Before any observations can be uplinked to Herschel they must go through a series of rigorous tests. The HSC is the "meat in the sandwich" between ICC and MOC when carrying out uplink validation. The aim is to ensure that Herschel is protected from receiving any commands that could, potentially, be harmful and that nothing that has not been fully validated gets even as far as MOC, let alone to the spacecraft.
The Instrument Control Centres (ICCs) usually have to prepare their observation requests under great stress and time pressure, so it is essential to ensure that everything that has been delivered is correct and self-consistent and using the latest version of the uplink software, orbit file, etc. Under pressure, it is easy to make a mistake and deliver a wrong file in the middle of dozens of correct ones. Similarly, there is information that a particular ICC does not and cannot know when it is preparing its own observations, especially when a particular day is shared between two or more instruments: how much time is needed to slew from the end position of the first instrument's observations to the start position of the other's? Is the slew pattern acceptable to Flight Dynamics? Do all the observations from the different instruments fit in to the time available when combined?
If an inconsistency is found in validation, it must be understood and, almost invariably, the delivery is rejected and must be re-delivered. Only when the uplink information has been fully validated does it then go to the HSC Mission Planners who put together the final observing schedule and apply the last layer of checks, comparing between the schedule that is expected from the ICC input and the one that is actually obtained when that input is processed at the HSC. If a discrepancy is found, however trivial, it must be queried and if a change has had to be made to the sequence of observations, approval for the change must be sought from the ICC. Only when the "i"s are dotted, the "t"s crossed and everything is shipshape and Bristol fashion will the planning files be passed to the Project Scientist for his approval of the schedule and then on to MOC for transmission to the spacecraft.
The HSC Uplink Validation Team:
Delivery validators - Larry O'Rourke and Mark Kidger
Mission Planning - Charo Lorente and the Mission Planning Gang (Álvaro Llorente, Fernando Rodríguez and Mar Sierra)
[M. Kidger, HSC ESAC posted 6 July 2009]