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MROI instrument Fringe Tracker Slow Switchyard Permutations
Julien Coyne, Chris Haniff, John Young Revision 0.3, Septemb er 18th, 2006

Cavendish Lab oratory Madingley Road Cambridge CB3 0HE UK
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Contents
1 10 Telescop es 1.1 Geometry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.2 Telescop e failure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.3 Delay line failure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 6 Telescop es 2.1 Geometry . . . . 2.2 Always . . . . . . 2.3 Telescop e failure 2.4 Delay line failure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 6 6 8 9 9 9 10 11

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List of Figures
1.1 1.2 1.3 2.1 2.2 2.3 The array - 10 telescop es. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The pads (on each arm) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Slow switchyard : inputs and outputs. . . . . . . . . . . . . . . . . . . . . . . . . The array - 6 telescop es. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The pads (on each arm) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Slow switchyard : inputs and outputs. . . . . . . . . . . . . . . . . . . . . . . . . 6 7 8 9 10 11

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Preface
The goal of this do cument is to identify the b eam p ermutations that the slow switchyard feeding the fringe tracker must allow.

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Chapter 1

10 Telescopes
1.1 Geometry

The full array is comp osed of 10 telescop es top ologically distributed as presented on Fig. 1.1.

Figure 1.1: The array - 10 telescop es. Three relay pip es on each arm connect the telescop es to the delay lines (see Fig. 1.2). The slow switchyard re-organises the b eams coming from the delay lines and feeds them to the fringe tracker (see Fig. 1.3).

1.2

Telescop e failure

The required p ermutations in case of a telescop e failure are presented b elow. Each delay line DL xx is represented by 'dxx', and each fringe tracker p ort yy is represented by 'pyy'. The asso ciation of a delay line to a fringe tracker p ort is noted := · No, So, Wo : Nothing to do · Nm, Sm, Wm : top ologically, the outer telescop e b ecomes the middle telescop e. Therefore the b eam coming from the outer telescop e should b e fed in the fringe tracker p ort corres6


Figure 1.2: The pads (on each arm)

p onding to the (non working) middle telescop e to allow fringe tracking on the available baselines on the arm. d3 := p2 d'3 := p'2 d"3 := p"2 · Ni, Si, Wi : top ologically the middle and outer telescop es b ecome the inner and middle telescop e on the arm. Therefore the switchyard should re-route the b eams from those two telescop es to the fringe tracker p ort corresp onding to the inner and middle telescop e. (d2, d3) := (p1,p2), (d'2, d'3) := (p'1,p'2) (d"2, d"3) := (p"1,p"2) · C : The strategy is to use an inner telescop e as the acting centre telescop e. The two other telescop es on the arm b ecome the acting inner and middle telescop es. The switchyard must re-organise the b eams accordingly. (d1, d2, d3) := (p c, p1, p2) (d'1, d'2, d'3) := (p c, p'1, p'2) (d"1, d"2, d"3) := (p c, p"1, p"2)

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Figure 1.3: Slow switchyard : inputs and outputs.

1.3

Delay line failure

When a delay line fails, one option is to re-route the b eam from the telescop e to another delay line (through the canisters on the pads). Since there are as many delay lines as telescop es, only 9 telescop es can b e used. The telescop e normally assigned to the hijacked delay line is not used. · DL 3, DL 3', DL 3" : Nothing to do · DL 2, DL 2', DL 2" : d3 := p2 d'3 := p'2 d"3 := p"2 · DL 1, DL 1', DL 1" : (d2, d3) := (p1,p2) (d'2, d'3) := (p'1,p'2) (d"2, d"3) := (p"1,p"2) · DL C : (d1, d2, d3) := (p c, p1, p2) (d'1, d'2, d'3) := (p c, p'1, p'2) (d"1, d"2, d"3) := (p c, p"1, p"2)

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Chapter 2

6 Telescopes
2.1 Geometry

The 6 telescop es array is presented on Fig. 2.3 : a centre telescop e, two telescop es on two arms and a single telescop e on the third arm. Without lossing in generality, the single telescop e is assumed to b e on the South arm.

Figure 2.1: The array - 6 telescop es.

A maximum of three relay pip es on each arm connect the telescop es to the delay lines (see Fig. 2.2). With 6 telescop es, only the longest relay pip es are used (and the asso ciated delay lines). The slow switchyard re-organises the b eams coming from the delay lines and feed them to the fringe tracker (see Fig. 2.3). Only 6 delay lines and 6 fringe tracker p orts are used.

2.2

Always

The delay lines assigned to the outer telescop es on the 10 b eams layout are p opulated first, then the delay lines for the middle telescop es (this allows access to pad 9 on each arm). Therefore the switchyard must re-route the b eams from those delay lines to the correct fringe tracker p orts. As b efore, each delay line DL xx is represented by 'dxx', and each fringe tracker p ort yy is represented by 'pyy'. The asso ciation of a delay line to a fringe tracker p ort is noted := · S: 9


Figure 2.2: The pads (on each arm)

d3 := p1 · N, W : (d'2,d'3) := (p'1,p'2) (d"2, d"3) := (p"1, p"2)

2.3

Telescop e failure

The strategy is basically the same as for 10 b eams. The only subtlety is that the p ermutations outlined in the previous section should also b e taken into account : · Si : Nothing to do · Nm, Wm : Nothing to do · Ni, Wi : d'3 := p'1 d"3 := p"1 · C: d3 := pC (d'2,d'3) := (pC,p'1) (d"2,d"3) := (pC,p"1) 10


Figure 2.3: Slow switchyard : inputs and outputs.

2.4

Delay line failure

As for the telescop e failures, the strategy mimics what has b een presented for 10 b eams while feeding the correct fringe tracker p ort (as presented in the b efore previous section) : · DL 3 : Nothing to do · DL 3', DL 3" : d'2 := p'1 d"2 := p"1 · DL 2', DL 2" : d'3 := p'1 d"3 := p"1 · DL C : d3 := pC (d'2,d'3) := (pC,p'1) (d"2,d"3) := (pC,p"1)

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