Community > Forum > Technology & Science > ion drives

ion drives

Posted by: Rob Goldsmith - Fri Nov 19, 2004 4:06 pm
Post new topic Reply to topic
 [ 5 posts ] 
ion drives 
Author Message
Moon Mission Member
Moon Mission Member
User avatar
Joined: Fri Jan 09, 2004 11:52 am
Posts: 1379
Location: Exeter, Devon, England
Post ion drives   Posted on: Fri Nov 19, 2004 4:06 pm
hello!

Just wandering about this ION Drive business. Anyone got any idea if anyone apart from the space agencies could harness it? Also completely random but just read on space.com that the TIE fighters in starwars used then, sweet! could a private company use this? its cheaper right?

_________________
> http://www.fullmoonclothing.com
> http://www.facebook.com/robsastrophotography
> robgoldsmith@hotmail.co.uk


Back to top
Profile WWW
Moon Mission Member
Moon Mission Member
avatar
Joined: Tue Feb 10, 2004 2:56 am
Posts: 1104
Location: Georgia Tech, Atlanta, GA
Post    Posted on: Fri Nov 19, 2004 7:27 pm
Here we go.....

TIE fighters are, unfortunately, fake. Worse still, they're pretty miserable fakes, at that.

An ion drive is based on the idea of taking a relatively massive but chemically inert (and non-radioactive) element (I think xenon is a popular one, but I'm not sure), and ramming a powerful electrical charge through it to ionize it (strip all the electrons off of it, or at least as many as practical). Then these ions are sent through an area of very strong positive charge, accelerating them away from the ship at insanely high speeds (reasonably close to lightspeed). Now, because you're basically put-put-putting out one atom at a time, your acceleration is almost nonexistant, only slightly better than the acceleration you get with a solar sail. (note: this is why no combat vessel will ever use an ion drive as we know it -- scratch the TIE fighters) However, the operation is cheap as far as mass is concerned (although xenon is pretty hard to come by), and can run off a single nuclear battery (like the kind in pacemakers, just bigger), making the ion drive great for a long, robotic interplanetary trip.

For operating cost, the ion drive is second only to the solar sail (can't beat free).
For overall cost (construction and operation), for mass, and for absolute top speed, the ion drive and the solar sail are about equal.
For acceleration, ion drives and solar sails are nearly worthless.

In summary: ion drives and solar sails are great for robotic exploration and automated cargo runs, when you don't need the payload to get to its destination very quickly -- like hauling in ore out of the asteroid belt, or sending a probe to the Oort Cloud. However, for human travel, you need higher acceleration. The only way to make an ion vessel really suitable for human use is to place a huge number (as in several hundred) of drives on the back of the ship, thus increasing your acceleration. However, the energy cost of operation has now increased to almost that of using a fission-powered fusion drive (which, by the way, has MUCH more acceleration, and is almost as cheap on mass), and you now have to increase the size (and therefore mass) of the entire vehicle, thus greatly increasing its inertia (and therefore reducing the potential acceleration).

Of course, for construction cost, the good old chemical rocket wins hands down -- it's cheap and easy to build and even cheaper and easier to maintain.

_________________
American Institute of Aeronautics and Astronautics
Daniel Guggenheim School of Aerospace Engineering

In Memoriam...
Apollo I - Soyuz I - Soyuz XI - STS-51L - STS-107


Back to top
Profile
Launch Director
Launch Director
avatar
Joined: Mon Nov 08, 2004 7:51 am
Posts: 19
Post    Posted on: Sat Nov 20, 2004 1:44 am
Just to add slightly to what spacecowboy said.
AFIK the most powerful iondrive has the equivilent accelleration to a peice of A4 paper resting on your hand, in other words not much.


Back to top
Profile
Space Station Commander
Space Station Commander
User avatar
Joined: Mon Oct 06, 2003 9:22 pm
Posts: 843
Location: New York, NY
Post    Posted on: Sun Nov 21, 2004 4:46 pm
anyone know what the theoretical acceleration of a solar sail powered by lasers based near the sun would be? i imagine it's more, though no clue how much more.

_________________
Cornell 2010- Applied and Engineering Physics

Software Developer

Also, check out my fractals


Back to top
Profile
Moderator
Moderator
avatar
Joined: Thu Jun 03, 2004 11:23 am
Posts: 3745
Location: Hamburg, Germany
Post    Posted on: Mon Nov 22, 2004 5:45 pm
At the NIAc-Site there is astudy I mentioned much earlier this year in quite another thread - a study including a table of the accelerations at different distances from the sun.

At 3 million km distance from sun a 10 kg-payload cn be accelerated up to 0.13c by a solar sale of 400m x 400m.

This I quote as I remember the numbers - I will post the link later this week.



Dipl.-Volkswirt (bdvb) Augustin (Political Economist)

EDIT:

"Table 1. Mission Times for Interplanetary and Interstellar Travel" in www.niac.usra.edu/files/studies/final_r ... ensen.html and in the .pdf-Version of this document, Page 16, says that at a Perihelion of 0.019 AU at a distance of one AU the acceleration is 100 m/s leading to a Terminal Velocity of 39,756 km/s (13%c) giving a time to Pluto of 1.7 days, a time to 10,000 AU distance of 1.2 years and a time to Alpha Centauri of 32 years. 0.019 AU are 2,850,000 km.

"Table 1 assumes the payload mass is negligible compared to the sail mass. If the payload mass is equal to the sail mass, accelerations will be reduced by a factor of two and trip times increased by 1.4. If the payload mass is only 10 percent of the sail mass, there will be little reduction in predicted accelerations. Also, we have made no assumption as to the size of the sail. Indeed, a small ultra-thin solar sail will accelerate just as well as a large ultra-thin sail, provided the payload mass fraction stays the same. The payload mass is the key variable that dictates sail size. With reductions in satellite size, micro-miniaturization, and fabrication of micro electro- mechanical systems (MEMS) and multifunctional structures (MFS), made possible by the needs for micro- and nano-satellites, the fabrication of solar sails is far more viable today than it was only twenty years ago, when solar sails were last considered seriously."


Back to top
Profile
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 5 posts ] 
 

Who is online 

Users browsing this forum: No registered users and 21 guests


cron
© 2014 The International Space Fellowship, developed by Gabitasoft Interactive. All Rights Reserved.  Privacy Policy | Terms of Use