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possible defense of thrusters...
Imagine your reaction mass/reaction chamber is in the center of the
ship. Let's say you have ducting on all three major axes. You just open the
ducting from the main reaction chamber whenever you want to thrust. The thrust
goes out any of the six directions (or combination of).
Thus you have equal thrust capability in all directions without the need to
install 'a second engine in the nose' and justifying *full*
turn/retrothrust
capability.
Of course, the best design for this is a big spherical ship.
But there are ways to imagine drive systems that don't necessarily mean you've
only got thrust to the rear.
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lot of the ships I've seen from Jovian Chronicles
(www.dp9.com<http://www.dp9.com>) have 'vanes' on the rear thrusters to
help turn the ships without retro rockets. Granted, not really useful for
braking.....
________________________________
From: gzg-l-bounces@vermouth.csua.berkeley.edu
[mailto:gzg-l-bounces@vermouth.csua.berkeley.edu] On Behalf Of Tom B
Sent: Thursday, December 11, 2008 11:27 AM
To: gzg-l@vermouth.csua.berkeley.edu
Subject: [GZG] Thrusters
One possible defense of thrusters...
Imagine your reaction mass/reaction chamber is in the center of the
ship. Let's say you have ducting on all three major axes. You just open the
ducting from the main reaction chamber whenever you want to thrust. The thrust
goes out any of the six directions (or combination of).
Thus you have equal thrust capability in all directions without the need to
install 'a second engine in the nose' and justifying *full*
turn/retrothrust capability.
Of course, the best design for this is a big spherical ship.
But there are ways to imagine drive systems that don't necessarily mean you've
only got thrust to the rear.
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can have rearward facing thrusters that have a cone that moves to effect
reverse thrust.
see
http://en.wikipedia.org/wiki/Image:Boeing_737-200_thrust_reverser.jpg
> On Dec 11, 2008, at 11:40 AM, Hudak, Michael wrote:
> A lot of the ships I've seen from Jovian Chronicles (www.dp9.com)
> On Thu, Dec 11, 2008 at 9:26 AM, Tom B <kaladorn@gmail.com> wrote:
The
> thrust goes out any of the six directions (or combination of).
A few big flies in the ointment are the thrust nozzles. If the nozzles extend
from nearly the center of the ship to the surface, they will consume huge
volumes (but not too much mass), they cannot overlap (nozzles for use in the
lowest ambient pressures have the widest bells*), and the whole nozzle must be
cooled. If there is ducting before the nozzles, pumping losses to get from the
main reaction chamber to the nozzle will make its presence known as heat, so
it will need more cooling than the really big nozzles.
Guide vanes in the thrust plume are fine for single-use boosters with
low burn-out times, or units that already have intensive maintenance
shedules, as they tend to be ablative.
* Not as serious an issue for aerospike nozzles, but the aerospike engine
reaction chamber is a surface mount, or you go back to the ductwork with
serious cooling needs. If you built a large disk shaped vessel with an
aerospike built around the edge, you might be able to thrust along the main
axis in either direction, at full power.
I like that idea of the thrust reverser. Also, if you need rapid deceleration,
you could flip the ship...
On Thu, Dec 11, 2008 at 9:38 AM, Ryan Gill <rmgill@mindspring.com> wrote:
> You can have rearward facing thrusters that have a cone that moves to
The
> thrust goes out any of the six directions (or combination of).
you know, maybe that is the idea of the half thrust rating for braking. They
use thrust reversers, and gimballed nozzles to steer... am I wrong here? I
mean, reversers would not be as efficient for braking. diverting thrust
creates heat issues on the diverting object.
> On Thu, Dec 11, 2008 at 10:57 AM, Bryan <brakeb@gmail.com> wrote:
wrote:
> You can have rearward facing thrusters that have a cone that moves to
have
> 'vanes' on the rear thrusters to help turn the ships without retro
The
> thrust goes out any of the six directions (or combination of).
Obviously your engineering imagination, and taste in PSB, are just as
legitimate as mine. That's what house-rules are for, but for me:
1. I imagine my interplanetary warships propelled by *at least*
deuterium-tritium fusion. The "exhaust ducts" would have to be
massive affairs equipped with superconducting magnets, cryogenic
cooling and other systems to control the plasma-stream. Essentially,
apart from the shared "reaction chamber", you'd still be building one
engine with Tn thrust plus five with T(n/2) thrust.
2. Man-made fusion for space-ship propulsion remains a fantasy, and I
am not a nuclear engineer, so I have no idea how feasible it would be to open
"ports" in six different directions from your main tokamak or whatever.
3. The structure of the ship would have to be stressed to take heavy
accelerations from six directions instead of just one. The designers would
have to allow for six major exhaust streams when positioning
crucial external systems like heat-radiators. Putting a nuclear
reactor in the middle of the ship, as opposed to one end, would probably imply
a greater mass of radiation shielding to protect the crew (obviously) and
ship's structure (from neutron embrittlement).
It seems to me that however you slice it, there'd always be a serious
trade-off in engine and structural mass to give a ship the ability to
accelerate in any direction implied by the thruster-push rules. A a
ship that was designed around a single thrust axis would be simpler,
and put less mass into engines and basic structure. The single-axis
design should either have a higher acceleration for any main-engine
thrust, or be able to put the extra mass into armour, weapons etc., or some
combination of the two.
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cisely. There's no doubt one can propose a rationale and mechanics for
thrusters, but I don't see how it can be made the most parsimonious solution,
at least for Terran physiologies. What one might do is come up
with some reason that a race had to settle on multi-axial main drives
rather than flipping the ship with thrusters. It would be an interesting
exercise.
Best, Ken
> --- On Thu, 12/11/08, Robert N Bryett <rbryett@gmail.com> wrote:
From: Robert N Bryett <rbryett@gmail.com>
Subject: Re: [GZG] Thrusters
To: gzg-l@vermouth.csua.berkeley.edu
Date: Thursday, December 11, 2008, 7:00 PM
Obviously your engineering imagination, and taste in PSB, are just as
legitimate as mine. That's what house-rules are for, but for me:
1. I imagine my interplanetary warships propelled by *at least*
deuterium-tritium fusion. The "exhaust ducts" would have to be
massive affairs equipped with superconducting magnets, cryogenic
cooling and other systems to control the plasma-stream. Essentially,
apart from the shared "reaction chamber", you'd still be building one
engine with Tn thrust plus five with T(n/2) thrust.
2. Man-made fusion for space-ship propulsion remains a fantasy, and I
am not a nuclear engineer, so I have no idea how feasible it would be to open
"ports" in six different directions from your main tokamak or
whatever.
3. The structure of the ship would have to be stressed to take heavy
accelerations from six directions instead of just one. The designers would
have to allow for six major exhaust streams when positioning
crucial external systems like heat-radiators. Putting a nuclear
reactor in the middle of the ship, as opposed to one end, would probably imply
a greater mass of radiation shielding to protect the crew (obviously) and
ship's structure (from neutron embrittlement).
It seems to me that however you slice it, there'd always be a serious
trade-off in engine and structural mass to give a ship the ability to
accelerate in any direction implied by the thruster-push rules. A a
ship that was designed around a single thrust axis would be simpler,
and put less mass into engines and basic structure. The single-axis
design should either have a higher acceleration for any main-engine
thrust, or be able to put the extra mass into armour, weapons etc., or some
combination of the two.
Best regards, Robert Bryett