...And while they'd pull on each other, I'd think the interaction wouldn't much resemble the Earth-Moon kind of mutual orbiting. Both the ship and the station would be more affected by the distant planetary or stellar body that they were co-orbiting, and would weave their individual orbits around that body in an interesting braid that wouldn't look like a neat and tidy ship-ellipse-around-fixed-station setup even from a close-up, moving reference frame. However, artificial gravity could certainly be created for this purpose of securing a ship to the vicinity of the station. Doesn't sound like a worthwhile endeavor, though. If one wanted to stabilize a ship via tractor beams or directional gravity, wouldn't one prefer to secure her in place, rather than in an orbit-like track? I guess the two ships orbit K-7 in "Trials and Tribble-ations" not because they have to, or even because they can - but solely because they don't want to appear too passive to the opposing ship. They don't want to power down or settle in place; they want to remain ready to pounce. Doing that little dance helps them the same way it helps a boxer... Timo Saloniemi
Hmmm A weavy-braidy thing IS what the Earth_Moon system does. Well actually, it's more of a helical, weavy-braidy thing, since the Sun is moving as well...
For anyone that wants a better understanding of orbits and orbiting, I suggest this simulator: http://orbit.medphys.ucl.ac.uk/. You'll find that orbits aren't intutive. Like I said before, only if you are have the power to decouple from gravity, gravity is going to control every aspect of orbiting. Each orbit--an altitude above the surface where a trajectory encircles the globe--has its own period and thus its own speed by which a spacecraft must travel at to retain that specific orbit. For example, in the ISS's orbit, that speed is around 17,500 mph, no matter what size the spacecraft is, or how much it masses. The Sputnik, the Soyuz, the Space Shuttle, the ISS, and even the fictional USS Enterprise will all travel at this speed in that orbit. Increasing thrust changes the shape of the orbit. If you are in a circular orbit and fire the engines, you will put the ship into a elliptical orbit. This is usually done at pericenter (periapsis, perigee, ect.) because you get an gravitational boost "falling" from apocenter (apoapsis, apogee, ect.) thus saving fuel. To make an elliptical orbit round, you spin the ship around to face backward and burn the engines at apocenter. The ship is now at a higher orbit, which has a longer period and a slower speed. To get into a lower orbit, the opposite manuevers are performed. Orbital inclination can be changed by reorienting the ship (usually 90 degrees from its flight path (in pitch I believe)) and firing the engines. This does not result in changing the size of the orbit or increasing the speed to any noticable effect. Science Fiction has mostly ignored orbital mechanics for the sake of the story, and had thus done a great disservice to the Sceince side of the fandom. I'm not going to speculate how Star Trek gets around this issue. I just simply suspend disbelief. One of the few movies that shows an approach to a planet in a believable manner is Alien.
Of course maybe the Enterprise deploys a "standard" series of mini-satellites around the planet as it approaches. These could relay comm and even transporter signals while the big E enters a boring Newtonian orbit
The changing of orbital altitude by means of short burns is something we do today because our engines lack endurance. This results in a series of ellipses, the final one of which meets our needs of orbital altitude. There's no reason why Trek starships should alter altitude in such a fashion, though. Their engines aren't endurance-limited - so even if they don't want to waste fuel or energy in a massive burst that would take them directly from the lower orbit to the higher one in an infinitely elongated transfer ellipse (i.e. a straight line), they are far likelier to use constant thrust (which gives a spiral) than two short bursts (which give the transfer ellipse). Just floating on an orbit of a given shape isn't a worthwhile goal for a starship, really. The ship wouldn't want an ellipse, or even any specific shape of ellipse, because ellipses are pretty stupid as flightpaths go: they take you away from where you want to be for much of the time, and they irritatingly keep you moving even when you are approximately where you want to be. A starship would want a specific position above a specific target - or then she would want a flightpath that covers as much of the planet's surface as possible in as short a time as possible. Even the latter need isn't easily met by freefall orbits; the search would go faster by using some sort of a powered flightpath, either something that looks like a classic polar orbit (slowly twisting to cover every inch of the ground below) but forced by the engines to be faster than a freefall orbit, or then a serpentine pattern that imitates a low orbit set at an angle against the equator (thus creating a sinusoidal "footprint") but takes that to non-Newtonian extremes. Freefall orbits would only be good for longtime parking, or for stealthy work such as impersonating natural objects. Or for starships that are so mortally wounded that their performance has fallen down to the abysmal levels of conventional rocketry. Timo Saloniemi
Lacking engine endurance, or fuel and delta V budget? The word "orbit" has a particular meaning, it is a gravitational curved path around an object or a point (barycenter). If a starship is to assume a particular position over a planet so that transporter and communication remains in line-of-sight, and this position is not in the planet's geostationary orbit, then I would argue that the starship is effectively ignoring or countering gravity and to answer T'Girl's original question, it is not orbiting. If the spacecraft is operating independent of gravity, then must we also assume it is not effected by the solar gravity as well, and thus has to "fly" beside the planet under its own propulsion as that solar system orbits the galactic core? Or do we conclude that the starship only has to ignore the gravity around the planet and keeps up as the planet orbits its sun? Or do we go the other direction and say that the starship ignores all gravity and thus had to keep up with the galaxy it is within to stay next to the planet? How do we decouple from one source of gravity and stay coupled to others? Is antigravity discriminate between magnitudes of gravity? Put another way, will a region of negative spacetime curvature orbit a region of positive curvature? I don't know the answers to these questions. They are there to think about.
