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Waspie_Dwarf

SpaceX Launch Scrubbed Again

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Engine trouble delays SpaceX launch on Thanksgiving

Topped with a television broadcasting satellite, SpaceX's Falcon 9 rocket fired its engines and was moments away from liftoff from Cape Canaveral on Thursday, but the commercial booster aborted the launch after computers detected the engines were too slow building up thrust.

Engineers raced to understand and resolve the problem, but they could not get comfortable enough to attempt the launch again before Thursday's time-constrained flight opportunity closed.

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Edited by Waspie_Dwarf

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Bummer. Well, the weather wasn't that great anyway. Unfortunately, those employees had to work on Thanksgiving only to scrub the launch. :(

Edited by Bluefinger

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Unfortunately, those employees had to work on Thanksgiving only to scrub the launch. :(

SpaceX wanted to try for a launch on Tuesday or Wednesday but were refused permission by the Federal Aviation Authority because it was feared it would add to holiday air congestion. Source: http://spaceflightnow.com/falcon9/007/131126faa/

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I'm just wondering what are the main factors that determine the length of a launch window? Sorry for my ignorance, I only 'got into' anything space related the week before Curiosity landed, but my God how I am obsessed with it now :) I'm guessing it's air traffic, but is it anything to do with where they want to place it into orbit?

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I'm just wondering what are the main factors that determine the length of a launch window? Sorry for my ignorance, I only 'got into' anything space related the week before Curiosity landed, but my God how I am obsessed with it now :) I'm guessing it's air traffic, but is it anything to do with where they want to place it into orbit?

I'm certainly no expert, but I'm pretty sure that air traffic has nothing to do with it.

However I'm pretty sure you're right that where they want to place it in orbit is key. Part of the problem is that velocity and orbital altitude are directly related, so if you want to arrive at a particular place at a particular time, you're limited on when you can leave from your starting place. So, for example, to get to the International Space Station you not only have to get to the same orbital altitude as the ISS, you need to get to where the ISS is at the same time the ISS is there.

In this case it's a geosynchronous orbit (an orbit which takes 24 hours to circle the Earth and so staying above a fixed point on the equator), and it's a comms satellite for some specific part of the Earth. So that means a specific altitude and a specific place above the Earth - in particular, directly above the equator. (BTW I'm happy to be corrected by anyone who actually knows this stuff.)

Firstly, the spacecraft is launched from somewhere that isn't on the equator, and it will be placed into a parking orbit fairly low - perhaps 200-300km above the Earth. However, because the launch was somewhere away from the equator the spacecraft's orbit will be at an angle to the equator - it will move north and south of the equator as it travels around the Earth.

Secondly, once the spacecraft has been checked out, it will fire its engine again to enter a highly elliptical orbit. The low point of the orbit will be the altitude of the parking orbit and the high point of the orbit will be the altitude of the geosynchronous orbit. This orbit will still be at an angle to the equator.

Thirdly, when the spacecraft is at the high point of its orbit, it will fire its engine again. This will have the effect of putting the spacecraft in a circular orbit at geosynchronous orbit altitude. However this orbit will also be at an angle to the equator. The spacecraft will now be taking 24 hours to circle the Earth but will still be moving north and south of the equator as it travels around the Earth. (If you were to mark out a ground track of the spacecraft it would trace out a figure-8 shape called an analemma.)

Finally, at the time the spacecraft crosses the Earth's orbit it will fire its engine a final time to change the angle of the orbit - what's known as a plane change - so that it orbits directly above the equator.

If all these burns are successful and take place at the right time, the spacecraft will end up in the desired location.

Now, working back - each firing of the engine has to take place at a specific time in order for the spacecraft to end up where it's needed, so the time of each burn helps determine the time of the previous burn, all the way back to the launch. So, for example, the fourth burn has to take place when the spacecraft crosses the Earth's equator, but it also has to take place when the spacecraft is directly above its target location. This means that one of the points where the spacecraft crosses the Earth's equator prior to the fourth burn must be above its target location, and that in turn affects when the third burn takes place. And so on.

The launch time can be changed to some extent because the spacecraft can be launched into a lower (faster) or higher (slower) orbit to provide some flexibility for the next burn.

Apologies if I've confused you, but while I can visualise this I have no idea how to illustrate it.

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With a geosynchronous transfer orbit the launch window constraints aren't really much to do with the planned final orbit. Once a satellite is placed into geosynchronous orbit it is checked out for weeks or months before becoming operational. During this time it is slowly moved into it's final position. Theoretically the launch could occur at pretty much any time.

What does become a concern is the health of the satellite. At some stage in the countdown the satellite will be switched to internal power. This means it is on battery power. Those batteries can only support the satellite for a finite amount of time before being recharged. This will be one of the limiting factors in the launch window.

Once in space the satellite will need to unfurl it's solar panels before it can recharge it's batteries. There is a necessity for the satellite to arrive at this point in it's orbit during day light, and in contact of a ground station.

These factors help determine the launch window in this case.

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