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

Tables include:

Examples

A move of 0.020 arcseconds takes 0.00000 seconds of slew, and 5 seconds of Guide Star reacquisition time, for a total of 5 seconds. 

A 2.5 arcsecond slew takes 23 seconds of slew time, and 17.5 seconds of reacq time, for a total of 40.5 seconds. 

A slew of 40 arseconds is well within a single visit’s guide stars, and takes 127.5 seconds to slew (interpolating between the 30 and 50 arcsecond entries above) and 97.5 seconds to reacq the guide stars, for a total of 225 seconds. 

A slew of 1 degree, or 3600 arcseconds takes 829.184 seconds of slew and 282 seconds to do a new guide star acquisition, totaling 1111.184 seconds.

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.

Table 1. APT guide star dither overhead

Slew Distance (arcseconds)

Guide Star Reacq Duration (seconds)

0.000000

5.000000

0.060000

17.50000

20.000000

65.00000

Guide star breaking distance

282.00000

Source: PRDOPSSOC-F-009

APT visit slew table

This table applies to all telescope moves modeled by APT, including slews between visits, as well as inside them.  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.

Starting at this distance (slew_distance) in arcsecs, the slew cost is X (slew_duration) in seconds (durations for distances between given values are interpolated):

Table 2. APT visit slew duration

Slew Distance (arcseconds)

Slew Duration (seconds)

0.0000000

0.000

0.0600000

0.000

0.0600001

20.480

15.0000000

20.480

20.0000000

23.296

20.0000001

101.632

30.0000000

116.224

50.0000000

137.728

100.0000000

173.568

150.0000000

198.656

300.0000000

250.112

1000.0000000

373.504

3600.0000000

572.416

4000.0000000

592.896

10000.0000000

804.864

10800.0000000

825.600

10800.0000001

521.216

14400.0000000

578.048

18000.0000000

628.608

21600.0000000

674.560

25200.0000000

716.928

28800.0000000

756.608

32400.0000000

793.856

36000.0000000

829.184

39600.0000000

862.848

43200.0000000

894.976

46800.0000000

925.824

50400.0000000

955.648

54000.0000000

984.320

57600.0000000

1012.224

61200.0000000

1039.104

64800.0000000

1065.344

68400.0000000

1090.816

72000.0000000

1115.648

108000.0000000

1336.448

144000.0000000

1537.408

180000.0000000

1744.000

216000.0000000

1939.328

252000.0000000

2112.192

288000.0000000

2278.272

324000.0000000

2440.320

360000.0000000

2599.936

396000.0000000

2757.632

432000.0000000

2914.240

468000.0000000

3069.888

504000.0000000

3224.832

540000.0000000

3379.328

576000.0000000

3533.376

612000.0000000

3687.104

648000.0000000

3840.512

Source:  PRDOPSSOC-F-009

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

Change log

 Click here to expand...

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.