New Topic! - Burt Ruten has nailed the space problem!

Loughman · 2005-06-23 23:35:48

One thing that I will never forget, told to me by astronaut John Young is that "all single planet species, are bound to become extinct."

clark · 2005-06-24 06:57:07

Okay brilliant nut jobs, getting up there is one isse, but getting down is another.

Can total orbital speed be bled off slowly through a series of small dips into the atmosphere? Think of it like a skipping stone, where the ship descends into the atmosphere, bleeds off some speed, then arcs up, comes back down and bleeds some more speed.

I expect GCN to tell me why it won't work. Others, please join in.

GCNRevenger · 2005-06-24 07:21:46

You mean to basically aerobrake to a velocity far below orbital velocity... Well, okay: it won't work.

If you were to bleed off much speed that way with a little poorly shielded vehicle, you would drop like a rock straight through the atmosphere, but you would still be going Mach 20 or so and would incinerate like a match head under a blow torch.

Its simple, you are trying to use drag to get down to 1/5th of orbital velocity before entering the thicker portions of the atmosphere... it won't work, you will fall back down to the thicker air before you bleed off enough speed. Poof!

clark · 2005-06-24 07:23:49

Okay, so explain how bouncing off the top of the atmosphere (ala the space bomber) is practical and different.

Palomar · 2005-06-24 07:33:38

Scramjet top speed is mach 25 (maybe higher).
Small private scramjet planes are not feasible. Ramjet ...maybe. I think there is something on it at the Joint Propulsion Conference. Maybe I'll report back when I get back.
You are talking about an advanced "varient" of the Scramjet, a "Regenerative" scramjet. Such an engine could get you going faster, maybe like Mach 20 or something, but such an engine would be very hard to build. We're talking needing materials that can handle liquid hydrogen (-300C or so) on one side, and 2,000-3,000C+ on the other... and still conduct heat efficenctly, be extremely strong, and resist both ablation and Hydrogen embrittlement. Oh, and do it a hundred times without serious overhaul too.
"Small private spaceplane" is not going to happen for a very, very long time if its possible at all.

*That "regenerative" scramjet sounds interesting, GCN.

I wish the X-43A tests hadn't ended.

--Cindy

GCNRevenger · 2005-06-24 07:41:39

Okay, so explain how bouncing off the top of the atmosphere (ala the space bomber) is practical and different.

Simple: a "skipper" tries very hard to avoid drag, not cause it, and use its lifting body/wings to preserve altitude without much/any additional engine firing. Doing this, it can stay "above" the atmosphere and coast longer then a regular pointy rocket could, which eliminates alot of drag and permits it to fly suborbital much further then a regular ballistic missile could for similar Delta-V.

Cindy: A regenerative scramjet is probobly the best bet for a real single-stage spaceplane, but I think its safe to say that such an engine would be a little ways off, and definatly not come cheap.

X-43 was a proof of concept, but it wouldn't lead to a regenerative engine any time soon. The USAF "Copper Canyon" study, which sorrta led to the X-30 "Orient Express" SSTO scramjet spaceplane, fingerd the top practical speed at around Mach 15 without regenerative cooling/preheating. That might be fast enough for a USAF superbomber, but thats too slow for a spaceplane... if the USAF wants to fool with them, fine, but NASA spending money on an engine that is beyond the limits of today's materials would be a waste.

Fledi · 2005-06-24 07:55:21

Its simple, you are trying to use drag to get down to 1/5th of orbital velocity before entering the thicker portions of the atmosphere... it won't work, you will fall back down to the thicker air before you bleed off enough speed. Poof!

It depends on what altitude you're at after the decceleration. When you're too high up, several hundreds of km it's true, gravity will pull you down to a high reentry speed, although still way below orbital. The vertical speed you get at the ground if you go from 100km to ground level without any drag from the air is 1.4km/sec for example. But since the atmosphere is getting thicker the lower you get you can use things like wings, chutes or propellers to slow down (that's what SSO did, too).

Since the heat from reentry is mainly caused at very high speeds, this is the smaller problem here, g-loads is what matters. These are high but still acceptable (SSO 4 to 5g).

