> On 25 Jun 98, at 8:51, Brian Bell wrote:
forces are strictly defined. A spacecraft capable of moving under it's own
power can actually maintain geosynchronous orbit at any altitude, simply by
using it's drive system to maintain the correct velocity.
Seeing as how FT is a space combat game, wouldn't a better definition be that
low orbit is at a range suficiently small to engage ground targets (and be
engaged by them) and high orbit is out of range? Presuming a planet could have
enhanced range SLM's that means (what?) 48MU is low orbit. Unless someone
wants to argue that acquiring launch velocity reduces the range of a salvo
missile?
TTFN
Jon
> On 25 Jun 98, at 9:58, Yum Yum Yab Yum wrote:
> >Ermm.. the way you explain that makes it sound like geostationary
Grin. I know. It's a classic undergraduate physics problem to get the students
to work out exactly what distance a geostationary satellite would have to
orbit at.
> >A spacecraft capable of moving under it's own power can
Does this mean a space shuttle isn't 'in orbit' while it's firing it's
manoeuvring thrusters? Or the satellite launching from it's bay isn't 'in
orbit' until it's rocket stops firing?
> but using the gravity well of the object to dictate your velocity. If
Um, no. A ship capable of variable drive can maintain any distance and
'orbital speed' it wishes, providing it's navigation and control systems are
up to it.
> >Seeing as how FT is a space combat game, wouldn't a better definition
That defines the exact area I agree - a one side of the table = planet
game it becomes a 'bar' across the table, whereas actual circular planets
scribe a bigger circle. The thing to look at may be that there's no point
arguing about what is 'high' or 'low' orbit (or indeed orbit at all) unless it
has some functional meaning in a game of FT, interesting as it might be to
discuss the physics of it.
TTFN
Jon
> Indy wrote:
[examples of low orbit from a scale based on a 12" diameter planet]
Would this give geostationary orbit at about radius 30"? (or 18" above the
surface)
> (another example, if anyone remembers the
Hey! some of us were only 4 then. :-)
[ NO, I'm not remotely interested in finding out how old everyone else
is, and I doubt anyone else is either after the "where does everyone live?"
thread.
]
> >> Geosynchronous orbit is where the unit (ship, station, etc.) is
> There is also a minimum distance above the surface of the body to
Err, the only minimum distance I can think of is the distance at which you've
entered the atmosphere (or for airless bodies: hit the surface).
> Geostationary orbits do require a particular distance. At least a
Its a particular distance, not a minimum one. If you go further out you're not
geostationary either - ie you take more than a day to complete each
orbit.
[ The obvoius example of this is the moon, much further out than
geostationary orbit, taking 28 days to complete an orbit.]
If you use the semi-offical scale of 1 turn = 20 mins then the Earth
would take 72 turns to rotate once. A ship in geostationary orbit would take
the same
time to complete one orbit (I think this is speed 2.5MU/turn). This
might be a little slow to game with. Still, you can allways tweak the scale to
suit your tastes.
> > by space stations/satellites that don't have any drives to speak
You can use Earth as a benchmark for figuring out scale of orbits. If you
take, for example, a globe 12 inches (mu) in diameter, a 'low orbit' is
upwards of 0.5 inch (mu) above the surface (example, at this scale, the Hubble
telescope, orbiting at 370 miles every 96.5 min is a *bare* half inch above a
12 inch diameter globe, and that's considered 'high-low orbit'; 'low'
orbits are prolly closer to 0.25 inch) (another example, if anyone remembers
the
fireball/meteoroid that skipped off of Earth's atmosphere back on August
10, 1972, the one that was filmed passing over the Rockies in broad daylight,
it
would have been, using the scale above, a mere 1/16th inch above the
surface of the globe)
> Geosynchronous orbit is where the unit (ship, station, etc.) is
There is also a minimum distance above the surface of the body to consider.
> Low orbit is any orbit that is traveling slower (faster ground
> requires you to
> centri(petal?)
Geostationary orbits do require a particular distance. At least a minimum
distance. For Earth this minimum distance is 35,000 km.
