Why do you aerospace engineers have such a hard time making spacecraft?

[gaming_addict]

I agree with some points by FredGarvin. Modern rockets must generate incredible chamber pressures to attain the desired efficiency and higher exhaust speeds. In order to 'practically' hybridize a rocket, some compromise has to be made and it's not going to be good on rocket efficiency. The compromise in efficiency may not justify the weight savings, complexities or even potential reliability issues with the design

For what it's worth, jet engines are not massive engines. I would keep the air breathing engines completely separate from rocket engines.

I might even improve on it that the turbojet/ramjet/scramjet package, hybrid or not, will be slung beneath the launch vehicle with it's own set of wings blending with the underside to not add to drag, it will detach once for example, mach 20 is reached and will glide back to Earth and land on a runway.

For convenience, launch site will be relocated to Guam or Hawaii. So by the time the vehicle is over US mainland, it should've reached mach 20(hopefully) so the jet package glider can land in an airport, refueled, and flown on it's own power to east coast, then transported(by sea or air) back to the launch site again.

 

[Danger]

* Technical engineering term for high temperature.[/size]

Thanks for the thorough analysis, Fred. Some of those things never crossed my mind at all.

(I should explain at this point that I 'invented' this thing about 30 years ago to power a mach 8 fighter/bomber that I also 'invented' for an SF novel which will never see daylight. It was intended to operate at 28,000° C, so could actually plasmacize ram air for thrust rather than relying upon the onboard hydrogen supply. The whole thing, of course, depended upon a fictional amorphous al/ti/polyurothane alloy with a failure temperature of 30,000°.
There was no combustion chamber; rather it used a 'thrust block' of the same material perforated like the core of a NERVA, heated by a 10MW neutral hydrogen accelerator, through which the propellant flowed.
The compressor was to be driven by a hugely powerful electric motor drawing from a pair of SNAP generators, later replaced by a 20MW cobalt 60 beta-source generator. It didn't feed to the engine, but to a gas separation system that pulled the hydrogen out and sent it to the fuel storage. The engine turbopump drew from that. There was no oxydizer, because it worked by pure thermal expansion.
All that I'm trying to do now is 'downgrade' the idea to see if it could be done with actual technology.)

I'm concerned about the aerodynamics of the intake ducting, since it can't be properly efficient for both configurations. I figure to maximize it for ram mode, since the compressor can compensate somewhat for bad flow in turbo mode.
The thermal soakback never crossed my mind, and I haven't a clue what to do about it other than either routing the fuel or other coolant around the compressor, or just putting it a lot farther away from the combustion chamber.
The different operating characteristics with different oxydizers also didn't occur to me. I'd have a pretty good idea of how to deal with it in an IC engine, by fiddling with the mixture and timing, but I really don't know nearly enough about rockets or jets to have clue in this case.
I just noticed while referring back to your post that Gaming Addict has weighed in while I was composing this. I'll just go ahead and post this, then read that one.

 

[Danger]

Good points, GA. I particularly like the 'gliding booster' idea. The only problem point that I can immediately think of, which is probably quite surmountable, is that the recess into which the booster fits for 'blending into the underside' could give pretty nasty aerodynamics for the re-entry phase. Perhaps a top-mount design would be more appropriate?

 

[gaming_addict]

The 'gliding booster' will have a perfectly 'flat top' design so the launch vehicle's (LV) underside, need not be specially shaped to maintain aerodynamic efficiency. It only has to have a flat bottom to have a smooth mating of the LV and glider.

The 'flat top' is actually a common design for hypersonic designs nowadays. In addition, the glider's wings with a span that is wider than the LV will also serve as additional lift source for the whole booster/launch package. When the glider has detached from the LV, the LV's main lift source will be from it's lifting body design and it's small wings that will be used to control the LV in reentry and landing.

The glider will be physically larger than the LV, but nearly all it's fuel will come from the LV, with a little jet fuel left for landing.

Nice idea for a fully reusable, fuel efficient launch package, but think that for a manned launch package, the glider, will be a large craft, may be larger than XB-70 bomber and has to fly at hypersonic speeds. You may even think of it as the mothership, instead of the LV! Given that we are no longer in a Cold War era, it may take decades to become practical :)

So yeah, maybe that answers the title of this thread, why not? Because the threat of a space-based war is no longer a possibility, at least for now.. The space program naturally won't be the highest of priorities.

 

[Danger]

Hmmm... sounds like a few minutes of work have gone into planning this.
I misunderstood about the mating surfaces; I thought you meant that the booster's bottom blended into the lines of the payload.

