Joseph Paul wrote:
> We just had a discussion about that with a new Doubting Thomas.

I zoned out of that after the signal:noise ratio zeroed out.
Sadly some threads degenerate that way.

In any case, the CSBA website has some useful reading material for people
outside the defence industry who want to know something about some current
thinking/controversies in that sector.

Grimmund wrote:
> If your objective is to jump in-system at 100D from the main world and
> land an i nvasion force on the planet, the location of ships too far
> away to impact the combat may not be terribly relevant to the invasion.

What does 'too far away to impact the combat' mean with Traveller
reactionless thrusters?
More than a few hours? How long is an invasion going to take?

For example, Jupiter to Earth is 6 days away at 1G brachistochrone (constant
acceleration/decel from midpoint), or a day away at 6G.

> On the gripping hand, an invader could, for example, send some sort of
> commercial ship ahead of the invasion fleet by several hours, to scout
> the target system and relay that information to the invasion fleet.

The 'spy trawler' or scout is going to need more time than that to get
useful info (vessel numbers, types, orbital elements) if we use the
astronomy literature as a model for observations and sensor limitations.

http://www.aura-astronomy.org/news/hdst.asp

It is relatively hard to look into the inner system, mask out the local sun,
and look for the reflected light off spacecraft or their infrared emissions.

Gravito-optical focusing and other Traveller handwaves are going to give you
smaller sensors for a given sensitivity but you aren't going to get around
the wave properties of light.

Richard Aiken wrote:
> On the fourth tentacle . . . near-c rocks are beginning to look attractive
> . . .

Never.
Endless reactionless thrust was and is a big whoops which should have fallen
out of Traveller.

1G of acceleration for an hour (1G-hour) is a delta-v of about 35.3km/sec.
New Horizon's solar escape trajectory? 16.5km/sec at launch.

IMHO reactionless drives should be thrust limited (so many G-hours before
you have to turn them off, or get near a massive body to offload the
momentum you stole to gain velocity in the first place, etc.)

Higher tech levels? More G-hours possible, more efficient drives (converting
reactor energy to kinetic energy of vehicle thrust).

"Special Supplement 3, Missiles" in JTAS 21 has a similar concept for ship's
missiles with thrust ratings in 1000 second space combat turns. So a 6G6
rated missile can accelerate at 6G for 1000 seconds, or 1G for 6000(!)
seconds: 1.67 G-hours or ~59km/sec delta-v.

Grimmund again:
> The other problem is that any drive powerful enough to accelearte a
> rock to that sort of speed will warm the rock quite a bit in the process.

Yes in ordinary circumstances. However, Traveller reactionless thrusters
appear to violate conservation of energy from the various design rules
(power in is less than addition rate of kinetic energy) so who knows?

Thanks to Anthony Jackson for a useful rule of thumb re: relativistic
impactors:
> If you have a 1,000 ton impactor, and you put a 1 ton object in front of
> it, the impactor turns into
> a cloud of material expanding at something like 10,000 km/sec. If you do
> it right, you may even get a
> donut-shaped cloud of gas, but even if you don't, blowing something up at
> the 100d limit will turn it
> into a cloud three times the size of the planet by the time it hits.

Rob O'Connor