It should also be said that it's possible to decrease heat loads from full to nearly full reentry speed through wings that cause lift and will allow to descend into thicker atmosphere at a slower rate.
Only the Space Shuttle (and Buran) uses this technique so far however.

Loughman · 2005-06-24 08:12:12

It's difficult to remain at a certain orbit while decreasing your velocity with out aerodynamic effects (and those are the same aerodynamics effects that are causing you to slow and heat up), lose-lose.

Hypersonics depends on a handful of technologies to emerge before they become reasonable. Concept X-planes have been experimenting with the ideas, but they are no where near the level of reliability that would be required for non-experimental purposes.

Somethings that need to happen: high-temperature/high-strength materials (for the engine and leading edges), more knowledge of injection dynamics for hypersonic flow and hypersonic flow in general, and some serious research in control systems needs to happen. It's nice to think about, and it's decent research, but if you're interested in going to space in the next 20 years put your money somewhere else.

GCNRevenger · 2005-06-24 10:19:54

Its simple, you are trying to use drag to get down to 1/5th of orbital velocity before entering the thicker portions of the atmosphere... it won't work, you will fall back down to the thicker air before you bleed off enough speed. Poof!
It depends on what altitude you're at after the decceleration. When you're too high up, several hundreds of km it's true, gravity will pull you down to a high reentry speed, although still way below orbital. The vertical speed you get at the ground if you go from 100km to ground level without any drag from the air is 1.4km/sec for example. But since the atmosphere is getting thicker the lower you get you can use things like wings, chutes or propellers to slow down (that's what SSO did, too).
Since the heat from reentry is mainly caused at very high speeds, this is the smaller problem here, g-loads is what matters. These are high but still acceptable (SSO 4 to 5g).
It should also be said that it's possible to decrease heat loads from full to nearly full reentry speed through wings that cause lift and will allow to descend into thicker atmosphere at a slower rate.
Only the Space Shuttle (and Buran) uses this technique so far however.

Not quite, the problem isn't from gaining speed because you are falling against gravity after deceleration, the problem is that you still have too much leftover speed from your orbital momentum, but not enough to maintain high altitudes. You will fall back to the thicker portions of the atmosphere, but you will still be moving too fast to survive without decent heat shielding and strong structures.

A "skipper" spacecraft would use its lift and perhaps short engine burns to return to a suborbital trajectory each time it started to dip into the atmosphere. The Pentagon's super-bomber will probobly not be going as fast (like, Mach 8 or something) which makes reentry much more gentle.

clark · 2005-06-24 10:21:38

A "skipper" spacecraft would use its lift and perhaps short engine burns to return to a suborbital trajectory each time it started to dip into the atmosphere.

So why not design an orbital ship that returns like this?

GCNRevenger · 2005-06-24 11:33:20

Can't:

-You are going too fast, all you would accomplish is to make an eliptical and poorly controlled orbit with a perogee velocity thats way too high.

-You would have to carry too much fuel to slow down enough to prevent this

-You would have to have rocket engines on the FRONT of your spaceplane. which would be very tricky and not a little heavy. And you couldn't use them in the atmosphere probobly.

-You can't use Scramjets in any direction except opposite your velocity vector since they rely on forward motion for compression. (I.E. no "reverse thrust")

-You can't use your wings backwards either

Fledi · 2005-06-24 12:01:38

Not quite, the problem isn't from gaining speed because you are falling against gravity after deceleration, the problem is that you still have too much leftover speed from your orbital momentum, but not enough to maintain high altitudes. You will fall back to the thicker portions of the atmosphere, but you will still be moving too fast to survive without decent heat shielding and strong structures.

