Bush Cancels trip to Pluto.

[KrazyHorse]

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?

[TCO]

I think it was Orion.

Daedalus was the human-powered airplane.

[KrazyHorse]

Daedalus turned this up: http://www.geocities.com/TelevisionC...9/DAEDALUS.HTM

[TCO]

Yeah...I think I've seen that before.

Here is Orion: http://www.friends-partners.org/mwad...s/probirth.htm

[aaglo]

Here is a quite nice "slideshow", where both daedalus and orion are included. There are basic info about antimatter-engines and interstellar ramjets...

[TCO]

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.

[Jack the Bodiless]

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.

[Roman]

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.

[Dauphin]

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.

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.

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.

[Dauphin]

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.

[KrazyHorse]

Originally posted by Roman


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

Judge for yourself.

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

[TCO]

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?

[Roman]

Yes, I see the point you are making. He seemed to suggest that multiple stage rockets are the only way to overcome the problem.

[General Ludd]

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.

[faded glory]

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.