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Explorer class ships fuel and power cycle



At 10:42 AM 3/12/96, David Levine wrote:
>Kelly Starks x7066 MS 10-39 wrote:
>> Dave, what have you forwarded to him of our recent correspondence?
>>
>> Kelly
>
>Um, nothing.  Instead of forwarding huge loads of
>mail, I thought a summary might have been better.  But
>most of this is technically above me...  Anyone want
>to give it a crack?
>
>David




Primary Drive System:
Externally Fueled Fusion Rocket
Fall 1995



Out of the likely ashes of my Multi-cycle Ram Augmented Interstellar Ramjet
(RAIR) drive, I kept one solid piece.  The idea of launching fuel to the
ship from a fixed launcher in Sol (our home starsystem).  The fuel/reaction
mass mixtures could be launched as anything from aspirin sized pellets, to
truck sized expendable mini-tankers.  The former could be scooped up and
fused as is, the later could be docked and off loaded.

I'm not going to go into a detailed analysis of the pros and cons of the
different systems, but their are a lot of pros and cons for each.  A stream
of pellets would be easier to launch and offer less impact danger to the
ship.  But the pellets would be harder to keep together at a distance from
the launcher, and harder for the ship to recover.  The ship would need a
ramscoop or something to scoop up its fuel, and when the packets drifted
too far to the sides, the ship couldn't pick them up.

Mini-tankers on the other hand could use onboard rockets to maneuver to
meet the ship.  Possibly the ship could beam power to them (via lasers or
microwaves) that could be used to drive the tankers attitude rockets, and
order it to maneuver in front of the ship for pick up.  Or a system like
passive laser launchers could be used (which is discussed below).  These
would just require the tanker to have a large block of reaction mass on its
backside.  The ship could boost, and steer the tankers remotely using
lasers; without any equipment on the tankers.  Either way the ship could
catch fuel tankers that had drifted thousands, possibly tens of thousands
of miles off to the side of the ships flight path.  Far more then possible
with a megnetic scoop system.

Either way an externally feed system would mean that, the ship wouldn't
need to carry the tremendous tonnage of fuel and reaction mass it would
need for the flight.  Launched acceleration fuel and reaction would only be
carried by the ship from the time it entered the holding tanks, to the time
it was burned.  How this would work in each phase of the flight is
described below




Laser fuel launchers.


Assume the average fuel canister is the size of a 6 meter in diameter
cylinder about 5 meters long.  I think that should hold about a hundred
tons of fusion fuel (6Li?) but of course that would vary with the type of
fuel.  This canister is heavily reinforced (you'll see why), and the ends
are covered in a thick plug of reaction mass (could be anything from fiber
reinforced ice, to solid Kevlar).  A floating laser 'tug' fires a laser at
this plug of reaction mass.  One quick pulse to vaporize a layer off the
bottom.  Then a heavy pulse to turn the vapor to super heated plasma.
I.E..  a pulsed rocket.  Keep repeating these cycle up a couple hundred
times a second, and you have a laser rocket.  Specific impulse is limited
by the type of reaction mass and the heat the laser brings it to.

Course corrections are handled in two ways.  The first involves aiming the
beam to one side of the base, rather than in the center.  The uneven thrust
will turn the canister, and subsequent pulses will thrust along the new
vector.  Precise course changes are handeled by burning a bit of reaction
mass off the side of a canister as it passes a laser tug.  This would give
precicly controled lateral thrust.

Note the canister has no internal systems.  Range is limited by the optical
precision of the laser.  Given what a Hubble telescope can do over
interstellar ranges.  I'll assume the system can aim acceptably out to
100,000 miles.  So, if you station a laser tug every 100,000 miles or so.
The tugs can take turns boosting a string of canisters.  Given orbital
mechanics.  (No stable orbits that can keep you in a straight line.)  They
will have to be continuously boosting themselves around to stay acceptably
close to the 'Launcher' track.  (The exact position of the tugs isn't
important, as long as they know exactly where they and the canisters are.)

