NASA's GRO Remote Terminal System (GRTS)

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The Compton Gamma Ray Observatory (CGRO) was a space observatory detecting light from 20 KeV to 30 GeV in Earth orbit from 1991 to 2000.The decision to build the ground station and devote a TDRS to the Compton GRO came after the observatory's tape recorders failed, restricting transmission of scientific data to real time only.
A Tracking and Data Relay Satellite (TDRS) is a type of communications satellite that forms part of the Tracking and Data Relay Satellite System (TDRSS) used by NASA and other United States government agencies for communications to and from independent "User Platforms" such as satellites, balloons, aircraft, and the International Space Station. TDRSS satellites are all designed and built to be launched to and function in geosynchronous orbit, 35,786 km (22,236 mi) above the surface of the Earth. The first Tracking and Data Relay Satellite was launched in 1983 on the Space Shuttle Challenger's first flight, STS-6.
The TDRS system was designed to replace a pre-existing worldwide network of ground stations that had supported all of NASA's manned flight missions and unmanned satellites in low-Earth orbits. The primary system design goal was to increase the amount of time that these spacecraft were in communication with the ground and improve the amount of data that could be transferred. These TDRSS satellites are all designed and built to be launched to and function in geosynchronous orbit, 35,786 km (22,236 mi) above the surface of the Earth.
The decision to build the ground station and devote a TDRS to the Compton GRO came after the observatory's tape recorders failed, restricting transmission of scientific data to real time only. On March 14, 1994, NASA announced the opening of a new, remote ground station in Tidbinbilla, Australia, called the GRO Remote Terminal System, to receive scientific data from the Compton Gamma-Ray Observatory (GRO) via a Tracking and Data Relay Satellite (TDRS) that was moved into position over the Indian Ocean.
A TDRS spacecraft would have to be moved and located somewhere over the Indian Ocean. Figure 1 depicts the percentage of coverage versus TDRS location in longitude degrees and is the result of a large number of computer runs to develop a reliable statistical result.
The GRO spacecraft radiates 32 kbs data to the F1 located at 85-degrees east longitude (this is in addition to support from the nominal two TDRSs). F1 receives the data using either the Multiple Access (MA) of Single Access (SA) capability. The data is transmitted to the Australian terminal called the Remote Ground Terminal (RGRT). Using dual 64 kbs Nascom lines, the data is sent to the WSGT, specifically to the GRTS dedicated Extended TDRS Ground Terminal (ETGT), and then to the GRO data processing center at GSFC.

NASA's GRO Remote Terminal System (GRTS)

by Hugh Pickens

This report summarizes four projects implemented by the Project Engineering Group (PEG) at AlliedSignal Technical Services at Columbia, MD between 1992 and 1998 while Hugh Pickens was engineering manager of the group. The four projects are:

Other projects completed by the Project Engineering Group during this period include:

  • Bermuda Radar Upgrade
  • MILA-Bermuda Re-engineering
  • Shuttle Forward Link
  • Landsat Ground Station
  • JPL X-Band Acquisition Aid Project
  • Guam GRGT TDRS Ground Terminal
  • Leo-T Ground Terminal

Contents

1992 Meteosat Project

NOAA's Decision to Borrow Meteosat Spacecraft from ESA

The United States normally operates two meteorological satellites in geostationary orbit, one each over the East and West Coasts. However, it had only one since the failure of GOES-6 in 1989. A planned replacement satellite was lost due to a launch vehicle failure in 1986. The remaining operational satellite, GOES-7, was repositioned midway over the United States. With the next GOES launch projected for April 1994 with a second GOES launch one year later if GOES-7 should fail, the East coast of the United States would be left without satellite weather coverage.

In 1992 NOAA's GOES weather satellites were at the end of their useful lives and could have failed at any time so NOAA made an agreement with the government of Germany to borrow a Meteosat Weather Satellite as a backup and drift it over from Europe to provide weather coverage for the US's Eastern seaboard in the event of an early GOES failure.

