust and acceleration of the vehicle.<br /><br />A variation on this concept is to use a ground accelerator to boost the vehicle up to ramjet speed without using the ducted rocket motors as a way of reducing the amount of propellant that needs to be carried. This reduces the size and cost of the overall vehicle at the expense of more operational complexity.<br />Some people are opposed to this addition of a ground accelerator, those in favor of it usually pointout how the Navy uses them all the time on their aircraft carriers.<br />______________________________<br /><br />TRCC -- Turbo-Rocket Combined Cycle<br /><br />This is an RBCC with afterburning turbines added into the flow path. The turbines are used to accelerate the vehicle up to ramjet speed. The pros and cons of this variation are a lot more complex and would take too much time and space for this forum. <br />

 

[propforce]

One interesting concept similar to what you have in mind is the Gryphon concept by the Adrews Space & Technology folks. <br /><br />As you're aware, one big problem for vertical launch is that engine thrust must be able to lift all the propellant weight off the ground, and consumed lots of them just get to Mach 1. So one would need big rocket engines for a vertical launch. For horizontal launch, huge wing span and landing gears must be designed, again due to the massive weight of propellant carried onboard.<br /><br />Most weight of those propellant is oxygen (86% for a LH2/LO2 system). AS&T folks has came up with an idea to eliminate that problem. They would have a first stage aircraft take-off without loading LO2, just with LH2. As the aircraft loiter it collects atmospheric air and separate out the oxygen and nitrogen, and store the oxygen in tanks. A technology called liquid air collection and enrichment (LACE) system. <br /><br />After the aircraft collected enough LO2, it fires the SSME engine in the back to accelerate to supersonic. I don't recall the separation Mach number, perhaps around Mach 5, then launch the 2nd stage expendable rocket. I'd presume the 2nd stage can be reusable as well, depending on design objective. The aeroheating on the first stage aircraft is highly reduced because of it's short time and high altitude (hence low air density) climb. <br /><br />Also, they would fly out west for a due-East launch so the aircraft will be flying toward the launch site. This eliminate a long subsonic flight back to launch site, also in case of emergency abort it's practically on top of launch site.<br /><br />An interesting concept. Too bad they were not funded to continue this work. <div class="Discussion_UserSignature"> </div>

 

[skywalker01]

<< There is a fully working RBCC scramjet engine available somewhere? >><br /><br />Not quite but very close. The last time I heard about it in the late 90's it appeared to be ready for flight testing in a small demonstration vehicle. The recent scramjet flight tests done by NASA make that even more true.<br /><br />In my opinion, RBCC, RBCC w/ground accelerator, or TRCC, are all very strong contenders for a much lower cost launch vehicle to follow the SDHLV.

 

[gunsandrockets]

"Airbreathing first stage built from ordinary existing turbojets. I've heard about this here and there, but nobody seems to be seriously interested."<br /><br />An intriguing idea, a VTO launch vehicle with a pure airbreathing 1st stage. I know many have been raining on this idea but until the hard numbers say otherwise I think the idea has merit.<br /><br />True the T/W ratio of a turbofan sucks compared to a rocket engine but that is not the correct thing to compare. What really needs comparing is the thrust of an airbreathing stage compared to the weight of an airbreathing stage, for an airbreathing stage would be much much lighter than a rocket stage with it's oxidizer supply. The real bulk and mass of a rocket stage is in the load of fuel and oxidizer carried not the weight of the rocket engines.<br /><br />I think in practice a turbo-fan 1st stage would also be smaller because it would only boost the launch vehicle up to about 70,000 feet maximum and a speed of Mach 3 before running out of air. Properly designed the turbo-fan 1st stage would restart when it descended back into the atmosphere and recover under power with a vertical landing.<br /><br />I think one thing that has prevented the use of an airbreathing VTO 1st stage is cost. I believe an airbreathing 1st stage would be more expensive than a rocket 1st stage and therefore a poor choice for an expendable design.

