So why not space planes?

[t0p]

I'm not a complete idiot, but physics has never been one of my strong points. So maybe someone with a better understanding of these things can explain this to me:

I've got a plane, right, with jet engines, rocket engines, and a wide wingspan. So, I take off, slowly gain altitude; when the air at high altitude is too thin to keep the jets working, the rockets kick in. I carry on gaining altitude, and eventually I pass the "boundary" where atmosphere becomes space. So I've attained space travel, without the need for booster rockets and the rest of the multi-billion dollar kit. Right?

Why doesn't that work? Why are we still messing round with rockets? Why isn't the "space plane" a viable way to get satellites into orbit?

[slackthumbz]

I'm not a complete idiot, but physics has never been one of my strong points. So maybe someone with a better understanding of these things can explain this to me:

I've got a plane, right, with jet engines, rocket engines, and a wide wingspan. So, I take off, slowly gain altitude; when the air at high altitude is too thin to keep the jets working, the rockets kick in. I carry on gaining altitude, and eventually I pass the "boundary" where atmosphere becomes space. So I've attained space travel, without the need for booster rockets and the rest of the multi-billion dollar kit. Right?

Why doesn't that work? Why are we still messing round with rockets? Why isn't the "space plane" a viable way to get satellites into orbit?

http://en.wikipedia.org/wiki/Escape_velocity

[Blutkoete]

You should also consider that coming down is also a problem (http://en.wikipedia.org/wiki/Heat_shield).

[Paqman]

Why doesn't that work? Why are we still messing round with rockets? Why isn't the "space plane" a viable way to get satellites into orbit?

In short: rockets are the only engine we've got that is reliable and powerful enough to climb into orbit.

The amount of energy it takes to lift something into orbit is enormously larger than it takes to get a plane to high altitude. You need to go much, much, much faster and a lot higher. This means you want to minimise the weight of your vehicle. Anything that isn't payload or avionics needs to be either engine or fuel (and most of that fuel is used to lift its own weight). So lugging around wings, air-breathing engines and all the other assorted cruft that's no use outside the atmosphere will just make your vehicle less efficient.

Hybrid aircraft/rocket systems do exist. Burt Rutan's X-prize winning system that is being developed into Virgin Galactic's new vehicle(s) (http://en.wikipedia.org/wiki/Scaled_Composites_SpaceShipTwo) is a good example. But that only does suborbital hops. It's more a very high altitude aircraft than a real space ship.

The US military are quite interested in hypersonic transatmospheric spaceplanes, as it would give them the ability to bomb anywhere in the world from bases in the US. NASA are definitely doing the research into hypersonic vehicles, but they're using some pretty gnarly propulsion. I wouldn't expect to see practical spaceplanes for good few years yet.

[cascade9]

No one has got into orbit (yet) froma hybird rocket/engine craft, but 'space' (at least the edge of) has already een done-

http://en.wikipedia.org/wiki/SpaceShipOne

http://en.wikipedia.org/wiki/Scaled_Composites_SpaceShipTwo

If, or when really, the concept has been proved, spaceship 2 works, they are going to build 'spaceship 3'- which will have true sub-orbital capabilities. Given the amount of funding that Rutan had to play with, if anybody wanted to spend anything like the budget that has been spent on rockets or even a nice % of that money, hybrid would be a clear winner. IMO anyway.

[Tristam Green]

No one has got into orbit (yet) froma hybird rocket/engine craft, but 'space' (at least the edge of) has already een done-

http://en.wikipedia.org/wiki/SpaceShipOne

http://en.wikipedia.org/wiki/Scaled_Composites_SpaceShipTwo

If, or when really, the concept has been proved, spaceship 2 works, they are going to build 'spaceship 3'- which will have true sub-orbital capabilities. Given the amount of funding that Rutan had to play with, if anybody wanted to spend anything like the budget that has been spent on rockets or even a nice % of that money, hybrid would be a clear winner. IMO anyway.

SR-71
X-15
U-2 (ultra-high-alt, edge of space)

t0p: the first two replies have your answers. the problem is escape velocity (Earth's gravity well isn't huge, but more than enough to keep us firmly planted lol), and the other problem is heat shielding for re-entry. One adds weight (heat shield) and both are immensely expensive, especially in terms of finding reusable means of doing so.