The European weather satellite Meteosat-3 originally operated at 0 degrees longitude over the equator. In August, 1991 it was drifted to a position of 50 degrees west over the equator to supplement NOAA's GOES system. However Meteosat needed to be relocated to 75 degrees west longitude to provide complete coverage of the East Coast of the United States. At 75 degrees west, Meteosat-3 was no longer within the field of view of the Meteosat station located near Darmstadt, Germany and this would put Meteosat out of line-of-site with its control center in Germany. To be able to continue the operations from ESA's European Space Operations Center (ESOC) it was necessary to build a Meteosat Relay station in Wallops, Virginia.

NOAA Contracts with Bendix to Implement Meteosat Ground Terminal at Wallops Island, Virginia

The only problem was that Meteosat was a pretty dumb satellite and had to be in constant contact with a Ground Station to operate so NOAA started a crash program to implement a Meteosat Ground Terminal at Wallops Island Virginia in six months. Peter Militch and I wrote a proposal to build the ground terminal over the Christmas holidays in 1992 and won the job.

Engineering Contract to Implement Ground Terminal

It was BFEC's first fixed price engineering contract and the project was basically run as a two man project with Peter handling the design and systems integration while I handled the scheduling, budgeting, logistics, and subcontractor management bringing in temporary technicians and installers as we needed them.

The key to the project's success was our decision to subcontract the one custom piece of equipment, a KA-Band triplexer to two different waveguide companies. We needed four couplers in all so we awarded a contract for one each to MDL and to M/A-Com with the carrot that we would award the contract for the other two to the first company to finish. Our strategy worked. At the end of the project, we had completed the $3.5 million Meteosat Ground System on schedule and on budget and made 15% profit on BFEC's first fixed price contract.

In early 1993 Peter Militch and I finished the Meteosat Project with the installation of a Ground Terminal at Wallops Island and NOAA began to drift a Meteosat Weather Satellite over from 50 degrees West to 75 degrees West moving approximately one degree per day in support of the Extended Atlantic Data Coverage mission to serve as a backup providing weather coverage for the US's Eastern seaboard in the event of an early GOES failure.

1993: Implementation of GRO Remote Terminal System (GRTS)

GRTS Project Gets Started

A similar emergency occurred at Goddard Space Flight Center in 1993 that required a crash program to deploy a new ground terminal and NASA called on AlliedSignal to help them recover from a big problem with the Gamma Ray Observatory. The Gamma Ray Observatory (GRO), launched in April 1991, was performing as designed until it became obvious in 1992 that both of its onboard tape recorders would fail, thereby reducing recovery of valuable science data to real-time only at a reduced data rate of 32 kbs.

Because the "best science" would be obtained within the next few years, speed in implementation was a high priority. Limited and fixed funding dictated maximum use of existing design and equipment. Protection of an aging and somewhat sensitive TDRS spacecraft (F1) required redundancy in the implementation. Despite the fact that F1 was near the end of its design life of 10 years, its remaining functionality meets the specific needs for the GRTS application. The mandate to have minimal annual maintenance and operations costs required some form of automation. With these requirements, the GRTS Project was started on September 1, 1992. A 13-month schedule to completion, a $12.1M million fixed budget, and a 10-year lifetime wee the primary programmatic constraints.

The original TDRS ground terminal in White Sands, NM had cost about $1 billion and the second TDRS Ground Terminal (STGT) cost about $600 million, but we were asked to implement a low cost terminal with limited capabilities for $12 million and given a deadline of 13 months have it operational. Thirteen months later on March 14, 1994, NASA announced the opening of a new, remote ground station in Tidbinbilla, Australia, called the GRO Remote Terminal System, to receive scientific data from the Compton Gamma-Ray Observatory (GRO) via a Tracking and Data Relay Satellite (TDRS) that was moved into position over the Indian Ocean. This is the story of that project.

Putting Together the AlliedSignal Engineering Team

I was asked to put together an engineering team and be project manager for the design and installation of a low-cost TDRS Ground Terminal co-located with JPL's Canberra Station in the Deep Space Network. I put together a team of about 25 engineers to design and integrate the system. I chose Joe Valvano as my lead systems enginner on the project. At its peak we had about 50 engineers and technicians dedicated to the project.

