formulaterp

Oh there's quite a few startups jumping into the space tourism industry. Bigelow is actually one of the better known and his chances of success are much better than some of the real yahoos out there. Technically, his ideas are entirely workable. The concept of an inflatable space station module was originally designed by NASA, but dropped in favor of the current ISS model. NASA has provided limited technical assistance, basically their plans and studies on the technology. I do have to question his business plan though. Just how big of a market exists for a space hotel? He plans on charging $1 million dollars a night!!!! He may have made a lot of money with his Vegas hotel chain, but he's not exactly Steve Wynn or Donald Trump. Bigelow's bread and butter is discount hotels. I wish him luck. Speaking of yahoos, for a real treat check out AERA's website. They look to be a competitor to Virgin Galactic. If you aske me, they look like a ton of hype and no substance whatsoever. http://www.aeraspace.com/home.html

There are various reasons why the orbital path of a comet may change over time. The most common are gravitational preturbances due to close passes of planets, especially Jupiter, and the thrust induced by venting as the comet approaches the sun. Generally these result in small differences on each pass. I'm not sure why you think this precludes our ability to spot them every 100 years or so. Perhaps you can clarify. Some more info: Comets aren't as regular as you might think, that is I wouldn't set your watch by them. For example everyone knows about Halley's comet. It was made famous because Sir Edmund Halley deduced that numerous sightings over time were in fact the same comet, traveling along a regular path about every 76 years. Using that information he predicted it's next arrival. However, the comet did not arrive until TWO YEARS after the predicted date. This is not unusual. Halley, despite its orbital period being nearly equal to a human lifetime, is considered a short period comet. We have identified several hundred, perhaps thousands of these. Long period comets, such as Hale-Bopp have orbital periods in the several thousands of years. It's almost impossible to say how many of them there are since a given civilization may only see it once.

Regarding maximum velocity, you are leaving out relativistic effects. Personally I don't think you have to worry about it too much. We won't be approaching even 0.01c anytime soon. As far as the Xenon fuel being used: Early ion engines (SERT I and II missions) used Mercury and Cesium as fuel. Over the past 3 decades or so, the industry has settled on Xenon due to lack of corrosive effects and much safer handling conditions. One has to consider environmental effects and safety precautions driving up the cost of developing any type of propulsion method. Ask any rocket scientist about Project Orion, a proposed nuclear propulsion system. Orion drops actual thermonuclear devices out the back of the rocket, detonates them, and the blast effect propels the craft forward. It's incredibly efficient, and can result in impressive velocities. But you try getting that proposal past the local town council.

Well let's just go ahead and assume the big bang created all sorts of wormholes. Do the wormholes still exist? Maybe, maybe not. Where's the evidence for them? There isn't any. Would the dissipation of energy as the universe expanded have closed these wormholes? Probably, but I don't have enough info to argue either way. Where does this leave us? Right back where we started. If a wormhole is possible, then it would require an incredible amount of energy to create one.

Here you go! Everything you ever wanted to know about ion engines, but were afraid to ask (note: .pdf file). And seriously, I mean everything. http://nmp-techval-reports.jpl.nasa.gov/DS1/IPS_Integrated_Report.pdf Well technically it's just Deep Space 1's ion engine. OK so I oversold it. Also there's this earlier thread: http://www.scienceforums.net/forums/showthread.php?t=5914

Yes, not only can you do it, that's how it's actually done. The space probes which have used ion engines (Deep Space 1, SMART-1, MUSES-C) were all launched by rockets using conventional propellent. The second or third stage motors put the probes into a parking orbit or sent them on their merry way and then dropped off. The propellent burns were on the order of minutes, the ion engines then "burned" for weeks, or months or years!! If you were designing a probe to go to Pluto or Alpha Centauri, you would want the biggest, most powerful conventional rocket motor you could afford to give yourself a kickstart. Once the fuel is exhausted you'd want to dump the motor and the fuel tanks and allow the ion engine to kick in. As mezerashi pointed out, the actual thrust of the ion engine is rather feeble. There's no point in carrying the excess mass of the conventional motor and depleted tanks with you. I'll leave out the 432 potential problems in mounting such a mission, but you probably get the drift. If you're so inclined, look up MUSES-C (aka Hayabusa). It's an ambitious JAXA project which uses an advanced ion engine to send a probe to an asteroid, deploy a hopper, collect a sample, and then return it to earth. It has been slowly sneaking up on the asteroid with it's ion engine for several months now. It actually uses small conventional motors on its final approach, but will revert back to ion power to send itself back to earth with the sample cannister. Neat stuff!! http://www.isas.ac.jp/e/enterp/missions/hayabusa/index.shtml