What reentry speed parallel to the ground are you talking about?
If it's nearly orbital I agree but if it's let's say only half you have lower heating up for the same amount of impulse from the air, since the air is moving slower alongside, that means molecules have lower energy to impulse ratio relative to the spacecraft compared to orbital speeds.
So I agree with the need for a strong structure, but definitely less heat shielding. (or why is the limit for non (edit:)regenerative scramjets Mach 15. )

By the way I find this Mach numbers talk a bit confusing, are you reffering to a certain speed of sound there? (since definition of Mach number is velocity/speed_of_sound with the speed of sound differing with density or medium)

GCNRevenger · 2005-06-24 12:45:05

The whole question is, can you gradually reduce your velocity from orbital speed (Mach 25) down to speed that you don't need heavy structures or heat shielding (say, under Mach 10) by using air drag or some other "easy" means. The short answer is no, because you are traveling way too fast, and you'd either fail to reenter or burn up.

Mach numbers are multiples of the speed of sound, which by convention is usually referring to the speed of sound at sea level air pressures and average temperatures, which is 1,225km/hr or so.

Fledi · 2005-06-24 12:52:20

Ok let's not discuss orbiting rotating space tether in this thread too.

But it is relevant for new X-Price goals like new altitude or horizontal speed records to gradually increase the performance of their low cost craft.

GCNRevenger · 2005-06-24 12:56:57

No, not really. Because other then squeezing an extra minute or two out of zero-G flight for tourists, there isn't any good reason to only go half way to orbit.

RobertDyck · 2005-06-24 14:25:27

We're talking needing materials that can handle liquid hydrogen (-300C or so) on one side, and 2,000-3,000C+ on the other...

One small correction: absolute zero is -273.15°C so it's impossible to get down to -300°C. Liquid hydrogen is normally stored at just below its boiling temperature so it doesn't consume a lot of heat to warm it, the heat of combustion goes to phase change to gas to produce thrust. Liquid hydrogen is stored at -254°C so that temperature is what a regenerative engine has to deal with.

The Space Shuttle Main Engine (SSME) is a regenerative rocket engine, so NASA already knows how to make regenerative engines. I don't see a problem with NASA building a regenerative SCRAM jet engine. Cindy, the term "regenerative" simply means the liquid hydrogen is sent through pipes that spiral around the rocket exhaust nozzle; liquid hydrogen cools the rocket nozzle so it doesn't melt and heat from the rocket boils liquid hydrogen to gas. Preheating fuel makes the rocket more efficient, as well as cooling the nozzle permitting hotter exhaust. Hotter exhaust means more gas expansion so more thrust.

Even the J-2 engines used for the 2nd and 3rd stage of Saturn V were regenerative. The F-1 engines for the 1st stage were fuelled by kerosene so they piped liquid oxygen around the nozzle. Liquid oxygen isn't as cold so it heated the oxygen more. Notice this resulted in F-1 engines having a huge gas pipe coming off the nozzle into the fuel pump. If NASA could use regenerative engines for Saturn V and Shuttle, a future engine could easily be regenerative.

Palomar · 2005-06-24 14:30:20

I don't see a problem with NASA building a regenerative SCRAM jet engine. Cindy, the term "regenerative" simply means the liquid hydrogen is sent through pipes that spiral around the rocket exhaust nozzle; liquid hydrogen cools the rocket nozzle so it doesn't melt and heat from the rocket boils liquid hydrogen to gas. Preheating fuel makes the rocket more efficient, as well as cooling the nozzle permitting hotter exhaust. Hotter exhaust means more gas expansion so more thrust.
Even the J-2 engines used for the 2nd and 3rd stage of Saturn V were regenerative. The F-1 engines for the 1st stage were fuelled by kerosene so they piped liquid oxygen around the nozzle. Liquid oxygen isn't as cold so it heated the oxygen more. Notice this resulted in F-1 engines having a huge gas pipe coming off the nozzle into the fuel pump. If NASA could use regenerative engines for Saturn V and Shuttle, a future engine could easily be regenerative.

*Thanks, Robert. I'd not heard of it before.