Why not? It's low-maintenance and worry free. Especially for a starship in a survey mission that might be orbiting a particular planet for days or weeks. You might think of this as an "anchor" orbit that allows the ship to run with engines nearly idle. Even if the engines aren't endurance-limited, it makes a certain amount of sense not to run the engines when you don't need to. Well that only covers, what, ninety percent of what starships do during peacetime? Seems pretty worthwhile to me.
This is exactly what I was proposing in my OP. Because planets rotate on their axis, the Enterprise is traveling around the planet, it is orbiting. It just is not in a freefall orbit.
So is riding an oceanic current or a prevailing wind, yet it's preciously seldom that a military ship or aircraft exploits such a marginal advantage. If a starship really had to worry about staying in orbit, it wouldn't be much of a starship; "Court Martial" seems to tell us that every captain knows the risks of a powered orbit, but that every captain also routinely accepts them for the (admittedly ill-specified) advantages provided by such a mode of orbiting. Being mortally wounded? I hope not! Being in longtime parking? It doesn't seem so. Starships come in, do fancy stuff for at most a couple of days, and hurry to the next location. Parking one for as long as a week sounds like highly exceptional circumstances in TOS and TNG eras alike. Even longterm survey missions involve ill-fated research vessels settling themselves on decidedly unsafe orbits, supposedly for better scientific gain. Really, we have yet to see a single Oberth sensibly placed on a safe and stable orbit! However, no doubt a starship can relatively effortlessly alter her orbiting mode from powered to freefall whenever the need for longterm idleness arises. A somewhat damaged ship on automatic can stabilize herself while stranded deep down in Earth's atmosphere, as seen in "Tomorrow is Yesterday". A derelict ship could thus probably stop herself from plunging to a fiery death all by herself in the usual case, explaining the likes of Exeter; it would take significant damage, or a near-total loss of power, for the ship to fail to settle on a stable orbit in an emergency. Yet such loss of power is distressingly routine when starship captains go and challenge divine powers or ancient machines... Timo Saloniemi
That's because military ships are no longer equipped with devices that can make use of them (sails, for example). Starships, however, ARE equipped with impulse engines and thrusters, the addition of which would be meaningless if starships were never intended to ever use them. Essentially, it's like a jet engine mounted on a space craft. Obviously, the space craft is designed to maneuver using other types of methods where the jet engine isn't all that useful... but why would it be equipped with a turbofan if it wasn't occasionally expected to fly in an atmosphere? Same with starships: why would you be equipped with impulse engines and thrusters if you're NOT occasionally expected to orbit a planet? Logically, this is hardly a given; the duration of "a couple of days" is pretty much plot convenience for the fact that a given episode has to end in less than an hour and it's tricky to convey a realistic passage of time for a mission on an alien planet; yet even in "Miri" it's implied that the away team is stranded for a period of SEVERAL days while Enterprise remains in orbit. Same again for "Omega Glory" where the Exeter is left unattended in orbit for a significant amount of time before the Enterprise shows up and finds a three-ton sack of flour that used to be the crew. And is explicitly not the case for the orbiting starships in TMP, TSFS and TVH, and especially in the latter case as those ships are able to maintain orbit even after being neutralized by the whale probe. But since the reverse is also true, you have eliminated any possible incentive to PREFER a powered orbit. Since the ship can come to a screeching halt above the planet and linger over a particular spot whenever it wants, they loose nothing by letting the engines idle until they have a reason to do some gravity defying. There's also the fact that not everything you're going to want to intercept in a particular orbit will be in a powered orbit and most will be in freefall orbits anyway; at least for populated planets and systems, this means you HAVE to go into a freefall orbit in order to dock with the local space station or to guarantee you won't accidentally knock half their communication satellites out of the sky when their orbits intersect your parking space. Take "Operation Annihilate" as an example: Enterprise circles Deneva, dropping hundreds of satellites into the planet's orbit. You could make the case they quickly pulled into a freefall orbit in order to deploy those satellites, but if Enterprise were to suddenly come to a halt and maintain a stationary position, those satellites them come whipping around the other side of the planet and become a navigational hazard, and you suddenly have to risk destroying them when your deflectors try to push them away. That or a lack of understanding (or attention to detail) by trek writers on what "orbit" actually means (coincidentally they used this same plot device multiple times on "Lost in Space"). That the reference to "the engines are off and now we're falling!" as a plot device disappear altogether by the end of TOS' second season and are never heard from again in TNG onwards. We do see a few ships PUSHED out of orbit by explosions and the like, but never the plummeting of a starship just by virtue of loosing power.
