After injection into the transfer trajectory towards the second Lagrangian point (L2) of the Sun-Earth system, Herschel and Plank will separate from the launcher and subsequently operate independently from Lissajous orbits of different amplitude around L2. The transfer to the operational orbit will last approximately 4 months; during this time there will probably be 3 navigational manoeuvres, two close to the launch (L+2 days and L+12 days), and the third close to the injection (10 days before). The LEOP can be considered to last until the first two trajectory corrections have been made. During these initial 2-3 weeks of spacecraft cooldown, the telescope will be heated to prevent from acting as a cold trap. The LEOP operations will be centred around the checkout of the spacecraft sub-systems and the navigation into the correct trajectory. Following the second navigation manoeuvre, the instruments will be switched on to start payload operations.

Once Herschel has been successfully launched and injected into the transfer trajectory towards the operational orbit, the spacecraft and instrument commissioning phase will commence for a nominal period of one month. A significant part of the spacecraft commissioning will already be interleaved with LEOP. Prior to the first trajectory manoeuvre, basic properties of the satellite (centre of mass, moments of inertia) and proper functioning of basic spacecraft sub-systems (RF, thermal control, power sub-system, data handling, attitude and orbit control, thrusters, SSR, etc.) will already have been established, at least to the extent that these sub-systems are required for spacecraft operations.

Spacecraft commissioning will be completed alongside instrument commissioning, which will focus on switch on, functional checkout of the prime instrument sub-systems and their modes, plus observations to confirm the instrument/satellite system characteristics (e.g. instrument aperture pointing) after the cryostat lid is opened, approximately 6-8 weeks into the mission.

At this point, the calibration and performance verification (PV) phase will commence. The PV phase is intended to obtain in-flight characterisation of all instruments e.g. in terms of stability, sensitivity, resolution, timing and other calibration parameters. It includes the validation of the instrument observing modes and the calibration and data processing of the resulting data. To achieve this, a schedule of astronomical observations and internal calibrations, defined and iterated pre-launch covering a nominal period of 2 months will be executed using normal observatory procedures. This schedule will be based upon an agreed in-orbit calibration plan generated jointly by the ICCs and the HSC. The plan contains a description of all planned calibration activities and associated calibration sources (internal and astronomical) required to characterise fully each instrument.

The PV phase will be followed immediately by the "science demonstration phase". Over the course of one month the observing capabilities of Herschel will be pushed to their limits in selected areas of the observation capability phase space, to evaluate and optimise the observation strategies. This will be used to decide how to perform "Key Project" observations in the optimum manner, to demonstrate the capabilities of the Herschel Space Observatory to the astronomical community and also for public relations purposes.

Once the goals of the PV and science demonstration phases have been met, Herschel will go into the routine science operations phase for a minimum of 3 years. Early on, mainly Guaranteed Time and "Key Project" observing programmes will be performed. Key Projects will be performed early in the mission to permit follow-up and to give the Guaranteed Time holders at the HSC to obtain real data to work with, in preparation for supplying community support to the open time observers with the benefit of a thorough knowledge of the entire observing chain from proposal submission to access and reduction of data.

All observers will be able to track the whereabouts of their proposals and will be notified when the resulting data can be accessed.

The Herschel post-operations phase will consist of the rundown monitoring phase (starting at the moment of helium boil-off), mission consolidation phase, active archive phase, and the archive consolidation phase (at which point the transfer to the subsequent historical archive phase takes place), and is the final formal phase of the mission.

The goal of this phase is, within the constraints of time and available resources, to maximise the scientific return from the Herschel mission by facilitating continuing widespread effective and extensive exploitation of the Herschel data. This will continue after the conclusion of this phase (i.e. in the historical archive phase).

The ultimate legacy of Herschel will be the historical archive, plus the sum of all the knowledge, both scientific and technical, derived from implementing and operating Herschel.

The historical archive phase is outside the funded Herschel mission. This phase commences after the end of the post-operations phase.

The historical archive will provide access to all Herschel observations and derived products. The products will all be derived in the archive consolidation phase during the post-operations phase in a consistent manner and to consistent standards using the best knowledge of Herschel instrument calibration and data processing. In addition, the software, documentation - manuals, etc.- and tools will be available from the historical archive.