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

[g_sat]

What are the remaining issues preventing the development of a totaly reusable orbital system, vertically launched or horizontally launched by way of its own power or with the aide of a mother ship to achieve altitude, that would return for a runway landing? <div class="Discussion_UserSignature"> </div>

 

[mlorrey]

The big problem is vehicle average Isp. Standard rocket fuel Isps, even LH2/LOX, do not provide enough fuel efficiency to get vehicles into orbit in one stage AND make them returnable to earth with a TPS. LH2/LOX fuel combination (450 sec Isp) requires a .89 mass fraction (i.e. 89% of a launch vehicles gross liftoff weight is propellant) or higher to get into orbit. This means all the structures, payloads, thermal protection system, engines, etc needs to come to no more than 11% of the GLOW.<br /><br />The problem is that rockets with no thermal protection for reentry have difficulty meeting this requirement.<br /><br />If, instead, you find a way to get higher Isp, you can use airframe structures that are more normal to the aviation industry, and include thermal protection in the airframe. For example, with an Isp of 505 seconds, you only need a mass fraction of .78. <br /><br />Nuclear propulsion has been proposed in the past for this reason, as it offers Isps of 600-1000 seconds: certainly more than enough to reach orbit in one stage and have a TPS and a payload and be manned. But of course, the radiation hazard makes this politically untenable.<br /><br />It turns out, though, that airbreathing engines, like turbines, ramjets, scramjets, get much higher Isps, between 1500-6000 sec, because they don't carry their oxidizer, they use the oxygen in the atmosphere, so because of that, the mass of the atmospheric oxygen doesn't need to be included when calculating Isp, or included in the fuel mass for the vehicle, so your LOX tank is much smaller and lighter. If you can operate your engines in a ramjet or scramjet mode for the lower third of a launch vehicles flight regime (mach 1-8.5), using the same fuel, you should be able to at least double the average Isp for the entire flight.<br /><br />This is why the X-43A program was so important, and ramjet/scramjet propulsion in general: it is the only way we are ever going to develop reusable single stage to orbit launch vehicles t

 

[rocketman5000]

I've found out very little about the RBCC and the GTX as a program status only technical information really. Were the models tested in wind tunnels flightworthy prototypes? Would be interesting to find out more about this system such as at what altitude would the scramjet run out of oxygen?

 

[scottb50]

As for doing an airplane type takeoff and climb to orbit I highly doubt the possibility until we develop technologies well beyond what we have today. And Nuclear in the atmosphere is a non-starter.<br /><br />A two stage vertically launched vehicle, capable of adapting an unlimited number of payloads could easily be done. <br /><br />Scramjets, Ramjets and just jets just add weight and complication. A simple flyback first stage and an upper stage that stays in orbit for re-use once launched could be done extremely economical. <br /><br />With a system like this those that like capsules could attach theirs to the second stage and those who like flyback vehicles could attach theirs. Cargo could be carried in various containers and shrouds would protect mission specific payloads.<br /><br />What makes it even more attractive is it could be done right now. <div class="Discussion_UserSignature"> </div>

 

[mlorrey]

The RBCC engine modules tested appeared to be identical to the ones proposed for the GTX flight test reference vehicle, and I haven't seen any indication that they were not the same exact design. The proposals I've seen for building the test vehicles seemed to imply that the engines were ready for flight test.<br /><br />There appear to be two basic designs. One is called a "strut-jet" and uses a rectangular structure strictly under the vehicle's ventral surface, with vertical struts that move in and out of the air stream, somewhat similar to the X-43A. The rocket mode engines are build into the aft edge of the struts, while fuel injectors are in the sides of the struts. <br /><br />The GTX designs are round designs with annular shock spikes on the intakes and feature a single aerospike rocket engine in the core. The spikes are detached from the airframe surface to divert away boundary layer stagnated air, and have partially divergent, partially aerospike thrust nozzles. They are two very different designs.<br /><br />According to my data, the hypersonic funnel is pretty discriminating. At Mach 10, one is flying at 100,000-120,000 feet. The subsonic to supersonic combustion transition ranges from mach 6 at 80,000 ft up to mach 8 at 120,000 ft under normal conditions.