--Cindy

GCNRevenger · 2005-06-24 16:07:30

We're talking needing materials that can handle liquid hydrogen (-300C or so) on one side, and 2,000-3,000C+ on the other...
One small correction: absolute zero is -273.15°C so it's impossible to get down to -300°C. Liquid hydrogen is normally stored at just below its boiling temperature so it doesn't consume a lot of heat to warm it, the heat of combustion goes to phase change to gas to produce thrust. Liquid hydrogen is stored at -254°C so that temperature is what a regenerative engine has to deal with.
The Space Shuttle Main Engine (SSME) is a regenerative rocket engine, so NASA already knows how to make regenerative engines. I don't see a problem with NASA building a regenerative SCRAM jet engine. Cindy, the term "regenerative" simply means the liquid hydrogen is sent through pipes that spiral around the rocket exhaust nozzle; liquid hydrogen cools the rocket nozzle so it doesn't melt and heat from the rocket boils liquid hydrogen to gas. Preheating fuel makes the rocket more efficient, as well as cooling the nozzle permitting hotter exhaust. Hotter exhaust means more gas expansion so more thrust.
Even the J-2 engines used for the 2nd and 3rd stage of Saturn V were regenerative. The F-1 engines for the 1st stage were fuelled by kerosene so they piped liquid oxygen around the nozzle. Liquid oxygen isn't as cold so it heated the oxygen more. Notice this resulted in F-1 engines having a huge gas pipe coming off the nozzle into the fuel pump. If NASA could use regenerative engines for Saturn V and Shuttle, a future engine could easily be regenerative.

Yes Robert, I know what absolute zero is.

There is a big difference between making a regenerative rocket nozzle versus a regenenerative aircraft, which is what you would need for a regenerative scramjet, the point is to take heat energy from the vehicle's skin, not the engine nozzle. I think this is an order of magnetude more difficult engineering feat... quite possibly it will require better materials then we have right now to be fully reuseable too.

The pipes will not only have to be able to readily absorb heat from the vehicles' leading edge & surfaces, but will have to withstand high internal hydrogen gas pressures and modest temperatures over a signifigant distance to carry the preheated gas to the Scramjet. And do this without weakening by hydrogen embrittlement, and do it dozens of times without replacement or serious maintenance.

I think this is a big challenge that won't be easily overcome soon for any small mom/pop/garage/university/AltSpace sum.

RobertDyck · 2005-06-24 17:01:09

I do not agree. The Space Shuttle enters the atmosphere at mach 25 with existing refractory heat shield system (tiles and thermal blankets). I believe that's all you need for a SCRAM jet spaceplane. Yes, putting cooling pipes all over a vehicle's skin is an order of magnitude more difficult, but I don't think we need it. In fact, I've stated elsewhere that an active cooling system for atmospheric entry is heavy and complicated, and those complications significantly increase the chance of failure. The same applies to launch, don't use regenerative cooling for the skin. Regenerative cooling is feasible for engines because you have all that fuel flowing into the engine anyway, and the nozzle is so close to where hot fuel is required. Hmm; to an extent we're arguing on the same side of the debate.

Here's a nice little test that I asked NASA to do: build the X-43D. I called it 'D' simply because the previous X-43 vehicles were A, B, and C. This one would be a small unmanned test vehicle like X-43A, but instead of a titanium skin it would use Space Shuttle refractory heat shield technology to permit faster speed. It would also be deployed from a Pegasus rocket that is air-launched from NASA's B-52B. The X-43A accelerated from mach 5 to mach 9.8, the X-43D would accelerate from mach 5 to mach 15. Yes, I said mach 15; previous studies said it's achievable so let's demonstrate it. I also said it should be equipped with a parachute so it could be recovered and fly more than once, and in case of Pegasus rocket failure the aircraft could separate from the rocket prior to rocket autodestruct.

GCNRevenger · 2005-06-24 17:10:20

"but I don't think we need it"

Then you are wrong. The reason why a Scramjet spaceplane would be regeneratively cooled is not to prevent it from melting, but rather to recover some of the energy wasted as friction with the thick atmosphere. The USAF abandoned the X-30 project in large part because the Scramjet just wasn't efficent enough to overcome the drag during use, which limits its practical maximum speed to Mach 15, too far from orbital velocity to make an SSTO spaceplane. The solution that was proposed was to make the whole vehicle regenerative, which would in theory get it up to Mach 20 and close enough to orbital velocity, but would have been an arduous and extremely expensive development.

