I got to thinking about space junk and what happened when an orbiting piece from an explosive bolt or equivalent hit a spacecraft, like the Shuttle. Okay, a fragment traveling 17,000 mph might not ever hit a Shuttle, also traveling at 17,000 mph. But it would be really bad to hit the shuttle at 34,000 mph.
So the question: Is there a “normal” direction for earth orbit. Number 2, does anything orbit the earth in the direction opposite the way the Shuttle or other low earth orbit (LEO) satellites do?
Yes, there is a general direction (almost?) everything orbits in. I don’t know how to describe it’s direction since there’s no frame of reference, so I can’t say if its clockwise or counterclockwise. There may be some things that orbit in the other direction.
There are 2 types of orbits: equatorial and polar. Equatorial moves west to east because we take advantage of the rotation of the Earth when we launch. That’s a very sizeable amount of speed, so as far as I know we have nothing orbiting east to west. Polar orbits run over the poles while the Earth rotates beneath it. North to South or South to North is meaningless in a polar orbit because it changes direction every time it passes a pole.
There are a number of different general kinds of orbits.
Geosynchronous orbits, by definition all go in the same direction since the satellite stays over the same location of the Earth.
Polar orbits go over the poles, but a large number of these are in sun-synchronous orbits - which means that they stay with the plane of their orbit at a constant angle to the line between the Earth and Sun - this allows them to always see the Earth with the same shadow angle. So these all travel in an apparent EW direction at the same speed.
Other low orbit satellites may have all sorts of orbits. The direction that they generally travel at is almost certainly influenced by the desire to get to orbit with the least cost - and so the speed of travel near the equator is used as an initial velocity and the launch always is to the East, and you may find a general preponderance of orbits with that direction - to go the opposite direction is pretty ruinous as you have to get rid of that velocity before you even get to add new - which is why polar orbiting satellites are a problem. Further, you need to add energy to get the orbit to get to a different plane to the latitude of the launch site - and so the choice of the plane will be influenced by the requirements of the satellite, the launch site, and the capability of the launcher (or the money to buy it.) Two satellites, both in low Earth orbit may cross at close to 90 degrees simply because the planes of their orbits have moved around to so intersect, even though both are in much the same basic orbit.
Then there are satellites in intermediate orbits - such as the GPS constellation, which have a set of orbital planes that allows them to always cover the Earth, and for which there is no easy way of talking about a preferred direction - although again the effect of the initial velocity of the launch site probably figures in there.
There are far more than just one or two families or orbits, and in fact the parameters of possible orbits are not only continuous in inclination from the ecliptic (the plane through the equator) from 0° (rotating exactly with the Earth), inclined either up or down in (prograde), to ±90° (polar orbit), to “backwards” (retrograde), but may also vary in altitude and eccentricity up to highly elliptical orbits like Molinya orbits used for high latitude communications satellites and those used for surveillance satellites.
The only orbit that is specifically fixed in altitude and inclination is the geostationary orbit (GEO), which lies in the ecliptic in a circular orbit in about 35,800 km in altitude allowing the satellite to remain motionless to anyone standing on Earth’s surface. Geosynchronous orbits (GSO) also orbit at the same altitude but at various inclinations that pass back over the same point on the surface once a day. In addition to GEO and GSO, orbits are classified in Low Earth Orbit (LEO) up to about 2,000 km altitude, Medium Earth Orbit (MEO) between LEO and GEO, and High Earth Orbit (HEO) above GEO out to the limits of Earth’s sphere of influence. Here is a comprehensive catalog of objects in orbit.
In order to prevent collisions in space, orbits have to be carefully specified and controlled. For the United States, the USSTRATCOM Joint Functional Component Command for Space (JFCCS) tracks objects in space and performs orbit determination with NASA, the Air Force, and US commercial launch and space vehicle operators through Joint Space Operations Center (JSpOC). Other major nations have their own tracking systems or cooperative agreements with those that do It is up to the operators, however, to voluntarily assure that they’re not going to pass close enough to another spacecraft or debris field to pose a significant risk of collision. The one exception to this is spots in GEO and associated radio frequency spectrum which is allocated by the International Telecommunications Union to prevent conflicts.
