SPACE

[zip accident]

Darkflame wrote:

This venture will get commercial R&D into developing cheap and inefficiant ship designs, and thats exactly what we need. We have got a long way to go, but its a start.

Inefficient?

I'd also argue about needing lots of people to build a space elivator. We need some, but I dought we need more then the ISS has.

First off, we need a counterweight in geostationary orbit. The tether has to be a mile thick in order to be strong enough to support it's own weight, with the most efficient materials we can currently speculate about (a rope three miles long will break under it's own weight, with no load). To moor something that massive we'll need one of the major asteroids. They ain't light (they wouldn't be useful if they were), and currently, luckily (else they'd be seriously dangerous to all life on earth), they aren't that near.

If were going to do all of that with robots, they have to be built up there (and that means taking the materials up), or they have to be taken up ready built. Either way, people are lighter.

The asteroid belt is a long way off, and mining it is going to take people, unless robots improve an awful lot.

Theres nothing against this principle of flight being used to get into orbit.

Yes there is. It's inefficient. It costs fuel to get to altitude, on top of the fuel you spend getting up to speed.

I suspect the shuttle, or any ground base launch, has hit mach ten or more before it gets to the launch height of this thing, and by doing that it's lost a lot of weight. That's weight that has to be carried up to launch height for this sort of design.

If all you ever intend to do is sub-orbital trips around the bay, then the speed is immaterial, so long as you get high enough, so they can make this more and more efficient, and cheaper and cheaper, without it ever coming near to an orbital solution.

[Darkflame]

. The tether has to be a mile thick

umm? a mile THICK?
I think something is wrong there, most proposals I have seen are much thinner. (although,granted, still pretty thick).

I believe one popular design is carbon nanotube based ribbons of irregular thickness (thinnest at ground level,getting thicker, the tapering off again), rather then a "rope" as such, and most of the research seems to be going in to getting these materials more then a few inch's long.

If your saying with even the "most efficient materials we can currently speculate", and are talking of carbon nano based tubes, then Id like a source, as I believe their tensil strenth to weight ratio is much better then your saying.
Of course,traditional ropes, steal or whatever would indeed break under their own weight without stupidly thick tops.

Yes there is. It's inefficient. It costs fuel to get to altitude, on top of the fuel you spend getting up to speed.

This design of ship means you don't have to take the oxygen component of the fuel with you for a large chunk of the journey, making it massively more efficient then the shuttle which has to carry that extra weight with it. Its also many times lighter in engine design and caseing itself. (again, mostly due to the fuel difference).

Of course, this is a lightweight approach all around, I'm not saying it can take the same loads as the shuttle, but for human to space systems, developing this sort of system makes sense. It needs less energy because its lifting vastly less, put simply. So the weight that "has to" be carried up in terms of fuel wont be as much as the shuttle has to carry up.
(and, equally importantly, the cost of the fuel the shuttle has used by this height is also vastly more).
Its doing a different thing, and its doing it with a different engine.

If all you ever intend to do is sub-orbital trips around the bay, then the speed is immaterial, so long as you get high enough, so they can make this more and more efficient, and cheaper and cheaper, without it ever coming near to an orbital solution.

The two commercial pushes I would guess would be;
a) As you say, quick around the world trips. (using earths rotation to your advantage)
b) Weightless tourism.

To get decent time weightless, there will be a push towards orbital craft. Your still not weightless for very long with SS2.

And even if it is height, surely the higher you go, the less speed you need to reach orbit as gravity falls off ?
==
Also, as a side comment, do you know of any studies about fuel use of sub-orbital trips around the world?
I'm thinking one strong advantage might be that if these things can become "common place" they might actually be more environmentally friendly. Sure, they use more fuel to get up high, but they also are in the air for less time. (say, on a London to New York trip).
Of course, the number of people each trip would also have to increase. So its a mater of plotting curve of person/weight fuel use/time spent.



Also, what about my half-way solution?
Sure the rope would still have to be incredibly long and strong.
But not going all the way to the ground would remove a lot of secondary problems from the equation. (atmospherics, for instance). I'm also thinking the effort to get a delta shape on the end of the cable (the lower half having plenty of slack and elastic qualitys), would be easier then doing the additional distance to the ground.
I'm just curious if this has been preposed before anyway.

[zip accident]

Darkflame wrote:

Surely the higher you go, the less speed you need to reach orbit as gravity falls off ?

Gravity doesn't fall off, much, until you're a long way out. 18,000 mph is a low orbit, higher ones are faster. Escape velocity, where you actually break free of the earths gravity field (but not the suns), is 25,000 mph.

The Earth is big. The atmosphere is only marginally thicker in comparison than a coat of paint on a beach ball, if at all.

umm? a mile THICK?
I think something is wrong there, most proposals I have seen are much thinner. (although,granted, still pretty thick).