Engineering staff at AlliedSignal who contributed to the GRTS project included: Frank Albert (Shipping), Bill Blevins (RER, Test Inject Subsystem, Canberra Implementation Team), May Blevins (Cable Assembly), George Broadbent (Training), Brian Canfield (USP/TTCP), Harry Clay (Shipping), Glen Confer (OMCS), John Coombs (Racks and Cables), Marian Coombs (Support), Wayne Danner (PMEL), Bill Dunkin (PMEL, Test Equipment Selection, Phase Noise Analysis), Rich Franchek (Digital Bit Syncs, PSK Demodulators), Fred Frey (RF Analysis, S-Band Antenna, Ku-Band Antenna, Canberra Implementation Team), Darrell Hale (Multiple Access Beamforming Equipment, Canberra Implementation Team), Bill Hitzeman (RF Analysis, S-Band Antenna, Ku-Band Antenna, EMI Testing, Canberra Implementation Team), Dave Huff (Canberra Implementation Team), Jeff Ingold (Timing System, Mini-PTE, Phase Noise Analysis and Testing, Multiple Access Beamforming Equipment, Canberra Implementation Team), Dan Jay (Test Inject), Dawn Keim (Logistics), Mike Keim (Shipping), Steve Kindurys (Ku-Band Transmitters, S-Band Transmitters, RF Acceptance Testing), Karen Knighton (Administrative, Travel), Harry Kreitzburg (PMEL), Joe Kueberth (S-Band Antenna, Ku-Band Antenna, Canberra Implementation Team), Ken Lee (RER), Steve Leslie (TURFTS), Jim Long (Civil Engineering, Canberra Implementation Team), Dave Love (OMCS, Canberra Implementation Team), John McKim (Canberra Implementation Team), Peter Militch (OMCS), Jim Perry (Logistics), Hugh Pickens (Project Management, GRTS Team Leader), Caroline Porter (Test Inject), Pat Price (Logistics), Monte Reiser (RF), Steve Renich (PLC's), Ed Richards (CVU, CC/DIS), Dick Rohrer (Canberra Implementation Team), Andrew Samchuck (OMCS), George Scheffey (USP/TTCP), Bill Seeley (RF), Linda Sisson (Racks and Cables), John Statham (PMEL), Larry Stein (Documentation, TQ), Chris Stevens (CC/DIS), Darlene Stream (Shipping), Joe Valvano (Systems Engineering, Presenter at PDR and CDR, Leader of Canberra Implementation Team), Julio Varela (RF), Brian Weidecker (Canberra Implementation Team), Carroll Whittington (PMEL), Jim Williams (OMCS), John Williams (Shipping, Receiving, Logistics, EC Preparation, Canberra Implementation Team), Steve Williams (QA), Tom Winters (Racks and Cables), Albert Wu (Timing System, Mini-PTE), and Christina Wu (OMCS).

GRTS Project Overview

The decision to build the ground station and devote a TDRS to the Compton GRO came after the observatory's tape recorders failed, restricting transmission of scientific data to real time only. Since Compton was compatible with TDRS, this ground station option was feasible. An on-orbit repair of Compton GRO was an alternative, but would have been much more costly.

"While the new ground station is devoted to Compton at this time, it has the potential for use by other Earth-orbital spacecraft. The TDRS system was designed to operate with all the TDRS spacecraft in view of a single ground station. As a result, coverage could not be provided in a small region on Earth -- the so-called Zone of Exclusion over the Indian Ocean.

"With activation of this ground facility, the TDRS system can, for the first time, provide global coverage," said Charles Force, Associate Administrator, Office of Space Communications, NASA Headquarters, Washington, D.C.

Work on the station was completed in a relatively short time and within its $12 million budget. Work began in September 1992 to implement a remotely controlled terminal at an existing NASA site and was a cooperative effort between the Australian Space Office and NASA

"We're very pleased that this project came in on budget and on time and that we are able to collect additional significant data from Compton in a cost-effective manner," said Frank Stocklin, Head, Radio and Frequency Interface and Mission Analysis Section, Goddard Space Flight Center (GSFC), Greenbelt, Md.