[cascade9]

SR-71
X-15
U-2 (ultra-high-alt, edge of space)


U-2- maximum altitude 70,000ft (roughly 21,500m). Prety much impossible to go higher than that, at that height its stall speed was only about 20k/ph less than its maximum speed.
Sr-71- maximum altitude (according to lockheed) 80,000ft (roughly 25,000m). Unoffically, it could get to at least 85,000ft, with 100,000ft the very edge of possibility. Very high, but still not space.
X-15- its a rocket with wings, not really what the OP was after. True, it did go over the 100Km 'space barrier' but only 2 times as far as I know.

[sdowney717]

http://www.qrg.northwestern.edu/projects/vss/docs/space-environment/2-whats-escape-velocity.html

need to go 7 miles per second

frankly speaking the gravity well prevents you from leaving earth.
however why cant a space ship simply climb at say 100 mph and in several days you will escape the earth. You can if you have enough fuel and an engine to do this.

I will quote someones post here
http://www.physicsforums.com/archive/index.php/t-178647.html


Right around 11 km/sec to totally escape, about 8 km/sec to attain orbit.
One thing that is often taken for granted is that escape velocity is an artificial hurdle set by technology.

You need to achieve that velocity before you run out of fuel and your engines shut down. You will need that velocity to be able to coast out of Earth's gravity well.

On the other hand, if you have a (futuristic) fuel supply that is unlimited, then there is no such thing as escape velocity. You could lift off and gain altitude at a rate of one mile per hour all the way to the Moon if you wanted to.

[Tristam Green]

U-2- maximum altitude 70,000ft (roughly 21,500m). Prety much impossible to go higher than that, at that height its stall speed was only about 20k/ph less than its maximum speed.
Sr-71- maximum altitude (according to lockheed) 80,000ft (roughly 25,000m). Unoffically, it could get to at least 85,000ft, with 100,000ft the very edge of possibility. Very high, but still not space.

forgive me for laughing at anyone accepting official numbers.



X-15- its a rocket with wings, not really what the OP was after. True, it did go over the 100Km 'space barrier' but only 2 times as far as I know.

Yes, the X-15 was a rocket with wings, and broke the 100km barrier, it qualifies as a space plane :confused:

http://en.wikipedia.org/wiki/Rockwell_X-30 <-- effectively a big X-15 that uses scramjets and rocket engines :|

[John Bean]

why cant a space ship simply climb at say 100 mph and in several days you will escape the earth. You can if you have enough fuel and an engine to do this.

More fuel equals more mass, which needs more fuel to achieve/maintain the required velocity. It's a catch-22 situation partially addressed by the use of multi-stage launch vehicles that are thrown away to reduce mass as they become empty of fuel.

[Blutkoete]

Please don't forget that reaching escape velocity doesn't mean it makes >>poof<< and you left Earth's gravity field.

In 5000 km (3107 miles) above Earth (e.g. http://en.wikipedia.org/wiki/LAGEOS), there is still 70% of Earth's gravity. If you stop moving or slow down, you start falling down (to be exact, they are falling all the time, but their's speed compensates it). That's why coming down (http://www.youtube.com/watch?v=WowZLe95WDY) isn't that easy - entering Earth's atmosphere at high velocities is dangerous.

People on the ISS aren't weightless, they just feel weightless because they move so fast.

Of course, with an unlimited supply of fuel, that doesn't matter, but most things don't matter with an unlimited supply of fuel.

[donkyhotay]

Of course, with an unlimited supply of fuel, that doesn't matter, but most things don't matter with an unlimited supply of fuel.

Which is why a space elevator or skyhook or something similar is kind of the holy grail of spaceflight, fuel becomes almost a non-issue. Something like that would make it really cheap to get into space and if it was easy to reach geo then it would be a pretty simple matter of launching things to the moon or other planets. If you built a space elevator that extends past geo then theoretically you could launch a spaceship by simply going to the end and just letting go at the right time, your ship flies off into space on it's own and physics does the rest (think of it working like a *really* big sling).

