Very Unusual Satellite

[Randall]

Actually ... speed, distance and mass are factors in celestial mechanics, but mass doesn't tend to kick in too much until you get up to planetary sizes. If you want to learn about it you need to review Kepler's Laws. I did this back in university in astronomy 101. We went out to the Rothney observatory and calculated the mass of Jupiter by observing and timing its moons. Don't ask me to go back and figure out the math again though without some serious brushing up.

 

[boomerang]

Very interesting, and sounds like you did an excellent job of observation and data recording.
A rogue asteroid seems possible. But one would expect to hear about this in the news media.

It seems like a body in a higher orbit would move more slowly in degrees/second across the sky than one closer in. But I will defer to the experts on this one.

I used to be heavily into telescopic planetary imaging with CCD cameras and powerful image sharpening software. On the forum where I used to hang, some members would image the ISS with results that were amazing for one guy with a telescope in his backyard. And rarely, members would post pics of weird looking objects in orbit. If anyone on the forum knew what they were, they weren't saying . But the imager was typically someone well known to the rest of us, and probably not faking. I am guessing "we" have some pretty strange stuff whizzing around up there.

 

[exo_doc]

I stand corrected.

Weird this, in my head I am thinking if the speed is X of something in low-earth orbit, then if you slow down does that mean you gain height?

Yes you speed up to gain a higher orbit.
BUT, you lose that extra velocity in gravitational drag, in other words....you accelerate for a few moments then coast into your new higher orbit all the while slowing back down (until you reach a predetermined calculated orbit) then do some fine manuevering to stabilize your slower orbital speed.

 

[Randall]

Yes you speed up to gain a higher orbit.
BUT, you lose that extra velocity in gravitational drag, in other words....you accelerate for a few moments then coast into your new higher orbit all the while slowing back down (until you reach a predetermined calculated orbit) then do some fine manuevering to stabilize your slower orbital speed.

The reason it seems confusing is the way in which "speed" is interpreted. To maintain orbit you need a constant velocity equal and opposite to the pull of gravity. Essentially a stable orbit is a perpetual free fall where you are moving fast enough that by the time you fallen some distance ( say 10 feet ) the ground that has formed into an approximate sphere around the planet's center of gravity is curved and is now also 10 feet farther away. To boost into a higher orbit, you don't need to apply thrust to increase orbital velocity ( although you could, but that get's into the concept of escape velocity ). What is required is thrust against the force of gravity, so for example you would face the craft directly away from the planet and fire the engines downward. By doing this you are not actually increasing your orbital velocity, only moving into a higher orbit.

 

[Goggs Mackay]

Yes, I have it right now, thanks guys. I know where I was going wrong - I was confusing the fact that any object accelerates to earth under gravity at 9.8ms-2 regardless of mass (neglecting air), and the need for orbits to have the same rate (the wrong part).

Another one that used to bug me was escape velocity. I could not understand why any rocket could not just plod straight up given enough fuel - it was not explained at school/uni that escape velocity only counts for ballistic trajectories.

Good, that's sorted - next!

 

[Ian]

The moon at about 238,857 miles from Earth takes 28 days to orbit; stand watching all night and you won't see it move much - apart from that caused by the Earth's rotation which we are not discussing here.

Low earth orbit (i.e. just clear of the upper atmosphere) is 100 to 200 miles approximately (ISS) and takes about 90 minutes to make one orbit, and when visible from the ground, take something like 10 minutes to arch across horizon to horizon.

The point being, the higher the orbit, the slower it appears to move.

A satellite much higher than 200 miles will take correspondingly longer to go horizon to horizon. With a bit of maths we could probably get some idea of the height from its apparent speed; I'd guess an altitude of three or four thousand miles. What is surprising about the OP is that it was visible (to the naked eye?) at that height. Whatever it was it must have been large and/or very reflective.

The Astra satellites in geostationary orbit at 22,236 miles are only visible though a telescope.

Regards,

 

[Randall]

Point of interest: Did you guys know we actually have satellites in geostationary orbit beyond the distance of the Moon?

 

[Randall]

Another one that used to bug me was escape velocity. I could not understand why any rocket could not just plod straight up given enough fuel ...

Actually ... you were completely correct. A rocket could do exactly as you imagined. The only thing is that they would have to maintain thrust in order to stay up there until they were well beyond Earth's gravity well, otherwise as soon as they shut off the engines they'd just fall back down again.

 

[Ian]

Point of interest: Did you guys know we actually have satellites in geostationary orbit beyond the distance of the Moon?

(Note: Geostationary satellites are in orbit above the equator. They appear stationary above that point and typically - but not exclusively - are used for satellite TV. Geosynchronous orbits are at the same height as geostationary orbits [OK, the molniya orbit is an exception], but in any plain other than over the equator - over the poles for example - so at the same time once per day appear over the same location.)

So there are satellites in orbit around the Earth, but beyond the orbit of the Moon, OK, understood. If they were visible they would appear to be stationary. They are beyond the Moon, but only take a day to orbit the Earth?

How do they do that and what are they used for?

Regards,

 

[Goggs Mackay]

I think I remember from singint (signals intelligence) lessons that some satellites are as far up as 27,000 k?

I did not know there was anything artificial further out than the moon!