Nesting of Mirror Shells

For small slope angles a (see above) the geometrical collecting area of a mirror shell is a thin circle with an projected area a of a « 2nr x l sin a where r is the mirror radius and l the length of a mirror element. For small angles a it can also be expressed with the focal length f:

Table 6.1 Satellite missions with Wolter telescopes

Mission

Year

Upper

Focal

Mirror

Degree

Effective

On-axis

of

energy

length (m) modules

of

area

resolution

launch

limit (keV)

nesting @ 1 keV (cm2)

(HPD)

S-054/Skylab

1973

4

2.13

1

2

15

48"

S-056/Skylab

1973

1.3

1.90

1

1

9

3"

Einstein (HEAO-2)

1978

4

3.44

1

4

100

4"

EXOSAT

1983

2.5

1.09

2

2

70

24"

ROSAT

1990

2.5

2.40

1

4

420

3"

BBXRT

1990

12

3.77

2

118

450

5"

Yohkoh SXT

1991

4.0

1.54

1

1

23

<5"

ASCA (Astro-D)

1993

10

3.50

4

120

1 200

180"

Soho CDS

1995

0.5

2.58

1

1

23

<5"

BeppoSAX

1996

10

1.85

4

30

344

60"

ABRIXAS

1999

10

1.60

7

27

560

25"

Chandra (AXAF)

1999

10

10.00

1

4

780

<1"

XMM-Newton

1999

15

7.50

3

58

4260

16"

Swift

2004

10

3.50

1

12

130

18"

Suzaku (Astro-E2)

2005

XRT-I

12

4.75

4

175

2250

120"

XRT-S

12

4.50

1

168

2250

120"

This is much less than the polished mirror surface. Nesting several mirror shells with the same focal length and the same optical axis into each other is an appropriate solution for an enlarged effective collecting area while keeping the telescope as compact as possible (Fig. 6.7). Nesting was first practiced for the solar X-ray telescope S-054 mounted on the Apollo platform on Skylab in 1973. It consisted of two small Wolter-1 mirror shells. The nesting of many thin-walled mirror shells allows good filling factors for a given area. Examples for such highly nested optics are ASCA, XMM-Newton, and Suzaku.

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