[Paqman]

however why cant a space ship simply climb at say 100 mph and in several days you will escape the earth.

Doesn't quite work like that.

Think of throwing a ball. If you throw a ball at a certain speed, it travels in a parabola, until it hits the ground again. If you throw it faster, it goes further until it's parabolic arc reaches ground level again.

In order to get into orbit, you need to throw it so hard that the arc matches the curvature of the earth. Basically the curvature of the earth is such that the ground is dropping away from you at the same rate that you're falling towards it. Reaching orbit is all about going phenomenally quick.

You better have a really strong arm to throw your ball that hard, btw.

[cascade9]

forgive me for laughing at anyone accepting official numbers.

Like I ever accept the offical line. I've not spoken to anyone directly, but I know people who know people.....

100,000ft is the highest I've ever heard anyone say that the SR71 could go. Even if it could go higher, there is no way its going to hit 100km where space 'offical' starts.

If you want more for you list of 'goes really high' then you can add these-

Mig-25 set an 'absolute' maximum altitude reccord of 123,00ft (37,500m). That is not teh same as what the other figures, because they were set in lwevel fligh, not in a power climb.
The A-12 (SR-71 precursor) could hit 95,000ft offically. Mainly because it was the same basic consturction as the Sr-71, but was short and lighter. I doubt that it could go any higher than the Mig-25s absolute though.



Yes, the X-15 was a rocket with wings, and broke the 100km barrier, it qualifies as a space plane :confused:

http://en.wikipedia.org/wiki/Rockwell_X-30 <-- effectively a big X-15 that uses scramjets and rocket engines :|

Forgive me for laughing, twice, at a wikipedia page on a plane that was canceled before it even got a prototype, and was announced by 'star wars' Reagan. :lolflag:

[philinux]

.

People on the ISS aren't weightless, they just feel weightless because they move so fast.



The feel weightless because they are in a constant state of free fall around the earth. Ultimate skydive!!

[Blutkoete]

The feel weightless because they are in a constant state of free fall around the earth. Ultimate skydive!!

Like the one in the last Star Trek movie, only permanent & without having to rescue Vulcan ;).

[Tristam Green]

Forgive me for laughing, twice, at a wikipedia page on a plane that was canceled before it even got a prototype, and was announced by 'star wars' Reagan. :lolflag:

Cancelled, reborn as the X-43, which was air-dropped by the same B-52 that dropped the X-15 :D

And so what if it was announced by Reagan? The math was sound, it was just the materials and cost that drove it under :(

[HermanAB]

The problem is that the earth sucks - really badly.

The second problem is that there is nowhere worth going to - so why bother?

The second point above is the main reason why space exploration is pretty much dead. There isn't anywhere to go to. We are stuck on this rock - sorry.

[Paqman]

There isn't anywhere to go to.

There is (quite literally) everywhere to go. The main obstacle to space exploration is the prohibitive cost of lifting mass out of Earth's gravity well, not any lack of imagination or destinations. The dozens of worlds and moons in our solar system alone will provide hundreds of years of exploration and discoveries.

[HermanAB]

why cant a space ship simply climb at say 100 mph
and in several days you will escape the earth

It can, but it will use an enormous amount of fuel to keep firing the engine for several days. This is not practical with a chemical rocket. Eventually if you do manage to get away from the earth, you will fall either into the sun or into another larger planet such as Jupiter, or another one of the gas giants.

That technique will only work if you have a practically inexhaustible amount of energy and reaction mass. E.g. a nuclear reactor and a huge dust scoop for gathering reaction mass to use in an interplanetary ram jet fashion.

[madjr]

a better way to reach space might be the space elevator :D




http://en.wikipedia.org/wiki/Space_elevator

http://www.howstuffworks.com/space-elevator.htm

[betrunkenaffe]

Just going to copy paste this out and then someone can tell me what I'm misunderstanding:


In fact a vehicle can leave the Earth's gravity at any speed. At higher altitudes, the local escape velocity is lower. But at the instant the propulsion stops, the vehicle can only escape if its speed is greater than or equal to the local escape velocity at that position. As is obvious from the equation, at sufficiently high altitudes this speed approaches 0 as r becomes large.

