Missions Working Group Charter

1. Introduction

The primary task of the ILRS is the timely collection, merging, archiving, and distribution of laser ranging data to various approved spacecraft properly equipped with retroreflectors.

Currently, artificial satellites tracked by the global tracking network fall into four major categories:

• Geodetic (e.g., LAGEOS 1&2, Etalon 1&2, Starlette, Stella, Ajisai, GFZ-1)
• Altimetric (e.g. ERS 1&2, TOPEX/POSEIDON, GFO-1)
• Space Navigation and Positioning (e.g. GPS, GLONASS, METEOR-2/PRARE)
• Special (e.g. TiPS, METEOR/Fizeau, RESURS-3, ADEOS/RIS)

Geodetic satellites are dedicated passive satellites used in defining the Terrestrial Reference Frame and gravity field and in scientific studies of tectonic plate motion, regional crustal deformation, Earth rotation and polar motion, postglacial uplift, etc. Such satellites generally require frequent and long term tracking (decades) to achieve their scientific goals.

Altimetric satellites are usually limited life missions lasting approximately three to ten years. Typical scientific goals include dynamic sea surface topography, mean sea level and wave height determination, global ocean circulation, ice sheet thickness and topography, and, with future laser altimeters, land surface topography including biomass estimation. The frequency and duration of laser tracking required is usually dependent on the desired radial accuracy for the orbit, the presence or absence of complementary microwave tracking devices such as GPS, DORIS, or PRARE, and the periodic need for inflight calibrations of these techniques and/or the altimetric sensors themselves.

Space Navigation and Positioning satellites provide an alternate means (usually based on microwaves) of obtaining precise geodetic positioning on the Earth or precise navigation in space. Laser tracking provides an independent means of calibrating the performance of these systems, further defining satellite force models, and/or directly tieing their orbits into the SLR reference frame with its well-defined geocenter and vertical scale height. Tracking can be of long term interest (e.g. GPS) or relatively short term (e.g. METEOR 3/PRARE).

Special satellites usually have a unique, short-term scientific or engineering goal such as the study of tether dynamics in Earth orbit (TiPS), testing the performance of new retroreflector designs (METEOR 2/Fizeau, RESURS-3), the evaluation and optimization of two color SLR systems (ADEOS/RIS), or intercontinental time transfer experiments (METEOSAT P2/LASSO). In one case (ADEOS/RIS), lasers provide the precise orbit predictions which permit ground-based lidars to rapidly acquire the onboard reflector for atmospheric experiments.

2. Responsibilities of the Spacecraft or Mission Sponsor

The Point of Contact for every organization requesting tracking support of new satellites or modification of the adopted tracking priorities is the ILRS Central Bureau.

It is the responsibility of the Spacecraft or Mission sponsor requesting laser tracking support to file a Laser Tracking Support Plan with the ILRS Central Bureau. In the past, NASA has generated the Laser Tracking Support Plans for most new missions, including many non-NASA experiments. These plans are required to obtain tracking approval at NASA and many non-NASA sites. In the future, it will be the responsibility of the spacecraft or mission sponsor to generate the plan and submit it in a timely manner to the Central Bureau. Pertinent information on the Mission will be extracted from the Plan and posted on the CSTG SLR/LLR Subcommission Web Page for easy access by individual stations.

The Laser Tracking Support Plan must provide, to the best of the sponsor's ability, the following information:

• Scientific and Technical Points of Contact for the Mission
• the scientific or engineering goals of the mission
• the proposed launch scenario and approximate dates
• expected duration of the mission
• special tracking requirements or restrictions (if any) during the pre-launch, launch, and post-launch phases of the mission
• the tracking sites requested to participate in the operational phase of the Mission and the frequency and duration of tracking required from those sites (required orbital accuracy may be substituted for this)
• the acquisition, tracking, and/or data services to be provided by the sponsoring organization for the Mission
• those acquisition and data services of a special or non-routine nature requested from the ILRS
• required timelines for data processing and delivery
• repository for scientific or engineering results resulting from the mission and a statement of availability of raw and/or analyzed data to the general SLR community

3. Roles and Responsibilities of the Missions Working Group

A laser station can only track one satellite at a time. The rapidly growing constellation of satellites tracked by lasers, combined with a vastly different tracking requirement for each satellite and limited tracking resources, necessitates the formation of a Missions Working Group to review all requests for laser tracking and to make a recommendation to the Governing Board regarding tracking and its relative priority with respect to other approved satellites.

• adequate scientific or engineering relevance and sufficient justification for laser tracking (to justify the additional workload of the tracking sites to site sponsors and obtain their concurrence)
• concurrence on the stated laser tracking requirements and recommended assignment of tracking priority to the Mission
• adequacy of the prediction service (generating institution, format, method and frequency of distribution)
• special requirements (e.g. time biases, drag functions, librating functions, calibration passes, accelerated data submissions)
• organization of the data flow from the data centers to the mission analysis centers

Responsible Government Official: Carey Noll
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Last modified date: Friday, November 05, 2004
Author: Carey Noll
Maintained by: Carey Noll