Virgin Galactic

[Aer'ki]

Yes? Your point is? It's a variation on the design of Space Ship One, which is just a small hybrid rocket, and other than the low cost, there is hardly anything interesting about it.

A cryogenic LH2 aerospike engine, in contrast, is light and efficient enough to allow for a single-stage-to-orbit operation. VentureStar is the project I was referring to. It is the only design so far that was likely to achieve the SSTO goal. With proper funding, its successor still might, especially since many advancements have been made in the field of composite materials.

My point is a two-stage dropship is probably more efficient right now than a single stage, and I was happy that Virgin went with a 2-stage design. When they get around to building their orbital dropship I hope they continue with the two-stage design. The aero-lift technology is just too useful to pass up for the first 10 miles up and will allow for larger payloads than a single stage dropship would.

[K^2]

It helps to increase maximum payload (by about 30% by my estimate) but it doesn't help reduce the cost. With SSTO, you only need to bring the orbiter with less than full tanks to the 10 miles altitude and speed. With aero-lift, you have to bring a fueled lifter and fully fueled orbiter to the same altitude and speed. Add to that the fact that it takes orbiter less than a minute to get there, but it's going to take lifter 10-20 minutes at least, with all the extra drag, and the cost or aero-lift becomes too high.

The only reason this works for Space Ship One / Galactic, is that their final speeds are nowhere near LEO speeds.

Of course, granted, sometimes it might make sense to pay through the nose to get these extra 30% from your orbiter rather than design a completely new one, but that's why the most obvious solution is to allow for both. Build a SSTO orbiter that can be air-lifted for 30% extra payload with some extra expense. And that's the sort of thing that the engineers had in mind, because, believe it or not, they are not all idiots.

[EvilSpaceAlien]

I can't remember reading it anywhere, but is it an international venture?

It's not governmental at all, if that's what you mean. This is purely a business venture by the Virgin corporation, as I understand it.

As Aer'ki said, it's not govermental. Also Spaceport New Mexico won't be the only spaceport that Virgin Galactic will operate out of. Spaceport Sweden is scheduled to open in 2012.

[Aer'ki]

It helps to increase maximum payload (by about 30% by my estimate) but it doesn't help reduce the cost. With SSTO, you only need to bring the orbiter with less than full tanks to the 10 miles altitude and speed. With aero-lift, you have to bring a fueled lifter and fully fueled orbiter to the same altitude and speed. Add to that the fact that it takes orbiter less than a minute to get there, but it's going to take lifter 10-20 minutes at least, with all the extra drag, and the cost or aero-lift becomes too high.

The only reason this works for Space Ship One / Galactic, is that their final speeds are nowhere near LEO speeds.

Of course, granted, sometimes it might make sense to pay through the nose to get these extra 30% from your orbiter rather than design a completely new one, but that's why the most obvious solution is to allow for both. Build a SSTO orbiter that can be air-lifted for 30% extra payload with some extra expense. And that's the sort of thing that the engineers had in mind, because, believe it or not, they are not all idiots.

I think you're misunderstanding. A two-stage dropship with Aero-lift doesn't use rocket fuel in the first stage. It uses Jet fuel or even props which is very, very, very cost effective compared to rocket fuel. Also, a large amount of the lift doesn't come from thrust, it comes from the wings of the first stage(mothership).

And the point of the mothership isn't to accelerate the spaceship, its to raise it up 10 miles...maybe 15 or more if you start using upper atmosphere engines. The acceleration to orbit still comes from the rocket fuel in the spaceship, but that acceleration is much faster, shorter, and cleaner since it doesn't have to contend with the lower, thicker atmosphere. The thrust can be mostly horizontal rather than necessarily vertical like a land based rocket launch.

As for NASA being idiots...I'm not refering to any one person, but the overall design elements that they're using are not functionally wise. Their going back to using capsules because of the nostalgic element is a telltale sign they don't know what they're doing.

If a little operation on a budget of only a few million can put a ship into space like Burt Rutan did, then what does that say for NASA? IMO it shows them up for what they are...a big, wasteful, inefficient government organization that both wastes money and cuts financial corners at the same time.

[Rodney Mal Doran]

It must be really annoying for the US government that they've hired a load of idiots to run NASA when all the people who actually know what they're talking about are on this thread...

[Rodney Mal Doran]

The real problem with NASA , in my opinion, is that they are asked to do things but not given the budget to accomplish them. Most of the above are technologically feasible but cost more than NASA has.

