regulator 0 #1 December 29, 2012 Proving yet again that Star Trek was scarily prescient, NASA has announced that its NEXT ion drive — NASA’s Evolutionary Xenon Thruster — has operated continually for over 43,000 hours (five years). This is an important development, as ion thrusters are pegged as one of the best ways to power long-term deep-space missions to other planets and solar systems. With a proven life time of at least five years, NEXT engines just made a very big step towards powering NASA’s next-gen spacecraft. Ion thrusters work, as the name suggests, by firing ions (charged atoms or molecules) out of a nozzle at high speed (pictured above). In the case of NEXT, operation is fairly simple. Xenon (a noble gas) is squirted into a chamber. An electron gun (think cathode ray tube TV) fires electrons at the xenon atoms, creating a plasma of negative and positive ions. The positive ions diffuse to the back of the chamber, where high-charged accelerator grids grabs the ions and propel them out of the engine, creating thrust. The energy to power the electron gun can either come from solar panels, or from a radioisotope thermoelectric generator (i.e. a nuclear battery, just like Curiosity). The downside of ion thrusters, though, is that the amount of thrust produced is minuscule: State-of-the-art ion thrusters can deliver a grand total of 0.5 newtons of thrust (equivalent to the force of a few coins pushing down on your hand), while chemical thrusters (which power just about every spacecraft ever launched) on a satellite or probe deliver hundreds or thousands of newtons. The flip side of this, though — and the reason ion thrusters are so interesting — is that they have a fuel efficiency that’s 10 to 12 times greater than chemical thrusters. Obviously, for long trips through space, fuel efficiency is very important. With such puny thrust, a NEXT-based ion drive would need to run for 10,000 hours — just over a year — to reach a suitable speed for space travel. Dawn, a NASA probe that’s powered by previous-generation NSTAR ion thrusters, accelerated from 0 to 60 mph in four days. As a corollary, ion thrusters only work at all because of the near-vacuum of space; if there was any friction at all, like here on Earth, an ion drive would be useless. The good news, though, is that the (eventual) max speed of a spacecraft propelled by an ion drive is in the region of 200,000 miles per hour (321,000 kph). Moving forward, it now remains to be seen if NASA will use the NEXT on an actual spacecraft. In 2011, NASA put out a request-for-proposals for a test mission that will likely use a NEXT engine, and presumably, following this successful engine test, we might soon hear more news about that. Other space agencies, including the ESA, are also working on spacecraft propelled by ion thrusters. http://www.extremetech.com/extreme/144296-nasas-next-ion-drive-breaks-world-record-will-eventually-power-interplanetary-missions?utm_source=rss&utm_medium=rss&utm_campaign=nasas-next-ion-drive-breaks-world-record-will-eventually-power-interplanetary-missions Quote Share this post Link to post Share on other sites
regulator 0 #2 December 29, 2012 Seems that since it isnt very high powered that conventional rockets would be needed to get the spacecraft in orbit and the use Ion thrusters from that point out. Quote Share this post Link to post Share on other sites
quade 3 #3 December 29, 2012 Ion propulsion is only going to be useful for small probes. F=MA Ion is very, VERY small F. As far as human travel is concerned, it's not really suitable.quade - The World's Most Boring Skydiver Quote Share this post Link to post Share on other sites
lawrocket 3 #4 December 29, 2012 QuoteSeems that since it isnt very high powered that conventional rockets would be needed to get the spacecraft in orbit and the use Ion thrusters from that point out. Indeed. The ion thrusters are slow but steady. Adding a velocity of a half a centimeter a minute isn't much, but over the span of 5 years it's mind boggling. My wife is hotter than your wife. Quote Share this post Link to post Share on other sites
blueblur 0 #5 December 29, 2012 QuoteIon propulsion is only going to be useful for small probes. F=MA Ion is very, VERY small F. As far as human travel is concerned, it's not really suitable. But as noted, in space there is no drag. As long as it is clear of any gravity-effects, it won't be an issue. It's similar to being able to push a car that is on inflated tires in neutral (low drag) versus pushing the same weight sitting flat on the ground (high drag). The force required is fractionally smaller.In every man's life he will be allotted one good woman and one good dog. That's all you get, so appreciate them while the time you have with them lasts. - RiggerLee Quote Share this post Link to post Share on other sites
BigBUG 0 #6 December 29, 2012 Hmm. I thought that ion drives were already used in late 80s in Deep Space mission? And later in 2007 with Dawn? Europeans have ion drive as a main corrective drive on their sattelite since 2009, I believe. Quote Share this post Link to post Share on other sites
quade 3 #7 December 29, 2012 QuoteQuoteIon propulsion is only going to be useful for small probes. F=MA Ion is very, VERY small F. As far as human travel is concerned, it's not really suitable. But as noted, in space there is no drag. As long as it is clear of any gravity-effects, it won't be an issue. It's similar to being able to push a car that is on inflated tires in neutral (low drag) versus pushing the same weight sitting flat on the ground (high drag). The force required is fractionally smaller. All that means is that eventually an ion drive can get things up to speed, but it doesn't change the equation; F=MA. If you have a larger mass, which is a requirement for manned space flight, it will take considerably longer and in the case of interstellar space travel far too long for humans. As for manned space travel within the solar system, it makes no sense whatsoever.quade - The World's Most Boring Skydiver Quote Share this post Link to post Share on other sites
