Minutes from CSTG SLR/LLR Subcommission Meeting

General Meeting
The Acropolis Congress Centre, Nice, France
Tuesday, April 21, 1998

The General Meeting of the SLR Subcommission was held at the Acropolis Congress Centre in Nice, France on Tuesday evening, April 21, 1998. The meeting agenda and list of attendees are included in Attachments 1 and 2, respectively.

International Laser Ranging Service (ILRS)

John Degnan presented the outcome of the weekend ILRS deliberations. On Saturday, April 18, the Steering Committee for the SLR/LLR Subcommission reviewed the ILRS proposals and prepared its presentation to the CSTG Executive and IERS Directing Boards. John Degnan presented the results at sequential meetings on Sunday morning and afternoon, April 19, and the CSTG Executive Board and the IERS Directing Board each gave their approval for implementation. Dr. Christoph Reigber appointed Bob Schutz of the University of Texas Center for Space Research as the IERS Representative to the new ILRS Governing Board.

Disposition of the Proposals

A tabulation of the proposals received in response to the Joint CSTG/IERS Call for Participation in the new ILRS is included in Attachment 3. They were intended to cover all aspects of the ILRS activity.

SLR Stations: Forty-five proposals for ILRS SLR Stations were received and accepted including several that are yet to become operational at new sites or to replace existing systems. Three stations (Simosato, Cagliari, and Riyadh) were noted as missing, but all have indicated that submissions are pending. It was noted that most stations within the WPLTN region had not noted their network affiliation. This was assumed to be a group oversight.

Data Centers: Three proposals for Data Centers were received and accepted, including two Global Centers (CDDIS and EDC) and one Regional Center (Shanghai Observatory).

A proposal by the University of Canberra to develop a "mirror site" to the Data Centers at the CDDIS and the EDC was not accepted in its present form by the Steering Committee.

Operations Centers: Six proposals were received for Operations Centers. Three proposed to service more than one station and were accepted. The remaining three were not.

Analysis/Associate Analysis Centers: Twenty-five proposals were received. Although none of the proposing centers currently satisfy all of the ILRS requirements for a full Analysis Center, it was agreed that those centers that came "very close" would be accepted with the caveat that any shortcomings be rectified over the next year. Several groups which had applied for full Analysis Center status were designated as Associate Analysis Centers but are free to reapply for full status upon meeting the full range of Analysis Center requirements. The categories of "Lunar Analysis Center" was introduced and will be included in the Terms of Reference. Of the proposing centers, three were accepted as full Analysis Centers, eighteen as Associate Analysis Centers, and four as Lunar Analysis Centers. Additional organizations can qualify for Full Analysis Centers at any time in the future.

Central Bureau: One proposal from the NASA Goddard Space Flight Center (GSFC) was submitted and accepted for the Central Bureau. John Bosworth of GSFC was named as Director and Mike Pearlman of the Harvard Smithsonian Astrophysical Observatory (SAO) was named as Secretary. Both automatically become Ex-Oficio members of the ILRS Governing Board per the ILRS Terms of Reference. In addition to the normal CB activities as described in the ILRS Terms of Reference, the GSFC proposal included (1) coordinators (small fraction of time) for the NASA, EUROLAS and WPLTN networks to strengthen the feedback process and (2) a part-time Science Coordinator to facilitate information flow, maintain science related bibliographies, and strengthen our advocacy mechanism.