 

[spacefire]

<font color="yellow">There is a fully working RBCC scramjet engine available somewhere?</font><br /><br />http://prc.uah.edu/current_projects/strutjet.html <div class="Discussion_UserSignature"> <p>http://asteroid-invasion.blogspot.com</p><p>http://www.solvengineer.com/asteroid-invasion.html </p><p> </p> </div>

 

[skywalker01]

It is great to see that work has continued on this propulsion system!<br /><br />Thank you for the link.

 

[propforce]

<blockquote><font class="small">In reply to:</font><hr /><p>.....My closest encouter with ejector rockets before this was the strutjet, aka, RBCC, which includes rockets in the ramjet/scramjet flow path. But in that case I was sizing a vehicle based on propulsion system data provided by Aerojet and the vehicle was flying a constant Q flight profile. <br /><br />Regarding the ratio of primary to secondary air flow of 1:4. How quickly does the performance boost from the ejector effect drop off as you move away from that condition? Is it fairly flat curve or steep? If you have are report numbers or links on this subject that you could recommend I would appreciate it. ....<p><hr /></p></p></blockquote><br /><br />Glad to hear that you have had some experience with ejector rockets. The ratio of secondary(air) to Primary (rocket exhaust) ratio is dependent on specific ejector design, and if the rocket exhaust is stoichiometric or if it's fuel rich, as well as if there're downstream fuel injector or not. Obviously mixing is better with a lower entrainment ratio but the amount of thrust augmentation is lower. A higher entrainment ratio helps the thrust augmentation but mixing becomes a problem. A 4:1 ratio is probably as good as it's going to get, IIRC. Every concepts have it's own unique mixing, or hypermixing, concepts. Bill Escher has a book out describing some of these concepts developed (and tested) back in the '60s performed by Marquardt, primarily on ejector-ramjet/ ejector-scramjet. Do a search on his name and you'd be sure to find many info.<br /><br />If you take a look at the flowpath of Aerojet's strutjet concept, you'd quickly realize that the rockets become so small compare to the airflowpath that the rockets look more like fuel injectors. Although its design was not to optimize ejector performance but over the mission-average ramjet/scramjet regime, nevertheless you'd get an idea that the rocket would look relatively small as compared to the entrained air flowpath.<br></br> <div class="Discussion_UserSignature"> </div>

 

[propforce]

<blockquote><font class="small">In reply to:</font><hr /><p>RBCC -- Rocket Based Combined Cycle <br /><br />Its a propulsion concept designed by Aerojet that has multiple small rocket motors in the flow path of a ramjet/scramjet. Since the rocket motors are within the flow path of the ramjet/scramjet the rockets are effectively ducted, i.e., have an ejector effect, which increases the effective performance of the rocket motors. <br /><p><hr /></p></p></blockquote><br /><br />Good description, except pardon me for one minor correction. Aerojet's strutjet concept is but <font color="yellow"><i>one of the RBCC concepts</i></font> The phrase RBCC became widely known back in 1996 when NASA MSFC issued R&D procurement in this area. Four propulsion contractor won, plus Penn State Univ., to develop each individual RBCC concept. They were Aeroject, Rocketdyne, P&W, and Marquardt. Aerojet proposed the strutjet concept, a derivative of old NASP engine concept, while both P&W and Rocketdyne regurgitated their old NASP engine concepts (P&W's later was also used in HyTech, as well as X-43A), while Marquardt proposed a modified ejector-ramjet configuration from what they performed back in the 60s.<br /><br />Both RBCC and TRCC are a subset of combined cycle propulsion, a fancy word for hybrid propulsion system, where one mix/ combine one form of propulsion with another in attemps to achieve a best overall propulsion system for a particular mission. For example, rocket-ejector-ramjet/scramjet, air-turbo-rocket, air-turbo-ramjet, etc.<br /> <div class="Discussion_UserSignature"> </div>

 

[propforce]

