Re: starship-design: New Idea from non member

[Zenon Kulpa <zkulpa@zmit1.ippt.gov.pl>]

> From: KellySt@aol.com
> 
> In a message dated 7/22/97 3:46:35 PM, jimaclem@juno.com wrote:
> 
> >---------start new idea -------------------
> >
> >Each transmitter could be a stationary fusion rocket with the beam
> >pointed in one direction, and the fusion exhaust (at very low speed)
> >pointed in the other.  Since the whole thing is stationary, it could be
> >refueled periodicly by robot tenders.  The fusion motor could tap most
> >of the kinetic/thermal energy of the fusion products to provide
> >electricity to power the transmitter, with a little left over kinetic
> >energy and a fair amount of mass to provide a counter balancing force.
> >
> >---------end new idea -------comments?-----
> 
> Cool, that would also get around the problem of the transmiters 
> moving during the transmition period.
> 
Eh, what do you mean by "stationary"?
Nothing in space is stationary, it will always orbit
around (or falling at) some other body.
You may make it "stationary" with respect to the Sun
making it hover at a distance due to constant thrust
toward the Sun (I wonder how large thrust it should be 
in the gravitational field of the Sun near the Earth orbit -
can physicists here calculate this?). However, the thrust
should also compensate for the recoil from the emitted
beam (quite large, I am afraid).
Moreover, refueling them would be a problem - a robot tender
going from Earth (or the asteroid belt) with the fuel
will have to decelerate away all its orbital speed
(30 km/s in the vicinity of Earth's orbit),
stay "stationary" on its rocket exhaust when at the transmitter
(or be firmly hooked to it, using transmitter increased thrust 
for hovering) and then accelerate again to this speed when going back.
And such a manoeuver will certainly shatter a little 
the transmitter itself, making the beam jiggling.

There will be similar problem with positioning the starship itself
on the straight-line (along the beam) course to the target system - 
first you must somehow annihilate its orbiting speed around the Sun
(which will be essentially perpendicular to the direction 
of the beam...).

-- Zenon