Surface to orbit spacecraft discussion from prometheuspan’s intro thread

[Pyrotex]

A good post as always, Nelson, but I believe you miss a critical point: the rocket equations apply to rockets, not air-breathing jets (or, for that matter propellers, or tethered flocks of hummingbirds tube fed sugar water and electrolytes ;))...

Excellent point, Craig!

I was assuming certain things about the "rocket plane" -- including that it used the best chemical fuel available in all of chemistry -- liquid H2, and the best oxidizer -- liquid O2. And by "best", I meant the most energy per pound.

 

As for the "air-breathing" rocket plane, the rocket equations still apply. They apply from a certain altitude, say 200,000 feet, and a certain initial velocity, say mach 15. At that point you "light the candles" and you rocket up into orbit. All that "air-breathing" stuff allows you to start there, rather than start at near sea level and zero velocity.

 

BUT... to get up to 200,000 feet and mach 15, requires mass you cannot throw away. The air-breathing engines (20 tons) go with you to orbit. The extra tankage for them (10 tons), the active thermal control system (5 tons), the extra strong structure for the skin (15 tons), the hypersonic inlet (10 tons)... :shrug: :eek_big: :eek_big:

 

So, go ahead, start your launch at 200,000 ft, mach 15, but subtract 60 tons from your payload.

 

Oh, wait a second! You were designing a system to take 50 tons to orbit! Oh, crap. Sorry about that.

:( Real bummer, dude. :shrug:

[prometheuspan]

All of these limitations heterodyne off each other.

Remove mass? Margin of strength is reduced too much.

 

the space shuttle and its rockets have been described as flying rocks. Modern space age light weight

materials can make a considerable difference.

 

This isn't an either/ or problem, its marginal solutions to all of these issues creating as a holistic end product something which can pull it off.

 

 

 

Increase mass? Margin of payload is reduced too much.

 

heavy weight engines are a problem and can be considered "payload", but "too much"

 

is both too vague and too simple by half.

 

Increase thrust? More mass needed.

 

or, a more efficient thrust system.

 

 

Run hotter? Hull melts.

 

No, run smarter.

 

 

Use more fuel for cooling? Tanks have to be larger.

 

I wouldn't try cooling from any angle other than using modern materials to distribute the heat,

and running mostly cold engine where the thrust is ignited at the last second.

 

Maser ignition is nice like that.

 

Larger fusillage? More heating at any given speed.

 

make it pointier.

 

 

Use ramjets to save on fuel? Spend more time at hotter temperatures.

 

Cold Ramjets are possible, you just ignite at the very last moment at the end of the compression tube.

 

 

Need to be safer (more reliable)? Need more backup systems, which means more mass, which means more fuel, ... and you're back to square one.

 

Its true that all of these problems inter -relate and cross modify each other, and that its a complicated problem.

 

Partial solutions do exist and we can work our way towards even better ones.

 

here are some images to get things cooking...

 

:hyper:

 

PDC4.01.a

[prometheuspan]

Alas, such an invitation runs afoul one of the site rules we mods and admins are committed to uphold:

The only type of linking (besides porn, pyramid schemes, hateful sites, and spam, of course) that will not be allowed on our site is when members solicit people to leave our site and join a competing service. That's just common sense. We won't allow people to use our site to promote a competing service any more than a brick-and-mortar store would allow his competitor to paste flyers all over his walls.

In short, bring your images and discuss them here. :cheer: It’s OK to quote from and link to other sites to address ideas you’re discussing in a hypography thread, but not OK to try and move conversations from hypography to other sites. :hyper:

 

frankly i'm confused. First off, the only person on that site who has information to make

them competent in such a discussion that i know of is me. I'm certainly interested in bringing people over to chat, but we are hardly in competition with each other on this.

 

Clearly the conversation would continue here, and clearly my reason for linking there is

the functionality, as well as what might also be considered a spam problem.

 

I'm not trying to move the conversation, I'm trying to splinter it to where the image system

works for my purposes and where you won't be annoyed that i posted 20 responses to myself.

