* Posts by Adam

2 posts • joined 3 Jan 2008

Plasma rocket space drive in key test milestone


Radiators guys, not wings

Typical space nuke power-plant is 25-30% efficient. Thus generating 10 MW electrical power makes about 30 MW of heat that can only be dumped by radiating it away. Thus big radiator surfaces.

Someone mentioned fusion drives, but even they will need BIG radiators, unless you're throwing bombs overboard and riding the plasma - in which case you need a big ablation plate and huge shock-absorbers.

Chiang-Diaz's 39-day ride to Mars needs a 200 MW power source that doesn't mass too much - ain't gonna happen soon. The 10 MW VASIMR takes a couple of hundred days for the trip.

The Electric Car Conspiracy ... that never was


There's efficiency and there's efficiency...

Internal combustion engines hooked up to current drive trains only get a tiny fraction of the energy of their fuel into actual driving power. Modern IC engines get about 38% thermal efficiency, which can be pushed a bit higher in some vehicles, but is much the same across models. Coupling that to the wheels is where all the energy is wasted - less than 20% (less than 10% in many vehicles) goes into actually driving the car.

Hybrids do much better by getting rid of all the frictional and mechanical losses in the drive train. Electric motors have a lot of advantages and that's the major one. Thus the high efficiencies hybrids get and even higher efficiencies when recharging via regenerative braking becomes even more efficient.

So long as petrol engines are powering a ridiculous transmission system the 12,444 W.hr/kg of petrol is effectively only 1,244 W.hr/kg or less. Thus batteries are somewhat closer to petrol in effective energy density. With a hybrid things improve out of sight for petrol - though the effective density is still only <4,800 W.hr/kg due to the nature of IC engine thermodynamics.

An EV powered up by a solar array would win hands down in terms of fuel efficiency and that's the "Great Green Dream" of many people who want to survive the present Energy Crisis in style. A lot of people want to cut the Middle-East Oil-Noose from around their necks.

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