Three Questions about a Satellite Launch Answered
On the afternoon of the launch of the Intelsat 30 satellite, Jon Harborne, Senior Manager, Intelsat Spacecraft Program Office, answers some frequently asked questions about what happens during and just after the launch.
Who controls the satellite when it’s launched?
It’s a carefully choreographed sequence. First, the SSL (manufacturing) team in Kourou powers up the satellite 10 hours before launch and gets everything configured. Then, Arianespace (the launcher) starts the launch day countdown and loads the rocket with liquid oxygen and hydrogen. After that, if everything is looking good, the launch base goes into the final countdown phase and launches the rocket.
Once the boosters are ignited, the rocket takes off under the control of its flight computers, and climbs and accelerates for about 28 minutes before releasing the satellite. Then at the Intelsat Launch Control Center in Long Beach, Ca. (pictured), we watch for telemetry from one of our downrange ground stations. When we get a good signal we send commands to configure the satellite for the next phase: orbit-raising.
What happens when the satellite is released from the rocket?
The Ariane 5 rocket releases the satellite into a transfer orbit, which is an elliptical orbit that just clears the atmosphere at 240 km above the earth on its nearest approach (perigee), and goes out as far as about 36,000 km at its farthest point (apogee). In the orbit-raising phase, the controllers use the satellite’s own propulsion system to boost the orbit to a circular path above the equator, with an altitude of just under 36,000 km. This is known as the geostationary orbit because in this orbit, satellites orbit the earth at the same rate as the earth rotates, and therefore appear to be stationary when viewed from the earth. This makes it easier for Intelsat to track them with a ground antenna pointing to a fixed point along the geostationary arc.
How long does it take to get the satellite on orbit?
Firing the satellite’s main thruster when the satellite is at its apogee has the effect of raising the perigee, and by doing this four or five times, the perigee is raised to the same altitude as the apogee, resulting in a circular orbit. In the case of Intelsat 30, it is expected to take about eight days to accomplish the orbit raising.