Organizational Issues

The Steering Committee agreed that the:

1. The Central Bureau should include a NASA Network Coordinator for symmetrical representation;
2. The Science Coordinator position within the Central Bureau should be carefully defined and filled for two-year terms through solicitation for proposals to the community;
3. The Lunar Coordinator will be Deputy Chair of the Analysis Working Group and serve as an alternate for the Analysis Coordinator as the voting ILRS representative to the IERS Board;
4. The ILRS Annual Report would include a small hard copy report with more extensive information made available on the web;
5. The CSTG SLR/LLR Subcommission Steering Committee will serve as an interim Governing Board until formal establishment of the ILRS Governing Board at the Laser Workshop in September. Furthermore, current heads of the Subcommission Working groups will act as interim ILRS Working Group Leaders. In particular, Richard Eanes and Andrew Sinclair will function as the interim chairs of the Analysis and Data Format/Procedures Working Groups respectively. In coming months, Richard Eanes will be contacting people nominated by their organizations to serve on the Analysis Working Group to plan the transition to full ILRS Analysis operations.
6. The first meeting of the ILRS Governing Board will be held at the Laser Workshop in Deggendorf following elections to be conducted via email.

It was also suggested that we might want to define the rule for change in representatives and Central Bureau when necessary in the Terms of Reference.

John Degnan will draft the responses to each of the proposals submitted to the Joint Call for Participation. The target date for full implementation of the ILRS is November 1, 1998. Member organizations are encouraged to review their obligations as ILRS components and meet them by the start date.

Selection of the Governing Board Members

As mentioned previously. three members of the ILRS Governing Board have already been designated:

John Bosworth and Mike Pearlman are Director and Secretary of the Central Bureau; and Bob Schutz has been selected by the IERS as its representative.

The remaining 13 GB members will be nominated and elected by their "peer groups". There was some confusion over the selection method for some of the other Governing Board Members. since the term "peers" in the Terms of Reference was somewhat ambiguous. The Steering Committee agreed to the following:

1. The NASA, EUROLAS, and WPLTN networks will each select two Governing Board Members from within their organizations, i.e. their "peers";
   
2. The Analysis Community will nominate and select two Governing Board members from its "peers";
   
3. The Data Centers and the Lunar Ranging community will each nominate and select one member from its "peers"; and
   
4. Two At-Large members will be chosen by the full SLR community membership. At its option, the Central Bureau may nominate At-Large candidates to fill gaps that it perceives in the Governing Board membership.

The current Steering Committee of the CSTG Satellite and Lunar Laser Ranging Subcommission will function as an interim Governing Board taking nominations and running the GB elections via email over the next few months. The new Governing Board will be installed at the September SLR Workshop in Deggendorf. It will supplant the current Subcommission Steering Committee but retain its IAG/CSTG affiliation. Elections 1, 2, and 3 will be completed by July 1 within their peer subgroups. Election 4 will be open to all ILRS Associates and completed by September 15.

For the purposes of nominating and voting for ILRS Governing Board members, an ILRS Associate must be affiliated with an approved ILRS organization (tracking station, operations center, analysis center, data center, or Central Bureau). Prior to elections, a message will be sent out via SLRmail requesting that all individuals on the current SLR mailing list identify which of the ILRS entities they support. Individuals who wish to be added to the list should contact Ms. Carey Noll at noll@cddisa.gsfc.nasa.gov.

Satellite Tracking Support

Van Husson has issued the SLR Station Performance "Report Card" for the last 12 months. A copy is available at

Global Performance Report Card (1st quarter 1998)

Van Husson reviewed the schedule of upcoming missions requiring SLR tracking.

Over the next year, the following retroreflector satellites are scheduled for launch: GFO-1, WESTPAC, Sunsat, and Champ. Requests for SLR tracking are anticipated for all of them.

GFO-1, a US Navy altimeter satellite, which was launched in February, has experienced a failure of all four of its on-board GPS receivers. The problem may be software related, but so far, repair has been elusive. The satellite has a NASA-furnished retroreflector array and the NASA SLR network is initiating some tracking for orbital maintenance. A request for support from the international network is anticipated.

The community needs to be reminded that lead-time is required for the Subcommission to organize tracking support. Furthermore, the Governing Board will have the power to approve, deny or modify requests for laser tracking based on a mission's scientific or technical relevance and its potential impact on other approved missions. Therefore, missions should submit their requests early in the planning phase and not assume that the spacecraft will be tracked simply because it carries a retroreflector onboard.