kallend 1,623 #8 December 29, 2012 QuoteProving yet again that Star Trek was scarily prescient,... ???? Didn't see any mention of dilithium crystals.... The only sure way to survive a canopy collision is not to have one. Quote Share this post Link to post Share on other sites
sfzombie 3 #9 December 29, 2012 actually, it makes perfect sense. the only use would be long range exploration or emergency evacuation of the planet. all you have to do to increase the velocity is add more engines. and compared to what we have right now (think dropping nuclear bombs from the back of the ship) it is the only feasible answer.http://kitswv.com Quote Share this post Link to post Share on other sites
billvon 2,394 #10 December 29, 2012 > all you have to do to increase the velocity is add more engines. The engines themselves (emitter and power source) have very poor thrust/weight ratios. They are great at accelerating a ship over the course of decades to very high speeds. But for manned exploration they're not that useful because it's difficult for people to survive in space for decades. However there are electric-propulsion engine variants like the VASIMR that promise to give something of the best of both worlds - a high thrust, low specific impulse mode for high accelerations, and a low thrust high specific impulse mode for gradual acceleration during cruise. To get these to a thrust level that's acceptable for manned exploration would require a high energy source of electric power like a fission reactor. I believe that NASA is mounting a VASIMR on the ISS in a few years to allow the station to reboost without using conventional fuel. Quote Share this post Link to post Share on other sites
GQ_jumper 4 #11 December 29, 2012 Quote Quote Proving yet again that Star Trek was scarily prescient,... ???? Didn't see any mention of dilithium crystals. they're in the flux capacitor History does not long entrust the care of freedom to the weak or the timid. --Dwight D. Eisenhower Quote Share this post Link to post Share on other sites
kallend 1,623 #12 December 30, 2012 Quote Quote Quote Proving yet again that Star Trek was scarily prescient,... ???? Didn't see any mention of dilithium crystals. they're in the flux capacitor Wow, you must be Wesley Crusher!... The only sure way to survive a canopy collision is not to have one. Quote Share this post Link to post Share on other sites
lawrocket 3 #13 December 30, 2012 Quoteit's difficult for people to survive in space for decades. Decades for us may end up being a few months to them. My wife is hotter than your wife. Quote Share this post Link to post Share on other sites
regulator 0 #14 December 30, 2012 can you tell me what the acronym for VASIMR is please sir? Quote Share this post Link to post Share on other sites
billvon 2,394 #15 December 30, 2012 >Decades for us may end up being a few months to them. Not at these accelerations. Now, if you had something that could accelerate reliably at 1G (or even 1/10 G!) such relativistic concerns would become an issue. Quote Share this post Link to post Share on other sites
billvon 2,394 #16 December 30, 2012 VASIMR - Variable Specific Impulse Magnetoplasma Rocket. Specific impulse is similar to a "miles per gallon" number in that it tells you how much force you get out of a given use rate of propellant. Solid rockets are very low but have very high thrusts overall, which is why they are used as boosters during launch. Some example numbers: Solid rocket 250s Good bipropellant liquid rocket 450s Ion engine 3000-20,000 VASIMR 3000-12,000 The maximum Isp of the VASIMR engines is lower but it can generate a lot more thrust than the ion engine. Quote Share this post Link to post Share on other sites
riddler 0 #17 January 1, 2013 There is also added risk for the increased speeds. Right now, Voyager 1 is traveling at about 8 miles per second, and has been for 35 years. You could create a spacecraft that began with conventional thrust, like Voyager, use gravity assist around a planet to really build up momentum, and then add Ion-drive engines to continually accelerate it to incredible speeds, potentially small fractions of light speed. The chances of it hitting something big, like an asteroid, in space is extremely small. There's a lot of space in space. But what about a single particle of space dust? Right now, we know that our own satellites are susceptible to micro-meteorite damage, which you are going to encounter when you're so close to a large body like Earth. That's much less likely in interstellar space, but one will probably find dust even beyond the Oort cloud. A single piece of space dust, when struck at astounding speed, may penetrate the hull of a spacecraft and potentially disable it. We really don't know what happens to micro particles when impacted at extraordinarily large speeds. Will it expand, disintegrate, tumble or what? Over the course of decades, it is likely that a fast-moving craft will encounter at least a few particles of dust, and if they are traveling at these speeds, a collision even with a tiny particle may end the mission entirely.Trapped on the surface of a sphere. XKCD Quote Share this post Link to post Share on other sites
BigMikeH77 0 #18 January 3, 2013 Gravity... What a drag. Quote Share this post Link to post Share on other sites