 

In my mind and experience, thats collaboration and site to site networking and co-supporting.

 

If my intention was to steal people off and away, I'd pm them. As it ends up working i tend to attract small followings without doing that, And I'm happier that way.

 

"As you may have gathered already, I’m enthusiastic about – one might even say a bit of a sucker for – space helicopter ideas. Despite the downfall of Rotary Rocket and their troubled Roton vehicle design, I think there’s merit to them, and would love to see more armature and professional work on them."

 

Me also. Tho i didn't find those models ..just one of them...

I think the other one crashed because it got too detailed and a third has got to be floating

around somewhere in the wrong file.

 

 

[*]A simple way to get rocket motors to use air for reaction mass,

 

yes, it solves or addresses a lot of problems. It also has some which were never resolved.

:)

[prometheuspan]

sometimes i wonder what would have happened to Einstein if the internet had already happened.

 

Would he have gotten people telling him hes nuts because he couldn't provide references or proofs?

 

Would they have told him not to post links to his formulas because thats stealing membership attention

away from the beloved site?

 

Would anybody have ever listened to him, or would he have just been drowned out in the noise?

 

They say only 4 people in the world were qualified to understand him. Back then his advantage was,

people didn't just spew all over looking for attention.

 

If the internet had been 100 years earlier, I think Einstein would have been a washed up internet spam

troll. Trying to reveal the secrets of the universe to a world much more concerned with being politically correct and maintaining assorted status quos than really solving humanities real problems.

 

Nobody would get it, they would all demand links to his references, and he would have to tell them it was just a thought experiment- but don't worry, hes clever enough to do thought experiments.

 

They would laugh, ban him, and on it would go.

 

 

As far as aspies go, he had way better than my math skills but way less than my social skills.

 

How would he deal with the mass pack psychology culture ? With the attacks and the cruelty and the noise?

 

I doubt it could have ended very well at all.

[prometheuspan]

I found the newer helicopter. Both are now included in that same thread i linked to.

 

Mostly just some concept art. If anybody has anything they want me to draw, let me know.

 

I will be loading a lot more images and for space planes I'm starting with the oldest first, so they do get

better as I learn to use the program.

 

PDC4.01.a

[CraigD]

Use more fuel for cooling? Tanks have to be larger.

I wouldn't try cooling from any angle other than using modern materials to distribute the heat,

and running mostly cold engine where the thrust is ignited at the last second.

Pyro is referring to a proven aircraft heat management technique. One pumps cool fuel under a hot surface, vaporizing it, then either exhausts the hot vapor by burning it in the engine, or venting it unburned.

Igniting jet fuel “at the last second” – which as know as afterburning – is not a significant engineering problem, as hot exhaust will light fuel injected via afterburner nozzles without the need for an igniter.

Maser ignition is nice like that.

A maser is simply a laser outputting in the microwave range (3e8 to 3e11 Hz) of the EM spectrum, rather than the visual range (4e14 to 8e14).

 

Laser aren’t very useful for igniting fuel in motors, because they must “dwell” on their target – the fuel, in this case – for a much longer time to raise it to ignition temperature than the usual technique of exposing it to a small amount of very high temperature plasma, as such mundane igniters as auto spark plugs produce

Larger fusillage? More heating at any given speed.

make it pointier.

“Make it pointier” – that is, decrease its frontal area and block drag coefficient – is a pretty sound way to reduce friction, and hence heating, on an airframe. :thumbs_up

 

:( It has a problematic trade-off, however. Recall that an airframe is essentially a container for useful and necessary material, for the most part, fuel (and, if a rocket flight phase is involved, oxidizer) and payload. Consider an airframe as a square prism with dimension [imath](X,X,L)[/imath], volume [imath]V= X \cdot X \cdot L[/imath], surface area [imath]A= 4 \cdot X \cdot L[/imath]. As ideally a container has mass only in its skin, mass is directly proportional to [imath]A[/imath]. Doubling [imath]L[/imath] while keeping [imath]V[/imath] constant results in an increase of area [imath]A'=\sqrt2 A[/imath], about 41%. This doesn’t take into account increases in mass due to necessary increases in internal or skin reinforcement, as structurally, the longer a rectangular prism becomes, the more reinforcement is required to maintain its rigidity.

