Some comments about zero point energy/ vacuum energy…

http://en.wikipedia.org/wiki/Vacuum_energy

http://en.wikipedia.org/wiki/Dark_energy

Not sure I want to go into definitions really,
there are the wiki articles after all, but
basically the idea (as I understand it) is
that if a certain volume of space is lowered
to a temperature of exactly zero degrees
Kelvin, a tremendous amount of free energy
is available. A famous example is the coffee cup
volume that boils the Earth’s oceans.

The potential for ZPE is quite interesting as
the free energy is not entirely free as some
form of chemically inert material would be
needed as “fuel”, so in fact the interesting thing
with regards to space travel is that it has only
limited use in a confined environment
(i.e. running on board ship systems)
when the propellant has been exhausted.

A small ZPE device could be fitted into the water
boiling central heating system in people’s homes
and into their cars. In both cases, the fuel used
would be plain water.

If we imagine a not entirely unrealistic science
fiction scenario, a civilization such as ours
would only be able to make the most of the
technique with an abundance of inert fuels like water.
On Earth, extended use would risk increasing
global warming, but the technology would be
perfect for terraforming Venus, as oxygen could
be produced as a by-product, and global warming
would be essential in making Mars habitable.

ZPE is mentioned in Arthur C. Clarkes’s 3001
as powering inertial drives aboard spaceships,
as well as being a general power source.
In the television series Babylon 5, although not
mentioned directly, I would imagine that ZPE is
the most likely power source for the Directed Energy
Weapons used by the Shadow’s Capital Ships.

The Vorlons probably also use the technology
in the main weapon aboard their Planet Killers
(top image), and is likely to power the braking
mechanism aboard their transport ships.

(notice the flower petal design. This opens when the ship decelerates, presumably allowing a Vorlon Transport to expend all its fuel/propellant in accelerating to speeds at least twice as fast as other ships)

ZPE is also a likely power source for at least some of the abilities demonstrated by Technomages.

Of course, in all the instances described from science fiction, ZPE is directly focused or transferred to momentum.

On analysis, Arthur C. Clarke's description is probably the least realistic as no propellant is descrbed, but ZPEis directly mentioned as a universal power source.