With GRO tape recorders not working, the observatory had been able to relay only slightly more than half of the science data it collected, because it could not point at a TDRS at all times. While coverage had been about 65 percent of each orbit, scientists could not collect that percentage of data because Compton's instruments had to be turned off during the part of the orbit when the spacecraft passed through the background radiation caused by the South Atlantic Anomaly.

"That had represented a significant obstacle to the scientific teams, even though we have been able to collect more science than expected," said Goddard's Dr. Neil Gehrels, Compton Project Scientist. "Now with the ground station and the TDRS, we're back where we want to be."

With a TDRS devoted to Compton, scientists will be able to collect about 30 percent more science. In addition, engineers will be able to keep better tabs on the health of the $500-million observatory, launched from the Space Shuttle Atlantis (STS-37) on April 5, 1991.

"It's difficult to place a dollar value on the additional science data obtained in this effort," Stocklin said, "but the restoration of data recovery capability is similar to that done for the Hubble Space Telescope and marks the second successful recovery of a major NASA observatory."

TDRSs receive data from Earth-orbiting satellites and re- transmits the data to a ground terminal in White Sands, N.M. Data from the Compton will be relayed from TDRS-1 to Tidbinbilla to an Intelsat satellite to a West Coast location and then routed to White Sands. Data then will be distributed to scientists around the world. Control of TDRS-1 and this highly automated ground terminal remains at White Sands, N.M., marking the first time NASA is controlling an out-of-view TDRS from that location.

Launched in 1983, TDRS-1 was the first satellite in the TDRS system and was operating beyond the end of its design life of 8 years when it was moved over the Indian Ocean. TDRS-1 had been located at 171 degrees west longitude over the Pacific. It is now at 85 degrees east longitude, in view of the Tidbinbilla ground station.

"In its current use, TDRS-1's useful life may be extended to the end of the decade and perhaps beyond," Stocklin said.

Compton Gamma Ray Observatory (CGRO)

The Compton Gamma Ray Observatory (CGRO) was a space observatory detecting light from 20 KeV to 30 GeV in Earth orbit from 1991 to 2000. It featured four main telescopes in one spacecraft covering x-rays and gamma-rays, including various specialized sub-instruments and detectors. Following 14 years of effort, the observatory was launched from Space Shuttle Atlantis during STS-37 on 5 April 1991, and operated until its deorbit on 4 June 2000. It was deployed in low earth orbit at 450 km (280 mi) to avoid the Van Allen radiation belt. It was the heaviest astrophysical payload ever flown at that time at 17,000 kilograms (37,000 lb).

Costing $617m, the CGRO was part of NASA's Great Observatories series, along with the Hubble Space Telescope, the Chandra X-ray Observatory, and the Spitzer Space Telescope. It was the second of the NASA "Great Observatories" to be launched to space, following the Hubble Space Telescope. CGRO was named after Arthur Holly Compton (Washington University in St. Louis), Nobel prize winner, for work involved with gamma ray physics. CGRO was built by TRW (now Northrop Grumman Aerospace Systems) in Redondo Beach, California. CGRO was an international collaboration and additional contributions came from the European Space Agency and various Universities, as well as the U.S. Naval Research Laboratory.

Tracking and Data Relay Satellite (TDRS)

A Tracking and Data Relay Satellite (TDRS) is a type of communications satellite that forms part of the Tracking and Data Relay Satellite System (TDRSS) used by NASA and other United States government agencies for communications to and from independent "User Platforms" such as satellites, balloons, aircraft, and the International Space Station.

The TDRS system was designed to replace a pre-existing worldwide network of ground stations that had supported all of NASA's manned flight missions and unmanned satellites in low-Earth orbits. The primary system design goal was to increase the amount of time that these spacecraft were in communication with the ground and improve the amount of data that could be transferred. These TDRSS satellites are all designed and built to be launched to and function in geosynchronous orbit, 35,786 km (22,236 mi) above the surface of the Earth.

