To the MONEY RING: Musk's SpaceX to attempt boldest mission yet

It's yet another fateful day for upstart startup rocket biz SpaceX and its visionary founder Elon Musk. Today the company will attempt for the first time to put a satellite into a geostationary transfer orbit - and so enter the main space arena in which serious commercial money can be made today. Geostationary orbit is the …

[NoneSuch]

"So, though it takes a lot more rocket poke to get up to GTO..."

That should be GEO (Geostationary Orbit) surely.

[I ain't Spartacus]

I'd imagine it's geostationary transfer orbit. Then the satellite will have a booster to get it the rest of the way to where it's going.

[John Sager]

GTO is highly ellptical with the apogee up close to the GEO altitude and the perigee only around the altitude of Low Earth Orbit. An extra motor on the satellite fires around apogee to bring the perigee up and circularise the orbit. It also often changes the inclination by a few degrees to bring it right over the equator.

[Tim Brummer]

GTO is Geosynchronos transfer orbit. The booster puts the satellite payload into GTO which loops between low earth orbit and GEO. At the high point an "Apogee kick motor" which is part of the payload makes the orbit into a circular GEO.

[Gene Cash]

Sigh... stupid clouds

I might get to see the launch, but it's looking pretty crappy & cloudy out there.

[Irongut]

Good luck SpaceX!

[John Smith 19]

Err.

Most space ports are not on the equator, so the best an LV can manage is to get it into GTO, at which point the Apogee Kick Motor here which gets it to the equator.

At GEO the on orbit thrusters finish up the orbit shaping to kill the residual velocity.

[bhound562]

Re: Err.

That is simply not true. Delta IV and Atlas rockets typically deliver payloads to GEO without the payload having to provide the final burn.

[Martin Budden]

80,000km > 35,786km

The SpaceX website says "The rocket will deliver the SES-8 satellite to a geosynchronous transfer orbit 80,000 km from Earth – that’s ¼ of the way to the moon."

80,000km is a lot higher than the 35,786km for geostationary orbit. Can someone clever please explain to me why they are going so high?

[Vulch]

Re: 80,000km > 35,786km

It actually takes less fuel that way, although it needs two engine burns to get to the final orbit rather than one. A burn at apogee (the 80,000km point) raises the perigee to GEO altitude, then half an orbit later a second burn drops the apogee and circularises the orbit.

There have been trajectories involving a trip round the moon calculated, although so far the only taker was a Russian launch that had a stage restart failure and used some of its manouvering fuel to do the loop and circularisation. It wasn't carrying enough fuel for a direct insertion. Satellite operators are very conservative and no-one wants to be the first to use a lunar fly-by for real, they all want someone else to demonstrate it works.

[Vulch]

Re: 80,000km > 35,786km

Missed the edit window...

The fuel saving is mostly in the plane change manouevre, the higher that is done the less fuel it takes. A launch from Kourou will generally go straight to GEO altitude as it's almost on the Equator anyway. From Cape Canaveral they need to lose 28.5 degrees of inclination so it takes less fuel to go higher, change plane and drop back, and from Baikonour you need to change by about 56 degrees which makes the Lunar fly-by option tempting.

[Jade]

Launch Window?

Why is there a launch window for a synchronous orbit? It's not like they are going to get any closer or further away from the launch destination/path...

[Sorry that handle is already taken.]

Re: Launch Window?

Could the relative positions of the sun and moon be significant to the placement of the satellite in orbit?

[Vulch]

Re: Launch Window?

Partly sun angle in the transfer bit of the orbit, and partly how long the launch team have been working. You do not want a tired ground control team, or have to try and manage a shift change part way through.

[bhound562]

Re: Launch Window?

Because there is an exact spot in that orbit that you want to be so that the satellite can service that part of the earth below it. To reach that exact spot in the orbit, there is an optimum launch time that will use the least fuel (propellant). There is some wiggle room in that optimum time where the coast times and the burn times can be adjusted to reach the target spot, but the further that you get from the optimum time, the more propellant that it takes to get there. Of course every rocket has a limit on the amount of propellant that it can carry. That determines the size of the launch window.

[Sorry that handle is already taken.]

Re: bhound562

I'm not sure if I've misunderstood your explanation, but it doesn't seem to address Jade's point that a satellite being launched to geosynchronous orbit is always going to be in the same location "above" the Earth relative to the launch site, regardless of when it is launched. It doesn't have to wait until the Earth's facing a particular direction.

[Malc]

Re: bhound562

Orbit is as much to with how fast you're going as what altitude you're at. The sat's final geosynchronous position doesn't depend on where it was launched from.

Play some Kerbal Space Program for a better explanation.