Space Plane - Space Plane

Ian · 2004-03-06 14:51:28

I wonder when Nasa will get it's space plane done? I also want to know when they will stop studying the aerodynamics of the plane and get to experimental tests. Does anyone have any theories about when it'll be completed and used?

Lars_J · 2004-03-06 16:06:12

What "spaceplane" are you referring to? The X-33?

That project was thankfully put out of its misery years ago - It was heading nowhere fast (specs getting worse and worse, deadlines pushed back further and further). It would appear that Lockheed Martin and NASA were willing partners in this "vaporware" project which in retrospect sunk billions of $$$ for nothing in return.

GCNRevenger · 2004-03-06 16:43:47

The trouble with a space plane is you have to have someplace to fly it to first... ISS will be gone soon, no space station is in mind to replace it (in LEO anyway), and its questionable how useful a fly-every-week shuttle would be to small-scale exploration that the Bush plan is advocating. In the distant-ish future, a true spaceplane would be handy for Earth/Moon crew & cargo transfers and for fueling of ships in LEO.

At the moment, there isn't a whole lot of work being done by Nasa on the topic, but since the USAF's requirements for a trans-contenental hypersonic bomber are similar to Nasa's requirment for a SSTO space plane, I imagine some work will go on.

Idealy, with the use of composits & advanced high-temp ceramics, double-duty Jet/Rocket engines under design, and of course the fabled SCRAMJET engine, then it might be possible... preferably Kerosene fueled, perhaps slush hydrogen, able to put at least 10 or preferably 20-25 tons to LEO in one go. These technologies are up-and-coming, so it will be a while before its practical to build it.

Lars_J · 2004-03-06 21:45:44

Scramjet is a dead-end technology for space access - and most certainly for an SSTO. I predict there will be no scramjet based launch vehicle for the next 50 years. Why?

- Scramjet propulsion only removes the need for an oxidizer (liquid oxygen) tank - BUT the majority of the volume/mass is taken up by the remaining fuel, so the savings are slight.
- An oxygen extraction part of a scramjet propulsion system would take up volume and mass, reducing the savings even further.
- Also note that scramjets only light up at several times the speed of sound. This forces a scramjet vehicle to use either A.) onboard fuel with rockets or B.) jet engines to accelerate to scramjet speed. Either option adds even more mass.
- To "top it off", an oxidizer tank is still not eliminated, since one still needs oxidizer once leaving the atmosphere. It's like not eating your cake and yet still not having any left.
- The scramjet propulsion trajectory is very inefficient - in order to use the scramjet system, the spaceplane neds to stay in the atmosphere for as long as possible, while building up orbital speed. This creates significant heating issues, and wastes a lot more fuel trying to work against atmospheric friction. On the other hand, a vertical ballistic trajectory of a regular rocket is the most efficient one, and it also gets out of the atmosphere quickly.

In conclusion - It is both simpler and more efficient for a launch vehicle to bring all the oxygen in its tank, instead of trying to scoop it up from the atmosphere. (And liquid oxygen is dirt cheap as well)

Scramjet may have its uses in military vehicles who need to go really fast inside the atmosphere for some bizarre reason. And even then, a "regular" transportation vehicle in a sub-orbital trajectory would still get you there faster.

All the $$$ being spent on scramjet research is $$$ that should be put to better use.

GCNRevenger · 2004-03-06 22:10:32

I think you give the scramjet too hard a time... difficult yes, impossible no, and with an Isp of >1,500 it will put conventional rockets to shame.

The oxidizer weight that you speak of is infact the majority of the weight of a hydrogen-powerd scramjet's propellant, get rid of that and 80% of the propellant mass is suddenly gone. Keep in mind that reducing fuel carriage yeilds a nonlinear decrease in vehicle mass. Even removing 3/4ths of the oxidizer needed is hardly what I would consider "slight".

What oxygen extraction componet? You mean the intake? Got that taken care of already I think...

Yes there is that annoying part, but Nasa has a solution, with a turbine jet engine that does double-duty as a rocket, so that cuts out an entire set of engines. With good aerodynamics, getting to mid-supersonic speeds shouldn't be hard. It will require a little oxygen in rocket mode, but not that much since it will already be at Mach 25 at the edge of the atmosphere for a minimal fuel mass; just a little nudge into orbit. Not at all like the gargantuan half-million-pound-thrust SSME monster, just a little push like a RL-10 Centaur.

