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The Mission

Orbits

The five THEMIS spacecraft (probes) were placed in highly elliptical orbits where the spacecraft line up at apogee every four days. The apogee rotates slowly around the Earth to cover the dayside, dawnside, nightside, and duskside of the magnetosphere. Initially, right after launch, the 5 THEMIS spacecraft were lined up in the same orbit. Since 2011, P1 and P2 have become ARTEMIS and orbit the moon, while the 3 remaining Earth-orbiting probes are able to synergize observations with other heliophysics missions such as Van Allen Probes (VAP) and Magnetospheric Multiscale (MMS).


Stage 32:  Dusk Science Phase, HSO Optimization with MMS and VAP
12/20/15 - 04/08/16

In the dusk science phase the apogee of P3, P4, and P5 are approximately 12 Re. The probes are separated by 1000 km to a few Earth radii at apogee. MMS is at opposition in dawn, and VAP is in the dayside sector.

Stage 31:  Tail Science Phase, Heliophysics System Observatory (HSO) Optimization with MMS and VAP
08/31/15 - 12/19/15

In the tail science phase the apogee of P3, P4, and P5 are approximately 12 Re. The probes are separated by 1000 km to a few Earth radii at apogee. MMS is at opposition in dayside, and VAP is in the dusk sector.

Stage 30:  Dawn Phase, VAP Conjunctions
05/13/15 - 08/30/15

In the dawn science phase the apogee of the P3, P4, and P5 orbits are on the dawnside of the magnetosphere. Probes 3 and 4 have apogees at 12 Re, and Probe 5 has an apogee at 13 Re. MMS preliminary orbital maneuvers to coordinate with THEMIS observations.

Stage 29:  Dayside Science Phase, VAP Conjunctions
01/22/15 - 05/12/15

In the dayside science phase the apogees of the P3, P4, and P5 orbits are approximately 12 Re. The probes are separated by approximately 500 km to 3000 km. Projected MMS launch and preliminary orbital maneuvers, systems checkout.

Stage 28:  Dusk Phase, Radiation Belt Science, VAP Conjunctions
10/17/14 - 01/21/15

In the dusk science phase the apogees of the P3, P4, and P5 orbits are approximately 12 Re and point towards the duskside sector.

Stage 27:  Tail Science Phase, VAP Conjunctions
06/29/14 - 10/16/14

In the tail science phase the apogee of P3, P4, and P5 are approximately 12 Re. The probes are separated by approximately 500 km to 3000 km.

Stage 26:  Dawn Phase, VAP Conjunctions
03/11/14 - 06/28/14

In the dawn science phase the apogee of the P3, P4, and P5 orbits are on the dawnside of the magnetosphere. Probes 3 and 4 have apogees at 12 Re, and Probe 5 has an apogee at 13 Re.

Stage 25:  Dayside Science Phase, VAP Conjunctions
12/25/13 - 03/10/14

In the dayside science phase the apogees of the P3, P4, and P5 orbits are approximately 12 Re. The probes are separated by approximately 500 km to 3000 km.

Stage 24:  Dusk Phase, Radiation Belt Science, VAP Conjunctions
09/18/13 - 12/24/13

In the dusk science phase the apogees of the P3, P4, and P5 orbits are approximately 12 Re and point towards the duskside sector.

Stage 23:  Tail Science Phase, VAP Conjunctions
06/11/13 - 09/17/13

In the tail science phase the apogee of P3, P4, and P5 are approximately 12 Re. The probes are separated by approximately 500 km to 3000 km.

Stage 22:  Dawn Phase, VAP Conjunctions
3/04/13 - 06/10/13

In the dawn science phase the apogee of the P3, P4, and P5 orbits are on the dawnside of the magnetosphere. Probes 3 and 4 have apogees at 12 Re, and Probe 5 has an apogee at 13 Re.

Stage 21:  Dayside Science Phase, Van Allen Probes (VAP) Conjunctions
11/27/12 - 03/03/13

In the dayside science phase the apogees of the P3, P4, and P5 orbits are approximately 12 Re. The probes are separated by approximately 500 km to 3000 km.

Stage 20:  Dusk Phase, Radiation Belt Science
10/15/12 - 11/26/12

In the dusk science phase the apogees of the P3, P4, and P5 orbits are approximately 12 Re and point towards the duskside sector.

Stage 19:  Tail Science Phase
04/13/12 - 10/14/12

In the tail science phase the apogee of P3, P4, and P5 are approximately 12 Re. The probes are separated by approximately 500 km to 3000 km.

Stage 18:  Dawn Phase
1/06/12 - 04/12/12

In the dawn science phase the apogee of the P3, P4, and P5 orbits are on the dawnside of the magnetosphere. Probes 3 and 4 have apogees at 12 Re, and Probe 5 has an apogee at 13 Re. P1 and P2 have now become ARTEMIS.

Stage 17:  Dayside Science Phase
09/30/11 - 01/05/12

In the dayside science phase the apogees of the P3, P4, and P5 orbits are approximately 12 Re. The probes are separated by approximately 500 km to 3000 km.

