Advanced Concepts for Ranging and Time Transfer: Applications and Mission Support

Wolfgang Schäfer TimeTech GmbH, Curiestrasse 2, 70563 Stuttgart, Germany

Significant advances have been achieved in the past 30 years in the fields of satellite ranging, time transfer and relative positioning of S/C. Technical drivers are GNSS, deep-space missions and precision metrology based on high performance frequency generation and accurate frequency-, time- and time-interval measurements. Ranging at cm-level stability, time transfer at sub-ns uncertainty and velocity measurements at the µm/s level can be readily achieved using standard technologies. These numbers could be improved by 2 or 3 orders of magnitude using state-of-the art developments and systems.

Major recent achievements are in the fields of ground- and space-based oscillators and clocks, time-keeping and time transfer. Besides traditional microwave-based links, high data-rate optical links will soon emerge. Interesting new capabilities and performance levels arise from the combination of time transfer and ranging results, which can be generated simultaneously using the same bi-directional link and equipment.

Actual standard ground- and space-based equipment is unlikely to cope with these advances and scientific needs in the foreseeable future (i.e. to 2040). This restricts achievable performance for most standard missions to traditional performance levels. More ambitious missions have to rely on dedicated and costly proprietary systems to match their needs. Such systems are often considered experimental rather than operational.

This presentation will identify a range of capabilities and possibilities arising from an integrated approach to combine available and existing technologies and installations to achieve improved overall performance, even under operational conditions. Examples are given, how advanced elements like clocks, data links, etc. could be added at low risk, using readily available measurement techniques.

The goal of this systems approach is a minimum impact and risk on existing installations and to avoid costly duplication of hardware. Science applications and mission operations will profit from continuously available ranging and time-transfer data, which will be generated without major impact on regular S/C operations and TM/TC activities.