Global warming

[Frank]

Photovoltaic cells is mostly a niche product, they're quite resource intensive to manufacture and don't deliver very high output.

I agree with your post, but have to nitpick:

The main reason why photovoltaic cells are as expensive as they are, is because they use wafers and wafer steppers, that can also be used to make chips that have a mark-up value that is at least an order of magnitude higher than that photovoltaic cell, if you want to be able to sell the same volume for the same profit.

That makes them expensive niche products.

The efficiency is great, though, as you get the energy basically for free. The only reason why it's an issue is in the pay-back time.

 

[Frank]

Are you sure subsonic flight is that much more efficient Grall? I mean it seems a significant quantity of energy is simply spent fighting 10ms^-2 accelleration towards the ground of a 100,000kg plane.

Water is pretty hard if you hit it hard enough, while it is soft if you go slow. Air is like that at high speeds, especially around and beyond the sound barrier. And a bad air ripple will damage or even destroy the plane, so it's dangerous as well.

That's why most commercial planes stay below or around ~1000 km/h.

 

[KimB]

However, to really get space travel off the ground we need to get over our somewhat irrational fear of everything nuclear. Nuclear-thermal rocket engines have enormous thrust and scale up much better than conventional chemical rockets. That'll be the only way to bring significant payloads into orbit. It would also be safer, you wouldn't need heat shields and airbrake through the atmosphere to get back down, you'd just fire the main engines instead to slow down for re-entry instead.

So it's not politically correct, hauling nuclear reactors that weigh x tons up through the atmosphere, so what. It's the only really feasible way.

I'm not sure anybody has come up with a way to use a nuclear reactor to achieve lift to orbit. This sort of thing makes good sense for travel once orbit is reached (through ion propulsion, for instance), but I'm just not sure that they can effectively output enough power for a ground launch.

I really think the only way of making orbits cost effective is to construct a launch platform, akin to the space elevator, or the space pier. If you can get objects into an orbital position without the use of any rockets, you'll have solved nearly all of the problem with regards to energy requirements for cost-effective space travel.

 

[Squilliam]

Water is pretty hard if you hit it hard enough, while it is soft if you go slow. Air is like that at high speeds, especially around and beyond the sound barrier. And a bad air ripple will damage or even destroy the plane, so it's dangerous as well.

That's why most commercial planes stay below or around ~1000 km/h.

But I always figured fuel use was a balance between flight time and drag and it wasn't always a given that flying slower was more efficient given you have to keep aloft for a longer period of time.

 

[FUDie]

But I always figured fuel use was a balance between flight time and drag and it wasn't always a given that flying slower was more efficient given you have to keep aloft for a longer period of time.

Go ballistic... Then flight time is short and air drag is less.

-FUDie

 

[Grall]

it wasn't always a given that flying slower was more efficient given you have to keep aloft for a longer period of time.

Friction (including air, engine losses, all that kind of stuff) increses exponentially with speed, so you can't "win" the fuel race by throttling up. You WILL spend more by going faster.

 

[Grall]

Go ballistic... Then flight time is short and air drag is less.

This has its own set of complications unfortunately including how to lift a decent enough payload up above the atmosphere without spending a stratospheric amount of money doing so, and they tend to outweigh (no pun intended) the air drag issue...

 

[Blazkowicz]

the landing may be a bit rough

 

[hoho]

I'm not sure anybody has come up with a way to use a nuclear reactor to achieve lift to orbit.

http://en.wikipedia.org/wiki/Project_Orion_(nuclear_propulsion)
You could basically create a "rocket" that launches from ground and goes to Mars directly.

 

[Mariner]

Photovoltaic cells is mostly a niche product, they're quite resource intensive to manufacture and don't deliver very high output.

Yeah, it drives me mad when I see idiots putting silicon PV cells on their roofs here in the UK. They think they are being 'green', but are ignorant of the fact that it will probably take decades to recoup the amount of energy used in their manufacture. Nothing wrong with solar cells in places which are, you know, sunny, but I'm afraid that the UK doesn't qualify as such!

On the other hand, solar water heating installations on rooftops can be useful, even here in grey and dismal Blighty.

The thin film cells currently being introduced by a huge number of companies may make PV more feasible as they are so much cheaper and less energy/resource intensive to produce. Lower efficiency, of course, so whether they'll ever be a truly viable option, I don't know.

Of course, regardless of that, we still need more improvement in battery technology to make smaller scale PV worthwhile.

As for the discussion about supersonic passenger airlines, I think the fact that Concorde is the only supersonic passenger which has flown (I'm ignoring "Concordski" here, obviously), yet no other such aircraft have been developed since gives a good indication that they aren't really a viable option with current technology.

Interestingly enough, the figures in the following chart indicate that a Gulfstream doesn't have fuel efficiency significantly better than Concorde, but these figures are still appalling in comparison to a standard airliner:

http://en.wikipedia.org/wiki/Concorde#Environmental

 

[Sxotty]

Mariner thin film solar cells are already viable CdTe for example.

The problem is partially hubris honestly. Everyone wants to create more efficient solar cells. Have you looked at the NREL chart? Anyway there is a race for more and more efficient cells instead of cheaper and cheaper ones. It doesn't matter that someone got 50% efficiency if it costs 1,000 times more than 10% efficient thing film ones.

Yes for space reasons (i.e. in outer space where area is constrained) they might have niche applications, but cost is really the important thing now.

 

[KimB]

http://en.wikipedia.org/wiki/Project_Orion_(nuclear_propulsion)
You could basically create a "rocket" that launches from ground and goes to Mars directly.

There's no way that there will be a rocket that uses nuclear explosions for propulsion in the atmosphere. Not only would this be pretty nasty for public health and the environment, but it's against a bunch of international treaties.