The first Tracking and Data Relay Satellite was launched in 1983 on the Space Shuttle Challenger's first flight, STS-6. The Boeing-built Inertial Upper Stage that was to take the satellite from Challenger's orbit to its ultimate geosynchronous orbit suffered a failure that caused it not to deliver the TDRS to the correct orbit. As a result, it was necessary to command the satellite to use its onboard rocket thrusters to move it into its correct orbit. This expenditure of fuel reduced its capability to remain in a geostationary orbit; by late 1997 the orbit had changed to the point that the satellite was able to see the South Pole, and an uplink/downlink station was installed at Amundsen-Scott South Pole Station in January 1998;[6] TDRS-1 was an important communication uplink for Antarctic research until 2009.

Decision to Go Ahead with a Ground System Solution

The Gamma Ray Observatory (GRO), launched in April 1991, was performing as designed until it became obvious in 1992 that both of its onboard tape recorders would fail, thereby reducing recovery of valuable science data to real-time only at a reduced data rate of 32 kbs (versus 512 kbs during playback). Under these conditions, only approximately 62-percent (worst case GRO attitude) of data could be recovered with the existing 2-TDRS constellation. In March 1992, the MO&DSD was requested to study approaches to solve this problem utilizing any combination of ground or space resources.

Link Analysis

By using the Communications Link Analysis Simulation System (CLASS), analyses were completed which quickly ruled out a ground station solution (i.e. high-cost with a relatively small increase in additional coverage) but indicated a TDRSS solution could produce a 33-percent increase in coverage - even under worst case GRO attitude conditions (i.e. 0-degree boom angle). To achieve this, a TDRS spacecraft would have to be moved and located somewhere over the Indian Ocean. Figure 1 depicts the percentage of coverage versus TDRS location in longitude degrees and is the result of a large number of computer runs to develop a reliable statistical result. Notice that using the two-TDRS solution at 174-degrees and 41 degrees west, approximately 62-percent coverage can be obtained.

Adding a third TDRS within view of the White Sands Ground Terminal (WSGT) produces an additional 6-percent of coverage. To obtain the maximum possible, an additional TDRS has to be located at approximately 80-degrees east longitude. This would produce in excess of 82-percent coverage which is a 33-percent increase relative to the 62-percent baseline (actually full 100 -percent coverage is possible depending on the attitude of GRO, which is science dependent, and also the blockage of the GRO high-gain antenna to TDRSS). Since these "optimum" locations were not in view of the WSGT control facility, the problem of locating this ground control facility had to be solved.

The Deep Space Network (DSN) sites at Madrid, Spain and Canberra, Australia were obviously the prime candidates. As can be seen from Figure 1, the Madrid and Canberra locations (to produce a 10-degrees elevation to the TDRS spacecraft) were not far from the "optimum" position. The Madrid solution suffered an approximate 2-percent penalty in coverage loss due to the South Atlantic Anomaly (SAA) effects on the GRO instruments (i.e. the instruments had to be turned off while flying through the SAA region). Other ground locations consistent with the maximum coverage point wee examined (e.g. east Africa) but were discounted primarily because they were not under direct NASA control.

The Australian solution was near the maximum geometric point, had a stable political and economic environment, and had a NÐSA-like culture/expertise. From a geometric viewpoint, the west coast of Australia and central areas were preferable. The east coast had a existing NASA facility at Canberra with the requisite infrastructure.

Decision to Co-locate GRTS at Canberra Deep Space Network Ground Station

A site survey team consisting of the Australian Space Office (ASO) and NASA visited five sites throughout Australia and considering various criteria such as existing infrastructure, accessibility to long-haul communications, transportation accessibility, etc., the site at the Canberra Deep Space Communications Complex (CDSCC) was recommended and selected.

