Orbit

THOR orbit
The orbital strategy of THOR has been chosen to maximize the time spent in scientifically interesting regions of pristine solar wind, foreshock, bow shock and magnetosheath. The orbital plane is close to the ecliptic plane. The exact inclination depends on the time of the year of the launch, maximising the time spent in the magnetotail current sheet and optimising the length of eclipses. The mission has 3 phases with each phase having a different orbit and corresponding to roughly one year. After the nominal mission, there are multiple possibilities for the extension phase, most of which would require lunar flybys for the orbital manoeuvres. One important alternative would be going to L1. However, there are also alternatives to go to the distant tail, Moon or flyby of some heliospheric target.

 Phase and primary target  Orbit  Comments
 Year 1
Bow shock & magnetosheath
 6 x 15 Re
Apogee at the dayside is around the 25% percentile position of the bow shock (25% of the time, the bow shock nose is at distances larger than ~15RE and 75% of the time at smaller distances). Such an orbit is ideal to obtain a long time series of regions around bow shock and in the magnetosheath. At the same time data from the solar wind would also be available.
 Year 2 
Pristine solar wind & foreshock
 6 x 26 Re
The rise of apogee gives long time series of the solar wind and foreshock regions. The bow shock and magnetosheath are traversed fast at the nose of the magnetosphere but there would be longer encounters of bow shock and magnetosheath on the flanks.
Year 3
Pristine solar wind & interplanetary shocks
6 x 45 Re The additional rise of the apogee makes THOR spend most of the time in the solar wind far from Earth. The possibility of lunar flybys should make it possible to keep the THOR orbit on the dayside for most of the year. This orbit is also well suited for the extended mission of THOR.

Expected bow shock and magnetopause location

The nominal location of bow shock and magnetopause for expected solar wind conditions 2025/26. The top panel shows the expected position of the bow shock (blue) and magnetopause (red) based on the daily averaged OMNI data and common models. The solid lines in the bottom panel show the mean position of bow shock and magnetopause, while the dashed lines show minimum, 25% percentile, 75% percentile and maximum position locations.