In order to determine precisely the oscillation frequencies we require long (> 1 month), uninterrupted observations of a given field. Interruptions in the data time series pushes power from the main spectral peaks into sidelobes. If we are to reconstruct the stellar oscillation spectrum faithfully we require an observing duty cycle of at least 95%.
The observing strategy it therefore very simple. The instruments are pointed at the chosen target field, and will then stay pointed at that field for at least a month. The next field will then be acquired, and the cycle repeated. In some cases it might be desirable to observe a given field for more than a month, and to observe certain fields more than once during the mission lifetime.
The choice of orbit has both scientific and technical impacts. In the case of the scientific return we require a free choice of targets in the sky, with the possibility to observe them for extended periods without interruptions due to Earth occultations or extended eclipse periods. Technically it is imperative that the orbit be above the radiation belts, as the sensitive CCD and MCP detectors carried by STARS are susceptible both to increased noise, and in the worst case radiation damage on passage through the radiation belts. From these arguments we conclude that a high Earth or L1 orbit would be highly desirable.
Of course the payload must be supported, and the usual spacecraft subsystems such as propulsion, communications etc. provided. For STARS a three axis stabilized bus is required as we need to image target fields for long periods. The PRISMA study has shown that a short term pointing precision of 3 and long term stability of 30 did not unduly compromise the photometric precision. Procurement of a third XMM bus, if possible, might be a cost effective alternative.
A mission lifetime of 3 years would allow more than 25 target fields to be observed with the possibility of extended or repeated observation of some fields. We would also suggest that consumable should be sized for an extended mission of up to 5 - 10 years, as this would allow an extensive study of activity cycles on some stars.