 

[Mariner]

Mariner thin film solar cells are already viable CdTe for example.

The problem is partially hubris honestly. Everyone wants to create more efficient solar cells. Have you looked at the NREL chart? Anyway there is a race for more and more efficient cells instead of cheaper and cheaper ones. It doesn't matter that someone got 50% efficiency if it costs 1,000 times more than 10% efficient thing film ones.

Yes for space reasons (i.e. in outer space where area is constrained) they might have niche applications, but cost is really the important thing now.

Yeah, I'm aware that various thin film cells have been announced (CdTe and CIGS, IIRC). However, last time I checked (albeit a few months ago), it was pretty much impossible for anybody to get their hands on them for a small scale installation.

I still think that improvements in battery tech are required for these low efficiency cells to become really useful to the man on the street, however.

A good job that billions upon billions is being spent on battery tech research. Hopefully somebody will really crack it. :smile:

 

[hoho]

There's no way that there will be a rocket that uses nuclear explosions for propulsion in the atmosphere. Not only would this be pretty nasty for public health and the environment, but it's against a bunch of international treaties.

Actually the fallout isn't really all that bad. I'd say it's not much worse than what coal plants or regular planes cause, just that it's more concentrated in one place (and thus arguably easier to control).

The fact remains that Orion is the only viable way to get huge masses to orbit at low cost and energy usage. Pretty much only comparable way would be to have a working space elevator and launch vehicles to other planets in orbit but we are quite far from working elevators. We have good enough CNT's, just not the glue to stick them together.

 

[Blazkowicz]

ah yes, I was about to mention that Project Orion .
It's actually so great that you might be able to reach Proxima Centauri in a (long) human lifetime using 50 year old technology. But it's not only dirty and scary, the EMP from the bombs might cause unacceptable damage to satellites and infrastructure on the ground. See operation Starfish Prime (actual nuclear explosions in LEO altitude!), you could get away with it in the early 60's but that feels a hard proposition now.

regarding nuclear ion propulsion, it may find a use in litteral space tugs. Launch huge things with the biggest heavy launchers in LEO, have them dock with the tug then slowly transfer to geostationary or other orbit.

that would may allow an evil military space station bigger than ISS in geostationary orbit to be built, though still at enormous costs.

 

[zed]

The fact remains that Orion is the only viable way to get huge masses to orbit at low cost and energy usage

FACT? viable?
theres so many variables that can go wrong with it

btw, I just read a book by stephen baxter with it in (not one of his better books)
http://en.wikipedia.org/wiki/Ark_(Baxter_novel)

personally Ild like to see more effort put into a spacegun
http://en.wikipedia.org/wiki/Project_HARP

Using an old U.S. Navy 16 inch (406 mm) 50 caliber gun (20 m), later extended to 100 caliber (40 m), the team was able to fire a 180 kilogram slug at 3,600 meters per second (13,000 km/h), reaching an altitude of 180 kilometers. The program was canceled shortly after this. The politics of the Vietnam War (then in its fifth year) and soured Canada/U.S. relations played their role in the project's cancellation. The project received just over 10 million dollars during its lifetime.

OK you cant shoot humans up, but given they reached the limits of space cheaply 40years ago with something not really designed for it, Ild love to see what they could do today

 

[Grall]

The fallout isn't really that bad? What planet are you living on?

The idea I was thinking of would involve using a nuclear reactor to superheat a heavy working fluid of some sort ("fuel") to create a reaction force, not popping off nuclear weapons like firecrackers in the atmosphere. That's some seriously dumb shit right there.

To just transport goods into orbit we could build a railgun inside a vacuum tube up the slope of a large mountain (or perhaps bore up through the inside of it), but for people we need something better than chemical rockets (and something that doesn't subject the cargo load to 20+ G acceleration...)

Hence the nuclear rocket engine thing.

 

[corduroygt]

The problem with travelling in space is that even if you're ejecting nukes and detonating them, you're going to run out of fuel/propellant. If we had the capability of producing unlimited electric power very cheaply, then I'd say a railgun would do the trick, combined with folding solar sails that would extend once you're up in space. Or you can detonate nukes once you're far, far, FAR from Earth.

 

[Frank]

If you have lots of energy, the amount of propellant is your main bottleneck.

If you take a basic warm water nuclear reactor, strip the heavy shielding and most of the control rods, and run it as close to critical as you can, while pumping propellant (water) through, it works quite well as a rocket engine.

The main problems are, that it does go critical if the water flow is disrupted, that it's hard to throttle, and that it emits a good bit of radiation.

Then again, many spacecraft and satellites use a few kilograms of plutonium coated with thermocouples, that would be quite the radiation and toxic hazard if something went wrong and they come down.

 

[Frank]

Mariner thin film solar cells are already viable CdTe for example.

The problem is partially hubris honestly. Everyone wants to create more efficient solar cells. Have you looked at the NREL chart? Anyway there is a race for more and more efficient cells instead of cheaper and cheaper ones. It doesn't matter that someone got 50% efficiency if it costs 1,000 times more than 10% efficient thing film ones.

Yes for space reasons (i.e. in outer space where area is constrained) they might have niche applications, but cost is really the important thing now.

I agree. Cost is everything. If the efficiency is only 4%, it's still viable as long as it's cheap enough and you have enough surface area.

Then again, that doesn't make them useful if you don't have that surface area available. And many of the current cheap, plastic ones deteriorate in a few years time.

I think too many people look at the efficiency figure and think: "WOW! That's really bad! Even a combustion engine does much better!" But that combustion engine needs expensive fuel. It's incomparable, and a big marketing failure.