1H. Laakso, SERENA - HEWG meeting, Mykonos, Greece, 8-11 June 2009

1

Coordinated MMO and MPO observations

Harri LaaksoESA/ESTEC, Code SRE-OS, Noordwijk, The Netherlands

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

2H. Laakso, SERENA - HEWG meeting, Mykonos, Greece, 8-11 June 2009

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

3H. 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

4H. 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?

5H. 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

6H. 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

7H. Laakso, SERENA - HEWG meeting, Mykonos, Greece, 8-11 June 2009

Example: One MMO orbit, part 1

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

Example: One MMO orbit, part 2

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