starship-design: Tight rope

[TLG.van.der.Linden@tip.nl (Timothy van der Linden)]

>>>>So, the sail/ship has to stay within about 1.E-6 lt-yr of the
>>>>focus to keep the power from dropping off by more than 10 percent.
>>>
>>>I read that as about 10,000,000 kilometers, or 32 light secounds.  Not a
>>>lot of slack over interstellar distences.  A sligh sail problem could have
>>>you well out of that pretty quickly.
>>
>>True, it would be a tight schedule: One minute too late at a certain place
>>and you have missed the beam for good.
>>Sailing on a beam means inherently that every second of the trip is planned,
>>slight deviations are allowed, but will be risky. A sail may sound as an
>>easy "engine", but you better have a good captain/navigator.
>
>Starting to sound like walking a muti light year tight rope.

Yes, it is, getting out of the helical movement is not the worst thing,
since the rotational acceleration is rather low, but the forward
acceleration is not. One engine failure for an hour and we have to drift
forever.
I see only two solutions, build a reserve engine based on fusion (or
whatever) so that in case of emergency a short (1 week?) burst can be
accomplished.
Or make the beam parallel, I wonder if this is possible when we make the
receiving and emitting antenna the same size.
Rex, can you confirm if this works?

Tim