Recover the X-43? Too much trouble, just build another one. And if you have a serious failure with the booster, then chances are your vehicle is gone too anyway. Soft-landing it would be hard too.

Edit: Also, Mach 15 is not fast enough for a spaceplane, but too fast for a suborbital bomber. So why bother? We have more important things to spend money on right now.

RobertDyck · 2005-06-24 17:21:29

"but I don't think we need it"
Then you are wrong. The reason why a Scramjet spaceplane would be regeneratively cooled is not to prevent it from melting, but rather to recover some of the energy wasted as friction with the thick atmosphere.

I also said they need to investigate "plasma magic". This is a seriously unprofessional name for a real principle of aerodynamics. The unprofessional name is one reason there isn't serious research in this area, someone has to come up with a better name. The idea is a microwave beam shines ahead of the aircraft to convert air into weak plasma. At subsonic speed the plasma converts back into normal air before the aircraft flies through it, but at supersonic or hypersonic speed the air doesn't have enough time. Flying through weak plasma reduces aerodynamic drag. This is a significant improvement for a fat, poorly streamlined aircraft. The better an airframe is streamlined the less effective the plasma; an extremely streamlined vehicle like X-43A would find the plasma no help at all. But the plasma could permit a shorter, fatter lifting body that comes closer to X-24A or HL-20, which would increase interior volume for fuel tanks while reducing surface area covered in heat shield. More fuel and lighter heat shield, that's what a rocket guy wants to hear. More importantly, reducing the length of the SCRAM jet intake surface would reduce heating of intake air. Yes, temperature difference between intake air and exhaust is critical for thrust; the microwave beam/plasma effect can increase maximum airspeed.

::Edit:: Thanks to Bill White for telling us about Plasma Magic.

Loughman · 2005-06-24 17:23:40

Only leading edges (wings, front edges and cowl leading edges) as well as the engine itself need significant thermal protection. There are materials (such as the TUFI tiles and thermal blankets used for the shuttle) but there are also newer materials with TRL (technology readiness level, NASA's way to measure how feasible a technology is to use in its current state) that are high enough to warrant using them rather soon. One comes to mind, Hafnium Diboride. It's been a while so don't crucify me if this is a little off, but this material would offer both the thermal protection needed and the reusability that the materials the shuttle uses do not offer.

Concerning reentry profiles, GCN is right. Two things are contingent on velocity: (1) your orbit is determined by it, so the slower you go the closer or lower your orbit, and (2) the amount of energy (heating) is transferred to your vehicle via fluid friction. The faster you go the hotter you are. So there is this trade, you either stay higher and fast (and away from air) or low and not quite so fast (and burn up, and hopefully you have some Hafnium Diboride wing edges). But the trick is that you cannot slow down with droping fast.

GCNRevenger · 2005-06-24 18:00:04

What? An X-24/HL-20/etc shaped vehicle paired with a high-hypersonic scramjet? Tell me you a joking...A "poorly streamlined aircraft" is a charcoal briquet at high hypersonic velocities, even the X-43 shape is pretty "blunt" at near orbital velocities! Such poorly streamlined shapes would never be practical for a scramjet SSTO. They can hardly handle the heat entering belly-first, which you can't do with scramjet engines, and the drag even with ionization "softening" would be too extreme to fix it.

Use of ionization is an interesting idea, but I seriously doubt that it will help you a whole lot, though it could perhaps put a modernzied X-30 closer to the orbital velocity line... Some problems I forsee though:

-If the air friction reduction is due to a decrease in pressure by thermal expansion, then you may also have decreased thrust since you have less air to draw into the engines, and not have an easier time keeping your vehicle any cooler.

-If its by reducing average molecular radius or something that does not increase temperature in front of the vehicle but reduces pressure, you will definatly have a drop in thrust.

-Ionized air may not combust as well, if you have already cleaved oxygen bonds and such.

-Extreme energy requirement very likely... hard to produce.

-Plasma can ablate much better then regular air can... you know, plasma cutters?