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

wikipedia wrote:

<unpasteable equation>

Using the density and tensile strength of steel, and assuming a diameter of 1 cm at ground level, yields a diameter of several hundred kilometers at geostationary orbit height, showing that steel, and indeed all materials used in present day mechanical engineering, are unsuitable for building a space elevator.

I don't know what you get from that equation if you plug in the numbers for carbon nanotubes, but I really doubt it will come in under a kilometre. I thought I remembered the figure of one mile from a previous discussion of this, four miles seems to ring a bell as well.

Seems there are some radiation problems too:

http://space.newscientist.com/article/d ... ation.html

I'm not sure I understand this one, but the people who seem to, seem to think it's a better idea.

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

Darkflame wrote:

This design of ship means you don't have to take the oxygen component of the fuel with you for a large chunk of the journey, making it massively more efficient then the shuttle which has to carry that extra weight with it.

Pilots need oxygen above 18,000 ft. Piston engines need superchargers too. I'm not convinced that the saving justifies getting to that altitude at such a low speed. The fuel the shuttle et. al. burn to get up to that height, is weight they don't have to carry from there on up, and they have the speed they've achieved already to build on.

Also, what about my half-way solution?
Sure the rope would still have to be incredibly long and strong.
But not going all the way to the ground would remove a lot of secondary problems from the equation.

It's difficult to hook up at the same speed.

http://en.wikipedia.org/wiki/XF-85_Goblin

http://en.wikipedia.org/wiki/F9C_Sparrowhawk

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

At mach <very silly indeed> the momentum that the craft would have to lose would make things very difficult indeed. You'd need an airport at the bottom of your tether, and that would be very heavy. Or you could try bringing the plane to a stall just below the end of the tether, which sounds like a recipe for missing it a lot. You'd be on rockets only at that point presumably, you wouldn't have the fuel for many attempts.

[teamonkey]

Gravity doesn't fall off, much, until you're a long way out.

It does fall off quite rapidly. At sea-level the force on a 1kg object is 9.81N. I've just done some back-of-the-envelope math (so I may be wrong by several orders of magnitude ), but at the top of the tether (geosynchronous orbit @ 35,768km above sea level) I make the force on a 1kg object to be about 0.22N.

I don't know what you get from that equation if you plug in the numbers for carbon nanotubes, but I really doubt it will come in under a kilometre. I thought I remembered the figure of one mile from a previous discussion of this, four miles seems to ring a bell as well.

It tells you on that wiki page:

A cable made of carbon nanotubes (a type of fullerene), would typically be just a millimeter wide at the base.

[benedictw]

NASA claims the taper factor for steel is 'tens of thousands' whereas Carbon nanotubes' taper factor is 21. Still doesnt mean its easily doable though.

[zip accident]

teamonkey wrote:

Gravity doesn't fall off, much, until you're a long way out.

It does fall off quite rapidly. At sea-level the force on a 1kg object is 9.81N. I've just done some back-of-the-envelope math (so I may be wrong by several orders of magnitude ), but at the top of the tether (geosynchronous orbit @ 35,768km above sea level) I make the force on a 1kg object to be about 0.22N.

I meant in relation to a plane/spaceship at 100 km up.

The diameter of the Earth is:

Wikipedia wrote:

12756.28 km

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

Call that 12,750 km approx.

Three quarters of the atmosphere's mass is within 11 km of the planetary surface.

In the United States, people who travel above an altitude of 80.5 km (50 statute miles) are designated astronauts. An altitude of 120 km (~75 miles or 400,000 ft) marks the boundary where atmospheric effects become noticeable during re-entry. The Kármán line, at 100 km (62 miles or 328,000 ft), is also frequently regarded as the boundary between atmosphere and outer space.

http://en.wikipedia.org/wiki/Earth's_atmosphere

If as you say geosynchronous orbit is @ 35,768km above sea level, that is over 3 earth diameters from the centre of the Earth. The difference between that far out and 100km above sea level is huge, at 100km there won't be enough distance from sea level to make any significant difference.

[zip accident]

teamonkey
It tells you on that wiki page:

A cable made of carbon nanotubes (a type of fullerene), would typically be just a millimeter wide at the base.

Yeah, but that's the tip.

It's the middle, up at the geosyncronicity point, that's thickest, and that's where I am talking about. I really don't know how to plug their number for nanotubes into their equation, or I would have done. And even then, they are talking about maybe materials that we might be able to make someday.

Thanks for letting me get the word "geosyncronicity" in, it's wonderful.

[Darkflame]

Yes its a great word.
I tried pluggin the numbers in myself but failed horribly.

Yes, I read the wiki artical after my post, but as it dosnt plug "speculative materials" into the equation I'm still not sure of this kilometer buisness.
It was my understanding that carbon nanotube based fibers could, in theory, lift 10's of thousands of times its own weight.
(for instance, this artical mentions a meterial that can lift 50,000 times its weight; http://www.memagazine.org/backissues/me ... dercl.html )

But again, dont know how that correlates to the maximum thickness point.

