Re: starship-design: the beamed power problem, again

["Kevin \"Tex\" Houston" <hous0042@maroon.tc.umn.edu>]

Kelly Starks x7066 MS 10-39 wrote:
> 
> At 10:52 AM 9/4/96, Steve VanDevender wrote:
> >Rex (DotarSojat@aol.com) and I have been having a private discussion on
> >my assertion that if you are beaming power to a starship to give it a
> >fixed ship-frame acceleration, you have only a finite amount of time
> >during which you can send power to the ship, no matter how long the
> >ship's trip time is.  For example, if you are beaming power to
> >accelerate a ship at 1 g, you have just short of a year after its
> >departure to beam power to it, no matter how far away you are sending
> >it, and you must beam increasing amounts of power towards the end of
> >that time to sustain the 1 g ship-frame acceleration.
>

I found another way to note the same thing.  A constant 1 G thrust
profile
mission, takes about 5years ship time and 13.25 years earth time, to go
11.9 light-years.  so on the last day, as your ship coasts into target
system, the light (microwaves) you are seeing left earth 11.9 years ago,
and 13.25 years after the start of the mission.  Thus that light must
have been emmitted ~1.35 years after the start of the mission (from
Earth's
perspective)

> I beleave the english translation of the following; is that after about a
> year of 1G acceleration, the ships moving at near light speed.  Since the
> microwaves are moving at exactly lightspeed.  At some point the beam can't
> really catch up with the ship in time to be usefull.
> 

But at turn-around the ship is only moving at a speed of .9905 C.  This
is 
because 11.9 light-years is too short a distance to get into the
_really_
strange parts of the trip.  The gamma for this is "only" 7.27  This is
not really all that bad.  The microwave wavelength will only shrink or
stretch (depending on your direction) by this amount.  Same with the
the power drop, and the time dialation factor.

How about a mission which has a constant beam power, the acceleration
would 
drop off toward the turnaround point.  In this case, the crew would
start off
with earth-like gravity, and towards the middle of the trip, the gravity
would
be more lunar-like.  ( a little less actually, but not for long)

The advantage would be simplified beaming requirements, and the
disadvantage
would be a slightly longer flight time.

Questions:  
What would the top speed relative to Earth be?
What is the total trip time. (crew time?)
how much of this time is spent at less than 1/2 G?


Kevin



> Kelly
> 
-- 
Kevin "Tex" Houston 	http://umn.edu/~hous0042/index.html