1 H. Laakso, SERENA - HEWG meeting, Mykonos, Greece, 8-11 June Coordinated MMO and MPO observations Harri Laakso ESA/ESTEC, Code SRE-OS, Noordwijk, The Netherlands H. Laakso, SERENA - HEWG meeting, Mykonos, Greece, 8-11 June 2009

2 1:4 Synchronization of the MPO-MMO orbits  There is no fuel for orbit maintenance  The orbits will evolve under the gravity field, causing a continuous phase shift between the two orbits  Currently the MMO and MPO orbital periods are 1:4 synchronized  This is not favorable to magnetospheric science because there will be close conjunctions only a few times for one short period of time (1-2 weeks) once a year A few close encounters ! The two spacecraft are never close to each other

3 H. Laakso, SERENA - HEWG meeting, Mykonos, Greece, 8-11 June 2009 Conjunctions During Synchronization  1:4 synchronization means that whenever MPO is at perigee (red square), MMO can be at four points (blue squares) that changes slowly due to orbital phase shift  When MMO moves to the perigee region, MPO has moved over the polar region  The orbital phase shift provides close encounters at the perigee only a few times within about 2 weeks

4 H. Laakso, SERENA - HEWG meeting, Mykonos, Greece, 8-11 June 2009 Benefits of Non-Synchronized orbits  It is highly desirable to have regularly repeated close encounters  Science objectives: many magnetospheric objectives will have benefits from having a large variety of different types of conjunctions, e.g.,  when MMO is at perigee, MPO should be located at various positions, e.g., over the poles or in the opposite side of Mercury  both satellites should regularly approach the perigee at the same time  Question: how often certain conjunctions should be repeated?  Instrument cross-calibrations: MPO and MMO carry similar in-situ instruments whose calibrations are challenging (aging, spacecraft effects etc):  The close encounters of <100 km will help the calibration activities  Question: how often close (<100 km, TBC) conjunctions should be repeated?

5 H. Laakso, SERENA - HEWG meeting, Mykonos, Greece, 8-11 June 2009 De-Synchronization of the MPO-MMO orbits MMO orbital period is 4*MPO orbital period + 10 min MMO orbital period is 4*MPO orbital period

6 H. Laakso, SERENA - HEWG meeting, Mykonos, Greece, 8-11 June 2009 De-Synchronization of the MPO-MMO orbits MMO orbital period is 4*MPO orbital period + 10 min MMO and MPO at perigee at the same time When MMO is at perigee MPO is at the opposite side

7 H. Laakso, SERENA - HEWG meeting, Mykonos, Greece, 8-11 June 2009 Example: One MMO orbit, part 1

8 H. Laakso, SERENA - HEWG meeting, Mykonos, Greece, 8-11 June 2009 Example: One MMO orbit, part 2

9 H. Laakso, SERENA - HEWG meeting, Mykonos, Greece, 8-11 June 2009