Minutes from CSTG SLR/LLR Subcommission Meeting

London, UK
September 23, 1997

Michael Pearlman/CFA

The Satellite and Lunar Laser Ranging Subcommission of the CSTG met at the Royal Astronomical Society offices in London, UK on September 23, 1997. Local arrangements were kindly provided by Dr. Andrew Sinclair of the Royal Greenwich Observatory in Cambridge. The main order of business was to review and discuss the International Laser Ranging Service (ILRS) document prepared by John Degnan and to agree on a course of action to bring the ILRS to fruition.

Attendees

Wolfgang Schlueter/IfAG, Wolfgang Seemueller/DGFI, Werner Gurtner/AIUB, Richard Eanes/CSR, John Degnan/GSFC, Andrew Sinclair/RGO, Yang Fu Min/Shanghai Observatory, Peter Shelus/UTex, Karel Hamal/TUP, Hiroo Kunimori/CRL, Vladimir Glotov/RSA, Maki Maeda/NASDA, and Mike Pearlman/CfA.

International Laser Ranging Service (ILRS)

John Degnan relayed comments from Gerhard Beutler, president of the CSTG, from Septembers IAG meeting in Brazil and discussions he had with Bob Schutz, SLR representative to the IERS, in July:

The IAG is very supportive of the ILRS concept; the current tendency is toward an ILRS organized under a CSTG umbrella, but the options remain open. It was noted in discussion, however, that with all of our efforts to use the IGS as a model, the IGS seems to be largely independent of the CSTG. Does CSTG have any influence on IGS? Where does the new CSTG Microwave Techniques Subcommission fit into this equation? The overall space geodetic structure should be discussed with Gerhard Beutler.

Independently, IERS has discussed getting SLR stations, analysis centers, etc. to reaffirm their commitments to IERS participation; John Degnan and Bob Schutz have agreed to pursue a joint CSTG/IERS Call for Participation in the new ILRS organization. In July, Bob Schutz had agreed to put together a first draft of the call.

The IERS wants both it and the ILRS to have a member on each others board (like the IGS). The current draft of the ILRS Terms of Reference prepared by the CSTG SLR/LLR Subcommission proposes that the two Analysis Coordinators for SLR and LLR (presently Richard Eanes and Peter Shelus) on the ILRS Governing Board serve as members of the IERS board with no reciprocity although this is subject to further negotiation.

John Degnan reviewed the comments he received on the draft ILRS document since our last meeting in Maratea in June. They are few and relatively minor in nature. He will prepare a revised draft and circulate it among the Steering Committee Members by the end of October.

Relationship with IERS

There was considerable discussion on the relationship between the IERS and the ILRS. Is IERS just another customer (e.g. ocean surface, relativity, etc.), or do we want to have a unique relationship? If an IERS representative were on the ILRS Governing Board, there is concern that other users might also want representation. Should the position perhaps be that of a user representative. This needs more thought.

Data Analysis

At the moment the IERS receives annual SLR solutions from any groups choosing to submit them. Solutions may differ considerably, and IERS takes the responsibility of selecting, comparing, and combining solutions for incorporation into their products. For some time we have felt great concern that our best wisdom may not be reflected in that product and that the SLR analysis community should be responsible for comparing, evaluating, and combining its own solutions, and producing a standard SLR product for IERS and other customers. Other solutions could still be made available to the community for specialized requirements, but general standards should be issued and enforced, and participating ILRS groups should commit to following such specifications. (It was noted that IGS has very stringent requirements for analysis centers, thus at least limiting the range of submissions with which it must contend.)

We need to learn a bit more about the IGS process for obtained combined solutions and how it might apply to laser ranging data.

It was agreed that, in the Call for Participation in the ILRS, a request be included for an Associate Analysis Center to be responsible for comparison of the SLR solutions.

A likely candidate for the comparison center is CSR, but resources and personnel are a major issue. They need to look at the job more closely.

Aside from critical comparison of solutions, other ideas to strengthen the SLR results were discussed. The Analysis Centers should be going to combined LAGEOS 1 and 2 solutions to get better geometry and data coverage. Should other satellites such as Starlette and Stella be added? Should lunar data be added? We really need to define the task and quantify the benefits.