Although the plane would have to spend alot of time in the atmosphere, this is where the most energy is needed to get into space, punching a hole through both the atmosphere and Earth's gravity, but this is also where the Scramjet is most efficent and beats out conventional rockets silly. Feature, not a bug.

Keep in mind that ceramics are nearing the temperature tollerance needed for Mach 25 flight, and that you need far less thrust than a rocket because you are using atmospheric lift instead of brute force.

Of course its simpler to use a rocket, but a rocket is fundimentally heavier and harder to recover than a airplane.

Lars_J · 2004-03-06 23:50:45

What oxygen extraction componet? You mean the intake? Got that taken care of already I think...

You don't think that the intake needs to process or purify the air at all? Or that the intake adds more mass and affects body design significantly? (see below)

but Nasa has a solution, with a turbine jet engine that does double-duty as a rocket, so that cuts out an entire set of engines.

And this double-duty engine will of course work with optimum efficiency below and and above scramjet ignition speeds? And don't forget the fact that the turbines will be dead weight once scramjet speeds are reached. There is no such thing as "free lunch".

With good aerodynamics, getting to mid-supersonic speeds shouldn't be hard.

There is quite difference between good aerodynamics and "passable" aerodynamics - all a glider needs to be able to land. (Or "flying brick" aerodynamics like the Shuttle)
All designs I have seen for scramjet craft require some pretty unique aerodynamic shapes in order to A.) be capable of flying at scramjet speeds and B.) efficiently funnel the air to the intakes. Designing an aircraft to behave well from Mach 0 to 20 (?) is practically impossible - and even moreso for a launch vehicle which needs to have a good size volume/mass ratio.

Although the plane would have to spend alot of time in the atmosphere, this is where the most energy is needed to get into space, punching a hole through both the atmosphere and Earth's gravity, but this is also where the Scramjet is most efficent and beats out conventional rockets silly. Feature, not a bug.

First of all, getting out of the atmosphere is not the hard part. (And there is no atmospheric "barrier" to punch through) Acellerating to orbital speed is the hard part. Altitude does not matter - speed matters. A hypothetical rocket launched from an extreme high altitude baloon would still have to reach the same speed. What matters is that accelerating though an atmophere requires more effort than acceleration through a virtual vacuum. Plain rockets spend most of their acceleration outside of the atmpshere. (The Shuttle reaches Max-Q, maximum air resistance at ~60 seconds, after that it falls off rapidly) On the other hand, a scramjet design needs to spend the vast majority of its time in the atmosphere - but the air resitance means that it has to pick up a whole lot more oxygen than a rocket would carry. So the atmospheric flight of the scamjet is indeed a feature of the design, but compared to a rocket - it is a bug.

Keep in mind that ceramics are nearing the temperature tollerance needed for Mach 25 flight, and that you need far less thrust than a rocket because you are using atmospheric lift instead of brute force.

Wrong, wrong, wrong. The raw amount of thrust required to reach orbit by a scramjet plane would be greater than that of a rocket. A universal principle in aerodynamics is that more lift means more drag. More lift means more drag, less lift meas less drag. The fact that any lift is generated implies that drag exists, and therefore you need an engine to overcome that drag. That is how aircraft stay flying. What makes an aircraft reach altitude and stay flying? Lift? Yes, but to get any lift you needed to spend energy in the first place to reach a certain speed, and to maintain that lift you need to spend enough energy to overcome drag.

And again, the energy you spend in getting and maintaing lift only gives you altitude. But it is irrelevant for the purposes of reach orbit - speed. It doesn't matter if you start at 0km or 100km altitude - you still need to reach orbital velocity. And that lift you have has been causing drag, causing you to spend more energy overall to reach the same speed. The only reason a scramjet launch vehicle would stay in the atmosphere is to scoop up fuel - lift is irrelevant, and actually only increases the inefficiency. That is the whole problem with a scramjet - how to extract enough out of the atompshere to overcome the basic problem of being in an atmopshere.

GCNRevenger · 2004-03-07 00:45:19

Actually no, the scramjet doesn't need to use pure oxygen, it can run on straight air, no purification required, and I believe you are a bit mistaken as to the design of the flight profile of a hypothetical scramjet SSTO vehicle...

