It seems obvious to me that space travel will not become much cheaper until a hybrid engine is developed that breathes oxygen while in the atmosphere. Most of the cost of launching a rocket (at least to near earth orbit) is in fuel used getting out of the atmosphere. If we can use oxygen from the air we can save huge amounts of fuel, and make lighter rockets and save even more fuel...
Thatcher was an idiot to shelve the UK research into this. Is anyone else doing research?
That and a solar egg system. Air breathing i hope won't hurt the atmosphere you know how humans abuse technologies
| dwcnps wrote: |
It seems obvious to me that space travel will not become much cheaper until a hybrid engine is developed that breathes oxygen while in the atmosphere. Most of the cost of launching a rocket (at least to near earth orbit) is in fuel used getting out of the atmosphere. If we can use oxygen from the air we can save huge amounts of fuel, and make lighter rockets and save even more fuel...
Thatcher was an idiot to shelve the UK research into this. Is anyone else doing research? |
The Skylon spaceplane would use this engine: http://en.wikipedia.org/wiki/SABREcheapest way to get massive amounts of stuff into space would be to build a space elevator.
http://en.wikipedia.org/wiki/Space_elevator
http://science.nasa.gov/headlines/y2000/ast07sep_1.htm
http://www.space.com/businesstechnology/technology/space_elevator_020327-1.html
we don't have the tecnology to build one now, mainly because we don't have a material strong enough, but with advancements in nanotec and other fields, I'm confident that I'll see one before I die (another 60 years or so)
Whoa.
Dude, I'm working on my PhD in Nanotechnology, specifically MEMS/NEMS (Micro electro-mechanical systems/Nano electro-mechanical systems - basically nanomachines), and I think your prediction is waaaay off. Short of some unforseen breakthrough, it's going to be a lot longer than that before we can build a space elevator.
Even if we were to develop sufficiently strong materials to stand the tensile stresses of a space elevator, there are still failure modes to consider. For example, what happens if a small meteorite hits one of the cables on its way down? It would probably cut the cable. More likely than not, there would be redundant cables designed to take up the stress if one or more cables were cut, but that's not the problem. The problem is that the sudden change in stress in all of the cables will be a shock that travels repeatedly up and down the cables at the speed of sound (the speed of sound in the cables, not the speed of sound in air) until it is damped out. If there are any other nicks, scratches or imperfections in the cables, that shock wave will create local stresses many hundreds - maybe thousands - of times the current overall stress. That might trigger secondary failures, which would cause more shockwaves, triggering other failures, and so on - a cascading failure mechanism.
And of course, if there is a failure, what happens? That depends on a lot of factors, including the location of the break. You could end up throwing people out into deep space, or wrapping tens of thousands of kilometers of flaming cable around the Earth. Engineers can't always design things so that they never fail, so they settle for designing things that if they do fail, they fail in a way that causes as little loss of life as possible (for example, you can't stop a car from being wrecked in a crash, but you can design it to crumple in such a way as to absorb as much energy as possible and protect the people inside). But how do we do that for a space elevator?
It's not always a matter of material strength. The design is a big factor, too. We've had much of the same materials used in skyscrapers for hundreds of years. The trick is putting those materials together in a way that maximizes their strengths and minimizes their weaknesses. We don't yet have anything approaching a plausible design for a construction of that scale.
The scale of the project may not be beyond imagination, but it is certainly beyond current engineering. I wouldn't be counting on it in the next 60 years either. | Indi wrote: |
Whoa.
Dude, I'm working on my PhD in Nanotechnology, specifically MEMS/NEMS (Micro electro-mechanical systems/Nano electro-mechanical systems - basically nanomachines), and I think your prediction is waaaay off. Short of some unforseen breakthrough, it's going to be a lot longer than that before we can build a space elevator.
|
You never can tell about "unforseen breakthroughs", can ya.
Indi, I'm curious if you read the Wiki citation he gave. Failure is discussed and the writer's thought is that thermal destruction could be an answer to failure modes where the structure would tend to fall back to Earth. Thoughts?
This is not my field, but I would think that once construction and strength issues were overcome, designing failsafes would not be a roadblock. | HoboPelican wrote: |
You never can tell about "unforseen breakthroughs", can ya.
Indi, I'm curious if you read the Wiki citation he gave. Failure is discussed and the writer's thought is that thermal destruction could be an answer to failure modes where the structure would tend to fall back to Earth. Thoughts?
This is not my field, but I would think that once construction and strength issues were overcome, designing failsafes would not be a roadblock. |
For sure an unforseen breakthrough could occur at any time, but the problem is that dozens and dozens of such breakthroughs would be necessary to make a space elevator conceivably feasible in the next three or four decades (in order for one to actually be built within six).
Anyway, if the necessary breakthroughs really are unforseen then no-one's estimate - his or mine - has any validity. You can't factor the unfactorable in a factoring. So, sure, someone could come along and make a space elevator possible next week. But you can't really count on that when making your forecast for next week. So I can't really count on unforseen breakthroughs when projecting the possible development of a space elevator.
But no, I hadn't read that article, but yeah, I've heard the idea that if the cable pops at the top it would burn up rather than fall to Earth, but I don't find the logic of that comforting.
