22-11-2001 03:17									#91
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quote: Originally posted by faded glory Ion propulsion is a joke.

Why write it off just like that. For far away missions it is very beneficial as over long periods of time it enables space probes to attain high speeds without using ridiculous quantities of propellant. Hence it makes space missions much cheaper.

quote: Controlled Atomic reactions is the way to go. Get to mars in 3 weeks. As opposed to 8 months with a normal chemical booster. NASA was designing the ship...the greenies did like it tho cause the word 'nuclear' was written all over it But imagine being able to reach mars in 3 weeks. Saturn in 9 months... and beyond. It had alot of potenetial using controlled Atomic reaction bursts to get it moving. But the greens worrys are justified. But there was a plan to assemble the ship in space and keep it above the earths atmosphere so there would be no danger.....

Well, as far as I am aware, there are two basic principles behind nuclear powered spacecraft. One actually uses nuclear to provide electricity for guess what - ion engines. That enables missions to places where solar panels are no longer useful.

The other way to power a spacecraft nucleary is to make the reactor heat up the fuel and then let it expand out through the nozzle, thus providing thrust. AFAIK this is more fuel efficient than chemical engines, but provides somewhat less thrust. It does provide very significantly more thrust than ion engine, but is less fuel efficient.

As you can see there is no easy solution. Different propulsion methods fit different objectives and missions.

BTW: I agree that the green rejection of nuclear power (both on spacecraft and on Earth) needs to be reevalued. Alternative energies are not reliable enough to ween us off fossil fuels on theur own.

	22-11-2001 03:19									#92
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quote: Originally posted by aaglo Construction&Civil engineer (no, not CIV-engineer )

I was considering aerospace engineering, but I have been persuaded to study economics and international relations instead.

	22-11-2001 03:21									#93
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quote: Controlled Atomic reactions is the way to go.

I think laser pushed sails are the way to go. Ultimately they are by far the most efficient in terms of energy usage. If set up properly.

	22-11-2001 03:23									#94
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quote: Originally posted by Roman Why write it off just like that. For far away missions it is very beneficial as over long periods of time it enables space probes to attain high speeds without using ridiculous quantities of propellant. Hence it makes space missions much cheaper. Well, as far as I am aware, there are two basic principles behind nuclear powered spacecraft. One actually uses nuclear to provide electricity for guess what - ion engines. That enables missions to places where solar panels are no longer useful. The other way to power a spacecraft nucleary is to make the reactor heat up the fuel and then let it expand out through the nozzle, thus providing thrust. AFAIK this is more fuel efficient than chemical engines, but provides somewhat less thrust. It does provide very significantly more thrust than ion engine, but is less fuel efficient. As you can see there is no easy solution. Different propulsion methods fit different objectives and missions. BTW: I agree that the green rejection of nuclear power (both on spacecraft and on Earth) needs to be reevalued. Alternative energies are not reliable enough to ween us off fossil fuels on theur own.

Concerning Nuclear Power Roman. No the idea behind the Nuclear engines had nothing to do with Ion. IT would have been a controlled and funneled nuclear reaction for propulsion. No Hiroshima or anything...a small reaction in bursts.

	22-11-2001 03:28									#95
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quote: Originally posted by faded glory Concerning Nuclear Power Roman. No the idea behind the Nuclear engines had nothing to do with Ion. IT would have been a controlled and funneled nuclear reaction for propulsion. No Hiroshima or anything...a small reaction in bursts.

Well as I pointed out there were two ideas about nuclear propulsion. One was essentially ion propulsion with using nuclear o produce electricity and the other involved a chemical propelant being heated by a nuclear reactor and then funneled through the nozzle to provide thrust. I guess you are talking about the second one.

I have never heard any suggestion about actually expelling the nuclear material itself to provide thrust. I think I am misunderstanding what you are writing - please clarify.

	22-11-2001 03:30									#96
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quote: Originally posted by Big Crunch quote: Controlled Atomic reactions is the way to go. Ultimately they are by far the most efficient in terms of energy usage. If set up properly.

Difficult to argue with that, considering they don't use any energy of their own.

	22-11-2001 03:34									#97
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quote: Originally posted by Roman Difficult to argue with that, considering they don't use any energy of their own.

Well you need to charge the laser.