Cold Ramjets are possible, you just ignite at the very last moment at the end of the compression tube.

I think you’re missing a couple of critical point about heat in hypersonic jet engines.

 

First, heat ...

Most of the heat from scramjets, ramjets, and to some extent high supersonic turbojets like the SR-71’s, come not from the hot exhaust gases from their burning fuel, but from air friction and compression of the air entering them.

 

Second, the meaning of “ramjet” and “scramjet” (a contraction meaning “supersonic ram jet”) ...

Like a turbofan jet engine, ramjets must slow the incoming air to less than the speed of sound before it is mixed with fuel and the mixture ignited to produce thrust. At around Mach 5, drag from slowing the incoming air exceeds the thrust it produces, and the engine can propel an aircraft or missile no faster. The incoming gas is also excessively hot, requiring complicated, heavy cooling systems to protect the engine and maintain its efficiency.

 

A scramjet doesn’t slow the incoming air to less than the speed of sound, avoiding as much as possible these problems. Its tradeoff is that it’s more difficult, and requires a longer, heavier burner chamber, to mix fuel with air and ignite the mixture when it’s moving so fast.

 

Hence, a surface-to-orbit vehicle that get’s a large part of its total impulse from an air-breathing (jet) engine almost certainly will use a scramjet, not a ramjet.

Its true that all of these problems inter -relate and cross modify each other, and that its a complicated problem.

 

Partial solutions do exist and we can work our way towards even better ones.

:thumbs_up I completely agree.

 

Where I think I differ from you, Pan, is that I think you need to thoroughly understand existing solutions – including the math and practical mechanics – to effectively work toward better ones. It’s a lot of work just to learn enough to begin work, and so far, though I like your pictures, I don’t see evidence that you’ve done enough of this beginning work.

 

There’s an obscure quote, by Gothe, I think, that I’ve not been able to find online, or recall the art theory book I read it in (or, in fact, had it read to me, in a 10th grade art appreciation class), translating to something like “originality is the downfall of many great artists”. It means not that originality is bad, but that striving for it to the exclusion of appreciating, taking, and using unoriginal ideas, is. This idea is even more applicable to the sciences, I think, than the fine arts, and one of the least appreciated. Those who successfully create new basic and applied science, almost or entirely without exception, are outstandingly versed in old science.

 

The segues well, I think, into ...

sometimes i wonder what would have happened to Einstein if the internet had already happened.

 

Would he have gotten people telling him hes nuts because he couldn't provide references or proofs?

Had the internet existed in 1905, when Einstein published his breakthrough papers on the photoelectric effect, special relativity, and mass-energy equivalence, I doubt he would have spent much time on it, other than, as physicists do now, to submit his papers to journals.

 

As they did not in and after 1905, I'm nearly certain few people would have told him he was nuts, as he did provide proofs and experimental predictions in his papers. Had there not been, they would not have been accepted for publication, as he submitted them to one of the oldest and most respected science journals in existence.

 

Simply put, that’s how science and math work. No matter how new, or even disturbing and threatening, it is, if a theory is rigorously presented, it will be respected and read. Better still, if a scientific theory makes experimental predictions that can be tested with means available at the time, it will be, and if they’re confirmed, the theory will be regarded as realistic. If people like and understand it - with all the work that entails – it may even be regarded as beautiful and true. (even if experimentally disproven, a theory may still be considered beautiful)

 

Finally, a note on hypography’s rules ...

Alas, such an invitation runs afoul one of the site rules we mods and admins are committed to uphold:

The only type of linking (besides porn, pyramid schemes, hateful sites, and spam, of course) that will not be allowed on our site is when members solicit people to leave our site and join a competing service. That's just common sense. We won't allow people to use our site to promote a competing service any more than a brick-and-mortar store would allow his competitor to paste flyers all over his walls.

