4 Final Report - Emits - ESA

4 Final
Report
4.3.3 Instrument design
4.3.3.1 Optical design
The instrument is based on a 1.5 m diameter all-SiC monolithic telescope, i.e. the same size as
Aeolus/ALADIN, formed by M1 & M2 mirrors in Cassegrain configuration. The PAN channel that
requires a long focal length is imaged by a Korsch telescope formed with a third converging mirror
following a flat folding mirror placed out of the M1-M2 axis. The other channels are separately imaged
by the Cassegrain telescope formed by M1 & M2 mirrors (as shown in Figure 4.3-5), or alternately by
the symmetric Korsch configuration. A first dichroïc plate is used to separate the UV-blue & Red-NIR
channels from the IR channels, and within each group a second dichroïc plate provides separation
between the focal planes. Four filter wheels (one for each focal plane) are used to select the narrow
channels in each band. Cold stops are required in front of the IR focal planes which need to controlled
at low temperatures (130 K for MWIR and 50 K for TIR).
M2
Doc. No: GOC-ASG-RP-002 Page 4-33
Issue: 2
Date: 13.05.2009 Astrium GmbH
M1
M3
PAN high resolution
detector
SW/MW IR
detector &
filter wheel
Figure 4.3-5: Multi-spectral imaging telescope optical architecture
Field correction
& focal length
adjustment
TIR detector
& filter wheel
UV-Blue detector
& filter wheel
Red-NIR detector
& filter wheel
The retained optical combination is based on three Korsch combinations with dioptric correctors (PAN,
UV-VNIR, IR) for focal length adjustment & aberration correction in the large FoV. Several folding
mirrors are required to accommodate the five channels in the volume below the M1 mirror.
From M2
TIR
MWIR
PANCHRO
RED-NIR
UV-BLUE
Figure 4.3-6: Optical configuration (after M2)
View from SVM