Two Line Elements

Short TLEs

Short term TLE vectors are generated twice a day: once in the morning (reference time 13:00 UTC on current day) and once in the afternoon (reference time 1:00 UTC on the following day). Their validity arc spans from their reference time to 12 hours in the future. Within the validity arc their accuracy is of around 300 m RMS (max error around 1 km); outside the validity arc the accuracy degradation is very fast, reaching several tens of km after a week. They permit to finely locate the satellite but they should never be used more than a couple of days outside their validity arc.

Long TLEs

Long term TLE vectors are generated once a day around noon (reference time 6:00 UTC on the following day or shortly after the end of the next planned manoeuvre). Their validity arc spans from their reference time to 10 days in the future. Within the validity arc their accuracy is of around 600m RMS (max error around 2km); outside the validity arc the accuracy degradation is very slow, keeping similar accuracy for several weeks. They can therefore be used for long term planning activities.

Metop-A

Metop-B