ILRS Structure

There was considerable discussion on the division of responsibility between the Central Bureau and working groups. There was general agreement that the Central Bureau should make as much use as possible of the (1) products generated by the data and analysis centers and (2) coordination capabilities of the operations centers. The Central Bureau should be the information clearinghouse, checking that the participants are fulfilling their obligations. It should be a small, perhaps geographically distributed, entity which consolidates activities to reduce duplication and allows the community to make more effective use of its resources.

Incoming requests for tracking support go to the Central Bureau, where requests are checked for completeness and then forwarded to the Governing Board where the review process is initiated.

Four standing working groups have been identified: Missions, Network Operations and Engineering, Formats and Procedures, and Analysis. Additional ad hoc working groups will be established as required. The Working Groups will provide technical expertise; working group chairpersons will be chosen from among the members of the Governing Board. Non-Board members can be appointed to the Working Group by their respective chairpersons.

John Degnan voiced concern that the ILRS Governing Board with 15 members (exclusive of the IERS representative) as structured in the ILRS document was too large. It was agreed to reduce the number of network representatives from 9 to 6 (2 per network) to make the Governing Board a little smaller and more balanced and to use the two at-large slots to help fill gaps in Board expertise or community representation.

Although a one-year pilot phase for the ILRS had been suggested, there was general consensus that the laser ranging operations and analysis was already well established and that we were merely reorganizing and streamlining functioning entities.

It was agreed to forego a pilot phase of the ILRS and move directly into the service. Activities will be added and amended as we progress and gain experience.

Call for Participation

The Call for Participation in the ILRS, to be issued jointly with the IERS, is being prepared by Bob Schutz and John Degnan. All participating components, including the Central Bureau, laser ranging stations, operations centers, analysis centers, data centers, etc. must respond with their commitment. Except for the Central Bureau, most of the response may be no more than a commitment to continue at the current level of activity. Proposals for the operation of the Central Bureau need careful organization, definition, and strong commitment.

The Call for Participation is scheduled for issue at the end of October. The proposals will be due three months later (end of January). Three months would be allowed for evaluation with the final selection (at least for the Central Bureau) planned to take place at the EGS meeting in Nice during the week of April 20, 1998. Six months would then be allocated for setup, and the service would begin formal operation in the October December 1998 timeframe.

The key to success is to form appropriate partnerships. Any integration that the regional stations can do through common regional operations centers will ease the burden on the Central Bureau. Members were urged to examine partnerships that would produce an effective Central Bureau.

Other Topics

GLONASS

GLONASS-67 has lost stabilization. No data has been received for about two months and the problem has been confirmed with the radio data. Concern was expressed that notification to the field stations was not more expedient. A request was made by the MCC that we substitute GLONASS 71 for the lost target. Richard Eanes confirmed that the analysis community continues its strong desire for high satellite data, and the need to study the coordinate system for the GLONASS-GPS connection is strong. Eanes reminded us that GLONASS is considerably easier to track than GPS. GLONASS-71 is considerably newer than GLONASS-63 giving us some hope that it will remain a good target for some time to come. It would probably be advantageous to organize a tracking campaign to get some momentum underway.

It was agreed to add GLONASS-71 to the CSTG satellite priority list in place of GLONASS-63. RGO will notify the laser ranging community and will begin issuing predictions within the week. Erricos Pavlis will be asked to compose the justification.

Glotov also announced that the next GLONASS launch in October would place three new satellites in orbit.

ADEOS

The ADEOS satellite failed in early July. The loss of the unique single, open cube corner is very unfortunate for both propagation and system development activities.

WPLTN

An executive meeting of the WPLTN was held in London on September 22. A copy of the notes from that meeting is available.

Next Meeting

The next two Full Subcommission Meetings will be held in Nice, France, during the week of April 20, 1998 and in Deggendorf, Germany, during the week of September 21, 1998 in conjunction with the EGS Symposia and 11th International Workshop on Laser Ranging Instrumentation respectively. If necessary, an opportunity for an additional Steering Committee meeting also exists at the WEGENER symposium in Norway in early July.

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Author: Carey Noll
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