[gurps] TL10 spacecraft, was: wish list

[Pauli Hakala]

Onno Meyer wrote:
> David replied to me:
>>>> The exhaust from
>>>> fusion rockets needn't be terribly radioactive.  A D-3HE fusion
>>>> reactor is fairly low radiation output.
>>>> David Scheidt
>>>> dmscheidt at gmail.com
>>> Talking about radiation, "fairly low" doesn't sound all that
>>> reassuring, expecially if space traffic starts to rival air
>>> traffic today. Consider what happened to nuclear freighters.
>> It really matters what kind of radiation you're talking about.  A
>> D-3He fusion reactor uses two inert (well, one of them is inflammable)
>> gases as fuel.  The primary products are heat, a proton, an alpha
>> particle, and some X rays.  Most of the Xrays will be absorbed by the
>> shell of the reactor, as they're radiated pretty equally in all
>> directions.  One end of a fusion rocket is open, so there will
>> escaping Xrays in that direction.  They'll get absorbed (as heat) by
>> the atmosphere in less distance than the exhaust will kill anything
>> the plain old-fashioned way:  by setting it on fire.  The proton and
>> alpha particle will be indistinguishable from the very high
>> temperature air or other reaction mass that's being shot out the back.
>>  There are essentially no long-lasting sources of radiation there.
>> Setting things on fire is much more of a problem.  The exhaust
>> temperature is very high.  For things that act something like
>> airplanes (with wings or lifting bodies) they can use the air-ram as a
>> sort of ducted fan until they're well air borne, and then turn on the
>> full power.
>>
>> Fission reactors, on the other hand, produce lots of particles that
>> hang around and emit radiation for (days/months/years/centuries),
>> depending on the particular reactions involved.  (They could be used
>> in a fully-closed thermal only mode, but I don't think they'd produce
>> enough thrust that way.)
> 
> Once upon a time, I wrote those. For frontier operations, they have 
> vectored thrust, despite the fact that they fry the landing zone. I
> figured that you could come down with a light touch, and never take 
> off twice from the same spot. 
> 
> I kind of dodged the question if a fusion air ram (and a fusion ram
> rocket) is supposed to be an pure ramjet. If so, it only works over
> 375 mph, and the initial acceleration must come from a water-based
> fusion rocket.
> 

Fusion Air-Rams are clearly described in V2nd as sucking in air
- i.e. actively breathing in air regardless of vehicle velocity. There
is no reason given to believe that fusion ram-rockets would behave
at all differently in an atmosphere. No minimum air speed is mentioned
anywhere for fusion air rams or fusion ram-rockets.

This does make sense, because at the point where your technology can
make a small miniaturized fusion reactor for a fusion air-ram, equipping
that same engine with air intake fans powered by that fusion reactor
should not be a problem, IMHO..


-Pauli
--
"Our ship is made out of darkness, she mocks the laws of nature.
With cables, ropes, tackle and sails, she moves on the waves
of the void. On her decks a red crew, dark as if painted with
blood. From among the hooded cloaks of crimson, eyes of
silver gleam darkly.. Oldest of all is Hiram of Malta, the Red
Commander. He knows the secrets of Schwarzchild Radii, of Neutron
Stars and Cepheids. His hidden paths we follow, like ghosts from
space we strike deep, only to disappear again soon, sometimes even
the fear itself is afraid of us.."
-CMX, Punainen Komentaja
(Translated from the Finnish song 'Red Commander' by CMX)