Stage 16:  Dusk Phase
06/23/11 - 09/29/11

In the dusk science phase the apogees of the P3, P4, and P5 orbits are approximately 12 Re and point towards the duskside sector.

Stage 15:  Tail Science Phase
03/16/11 - 06/22/11

In the tail science phase the apogee of P3, P4, and P5 are approximately 12 Re. The probes are separated by approximately 500 km to 3000 km.

Stage 14:  Dawn Phase, ARTEMIS Mission begins
12/09/10 - 03/15/11

In the dawn science phase the apogee of the P3, P4, and P5 orbits are on the dawnside of the magnetosphere. Probes 3 and 4 have apogees at 12 Re, and Probe 5 has an apogee at 13 Re. P1 and P2 have now become ARTEMIS.

Stage 13:  Dayside Science Phase
09/02/10 - 11/30/10

In the dayside science phase the apogees of the P3, P4, and P5 orbits are approximately 12 Re. The probes are separated by approximately 500 km to 3000 km.

Stage 12:  Dusk Phase
06/01/10 - 09/01/10

In the dusk science phase the apogees of the P3, P4, and P5 orbits are approximately 12 Re and point towards the duskside sector.

Stage 11:  Tail Science Phase
03/02/10 - 05/31/10

In the tail science phase the apogee of P3, P4, and P5 are approximately 12 Re. The probes are separated by approximately 500 km to 3000 km.

Stage 10:  Dawn Phase
12/29/09 - 03/01/10

In the dawn science phase the apogee of the P3, P4, and P5 orbits are on the dawnside of the magnetosphere. Probes 3 and 4 have apogees at 12 Re, and Probe 5 has an apogee at 13 Re. P1 and P2 have now become ARTEMIS.

Stage 9:  Dayside Science Phase
06/15/09 - 09/30/09

In the dayside science phase the apogee of the orbits are on the dayside of the magnetosphere. Probe 1 apogee is at 30 Re, Probe 2 at 20 Re, Probes 3 and 4 at 12 Re, and Probe 5 at 13 Re.

Stage 8:  Radiation Belt Science Phase
04/15/09 - 06/15/09

The radiation belt science phase is also called the “Dusk phase” because the apogee of the orbits are on the dusk side of the magnetosphere. Probe 1 apogee is at 30 Re, Probe 2 at 20 Re, Probes 3, 4, and 5 at 12 Re.

Stage 7:  Tail Science Phase
12/15/08 – 04/15/09

In the tail science phase the apogee of the orbits are in the magnetotail. Probe 1 apogee is at 30 Re, Probe 2 at 20 Re, Probes 3, 4, and 5 at 12 Re.

Stage 6:  Dawn Phase
10/15/08 - 12/15/08

The apogee of the orbits is on the dawn side of the magnetosphere. Probe 1 apogee is at 30 Re, Probe 2 at 20 Re, Probes 3, 4, and 5 at 12 Re.






Initial Mission Phase THEMIS orbit parameters:

  • Injection: 1.07 x 15.4 Re (all probes in the same orbit)
  • Probe 1: 1.3 x 30 Re
  • Probe 2: 1.2 x 20 Re
  • Probes 3 and 4: 1.5 x 12 Re
  • Probe 5: 1.5 x 10 Re

The different orbit configurations define the five stages of the mission:

Stage 1:  Injection or “Coast” Phase
02/15/07 - 09/15/07

Right after launch all spacecraft are lined up in the same orbit with a 15.4 Re apogee.

Stage 2:  Orbit Placement Phase
09/15/07 - 12/15/07

The orbit placement phase is also called “Dawn phase” because the apogee of the orbits are on the dawn side of the magnetosphere. Probe 1 apogee is at 30 Re, Probe 2 at 20 Re, Probes 3 and 4 at 12 Re, and Probe 5 at 10 Re.

Stage 3:  Tail Science Phase
12/15/07 – 04/15/08

In the tail science phase the apogee of the orbits are in the magnetotail. Probe 1 apogee is at 30 Re, Probe 2 at 20 Re, Probes 3 and 4 at 12 Re, and Probe 5 at 10 Re.

Major (4 day, P1, P2 and inner probe) Conjunctions
Minor (2 day, P2 and inner probe) Conjunctions
Daily (inner probes with GBOs) Conjunctions ->00:30-12:30UT

Stage 4:  Radiation Belt Science Phase
04/15/08 - 06/15/08

The radiation belt science phase is also called the “Dusk phase” because the apogee of the orbits are on the dusk side of the magnetosphere. Probe 1 apogee is at 30 Re, Probe 2 at 20 Re, Probes 3 and 4 at 12 Re, and Probe 5 at 10 Re.

Stage 5:  Dayside Science Phase
06/15/08 - 10/15/08

In the dayside science phase the apogee of the orbits are on the dayside of the magnetosphere. Probe 1 apogee is at 30 Re, Probe 2 at 20 Re, Probes 3 and 4 at 12 Re, and Probe 5 at 10 Re.

Major (8 day, 5 probe) Conjunctions
Major (4 day, P1, P2 and inner probe) Conjunctions
Minor (2 day, P2 and inner probe) Conjunctions
Daily (inner probes with GBOs) Conjunctions