Re: Quick question about a STL trip - and another...

In message
<c5e1eab9-2ce0-4a32-954e-2296f010416d@xxxxxxxxxxxxxxxxxxxxxxxxxxx>,
IsaacKuo <mechdan@xxxxxxxxx> writes
On Aug 21, 11:28 am, Jacey Bedford <lookin...@xxxxxxxxxxxxxx> wrote:
In message
<dbfdda79-0083-4bbb-8545-51a908596...@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>,
IsaacKuo <mech...@xxxxxxxxx> writes

My prefered braking drive is a kinetic impact powered rocket.
<Snip good stuff>

Probably a dumb question, but this impacts on something I'm just
starting to work on right now...

In a generation ship what kind of changes would the passengers and crew
feel/hear/sense on board ship between a) normal drive, b) deceleration
and c) we've arrived?

If we're talking about a generation ship, then it's okay to have
acceleration and deceleration times on the order of decades.
This reduces the required power level of the drive, and may
have other practical benefits. In particular, there are no issues
with slanted artificial gravity. Assuming the starship uses
spin gravity, an acceleration or deceleration of 0.1m/s produces
a small slant.

Oh, sorry, I'm showing my ignorance now... Slanted gravity?

What is heard or felt depends on the type of drive. For the
relativistic kinetic impact drive I propose,
....<Snip good stuff>

Oooh, that's lovely. (Reaches for notebook and starts scribbling)

I appreciate there'd be masses of shielding between drives and the human
payload and I reckon people would treat base line background noise as
silence and only notice when it changed.

This depends on the nature of the drive in question. For
a relativistic kinetic impact rocket or an aneutronic fusion
reactor, no such shielding is required. Natural background
radiation is far more of a concern. For an antimatter drive,
highly penetrative gamma radiation may be a concern.

With the relativistic kinetic impact rocket I propose, the
drive system is more or less "around" the payload. In
principle, you could use a smaller central magloop and
space away the crew compartments on the end of tethers.
However, it would be better to simply make the magloop
that much larger. Even if you keep the mass constant,
a larger magloop is able to more effectively deflect
particles--including background cosmic radiation.

OK, got that, thanks. Large magloop it is.

What about crew? How close would they have to get to the drives/working
parts for maintenance? (I'm talking about shipboard not external.)

Within maybe 1,500km? The crew can and should use
remotely operated robots for maintenance. You need
them anyway in order to work where there's dangerous
radiation and/or electricity and/or temperatures and/or
pressure. These robots will also probably be essential
after arrival at the destination in order to get cracking
at mining local resources.

What would be the range of a ship outward bound from Earth for eighteen
generations (a generation is flexible, say 20 - 30 years per generation
or even longer if life expectancy has increased) - anything from 350 to
up to 500 - 600 years in transit?

This depends on the cruise velocity. For a 350+ year
journey, I'd say you'd want to spend the energy to
get the thing up to a decent relativistic speed--maybe
0.75c (a relativistic gamma of ~1.5). That implies maybe
a 400+ light year range.

<Snip>

It may be optimal to start off as
a bunch of small ships, but to "link up" into one
really big "ship" for most of the journey.

Hmm... Interesting. How would that work in practical terms? Would the
ships be able to easily link to transfer personnel since they
are stationary relative to each other? Would it be something
they would be likely to do casually or would it be a serious and
hazardous undertaking? (Hey, Flash Gordon would have jumped from
one 'wing' to the other!)

Once a fleet is launched it has to be self-sufficient but presumably
they'll keep in contact with Earth for as long as possible. How long
will that be?

However long you want it to be. Most plausibly, they'll
keep periodic communications for the entire journey.

And after 500 years of subjective shipboard time at those speeds, how
much time will have passed on Earth?

This depends on the cruise velocity. With a velocity
of .75c, about 750 years will have passed on Earth.
The starship will be around 550 light years from
Earth, so don't forget to add that time delay to
any communications.
,Snip>

Isaac Kuo

Thanks Isaac, fantastic stuff. .75c is fine.

In practical terms how do I (roughly) estimate the time lag for
contacting Earth at various points on the journey. And it probably has
to be an estimate not a calculation because my grasp of maths is too
sucky for even the simplest of equations (I had my last maths lesson in
1967...)

My ships have lost contact with Earth many generations earlier. Messages
just stopped for no apparent reason. I need to work out some kind of
timeline

When they get to where they are going they find a colony there because
FTL/wormhole technology has overtaken them (not a surprise) but the new
colony is already several generations past their promised supply ship,
abandoned.

Hilarity ensues... Or something like that.

If I've got the relative times at the start and end of the journey, how
complicated is it to work out a timeline, Earth subjective time and ship
subjective time?

i.e. Gen ship leaves earth:
Earth Year 3000; Ship Year 0

Wormhole expedition departs from Earth
Earth year (say) 3550 ; Ship year WHEN?
How long for ship to receive message to say Wormhole expedition has
departed?

Gen ship sends last routine message to Earth
Earth year 3552 (Yes?)

What is the earth year at the point at which 'head office/mission
control' should be responding to the routine message?

Gen ship gives up on ever receiving a response from Earth again
Ship year WHEN?

Gen ship arrives at destination
Earth Year 3750; Ship year 500
And presuming they sent a message on arrival - how long for the message
to reach Earth and what Earth year would it arrive? (And how long
ship-time will they wait to see if a reply is coming.)

I really appreciate your help with this. Many thanks.

Jacey

--
Jacey Bedford
jacey at artisan hyphen harmony dot com
posting via usenet and not googlegroups, ourdebate
or any other forum that reprints usenet posts as
though they were the forum's own

.

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