Given this system the 'launcher' can be as long as the number of tugs, or
as you need at the moment.  If you space the tugs out every 60,000 miles
for 100,000,000 kilometers (about a 1,000 tugs spaced from here to Mars.)
The average G load on a canister exiting at a speed of 1/3rd the speed of
light, is 100,000 m/s^2, or about 100,000 G's.  Which seems acceptable for
a solid block of reinforced metal and whatever.

The major problems with this system are the amount of reaction mass, and
power, nessisary to reach the desired maximum speeds may be prohibative.
So a laser sail may be nessisary for the primary speed boost.





Laser fuel Scoop.


The ship uses a variation of the fuel launcher to catch the fuel canisters.
The ship uses bow lasers that fire on the back of the canister to boost it
forward and steer it onto the ships course vector.  Assuming the laser
booster can function hitting the base at over 60 degrees off the canisters
axis, and can hit the target at 100,000 km.  The ship can 'catch' (I.e.
Stear to itself) a fuel canister over 80,000 km off to the side.  Far
better than the scoop systems we were considering.  Which could increase
the range at which the ship can be externally fueled.  (Hopefully out to
about 3,000 au's, since it would take that far for the ship to boost to
1/3rd c.)

If we assume a fusion fuel with a specific impulse of 2 million (we might
even get to 2,400,000 if we push it) the ship would need to receive 5 times
its weight in fuel to boost it to 1/3rd of light speed (100,000,000 m/s).
If the canister and its reaction mass is added into the ships budget it
might be able to use less fusion fuel (thou more total mass) to get to same
speed.




Accelerating out of Sol, our star system.


The ship would be heavy.  Not only with the weight of its own systems and
structure, but food and equipment for the mission, exploration equipment,
the crew and their homes; and weighing dozens of times all the rest
combined, deceleration fuel (See fusion rocket mass tables).  The ships
maximum speed is limited by deceleration (braking) fuel it can carry.
Given the years of flight time involved, every effort will be made to load
the ship with fuel.

Pulling out of Our star system, Sol, the ship will accelerate at one ship
G, accelerating 10 meters per second, per second.  An orbiting set of laser
tugs will boost the fuel and extra reaction mass the ships motors will need
for this acceleration run.  The ship will be continuously picking up these
fuel packets, and feeding their contents into the fusion motors.  This will
continue until the ship reaches the maximum speed it can slow down from.
If the orbiting launcher can still get fuel within pickup range of the
ship.  Extra fuel can still be sent out to increase the breaking supply.
Possibly enough to extra fuel to allow the ship to accelerate a little
more, and cut down the long flight.

Because of the deceleration fuel limitation, it is unlikely that the ship
can get to more than a quarter or a third of the speed of light.  But
that's still a 100,000 kilometers per second.  The ship will need to
protect itself against impacts.  One of the simplest ideas is to push
several miles of charged dust ahead of the ship.  Ramming a cloud of
charged iron dust at 360,000,000 kilometers per hours will turn most
anything into ionized plasma.  Which can be shoved ahead of the ship, or
off to the sides, by the charges dust cloud handler.  Effectively most
anything you run into at speed will become more shielding dust.




Decelerating into the target star system.

Now for the bad news - you have to slow down.  We can't pre-load a
deceleration course track into the target star with fuel across
interstellar distances.  So your stuck with the fuel you brought along.
Unless we can come up with a neat magnetic trick to brake the ship in empty
space (sorry no luck), its fire up the reactors and put engines into
reverse.  As the tables in fusion rocket shows, even slowing down from
1/3rd light speed would force the ship to carry 50 - 100 times its weight
in fuel.



Cruising around the target star system

At low speed interplanetary runs, the drive works like a conventional
fusion rocket burning stored fuel and reaction mass.  But the engines that
could bairly get us across interstellar space.  Can now make this huge ship
commute around the confines of a starsystem with ease.  A ten hour burn of
the main engines will would get you from Earth to Jupiter in about a month,
or Mars in a week.  A two day burn would get you to Jupiter in less than a
week.  Under four days of constant burn will get you to Mars.  About a week
of constant burn will get you to Jupiter.

