At the end of the PolarMonitoring project, ESA decided to make additional analyses related to the CRISTAL orbit. A Contract Change Notice (CCN) was established for that purpose.
The main objective of this CCN study was to define an optimal orbit for the future CRISTAL mission. This work was divided in two main tasks:
- Research of new orbit candidates: Before the study, several orbit cases have been suggested by ESA and CNES. A first task was to seek for new orbit candidates based on MAG requests (see below). CLS only was involved in this work.
- Analyses of the orbit candidates: The orbit candidates were analyzed side by side, and ranked based on their capabilities to fulfill MAG specifications. Analyses were made on different surfaces. Lancaster University was responsible for the ice sheet surface, FMI for the sea-ice surface and CLS for the ocean.
Before the study, the MAG made clear specifications of the orbit characteristics, to fulfil user requirements over different surfaces:
- Weekly sampling is first priority for sea ice thickness objective.
- Monthly sampling is first priority for land ice objective.
- For Antarctica, monthly sub-cycle will be sufficient; for Greenland, <30 days sub-sampling would be desirable.
- Regular, homogeneous sampling is generally favorable.
- Additional sub-cycles such as 4 days sub-cycle, and quarterly sub-cycles are nice to have.
- The orbit must complement Sentinel-3 orbit pattern.
- A 15 days sub-cycle for mid-latitude mesoscale is desirable for oceanographic purposes and objectives but the lack of such sub-cycle should not be a criterion to reject an orbit.
In addition, the orbit must also be in adequation with two strong mission requirements: northern and southern poles must be covered (+/- 88° at least), along with a yearly cycle. Making the CRISTAL orbit similar to CryoSat-2 one, to ensure the continuity between the two missions.
The technical note written at the and of this task is available here: PMM_Orbit_CCN