Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Aerospace Propulsion system used in Space probes?

  1. Aug 7, 2012 #1
    What is the power source for space probes and how it is sustained for long flights in space?
    Also how do space probes reach phenomenal speeds (Helios attained 252,792 km/h !!)
  2. jcsd
  3. Aug 7, 2012 #2
    http://www.nasa.gov/missions/index.html has pages for current and past missions. My quick survey indicates that fuels are identified on many.

    Liquid hydrogen is popular. Hydrazine is listed. Pu-238 has been used on most robotic missions, but I've heard concern that the supply is too small to do all NASA will want in the future.
  4. Aug 8, 2012 #3
    Thanks for the info, but how is it possible to achieve high speed in space when compared to earth . In earth the max speed achieved is around 7 mach
  5. Aug 8, 2012 #4
    I am not an expert in this, but I would guess it is simply Newton's second law in action: whenever you apply a net force to a body, the body accelerates.

    The Deep Space 1 mission was sent tot look at Comet Borrelly in 2001. It had an ion drive, so by flinging off Xe ions, it experienced a thrust about equal to the weight of a sheet of paper. After about 600 days it was moving 11,000 km/h.

    I don't understand your second sentence. Are your saying that is the speed record for something in the Earth's atmosphere?
  6. Aug 10, 2012 #5


    User Avatar
    Gold Member

    Orbital velocity is about 17,000 mph.
    The highest speeds reached by classical rockets are somewhere in the 30-50,000 mph,
    for outer planet probes.
    It is common to use orbital slingshot manoeuvers to speed up these probes, which dramatically reduces the fuel required by exploiting the gravity well of the planets.
    Falling down the gravity well to the sun is also an excellent way to achieve very high speeds, as comets demonstrate regularly.
  7. Aug 10, 2012 #6


    User Avatar
    Science Advisor
    Gold Member

    It depends, but most are launched into orbit using chemical rockets. New probes might be using ion drives in the not too distant future, which can sustain low amounts of thrust for a long time (instead of high thrust for a very short time like a chemical rocket).

    Helios' max speed is a close pass of the sun. In an eccentric orbit, the closer something comes to the body it's orbiting the faster it goes.

    You're talking about max speed in the atmosphere. In space, the maximum speed is limited by the amount of fuel you're carrying and the rocket equation. Since there's no air in space there's no drag, so you can sustain very high speeds (the space shuttle orbited Earth at about 30,000 kph, Mach 25).
  8. Aug 11, 2012 #7
    Nope, was just trying to give a comparison. But you have answered my question
  9. Aug 11, 2012 #8


    User Avatar
    Staff Emeritus
    Science Advisor

Share this great discussion with others via Reddit, Google+, Twitter, or Facebook