# Re: Engineering Newsletter

```ReplyTo: Kevin

>1) about the timing problem.  Since "Asimov" and the beam are traveling
>in the same direction, the beam starts at the same time that the "Asimov"
>does.  Also, the beam only needs to be on for about 1.5 years due to
>relativistic effects

The Asimov will take at least 1 year to accelerate.So the beam won't start
at the same time but at least 1 year later. Also the beam of photons travels
with the speed of light so it has be beamed another 5 years later, so that
it does not catch up with the Asimov prematurely.
Besides that problem, the beam then still has to be aimed exactly at the
place where the Asimov will be after about 15 years, and it should be there
at that time and not a month later.
Maybe I haven't used the correct
To me this still seems to be a timing problem. If I'm wrong, tell me where.

>2) this isn't a maser sail, the momentum imparted by the beam itself is
>negligible compared to the momentum generated by the engine exhaust.  and
>since the engine exhaust can be directed either foreward or backward,
>this is not a problem

What matters is the energy:momentum ratio of the beamed power.
For the photons in the beam that ratio is:

E:p = c:1   where c=3E8

For the Asimov moving at 0.7 c that ratio is:

E:p = 0.4c:1

The beam needs to have about 1/0.4=2.5 times less momentum than the Asimov,
but that is still a lot, so I can't agree with you that the momentum of the
beam is neglectable.

Using a particle beam would make the problem worse because you would get the
same energy:momentum ratio as the ship. Also a particle beam would mean that
the amount of received particles increases as the Asimov slows down.

>> Using ISM would be great, but it seems that only VERY BIG scoops could do
>> the trick. I still haven't seen a formula about a scoop field. Kevin you
>> seem to have one, is it possible that I could see that formula?
>>
>I have posted it several times, i will do so again soon.  i can't seem to
>locate it right now, but it's not hard to derivate

OK, I look forward to it. (I haven't seen it in any newsletter for at least
the last 4 months and don't know how I should derive it.)

>> Maybe we should find a nearby star in a nebula, that sure would increase the
>> ISM-density. I'm not sure if there are any nearby nebulae. Does someone know
>> more about that?
>>
>then how do we get from the nebula to the target system?

My hopes were that the star was in or nearby the nebula, so once you are
almost to a standstill you are near your destination.
Maybe a nebula implies lifeless planets, but I don't know enough about that.

Timothy

```