The point moreover is that all the energy used is put into the kinetic energy of the satellite. With chemical rocket propulsion almost all of the energy created is wasted on the ejectile.

quote: I have never heard any suggestion about actually expelling the nuclear material itself to provide thrust.

Similar

How do you funnel a nuclear reaction! Even a mini one.

	22-11-2001 03:50									#98
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quote: Originally posted by Big Crunch Well you need to charge the laser.

I assumed you were talking about the idea to tap solar wind. I am not sure just how workable it is, but if it did work no further energy input would be required. The laser idea is probably more practical, though.

quote: The point moreover is that all the energy used is put into the kinetic energy of the satellite.

Is all energy converted into kinetic? I did not realise that, but than again I am not an expert on the subject. I thought the light, or whatever the laser emits is reflected back by the 'reflective sail'. However, since the light still exists it contains much of its energy, so only a tiny fraction of the energy is converted into the kinetic energy of the spacecraft. IIRC you are a physicist, so I would be grateful if you explained it to me (I don't mind equations, but do not make them too mind boggling).

	22-11-2001 03:55									#99
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I have actually heard of designs that use the direct impulse from nuclear explosions.

	22-11-2001 04:03									#100
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quote: Originally posted by GP I have actually heard of designs that use the direct impulse from nuclear explosions.

How????

	22-11-2001 04:11									#101
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I don't know all the details, but I think they have a plate at the back of the ship and they explode the bombs against the plate. Not sure of all the construction, megatonnage, and geometric details. I think the design is theoretical. Untested.

	22-11-2001 06:23									#102
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Big Crunch - please!!!

	22-11-2001 09:09									#103
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Roman Nuclear reactions dont have to be that big. They can be downsized...diverted.....mixed and funnelled. Ill try and grab a link about NASA's program in the 70's concerning nuclear propulsion.

I think the biggest issues

1) How to shield the crew from radiation
2)How to keep somthing from going wrong and it falling back to earth.
3) How to get good PR considering the program was at its peak in the late 70's. (died right after 3 mile island ironically )

	22-11-2001 11:23									#104
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You can find information abou fusion propelled spacecrafts from here. But I suggest that you don't believe everything you read from the internet.

Besides, it seems that fusion propulsion (FP from now on) is still science fiction (NASA estimates that the development of FP will take some 25 years)

	22-11-2001 11:26									#105
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quote: Originally posted by Big Crunch quote: As to the speed the engine can reach - this is very misleading. In theory, every engine can attain any possible speed, but needs varying amounts of fuel to do so Using single stage engines the amount of fuel required to increase its speed by x kms-1 increases exponentially. It one of the reasons that launch rockets are multi-staged, a single stage rocket can not reach orbit.

This is false. The logarithmic increase of deltaV for linear increase of fuel is not a flaw in single-stage designs; it is a flaw in using a reaction engine which must carry its entire supply of propellants on board (to wit, any rocket). Multiple stages simply aid a rocket approach this theoretical limit more closely. The reason an ion rocket has a higher practical top speed is that its propellants are ejected at a much higher velocity than those from a typical chemical rocket. It thus gains more thrust/unit mass of propellant, resizing the logarithmic curve dramatically in our favour. In fact, the terminal velocity of two identical rockets, one with chemical propellants which have Effective Jet Velocity (EJV-the speed at which burned fuel exits the rocket) of X m/s and one with ion propellants with EJV of Y m/s are simply related by the ratio Y/X. Given that ion drives (being much higher "temperature") have an EJV orders of magnitude higher than chem rockets, you can see that the implications are astounding. Admittedly these ion drives have a low rate of mass expulsion and have a correspondingly low thrust, but you can accelerate for years on a fuel supply which would be exausted in minutes by a chem rocket.

	22-11-2001 11:29									#106
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quote: Originally posted by GP I have actually heard of designs that use the direct impulse from nuclear explosions.

Can't remember the name of this one. Daedalus?

	22-11-2001 12:03									#107
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I think it was Orion.

Daedalus was the human-powered airplane.

	22-11-2001 12:13									#108
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Daedalus turned this up: http://www.geocities.com/Television...49/DAEDALUS.HTM

	22-11-2001 12:46									#109
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Yeah...I think I've seen that before.

Here is Orion: http://www.friends-partners.org/mwa...es/probirth.htm

	22-11-2001 12:51									#110
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Here is a quite nice "slideshow", where both daedalus and orion are included. There are basic info about antimatter-engines and interstellar ramjets...

