From Robert (ESA), 18 April, currently in the Lake District, UK
With all the excitement going on in the Arctic, one might think it’s business as usual back in Europe operating CryoSat’s main payload, SIRAL. Far from it; on top of the routine monitoring of CryoSat's health, there have been a number of background activities going on over the last few months to assure the success of the Arctic campaign.
CryoSat ground path (green) NASA P-3 path (yellow) (credits: R. Cullen)
First of all, we need to make sure SIRAL is being commanded as expected. The science measurement mode commands are transmitted to the satellite about a week before the radar is operated.
The team at ESA very confident that the automatic commanding is correct – as it has been since the facility that generates the commands was brought into operation early May last year.
Nevertheless, it’s worth a check during the critical period of a validation campaign.
Also, there’s CryoSat's orbital path to consider. Since the ground and air teams need to know to an accuracy of meters where the CryoSat ground track will be, it’s left to the experiment teams to determine this using the latest orbit predictions supplied from the Flight Dynamics Team based in ESA-ESOC, Germany.
The closer we do this to the CryoSat overpass, the more accurate the prediction is. Recently, there has been a lot of solar activity and this affects the accuracy of the prediction and how long it is valid for. It was therefore necessary to re-emphasise to the experiment teams the need to tune the air experiment flight plan as late as possible.
CryoSat's path on 15 April (credits: R. Cullen)
Furthermore, early last week it became clear that CryoSat was approaching its 'reference orbit dead band zone', which is an across track distance about the nominal reference for which CryoSat is kept to achieve its mission objectives. Ideally, one would want to avoid any maintenance manoeuvre to keep CryoSat as close as possible to its mission reference orbit. It became clear it was best to do this last Thursday to avoid a larger manoeuvre later in the campaign.
The first ground team activities with NASA and CryoSat under flights were planned for 15 and 17 April respectively, so it was a tough call for the Mission Manager to agree to the manoeuvre, albeit a necessary one.