The idea is that it will go from low subsonic to near orbital velocities and the edge of space while in the atmosphere with a small mass of propellant (with hydrogen, MUCH smaller than rockets) since no oxidizer is needed. It needs much less raw thrust than a rocket (first stage anyway) too because
1) it isn't flying straight up
2) the craft has lift
...so the engines don't need to be as powerful as a conventional rockets' because the rocket (at least the first stage) must lift the entire mass of the fueled vehicle unassisted.

Furthermore, when the scramjet vehicle reaches the edge of the atmosphere at mach 25 ground speed, accessing orbital velocities is fairly easy; nose up to leave the atmosphere, then light the rocket... you are already most of the way to orbital velocities, and now there is very little air resistance, so a small boost is all thats needed. So, overall, the thrust required to reach orbit for an airplane is fundimentally smaller than it is for a conventional launchpad rocket.

Of course it stays in the atmosphere to scoop up propellant, but its free propellant you don't have to lift, hardly irrelivent, especially considering a rocket's (LOX/LH2) propellant mass is almost 90% oxygen by mass (closer to 80% with fuel-rich mix I figure)... Although considerable energy is spent defeating drag that a conventional rocket doesn't have, the Scramjet's far higher propellant efficency and no need for million-pound-thrust "controlled explosion" giant rockets (and their requisit multi-G longitudal stress construction) with its atmospheric lift, can be the superior mode of space travel. Cutting one pound of fuel mass reduces total vehicle mass by more than a pound, i'm sure you are aware...

Zero to 15,000mph in a shallow climb without using a single gram of LOX, with LEO a mere 2000-3000mph away, and mass of fuel required is the definition of launcher efficency... You don't fly a scramjet spaceplane like you do a rocket, so its not "wrong wrong wrong," its a whole different way of solving the problem.

RobertDyck · 2004-03-08 11:04:37

Hey, cool! GCNRevenger and I are in agreement.

I think Lars_J might be talking about a technology that NASA long since gave up as not practical, but India is looking at: launching with no oxidiser at all and concentrating it from the air during flight. The idea is to use fuel/air during flight, but concentrate and store pure oxygen for LOX/LH2 mode during the nudge into orbit. I agree with NASA that this idea is not a good idea, it would waste fuel to spend extra time in the atmosphere just to reduce time spent carrying oxidiser from the ground. You?re better off carrying the oxidiser from the ground that you?ll need once in space, but operate the SCRAM jet in air-breathing mode as long as possible to eliminate the need to carry oxidiser at all.

Last I read a document on NASA?s 3rd generation shuttle, their idea is to use a Rocket Based Combined Cycle engine for the main engines, and a magnetic catapult to throw it into the air. The catapult would act like the steam catapult on an aircraft carrier that launches fighter jets, but the magnetic version can achieve greater speed. You see an RBCC engine has 4 modes of operation: RAM jet, SCRAM jet, air augmented rocket, and normal rocket. A RAM jet literally rams air into the engine, it doesn?t have a turbine; it?s basically a shaped tube with fuel injectors. It?s very simple, but you have to carefully shape the tube; that is the internal airflow path of the engine. The problem with a RAM jet is that you require close to mach 1 (the speed of sound) to start the engine; that?s why NASA is looking at a high-speed catapult to launch it. A normal RAM jet slows airflow inside the engine below the speed of sound, so it?s limited to airspeed of just over mach 3. A SCRAM jet is a Supersonic Combustion RAM jet, so it isn?t limited to airspeed of mach 3.6 or whatever. The ratio of combustion speed to airspeed will determine air heating during intake. Burning fuel heats the air more, and that heat causes the gas expansion that generates thrust. If the air is heated so much during intake that burning fuel doesn?t heat it much, then the engine barely generates any thrust at all. Supersonic combustion permits the air to flow faster inside the engine, which provides cooler air to the combustion chamber so you get more gas expansion from burning fuel. That solves heating by intake compression, but you have to be careful that supersonic friction doesn?t cause intake heat anyway. SCRAM jet design also has to deal with fuel/air mixing; conventional jet fuel doesn?t mix with air in a supersonic air stream, it just pours unburned out the back of the engine. That?s why most SCRAM jet engine designs use hydrogen; cryogenic liquid hydrogen can cool the engine, and hydrogen gas is injected into the air stream so it mixes without a problem. Some Air Force contractors are working on SCRAM jet engines that use hydrocarbon fuel; much easier to store but airspeed limited to somewhere between mach 6 and 7.

