ESA has investigated the possibility of merging two of the next scientific missions of its HORIZON 2000 Programme, the fourth cornerstone mission, the Far InfraRed and Sub-millimetre Telescope (FIRST) and the third Medium-sized Mission M3, Planck (formerly Cobras/Sama).
FIRST is a multi-user observatory, which targets the infrared and sub-millimetre part of the electromagnetic spectrum, covering approximately the wavelength range from 80 m to 670 m. The Planck mission is a survey mission dedicated to mapping the temperature anisotropy of the cosmic background radiation.
The merging of the missions was studied in view of the programmatic constraints on both missions, the fact that they use a similar orbit (around the 2nd Lagrangian libration point L 2 ), the partial parallel development of both missions and the potential cost savings. The decision taken during the ESA Science Programme Committee (SPC) meeting held at the end of May 1998 is that the two missions will be implemented in the so-called 'Carrier' solution. Both satellites will be designed and launched together, and then will be separated.
The cryogenic system of FIRST is based on a Superfluid Helium Dewar at 1.65 K (Infrared Space Observatory-ISO technology) with a design lifetime of more than 3 years. The very low temperature (0.3 K), required in the bolometer instrument will be obtained from a dedicated 3 He-sorption cooler. The cryogenic system of Planck uses a sequence of passive radiator (60 K), H 2 Joule-Thomson (JT) Sorption cooler (20 K), JT mechanical cooler (4 K), and dilution refrigerator (0.1 K).