 

[FredGarvin]

I might even improve on it that the turbojet/ramjet/scramjet package, hybrid or not, will be slung beneath the launch vehicle with it's own set of wings blending with the underside to not add to drag, it will detach once for example, mach 20 is reached and will glide back to Earth and land on a runway.

No offense, but you're getting silly now. Theoretically it's fun to say we'd like to do something, but there is no way, currently, that one would ever get an engine with a rotating group to survive anywhere near M20. We're having a tough enough time at M4.

Let's not get too carried away with wet dreams and stick to what is plausible. This forum is not meant to be a sounding platform for sci-fi ideas and the like.

 

[gaming_addict]

No offense, but you're getting silly now. Theoretically it's fun to say we'd like to do something, but there is no way, currently, that one would ever get an engine with a rotating group to survive anywhere near M20. We're having a tough enough time at M4.

Let's not get too carried away with wet dreams and stick to what is plausible. This forum is not meant to be a sounding platform for sci-fi ideas and the like.

Read below! You really offended me by making me sound stupid without first reading my whole idea and opinion!

I DISPROVED MY OWN IDEA! BACKTRACK TO POST #34, 4TH PARAGRAPH!

Nice idea for a fully reusable, fuel efficient launch package, but think that for a manned launch package, the glider, will be a large craft, may be larger than XB-70 bomber and has to fly at hypersonic speeds. You may even think of it as the mothership, instead of the LV! Given that we are no longer in a Cold War era, it may take decades to become practical :)

And here's another by yours trully:

One of them actually envisioned a turbojet that 'morphed' and doubled as rocket engine. The turbojet seemed to close it's inlet

and that answers his rantings about:

..but there is no way, currently, that one would ever get an engine with a rotating group to survive anywhere near M20. We're having a tough enough time at M4.

Whoever in his right mind would expose a helpless turbine engine in the ferocious speeds of mach 20? And don't you think closing an inlet is impossible, the Concorde engines does it during emergencies without drag penalty.. :zzz:

We do have an engine that goes from full stop to mach 4, the J-58 turbojet/ramjet hybrid used by SR-71, unfortunately, the SR-71 cannot take the heat from mach 4 flight.

Please don't try to sound smart by replying at warp factor 9.999.. Read carefully, understand, maybe research first... ok? Otherwise, you could sound quite the opposite of what you think you are

 

[FredGarvin]

Read below! You really offended me by making me sound stupid without first reading my whole idea and opinion!

I DISPROVED MY OWN IDEA! BACKTRACK TO POST #34, 4TH PARAGRAPH!



And here's another by yours trully:



and that answers his rantings about:



Whoever in his right mind would expose a helpless turbine engine in the ferocious speeds of mach 20? And don't you think closing an inlet is impossible, the Concorde engines does it during emergencies without drag penalty.. :zzz:

We do have an engine that goes from full stop to mach 4, the J-58 turbojet/ramjet hybrid used by SR-71, unfortunately, the SR-71 cannot take the heat from mach 4 flight.

Please don't try to sound smart by replying at warp factor 9.999.. Read carefully, understand, maybe research first... ok? Otherwise, you could sound quite the opposite of what you think you are

You are the one that is throwing out fanciful "ideas" that have no premise in current capabilities. My comment was in regard to the fact that we like to try to keep this board on a professional level. Having little "I think it would be cool to do this" conversations with no earthly technical clue as to what you are talking about is not a discussion. It's a circle jerk. Most of the stuff you are spouting off about belong in the skepticism and debunking forum. I really don't care if I offended you or not.

Any time you want to put up your video game playing experience versus my actual experience, I'll be more than happy to oblige.

 

[berkeman]

Please don't try to sound smart by replying at warp factor 9.999.. Read carefully, understand, maybe research first... ok? Otherwise, you could sound quite the opposite of what you think you are

gaming_addict,

You need to mellow your tone. You are out of line when you are telling Fred to "maybe research first".

Please confine your posts here in the technical forums of the PF to well-grounded scientific ideas and questions.

 

[gaming_addict]

You are the one that is throwing out fanciful "ideas"

So I am, and I admit it. But I've also let everyone know on post 34 paragraph 4 that my idea is fanciful. I thought you would agree, I bet you would!

Anyway, I hope it ends here, I don't want to go much off topic and waste time. I apologize to all for wasting some of your time.