As for weight savings due to eliminating oxidiser: let?s look at a modern rocket. I?m tempted to compare performance using the Saturn V, but to be fair let?s look at something modern. The Delta IV Large (also known as Delta IV Heavy) has a payload capacity of 25,800kg to 185km orbit at 28.5? inclination. It has a total mass of 733,400kg including 598,920kg propellant for the 3 common core stages. LOX/LH2 typically has an optimum oxidiser/fuel ratio of 4.00 so that means 80% of the propellant mass is LOX. (calculated as 4.00 / (1 + 4.00) = 4/5 = 80%) That is 479,136kg of liquid oxygen. That mass of oxygen is greatly in excess of the payload capacity, and it doesn?t include eliminating mass of the tanks. If you can achieve that much increase in launch vehicle efficiency, you would want to reduce the size of the entire vehicle. That would dramatically reduce the size of the vehicle, and you?ll notice I?m not talking about eliminating the LOX tank of the upper stage.

By the way, I think a turbojet or fan jet would be better for take-off because it would permit launching from any airport, and powered landing. The turbine may be dead weight most of the time, but powered landing would greatly increase safety.

GCNRevenger · 2004-03-08 13:29:52

Thats pretty close to accurate... take off with a turbine engine from a runway, reach modest and high supersonic speeds for minimal fuel mass, then light the Scramjet... In order to keep the vehicle cool and to preheat the hydrogen, the liquid or slush LH2 would be pumped through pipes in the leading edge surfaces, just like in a regenerative rocket nozzle. So, the drag actually adds some heat energy to the fuel, which greatly reduces the "waste" of energy by flying in the atmosphere. Using only air as the oxidizer, no LOX need be used to reach the Mach 20-25 region and leave the atmosphere entirely. There, Nasa's "double duty" turbine/rocket engine could use a small amount of LOX brought up in tanks for the final short orbital insertion/circulization burn.

Looking at the Delta-IV CBCs if you could ditch the oxidizer, imagine how much less hydrogen you would need since you don't have to lift half a million pounds of oxygen! Even further, consider how much smaller the big fuel tanks would have to be, especially if the Scramjet airplane uses slush hydrogen that occupies 3/4ths the volume of liquid... and finally, you don't have to make the airplane strong enough to withstand the 3-4G accelerations along its thrust axis since you can take a more liesurely path to orbit.

Bill White · 2004-03-08 13:59:16

Thats pretty close to accurate... take off with a turbine engine from a runway, reach modest and high supersonic speeds for minimal fuel mass, then light the Scramjet... In order to keep the vehicle cool and to preheat the hydrogen, the liquid or slush LH2 would be pumped through pipes in the leading edge surfaces, just like in a regenerative rocket nozzle. So, the drag actually adds some heat energy to the fuel, which greatly reduces the "waste" of energy by flying in the atmosphere. Using only air as the oxidizer, no LOX need be used to reach the Mach 20-25 region and leave the atmosphere entirely. There, Nasa's "double duty" turbine/rocket engine could use a small amount of LOX brought up in tanks for the final short orbital insertion/circulization burn.
Looking at the Delta-IV CBCs if you could ditch the oxidizer, imagine how much less hydrogen you would need since you don't have to lift half a million pounds of oxygen! Even further, consider how much smaller the big fuel tanks would have to be, especially if the Scramjet airplane uses slush hydrogen that occupies 3/4ths the volume of liquid... and finally, you don't have to make the airplane strong enough to withstand the 3-4G accelerations along its thrust axis since you can take a more liesurely path to orbit.

Can you use the same engine for take-off and circularization and later landing? How soon can America build one? :;):

This all seems to add to the opinion expressed by deGrasse-Tyson:

SPACE.com: What is the biggest challenge for the (Aldridge) commission?
Tyson: It is not the engineering or a prioritizing of the science. Those problems are an investment of intellectual capital and are simple compared with the real challenge. The vision must sustain public support longer than a presidential election cycle or political cycles in general, as well as economic cycles.

RobertDyck · 2004-03-08 15:28:42

The next step in developing this technology was the X-43A. It was to be a scale model vehicle launched on a Pegasus rocket, which was launched from NASA's B-52. The Pegasus was going to accelerate it to mach 7, then the X-43A would separate and fly on its own power. The first launch would just sustain mach 7, but later flights would accelerate to mach 10. Unfortunately the tail fins of the Pegasus broke off during the first test flight. Investigation blamed the contractor who build the rocket. Now that the investigation is done, the way is clear for another test flight.

