Spitzer Documentation & Tools
Spitzer Telescope Handbook
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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.)

focalplane1

 

 

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

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