Spitzer Documentation & Tools
Spitzer Telescope Handbook

 

3.10       Focal Plane Layout

Figure 3.15 shows the actual location of the pick-off mirrors that feed the science instruments as viewed from above (looking down the boresight). The Y- and Z-axis directions are the same as the telescope coordinate systemshown in Figure 3.4; the +X direction comes out of the page. Figure 3.15 shows the Spitzer entrance aperturesas projected onto the sky and appears inverted compared to Figure 3.1, due to the combined effects of looking out from behind the focal plane and the projection of the sky onto the focal plane through the telescope optics. (To understand this inversion, recall the 3-D geometry and the fact that a Cassegrain telescope inverts its image.)

 

 

Figure 3.15: Schematic view of Spitzer focal planefrom above, looking down the boresight. The solar panel is on the IRS side of the spacecraft. This figure shows the region of the focal surface where the pick-off mirrors for each instrument are located. This is in contrast to where the apertures project onto the sky. See Figure 3.1 for comparison.

 

Table 3.5. Spitzer focal plane layout: approximate offsets from boresight to aperture centers.

Aperture Z (') Y (')
IRAC 3.6 m 2.86 3.67
IRAC 3.6 m subarray 4.97 5.88
IRAC 5.8 m 2.86 3.61
IRAC 5.8 m subarray 0.72 5.71
IRAC 4.5 m 2.72 -3.05
IRAC 4.5 m subarray 4.80 -0.92
IRAC 8.0 m 2.75 -3.07
IRAC 8.0 m subarray 0.65 -0.97
IRS SL 1st order 12.03 -2.79
IRS SL 2nd order 11.91 -4.09
IRS LL 1st order 4.41 -14.00
IRS LL 2nd order 1.21 -14.07
IRS SH 10.56 10.01
IRS LH 10.42 -10.23
IRS Red Peak-Up 11.63 2.00
IRS Blue Peak-Up 13.52 1.91
MIPS 24 m -6.72 4.25
MIPS 70 m default -6.53 -8.06
MIPS 70 m fine -7.10 -6.81
MIPS 70 m default side A -7.95 -8.11
MIPS 70 m fine side A -6.39 -6.71
MIPS 160 m -7.35 12.11
MIPS SED -6.06 -9.44

 

Table 3.5 gives the measured offsets from the center of the field of view to the centers of the main science apertures. The values were determined post-launch based on the results from the focal plane mapping survey during IOC+SV.

 

Each of the fields of view that are used has a code that specifies the position in the focal plane. The uplink software uses the field-of-view index for commanding the target position, and the pipelines similarly use it to reconstruct where the telescope was pointing. These indices and field-of-view names appear in the headers of Spitzer data, and are listed in Table 3.6.

Table 3.6 Field-of-View Indices.

FOV name FOV index
Telescope Boresight 1
PCRS 1A 4
PCRS 1B 5
PCRS 2A 8
PCRS 2B 9
IRS red peak-up FOV center 18
IRS red peak-up FOV sweet spot 19
IRS blue peak-up FOV center 22
IRS blue peak-up FOV sweet spot 23
IRS SL 1st order 1st position 26
IRS SL 1st order 2nd position 27
IRS SL 1sr order center position 28
IRS SL module center 29
IRS SL 2nd order 1st position 32
IRS SL 2nd order 2nd position 33
IRS SL 2nd order center position 34
IRS LL 1st order 1st position 38
IRS LL 1st order 2nd position 39
IRS LL 1st order center position 40
IRS LL module center 41
IRS LL 2nd order 1st position 44
IRS LL 2nd order 2nd position 45
IRS LL 2nd order center position 46
IRS SH 1st position 50
IRS SH 2nd position 51
IRS SH center position 52
IRS LH 1st position 56
IRS LH 2nd position 57
IRS LH center position 58
IRAC center of 3.6 and 5.8 arrays 67
IRAC center of 3.6 array 68
IRAC center of 5.8 array 69
IRAC center of 3.6 subarray 70
IRAC center of 5.8 subarray 72
IRAC center of 4.5 and 8.0 arrays 74
IRAC center of 4.5 array 75
IRAC center of 8.0 array 76
IRAC center of 4.5 subarray 77
IRAC center of 8.0 subarray 79
IRAC between arrays 81
MIPS 160 center 87
MIPS 160 large only 89
MIPS 160 small 91, 92
MIPS 24 center 95
MIPS 24 small 99, 100
MIPS 24 large 103, 104
MIPS SED 105, 106, 121, 122, 123, 125, 126
MIPS 70 center 107
MIPS 70 TP 109
MIPS 70 default small 111, 112
MIPS 70 scan 113
MIPS 160 scan 114
MIPS 70 default large 115, 116
MIPS 70 fine 117, 118, 119, 120, 124, 127

IPAC Caltech
Jet Propulsion Lab NASA