The issue isn't that you can't take off and slowly escape Earth's orbit because as long as you maintain an upwards ascent, you will eventually leave. The issue is propulsion, all current technology that provides sufficient force to exceed the escape velocity is based on combustion. When you get high in the atmosphere, the air is too thin and so even combustion becomes unreliable. We would need sufficient speed in order to maintain our escape velocity even after the engines stop generating enough force.

The ball analogy is fine if you assume you are doing all your force once and never again afterwards, no flight is based on that.

[HermanAB]

There is (quite literally) everywhere to go.

Nope - Consider the opposite argument:
If Mars and/or Venus were green and wet with plants, animals and other things capable of sustaining human beings, then there would have been a race to colonize and space travel between the planets would have been a reality.

As it is, Mars and Venus are not green and space exploration is dead and will remain so, until we can figure out how to travel to another star system. Travel in our own star system is useless, since we cannot gain anything from it.

There simply isn't anything out there, that we don't already have down here. Sorry...

[Tristam Green]

why cant a space ship simply climb at say 100 mph
and in several days you will escape the earth

It can, but it will use an enormous amount of fuel to keep firing the engine for several days. This is not practical with a chemical rocket. Eventually if you do manage to get away from the earth, you will fall either into the sun or into another larger planet such as Jupiter, or another one of the gas giants.

That technique will only work if you have a practically inexhaustible amount of energy and reaction mass. E.g. a nuclear reactor and a huge dust scoop for gathering reaction mass to use in an interplanetary ram jet fashion.

I remember some old designs for massive "Generation Ships" with that very concept.

[Blutkoete]

The issue isn't that you can't take off and slowly escape Earth's orbit because as long as you maintain an upwards ascent, you will eventually leave.

As long as you maintain an upwards ascent, you will leave. But this is not an one-dimensional problem of flying in one direction, it's a multidimensional problem of forces pushing you towards space while other forces try to pull you down.

[John Bean]

There simply isn't anything out there, that we don't already have down here.

I wonder how many times that sort of thing has been said to explorers over the millennia... and how many times it proved to be untrue.

[Blutkoete]

I wonder how many times that sort of thing has been said to explorers over the millennia... and how many times it proved to be untrue.

Max Planck (quantum physics) was advised not to study physics because "everything to be found has already been found". That was at the beginning of the 20th century.

[Paqman]

The ball analogy is fine if you assume you are doing all your force once and never again afterwards, no flight is based on that.

You have to shut off your engine at some point. Even ion engines have limited fuel, and you'll never get off the ground with one of those.

[Paqman]

Nope - Consider the opposite argument:
If Mars and/or Venus were green and wet with plants, animals and other things capable of sustaining human beings, then there would have been a race to colonize and space travel between the planets would have been a reality.


Forget sending humans. Unless we start creating new types of human designed for alien environments you're never going to have colonies on other other worlds. Small outposts maintained at huge expense maybe, but not colonies. For the current model of homo sapiens, Earth is where we'll stay, but that doesn't mean we won't have a presence in space and on other worlds.

Space exploration is a game for machines, not people. The practical obstacles for human space flight even within the solar system will ensure that for the forseeable future. When you start talking interstellar distances then IMO we'll never be sending human meat that kind of distance. Digitised human or AI consciousness could be transmitted across interstellar distances cheaply and quickly, but the sci-fi idea of sending a clunky box full of humans across light years just stretches credibility.



Travel in our own star system is useless, since we cannot gain anything from it.


Is knowledge worth nothing? Humans love to explore, and there's plenty of stuff out there to keep us interested. Just look at all the cool things we've discovered in the solar system in just the last few years.

[sdowney717]

Earth is a kind of space ship.
I wonder how happy people would be on a true interstellar space ship.
Considering they would likely be on it till their dead.
You likely wont be coming back.
It would be a different story if you could go and come back to tell someone about it. and could travel huge distances quickly, otherwise it is a tomb.

[Frak]

There is (quite literally) everywhere to go.

Nope - Consider the opposite argument:
If Mars and/or Venus were green and wet with plants, animals and other things capable of sustaining human beings, then there would have been a race to colonize and space travel between the planets would have been a reality.