Surprisingly few collisions in orbit have occurred so far, but those that have produced wide debris fields, and we’ve been fortunate that they haven’t resulted in cascade failures (also called Kessler Syndrome, portrayed in highly exaggerated fashion in the film Gravity.) As more commercial spacecraft are placed in orbit with less controls and propulsive capability, especially the smallsat category of spacecraft, will experience more collisions and greater debris pollution. Fortunately, the current provence of smallsats is almost exclusively in the lower regions of LEO in which orbits naturally decay within a few years, but in higher orbits the debris fields can persist for decades or even centuries.
Sorry, but this is a mistaken definition of “ecliptic”. The ecliptic is not the equatorial plane, but rather the plane of the Earth’s orbit (or alternatively, the apparent path of the Sun through the sky). It’s tilted some 22.5 degrees from the equator. Unless rocket scientists use this other definition, in which case there could be problems if they have to talk to astronomers.
The orbit itself is fairly close to a circle going around the Earth at some particular altitude. And the satellite is generally moving from West to East, as shown by the arrowheads on the pic. But since it is tilted versus the Earth’s equator, the satellite also moves North & then back South as it goes around and around the Earth.
Now imagine a second satellite also orbiting in the same way. But not exactly synchronized with the first satellite. It’d be easy for one to be going Northeast when the other one came by going Southeast. And they’d collide at something like a 90 degree angle.
Notice the angle at which the various lines cross on that pic. On that pic those are different cycles of the same orbital path of a single satellite. But they could just as easily be representing cycles of different satellites crossing paths every so often.
Most stuff put into orbit by people probably does go around the same way the Earth rotates, because it requires so much extra energy to put something into a retrograde orbit (one that goes the other way than the Earth rotates). You wouldn’t do it unless you had a good reason to. Some satellites are in retrograde orbits, though. There are also satellites in or near polar orbits.
Some other planets have natural satellites in retrograde orbits. Neptune’s moon Triton is in such an orbit, as is at least one moon of Saturn.
The ecliptic plane (in generic terms) is the reference plane that the orbital inclination is measured against in whatever coordinate system you are operating. You are correct that in general usage the ecliptic refers to the celestial or solar ecliptic (the plane in which the Sun transits the Earth-centered sphere and through which the universe appears to rotate, and has an angle of obliquity to the Earth’s rotational axis of about 23.4 degrees) but for Earth-orbiting satellites using an Earth-centered Earth-fixed (ECEF) reference frame this is essentially immaterial unless the satellite has to make celestial observations, in which it is referred to as the celestial or solar ecliptic, and the equatorial plane is referred to as the Earth ecliptic or just “plane of reference” (which gets confusing because there can also be other planes of reference in Earth centered internal reference systems or in specifying constellations of orbits). To further confuse, when making extrasolar observations there is also the galactic plane (sometimes called the galactic ecliptic) at which the celestial ecliptic lies at approximately 60 degrees. For precision when performing orbital mechanics calculations it is actually necessary to specify the reference frame in which the calculations are being performed and then perform transforms between reference frames; even a small difference in the frames can translate into a large error in the resulting trajectory.
You must remember that in space ‘relative speed’ is everything. Even if an object is ‘only’ traveling at 16,900 mph it would hit the Shuttle (or technically, the Shuttle would hit it) at 100 mph. And orbital speed varies with exact mass and altitude. So it is not merely objects orbiting in the opposite direction that are a danger, but pretty much everything*!* (at least everything at roughly the same LEO (low Earth orbital) altitude).
BTW they are usually referred to as prograde (same direction) and retrograde (opposite direction) orbits.If looking ‘down’ at the Earth from directly above the North Pole prograde would be counter-clockwise and retrograde clockwise (consider that the Earth rotates west to east)…
Arthur C Clarke always pointed out that the possibility of retrograde orbits negated the fear of the Massive Orbiting Highly Armoured Death Star Space Station.
All you need to do is put your warhead in a similar retrograde orbit. Now, your warhead is fairly primitive - a big bucket of old bolts. But if one of them hits the space MOHADSSS, it hits it at 34,000 mph. A handful of those will do some serious damage.
Oh, and if you get the orbit slightly wrong, and miss the MOHADSSS by a couple of hundred miles, not to worry. In a few hours, they’ll go past each other again - and your cloud of bolts will slowly be getting bigger…
