EXIST Mission Design Summary
The High Energy Telescope (HET) is the primary detector system, and is complemented by the Low Energy Telescope (LET), which has better spatial resolution. HET uses CsI anti-coincidence shielding to reduce the particle-induced background. This active shielding can also be used to detect photons up to roughly 20 MeV, with spatial resolution roughly equal to the collimation of each HET sub-telescope.
| Parameter | HET | LET |
|---|---|---|
| Energy range | 10-300 keV (10-600 keV goal) | 4-30 keV |
| Energy res. (FWHM) | 1-2 keV (10-100 keV) 2-6 keV (100-600 keV) |
0.5 keV |
| Sensitivity (5σ in 1yr) | 0.05 mCrab* (10-100 keV) 0.5 mCrab* (200-600 keV) |
0.05 mCrab* |
| Sens. (5σ each orbit) | 2 mCrab* (10-200 keV) 20 mCrab* (200-600 keV) |
2 mCrab* |
| Field of View (FoV) | 154° x 64°=2.5 sr (fully coded) ~3.6 sr (partially coded) |
160° x 65°=2.5 sr (fully coded) ~3.1 sr (partially coded) |
| Survey coverage | Full sky each orbit (95 minutes) | Full sky each orbit (95 minutes) |
| Pointing accuracy | 0.5° stability, 5" aspect | 0.5° stability, 5" aspect |
| Angular resolution | 6.1' | 1.0' |
| Source localization (5σ) | 74" | 12" |
| Temporal resolution | 10 µs | 10 µs |
| Telescopes | 19 coded-aperture sub-telescopes Each has 21° x 21° FoV |
32 coded-aperture sub-telescopes Each has 16° x 16° FoV |
| Masks | Uniformly Redundant Arrays 5mm thick tungsten 2.5mm square mask pixels |
Uniformly Redundant Arrays 0.5mm thick tungsten 0.2mm square mask pixels |
| Detectors | 5.96 m2 CZT 20mm square crystals, 4mm thick 16x16 1.25mm pixels per crystal |
1.28 m2 Si strip 20mm square crystals 100x100 0.20mm pixels per crystal |
| Collimators/Side Shielding |
20% active (CsI) 80% passive (graded-Z) |
100% passive (graded-Z) |
| Rear shielding | 1.3cm thick CsI | graded-Z |
* 1 mCrab = 10-11 erg/cm2/s in band ΔE=E-0.5E
Spacecraft Schematic