Ionic based engines have been around for a bit (greater than 7 years). They have a very high impulse rate, in fact as high as 15,000 to be approximate. Problem is while their specific impulse is extremely high their actual thrust to weight ratio and thrust period is low. Over time these suckers can literally send a satellite or any other object at very high velocities while being extremely efficient, the problem is that it takes a very long time to reach those velocities.

ram jet ion propulsion. Instead of carrying gas on the ship, use large intakes to collect and propel space gas and dust.

The ionic ramjet idea is a good one, but the density of dust in interplanetary space is VERY low. The science fiction books that mention propulsion systems like this have collectors of one sort or another that cover hundreds of square miles. I don't think that we have any material that can be deployed that far without being prohibitively massive. Most of the science fiction books that are based on interstellar travel mention 'millenium' ships leading the way, with predictable results, and the next phase based on advances in physics theory, not break throughs in engineering, or modifications of existing technology. I think that ESA is in the forefront of the ion propulsion field right now and I think I read recently that they have a vehice that there will be launching within the next few years. (?)

It isn't the dust that an ionic ramjet would use, it would be atomic and subatomic particles that are spewed out by the sun. Outside the orbit of say, Neptune, you may have to go to nuclear rockets or fusion powered magnetic field drive.

I like pulse nuclear detonation. For several reasons over what you guys have mentioned. Basically the idea is that I drop a nuclear bomb out the back door and use the shockwave to propell my ship. 1. You can launch ships from earth that are truly massive(One estimate had ships that weighed 2 million tons!) 2. You can achieve a max speed(theoretically) of about 4% the speed of light. 3. The principle has been tested using conventional explosives(The prototype was called put put that launched itself a couple hundred feet in the air) 4. Allows us to build ships that are robust and could protect the occupants from hazards like micrometeors and radiation(Think 4 inch think steel hulls and the like). 5. Gives us a good way to get rid of nuclear weapons. I personally think that if they can find a cleaner type of nuke, that this would be THE way to go. Heck, I'd do it now, just in an isolated wasteland like chile's atacama desert. This system was originally going to built in the 1960's but then the nuclear test ban treaties came and killed it :(*.

http://www.space.com/spacelibrary/books/library_projectorion_020709.html This is just a link an article about Project Orion which was a ship that would have used Nuclear Pulse detonation propulsion.

Antimatter/Matter drive.

http://www.vectorsite.net/tarokt_3.html extract follows; "Several other types of advanced rocket engines are now in laboratory development, but have never been flown on a space mission. They include the "magnetoplasmodynamic" drive; the "pulsed inductive" drive; and the "variable specific impulse magnetoplasmodynamic rocket (VASIMR)" drive. " http://www.space.com/businesstechnology/technology/vasimr_rocket_020807-1.html extracts follow; "The VASIMR wonder rocket is chock-full of technology. Its high-tech innards involve superconducting magnets working at space temperatures; tightly packaged power generation and conditioning gear; compact and robust radio frequency systems; a hybrid magnetic nozzle; and lightweight heat shields and cooling technology." "Along with Johnson Space Center experts, VASIMR's talent pool draws from seven universities and two national laboratories, such as MIT, Oak Ridge National Laboratory, Rice University and the University of Texas at Austin." "It's an expanding research effort," Chang-Diaz said. "We're developing something that is very new and very different from the established electric propulsion framework." "One VASIMR study hypothesized using a 200-megawatt nuclear power system. The result, he added, showed that 20 metric tons could be delivered to Mars in 39 days." "Now that's the way you want to go," Chang-Diaz said. "Astronauts will really warm up to that idea very quickly. So if you're going to go nuclear, go all the way. Go with the gusto." "In 22 years of working on the project, finding money has always been an ongoing wrangle, Chang-Diaz admitted. "But it seems to be more of a struggle now for some reason. Our funding right now is our major limitation. That has become pretty clear." "To run the JSC Advanced Propulsion Laboratory takes on the order of $1.4 million a year. That budget includes an entire team of some 50 scientists from all over the United States, Chang-Diaz said." "Loads of small visionary projects vie for small pots of NASA's advanced propulsion money. There are lots of mouths to feed, the astronaut said, keeping everybody on a starvation diet. Not a very conducive scenario for people to work together, he said, and that tends to polarize propulsion groups." end of quotes; I reckon space propulsion ideas can be roughly divided up into; 1. Getting out of the earths gravity well. 2. Getting between planets at ~1g thrust. 3. Getting the hell out of the neighbourhood (but don't start her up in the backyard) I think electrically accellerated ion drives could meet the last requirement if you are not sending adult humans (maybe just the embryoes?). All the fission nuclear power ideas face the problem of how to get out of the gravity well without poisoning us all. Has any rocket system made a better than 2% failure rate? If we lauch about 25 fission propulsion missions we have a better than evens chance of a big screw up. I think we can't build a spacefairing civilisation on those odds. The only way I see around the problem is to developed multistage chemical energy flyback aircraft/spacecraft which have redundancy and resilance in the case of software upset or technical failure. These can deliver fission powered systems into LEO where they can slowly boost themselves higher using ion drive/negative ion neutral beams powered by TOPAZ style reactors. Once the system is beyond the earths gravity well the crew can join the ship using a shuttle of some sort. The system and crew can then light the fusion or fission fires and head off into the void. Such a system has the advantage taking multiple propulsion technogies along with it giving it maximum flexiblity in the case of failure. FYI I have a bias toward Culham.

before focsuing on interplanetary or even interstellar travel, why not give more support to developing a Space elevator? Currently it costs something like US$10K to lift one pund into orbit.. some projections say a space elevator could do the job for $100/lb. Hey, I'm willing to wait 50 years to get the thing done but to me it's probably one of the key technologies we'll havew to develop if we ever really want to explore and exploit space.