	22-11-2001 13:47									#111
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Check out that document on Orion. Pretty interesting. Freeman Dyson was one of the big designers there.

Big difference between Daedelus and Orion is that Orion uses current (actually 30 year old) technology and Daedelus depends on fusion micro-explosion control of a sort which hasn't been created yet.

	22-11-2001 16:57									#112
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In the film "Deep Impact", the Messiah spacecraft was supposedly powered by an Orion drive.

It also featured in the novel "Footfall" (Niven and Pournelle). They launched from Earth's surface to thwart an alien invasion, nuking the launch facility in the process.

	22-11-2001 17:52									#113
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quote: Originally posted by KrazyHorse This is false. The logarithmic increase of deltaV for linear increase of fuel is not a flaw in single-stage designs; it is a flaw in using a reaction engine which must carry its entire supply of propellants on board (to wit, any rocket). Multiple stages simply aid a rocket approach this theoretical limit more closely. The reason an ion rocket has a higher practical top speed is that its propellants are ejected at a much higher velocity than those from a typical chemical rocket. It thus gains more thrust/unit mass of propellant, resizing the logarithmic curve dramatically in our favour. In fact, the terminal velocity of two identical rockets, one with chemical propellants which have Effective Jet Velocity (EJV-the speed at which burned fuel exits the rocket) of X m/s and one with ion propellants with EJV of Y m/s are simply related by the ratio Y/X. Given that ion drives (being much higher "temperature") have an EJV orders of magnitude higher than chem rockets, you can see that the implications are astounding. Admittedly these ion drives have a low rate of mass expulsion and have a correspondingly low thrust, but you can accelerate for years on a fuel supply which would be exausted in minutes by a chem rocket.

This is exactly what Big Crunch implied when he talked about multi/single stage rockets.

	22-11-2001 18:31									#114
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quote: Originally posted by Roman Is all energy converted into kinetic?

No it isn't I misinformed you. All the energy is retained though. I shall explain in a mo.

quote: However, since the light still exists it contains much of its energy, so only a tiny fraction of the energy is converted into the kinetic energy of the spacecraft.

If the photon is absorbed rather than reflected all the energy is maintained on the craft, as well as imparting an impulse. If you have a solar cell absorbing the laser for powering the craft then you kill two birds with one stone. You power the craft and you propel the craft.

quote: Admittedly these ion drives have a low rate of mass expulsion and have a correspondingly low thrust, but you can accelerate for years on a fuel supply which would be exausted in minutes by a chem rocket

Think about how much energy is wasted though. Most of the energy produced is lost to the propellant. Ion rockets use more energy but require less mass. Thats why they are desirable - they reduce payloads.

	22-11-2001 18:37									#115
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quote: Originally posted by Jack the Bodiless It also featured in the novel "Footfall" (Niven and Pournelle). They launched from Earth's surface to thwart an alien invasion, nuking the launch facility in the process.

I remember that book. They nuke Kansas because some elephantesque aliens had landed there.

	23-11-2001 04:26									#116
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quote: Originally posted by Roman This is exactly what Big Crunch implied when he talked about multi/single stage rockets.

Judge for yourself.

quote: Using single stage engines the amount of fuel required to increase its speed by x kms-1 increases exponentially. It one of the reasons that launch rockets are multi-staged, a single stage rocket can not reach orbit.

I took this to imply that multi-stage engines were not limited by a logarithmic curve, which is untrue.

Plus, this could just be taken as tit-for-tat

	23-11-2001 05:51									#117
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I don't see why the fundamental thrust equations make a launch rocket require multiple stages. Essentially the lighter you can make the fuel container, the less you need multiple stages. The issue here is fuel container weight, no?

	23-11-2001 06:20									#118
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Yes, I see the point you are making. He seemed to suggest that multiple stage rockets are the only way to overcome the problem.

	23-11-2001 06:24									#119
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I haven't really been following this discussion, but just to chip in - NASA and the plane manufacturer Locke (that is the correct name, right?) are working on a space shuttle that will fly out of the atmosphere like a plane, rather then the current method of blasting it out with rockets.

	23-11-2001 07:29									#120
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Osweld the Locke program (Next generation Shuttle) was canceled.

Al Gore got it going in 1996. It was promptly scrapped late last year.

There currently is no planned shuttle replacement.