<< post edited a bit by berkeman to keep the discussion on-topic >>

 

[gaming_addict]

Hmmm... sounds like a few minutes of work have gone into planning this.
I misunderstood about the mating surfaces; I thought you meant that the booster's bottom blended into the lines of the payload.

The 'orbital' stage would resemble the X-33(SSTO), while the jet booster stage would resemble the X-43(Hypersonic craft propelled by scramjet), but larger than X-33. The X-33 with flat bottom would be on top, while the X-43 with flat top would be below. The flat surfaces will meet together.

http://en.wikipedia.org/wiki/Boeing_X-43
http://en.wikipedia.org/wiki/Lockheed_Martin_X-33

But whether a hypersonic vehicle is capable of taking something as X-33 or even a very lean version without huge performance penalty is still largely unknown. We still have to await the any future scramjet tests, especially if they are capable of piggybacking aerodynamic payloads like a scaled down X-33 for example...

I thought my idea is original but when I read that they are planning to use scramjets as booster stages. They might use the 'glider booster' idea too. :)

 

[Sojourner01]

How about this? http://www.reactionengines.co.uk/sabre.html

They seem to be doing pretty well on this project - though I do wonder why they haven't flown a prototype yet because they've been operational for some time.

 

[FredGarvin]

Where on the website does it say that that engine is operational?

 

[russ_watters]

Eeek - looking at the company website, it looks like the kind of boondoggle that drives me bonkers. They were able to get people to invest in the company and now they are fiddling-around with R&D that may or may not turn into any real product. They are certainly nowhere close to building their engine - the talk only about building and testing a heat exchanger!

 

[joema]

The 'orbital' stage would resemble the X-33(SSTO), while the jet booster stage would resemble the X-43(Hypersonic craft propelled by scramjet), but larger than X-33. The X-33 with flat bottom would be on top, while the X-43 with flat top would be below. The flat surfaces will meet together...I thought my idea is original but when I read that they are planning to use scramjets as booster stages. They might use the 'glider booster' idea too. :)

The concept of a HTHL SSTO with scramjet lower stage has been studied since the 1960s: http://www.abo.fi/~mlindroo/SpaceLVs/Slides/sld016.htm

In the mid-60s artist's depictions of a "Siamese" delta-winged TSTO with a scramjet lower stage were published in various popular-level books and magazines. The lower stage had a flat top and the upper stage a flat bottom.

"Winging into space" has always had a romantic appeal. However the cold hard facts are scramjet TSTO or SSTO is incredibly expensive and technically challenging. Indeed, it's been called "getting to space the hard way": http://en.wikipedia.org/wiki/Scramjet

Unlike the casino game of craps, you don't get extra payoff for getting to orbit "the hard way". Rather you want to get there the easiest, simplest way possible.

Given current technology, that's probably some kind of a rocket.

A scramjet TSTO or SSTO would save some money on propellant, as it uses oxygen from the atmosphere. However the liquid oxygen burned by a large rocket booster is almost free. E.g, the gigantic space external tank holds 553,000 liters of LOX, which costs only about $12,000.

 

[gaming_addict]

A scramjet TSTO or SSTO would save some money on propellant, as it uses oxygen from the atmosphere. However the liquid oxygen burned by a large rocket booster is almost free. E.g, the gigantic space external tank holds 553,000 liters of LOX, which costs only about $12,000.

Actually, an SSTO may or may not use air breathing engines. But it was proven even with scramjet equipped types, won't have the payload carrying capacity of multistage rockets.

I'm familiar with the cost of LOX, it's cheap but carrying the weight of LOX will incur a larger amount of fuel burned. The air in the atmosphere is free and doesn't need to be carried around for scramjet.

Anyway, I've realized that if we use TSTO and mix air breathing engines with it. We might get better fuel economy. But due to the complexity of technology used, the operational costs might exceed the cost of fuel used. It might not be practical in the end.

 

[laurelelizabeth]

Oomair, you might be getting misled by some ideas that have been kicking around for atmospheric machines, such as taking off with turbojets and switching to scramjets when supersonic. Those things are not intended to go orbital, and they don't have to carry an oxydizer.

Haha spoken like a true rocket scientist :) that just went over my head, (then proceeded to accelerate towards the ground at -9.8m/s^2)

 

[laurelelizabeth]

What if they made one at a higher altitude, where there would be slightly less air and very slightly less gravity? Or maybe that would be too unpractical if you had to make it in cold conditions...

 

[Danger]

Haha spoken like a true rocket scientist :)

I'm not, but I consider that error a compliment.
Your second post needs clarification. What if they made what at a higher altitude?