As it is, Mars and Venus are not green and space exploration is dead and will remain so, until we can figure out how to travel to another star system. Travel in our own star system is useless, since we cannot gain anything from it.

There simply isn't anything out there, that we don't already have down here. Sorry...
Everything that can be invented has been invented?

[donkyhotay]

There is (quite literally) everywhere to go.

Nope - Consider the opposite argument:
If Mars and/or Venus were green and wet with plants, animals and other things capable of sustaining human beings, then there would have been a race to colonize and space travel between the planets would have been a reality.

As it is, Mars and Venus are not green and space exploration is dead and will remain so, until we can figure out how to travel to another star system. Travel in our own star system is useless, since we cannot gain anything from it.

There simply isn't anything out there, that we don't already have down here. Sorry...

Thats because (like most people) you're stuck on the idea of planets. Colonizing planets is a bad idea because of the cost inherent in escape velocity. On the other hand once you're out in space there are many asteroids/moons/etc. out there to live on. No need to mess with planets, just build orbitals around the sun, after a few generations you'll be so used to living there that there won't be much reason to hang around the sun and (assuming you have decent engines/fuel) you just slowly wander out to the next star. Centuries later you arrive, once there you spend a century or two building more orbitals (ignoring the planets) and expanding through the new system. Once you're ready you simply go off to the next star system (each orbital going it's own way) and continue doing this practically forever. Not tying ourselves to planets we can survive long after the point where the universe isn't creating main sequence stars (the kind necessary for planets to be habitable for us) since you just need stars for energy (and potential asteroids/comets/etc floating in their vicinity). Theoretically we can continue surviving this way until the red dwarfs all go out (and they're the longest lasting star types known). A race that does this is a race that I would bet will survive for a long time. A race that keeps itself stuck on planets (even if it colonizes other planets) is going to have issues in the long run when the stars go out (assuming they even last that long).

[Frak]

Thats because (like most people) you're stuck on the idea of planets. Colonizing planets is a bad idea because of the cost inherent in escape velocity. On the other hand once you're out in space there are many asteroids/moons/etc. out there to live on. No need to mess with planets, just build orbitals around the sun, after a few generations you'll be so used to living there that there won't be much reason to hang around the sun and (assuming you have decent engines/fuel) you just slowly wander out to the next star. Centuries later you arrive, once there you spend a century or two building more orbitals (ignoring the planets) and expanding through the new system. Once you're ready you simply go off to the next star system (each orbital going it's own way) and continue doing this practically forever. Not tying ourselves to planets we can survive long after the point where the universe isn't creating main sequence stars (the kind necessary for planets to be habitable for us) since you just need stars for energy (and potential asteroids/comets/etc floating in their vicinity). Theoretically we can continue surviving this way until the red dwarfs all go out (and they're the longest lasting star types known). A race that does this is a race that I would bet will survive for a long time. A race that keeps itself stuck on planets (even if it colonizes other planets) is going to have issues in the long run when the stars go out (assuming they even last that long).
Theoretically, we could survive forever without the need of any natural energy emitter; the fusion reactor just hasn't reached fruition yet.

[Paqman]

No need to mess with planets, just build orbitals around the sun

+1

Once you've got a good energy source and the ability to manage a self-contained ecosystem then colonising open space is reduced to an engineering problem. It's incredibly unlikely that we'll ever find planets or moons that are similar enough to Earth that even heavily modified humans could live there. So if you're going to build an artificial environment to live in, why do it on the surface of an a planet or moon when you could do it more cheaply in space?

[Frak]

+1

Once you've got a good energy source and the ability to manage a self-contained ecosystem then colonising open space is reduced to an engineering problem. It's incredibly unlikely that we'll ever find planets or moons that are similar enough to Earth that even heavily modified humans could live there. So if you're going to build an artificial environment to live in, why do it on the surface of an a planet or moon when you could do it more cheaply in space?
Or when when we wake up, get rid of the idea that greed drives the human race, and build these for the sheer need of them and not based on a stock price.

[98cwitr]

just hook a big cable to the moon and wench...bam, space gondola

[donkyhotay]

Theoretically, we could survive forever without the need of any natural energy emitter; the fusion reactor just hasn't reached fruition yet.

