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Old March 6th 05, 08:47 AM
Ron Wanttaja
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On Sun, 06 Mar 2005 14:03:42 +0800, Stealth Pilot wrote:

On Sat, 05 Mar 2005 19:11:22 GMT, Ron Wanttaja
wrote:



Let's assume an open-cockpit single-seater. Call it 200 lbs for the pilot,
another 100 lbs for his suit, 500 pounds of airframe, 20 pounds of avionics, and
50 pounds for batteries and life support supplied. Let's assume our rocket fuel
has a specific impulse of 250 seconds. That's a dry weight of about 870 pounds.


forgive my iggorance.
are we talking earth pounds, moon pounds or mass?
and if we are talking mass is it roman catholic, anglican or
engineering?


Now stop that. :-)

what is actually needed is for someone to do a Wright Brothers on
gravity.
aviation would go another quantum leap forward if we could just negate
the aircraft weight without all that drag.
it is amazing that with all our progress we havent made one single
inroad into understanding or controlling gravity.


You've hit the nail right on the head. Right now, space travel is at the
equivalent level of the Montgolfier brothers. Chemical rockets are a dead end;
the moral equivalent of de Rozier's combination hot air/hydrogen balloon.

Heavier than air flight wasn't possible until the invention of the internal
combustion engine. Similarly, the true exploitation of space is waiting for a
system that will produce good acceleration without the need of tons of fuel.

It's sort of in our grasp, now. Chemical fueled engines have Specific Impulses
(Isp) in the range of 200-300 seconds. Modern electric propulsion units see
ISPs up to about 3000 seconds.

What does that mean? Well, I used an Isp of 250 for the thrust-hovering moon
buggy. If you recall, it needed 25 million pounds of fuel for Rich's
cross-country.

With an ISP of 3000, the fuel requirement drops from 25,000,000 pounds...to a
bit over 1,000. Yes, about four orders of magnitude. These units are
operational *now*...they're used on communications satellites.

They produce a lot of thrust for very little fuel, but the actual amount of
thrust they produce is minuscule. The commsats use them to compensate for the
north-south wobble their orbits get from the uneven distribution of mass within
the earth. They need 150 FPS of delta-V per year, and they run the electric
propulsion nearly constantly.

As you might expect, they require a lot of power. But a dozen miles from Rich's
house, a number of airtight spacecraft hulls complete with operational nuclear
power plants lie in storage. The Navy calls them, "mothballed submarines."
Back when a tsunami hit Hawaii forty or so years ago, they powered Honolulu with
the output of *one* of these subs.

Cooling them in space, where you don't have access to billions of tons of cold
sea water, is left to the good offices of your local thermal engineer.

Ron Wanttaja