 

[mlorrey]

A multi-mode RBCC engine capable of Rocket-ejector takeoff, ramjet flight, scramjet flight, and pure rocket flight all the way to orbit exists RIGHT NOW. This is the 21st century, Scott, not the 1960's. Apollo and Space Shuttle Flyback boosters are 40 and 30 year old technologies. RBCC powered launchers do not require advanced technologies beyond what we have today. You don't need multiple types of engines, you need one type of engine capable of all modes of flight. Most of all you need people who believe in the future, not the past.

 

[scottb50]

Gee, does Acme build them? I don't see too many in operation. Seems like a scramjet needs a Pegausus to get fast enough to start.<br /><br />But your right, lets forget about the past, wipe the slate clean and start over. <div class="Discussion_UserSignature"> </div>

 

[rocketman5000]

Pegasus = rocket booster; RBCC = rocket booster/ramjet/scramjet. A complex engine that solves the tricky part of trying to put 2 to 3 types of engines on an airframe and keep the weight to a minimum

 

[tomnackid]

I seem to be bringing up Andrews Space a lot here lately--the fact is they are a small company (by aeerospace standards) that seems to be doing a lot of innovative R&D for NASA and DARPA with a pretty low profile--anyway, they have developed an air liquefaction system that is efficient and compact enough to fly in a vehicle. Apparently they have a contract with DARPA to develop a HTOL flyback booster called Gryphon around this technology. By extraction liquid oxygen from the air the Gryphon will be able to ignore the problems associated with supersonic combustion and instead use conventional turbojets for low speed flight and conventional liquid fuel rockets for high speed flight. I also assume that being able to manufacture and store liquid oxygen on board the vehicle will allow to spend less time in the atmosphere than a scramjet powered vehicle. Once your LOX tanks reach the optimum level fire the rockets and go into a steep climb and get out of the soup quickly. The optimum amount of LOX needed before leaving the atmosphere will be a trade off between the mass penalty for carrying the LOX vs. the penalty for atmospheric drag (I'm assuming--but it sounds reasonable).<br /><br />Heres a link to Andrews if you wan to see what kinds of thing they are working on. http://www.andrews-space.com <br /><br />Not sure how far DARPA is intending to take the Gyrphon concept, but I think a lot of the people around here bemoaning the "death" of spaceplanes and nuclear propulsion will be pleasantly surprised by the kind of research quietly going on out of the media limelight.

 

[mlorrey]

An RBCC is not just a scramjet, Scott, which should be obvious to anybody of intelligence reading anything I've said about them. That you insist on distorting the issue marks you as a troll and a waste of time. <br /><br />Andrews Space is owned by a couple of former Boeing engineers from the Kent Space division. Their liquifaction tech seems pretty neat, though I haven't seen any specifics on its performance, whether it is better than the HOTOL type system or not.<br /><br />Even if their system works, they will essentially be launching from a conventional altitude at subsonic or low supersonic speeds, giving a delta v boost of 250-350 m/s, unless they plan on doing a dual mode, running the turbine engines alongside the rockets up past mach 3 at all. That would give them about 1000 m/s advantage. However, relying on plain vanilla LH2/LOX rocket propulsion from low supersonic to orbit will limit their average Isp significantly, they may have trouble meeting mass fraction requirements, especially given the low density of LH2.

 

[summoner]

Thanks for that link. I also like the idea of their minimag orion engine. <div class="Discussion_UserSignature"> <p> </p><p> </p><p> </p><p> <br /><table cellpadding="0" cellspacing="0" style="width:271px;background-color:#FFF;border:1pxsolid#999"><tr><td colspan="2"><div style="height:35px"><img src="http://banners.wunderground.com/weathersticker/htmlSticker1/language/www/US/MT/Three_Forks.gif" alt="" height="35" width="271" style="border:0px" /></div>

 

[tomnackid]

However, relying on plain vanilla LH2/LOX rocket propulsion from low supersonic to orbit will limit their average Isp significantly, they may have trouble meeting mass fraction requirements, especially given the low density of LH2. <br />-------------------------------------------------------------------------------------<br />There is nothing in their literature that says they are using LH. In fact I would assume that since they don't have to worry about supersonic combustion they would go with a simple, reliable LOX/kerosene system. There literature also seems to suggest that they intend to do their stage separations at high altitudes and high supersonic (hypersonic?) speeds.