In short, bring your images and discuss them here. :) It’s OK to quote from and link to other sites to address ideas you’re discussing in a hypography thread, but not OK to try and move conversations from hypography to other sites. :naughty:

 

frankly i'm confused.

Following this rule is not too difficult. Just don’t post sentences like “come to <another website> to see <the subject of a hypography thread>”. Rather quote the text in your hypography post, and provide a link back to the other website. If, is as the case with your recent RBEF posts, there is not text to quote, only images, you may imbed them in your post by typing , or, if you prefer, clicking on the insert image button above the reply to topic input form.

 

For example,

renders as

 

Alternately, you can upload an image as a clickable thumbnail appearing at the bottom of your post by clicking the Manage Attachments button below the input form, as below.

[prometheuspan]

First, heat ...

Most of the heat from scramjets, ramjets, and to some extent high supersonic turbojets like the SR-71’s, come not from the hot exhaust gases from their burning fuel, but from air friction and compression of the air entering them.

 

thats an aerodynamics problem best solved by having a long compression tube with internal ruts

in order to maintain optimal cooling.

 

 

Second, the meaning of “ramjet” and “scramjet” (a contraction meaning “supersonic ram jet”) ...

Like a turbofan jet engine, ramjets must slow the incoming air to less than the speed of sound before it is mixed with fuel and the mixture ignited to produce thrust. At around Mach 5, drag from slowing the incoming air exceeds the thrust it produces, and the engine can propel an aircraft or missile no faster.

 

Unless you redesign a super sonic engine with no fuel just air burning. Its two different engines.

 

Hence, a surface-to-orbit vehicle that get’s a large part of its total impulse from an air-breathing (jet) engine almost certainly will use a scramjet, not a ramjet.

 

No, it will use a magnetic ram rocket, with a maser ignition system, just like i said.

 

The magnetic field also helps with the heating friction by carrying the particles in its stream.

 

Thats what the magnetic slide plating is for at the front of the engine.

 

 

 

 

Where I think I differ from you, Pan, is that I think you need to thoroughly understand existing solutions – including the math and practical mechanics – to effectively work toward better ones.

 

This assumes i don't understand them, or that studying a bone tool will have anything meaningful to impart to the process of crafting a modern wristwatch.

 

 

"It’s a lot of work just to learn enough to begin work, and so far, though I like your pictures, I don’t see evidence that you’ve done enough of this beginning work."

 

I'm drawing bodies here, you haven't asked to see nor have i posted drawings of engines.

 

 

There’s an obscure quote, by Gothe, I think, that I’ve not been able to find online, or recall the art theory book I read it in (or, in fact, had it read to me, in a 10th grade art appreciation class), translating to something like “originality is the downfall of many great artists”. It means not that originality is bad, but that striving for it to the exclusion of appreciating, taking, and using unoriginal ideas, is.

 

You keep talking about me. I'm not interested in me. You are boring me and only demonstrating

you have issues.

 

You don't know me and you don't know what i do or don't know.

 

I will repeat again, i posted the oldest images first. I have much newer images and designs of engines

instead of whole craft.

 

You aren't asking to see more work, and you aren't critiqeing the work i have. Your just giving me a pile of doody.

 

This idea is even more applicable to the sciences, I think, than the fine arts, and one of the least appreciated. Those who successfully create new basic and applied science, almost or entirely without exception, are outstandingly versed in old science.

 

Thats great, its not always true, but its an interesting general mechanic of it all.

Its got less than nothing to do with me.

 

"As they did not in and after 1905, I nearly certain people would have told him he was nuts, as he did provide proofs and experimental predictions in his papers. Had there not been, they would not have been accepted for publication, as he submitted them to one of the oldest and most respected science journals in existence."

 

You seem to be intentionally missing the point.

 

Simply put, that’s how science and math work. No matter how new, or even disturbing and threatening, it is, if a theory is rigorously presented, it will be respected and read.

 

untrue, and a silly claim.