Impulse engines move you from A to B with contemptuous disregard of Hohmann orbits or other freefall maneuvering. Thrusters move you 4.7 meters to the right and a hundred meters up. Neither implies that classic freefall orbits would play any role in starship movement. The emphasis being on "stranded". Starships may be forced to loiter for more than a few days, in which case they may eventually resort to freefall orbiting. It's likelier that they don't, though, as this would deprive them of constant line-of-sight with said stranded landing party. Short stays may be a "plot convenience", but the entire Star Trek universe is built as one big plot convenience. Starfleet's charter is to perform missions that are convenient for the plot, that is, short visits to usually Earth-like planets. Conveniently, too, when we see our favorite starship maneuvering around the planet, she's indeed doing just that: performing tight twists and turns for the camera, as if flying in a pattern eight above the target area. It's extremely seldom that we'd see anything resembling idle freefall orbiting. Hmm. Only Spacedock is seen maintaining orbit, which is sort of to be expected. The ships within would then naturally do that as well. ...Save for the original and ubiquitous one of never letting the landing party out of sight. The engines would stay on until something exceptional happened that required leaving the landing party unattended. I will. After all, to deploy an efficient pattern, the Enterprise couldn't shut down her engines for a second; she'd have to give each sat a specific, separate orbit. And TOS-R suggests the sats didn't have much of a propulsion system of their own, so the engines of the Enterprise would be doing all the work. To be sure, it only was a plot device in one episode, "Court Martial". In all the others, the plot complication included an outside force pulling the starship to her doom. Yet later Trek went on to reinforce the idea that transporters are line-of-sight only, capable of penetrating at most two kilometers of bedrock - while maintaining that the mothership would never be below the horizon in any landing party adventure, be it a short recce mission or a survey of indefinite but great length. TNG also kept giving us the "starship flies in tight curves" visuals... Timo Saloniemi
I expect all of the Denevan satleiites were in freefall orbits designed for maximal surface coverage. I would not see a need for any propulsion of them for such a short term mission.
The Ent has the demonstrated capability to do both and will do either or both depending on the mission. And later on, while serving on the Potemkin, Riker will hang over a planet's magnetic pole to confuse an opponent's sensors (TNG - Peak Performance).
On the point of "Omega Glory" we actually get to see both types of "orbits" in action The Exeter is in orbit for a long time, most likely in a geosynchronous orbit as it is unattended autopilot. When Kirk & Co find out that they've been infected, they beam down to the planet below. In the following scene, we learn that the Enterprise then moves to a lower orbit (or more correctly altitude as they're probably hovering) to stay close to the landing party and beam down medical supplies and equipment. Incidentally, T'Girl, this would imply that starships can use their transporters at geosynchronous orbit distances... Going back to "Court Martial", maybe the repair order is stacked by altitude with the priority ones being closer to the planet? Afterall, did anyone see other starships being serviced in Enterprise's immediate altitude?
TOS-R shows a fellow starship right next to the Enterprise, yes. The saucer is tilted so that we don't really get to see that it says "Intrepid, NCC-1631" there... On the issue of the Exeter remaining in orbit for half a year, I'd like to raise the parallel issue of the fake Enterprise seemingly orbiting Gideon without anybody operating the engines. Yet Kirk thinks this could be his own starship, recently mysteriously deserted - even though it would seem obvious that Spock should maintain constant line of sight with the beamdown coordinates, rather than go round and round the planet. Should we think, then, that the ship can maintain a holding pattern even when uncrewed (she's not in gideosynchronous freefall there, we see the surface of Gideon move, and the altitude doesn't seem high enough for gideosynchronicity, either)? Well, Kirk also says that the power of the ship regenerates and will last basically indefinitely - supposedly on the mode of operation that Kirk finds the fake ship in. Is that mode freefall orbiting or impulse-powered holding-pattern orbiting? You decide... Timo Saloniemi
Hehehe, that TOS-R should be the "R-universe" But I see what you mean so things are a little different in TOS-R... Actually now, after glancing through "Omega Glory", "Court Martial" and "Mark of Gideon" (all TOS and not -R versions) - I'm not so sure about the hover orbit for "Court Martial" if we're going by the FX. "Court Martial" - the Enterprise is going against the rotation of the planet below and doesn't look like it is staying above a specific point. "Omega Glory" - actually does look like both the Exeter and Enterprise remain above a stationary point. Interestingly, the bridge view from the Enterprise shows the planet stationary but the stars continuing to move "Mark of Gideon" - again, it looks like the Enterprise is staying above a position as the FX shows them either following the rotation (and point) above the planet and the viewscreen shows the planet features relatively unchanging. In "This Side of Paradise" he sort of answers it: For the Gideon situation, the orbit question might not be applicable anymore since in Kirk's mind, he just took the ship out of warp and they're somewhere in space...
So that's how the natives got to live a thousand years or more: their years were three days long! Timo Saloniemi