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Building an Ion-thruster

  1. Sep 27, 2015 #1
    Would it be possible to build an approximately 10x10x10 cm ion-engine to put on a cube sattelite? I am a university student, so we have a lot of tools, but not a lot of money.
    What do I need to consider and how much would it cost?
     
  2. jcsd
  3. Sep 27, 2015 #2

    anorlunda

    Staff: Mentor

    Before the question of "could you", think of "should you".

    It is easier to conceive of a thruster that makes a trivial small thrust. But what would the point be?

    If it makes a significant thrust, then it could disrupt the orbit of the sattelite and NASA would probably not allow it.
     
  4. Sep 27, 2015 #3

    russ_watters

    User Avatar

    Staff: Mentor

    I suspect you could make a thruster that small, but powering it would be a problem.
     
  5. Sep 28, 2015 #4
    Thank you for the answers. With regards to the should, I do not know a lot about sattelite orbit legislation, but I imagine there are some international rules so they do not collide. But what if I wanted to fly my sattelite to the moon and orbit that instead?

    How large would the solar panels need to be in order to sustain a small ion-thruster? Or should it just carry a large battery? (I imagine this would be ineffecient due to the added weight.)
     
  6. Sep 28, 2015 #5

    anorlunda

    Staff: Mentor

    If you are ready for a project like that, you should be able to do basic engineering mathematics. How much energy would it take to lift 5kg from Earth orbit to Lunar orbit?
     
  7. Sep 28, 2015 #6
    Alright, I did not expect demands of simple considerations, but thank you for enlightening me. When I said I didn't know a lot about the legislation I could perhaps have expanded that to sattelites in general, as it was a friend who asked if I could build such an engine.

    $$ \int_{160000}^{380000000} G*m1*m2/x^2 dx = 1.24*10^{10} Joule $$

    I did consider the attraction from the moon aswell, but found it to be on the order of $$ 10^{8} Joule$$ and the length to the moon is an aproximate average.

    To be honest I have no idea what these numbers mean, but I have heard of people going far into outer space with ion engines.
     
  8. Sep 28, 2015 #7

    anorlunda

    Staff: Mentor

    OK, I was unable to check your numbers, but let's use them to answer your question about solar panels. If a Joule is one watt-second, estimate how many seconds you think it will take to accelerate/decelerate in the mission, and you can calculate the number of watts of solar panel you need. Then estimate the square meters and the mass of that amount of solar panels.

    If you are really serious about researching this project, you will need much more work, and more education. But dreams and curiosity might motivate you to get an engineering education.
     
  9. Sep 29, 2015 #8
    Well from googling around a bit and doing some calculations I found that one would need about 1.5 kg of solar sattelites which is not unacceptable.

    Given the mission takes a year, and solar panels can produce 300 W/kg (https://en.wikipedia.org/wiki/Solar_panels_on_spacecraft) . This is given a 100% efficient engine though.

    $$ 1.24*10^{10} Joule /(1 year) = 392 W$$

    $$ \frac{392 W }{ 300(W/Kg)} = 1.3 kg$$
     
  10. Sep 29, 2015 #9

    anorlunda

    Staff: Mentor

    I admire your persistance. Next step, consult https://en.wikipedia.org/wiki/Ion_thruster which says

    Ion thrusters have an input power spanning 1–7 kilowatts, exhaust velocity 20–50 kilometers per second,thrust 20–250 millinewtons and efficiency 60–80%.[1][2]

    The Deep Space 1 spacecraft, powered by an ion thruster, changed velocity by 4300 m/s while consuming less than 74 kilograms of xenon. The Dawn spacecraft broke the record, reaching 10,000 m/s.
    Neglect the difference between 392 w and 1 Kw; we should deal onlly with orders of magnitude.

    What is your estimate of the total mass of the spacecraft including reaction mass? What acceleration profile is needed to accomplish the mission? You should be able to estimate how many micronewtons of thrust are required and compare that with the 20 or more micronewtons Wikipedia says you can get at minimum power.

    At this point, we are neglecting the actual orbital mechanics of an Earth-Moon trajectory; just use straight lines.

    You may also learn more by studying NASA's descriptions of the Deep Space 1 and Dawn spacecraft.
     
  11. Oct 3, 2015 #10
    Had some busy days, anyway if we consider the mass of the sattelite to be a 10x10x10 aluminium cube + the solar panels. We get a weight of 1.5 kg+(density of aluminium *1000 cm^3)=4.2 kg. This is probably a crude approximation, but at least it will be in the ball park.

    The acceleration profile is calculated with $$ G*mass of earth/r^2 $$ where the mass of the satellite is divided out. I have an imgur link for the graph: http://imgur.com/62BNkrf

    The peak acceleration is at the start from low earth orbit, 160000 meters and was calculated to give $$6.5*10^4 Newton$$ which is somewhat more than 20 milinewton, so I probably made a mistake.
     
  12. Oct 3, 2015 #11

    anorlunda

    Staff: Mentor

    We all make mistakes. Don't feel bad. Once again, I admire your persistance.

    One mistake made very frequently is to assume that our ideas have not been thought of and perhaps already investigated by other people. In today's world, it is very difficult to have a truly original idea. Therefore, the first step after conceiving an idea is not to check its viability, but rather its originality. You could have started with NASA public information.
     
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