Jet planes only can fly fast as they do just because the resistence of
the air that surrounds them. How possibly can we possibly expect a
spaceship - in an outer space mission - goes as faster as a jet plane
if there is no air resistence acting over there? How could it keep on
accelerating? Is there any practical solution for that, based on the
technology we achieved nowadays?

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Request for Question Clarification by techtor-ga on 16 Feb 2005 08:24 PST

Hello Carioca35,
Do you mean to ask, what is the fastest possible speed a space vehicle
can achieve? And do you wish to know the factors affecting this?

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Request for Question Clarification by pafalafa-ga on 16 Feb 2005 08:26 PST

A jet plane actually does not need air to go fast.  The air in
necessary for two things:  (1) creating lift so the jet plane can fly 
(2) providing oxygen for the fuel to burn.

However, the speed of the jet is related to the amount of thrust
created by burning the fuel.

A spaceship carries its own oxygen supply, so it can burn fuel even in
the absence of any air.  The thrust of the engines provide both speed
and lift, so that no air is needed.

In fact, the absence of air resistance is one of the factors that
allows a rocket to go really fast!

Is this the sort of explanation you were looking for?

If not, please let us know in a bit more detail how we can best help
you with your question.

Thanks,

pafalafa-ga

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Clarification of Question by carioca35_-ga on 19 Feb 2005 09:03 PST

Anyway, oxygen is a spaceshipīs limited resource, so, within space, it
can extinguish anytime. And I guess - in a long run - if you donīt
have oxygen, you will not be able to burn fuel in order to get an
appropriate thrust to accelerate or stop the vassel.

I would like to know if someone knows how this problem can be solved.

Hello Carioca35_,

Let me restate the main question slightly and then answer it. The
other questions will be answered below as well.

  How does a space ship [w/o air] travel faster than an airplane [in air]?

The motion of both the space ship and airplane is basically dependent
on a rule called "Newton's Third Law of Motion", described in brief at
  http://hyperphysics.phy-astr.gsu.edu/hbase/newt.html
[scroll near to the bottom]
which basically states that
  For every action, these is an equal and opposite reaction.
In the case of the space ship, when it "burns fuel", the "action" is
the motion of the burnt fuel to the rear of the ship, and the
"reaction" is that the space ship moves forward. Once the ship is out
of the atmosphere, there is basically no practical limit to the speed
- provided you have enough fuel. Fuel becomes a limit much sooner than
other limits such as the speed of light.

Several other commenters have indicated that the fuel is burnt by a
combination of fuel and oxygen. This type of fuel is NOT required to
make a space ship or rocket work. For a simple example of this,
consider a "water rocket" that can be picked up at a toy store and
explained quite well at:
  http://users.bigpond.net.au/mechtoys/waterrocket.html
In this case, no fuel is "burnt". The rocket moves up (and may work
quite well in outer space) because the water (the fuel) is pushed
through the nozzle by the compressed air.

There are several other methods to create space ship engines. Some of
the more notable ones include:

nuclear blasts, described briefly at
http://www.scibooks.org/orion.html

ion drive, efficient to use if you don't mind taking a while to accelerate at
http://www.space.com/scienceastronomy/solarsystem/deepspace_propulsion_000816.html

bussard ramjet, a theoretical interstellar engine at
http://www.bbc.co.uk/dna/h2g2/alabaster/A600436

and several others.

With this as context, now to answer the other two questions.

Q: How could it [the space ship] keep on accelerating?
A: The space ship can't. Eventually you will run out of fuel. The ion
drive described in the link above ran for over 200 days of operation,
but eventually it ran out of its fuel. At that point the space craft
will coast and move based on the gravity of the sun, planets, moons,
etc.

Q: Is there any practical solution for that, based on the technology
we achieved nowadays?
A: The Bussard ramjet describes the engine for an interstellar space
ship. In this case the fuel is small particles of hydrogen spread
throughout the universe.  Science fiction authors have written stories
about use of that type of engine. The book "Tau Zero" described in the
link above has a ship that "breaks" on route to another star. The crew
decides to "keep going" and see if they can land somewhere else but
that does not work very well either and they keep going faster and
faster. [I won't spoil the ending]

We cannot build such a ship today but we have ideas on how to do so.
Maybe not so practical after all.

I hope this answer explains how space ships (or rockets) work and how
they go faster - much faster - than airplanes. For more information,
try searches like

  Newton's law of motion
  air water rocket toy
  nuclear bomb rocket orion
  ion drive rocket
  bussard ramjet rocket

to get more information.  

If the explanation is unclear to you or you need an expanded
explanation of a part of the answer, please make a clarification
request.

  --Maniac
?

The air resistance *limits* how fast a plane can go.  It doesn't
enable the plane to accelerate.

It sounds to me like you are thinking that a spaceship could never
accelerate because there is nothing in space for it to push against. 
This is a common mistake.  In fact, the New York Times ran an
editorial in the early days of rocketry ridiculing the idea of space
travel for just this reason.  (They printed an apology on the day that
man landed on the moon.)

Rockets accelerate because of conservation of momentum, not because
the exhaust of their engines pushes against anything.

there is actually different space propulsion technology called
ion-drive technology that allows for a consistent acceleration the
specifics of how it works i cannot recall however.

Another consideration...

If you could overcome the limited fuel problem you?re still limited by
the speed of light (as mentioned by maniac above).  This is due to
Einstein?s theory of Relativity, which states that as an object
increases speed, its mass also increases.

Mass (effective) = Mass (rest) / (1 ? v^2/c^2)^1/2

where v = speed, and c = speed of light.  At low speeds this increase
in mass is negligible, however as you approach the speed of light it
becomes quite significant.  Since E = mc^2, this means that the
increase in mass ?uses up? energy.  This energy comes from your
engines.  So instead of putting all your energy into accelerating,
some of it is now going towards increasing your mass.  When you get
close to the speed of light, almost all of your energy is getting
turned into mass, and you?re hardly accelerating!  This is why you
can?t go the speed of light.

I?m sure this wasn?t the exact answer you were looking for, but I hope
that you?ll find it to be an enlightening side note.

-namcaps

There does exist a means of propellantless propulsion for a starship. 
Based on the work of Miguel Alcubierre and Albert Einstein it utilizes
a huge, resonant, neutral, electromegnetic field to react off of
space/time itself.  If you want to go lightspeed, your starship has to
behave like a photon of light.  It is the only feasable way that man
will ever travel freely in outer space.  See the webpage on this
design at:   www.ovalecotech.ca