MESSENGER RSS Delta-differential One-way Range Data Record (DDOR)

DDOR – Delta-differential One-way Range Data Record

Instrument: MESSENGER Radio Science Experiment

PDS Data Set ID: MESS-V/H-RSS-1-EDR-RAWDATA-V1.0

For more information about RSS DDOR Products, see the EDR Product SIS.

The Radio Science Subsystem (RSS) Delta-differential One-way Range Data Record (DDOR) measurements complement the normal Doppler and ranging data, which are best along the Earth-spacecraft line. DDOR data provide measurements that are analyzed to obtain position information that is orthogonal to the Earth-spacecraft line, a measurement that is only inferred indirectly from Doppler and ranging measurements. The DDOR measurements are largely independent of some common tracking and navigation errors such as media, station locations, UT1 and polar motion.

DDORs are the difference between two Very Long Baseline Interferometer (VLBI) measurements of the spacecraft and a nearby quasar. This ties the Earth-spacecraft direction to a quasar location in the plane of the sky. This achieves highly-accurate measurements of the location of the sacecraft perpendicular to the line of sight, or the angular (not range) location of the spacecraft relative to Earth. Accuracies can be 10 nanoradians (1.5 km at 1 AU) or better. A single DDOR determines the angle along a baseline between the two VLBI antennas. To get both declination and azimuth (location in two dimensions) requires different baselines such as Madrid-Goldstone (east-west) and Goldstone-Canberra (more north-south).

RSS DDOR products have the following file names:

yydddhhmmSC236DSSnnDDOR_234.DAT (with detached PDS label)

where:

yydddhhmm = start time year, day of year, hour, and minutes

nn = Deep Space Station (DSS) number; DDOR observations involved at least two DSN stations, but the file name contains only one DSN station, the one that is identified in the original product file name

14 = Goldstone 70 m antenna

15 = Goldstone 34 m high-efficiency antenna

24 = Goldstone 34 m beam waveguide antenna

25 = Goldstone 34 m beam waveguide antenna

26 = Goldstone 34 m beam waveguide antenna

In ODE, DDOR products have the following product IDs:

YYDDDHHMMSC236DSSNNDDOR_234