<blockquote><font class="small">In reply to:</font><hr /><p>True the T/W ratio of a turbofan sucks compared to a rocket engine but that is not the correct thing to compare. What really needs comparing is the thrust of an airbreathing stage compared to the weight of an airbreathing stage, for an airbreathing stage would be much much lighter than a rocket stage with it's oxidizer supply. The real bulk and mass of a rocket stage is in the load of fuel and oxidizer carried not the weight of the rocket engines.<p><hr /></p></p></blockquote><br /><br />I like the idea of using turbo-fan engines for landing, even for a vertical landing, but not for take-off. It's power density is still way below what traditional pump-fed liquid rocket engine can offer.<br /><br />The <font color="yellow">structural weight</font>of an airbreathing stage will always be bigger than the structural weight of a rocket stage for an equivalent delta-vee performance. An airbreathing stage relies on wings for aerodynamic lift and propulsive thrust. The same air becomes hostiles at speed greater than Mach 3 as aeroheating forces additional thermal protection on the airframe (more structures). All these add weight onto an airbreathing stage, while the rocket just punch through the atmosphere by brute force. <br /><br />When it comes to cost, structures always cost way more than propellant.<br /><br />Trouble with rocket though, it becomes very costly when it has to come back and be reusable !! <div class="Discussion_UserSignature"> </div>

 

[spacefire]

the 'wings' are barely there. the configuration is a lifting body. check out the HyperX, the overall vehicle shape is the same as for an SSTO. <div class="Discussion_UserSignature"> <p>http://asteroid-invasion.blogspot.com</p><p>http://www.solvengineer.com/asteroid-invasion.html </p><p> </p> </div>

 

[spacefire]

<font color="yellow">When it comes to cost, structures always cost way more than propellant.</font><br /><br />however, we aare talking about a reusable system here.<br /> <div class="Discussion_UserSignature"> <p>http://asteroid-invasion.blogspot.com</p><p>http://www.solvengineer.com/asteroid-invasion.html </p><p> </p> </div>

 

[no_way]

I cant understand peoples fascination with airbreathing launch at all. The idea of using "free" oxidiser from atmosphere for boosting might sound technically neat, but get this: LOX in the tanks costs next to nothing.<br /><br />Spending time in atmosphere when you actually want to reach orbital speeds is kinda pointless, unless you wanna do hypersonics which is expensive and finicky as hell.<br /><br />And once again, making your launchers even more complex ( more than one type of propulsion ) is not a great way to achieve better reliability nor lower cost.<br /><br />It needs to be reiterated, fuel and oxidiser cost practically nothing when compared to total launch costs. Even if you build truly low-performance rocket with payload fraction of 0.1 your fuel costs are insignificant. So theres actually no need for higher performance or new propulsion types or anything, chemical rockets are good enough.<br />You just have to design for high flight rate ( and thus probably reuseablity ) from ground up. And from high flight rate follow the requirements for good maintainablity, fast turnaround etcetera.

 

[spacefire]

even if the structural weight ratio is higher, the overall weight of the vehicle is lower=> better payload ratio since the ISP of the scramjet is higher than that of a rocket. <div class="Discussion_UserSignature"> <p>http://asteroid-invasion.blogspot.com</p><p>http://www.solvengineer.com/asteroid-invasion.html </p><p> </p> </div>

 

[skywalker01]

<<I cant understand peoples fascination with airbreathing launch at all.>><br /><br />Then you should sit down and perform a bottoms up weight, performance, and cost analysis of both an air breather and an all rocket vehicle sized for the same payload and destination orbit. Looking at just the cost difference of the various components totally ignores the impact of those components on the take-off weight and size of the vehicle as well as both the development cost and the operating cost.<br /><br />For example: <br /><br />A HTOHL TSTO airbreather (with expendable rocket powered upper stage and a staging velocity of Mach 16) that can operate from any 10,000 ft long runway, with a payload size of 17,500 lbs to LEO, and has a take-off weight of 385,000 lbs. <br />User cost to orbit, including amortization of investment and profit, is $1200/lb.<br /><br />A VTO rocket with the same payload will have a take-off weight in the 1.4 million pound plus range, will require a multi-million dollar custom launch pad, and will cost at least $2,500/lb to LEO.<br /><br />If you had a choice between these two and you were paying for the ticket out of your own pocket which would you choose?

 

[no_way]

Thats pertty much bollocks, pardon my language. How do you arrive at your cost figures ?<br /><br />Performance btw, is often inversely proportional with cost.