 

 

 

Following this rule is not too difficult. Just don’t post sentences like “come to <another website> to see <the subject of a hypography thread>”. Rather quote the text in your hypography post, and provide a link back to the other website. If, is as the case with your recent RBEF posts, there is not text to quote, only images, you may imbed them in your post by typing , or, if you prefer, clicking on the insert image button above the reply to topic input form.

 

i can tell a few other details slipped past you, like having too many images to post on your forum.

 

if you are unwilling to share the internet with other sites in a collaborative fashion, then you are the ones who have issues.

 

You have a science site and a lot of good people here. Its too bad you don't have real metaprocess or

a meaningful way to appraise and empower moderators not make idiots of themselves by being net fascists.

 

I am increasingly bored. To be honest, there is very little that you guys have to offer me, some mental stimulation, but I'm the one who knows what he is talking about and you guys are all just muggles.

in a hobbyist forum, not a science forum.

 

To be a science forum, it would have to have things like metaprocess derived from psychology-

 

not the same old groupthink + pack psychology as any troll forum anywhere.

 

by all means, enjoy your site...

 

this isn't what I'm looking for, and I won't be recommending it to anyone.

[Pyrotex]

“Make it pointier” – that is, decrease its frontal area and block drag coefficient – is a pretty sound way to reduce friction, and hence heating, on an airframe.

;)

 

Decreasing the frontal area (the "cross-section") does indeed reduce air friction.

However, making the nose more "pointy" actually increases airframe heating.

 

Back in the 1960's this was a major problem with ICBMs. Everytime, the military tested a re-entry warhead, it was badly melted. More pointy, more melted (given a constant cross-section). The reason was, the pointier the nose, the closer the contact of the nosecone with the hypersonic airstream going past. Then somebody added 2 and 2 and got...

 

"Why don't we make the nosecone shaped like a bowling ball?" And it worked. With the same cross-section, a blunt rounded nosecone creates a shockwave in front of the nose. This shockwave becomes the "surface" that the airstream hits and goes around. This shockwave becomes the barrier that is raised to temperatures in excess of 10,000 C. And the shockwave can be engineered to be separated from the nose by as much as desired. The blunter the nose, the further ahead you place the shockwave.

 

The pinnacle use of this idea was the heat-shield used by the Mercury, Gemini, Apollo spacecrafts. The temperature at the shockwaves was over 20,000 C, but separated from the heat shield by more than 20 cm. The heatshield itself never got over 1,000 C.

 

The scramjet engine (based on Russian engineering, BTW) did indeed exceed Mach 10. But the entire flight was less than 1 minute. About 20 seconds, I think. And the vehicle was tiny--small enough to be launched out of a (9 inch ?) cannon. So, its thermal problems were not severe. Any good hi-temp steel (or titanium) could have survived Mach 10 for 20 seconds.

 

Pushing a 500 ton space plane at Mach 3 to Mach 15 for half an hour or more is an entirely different kettle of squid.

[CraigD]

“Make it pointier” – that is, decrease its frontal area and block drag coefficient – is a pretty sound way to reduce friction, and hence heating, on an airframe.

:D

 

Decreasing the frontal area (the "cross-section") does indeed reduce air friction.

However, making the nose more "pointy" actually increases airframe heating.

Mea culpa. ;) You caught me being overly creative with my interpretation of “pointier”, taking it to mean “with a smaller frontal area for the same volume, rather than the more common meaning, “tapered”. I was trying to be charitable to Pan, which didn’t work out well :(

 

You’re very correct, I think, in pointing out the importance of the boundary layer - the layer of air between the aircraft skin and the effectively stationary atmosphere through which it moves. IMHO, aeronautics has just begun to scratch the surface (no pun intended) of boundary layer control, especially when it comes to “active aerodynamics” such as powered air jets and arrays of small computer controlled flaps. Though serious and interesting research into active aerodynamics is ongoing, the pinnacles of implemented boundary layer control schemes remain technology older than many of us, like the airflow interrupter vanes you can see on in front of control surfaces on airliners wings (to prevent them from become ineffective if the plane accidentally reaches transonic speeds), and the aerospike on the nose of Trident missiles (which reduce drag).