First, it certainly seems to presuppose the thermal properties of the materials used. But if you consider that the materials used would have to be relatively immune to thermal expansion (because over that length, even minute thermal expansion would have huge consequences in the geometry of the structure), hard as hell (to be strong enough to do the job and resist meteorite impacts) and have very low skin drag coefficients (so that the cable isn't affected too much by winds at various altitudes), then it's not such a leap to suppose that it would not be that easy to burn away to nothing. I mean, the shuttle comes in a hell of a lot faster than that cable would fall, and it survives with current materials that are not nearly capable of doing the job of a space elevator material.
Second, even if it that article is correct when it carefully states that the upper portions of the cable would burn up... what about the lower portions? You could still end up with thousands and thousands of kilometers of flaming cable falling down. You could end up tracing a line of destruction almost a quarter of the way around the equator - and that's without being affected by the upper portions of the cable, that's just the lower portions.
I'm not convinced this is doable within the next few decades. And it's not just that it's currently not possible, there's the auxiliary questions of economics, politics, social impact, etc. - science is happy to consider only the first issue, but engineering requires consideration of all of them. It's not just a matter of creating the material, it's about finding a way to manufacture a couple hundred kilometers of it economically. There is currently not that much available to us in space to justify that kind of expenditure. Who would control the elevator? Where would it be built? Compared to the actual mechanics of the construction of the thing, these may sound like trivial issues, but wars get fought over that kind of "trivial" stuff, so it cannot be ignored.Indi since you are studying nanotech i think i should ask this here.
I've read that nano robots are being made to look for cells that are infected with disease such as hiv. These robots destroy the cells that are infected. My question is, in reality, how close are we to making such things?
i think its funny that someone getting their PhD in nano/micro technology is contradicting the idea of what would be the largest man-made structure
| linexpert wrote: |
Indi since you are studying nanotech i think i should ask this here.
I've read that nano robots are being made to look for cells that are infected with disease such as hiv. These robots destroy the cells that are infected. My question is, in reality, how close are we to making such things? |
I'm not sure - I don't deal with the biological stuff. I have no idea how big or small a cell is, in relation to a NEMS, or what sensors and effectors a NEMS would need to detect and destroy a diseased cell.
I wouldn't hold my breath, though.
| superbonfire wrote: |
| i think its funny that someone getting their PhD in nano/micro technology is contradicting the idea of what would be the largest man-made structure |
You could be dropped in moments by a virus or killed by less than 200 μg of VX. A black hole smaller than the radius of an oxygen atom could destroy our entire solar system, given time.
The small stuff matters. | Indi wrote: |
| You could be dropped in moments by a virus or killed by less than 200 μg of VX. |
Was that a threat? 
Indi, size of bacteria ranges from approximately as small as the largest viruses to large enough for single cells to be visible by the naked eye. In numbers that's from about 0.1 to about 600 µm over a single dimension.
Does that help answer the question?
Edited 8:53
Actually, I found references to nano-baceria the size of virii. That about 20 to 250 nanometers, but so far little is known about them it seems. | HoboPelican wrote: |
| Indi wrote: | | You could be dropped in moments by a virus or killed by less than 200 μg of VX. |
Was that a threat? |
^_^
| HoboPelican wrote: |
Indi, size of bacteria ranges from approximately as small as the largest viruses to large enough for single cells to be visible by the naked eye. In numbers that's from about 0.1 to about 600 µm over a single dimension.
Does that help answer the question?
Edited 8:53
Actually, I found references to nano-baceria the size of virii. That about 20 to 250 nanometers, but so far little is known about them it seems. |
Nah, not really. See, it's not just a matter of relative size, it's a matter of what is necessary to first detect and second repair/destroy damaged or diseased cells.
For example, how do we currently determine whether a given cell is diseased or not? To my knowledge, a researcher looks at it through the microscope and makes a judgement call. Perhaps some chemical tests can be performed in a petri dish, but still, how are the results of those tests detected and interpreted? Doesn't a human observer still make the final judgement call?
In order for a NEMS to do what you're asking it to do, it has to be able to:- navigate in the medium the cells are in.
- detect the presence of cells in the surrounding medium and navigate to them.
- analyse the cells and determine what kind of cell they are.
- analyse the cells and determine whether or not it is a healthy cell given its cell type.
- take action to repair cell damage, or simply kill the cell in a way that does not allow whatever was infecting the cell to spread.
As I said, I don't actually deal with the biological end of things... yet (as much as I want to avoid it, I know it's inevitable that I have to deal with it eventually). I don't know what would be necessary to differentiate a healthy cell from a diseased one, or how a cell could be repaired/destroyed (could you just rend the cell wall apart and that would safely kill the cell and whatever was infecting it?). So I can't really give you a fair estimate on when such capability will be possible. | Indi wrote: |
| ...yet (as much as I want to avoid it, I know it's inevitable that I have to deal with it eventually). I don't know what would be necessary to differentiate a healthy cell from a diseased one, or how a cell could be repaired/destroyed (could you just rend the cell wall apart and that would safely kill the cell and whatever was infecting it?). So I can't really give you a fair estimate on when such capability will be possible. |
FYI-The current idea for drug delivery to cancerous cells is to tie the drug to a protien "key" that binds to specific cancer cells. This is not my area either, but listening to wife and her friends has given me that little bit of knowledge that can be dangerous. 
Possibly in the future, nanos could mimic a keyed structure from a biopsy sample...
Better to not think about it now. Been up for ....40 hours now and I need to crash.
