sanman wrote:
Australian engineers have just announced what they claim is a much
more efficient ion thruster:

http://www.e4engineering.com/item.as...ews&ch=e4_home

It's been pointed out that ion thrusters are more efficient on Isp,
but they produce less thrust -- too little to be of use for launching
to orbit. By a factor of how much are ion thrusters too weak for
achieving escape velocity?
By how many times would the above system have to be improved to be
used for SSTO?

Efficiancy isn't the problem.
Physics is.
Current ion thrusters are well over 10% efficiant, (I think it's
around 70%) in converting electrical energy to kinetic energy of
the exhaust.

The problem is that for an ISP of 5000 seconds, you've got to
provide at least 2.5 billion joules per kilo of propellant.

A large power station provides about 2.5 gigawatts, and will provide
enough power to run about a kilo a second through your thruster,
for a thrust of about 5000Kg.
Most power stations weigh considerably more than this.

Compare this with typical chemical systems which only need around
25 million or so, to get an ISP of 500.

Now, add the huge amount of electrical circuitry, generators, ...
You might be able to do SSTO from eros, but nothing much bigger.


I presume that nuclear power can be used to augment the
thrust/efficiency of electric propulsion. Would it be enough?

No.
Electricity generation plant is HEAVY.


--
http://inquisitor.i.am/ | | Ian Stirling.
---------------------------+-------------------------+--------------------------
What a wonderfull world it is that has girls in it! -- Robert A Heinlein.