RobertDyck · 2005-06-24 18:05:08

I shouldn't distract from Loughman's comment, but I want to point out that GCNRevenger said the study he quoted concluded that mach 15 is the highest practical speed, but I proposed the X-43D go to mach 15, the same speed. Even "Plasma Magic" isn't necessary for that.

I stated a later experimental UAV, the X-43G, would use a RBCC to fly to mach 15 strictly airbreathing, then use LOX to accelerate further. It would transition smoothly from SCRAM jet, to air augmented rocket, to LOX/LH2 rocket. I didn't say what speed you would complete the transition to rocket mode, but hopefully it would be mach 20.

GCNRevenger · 2005-06-24 18:27:10

No way, dumping LOX into a Scramjet engine isn't going to fix your problem, you keep on adding heavy things (microwave beam, LOX, etc) and thats going to slow you down too much.

Here are some interesting sources:
http://www.astronautix.com/lvs/x30.htm] … vs/x30.htm
http://www.astronautix.com/craft/x43.ht … ft/x43.htm

Mach 15, that I recall seeing when reading about future X-43 derived vehicles, is probobly going to be pretty hard to achieve. Perhaps that figure was for a version with regenerative cooling and wasn't mentioned? That might be more in line with the old 1980s/90s USAF study, which pegs "regular" scramjets at Mach 9 max and 90s level tech regenerative scramjets at Mach 17.

New Mars Forums

Announcement

#26 2005-06-23 23:35:48

Re: New Topic! - Burt Ruten has nailed the space problem!

#27 2005-06-24 06:57:07

Re: New Topic! - Burt Ruten has nailed the space problem!

#28 2005-06-24 07:21:46

Re: New Topic! - Burt Ruten has nailed the space problem!

#29 2005-06-24 07:23:49

Re: New Topic! - Burt Ruten has nailed the space problem!

#30 2005-06-24 07:33:38

Re: New Topic! - Burt Ruten has nailed the space problem!

#31 2005-06-24 07:41:39

Re: New Topic! - Burt Ruten has nailed the space problem!

#32 2005-06-24 07:55:21

Re: New Topic! - Burt Ruten has nailed the space problem!

#33 2005-06-24 08:12:12

Re: New Topic! - Burt Ruten has nailed the space problem!

#34 2005-06-24 10:19:54

Re: New Topic! - Burt Ruten has nailed the space problem!

#35 2005-06-24 10:21:38

Re: New Topic! - Burt Ruten has nailed the space problem!

#36 2005-06-24 11:33:20

Re: New Topic! - Burt Ruten has nailed the space problem!

#37 2005-06-24 12:01:38

Re: New Topic! - Burt Ruten has nailed the space problem!

#38 2005-06-24 12:45:05

Re: New Topic! - Burt Ruten has nailed the space problem!

#39 2005-06-24 12:52:20

Re: New Topic! - Burt Ruten has nailed the space problem!

#40 2005-06-24 12:56:57

Re: New Topic! - Burt Ruten has nailed the space problem!

#41 2005-06-24 14:25:27

Re: New Topic! - Burt Ruten has nailed the space problem!

#42 2005-06-24 14:30:20

Re: New Topic! - Burt Ruten has nailed the space problem!

#43 2005-06-24 16:07:30

Re: New Topic! - Burt Ruten has nailed the space problem!

#44 2005-06-24 17:01:09

Re: New Topic! - Burt Ruten has nailed the space problem!

#45 2005-06-24 17:10:20

Re: New Topic! - Burt Ruten has nailed the space problem!

#46 2005-06-24 17:21:29

Re: New Topic! - Burt Ruten has nailed the space problem!

#47 2005-06-24 17:23:40

Re: New Topic! - Burt Ruten has nailed the space problem!

#48 2005-06-24 18:00:04

Re: New Topic! - Burt Ruten has nailed the space problem!

#49 2005-06-24 18:05:08

Re: New Topic! - Burt Ruten has nailed the space problem!

#50 2005-06-24 18:27:10

Re: New Topic! - Burt Ruten has nailed the space problem!

Board footer