4 Responses

1. jet sucks in air n pushes it out
   no atmosphere in space,no air to suck,no air to push
   rocket works on principle of thrust force
   it carries fuel
   force=(velocity of expulsion of fuel/total mass of fuel)(dm/dt)
   ie rate of loss of mass
   In ion propulsion system,instead of use of heavy normal fuels,ionized Xe is used and accelerated through a solenoid and pushed out at high speed thus we get more thrust carrying lower mass
   thats it

2. Rocket propulsion relies on the expansion of gases in a chemical reaction to push against the tail of the rocket and move it forward.

   Typical rocket fuel is liquid hydrogen, with liquid oxygen as the oxidizer. This reaction is exothermic and does not require additional atmospheric oxygen to proceed, so the reaction can take place even in a vacuum, in space.

   A jet engine relies on atmospheric oxygen and compressors to burn jet fuel and achieve thrust.

   Ion propulsion uses an electric potential difference created in the engine to accelerate ions (charged atoms) out the back of the rocket, producing thrust that propels the rocket forward. The ions may be generated by a source carried on the rocket, or they could theoretically be gathered from the interstellar medium.

3. All propulsion systems work by changing the momentum of the vehicle. Rockets work by throwing mass out the back – throwing hot gas as fast as possible. Rockets therefore have to carry their “change of speed” mass with them, making them very inefficient.
   Jet engines gather air, heat it and fire it out the back in oder to change speed. They require air in order to work and so won’t work in space.

   Ion engines fire small amounts of mass, extremely quickly, out the back. They need to carry the mass with them but the energy required to speed up the mass can be gathered from sunlight, or onboard reactors resulting in much improved afficiency. Unfortunately, up to now, such engines will only produce rather slow changes in velocity meaning journey times of many years,not suitable for human impatience.

4. Newt’s third law…for every force there is an equal but opposite force.

   The force is the thrust of the rockets, the equal but opposite force then pushes on the rocket to make it go forward. Rockets can create that thrust by burning fuel. The fuel can burn in space because the rocket also carries its own oxygen.

   Jet engines won’t work in space because they don’t carry their own oxygen. Their oxygen comes from the air. Other than that, jets and rockets work the same way…equal but opposite forces push them.

   The ion drives, like NASA’s Deep Space 1, also work the same way…equal but opposite forces. But, and this is a big BUT, the difference is in the fuel. Where jets and rockets use chemical fuel, the ion drives use ions, which are charged particles. Because they have charge, they can be dragged along by electro magnetic forces, just like the ions in the beam of an analog TV are dragged back and forth on the screen to form a picture, by using electro magnets.

   As you might guess, ions are not very heavy; so it takes a lot of them to get just the tiniest of thrust. So ion drives are usually lifted into space by chemical rockets before they are activated on ions. Then they can be fired for very long periods of time. Which means they can accelerate slowly but for a long time and, thereby, gain respectable velocities to fly and circle comets millions of miles in space.

   Impulse is defined as dP = F dt. This simply says that, for a fixed thrust (F) if we apply that thrust for a long time dt, we can make a huge change in momentum dP = m(V – v) where V > v are the final and initial velocities changed over the period dt. And that’s how ion drives get up to speed…low thrust F but for very long times dt.