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Laser ranging to Mars

Laser ranging to Mars. Shapiro delay: can measure (1+ )/2 effect to ~ 210 -6 level with 1 cm range precision to Mars translates to 410 -6 determination of : 10 better than Cassini Strong EP:

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Laser ranging to Mars

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  1. Laser ranging to Mars • Shapiro delay: • can measure (1+)/2 effect to ~ 210-6 level with 1 cm range precision to Mars • translates to 410-6 determination of : 10 better than Cassini • Strong EP: • If sun’s grav. self energy (few parts in 106) or radiant energy in photons (10-7) falls at an anomalous rate toward Jupiter, orbits are polarized toward Jupiter: more so the farther from the sun • at Mars, this polarization is 850 meters ( = 4 -  - 3 is Nordtvedt parameter) • 1 cm precision gets  to few times 10-6 precision

  2. Shapiro delay to Mars • Figure shows range rate from Shapiro delay alone (i.e., after taking out orbital range rate) • Thus centimeter range precision two days in a row gives 10-4 measurement this is a pdf conversion from postscript. Looks bad. Original from John Anderson. I can try to get a better one.

  3. Laser Ranging as a NAV-COMM tool • Optical comm links can serve multiple purposes. • laser links between spacecraft and to earth can perform a variety of functions: • optical communication • navigation via range measurements • fundamental physics via range measurements • Any optical communications link referenced to a good clock can be utilized to provide accurate range measurements • Transponder “beacons” throughout solar system would provide a navigational network (GPS equivalent) and allow solar system “grand fit” to nail down gravitational physics

  4. Interplanetary Laser Link Milestone • Farthest laser link established May 2005: 24 million km • MESSENGER spacecraft en-route to Mercury • Used laser altimeter as asynchronous transponder (advertise John Degnan’s talk here) • 20 cm range precision achieved • 10-11 precision • pathbreaking result important for interplanetary ranging, laser comm, navigation • MET=mission elapsed time • MLA=mercury laser altimeter • GGAO= goddard obs ground station Smith et al., 2006: Science, 311, 53

  5. ISS Reference spacecraft DR-Earth ~ 2 AU ~ 1º Earth DR-T ~ 0.03 AU Sun Expected accuracies: Apparent position of the Target spacecraft DT-Earth ~ 2 AU True position of the Target spacecraft 3 lengths & 1 angle measured Geometric redundancy allows for accurate measurement of relativistic gravitational light deflection to 1 part in 108. LATOR: the Laser Test of Relativity CWS redo this idea

  6. LATOR concept • three spacecraft/platforms form triangle whose edges are measured via laser ranging • in Euclidean geometry, these three measurements uniquely determine angles within triangle • in curved spacetime of solar system, interferometric measurement of the interior angle at one vertex provides measure of spacetime curvature • two spacecraft 1 apart on the far side of the sun allows measurement of curvature to < 10-8, translating into similar precision measurement of 

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