If I remember my astronomy/physics correctly, by the time the red dwarfs go out most matter will be locked up in the corpse of stars (black holes, neutron stars, etc.) and won't be accessible (barring super-tech we can't theorize at this point). There would still be a few nebulae floating around from the last novae however if we've been spreading out the entire time there will be so many of us that those few little pockets of easily accessible matter will be (relatively) pretty meager. I'll admit I could be completely off here since I'm not an expert on the subject.


Or when when we wake up, get rid of the idea that greed drives the human race, and build these for the sheer need of them and not based on a stock price.

Sadly I doubt that'll happen any time soon, if we as a species was focused more on communal need and less on individual greed then everything would be FOSS.

[Frak]

If I remember my astronomy/physics correctly, by the time the red dwarfs go out most matter will be locked up in the corpse of stars (black holes, neutron stars, etc.) and won't be accessible (barring super-tech we can't theorize at this point). There would still be a few nebulae floating around from the last novae however if we've been spreading out the entire time there will be so many of us that those few little pockets of easily accessible matter will be (relatively) pretty meager. I'll admit I could be completely off here since I'm not an expert on the subject.
As far as I'm aware, you're correct, but I have hopes that we'd found a way around that by then. What about matter-synthesis? Just because it's said matter can't be created doesn't mean it won't be broken in the future.

[Warthaug]

There simply isn't anything out there, that we don't already have down here. Sorry...

Right up until the earth get's hit by a asteroid, or we humans do something unsurvivable to the environment.

All species on earth eventually go extinct. If we want to avoid that we have only one option - leave earth. Right now all the eggs are in one basket...

Bryan

[Paqman]

Or when when we wake up, get rid of the idea that greed drives the human race, and build these for the sheer need of them and not based on a stock price.

Economics isn't about greed, it's about the fact that there's a finite amount of energy and resources available. Even in a completely altruistic, greed free society efficiency would still be something to strive for. Building things in an inefficient (ie: expensive) way will never be a good thing.

In reality of course, human nature isn't going to change much. So everything will always have a price tag on it.

[Ebere]

Doesn't quite work like that.

Think of throwing a ball. If you throw a ball at a certain speed, it travels in a parabola, until it hits the ground again. If you throw it faster, it goes further until it's parabolic arc reaches ground level again.

In order to get into orbit, you need to throw it so hard that the arc matches the curvature of the earth. Basically the curvature of the earth is such that the ground is dropping away from you at the same rate that you're falling towards it. Reaching orbit is all about going phenomenally quick.

You better have a really strong arm to throw your ball that hard, btw.

Or in other words... Throw your ball at the ground, and miss on purpose...

[Tristam Green]

Or in other words... Throw your ball at the ground, and miss on purpose...

That's just the secret to flying, silly.

[Frak]

Economics isn't about greed, it's about the fact that there's a finite amount of energy and resources available. Even in a completely altruistic, greed free society efficiency would still be something to strive for. Building things in an inefficient (ie: expensive) way will never be a good thing.

In reality of course, human nature isn't going to change much. So everything will always have a price tag on it.
I'm just saying that we're nearing a point in the human race where all resources (besides water) are becoming non-finite. We have the technology now to produce energy without the need of a finite-resource with no by-product. When humans no longer need to participate in the means of production, we can focus on the intellectual aspects of protecting our species as opposed to arguing over what resources go where.

We are living in an age where we can now produce materials stronger than the strongest metals for a millionth of the cost, but because scarce resources sell better, it hasn't really been developed into fruition. (I'm looking at you, Buckminsterfullerene).

[Ebere]

Build a space plane, mostly for re-entry.

Put it on the back of a really big plane which has the capability of reaching the edge of space.

Fly the big plane up there, let the space plane take off, then fly the big plane back down.

The space plane does not have to carry as much fuel, to get itself into space, and more weight can be given over to re-entry measures. (Heat shield, etc.)

No, wait. I think that's been done.

Why don't they still do that ?

[Frak]

Build a space plane, mostly for re-entry.

Put it on the back of a really big plane which has the capability of reaching the edge of space.

Fly the big plane up there, let the space plane take off, then fly the big plane back down.