To get nit-picky: 479,136kg of oxygen is 1,056,314 pounds. Also the oxidiser/fuel ratio deals with mass, not volume. Hydrogen has much greater volume per unit mass, so ditching the oxidiser would eliminate 4/5 of the propellant mass but only a fraction of the volume. In fact, LOX is 0.8767 l/kg while LH2 is 14.128 l/kg so you would eliminate 19.9% of propellant volume. RP-1 is almost pure kerosene, which has a density of 0.799 kg/l or 1.25 l/kg so it would use much smaller tanks if you can get it to work in a SCRAM jet.

GCNRevenger · 2004-03-08 15:57:06

Whoops, skipped the kilogram conversion... i'm an American, I don't think in metric.

Hydrocarbon fuels would be great, and that is the direction that the USAF is going, but its unclear if they can combust fast enough for Mach 25 flight... Mach 15 is high enough for the air force.

When I was previously talking fuel volumes, i'm taking into account that you don't need near as much hydrogen to begin with (volume or mass) since you don't need to lift all that oxygen, and this situation can be improved further by using slush hydrogen.

dicktice · 2004-03-08 16:43:15

Doesn't all this discussion appear to be zeroing-in on the specs for a multi-engine type flyback-booster, pretty much the way we should have done what turned out to be the Space shuttle, in the first place?

RobertDyck · 2004-03-08 17:19:57

No, not at all. A flyback-booster assumes you start with a rocket booster. A SCRAM jet shuttle would start with an aircraft with air-breathing engines; then add a LOX tank to permit the engines to operate as LOX/LH2 rocket engines. You could use JP-1 or RP-1 in the jet engines for subsonic and supersonic operation, then shift to LH2 for hypersonic SCRAM jet operation before finally shifting to LOX/LH2 rocket engine mode. A very low LH2 flow could be added for cryogenic cooling when operating in supersonic mode, or perhaps a smooth transition between pure JP-1 and pure LH2 as speed increases. This would be a tri-propellant engine. But if the air-breathing engine can achieve mach 20 or higher then you will need a heat shield for the airframe. Hypersonic lifting flight demands a lifting body. Once you have all that, you might as well just give it the extra nudge into orbit rather than a separate orbiter. That gives you a Single Stage To Orbit (SSTO) Reusable Launch Vehicle (RLV).

ERRORIST · 2004-03-08 17:48:15

Why can't you use a series of land based particle beams to shoot the fuel down the throat of a scram jet untill it reaches escape velocity instead of carrying the fuel on board?

GCNRevenger · 2004-03-08 17:53:03

1: You'd never hit the intake
2: You can't move much gas with a particle beam
3: Radiation
4: At Scramjet speeds, the air surrounding the vehicle will aproach ionization energy, blocking the particles
5: A hundred billion reasons I haven't thought of yet
6: You'd never hit the intake

RobertDyck · 2004-03-08 18:37:14

Particle beams? With enough fuel transfer to power an engine? Does this mean you view the idea of a SSTO RLV is science fiction?

GCNRevenger · 2004-03-08 18:43:28

I don't know why I even replied...

The Scramjet does work, it has been wind-tunnel tested to supersonic velocities... the question is, can an airplane powerd by it reach Mach 20+ without being made of Unobtainium. Chances are good it can be done, it just can't be done easily.

RobertDyck · 2004-03-08 19:12:29

Wind tunnel tests using hydrocarbon fuel have already proven it works to mach 6, and with hydrogen fuel to mach 10. The heat shields of the Space Shuttle work when entering the atmosphere at mach 25 so we know that works as well. The question is whether we can integrate an airframe with a SCRAM jet engine. It is believed to work to mach 10 at least, but X-43A will have to prove it. NASA is working on it.
January 22, 2004: [http://www.dfrc.nasa.gov/Newsroom/NewsR … 04-03.html]Dress Rehearsal Flight of X-43A Successful; Hyper-X Free Flight Soon
February 17, 2004: [http://www.dfrc.nasa.gov/Newsroom/NewsR … 04-06.html]X-43A Flight Delayed

The U.S. Air Force is now developing a SCRAM jet engine for the X-43C, which NASA is scheduled to fly in 2008. It will accelerate from mach 5 to mach 7, reaching a maximum potential speed of about 5,000 mph.

