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Orbit

Swot orbit will be a non sun-synchronous 21-days orbit, at 890.6 km with an inclination of 77.6°. The wide-swath will able a more complete ground coverage than with previous nadir-altimeters.

Orbit requirements

Swot orbit (left the full 21 days, right in 3 days)
  •  Global coverage and more frequent sampling dictates a compromise in orbit repeat period of 21 days with 10-day subcycle.
  •  Inclination of 77 degrees to achieve non sun-synchronous orbit to minimize tidal aliasing and to ensure coverage of major water bodies on land.
  •  1 day repeat period during the initial cal/val phase for fast sampling to achieve the cal/val objectives and study rapidly changing phenomena.

Orbit Characteristics

Fast-sampling orbit Science orbit
Repeat orbit parameters (N+P/Q) 14+0/1 13+19/21
Mean semi-major axis (m) 7235379.8 7268718.9
Altitude (km)(mean sma minus equ. radius) 857.244 890.582
Inclination (deg) 77.6 77.6
Mean Eccentricity 0.00105 0.00105
Number of orbits per cycle 14 292
Nodal period (sec) 6131.25 6173.62
Exact repeat cycle duration (days) 0.99349 20.86455
Longitude gap between 2 consecutive ground tracks (deg) 25.714 25.890
Longitude gap between 2 adjacent ground tracks (deg) 25.714 1.233
Drift of RAAN local time(minutes/day) -9.44 -9.35
Duration for 24h RAAN local time change (days) 152.6 154.0

*RAAN = Right Ascension of Ascending Node

Reference orbit files

Fast-sampling orbit (Calibration/validation Orbit)

Please find below the reference orbit files for the fast-sampling orbit.

Please note that the longitude of the reference ground track descending node is : -118.96 deg (shift to meet SWOT Calval group recommendations after New-York meeting (April 2015) : at 42.5deg N, longitude between 78.2deg E and 78.3deg E)

Ephemeris files (.txt)

Ephemeris in terrestrial frame.

Ephemeris length = one day (86400 sec), time-step = 30sec

Cross-overs times & passes

For each latitude (North as well as South), the number of passes and the time difference between the ascending and the descending passes at the crossovers are computed.

Calval orbit

See the kml file for an overview of those crossovers.

Latitude (degrees N or S)minimum Difference in passesminimum time (s)minimum timesupplement in passes to the cyclesupplement in time (s) to the cyclesupplement in time to the cycle

35.7

13

38606

10h43min26s

15

47231

17h07min11s

61.6

11

31537

08h45min37s

17

54300

15h05min00s

70.2

9

25058

06h57min38s

19

60779

16h52min59s

74.2

7

18733

05h12min13s

21

67104

18h38min24s

76.3

5

12467

03h27min47s

23

73370

20h22min50s

77.3

3

6229

01h43min49s

25

79608

22h06min48s

 

Science orbit

 See the kmz file for an overview of those crossovers, and the xls file for a complete list (only 8 of them listed below)

Latitude (degrees N or S)minimum Difference in passesminimum time (s)minimum time (days)minimum time (hh:mm:ss)supplement in passes to the cyclesupplement in time (s) to the cyclesupplement in time to the cycle (days)supplement in time to the cycle (hh:mm:ss)

77.3185

3

6273

0

01:44:33

581

1796424

20

19:00:24

76.2644

5

12556

0

03:29:16

579

1790141

20

17:15:41

74.1378

7

18867

0

05:14:27

577

1783830

20

15:30:30

70.0412

9

25239

0

07:00:39

575

1777458

20

13:44:18

61.1151

11

31774

0

08:49:34

573

1770923

20

11:55:23

33.4475

13

38959

0

10:49:19

571

1763738

20

09:55:38

38.1448

15

47639

0

13:13:59

569

1755058

20

07:30:58

62.3626

17

54703

0

15:11:43

567

1747994

20

05:33:14

...........................

 

 

Ground track and Swath files (.kml)

 

Example of the SWOT fast-sampling orbit ground track

Science orbit

Please find below the reference orbit files for the science orbit.

Please note that the longitude of the reference ground track descending node is : -144.67 deg (shift to meet SWOT Science Definition Team recommendations after Toulouse meeting (July 2015) : one science pass is aligned with CalVal pass n°3). 

Ephemeris files (.txt)

Ephemeris in terrestrial frame.

Ephemeris length = 21 days (1814400 sec ), time-step = 30sec

Ground track and Swath files (.kml)

 

Example of the SWOT science ground track
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