Thousands of engineers have worked on the seventh and eighth navigation satellites of Europe’s Galileo constellation in recent years, but last Friday marked the very last time the spacecraft were glimpsed by human eyes.
The team from ESA and builders OHB in the S3B building of Europe’s Spaceport in French Guiana looked on as the focus of their work disappeared from view.
The pair of satellites – already resting atop their Fregat upper stage and attached to their dispenser – was enclosed within the halves of the Soyuz rocket’s protective fairing.
This unit was moved yesterday to the launch site, where it will be lifted atop the first three stages of the Soyuz ST-B to complete the vehicle for Friday’s launch.
Last week saw the two satellites being fuelled in the Spaceport’s S5A preparation hall and then brought together atop the dispenser that will support them during the rigours of ascent.
The dispenser’s final task is to release them in opposite directions once their 22 522 km-altitude orbit is reached. The satellites themselves will then gradually lower themselves to their working 22 322 km orbit.
After fuelling, the satellites plus dispenser were moved to the S3B processing building, where their Fregat was already fuelled and waiting.
The reignitable Fregat is as much a spacecraft as a rocket stage. Once the Soyuz reaches low orbit, Fregat will take over the task of hauling the satellites higher through a pair of burns.
The two Galileos and their dispenser altogether weigh more than one and a half tonnes, so the attachment operation took place with great care and precision.
Then the fairing halves were slowly slid into place around them and closed. Enclosed in this way, the satellites will be protected from the harsh slipstream and vibration of the first few moments of launch, when the Soyuz is still travelling through the thickest layers of atmosphere.
The fairing is due to be ejected 3 min 29 sec after liftoff.
Until liftoff, the satellites remain connected to the outside world via power and data links, allowing ESA’s Galileo team keep a check on their battery charging and the health of their atomic clocks.
The satellites stay switched off during launch, and will be activated automatically on separation from the dispenser.
Launch is due at 21:46:18 GMT (22:46:18 CET, 18:46:18 local time) on 27 March. The satellites are scheduled for release upon reaching their set orbit 3 h 47 min 57 sec after launch.