1. Seismic network of landers on Mars: Proposed positioning of landing ellipses and evaluation of the encountered range of slopes
Michael G., Hauber E., Oberst, J., Jaumann R.
Institute of Planetary Research, German Aerospace Centre (DLR), Berlin

2. desired configuration
The optimal configuration is a triangle of 3 landers separated by 30 degs, with a fourth station at an antipodal location. The triangle ideally should enclose a seismically active region: the favoured options are Tharsis and Elysium

3. constraints
The proposed mission design for the former Netlander mission:
allows for a maximum spread of landing times of 2h 40 min, which means that the possible landing sites fall within two bands of around 40degs width in longitude: one for prograde and the other for retrograde entries.
The reachable latitude range is expected to be 34S-53N.
Constraints imposed by the parachute and airbag systems determine that the sites should be at an altitude of no more than the 0 m MOLA level.
For the Netlander design, the 3-sigma landing ellipse is of the order of 540x55 km. Varies somewhat depending on the site.  (cf. Gusev crater, the Spirit rover landing site, at 170 km across)
Ellipse semi-major axis orientated along entry trajectory (perpendicular to trace of reachable sites)
the local slope should be < 15° on 5m scale, and the area free of obvious hazards

4. Amazonia network

5. Ladon basin

6. slope range
MOLA – 500m baseline

7. 3d view
MOLA/Viking MDIM

8. difficult sites – Lycus Sulci

9. slope range

10. altitude range
MOLA

11. 3d view

12. alternative sites – Olympus south

13. slope range

14. altitude range

15. 3d view
swap for hrsc?

16. Elysium network

17. Tharsis network – T1 variant

18. Amazonia variant – Olympus south

19. Chryse network

20. table of sites

21. conclusion
540x55km 3 landing ellipses can be optimally placed such that the 15º local slope constraint is violated with maximum 2.2% probability for the Amazonia network (at Ladon basin)
Amazonia network offers the safest sites with the current constraints
Elysium network has good possibilities, although the retrograde entries may be constrained to ~11ºN; Ladon basin would be a good antipode, if time constraint relaxed by 50%
proposed Tharsis variants require significant relaxation of the landing time constraint (300% for T1)
(note that Hellas ellipses are expected to be significantly larger, and the landing systems may need to operate differently)
There are several feasible Chryse network configurations in the north; other than Hellas, a site east of Dao Vallis might serve as the antipode
An Amazonia network with a site south of Olympus Mons appears to be an interesting variant
G. Michael acknowledges the European Community's Human Potential Programme under contract RTN , MAGE.