The space plane does not have to carry as much fuel, to get itself into space, and more weight can be given over to re-entry measures. (Heat shield, etc.)

No, wait. I think that's been done.

Why don't they still do that ?
The fuel for the larger plane is crazy expensive.

[donkyhotay]

As far as I'm aware, you're correct, but I have hopes that we'd found a way around that by then. What about matter-synthesis? Just because it's said matter can't be created doesn't mean it won't be broken in the future.

Matter synthesis is possible but requires energy to do. We can convert matter to energy right now, and we can theoretically convert energy to matter in the future (star trek replicators). Problem is we need one or the other. So we either have a large debris field we harvest or we hang out near a star and soak up the power. However if we can't access the matter cause it's locked in an inaccessible form (trapped in a black hole) *and* we can't get enough energy from radiation (stars gone out) then we're toast. Theoretically we can get some power from from the proton decay of the stellar corpses and hawking radiation from the black holes but this is pretty minimal by our standards and even with super-tech efficiency I don't think it would be enough. Even if it was enough once those all evaporate away then thats pretty much it unless we figure out how to create new universes (possibly tapping into the quantum foam). Even still, if we're going to have any hope of surviving for as long as we can we need ditch the idea of colonizing/living on planets which is my original point.

[Warthaug]

just hook a big cable to the moon and wench...bam, space gondola

The moon orbits the earth too slowly for that to work. You'd either snap the cable, or the earth would reel in the moon fishing-rod style.

Bryan

[Paqman]

The space plane does not have to carry as much fuel

If you're talking about reaching orbit, then you'd still need a sizeable percentage of the fuel you would if you just took off from ground level. The difference between the energy cost to fly to the edge of space and the cost to make low earth orbit is pretty big.

For less energy-consuming suborbital hops, then what you describe is exactly what Virgin Galactic will be doing.

[Ebere]

The fuel for the larger plane is crazy expensive.

As expensive as the fuel for those 'over compensation'-shaped rockets they are now using ? (And all the hardware that just gets kicked off.)

[Warthaug]

As expensive as the fuel for those 'over compensation'-shaped rockets they are now using ? (And all the hardware that just gets kicked off.)

In the end, the big plane will probably cost you more. The amount of energy needed to get to the edge of space is but a tiny percentage of the amount needed to achieve even the lowest of stable orbits.

Hence, using a big plane doesn't save you much in terms of the total fuel your space plane uses, and your minimal fuel savings come at the cost of a large, fuel-hungry plane.

Like paqman said, a carrier plane is great for suborbital hops; not so great if you want to get into orbit.

Bryan

[98cwitr]

The moon orbits the earth too slowly for that to work. You'd either snap the cable, or the earth would reel in the moon fishing-rod style.

Bryan

moon-reel ftw


jp, good point though.

[donkyhotay]

The moon orbits the earth too slowly for that to work. You'd either snap the cable, or the earth would reel in the moon fishing-rod style.

Bryan

Strangely enough it is theoretically possible for us to do that with mars. Deimos orbits at just a little bit slower then the rotation of mars. Although we don't have the tech now it is theoretically possible for us to adjust deimos into an orbit where it would function as the end of a space elevator on mars. The biggest problem with this would be phobos as it passes directly between mars and deimos in it's orbit and would interfere with a space elevator there.

[Ebere]

Strangely enough it is theoretically possible for us to do that with mars. Deimos orbits at just a little bit slower then the rotation of mars. Although we don't have the tech now it is theoretically possible for us to adjust deimos into an orbit where it would function as the end of a space elevator on mars. The biggest problem with this would be phobos as it passes directly between mars and deimos in it's orbit and would interfere with a space elevator there.

If you can move diemos, you can move phobos.

And if you are going to that trouble for a lunar system on another planet, so far away, I'd think you'd probably go to that trouble for our own moon, first.

[Warthaug]

If you can move diemos, you can move phobos.

And if you are going to that trouble for a lunar system on another planet, so far away, I'd think you'd probably go to that trouble for our own moon, first.

