Re: Maneuvering a Spaceship

On Aug 7, 5:46 am, MacFrag...@xxxxxxxxxxxxxx wrote:

Thrustless: attitude control by gyroscopes / reaction wheels. These
can be powered with electricity, i.e. you don't need propellant. Also,
to slow them down you can hook them to a dynamo which will give you
back some of the juice. Very convenient.
I also read the buzzword "magnet torque" but failed to find easy-to-
digest info on that on the web.
Questions here: how massive do these systems have to be; and how
quickly can they turn a ship around?

Typically you don't use reaction wheels if you want to turn
quickly. You use them if you want to turn precisely. This
could be used for aiming of a fixed spinal weapon (like an
x-ray laser...mirror based lasers and particle beams
are easy to steer without rotating the entire vehicle).

Note that a reaction wheel does not need to necessarily
be dead weight. You could use a secondary weapon
turret or an external missile pod as a reaction wheel,
or a sensor mount, or propellant tanks. In principle,
you could use circulation of propellant within a tank
as a crude reaction wheel, but there may be practical
difficulties.

Thrust: attitude control by small maneuvering jets. You need a
cartload of jets to cover all six axes (rotation and translation) -
the Space Shuttle has some 46 of them iirc, though with a favourable
hull geometry, you may get away with 12 fixed thrusters, even less
with gimballed thrusters (but those have to be more powerful). The
point is: you want them to be small and light and at the same time
have high thrust. That certainly means high propellant flow.
Question here: what thruster technologies lend themselves to the
purpose, harnessing high thrust in a small frame?

Chemical rockets. That is the only technology that fits this bill.

However, real life spacecraft often need to conserve propellant
much more than they need high thrust. Various electric thrusters
can be suitable for countering reaction wheel buildup. In your
situation, none of these are necessary.

Background technology: in my setting I have torchships with main
engines in the TW range, capable of 1G main axis acceleration for
extended periods of time (delta-V in the thousands of m/s; more with
reduced accel). Those main drives may feature gimballing or thrust
vectoring to a certain extent. The standard propellant is LOx.

With this sort of capability, the ONLY method for gross
rotation which makes sense is to gimbal or vector the
main drive's thrust. This is so much capability that it's
worth "wasting" thrust on moving forward a bit while rotating.

Additionally, the ships will have electrical power plants in the GW
range.
My guess is that they'd use gyros for routine maneuvers, supplemented
by thrusters in time critical / emergency situations.

I don't think gyros would be used at all for any maneuvers,
except perhaps for fine aiming of a spinal x-ray laser.
It's plausible that vibrations from the main drive would
make precise aiming of a long range beam weapon
impractical. As such, you'd use something else to
rotate the ship around to aim a fixed weapon.

Isaac Kuo
.

Relevant Pages

  • Re: Heavy Lift Design for Mining/Cargo Propulsion
    ... pellet blasted into the thrust dome. ... You have a reaction - be it chemical, nuclear, matter-anti-matter ... Plutonium fission reactions in a magnetic chamber produce actinide ... Propellant: Hydrogen and Oxygen ...
    (sci.space.policy)
  • Re: Ground-powered Rocket
    ... > vaporises and produces thrust once out of the atmosphere. ... > which translates into more thrust per kg of propellant ... > Microwave Thermal Rocket Launcher," Proc. ... The advantage of the microwave beam or laser, ...
    (sci.space.policy)
  • Re: rocket motors
    ... Not extra thrust, in that case, but, ... The propellant mixture in each SRB motor consists of an ammonium ... perforation in each of the aft segments and aft closure. ... that holds the mixture together, also acting as secondary fuel, ...
    (rec.pyrotechnics)
  • Re: Ares *VI*???
    ... "Each new reusable 5.5 segment SRB, ... pounds of propellant which will produce a peak of 3,774,000 million ... lbs of thrust and will have a vacuum Isp of 275.5 seconds. ... percent larger SRB's will burn for... ...
    (sci.space.policy)
Loading