Fascinating! I never considered this before. I always assumed that if they’re “in orbit” they’re just coasting, i.e., in freefall. Obviously, that simply wasn’t true, at least not always.
That’s correct too, right after McCoy delivered his line, I think.
They referred to the body in question as a “moon”, so “lunosychronous” would somehow seem more appropriate, but, IIRC, the term they used in the episode was “stationary orbit”. I guess that forgives the messed up astrodynamics.
Whatever. But I doubt the ship is spinning in the polar mode; its orientation wouldn’t change. It’s simply hovering, which means that it’s not “in orbit” at all.
I have to admit, the ‘non-orbiting orbit’ fits the facts in the episodes best. It always used to bug me, in episodes like Court Martial, that the ship would start spiraling in as soon as power was removed. Even as a kid, I was like “don’t they even understand orbital mechanics?” (I was a precocious child…)
But if it is the *term *that changed meaning, then it makes sense. A ‘standard orbit’ doesn’t mean ‘moving around the center of mass in freefall’, but means ‘hover over the spot of interest’. Orbiting, as it were, in perfect synchronicity with the surface. Like ‘dialing’ a phone, the term remains even if it is no longer factually correct.
The case of Mirror, Mirror, where the target moves out of range as the planet rotates, is then the anomalous case. Maybe EvilSulu was a sloppy helmsman?
Check out this awesome website! I especially love the Deleted Scenes feature:
http://www.startrekhistory.com/index2.html
Check out the script in “The Savage Curtain.” Spock explains orbital mechanics to Lincoln in classic free-fall terms.
Bumped.
I just finished a novel, set in the present day, about the virtual collapse of civilization after a global pandemic. It’s mentioned that there’s no more space travel. If nothing were done to maintain their orbits, how long would it before all or most of the current satellites fell from orbit and burned up in the atmosphere?
Calculator that purports to answer that question for satellites in nominally circular orbits with apogee under 500 km. Looks like a lot of the numbers come from articles like this blog post. When I plugged in the mass of the ISS and an area of 2500 m^2, I got a lifetime of around 32 years. I’d guess lighter sats with the same proportions would do even worse.
The lifetime of the parking orbits for the decaying Soviet nuclear reactors that powered their radar satellites was estimated to be in the 500 years range, and it had an apogee of only 1000 km or so. See, this article from the FAS on Soviet space-based nuclear reactors.
Based on that, I’d figure the orbital lifetime of anything in geosync to be essentially infinite. Probably a similar case for the GPS and STSS birds. What’s the estimated lifespan of a satellite in a Molniya orbit, with perigee ~600 km?
Low orbit ones (like the ISS) have lifetimes measured in years or decades. Geosynchronous satellites might be able to stay in orbit for many centuries or milennia.
So that is how Janice got her yeoman job. Connections and networking is still the way to go in the 23rd century.
We almost have very crude self-driving cars. By the 23rd century I think that some sort of auto-pilot that could initiate thrust with the impulse engines when needed would be required. Like 20 seconds every half a year.
We have to remember that the whole USS Enterprise, the command ranks, basically everything about the service was based upon current, at the time, naval warfare.
Hard astern, battle stations, full stop, reverse engines, lay down a photon torpedo (depth charge) spread, silent running, belay that order, etc. It wasn’t Wagon Train in space. It was WWII naval battles in space.
I’ll be in my Ready Room.
True, but a geostationary satellite needs occasional orbital corrections to stay above a specific longitude, otherwise it will start to drift along the orbit. After it runs out of propellant, your weather satellite won’t stay above your country. A broadcast satellite won’t stay where everyone’s satellite dishes are pointed to.
AIUI, geostationary satellites without correction will migrate to one of two specific longitudes, although I don’t remember what those are. They won’t all collide at those places. Perturbations by the Sun and Moon will no doubt cause them to oscillate in latitude, so they won’t all be in the same place at the same time.
You’re right, there are two spots that are stable. From wikipedia:
But I think that means the satellites go into a halo orbit around one of these equilibrium points, and not actually reach that spot.
How many current satellites are in the first category, and how many in the second?
Conventional telecommunications satellites & broadcast satellites are in geostationary orbit. The satellite stays fixed in the sky, so a fixed antenna stays pointed at the same satellite all the time.
Weather satellites are also in geostationary orbit. It allows one satellite to observe the same part of the Earth all the time. The US operates two (plus spares), one above the east coast and one above the west coast.
Most other types of satellites are in low earth orbit. It’s easier (and much cheaper) to get to, and it’s closer to the Earth, which can be an advantage (e.g. for observing the earth). So spy satellites, earth-observing science satellites, astronomical satellites, etc are mostly in low orbit. And some types of telecommunications satellites are in low orbit, like satellite phone networks (e.g. Iridium) and the new satellite internet networks (e.g. SpaceX Starlink) - they are constellations of many satellites, so even though they are in low earth orbit, at least one is accessible at any time. All crewed space stations are (and have been) in low earth orbit as well.
In addition to those, there are several constellations of navigation satellites: GPS, or course, but also European, Russian, Chinese, Japanese, and Indian constellations. These are in intermediate height orbits, about halfway between LEO and geostationary orbits. Roughly 20,000 Km give or take a thousand or two kilometers. It’s also known as Medium Earth orbit. GPS birds, in specific, orbit at 20,180 Km and the others at different heights to avoid potential collisions.
Oops, slight correction on that. The Indian and Japanese systems do not orbit in MEO, but rather in either geostationary or geosynchronous orbits. They only cover the areas near the two countries.
Just throwing out a data point:Vanguard I, the US’s first satellite is still in orbit over 61 years later. Current altitude is 8,619 kilometers (5355.6 miles). So about 1/4 to geostationary. A ways out there but still estimated to have a lifetime in orbit of 240 years. And it’s a small, almost roundish object (but OTOH low mass).
(Fun fact: it is one of the two oldest artificial objects still in orbit. The other is its 3rd stage booster.)
What with the Moon and all, geostationary sats in Earth orbit aren’t going to last, um, astronomical periods of time.
According to this graph, GPS satellites in 12,550 mile-high orbits have an orbital lifetime in the millions of years. Communications satellites in 22,500 mile-high geostationary orbits should equal or exceed that.