Not quite as simple of that. Its a matter of scale. Deimos and Phobos are very tiny (10^15 kg-ish), basically large asteroids, so moving them is "trivial". Our moon is enormous (10^22 kg), one of the largest moons in the solar system, and . So moving it is not trivial. Not to mention, placing it in geosynchronous orbit would raise enormous tides on earth.

Bryan

[Sporkman]

Strangely enough it is theoretically possible for us to do that with mars. Deimos orbits at just a little bit slower then the rotation of mars. Although we don't have the tech now it is theoretically possible for us to adjust deimos into an orbit where it would function as the end of a space elevator on mars. The biggest problem with this would be phobos as it passes directly between mars and deimos in it's orbit and would interfere with a space elevator there.

You could have the cable oscillate such that it reaches its peak displacement as Phobos passes through (read about that in one of those Mars novels).

[Mr. Picklesworth]

Not quite as simple of that. Its a matter of scale. Deimos and Phobos are very tiny (10^15 kg-ish), basically large asteroids, so moving them is "trivial". Our moon is enormous (10^22 kg), one of the largest moons in the solar system, and . So moving it is not trivial. Not to mention, placing it in geosynchronous orbit would raise enormous tides on earth.

Expanding on that last point, messing with Earth's moon would be an incredibly dumb mistake. It would be a slightly more stylish way to go out than being unexpectedly blown up by a giant asteroid impact, and it could create an interesting scenario for some future civilization, but it certainly would not end well for us. Water is important stuff, after all, and the moon has a fascinating effect on it.

There is a pretty detailed Wikipedia article on space planes (http://en.wikipedia.org/wiki/Spaceplane). I keep being reminded of the Kliper (http://en.wikipedia.org/wiki/Kliper) spacecraft proposal, which probably isn't going anywhere but has some interesting stuff. One design would have a separate “space tug” that stays in orbit, and Kliper would dock with it after launching. Unfortunately, the launching mechanism is pretty weak ;)

It's pretty well realized that the only way to get a ship big enough that it will support a crew to Mars, for example, is to assemble it in orbit. As I understand it, one of the lasting benefits of ISS is that it is just such a thing (granted, not exactly mobile, but pretty huge), so it provides a lot of information and field experience.

If you happen to have a copy of Windows at hand, this simulator is a great way to learn about space flight:
http://en.wikipedia.org/wiki/Orbiter_(simulator)
Preview release here (the 2006 release is puny by comparison): http://orbiter-forum.com/project.php?projectid=1

Orbiter has a steep learning curve, but it's incredibly satisfying to launch a space shuttle from Earth, dock with the space station, then land back at the Kennedy Space Centre. (And there is a nice tutorial to help you do so). When it's all done, you'll find that you've learned a lot, and probably have a sudden urge to become an astronaut.

[Warthaug]

If you happen to have a copy of Windows at hand, this simulator is a great way to learn about space flight:
http://en.wikipedia.org/wiki/Orbiter_(simulator)
Preview release here: http://orbiter-forum.com/project.php?projectid=1


I love orbiter, and I would recommend it to anyone interested in space flight. Some people have reported a degree of success with wine, but in my experience it has to be run under windows.

Bryan

[donkyhotay]

If you can move diemos, you can move phobos.

And if you are going to that trouble for a lunar system on another planet, so far away, I'd think you'd probably go to that trouble for our own moon, first.

As mentioned previously, moving our own moon is impossible within the forseeable near future (say the next 100 years or so) and a 100% stupid idea even if it was possible (just think of that lame time machine movie remake that came out a few years ago actually happening). Deimos is possible to move because it's so small, even then we're talking about moving it a relatively small amount. Even phobos would be difficult to budge enough that it wouldn't interfere with a space elevator however the idea of an oscillating elevator sounds familiar (I think I've heard of it somewhere as well) so it's possibly doable. Of course in a few million years phobos will disintegrate into a ring around mars which won't work with an oscillating elevator but hopefully by then we have something better. (c;

[Paqman]

You don't really need to attach the top of a space elevator to anything anyway. Just make sure it's centre of mass is in geosynchronous orbit and all is well.

[donkyhotay]

You don't really need to attach the top of a space elevator to anything anyway. Just make sure it's centre of mass is in geosynchronous orbit and all is well.

True, but if you have a convenient mass in the right location you might as well use it.