 

[mlorrey]

The reason I suspect they are using LH2 is that I believe that their liquifaction system relies on it to cool the system, unless they are using liquid nitrogen.<br /><br />Actually, if they started out with a tank of liquid nitrogen, and just bubbled air through it, the nitrogen should condense the oxygen out of the air as the nitrogen evaporates, thus resulting in a tank full of LOX by the time the rocket ignites. Given the lower density of nitrogen vs oxygen, this could be a cheap and easy way to lighten one's take-off mass.

 

[gunsandrockets]

"What are the remaining issues preventing the development of a totaly reusable orbital system, vertically launched or horizontally launched by way of its own power or with the aide of a mother ship to achieve altitude, that would return for a runway landing?"<br /><br />The biggest problem with developing a totally reusable launch-vehicle-system is thermal-protection for reentry. Reentering the Earth's atmosphere has relied so far upon passive thermal-protection systems such as ablative heatshields or the extremely temperature resistant and highly insulative ceramic-tiles.<br /><br />The main issue with thermal protection is the system must be light-weight, yet for practical reusability the system must also be extremely durable. This is one of the principle engineering flaws of the Space Shuttle as the ceramic-tile and reinforced-carbon-carbon thermal-protection-system it uses is too fragile.<br /><br />Some ways around the thermal issue is to abandon full reusability, that way reducing the amount of structure that needs thermal protection. The Space Shuttle uses this idea by employing an expendible drop tank.<br /><br />Another way around the thermal problem is by employing a staged vehicle. That way the 1st stage, which tends to be the heaviest and largest, never goes fast enough to require thermal protection. The Space Shuttle also uses this idea.<br /><br />One well thought out method that employs these concepts is the t/Space proposed airlaunched-rocket and reusable manned CXV space-capsule. The 1st stage of the system is a very large and completely reusable jet aircraft. The last stage is the completely reusable CXV space-capsule. In between those stages is the simple pressure-fed two-stage liquid-propellent rocket which is completely expendable.<br /><br />If one wants to develop a fully reusable launch vehicle, new types of thermal-protection are needed. Active thermal-protection may be the key to this. Before Rotory-Rocket went belly up, they were going to us

 

[why06]

Could a possible magnetic feild protect the ship during re- entry powered by electro-dynamic tethers which would slow it down.<br />I was thinking about slowing the ship down during re-entry so I was surprised when you announced they were thinking of taking the ship down in reverse.<font color="yellow"></font> <div class="Discussion_UserSignature"> <div>________________________________________ <br /></div><div><ul><li><font color="#008000"><em>your move...</em></font></li></ul></div> </div>

 

[g_sat]

Thank You mlorrey for your answer. I can't figure out what, "Isp" and "ESAS" are, but I too feel that we are going the wrong way with our development program (while we are at it, let's trade in our SUV's for covered wagons to deal with fuel prices). In my opinion, pushing the envelope use to be what Nasa was all about. <div class="Discussion_UserSignature"> </div>

 

[g_sat]

So are the powers that be not thinking clearly, following some secret commandment or is their something else to the reasoning behind not following this approach? <div class="Discussion_UserSignature"> </div>

 

[gunsandrockets]

Short answer no.<br /><br />Long answer. Your tether would melt during reentry therefore no power to your magnetic field. Even if you had power to generate a magnetic field, a magnetic field would have zero effect upon aerodynamic heating of the vehicle or remove any heat from the vehicle during reentry.

 

[scottb50]

I think I have been around here long enough to not be a troll. I also realize an RBCC is not just a scramjet. I just fail to see any advantage it would have.<br /><br />A turbojet will take you to about mach3, a ramjet to mach 5-6 and a scramjet to mach 10-12, then you need a rocket to get to orbital velocity. I simply think it would be much simpler, lighter and more efficient to just use rockets.<br /><br />What I have proposed uses a flyback first stage with engine nozzles optimized for maximum thrust in the atmosphere and the nozzles on the second stage optimized for operation in Space. The main idea being getting above the atmosphere as quickly as possible to eliminate the structure required to reach the speeds a variable cycle engine would require since it would need to work in the atmosphere at very high speeds for extended periods to prove effective. <br /><br />I also have no problem with using turbine engines, up to about mach1, if you need them for the return of the first stage they might as well contribute thrust for the launch rather than being dead weight. Beyond that they make little sense due to the inlet problems that would have to be overcome to operate at even higher speeds. <div class="Discussion_UserSignature"> </div>

 

[why06]

