Re: TML nightly: Msgs 6927-6932 V69#17

> Simon Hibbs
> From: [email removed]
[stuff...deleted]
>
> HEPLAR drives are not a recent idea, Larry Niven's stories have
> included a similar system for a long time, the basic idea is just to put
> a hole in a fusion reactor and bigo - instant fusion drive. (Simplified,
> but that's the theory). Another axiom from Niven's Known Space series is
> that the efficiency of a propulsion system is directly proportional to it's
> efficiency as a weapon. If you work out the exhaust velocity of a HEPLAR
> thrust jet, it approximates to one quarter of the speed of light! There are
> two problems with this: a) I very much doubt that a fusion drive is capable
> of generating exhaust velocities even approaching this. b) If I were
> responsible for planetary space traffic controll, I would not allow a HEPLAR
> drive inside the orbit of the moon, let alone land on the planet's surface.

Sticking to the GDW definition of Plasma Physics,  You're absolutely
correct on both points!

> Even worse, Some of the example planetary vehicles use HEPLAR propulsion!
> Anyone care to calculate the weapon statistics for a typical HEPLAR drive?

When within a planetary atmosphere it should behave like a
plasma/fusion weapon of similar output.  However, it should also be as
harmless as a fusion gun in space.  All the charged ions from the
plasma will repell each other once outside of the confines of the
power plant's magnetic containment field, thus instanting dissapating
the exhaust.

> There is a way round this : use a denser fluid as the exhaust gas. The most
> suitable medium is probably water. By mixing the exhaust hydrogen with an
> inert medium you actualy increse the efficiency of the drive. A lot of the
> energy in a pure hydrogen exhaust would be lost as thermal radiation and
> gamma rays, contributing no thrust. These would be absorbed by a dense
> exhaust agent and so increase efficiency. Also, water is denser than hydrogen,
> so the volume of reaction mass would be reduced.

The amount of additional thrust from this would be minimal when
compared to the *incredible* amount from the HEPlaR drive.  Once the
water is heated to a certain point all you'll get is increasingly
ionized hydrogen and oxygen without any increaing gains in thrust.

All thing considered, I'll stick to the HEPlaR as it is.  If you look
too closely at the 'science' behind Traveller you'll find all kinds of
problems with it.

Remember to have fun and leave the 'Hard science' out of Traveller.

- -EF