 

[russ_watters]

The primary obstacle for a spacecraft to overcome in reaching orbit isn't altitude it is speed.

 

[gaming_addict]

Yup, high altitude only helps so you could go insanely fast without vaporizing. That tiny bit of less gravity at higher altitudes doesn't help at all.

 

[Danger]

Fred, I just thought of something else. If your exhaust is electrically active, such as a plasma, could a variable nozzle be made using a magnetorestrictive collar rather than a mechanical device?

 

[FredGarvin]

Fred, I just thought of something else. If your exhaust is electrically active, such as a plasma, could a variable nozzle be made using a magnetorestrictive collar rather than a mechanical device?

I really don't know about how well they are using magnetic shielding for ion drives. I haven't heard of them being able to control it like that. Someone else would have to answer that one for sure.

 

[gaming_addict]

Fred, I just thought of something else. If your exhaust is electrically active, such as a plasma, could a variable nozzle be made using a magnetorestrictive collar rather than a mechanical device?

Magnetorestrictive equipment could be heavy. Although, it gives me an idea to separate the plasma into positive and negative ions using a plain magnetic field.. it could probably give very high voltages. I would route the negatively charged electric field to the wing leading edge, the whole frontal area and the upper part of lifting surfaces to eliminate or reduce shockwaves, and hence, drag.

On a second thought.. On LH-fueled scramjets, highspeed of plasma could bring about strong internal magnetic fields, ion separation could occur with no certain pattern. A small amount of rotation could be introduced to the plasma flow such as a slightly helical exhaust pipe design or spiral 'riflings'. The slight rotation of the plasma exhaust would bring the heavier positive ions to the walls of the combustion chamber and the negative ions to the center.

The positively charged combustion chamber could then be used to charge an interior metallic plating in front of the vehicle to high positive voltage, so external plate(acting like a capacitor) attracts negative ions from air and gets negatively charged. The negatively charged plating would then help to reduce shockwaves and shockwave drag.

 

[laurelelizabeth]

I'm not, but I consider that error a compliment.
Your second post needs clarification. What if they made what at a higher altitude?

haha... i just thought that would sound clever to say ... it is a compliment

About the second post (oopsie, did i double post?) I was just thinking that if they made the spacecraft 's at a higher altitude then theoretically there would be less gravity... Although I'm assuming it wouldn't make a difference.

 

[Astronuc]

I'm familiar with the cost of LOX, it's cheap but carrying the weight of LOX will incur a larger amount of fuel burned. The air in the atmosphere is free and doesn't need to be carried around for scramjet.

Yep. Much of the work that surface launch rockets do is lifting the propellent.

See this page - http://www.braeunig.us/space/specs/shuttle.htm

EXTERNAL TANK
Length: 46.88 m
Diameter: 8.40 m
Dry mass: 35,430 kg for earlier version, later reduced to 29,930 kg in later models, 26,330 kg for aluminum-lithium alloy Super LightWeight version
Oxidizer: liquid oxygen
Fuel: liquid hydrogen
Propellant mass: about 730,000 kg
Pressurization: 3.0 atm LH2, 1.43 atm LOX
Feed lines: supplies SSMEs through two 43.2 cm diameter outlets
Insulation: 25 mm-thick polyurethane foam
Separation: after about 530 s, 110 km altitude, for destructive reentry

SOLID ROCKET BOOSTERS
Length: 45.46 m (including forward skirt and nose fairing)
Diameter: 3.71 m
Empty mass: each 82,879 kg
Propellant: TB-H1148 HB Polymer
Propellant mass: each about 504,000 kg
Thrust: combined thrust 29.36 MN SL (maximum thrust at launch reducing by 1/3 after 50 s)
Burn time: about 124 s
Steering: nozzle gimbaled +/-8o by two hydraulic actuators
Separation: after burnout at about 124 s, 45 km altitude (triggered when pressure falls to 3.4 atm), the boosters are separated pyrotechnically and fall into the Atlantic for recovery. Landing speed <100 km/h under 3 x 41 m diameter parachutes
Separation motors: 16 flown per Shuttle mission; each 73 kg mass, 34.5 kg HTPB propellant, 0.8 s burn time, 82.6/129.5 kN vac avg/max thrust, 78.1 kNs total impulse

The solid rocket boosters are there to get the EXTERNAL TANK to fly with the Shuttle. The ET is feeding the Shuttle.

NASA's Space Shuttle includes a reusable manned spacecraft capable of delivering up to 25,000 kg of cargo into low Earth orbit.