[K^2]

I think you're misunderstanding. A two-stage dropship with Aero-lift doesn't use rocket fuel in the first stage. It uses Jet fuel or even props which is very, very, very cost effective compared to rocket fuel.

No, it's not more cost effective. SSTO craft use cryogenic H2 for fuel, which is about the same cost per-Joule as Jet A.

Also, a large amount of the lift doesn't come from thrust, it comes from the wings of the first stage(mothership).

The glide ratio of the carrier will be at most 10. (747 is a 4, for example). This means that with equal efficiency propulsion, you'll need about 10 times more fuel to maintain altitude with vertical thrust versus lift. Rocket gets to 10 miles in about 40s, as mentioned before. Unless your carrier can get there in 400s, you are saving nothing with lift. Reality check, it will take 10-20 minutes at least.

And the point of the mothership isn't to accelerate the spaceship, its to raise it up 10 miles...maybe 15 or more if you start using upper atmosphere engines. The acceleration to orbit still comes from the rocket fuel in the spaceship, but that acceleration is much faster, shorter, and cleaner since it doesn't have to contend with the lower, thicker atmosphere. The thrust can be mostly horizontal rather than necessarily vertical like a land based rocket launch.

By the time a rocket reaches 10 miles, it has barely broken the sound barrier. Drag is not a major factor until later in flight. As for gains from altitude, it is laughable. Energy required to raise 1kg to 10 miles is 160 kJ. Energy required to take 1kg to orbital velocity is 28 MJ. You provide a little less than 0.5% of total energy required, and you do this at the stage when it is easiest for the rocket to accelerate anyhow.

As for high altitude engines, the aerospike is almost as efficient in atmosphere as it is in vacuum. Taking it to 10 miles does not help its function at all.

When computing the boost you actually get with launch to LEO, I have factored in the extra altitude, motion of the carrier, drag, and even rotation of the Earth present in both cases. That's where I got the 30% extra useful load from. That was a good best-case estimate, and that's all you are going to get. 30% extra cargo, and you will pay for it in full with costs of Jet A fuel for the carrier.

SSTO is the way to go with launch vehicles right now. People knew that when making Shuttle, but unfortunately, materials just weren't there back then. SSTO was the goal, but eventually they had to rely on the external tank and boosters to make it work. Now the tech is here in form of aerospike engine and composite materials. We can build a cost-efficient reusable SSTO vehicle, and it would make for cheapest delivery of cargo and man power to orbit we can hope for at the moment.

[Aer'ki]

No, it's not more cost effective. SSTO craft use cryogenic H2 for fuel, which is about the same cost per-Joule as Jet A.

The glide ratio of the carrier will be at most 10. (747 is a 4, for example). This means that with equal efficiency propulsion, you'll need about 10 times more fuel to maintain altitude with vertical thrust versus lift. Rocket gets to 10 miles in about 40s, as mentioned before. Unless your carrier can get there in 400s, you are saving nothing with lift. Reality check, it will take 10-20 minutes at least.


By the time a rocket reaches 10 miles, it has barely broken the sound barrier. Drag is not a major factor until later in flight. As for gains from altitude, it is laughable. Energy required to raise 1kg to 10 miles is 160 kJ. Energy required to take 1kg to orbital velocity is 28 MJ. You provide a little less than 0.5% of total energy required, and you do this at the stage when it is easiest for the rocket to accelerate anyhow.

As for high altitude engines, the aerospike is almost as efficient in atmosphere as it is in vacuum. Taking it to 10 miles does not help its function at all.

When computing the boost you actually get with launch to LEO, I have factored in the extra altitude, motion of the carrier, drag, and even rotation of the Earth present in both cases. That's where I got the 30% extra useful load from. That was a good best-case estimate, and that's all you are going to get. 30% extra cargo, and you will pay for it in full with costs of Jet A fuel for the carrier.

SSTO is the way to go with launch vehicles right now. People knew that when making Shuttle, but unfortunately, materials just weren't there back then. SSTO was the goal, but eventually they had to rely on the external tank and boosters to make it work. Now the tech is here in form of aerospike engine and composite materials. We can build a cost-efficient reusable SSTO vehicle, and it would make for cheapest delivery of cargo and man power to orbit we can hope for at the moment.

Ahhh, your college professor must have gone nuts grading your papers. You're calculations are completely off.

1. You're assuming that all engines provide the same thrust...they don't. Also, aerodynamics of the craft affect drag...which then again change the number for lift required to reach orbit.
Also, if you make the presumputous statement that only a certain number of joules are required to reach orbit is assuming a certain number of seconds duration of thrust...which will be different for different engines, different craft, with different payloads. It will NEVER be the same. It's not a constant.

