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 in 2007, 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 THEMIS probes are able to synergize observations with other Heliophysics System Observatory (HSO) missions such as Van Allen Probes (VAP), Magnetospheric Multiscale (MMS), CLUSTER (CL), Geotail (GT) and Arase (ARA).

Stage 48: Dusk Science Phase, HSO Optimization
08/15/20 - 11/31/20

In the dusk science phase the apogee of P3, P4, and P5 are approximately 13 Re. MMS is in the tail. THM is an MMS-resonant string-of-pearls, studying connections to both magnetopause and inner magnetosphere.

Stage 47: Tail Science Phase, HSO Optimization
04/30/20 - 08/14/20

In the tail science phase the apogee of P3, P4, and P5 are approximately 13 Re. MMS is in the dawn sector. THM-MMS on resonant orbits, to study dayside-nightside reconnection simultaneously. From its kinetic-scale separations THM explores the dissipation of flow and magnetic energy in the tail while MMS captures their effects in the inner magnetosphere. Once every other MMS orbit, MMS is at the reconnection point and THM is at magnetopause to capture day/night connections. The other MMS orbit THM is at in-bound leg (string of pearls) studying link of Rx/injections to inner magnetosphere over a wide range of L-shells.

Stage 46: Dawn Science Phase, HSO Optimization
01/1/20 - 04/29/20

In the dawn science phase the apogee of P3, P4, and P5 are approximately 12-16 Re. MMS is in the dayside sector. THM-MMS on resonant orbits, to study the dominant energy conversion in the tail from kinetic scale separations while MMS studies the link to inner magnetosphere.

Stage 45: Dayside Science Phase, HSO Optimization
10/15/19 - 12/31/19

In the dayside science phase the apogee of P3, P4, and P5 are approximately 12-16 Re. MMS is in the dusk sector on resonant orbits, to study the evolution of reconnection and its relationship to the growth of low-latitude boundary layer instabilities, such as Kelvin-Helmholtz.

Stage 44: Dusk Science Phase, HSO Optimization
07/01/19 - 10/14/19

In the dusk science phase the apogee of P3, P4, and P5 are approximately 12-16 Re. THM-MMS on resonant orbits, to study dayside-nightside reconnection simultaneously.

Stage 43: Tail Science Phase, HSO Optimization
03/31/19 - 06/30/19

In the tail science phase the apogee of P3, P4, and P5 are approximately 12-16 Re. MMS is at opposition in the dawn sector. THM-MMS on resonant orbits, to study energy conversion further out in the magnetotail, as ART+MMS provide the high-fidelity solar wind and its variations due to foreshock interactions. Near perigee, MMS studies effects of injections. Two or three THM-GBO conjunctions (once per 4 or 8 days) also explore the dominant energy conversion in the tail and the drivers of nightside reconnection, while MMS captures the global drivers of these phenomena at the dayside.

Stage 42: Dawn Science Phase, HSO Optimization
11/16/18 - 03/30/19

In the dayside 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 the dayside. THM-MMS on resonant orbits, to study dayside-nightside reconnection simultaneously.

Stage 41: Dayside Science Phase, HSO Optimization
08/29/18 - 01/01/19

In the dayside 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 the tail. THM-MMS on resonant orbits, to study dayside-nightside reconnection simultaneously.

Stage 40: Dusk Science Phase, HSO Optimization
05/20/18 - 8/28/18

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 the dawn sector, and VAP is in the tail sector. THM is on MMS-resonant orbits, exploring asymmetries of reconnection and drivers of magnetopause boundary layer flows.

Stage 39: Tail Science Phase, HSO Optimization
02/13/18 - 5/19/18

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. THM on sidereal period resonances, together with GBOs studies reconnection fronts, injections, links to VAP in the dawn sector; MMS studies drivers at opposition in the dayside.

Stage 38: Dawn Science Phase, HSO Optimization
07/23/17 - 2/12/18

In the dawn 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 the dusk sector, and VAP is in the dayside sector. THM is on MMS-resonant orbits, exploring asymmetries of reconnection and drivers of magnetopause boundary layer flows.

Stage 37: Dayside Science Phase, HSO Optimization
04/20/17 - 7/22/17

In the dayside 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 with MMS at opposition in the tail. THM and MMS study dayside and nightside reconnection simultaneously; VAP determines geoeffectiveness in the dusk sector.

Stage 36: Dusk Science Phase, HSO Optimization
01/13/16 - 4/19/17

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 the dawn sector in ascend phase (1x). L-shell crossings determine particle sources and wave contribution to inner magntosphere particle flux growth/decay. VAP is in the dusk sector.

Stage 35: Tail Science Phase, HSO Optimization
10/28/16 - 1/12/17

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, to detect reconnection fronts, electron injections, and links to VAP waves in the dusk sector. MMS is at opposition in the dayside, and VAP is in the dusk sector.

Stage 34: Dawn Science Phase, HSO Optimization
07/30/16 - 10/27/16

In the dawn 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 the dusk sector, and VAP is in the tail sector. Coordinated L-shell crossings determine particle sources and wave contribution to inner magnetosphere particle flux growth/decay.

Stage 33: Dayside Science Phase, HSO Optimization
04/09/16 - 07/29/16

In the dayside 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 the tail at the plasma sheet boundary studying flux transport, and connects to VAP in the dawn sector.

Stage 32: Dusk Science Phase, HSO Optimization
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
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

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

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

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