 

Realizing a “smart” active system that keeps the large part of air friction heating in a layer of air that’s shed behind the aircraft could revolutionize (pardon the buzzspeak) hypersonic aircraft design.

The scramjet engine (based on Russian engineering, BTW) did indeed exceed Mach 10. But the entire flight was less than 1 minute. About 20 seconds, I think. And the vehicle was tiny--small enough to be launched out of a (9 inch ?) cannon. So, its thermal problems were not severe. Any good hi-temp steel (or titanium) could have survived Mach 10 for 20 seconds

As best I can tell, though the Russian GLL Holod was the first scramjet flown, on 28 Nov 1991, its top speed was mach 5.8

 

The fastest sustained powered aircraft flight was 12,144 km/h (mach 9.8) the by the X-43A on 16 Nov 2004.

 

By design, the scramjet ran only 10 to 11 seconds. A (much larger than it – about 18000 kg) discarded rocket stage, not the scramjet, was used to accelerate to that speed. Rocket and scramjet were both air released from under the wing of a B-52 at altitude 13157 m, scramjet separated from rocket at 34000 m

 

I’d call the X-43A little for an aircraft, but not tiny. At 3.7 m long x 1.5 m wide by 0.6 m high, massing 1300 kg, it’s like a small, very solid automobile.

 

Even with this short flight, heat problems appear to have been significant enough for the X-32A to use a water cooling system to avoid melting its leading edges and other hotspots.

 

Best images, specifications, and story I’ve yet read on the X-43A and its first, slower 2004 flight are in this BBC article. I can’t find much more on the GLL Holod or its successor, the Igla, than at this mention in a wikipedia article.

[Pyrotex]

Thanks Craig. I was confusing the Russian scramjet and the American X-43 which was much larger and went faster. So they still needed active cooling for just a few seconds? Wow.

 

Slamming into air (even thin air) at 10 micro-C generates a LOT of heat.

 

Coincidence: at some altitudes, the speed of sound almost exactly equals 1/million of speed of light, C.

[TheFaithfulStone]

Ohhh.... can we talk about my favorite crackpot space theory?

 

Ladies and gentleman I give you the The Airship to Orbit (PDF Warning)

 

Reasons why this is right up there with giant octopi and Trunko for my all time favorite crackpot theory.

1. It's WAY to dumb to actually work.
   
2. It's not possible that they actually think this could work, right? I must have missed something. Because it's impossible on it's face.
   
3. NO. It's totally dumb. Isn't it?
   

 

But, like most crackpot theories, there's the germ of a good idea in there. The rockoons are a (grossly inefficient, but romantic as hell) way to make rockets. It's perfectly possible to float to around 100,000 ft in a ballon, and once you're that high up, you're about 2/3 of the way to "space." (You're still well shy of orbit, but now you have a different problem.)

 

If I remember correctly, the idea was to paint this 8 mile long balloon lifting body with thin film solar cells and use ion engines (of some description - might have been Hall Effect thrusters, or some kind of idealized VASIMIR) to slowly, over a period of several weeks, accelerate to orbital velocity while moving upward.

 

Like I said, I'm 100% positive that this wouldn't work (mostly because ion engines are pretty flippin' heavy, and they produce VERY little thrust.) but it's one of my favorite goofball space theories.

[CraigD]

Ohhh.... can we talk about my favorite crackpot space theory?

 

Ladies and gentleman I give you the The Airship to Orbit (PDF Warning)

 

Reasons why this is right up there with giant octopi and Trunko for my all time favorite crackpot theory.

1. It's WAY to dumb to actually work.
   
2. It's not possible that they actually think this could work, right? I must have missed something. Because it's impossible on it's face.
   