"The largest of the Hyper-X test vehicles, the X-43B, could be developed -- and would fly -- later this decade. Successful ground- and flight-testing of various engine configurations aboard the X-43A and X-43C will determine whether a rocket- or turbine-based combined-cycle engine powers the X-43B."

NASA is hoping to have a third-generation shuttle by 2025.

GCNRevenger · 2004-03-08 19:16:25

Or rather Nasa DID hope to have one by 2025... the Bush space plan will preclude the creation of a Shuttle-II until there is a good place to fly it to I imagine, barring a great deal of money from the USAF for an aircraft that they don't have a vital need for ATM.

Ad Astra · 2004-03-08 20:34:57

I agree that a scramjet is impractical for SSTO, but it would make a great first stage for TSTO. The scramjet operates ideally under Mach 12; this would be a good staging velocity for launching a smaller space plane. It would be difficult to use a LACE (liquid air cycle engine) system, and the weight penalty might not justify it, so the idea should be dropped.

GCNRevenger · 2004-03-08 20:50:05

It may not be practical with today's materials and simpler engines, but the next generation ones will come pretty close if not meet the challenge. The liquid air concept is alot of trouble, thats why alot of these Scramjet projects use plain old un-liquified atmospheric gas. Single stage to orbit is ultimatly the only game in town to make humans a spacefaring civilization.

RobertDyck · 2004-03-09 00:36:44

TSTO will always be less safe and more expensive than SSTO. Separation at hypersonic speed can easily result in re-contact, meaning collision. TSTO requires each stage to have engines, instruments, electronics, airfoils, landing gear, and redundant backups. TSTO at least doubles the cost, and coordination means more. TSTO is a cop-out when the propulsion system isn't good enough. If you can get a SCRAM jet engine to work with a hypersonic airframe, then you have a propulsion system that has potential for SSTO.

The current shuttle found the cost of recovering, refurbishing and refuelling SRBs cost 90% as much as purchasing new ones. Liquid fly back boosters are huge with large wings, landing gear, and fuel required for powered flight back toward the landing strip. The original 1970s design of a TSTO shuttle would have been safer and less expensive to operate that the one that was built, but congress didn't want to pay the development cost. I don't think a TSTO will ever be built now either, so NASA's current idea for a second generation shuttle won't be built. We'll use expendable rockets to lift expendable capsules until some future administration gets tired of paying for expendable vehicles. The intelligent strategy is to develop a fully reusable vehicle, one that doesn't require a complete overhaul of every system before every flight. That will require greatly reduced fuel tanks. A SCRAM jet eliminates the liquid oxygen, so it saves a lot of weight. Liquid hydrogen still requires tanks too large. According to Encyclopedia Astronautica, slush hydrogen has 20% greater density. That isn't sufficiently dense either; kerosene is 11.3 times as dense as LH2. You have to keep the spacecraft volume down for atmospheric entry. Some sort of tri-propellant mix might be the answer.

The real start to developing low cost access to orbit is the X-43. Hypersonic aircraft design will probably require a lot of research, but it's necessary if you ever want safe, affordable access to space. The 12-foot long X-43A is the perfect way to start.

GCNRevenger · 2004-03-09 09:05:56

The economics of the thing is the real question... TSTO requires two large aircraft, which each seperatly have to be serviced between flights and then re-mated which is somthing you can't do at your local airport. And of course the issues of duplicity of hardware and the added mass & risk of a reliable supersonic/hypersonic seperation mechanism... the USAF doesn't even know where the bomb bay for its Falcon bomber will go yet to ensure good seperation.

One ship that can be launched without special ground facilities beyond trunk-portable stuff and cryogenic storage has a great deal more flexibility and ease of use... that being said, I agree that its questionable if current Shuttle-era engineering can make it top Mach 20, so this is still a project for the generation-after-next of spacecraft, but this is also arguably when we hope to need it.

Today and for the next 15-20ish years, Nasa just isn't going to have a huge need for a fly-every-week space craft, especially since assembling things in orbit ISS style is a pain and could be avoided with a large HLV, so the introduction of such a ship should coincide with "whats after" the Bush space plan. Since making a Scramjet SSTO is hard though, and crash-course engineering is a undesireable, it makes sense to continue low-intensity development.