If as you say geosynchronous orbit is @ 35,768km above sea level, that is over 3 earth diameters from the centre of the Earth. The difference between that far out and 100km above sea level is huge, at 100km there won't be enough distance from sea level to make any significant difference.

Ok, accepted. The difference is marginal for that scale.
I was fooled by the atmosphere itself...I was thinking it must reduce a fair bit, else the atmosphere would be thicker for longer.

That said, height still gives you the advantage of the world taking longer to "drop off" under you, surely making orbit easier from a purely geometric standpoint?

It's difficult to hook up at the same speed.

http://en.wikipedia.org/wiki/XF-85_Goblin

http://en.wikipedia.org/wiki/F9C_Sparrowhawk

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

At mach <very silly indeed> the momentum that the craft would have to lose would make things very difficult indeed. You'd need an airport at the bottom of your tether, and that would be very heavy. Or you could try bringing the plane to a stall just below the end of the tether, which sounds like a recipe for missing it a lot. You'd be on rockets only at that point presumably, you wouldn't have the fuel for many attempts.

Yes, an airport would be out of the question.

I was thicking indeed that the burn could be timed so that the craft is at a near stand-still at its apex in relation to the delta and the rest of the energy distributed in the "up swing".
For aiming purpose's I was thinking some gps becons could locate the cable precisely for the craft, which could then adjust fuel use and aim accordingly?
Very Hard, certainly.
But i think everything we are talking about falls in that catagory one way or the other

Another advantage with this technique is flexibility. You wouldnt actualy need the elivator in geostationary orbit, you could have it at a lower one, so it trails above many countries.
Of course,youd run into poltical problems, but when financing a space elivator you might get more countries interested in helping if they could make use of it every X days.

Pilots need oxygen above 18,000 ft. Piston engines need superchargers too.

Sure. But I still think its signifcantly less then what the shuttle needs to carry.

[zip accident]

Darkflame wrote:

That said, height still gives you the advantage of the world taking longer to "drop off" under you, surely making orbit easier from a purely geometric standpoint?

Earth's diameter is 12,750km approx, so radius is 6,375km, 100km is 1/64th of that. It really isn't enough to make much difference at all.

A person standing up at sea level has Earth making up the lower half of their visual field, presumably 89.999999999 or so degrees. I doubt whether that changes to anything much below 85 degrees at 100km, but I could be wrong about that, flight sims like to make that earth fall away fairly fast.

If something was up at the geostationary point, but not in orbit, it would fall toward the Earth, gaining speed, and at that distance the Earth would be quite small, so easy to miss, and all the object has to do is miss the Earth, including the atmosphere, and it would be in orbit, having gained enough speed from the height it fell. A highly eccentric orbit, which would go up to the height it fell from, but an orbit.

At 100km, you're much too close for that to be useful.

Sure. But I still think its signifcantly less then what the shuttle needs to carry.

Well, it all comes down to proportions, the shuttle is relatively big and heavy, and carries a heavier payload. The question is, has the shuttle burned enough of it's fuel and oxygen by the time it gets to that height that the proportion of oxygen saved by not using rockets is of value. I suspect that by that height the shuttle has burned enough fuel etc that the advantage of not starting at ground level is minimal (or maybe negative), and on top of that the shuttle (or whatever rocket replaces it), has a lot of useful speed at that height, which the other device doesn't have.

Another advantage with this technique is flexibility. You wouldnt actualy need the elivator in geostationary orbit, you could have it at a lower one, so it trails above many countries.

At mach speeds? think of the friction! The counterweight would lose height, and crash down.

[Zoot]

Heads up guys - cold nights and clear skies make ISS watching very nice. Just got a lovely clear skies run that lasted 5 minutes, and it was so clear that you could make out the solar arrays for the whole run.

Lovely - don't forget HEAVENS ABOVE

[Zoot]

Shuttle launch tonight. Atlantis. Launch-time is 2:45pm EST which 19:45 our time, I think.

[F-ZeroOne]

Japan to build orbital solar power generator array. Republic of Azadistan [1] suddenly very worried.

http://www.engadget.com/2008/02/07/japa ... er-arrays/

[1] For that minority of YakYakers who aren't fans of Mobile SUIT GUNDAM - the latest GUNDAM series features the assembly of, and access to, a global network of solar power arrays as a major plot element. It would be easy to dismiss this announcement as coincidence, if various Japanese governmental organisations hadn't already revealed themselves to be the Worlds most otaku elected bodies.

[Fil]

As long as they don't start dropping space colonies on everyone.

[axel000]

So a safe docking today, can't wait to see the lab bay door opened. Hmmm new hardware.

On a down note, Armadillo Aerospace's lunar lander blew up on the pad today after a few very impressive flights at the x-price cup. Close to winning but not close enough.



Apparently the engine blew itself apart.

Lunar Lander Challenge trailer

More x-prize updates here.

[F-ZeroOne]

Rocket Science: it either works perfectly, or its falling in flaming pieces around a 50 mile radius.