3. NO. It's totally dumb. Isn't it?
   

Thanks for the reference to JP Aerospace’s “airship to orbit” design. :thumbs_up I vaguely recall these folk from their failed attempt to win the SFF’s CATS prize in 1999 with a balloon-launched rocket, but was unaware of their more ambitious plans, or that they remained a financially viable enterprise.

 

To summarize what I’ve just read, the “airship to orbit” scheme isn’t a single ground-to-orbit vehicle, or even a multistage stack like the rocket system that have been successfully orbiting payloads for the past half century, but uses 3 very different vehicles:

• Modest-size (as small as 250 m or so length, about that of the Hindenburg) ground-to-140,000 feet (42700 m) v-shaped propeller-driven cargo airships called “Ascenders”
  
• Huge (about 5 km diameter), starfish-shaped permanently airborn balloon-supported platforms, called (rather poetically) “Dark Sky Stations” (DSS)
  
• A bigger-than-ever made (about 1.8 km long) v-shaped air/spaceship, assembled at the DSS from materials delivered by the Ascender”, called (rather unimaginatively) the “Orbital Ascender”
  

While this is pretty far-out, unconventional stuff, I don’t think it’s crackpot. As outside-the-box design goes, I’d call it brilliant, and that JP’s built and flown several test models, gathering data to design increasingly large scale models, while remaining financially viable by flying more conventional commercial balloon missions, testifies to their seriousness. That they are expert, and, it appears, growing more so, in the business of making money with these systems, is IMHO another important indicator of the viability of their seemingly unachievable plan.

 

Though flying a payload to a 5 km balloon-born transport depot at 42.7 km altitude, after first building the depot, is no easy feat, the Orbital Ascender seems to me the most unprecedented and difficult component of the system. What a giant airship must do to get from floating at 42.7 km to even the lowest orbit is daunting. A free-floating “geostationary” vehicle at 42.7 km over the equator has a speed of about 500 m/s (1800 km/h, 1100 MPH). The orbital speed for that altitude – the point at which the vehicle no longer needs atmospheric lift, and can begin rising to a higher orbit, is about 7900 m/s (28000 km/h, 18000 MPH). Propelling a giant, ultra-light, flexible vehicle to such a speed, while it interacts with the thin atmosphere at that altitude, strikes me a s mind-boggling challenge, regardless of how it gets its power and propulsion.

 

On the upside, the Orbital Ascender looks to me to have about [imath]200000 \,\mbox{m}^2[/imath] of overhead area, so a ball-park estimate of its available solar electric power, assuming 5% photovoltaic efficiency (about 1/10th that of aerospace-quality solar cells), is 12 MW. Since we know pretty precisely what the density of the OA must be – about that of air at 43 km altitude, [imath]0.00086 \,\mbox{kg/m}^3[/imath], we can work out its mass, about [imath]2 \cdot 2000 \cdot 25^2 \cdot \pi \cdot 0.00086 = 6700 \,\mbox{kg}[/imath], and … well, after lots of mechanical estimates, I’m satisfied the power to mass ratio of this thing is reasonable.

 

JP claims to have done simulations, finding that using more-or-less-COTS ion thrusters, the OA could reach orbit in 3 to 9 days.

 

What concerns me most about this scheme is the need for the OA to go so fast (7900 m/s) in the relatively dense atmosphere at 43 km altitiudeatmosphere to space. Imagining It’s essentially flexible skin would cope with complex pressures of moving air over it brings to my imagination all sorts of terrible scenarios ending in it being ripped apart.

[TheFaithfulStone]

well, after lots of mechanical estimates, I’m satisfied the power to mass ratio of this thing is reasonable.

 

JP claims to have done simulations, finding that using more-or-less-COTS ion thrusters, the OA could reach orbit in 3 to 9 days.

 

Yeah, the OA part was always the sticking point for me too. I actually did a fair amount of research on this, and there were a couple of other points that made me rethink the "impossible on it's face" initial impression.

 

Most of the rocket scientist I know were telling me that the problem was in the power to mass ratio of the OA - that there was no way you could get enough power in a light enough frame to actually transport any payload any higher than about 180,000 ft or so, and that there was no way anything like that could get up to orbital speed.