Lars_J · 2004-03-09 10:13:40

(finally back to the thread...)
I still believe Scramjet if fundamentally the wrong way for cheap access to space - at our current and forseeable level of technology - in other words, no magic particle beams. :;):

Scramjet designs still appear to have the following drawbacks:
Engine technology:
- 3 modes of propulsion needed: jet / scramjet / rocket (this adds complexity and mass, even with a "multimode" engine)
- How fast will an scramjet go before the rocket propulsion has to take over? At what speed and altitude will it have to be cut off?
Aerodynamics:
- An aircraft designed to be efficient at scramjet speeds will be difficult to control at landing and takeoff. This is a difficult enough problem for supersonic aircraft, and it will be even moreso for a hypersonic one.
- Lets not forget "center of mass" issues - This is a significant issue for the shuttle (with very small margins), and it will be even worse for a winged vehicle where a significant part of the vehicle will be tanks that are either full (takeoff) or empty (landing).
Material issues:
- Prolonged heating in the atmosphere. Extended atmopsheric exposure at Mach 10-20 will be brutal, no matter what material is used. And unlike the shuttle, which re-enters trhe atmosphere at a high angle of attack and onlty needs heavy protection underneath and in front, the scramjet vehicle will expose the entire body to the same contditions.

So what do I think will work? I am a strong believer in VTOVL (vertical takeoff, vertical landing) for cheap access to space - and eventually an SSTO RLV. And VTOVL will not suffer from the drawbacks I listed above for a scramjet vehicle. Does VTOVL have other drawbacks? Yes, but I believe those are easier problems to solve.

Here is how I see the path towards cheap access to space:
1. Two-stage VTOVL
Staging at hypersonic speeds will be problematic, so the solution is to stage above the atmosphere. (Well, the vast majority of it, anyway).
- Stage 1: Launches the vehicle stack in a high ballistic orbit, similar to Alan Shepards first flight. The top of the trajectory is at 100-150 km altitude, where the orbital stage 2 is released just before reaching. The first stage falls back to earth, and is recovered with parachutes/airbags. A further development might have a powered vertical landing to become a more reusable first stage.
- Stage 2: separates at 100-150 km, and accelerates to orbital speed. The Orbital stage reenters either side first (like a lifting body) or tail first, and lands with parachutes/airbags. A further development might have powered landing for increased reusability.
2. SSTO RLV
The SSTO RLV would be use a radial aerospike engine, launching vertically, reentering vertically, and landing vertically. The radial aerospike engine would do double-duty as a heat shield, allowing the rest of the vehicle to use fairly tame materials. Since the only acceleration/deceleration loads would be vertical, the design could be structurally fairly simple and light (composite cylindrical/conical tanks), with the bottom containing the heavy parts - aerospike radial nozzle and heatshield.
A rough design and flight profile can be seen here:
[http://flab.eng.isas.ac.jp/member/ito/w … h/NASA.jpg]radial aerospike SSTO flight profile
The crew/cargo module would be mounted on top, and could easily be detached (w/ parachute) in case of an emergency.

[http://www.engineeringatboeing.com/arti … design.jsp]Boeing/Rocketdyne page about nozzle design, including radial aerospike

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#10 2004-03-08 13:59:16

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#11 2004-03-08 15:28:42

Re: Space Plane - Space Plane

#12 2004-03-08 15:57:06

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#13 2004-03-08 16:43:15

Re: Space Plane - Space Plane

#14 2004-03-08 17:19:57

Re: Space Plane - Space Plane

#15 2004-03-08 17:48:15

Re: Space Plane - Space Plane

#16 2004-03-08 17:53:03

Re: Space Plane - Space Plane

#17 2004-03-08 18:37:14

Re: Space Plane - Space Plane

#18 2004-03-08 18:43:28

Re: Space Plane - Space Plane

#19 2004-03-08 19:12:29

Re: Space Plane - Space Plane

#20 2004-03-08 19:16:25

Re: Space Plane - Space Plane

#21 2004-03-08 20:34:57

Re: Space Plane - Space Plane

#22 2004-03-08 20:50:05

Re: Space Plane - Space Plane

#23 2004-03-09 00:36:44

Re: Space Plane - Space Plane

#24 2004-03-09 09:05:56

Re: Space Plane - Space Plane

#25 2004-03-09 10:13:40

Re: Space Plane - Space Plane

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