Once in system the main ship will be shuttling surface teams, support
ships, and equipment around the star system.  It size and speed will allow
it to drag around tremendous loads of equipment or raw material.  It could
haul ore in to a construction site for a space colony.  Or to a fuel ore
processing facility.  (Note the crews will need to find enough fuel to get
the ship out of the starsystem.)  The starship will be carrying all the
exploration equipment and personnel to anywhere of interest in the
starsystem.




Accelerating out of the system to go home.




As the exploration phase comes to an end the support crew will be
processing the tremendous tonnage of fuel ore necessary to refuel the ship
for the boost to home.  This fuel could be carried on the ship.  All those
fuel tanks you emptied decelerating into the starsystem could be filled to
accelerate you back to home.  (Assuming you can find that much fuel!)  Or
(possibly) the crew could construct a fuel launcher system like the one the
ship used to leave home.

If an automated fuel launcher could be constructed in the target
starsystem, and the one near earth relied upon for braking fuel, the ship
could launch with her fuel tanks nearly empty.  Without the massive load of
fuel and exploration equipment the ship could weight a hundredth of its
loaded weight when it left Sol.  This would allow it to boost faster and to
higher speeds, even if the local fuel launcher could only launch (and the
local mines only supply) a tiny fraction of the fuel the Sol launcher
could, launched to a shorter range than the sol Launcher could.  With such
a lightly loaded ship, most of the drive systems would be unnessisary.
Allowing eiather further weight reduction of the ship, or allowing
tremendous redundancy in the equipment.

A automated launcher system would not only give this missions crew a much
shorter flight home.  It could allowing future missions into this star
system a much shorter round trip.  However an automated fuel launcher may
be too complicated for the crew to construct.  It would require the
construction of a thousand laser tugs and tens of thousands of the filled
fuel canisters.  But if enough construction gear can be brought along (or
some ultra-tech like self replicating machines is assumed), this would
greatly expand the amount of flights and exploration we could do to this
star system.




Decelerating into of Sol, our star system.

Since the ship can assume that the orbiting fuel launcher in Sol will be
turned on to help it slow down.  The ship wouldn't need to be heavily
loaded down with deceleration fuel.  By this point in the mission the ship
will be comparatively light.  Its fuel tanks empty.  Most of the food and
consumables consumed.  Probably most of the exploration gear left behind.
The ship will be coming home needing fuel.  Or will it?

The ships cruise speed will be a fraction of the speed of light, and it
will be flying straight toward the fuel launcher.  Obviously a nice neat
docking with the incoming fuel packets is out of the question.  You could
of course use the scoop lasers to steer a mini-tanker in front of the ship
and then explode the tanker.  The contents will slam into the ships forward
dust shield and be heated to plasma.  That plasma could be scooped up and
channeled into reactors to p@fd engines.  s that
necessary?

Whatever blasts through the dust shield is going to be hot! The forward
electromagnetic barriers that shove the dust ahead of the ship are going to
be ramming into, and pushing forward, a plasma ball an eighth of a mile in
diameter and unknown length, ahead of the ship.  If their is any fusion
fuel in the mess, its probably going to be fusing out ahead of the ship.
Effectively the front of the ship will be an open fusion motor.  If the
launcher isn't firing fuel.  Whatever it is launching is still going to be
a hellish fireball ahead of the ship.  Effectively the ship will be
breaking against this artificially induced drag source.  Converting its
kinetic energy into heat in the plasma.

You wouldn't even need to run the reactors to keep the electromagnetic nose
shield charged.  Ducting a little of the plasma through a central core will
allow you to use the core as a generator.  Converting the energy of the
high speed plasma into electricity.  Or more correctly converting the ships
kinetic energy past the plasma stream into electricity.  If you want to get
tricky a magnetic 'wiggler' in the plasma stream could be used to convert
some of the energy into a forward laser.  The forward blast from a plasma
laser charged by the kinetic energy of a few hundred thousand tons of
charging starship should clear anything out of your path.  It certainly
will show everyone the explorers have returned home.


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Kelly Starks                       Internet: kgstar@most.fw.hac.com
Sr. Systems Engineer
Magnavox Electronic Systems Company
(Magnavox URL: http://www.fw.hac.com/external.html)

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