well, somewhere I found the following figures, but I don't know how representative they are:

* Nuclear: 20.000 m/s – 50.000 m/s
* Ions (HiPEP, VASIMIR): 30.000 m/s – 50.000 m/s
* Ablative Laser Propulsion (ALP: LAPPS): 200.000 m/s - 32.000.000 m/s
* Anti-Matter (AIMStar): 600.000 m/s
* Nuclear Puls Propulsion (Orion, Deadalus): 100.000 m/s – 10.000.000 m/s

My first try was use of an engine with exhaust speed of 200.000 m/s:

For 100t of ship mass and 60 year flight time I got a 3,5*10^100 kg of reaction mass. ouch. eek

Second try with 32.000.000 m/s (which is itself 10% c, an extraordinary and probably unreliable value):
405 t of propellant (which, at present, is gold laugh )

for 60 years the needed acceleration/deceleration is: 2,322252 * 10^-2 m/sē, which seems pretty small.
But to accelerate the overall mass of ~500 t we would need ~ 11.6 kN ? (at the beginning).

Somewhere it was stated LAPPS could achieve a thrust of 0,031 N per MW, I'm hard wishing for an advancement of the factor 100 (! blush )
So we get 3 N per MW, which means we would need ~366GW.

A nuclear reactor for 1.6 GW already has a mass of more then 10.000 t, 100times the load capacity, let alone the fission material for 60 years. cry

I don't know the figures for VASIMIR and co, but it all sounds very unlikely. Either we need lots of propellant or a really big nuclear power plant.

Thats why I thought an orion style propulsion, without the need for external energy might be more feasible.

Edited by Momos (05/28/10 08:43 AM)