 

If I had to guess, I suspect something like Buckypaper is what they have in mind for the skin of the thing. Lightweight, high tensile strength, and electrically conductive, and insulating.

 

I think to a certain extent they're sort of counting on "technology inflation" - wherein currently exotic things like carbon nanotubes and aerogel will be pretty common by the time they get ready to actually fly the thing. On the one hand, it's sort of bad engineering to count on advances in materials science to make your gadget work - on the other hand, it's not like the space elevator where they're saying "All we need is to achieve the absolute theoretical limit of tensile strength in CNTs and we've got ourselves a space elevator! Oh, and learn how to make a whole lot of them."

[Pyrotex]

the space shuttle and its rockets have been described as flying rocks.

By uneducated idiots, perhaps.

Modern space age light weight materials can make a considerable difference.

The Shuttle *IS* made of the most advanced light weight materials.

...heavy weight engines are a problem and can be considered "payload", ...

No they cannot. "Payload" -- BY DEFINITION -- is the cargo you are carrying to orbit. Engines are part of your vehicle.

... or, a more efficient thrust system.

The Shuttle Main Engine is the most efficient chemical rocket ever devised, burning the best fuels (H2, O2) at the highest temperature possible without melting the engines. Any "more efficient" thrust system would have to be a different KIND of engine -- perhaps ion, plasma or nuclear.

No, run smarter.

How would YOU know?

I wouldn't try cooling from any angle other than using modern materials to distribute the heat, and running mostly cold engine where the thrust is ignited at the last second.

This makes no sense. You have to ignite the engines when you launch. You can't run a rocket (or jet) engine "cold". It's either running or it's not. The hotter a rocket engine runs, the more efficient it is. The engine's heat has NOTHING to do with the heat encountered by the fusillage, caused by atmospheric friction. :doh:

:eek2:

...Cold Ramjets are possible, you just ignite at the very last moment at the end of the compression tube.

This makes no sense. Last moment of WHAT? If the ramjet is off (cold) then how do you get up to speed? All jet and rocket engines are members of the class of Thermal Engines. Being HOT is what they do. That's how they generate thrust.

... here are some images to get things cooking...

Wow. Interesting. Yeah. Right. Okay.

I don't mean to be ugly about this, but I was drawing better rockets using paper and pencil back in the ninth grade. But then, I was reading Robert Heinlein and Isaac Asimov, so I already knew something (real) about rocket propulsion and physics.

 

Er... Uhhh... have a nice day. ;)

[Moontanman]

Hey pyro, night grade huh? i was designing nuclear engines then, i had huge detailed drawings of nuclear reactors for surface to orbit craft. I also drew up designs powered by ozone and hydrogen, tanks of frozen ozone and frozen hydrogen to save space. Of course I went nuts at 17 and got married and the rest is history or actually not history, ;) I still think nuclear is the only real option, if we lived on Mars things would be easier (space elevator made out of kevlar!) but the Earth has high gravity and well you know what that means...

[Pyrotex]

Hey pyro, ninth grade huh? i was designing nuclear engines then, i had huge detailed drawings of nuclear reactors for surface to orbit craft. ...

Yeah! Me too! I still have one drawing I did when I was about 18. It was spherical, about 500 ft in diameter, had maybe a dozen decks, each deck diagrammed with staterooms, life support, computers, etcetera. It was powered by eight fusion engines clustered on the outside of the hull. The fusion engines were driven by a circular particle accellerator. There were bays for four chemical rocket craft for making landings on airless moons and asteroids.

 

So much fun. So much fun. ;) :doh: :eek2:

[Pyrotex]

The Air Breather's Burden (ABB)

 

I found a **wonderful** short article by a Mr. Spencer, on a variant of the classic Rocket Equation (CRE), derived by Mr. Zubrin, of manned mission to Mars fame. It expands the CRE to show the effects of breathing air to get your oxidizer on a basic SSTO rocket. This would be the ABB variant of the CRE.

 

Take a look