SPICA is part of the JAXA future science programme and is planned for launch in 2018/2019. The mission follows on both scientifically and technically from the highly successful AKARI mission. High sensitivity observations in the MIR/FIR are made possible thanks to the large 3.2-metre telescope, which is actively cooled to below 6 K to effectively eliminate the non-astronomical photon noise. High spatial resolution will be achieved thanks to the large aperture, monolithic primary mirror and the appropriate fabrication tolerances on the mirror surfaces and telescope structure, thereby achieving diffraction-limited performance at 5 µm.
The layout of the SPICA spacecraft is schematically illustrated in Figure 1. The main elements of the spacecraft include the Telescope Assembly (including instrument suite), sunshield/stray-light baffles, solar array and the spacecraft bus.
The Telescope Assembly and instrument suite are cooled to < 5 K with a system of mechanical cryocoolers and passive radiative cooling. This obviates the need for a heavy cryostat and a store of consumable liquid cryogens to provide cooling capacity and means that the total mass of the spacecraft is kept to 2600 kg including 180 kg of propellant. This approach also has the benefit of a warm launch for the payload which makes environmental vibration qualification simpler and opens up the possibility of employing engineering solutions for thermally and mechanically efficient cryogenic structures.