Slew Times

JWST's Astronomer’s Proposal Tool (APT) estimates duration for each step in the proposal. This page provides reference tables used in estimation, including slew times, guide star breaking distance, and dither overhead duration

Slew reference tables

   see JWST Slew Times and Overheads

  • Duration of Initial slew is 2100 seconds for each new observation, or first visit of a multiple-visit observation (from PRD spacecraft_parameters).
  • For subsequent slews, overhead is the slew duration based on distance as as shown in Table 2, plus any guide star dither overhead as shown in Table 1

Tables include:

APT guide star dither overhead table

There is an additional overhead for the Guide Star Reacquisition based on the amount of movement in a Slew or SAM, when guiding on FINE, MOVING, or TRACK Modes. Overheads durations are shown in Table 1. 

Table 1.  APT guide star dither overhead

Slew Distance (arcseconds)

dither_overhead from PRD (seconds)

0.000000

5.000000

0.060000

21.00000

25.000000

66.50000

Source: PRDAPTSOC-054, GS_dither_overhead

APT visit slew table

This table applies to all telescope moves modeled by APT, including slews between visits, as well as inside them. Distances between values are interpolated. Note that the distance you can slew within a visit is based on the Galactic latitude of the target, as shown in the Guide Star Breaking Distance table.


Table 2. APT visit slew duration

Distance (arcsecs)

Duration (seconds)

0.00000000.000
0.06000000.000
0.060000120.480
15.000000020.480
20.000000023.296
25.000000026.112
25.0000001157.696
30.0000000167.424
50.0000000198.656
100.0000000250.112
150.0000000286.208
300.0000000360.704
1000.0000000538.880
3600.0000000825.600
4000.0000000855.296
10000.00000001160.704
10800.00000001190.656
10800.0000001541.440
14400.0000000625.152
18000.0000000698.880
21600.0000000765.696
25200.0000000827.136
28800.0000000884.224
32400.0000000937.728
36000.0000000988.416
39600.00000001036.800
43200.00000001082.880
46800.00000001126.912
50400.00000001169.664
54000.00000001210.624
57600.00000001250.304
61200.00000001288.704
64800.00000001326.080
68400.00000001362.432
72000.00000001397.760
108000.00000001622.912
144000.00000001810.816
180000.00000002040.640
216000.00000002249.984
252000.00000002433.280
288000.00000002609.792
324000.00000002782.784
360000.00000002953.728
396000.00000003123.200
432000.00000003291.584
468000.00000003459.456
504000.00000003626.880
540000.00000003793.792
576000.00000003960.640
612000.00000004127.168
648000.00000004293.568

Source: PRDAPTSOC-058-002, visit_slew


Guide star breaking distance table

Table 3. Guide star breaking distance

Galactic Latitude (degrees)

Visit Splitting Distance (arcseconds)

0

80

5

80

10

70

15

65

20

60

25

55

30

55

35

50

40

50

45

45

50

40

55

40

60

30

65

40

70

35

75

35

80

45

85

45

Source: PRDAPTSOC-054, visit_splitting_table

Change log

October 17, 2022

  1. PROPINSTJWST-91557 Updated Table 2 with slew values from PRD. Added link to JDOX article. Removed Examples section as JDOX has better examples.


July 15, 2022

  1. PROPINSTJWST-91530 Updated Table 1 with overheads from PRD. 
  2. PROPINSTJWST-91546 Updated Table 2  with slew values from PRD.


May 24, 2022

  1. PROPINSTJWST-91524 Updated "Table 1. APT guide star dither overhead" with current PRD and -16 second adjustment.


Version 3 (August 24, 2017)

  1. PR 88514 - updated slew duration table and dither overheads table


Version 2 (July 18, 2017)

  1. Editorial change only (modified TOC macro in first paragraph to exclude recursive heading)


Version 1 (June 6, 2017)

  1. Initial version.