Flight Question trying to understand Geostationary / geosynchronous orbits

[spacekid1998]

hello

why is it that a gso / geo orbit must be at about 35,700 km ? thank you

 

[supersonic]

That is the spot where an orbit takes 24 hours. Go lower your orbit's faster, go higher it's slower.

---------- Post added at 01:25 AM ---------- Previous post was at 01:18 AM ----------

Also, [ame="http://en.wikipedia.org/wiki/Geostationary_orbit"]this[/ame] may help.

 

[Izack]

Also, interestingly enough, a tower 35 786km (Geostationary orbital altitude) tall would experience 0 g on its top floor. Go any lower and you experience gravity, and go any higher and 'gravity' is upside down.

Sorry if I'm just making this more confusing.

 

[spacekid1998]

oh, but what if i was at like 60,000 km then cant i just burn prograde to speed up to earth's rotation ?

 

[fireballs619]

No, because you would be increasing your orbit then, so it is longer than 24 hours. At 35,700 km, your orbital period (T) is exactly 24 hours. You go around earth once every 24 hours, and, since that is the speed at which the Earth revolves, you always stay aabove the same spot.

 

[Izack]

I think you need a crash-course on orbital mechanics.

Basically, orbital speed is directly proportional to orbital radius (altitude), as per Kepler's Third Law. If you speed up, your semi-major axis will increase, and you will gain altitude while eccentricity approaches 1 (escape orbit.)

 

[spacekid1998]

so what if i was at 100km and burned retrograde to slow down

 

[Izack]

You would lower your semimajor axis, and start to lose altitude.

Take a look at [ame="http://en.wikipedia.org/wiki/Astrodynamics"]this[/ame] page. It's pretty interesting.

 

[KosmoKen]

so what if i was at 100km and burned retrograde to slow down

Then you would go faster, of course.

 

[spacekid1998]

oh thanks a lot, i understand now.. so the altitude is proportional to velocity. also, now that im in geosyncronous orbit, how do i make it over the equator? im using align planes but im not sure how to make the custom orbit (Shift + E). it tells me to input ecliptic inclination

 

[Izack]

Then you would go faster, of course.

Can you please explain this joke? I never got it.

 

[KosmoKen]

Can you please explain this joke? I never got it.

Its no joke, its rocket science! You were just explaining what it means to spacekid1998, you just don't realize it .

 

[supersonic]

oh thanks a lot, i understand now.. so the altitude is proportional to velocity. also, now that im in geosyncronous orbit, how do i make it over the equator? im using align planes but im not sure how to make the custom orbit (Shift + E). it tells me to input ecliptic inclination

Geostationary Orbit is only over the equator.

 

[Izack]

Its no joke, its rocket science! You were just explaining what it means to spacekid1998, you just don't realize it .

I don't quite get it, though. Is it that you speed up relative to a nearby object in an orbit similar to your previous one? Your vertical speed can increase, depending on where you are at the burn, I guess...

Maybe I'm just tired. Uptime ~28 hours now, I reckon. If I'm missing something obvious, please hit me with Orbiter.pdf (all 134 pages.)

EDIT: Duhh!!!! You lower PeA, so you speed up as your altitude decreases! :rofl:

 

[eyu100]

Well actually you can stay above the same spot on Earth while not at 35.7k km as long as you have fuel remaining... If you are below that altitude, you can orbit slowly and constantly thrust away from the center of the Earth to stay up; if above that altitude, you must orbit fast and thrust *toward* the center of the Earth to stay down.

 

[spacekid1998]

also guys what is the best angle to launch at to raise your apa to 35.7m? i mean which one puts you up there efficiently?

 

[KosmoKen]

also guys what is the best angle to launch at to raise your apa to 35.7m? i mean which one puts you up there efficiently?

It's usually always best (fuel efficient) to do each burn as a prograde burn. To make it easier on yourself, get yourself in a circular orbit (200x200km or something) first, then raise yourself with one or more prograde burns to the altitude you want.

 

[Izack]

[ame="http://en.wikipedia.org/wiki/Hohmann"]Hohman Transfer Orbit[/ame]

 

[Bj]

Take a look at:

Go Play In Space

The most efficient way to go to geostationary orbit, is to launch from the equator and go directly 90E. Of course that doesn't happen, so what you should do is lanch from cape going 90E, then when you are about to hit the descending node, (which is passing the equator from the north hemisphere to the south) burn orbit normal (+) (towards the north hemisphere) until your orbit runs equilateral. Then burn prograde (so you will raise your orbit, but you will appear to slow down relative to Earth, once you reach a higher orbit of course.)

Placing your satellite in a specific spot is a different matter, its position would depend on when you launch. :thumbup:

 

[spacekid1998]

much love <3