IGEX 98 Campaign

Werner Gurtner presented a briefing on the International Glonass Experiment, IGEX 98 Campaign. (See Attachment 4)

Commercial dual GPS/Glonass receivers now available will allow us to use the combined satellite complex for improved navigation and positioning. Some deficiencies exist in the 12 to14 satellite Glonass constellation, but the availability of laser retroreflectors with relatively large cross-sections on all of the Glonass satellites may provide the opportunity to use SLR to improve the definition of the Glonass satellite orbits.

The Radio Techniques Subcommission of the CSTG (Pascal Willis) has solicited proposals for participation in a test of the combined GPS/Glonass capability including receiver performance, station operations, data flow, data processing software, orbital modeling, etc. Proposals, which are due on 29 May 1998, will address ground station placement, observations periods, satellite preferences, and the proper strategy for SLR support. Once the proposals are evaluated, the Radio Subcommission will formulate a request for SLR support. It is anticipated that a SLR support request would include a campaign for three to six months on 2 to 3 Glonass satellites, starting in the September 1998 timeframe. Stations would be asked to track each satellite for 15 minutes per pass in 5-minute intervals interspersed among other tracking requirements.

The Glonass satellites are considered to be good SLR targets, capable of supporting accuracies of a few cm or better. The current feeling is that Glonass orbits of 10-20 cm quality would make this capability very worthwhile.

We need to determine:

1. Are there any IGEX proposals that propose to use SLR data in their Glonass analyses?
2. How much SLR data is needed to get to the 10-20 cm level?
3. How much data is already available and what quality orbits can be calculated with it?
4. Is an adjustment of CSTG priorities between GPS and Glonass tracking necessary?

It was suggested that the SLR Analysis Centers be contacted to try to stimulate strong responses to the solicitation.

Eleventh International Workshop on Laser Ranging

The Eleventh International Workshop on Laser Ranging, to be hosted by the BKG, will be held in Deggendorf, Germany on 21-24 September. See details on the Workshop Home page which is accessible via the CSTG Subcommission page. It was noted the Hermann Seeger will be retiring from service right after the Workshop, and some suitable festivities are being planned.

Special Tracking Campaign on GEOS-3

Frank Lemoine from GSFC presented a request for a 3 to 6 month SLR tracking campaign on GEOS -3, which was the launched as the first global satellite radar altimeter (see Attachment 5). Orbital simulations show that it is among the top five candidates for improvement of the current gravity field models. At an inclination 115 deg., its orbit is unique among retroreflector satellites, and its geometry presents a reasonably high mass-to-area ratio and a high laser signal link.

SLR tracking has been reestablished and has verified satellite orientation (with the gravity gradient boom). Some degradation in nadir orientation is expected due to the loss of the momentum wheel, but this should only be in the neighborhood of a few degrees. Historical data is being analyzed to study the quality of orbital fit.

The campaign should be scheduled to avoid periods of high solar activity.

The Subcommission noted the advantage of "bringing back" satellites like Diademe and GEOS-3 from the SLR historical satellite complex to satisfy new requirements. The Subcommission approved a six-month campaign with details and priorities to be worked out between Frank Lemoine and the Subcommission Steering Committee.

Formats

The year "2000" format issue was discussed. Activities are underway everywhere to scope and fix the problem. Participants were reminded that in addition to analysis software, operations software in the field might also be very vulnerable.

The millennium change may also introduce a problem through our convention for spacecraft numbering and the resulting string of "leading zeros".

The issues were deferred to the Formats and Procedures Working Group (Andy Sinclair and Van Husson), but in reality, each group will have to work out its own problems. Early testing is highly recommended.

Next Meeting

The next meeting of the Subcommission will be held at the Laser Workshop in Deggendorf in September. At that time the selection of the ILRS Governing Board will be complete and the transition to the new ILRS can be initiated.

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Last modified date: Friday, November 05, 2004
Author: Carey Noll
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