scope:

PURPOSE

Delta Differential One-Way Ranging (Delta-DOR) is a Very Long Baseline Interferometry (VLBI) technique that can be used in conjunction with Doppler and ranging data to improve spacecraft navigation by more efficiently determining spacecraft angular position in the plane of sky. It involves the simultaneous use of multiple ground stations, possibly belonging to different agencies, for acquisition of both spacecraft and quasar signals.

The quasar sources required for Delta-DOR measurements have to be known a priori. The quality of a Delta-DOR measurement depends on the availability of compact and strong quasars, together with the knowledge of their precise positions.

Delta-DOR operations require a quasar catalog, geared to Delta-DOR measurements.

Historically, quasar catalogs are populated by astronomers, via VLBI campaigns. This is highly valuable information for Delta-DOR measurements, and established reference catalogs exist today.

The X-band catalog adopted as a starting point for this book is based on the one reported in reference [1]. This catalog has been adopted because it has been developed and used, over the years, to perform Delta-DOR measurements.

This catalog is now available as a SANA registry (reference [3]):

An update to an X/Ka-band quasar catalog is under preparation.

All space agencies should support the extension of the existing catalog as follows:

a) increasing the number of observed, validated, and cataloged X-band sources;

b) further developing an X/Ka-band catalog;

c) providing separate correlated source flux estimates for each quasar, each frequency band, each baseline;

d) providing information on flux variation versus time on each baseline of interest.

The purpose of this Recommended Practice is to provide:

- specifications for a quasar catalog to be used in Delta-DOR measurements;

- procedures and qualitative criteria to evaluate whether the updates of such catalogs are acceptable;

- description of the registries to be included in a quasar catalog;

- procedures to update SANA entries;

- informative description of building a catalog update.