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LEOPing in orbit

How do we make contact and take control of our satellites immediately after launch?
In this series of Commissioning Blogs, we’re going to give you a snapshot of the tasks that need to be performed to establish the position of the satellite in orbit, place it in a stable attitude, check out all the on-board systems, and test and commission the payload.

The Launch and Early Operations Phase (LEOP) immediately after the launch of a satellite is the first part of the in-orbit commissioning process - a managed series of tests and operations that conclude with the commissioned satellite being handed over to the customer. Here at SSTL we are currently in the LEOP phase for KazEOSat-2, launched on 19 June from Yasny in Russia: the satellite is being tracked from both from Mission Control here at SSTL, and also from our customer’s satellite centre in Astana, where initial in-orbit operations are well underway.

Our satellite is powered off through its ride into space on-board the launcher. All being well, our satellite separates from the launcher at a pre-determined point (its orbit injection) and as it does so the power system activates and the receivers power up. Once in range of the ground station it’s over to our Ops team to make contact with the satellite and take control.


KazEOSat-2 during end-to-end testing in SSTL's cleanrooms earlier this year

First things first
The first task during the LEOP phase is to determine that the satellite has made it into the correct orbit, so that our ground station dish antennas can be pointed accurately during the first pass. The launch agency provides initial orbit parameters and within the next 24-48 hours we receive additional data from the North American Aerospace Defense Command – NORAD – who track all orbiting objects using powerful radars.

Locking on
Our satellites usually make six passes over our ground station here in Guildford over a 24 hour period, and each pass ranges from a short 2 minute horizon-grazing pass to a good overhead pass of up to 15 minutes duration. The satellite's first pass is always met with some trepidation while we send commands to turn on the downlink and listen out for a signal. Even on a good pass it’s still a relatively short communications window when we can upload commands and receive telemetry, so the team initially work in shifts to take advantage of every pass. Quite a lot of pizza is delivered here during LEOP!

A busy Mission Control room here awaiting the first pass of KazEOSat-2 last week



















Full health check
After contact is established, our next priority is to download general “health-check” telemetry which tells us how critical subsystems are performing, and to analyse the tumble rates which our engineers feed into complex algorithms to help them work out the manoeuvres that will be necessary to stabilise the spacecraft’s attitude.

Once the LEOP team have established that the power system and uplink and downlink communications are working satisfactorily we can start to upload the mission software to the on-board computers, including the algorithm for de-tumbling the spacecraft. This is achieved by using a combination of firing the magnetorquers (electromagnetic coils which interact with the Earth’s magnetic field ) and using the satellites reaction wheels, to achieve a slowing of the tumble, finally resulting in a stable NADIR (Earth pointing) configuration.


Interior of the NigeriaSat-2 spacecraft. Two of the Satellites reaction wheels can be seen middle right. The spacecraft’s two propulsion tanks, which provide thrust for in-orbit manoeuvres used for orbit maintenance through the mission, are visible on the left of the image

LEOP phase complete
With the satellite now stable and healthy in orbit, LEOP is complete and we can begin platform, payload and full ground system commissioning - we'll cover that in future Blogs so do check back! 

 

 
 

 

 

24 June 20140 Comments1 Comment

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