Yeah what happened to the days when NASA tried to fly to the moon with the technology of a cellphone in the ship and a laptop at the launch center. Now their hung up on the ISS. Don't get me wrong that is a great accomplishment just not very exciting.<br /><br />Oh and Isp stands for specific impulse<br />here is a link to it http://en.wikipedia.org/wiki/Specific_impulse it's basically the amount of propellant used to achieve a desired momentum. Notice this has nothing to do with the time it takes to reach this momentum or even the energy consumed from it as in the case of Ion engines. <font color="yellow"></font> <div class="Discussion_UserSignature"> <div>________________________________________ <br /></div><div><ul><li><font color="#008000"><em>your move...</em></font></li></ul></div> </div>

 

[why06]

I still don't see what's wrong with using the RBCC engines. Could someone put this into laymen's terms.<font color="yellow"><br /></font> <div class="Discussion_UserSignature"> <div>________________________________________ <br /></div><div><ul><li><font color="#008000"><em>your move...</em></font></li></ul></div> </div>

 

[why06]

I also think I have a simple design that woul capture the best of both worlds. Get this! Everybody knows when a bomb is set off it creates a sudden expansion of the air. Right! And then air is forced back in due the nature of gasses. The rocket will be specially designed with an opening at both ends and work like a pulse propulsion engine, setting off thousand of explosions a minute powered by rocket fuel. The explosions would be focused out the back then air would be suckedin extremelly fast. This would compress it and make for an optinum explosion. The best part about it is that it is a realitively simple design and offers few problems in between the change of air to space. I saw it off the internet some where. <img src="/images/icons/smile.gif" /><br /><font color="yellow"></font> <div class="Discussion_UserSignature"> <div>________________________________________ <br /></div><div><ul><li><font color="#008000"><em>your move...</em></font></li></ul></div> </div>

 

[gunsandrockets]

"I simply think it would be much simpler, lighter and more efficient to just use rockets. "<br /><br />I tend to agree. But I also think airlaunched rockets are an exception. The Soviets had another interesting exception.<br /><br />The Soviets in the early '60s proposed a solid-propellent mobile ICBM that used a hybrid air-breathing/rocket 1st stage. Very interesting, the hybrid 1st stage reduced the overall weight of the ICBM by half. The principle was actually flight tested successfully for smaller tactical range rockets.

 

[tomnackid]

Wasn't that the same principle of the American Navaho from the 50's? i think the Navaho was even looked into as the basis for a reusable launch vehicle.

 

[CalliArcale]

<blockquote><font class="small">In reply to:</font><hr /><p>Could a possible magnetic feild protect the ship during re- entry powered by electro-dynamic tethers which would slow it down. <p><hr /></p></p></blockquote><br /><br />As has already been pointed out, you probably won't be able to get sufficient power from your tether because the tether itself would be directly exposed to the heat. However, if we look at it more hypothetically, imagining a magical electricity generator, it's still not very likely. Basically, you need to insulate your craft somehow from the enormous heat being produced. As the vehicle moves through the air, it will compress the air ahead of it. At supersonic speeds, it compresses the air enough to heat it up pretty significantly. By the time you get to reentry speeds (which are generally in excess of Mach 15), it's heating it up into a plasma at thousands of degrees Fahrenheit. The faster your reentry, the more heat you'll have to cope with.<br /><br />Two strategies have been used so far. Ablative heatshields (such as on Apollo or Soyuz or the planned CEV) deliberately allow the plasma to "burn" away the shield. It consumes energy to burn away a layer of ceramic or whatever ablative material is chosen, so burning the shield away has a cooling effect. So the shield has to be thick enough that you don't run out of ablative material before <br /><br />The other strategy is insulation. You get the spacecraft sufficiently insulated that the heat doesn't affect it. This is what the Shuttle uses. Those ceramic tiles and reinforced carbon-carbon panels are amazingly good at insulating. They're also very light compared to an ablative shield, and unlike an ablative shield can be used more than once. But they are definitely more expensive, and very fragile.<br /><br />Magnetism will not insulate your craft sufficiently to protect it from these hot gasses, nor will it consume heat in the process of ablation. You could, theoretically, use magnetism to defle <div class="Discussion_UserSignature"> <p> </p><p><font color="#666699"><em>"People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff."</em>  -- The Tenth Doctor, "Blink"</font></p> </div>