2. Most of the space shuttle's fuel is used to raise it the first 10 miles. Fuel is heavy, so the more fuel you carry, the more fuel you need to lift that extra fuel.

3. A jet can reach an altitude of ten miles with less fuel than a rocket OF EQUAL MASS. The wings produce lift without using fuel. A rocket only produces lift through fuel expansion, so don't be crazy saying that a rocket is more fuel efficient than a winged craft. That's just nuts. Also, a plane doesn't have to use jet fuel, it can use props driven by electricty no less.

4. Rockets only getting to the sound barrier in ten miles? Care to specify the size of those rockets? Think about this...a fighter jet can go past the sound barrier in less than ten miles...and a rocket can't? Seriously, think about these things before you post them.

5. Since the weight of the craft going to orbit is critical to how much thrust is required, using a first stage aero-carrier reduces the size of the orbital craft because that craft doesn't have to travel the first leg, nor does it have to carry the fuel required to do so. This means larger cargo/fuel ratio, hence making the aerolift structure more efficient pound for pound.

6. Aerospike engines require some atmosphere...they can't operate in vacuum. That's why they have 'aero' in the name. Seriously...

[Krazeh]

6. Aerospike engines require some atmosphere...they can't operate in vacuum. That's why they have 'aero' in the name. Seriously...

Do you actually do any sort of research before you post?? I'm gonna have to assume you don't because even the most cursory research on aerospike engines would tell you they work perfectly well in a vacuum. They'd hardly be considered to be the baseline engine for any SSTO vehicle if they were unable to operate in space would they?

[K^2]

Most of the space shuttle's fuel is used to raise it the first 10 miles. Fuel is heavy, so the more fuel you carry, the more fuel you need to lift that extra fuel.

Gods, you don't even know basic rocketry, do you?

Rocket propulsion is about momentum. That means, it's not about weight of the thing. It's about how long you need to support that weight. (Impulse = Force * Time for the impaired). Gravitational potential difference between sea level and 10 miles up is insignificant. Gravity will pull you down at 9.8m/s² here and there. The first 10 miles are significant because craft spends nearly 40s there, and therefore looses nearly 400m/s of final velocity to gravity. A craft that starts from rest from altitude of 10 miles up will need just as much fuel as from sea level to achieve orbit, minus minute changes due to lower atmospheric density. Why? Because it still needs to spend the first 40s in 9.8m/s² gravity and waste 400m/s of its final speed. The next 10 miles, regardless of where you start, will take less than 25s, so it will steal less than 250m/s from your final velocity. By this point centrifugal effect kicks in, and effective gravity quickly goes to zero.

Total loss, due to air resistance and gravity is 1.5-2 km/s.

In terms of energy, if you are going to take potential energy needed to raise fully fueled craft to 10 miles, you are way off base. Why? Because the craft that exhausted fuel to go up 10 miles, and accelerate quite substantially along the way, does not need to raise nearly as much fuel the next 10 miles as the fully fueled craft starting from 10 miles. The net result is that the extra energy you need is EXACTLY the potential difference times the mass of the PAYLOAD. So if you have 1kg of payload, the extra energy you need to start from 10 miles lower is only 1kg * 9.8m/s * 10 miles. Not Fully_Fueled_Mass * 9.8m/s² * 10 miles. If you actually go ahead and compute total energy from rocket formula and optimal takeoff trajectory, you'll get exactly that. Anybody who has studied ANY orbital mechanics would know that. Of course, you are not one of these people, so I'll let that one slide.

This is where my comparison of kinetic vs potential energy per kg of PAYLOAD comes in. And 10 miles worth of potential energy is a drop in a bucket.

There are precisely three benefits that aerial launch provides.
1) Lower drag. Not going to win all that much with 10miles, though. If you had a good way to launch from 40-50 miles, we'd talk.
2) Velocity of the carrier. That's actually the BIGGEST factor, and you just throw it out.
3) Improved efficiency of classical engines at lower pressure. But aerospike is designed around it, so its not relevant.

[Dragon_Heart]

K2 what the hell do you do for a living?

[K^2]

Physics.

[Alx]

@Ksquared shouldve figured ive actually learned alot from reading these post's of yours so thanks.

[escyos]

space travel!!!

more like upper atmosphere travel for 500 million dollars. such a waste, in 10 years time they will have something better for half the price!

[K^2]

People said that 50 years ago. We had no advances to speak of in space exploration since the 70's, short of a few things allowed by modern robotics. It is a shame, really.