Re: Obliterating the Rocket Equation with a Torusail

You imply that we can travel round the solar system comfortably now,
but that the only conceivable method of interstellar propulsion is
bombtrack.
This is simply incorrect.

> Specific energy density. High exhaust velocity doesn't really
> gain you anything if your fuel doesn't have the energy density
> to support it. For example, fission fuel has sufficient energy
> density to theoretically accelerate itself to around 3.7% of c.

So use deuterium with fusion, giving much higher Ve, 0.1C
and higher. If you wish to make a point that nuclear light
bulb/photovoltaic conversion/ion drive
is worthless for interstellar travel, you must assume the
best possible such drive and destroy
it. Not describe the least likely implementation.

> if you attach a nuclear-light-bulb fission reactor to an ion
> drive which has an exhaust velocity greater than 3.7%c, then
> you'll be consuming more fuel than the amount of propellant
> you can exhaust. In short, you'll be dumping some spent fuel
> overboard while accelerating the rest of the spent fuel through
> the ion drive. This turns out to give you less thrust and less
> delta-v than accelerating all of the spent fuel to 3.7%c.

Nothing in what I wrote implied that I didn't understand that the Ve of

an ion drive must match the reactor power output.

Even with your own fuel and numbers,
given an exhaust of 0.037C and a mass ratio
of say 500, this would give a delta V of loge(500)*0.037C = 0.22C,
which allows a cruise of 0.11C, which allows a 10 ton probe with
5000 tons of fuel to get to alpha-centauri 3.7 L.Y times 1/0.11 = 33.6
years,
which is a finite time, hence interstellar travel is possible,
so the idea is not "worthless", even on your own incorrect assumptions.

.

Relevant Pages

  • Re: Obliterating the Rocket Equation with a Torusail
    ... > You imply that we can travel round the solar system comfortably now, ... No, I specifically talk about _fast_ interstellar propulsion, and I ... fission fuel has sufficient energy ... The worst part is the ion drive--thrust/weight ratios for ion drives ...
    (rec.arts.sf.science)
  • Re: Best choice of FTL fuel?
    ... Neither make FTL travel, including "wilderness refuelling", too easy, nor too difficult. ... Primitive star travel could involve cryogenic storage of hydrogen and helium (for FTL fuel), and only later on do they rediscover how to make carbon nanotubes. ... I had ruled that FTL drives use the same fuel as ...
    (rec.arts.sf.science)
  • NEWS: Fuel prices shrink the map as RV nation hits the road
    ... Fuel prices shrink the map as RV nation hits the road ... chief executive of Travel Oregon. ... Davidson said his agency has calculated that the rising fuel costs ...
    (rec.outdoors.rv-travel)
  • =?iso-8859-1?Q?Re:_=A390_to_fill_my_car_up?=
    ... Now I travel 18 miles a day. ... HR lady mentioned that if fuel went up much more, ... costs were high then. ... petrol costs are so prohibitive they couldn't afford to take certain ...
    (uk.media.tv.misc)
  • Re: Konstantin Tsiolokvsky was wrong?!
    ... If the fuel is fed at a constant rate and he ... You still burn fuel, ... point of view of the rocket. ... and a constant exhaust velocity is a very good ...
    (sci.physics)