EXOSAT was the European Space Agency's first three-axis stabilised spacecraft. All three instrument packages were co-aligned, although the individual quadrants of the ME (Medium-energy instrument) could be pointed off-axis to assist in background subtraction.

Together, the three instrument packages gave coverage over a wide energy band pass between 0.05 and 50 keV. The LE (Low-energy imaging telescopes) had the highest sensitivity.

Two LE telescopes (Low-Energy Imaging telescopes)

• double nested Wolter Type 1 grazing-incidence optics
• CMA (Channel-multiplier array) or PSD (position sensitive proportional counter) could be moved into the focus ME

Low-energy imaging telescopes (LE): 0.05-2.0 keV . Laboratory for Space Research (Leiden), Space Research Laboratory (Utrecht), Mullard Space Science Laboratory (UCL, London)

(Medium-Energy instrument)

• four independently-movable quadrants, each equipped with two proportional counters
• typically two quadrants on target, while other two offset to observe adjacent areas of empty sky

Medium-Energy instrument (ME): 1-20/5-50 keV. University of Leicester, Max Planck Institute (Garching), University of Tubingen

GSPC (Gas Scintillation Proportional Counter)

• had better spectral resolution than ME, but smaller effective area

Gas Scintillation Proportional Counter (GSPC): 2-16/2-32 keV. ESA/SSD, MSSL, Universities of Palermo and Milan.

The Low Energy Telescope