> A spacecraft capable of moving under it's own power can
If you are using your drive system to maintain position, you are not 'in
orbit'. By definition to be in orbit you aren't using your drive systems, but
using the gravity well of the object to dictate your velocity. If you want to
maintain a stationary position above a certain point over a planet and be
significantly less than that planet's geostationary limit, you need to apply
drive power to prevent you from falling down the gravity well, and you are not
'in orbit'. Everything else in orbit will be whipping by you quite fast.
> Seeing as how FT is a space combat game, wouldn't a better definition
Depends on the scale of your planet. ;-)
> Unless someone wants to argue that acquiring
Nah. :)
Mk
> Orbital mechanics are.. Low orbit is anything above the atmosphere,
I was using the following definition: The term high and low orbit come from
the speed at which an object orbits the planet. It seems strange, but is true
that to move faster in relation to the ground (in orbit) that you decrease
your orbital velocity. This causes you to "fall" toward the earth and actually
gain ground speed (due to the smaller orbital path). Geosynchronous orbit is
where the unit (ship, station, etc.) is traveling at such a speed in orbit
that it remains above the same spot on the globe. Low orbit is any orbit that
is traveling slower (faster ground
speed/smaller
orbital path) than geosynchronous orbit. This is falling toward or spiraling
in toward the planet. High orbit is any orbit that is traveling faster (slower
ground speed/larger orbital path) than geosynchronous orbit. This is
spiraling out from the planet.
I'm sorry BUT! The lower you are the MORE speed you need to counteract the
higher gravity; the higher you are the LESS speed you need to counteract the
lower gravity. A geosynchronious orbit veocity is slower than the near earth
orbit velocity. Low orbit periods are like 90 minutes (alt 100 Mi.
4,100 radius -4.8 Mi/sec) Geo orbit is 24 hour (alt 22,400Mi. - 26,400
mi. radius.- 1.9 Mi./sec) approximately.
Tom Hughes
On Thu, 25 Jun 1998 08:51:37 -0700 Brian Bell <brian.bell@axom.com>
writes:
> Orbital mechanics are.. Low orbit is anything above the atmosphere,
The un-educated view of this orbit bombardment question.
A planets defences will really only exist near areas of importance. Cities,
military bases etc. No planet is going to have missile or defence batteries
placed every 10 miles or so across the whole planets surface.
I belive warfare for planets would go along these lines.
Orbital defences are the first line of defence. If they are destroyed then the
attacking fleet can either land forces or simply throw rocks at the planet.
Now there will be nothing a planets defences could do to shoot down incoming
rocks. (without some fantastical future weapon). But if the invaders actually
want the planet then they land forces. The planetary defenders must then move
quickly to repel the attackers as soon as they land.
In my opinion missiles either from the planets surface would move far to
slowly to pose a threat to orbiting ships.
In my own background after orbital defences are destroyed the planet protects
itself by launching space capable fighters and streamlined ships to continue
the space combat.
> [examples of low orbit from a scale based on a 12" diameter planet]
Actually about a yard out (36") is what we figured was geostationary orbit.
The moon at that scale sits out ~30 feet.
Mk
> >A spacecraft capable of moving under it's own power can
Does this mean a
> space shuttle isn't 'in orbit' while it's firing it's manoeuvring
'By definition' was a poor choice of words on my part, I must admit. 'By
definition', any body which goes around another body (nevermind if it's a
circular, elliptoidal, or spiral path) is considered 'in orbit'.
As for using drives to maintain orbit, I was thinking more along the lines of
one's main drive system, not maneuvering thrusters. The shuttle doesn't and
can't really use its main drives to 'maintain' an orbit; the manuevering
thrusters are primarily for that: maneuvering, to a higher or lower orbit. It
really isn't using them to maintain it's current orbital level (whatever that
may be). Their velocity and altitude will keep them sitting there 'in orbit'
fine without need of fine controls of the maneuvering thrusters.
As for the satellite, I wouldn't consider it 'in orbit' until it's had it's
orbit established. It's rocket firing to move it up to that orbital level to
me isn't 'in orbit'. But then you can go back to the definition above and blur
it some...actually, the more I think about that definition - gotten from
the
vaunted dictionary - the worse you can 'slur' what is and is not 'in
orbit'. My brain hurts. Unless we come up with a more rigorous definition of
what is 'in orbit', I don't think debating it is going to be worthwhile.
Mk