The CDSCC location did have some negative geometric features. A lower than desirable elevation angle to the optimum TDRS location at 81-degrees east required a shift to the 82-degrees east location (a subsequent shift to 85-degrees east was necessary to accommodate the high inclination excursion of the F1 TDRS throughout the next 10 yeas). As can be seen from Figure 1, this shift did not significantly reduce the percent coverage. A second problem was related to the inability of the F1 to point its space-ground -link antenna far enough southward to cover CDSCC. After extensive analysis and testing, a 2-degree south roll bias solution was selected and the necessary software changes to the WSGT were initiated.

During the summer of 1992 implementation studies for the supporting ground terminal were completed. Because the "best science" would be obtained within the next few years, speed in implementation was a high priority. Limited and fixed funding dictated maximum use of existing design and equipment. Protection of an aging and somewhat sensitive F1 required redundancy in the implementation. Despite the fact that F1 is near the end of its design life of 10 years, its remaining functionality meets the specific needs for the GRTS application. The mandate to have minimal annual maintenance and operations costs required some form of automation. With these requirements, the GRTS Project was started on September 1, 1992. A 13-month schedule to completion, a $12.1M million fixed budget, and a 10-year lifetime wee the primary programmatic constraints.

Design Concept for GRTS Station

The GRO spacecraft radiates 32 kbs data to the F1 located at 85-degrees east longitude (this is in addition to support from the nominal two TDRSs). F1 receives the data using either the Multiple Access (MA) of Single Access (SA) capability. The data is transmitted to the Australian terminal called the Remote Ground Terminal (RGRT). Using dual 64 kbs Nascom lines, the data is sent to the WSGT, specifically to the GRTS dedicated Extended TDRS Ground Terminal (ETGT), and then to the GRO data processing center at GSFC. Telemetry, Tracking, and Command (TT&C) for the F1 flow from/to the ETGT continuously, also through the 64 kbs lines. The satellite controllers at WSGT are in complete control of the F1 spacecraft as well as the RGRT. The Network Control Canter (NCC) at GSFC has overall scheduling and management control. The GSFC Flight Dynamics Facility (FDF) performs its usual tracking and orbit determination function.

The node at RGRT contains the antennas, receivers, transmitters, and associated computer controls. Much of the equipment was placed in the existing DSS-46 building. To ensure minimal impact to ongoing operations at CDSCC, all of the RGRT equipment was placed in special RFI-tight racks. The high-powered transmitters were placed in newly constructed buildings, one S-Band and a separate K-band, to minimize self and external interference. Special attention was paid to the grounding process to preclude ground loops and possible impact to ongoing operations. The RGRT antennas were located so as to minimize impact to any current or future place at the CDSCC. A required MA calibrator, which radiates at 2287.5 MHz, was moved to a remote location approximately 2 km from the prime site and behind a hill to minimize interference to any sensitive (i.e. low-signal level) operations at CDSCC. All of the construction was performed by the CDSCC in 4 months. This consisted of two antenna pads in difficult terrain, two new S-band/K-band transmitter buildings, extensive cable trays and grounding, and a 2 km fiber cable run to the remote calibrator site - truly an amazing effort in that amount of time.

The other major node at ETGT contains all of the command and telemetry processing and unique software for the F1, the spacecraft controller personnel, and the interfaces to the GSFC for GRO data, the NCC, and the FDF. As with the other TDRS spacecraft, complete control still exists at ETGT. The uniqueness here is that it is a remote control operation of an out-of-view TDRS. The entire GRTS is connected by redundant Nascom 64 kbs lines from/to CDSCC to ETGT. Through these lines flow 8 kbs digital voice, TDRS telemetry and command data, e-mail, RGRT status, and GRO 32 kbs data. Automatic failover to a single 64 kbs lines in case of failure of one line is included.

Automated System to Minimize Staffing

To achieve the minimal operations staffing requirement, a distributed computer system, namely, the Operations Monitor and Control System (OMCS) was implemented. This consists of identical workstations at each of the primary nodes, (RGRT, ETGT and NCC), at which complete status and control of the RGRT can be exercised. That is, an operator at ETGT has complete knowledge of all RGRT equipment and can effect failover to redundant chains if necessary. RGRT maintenance is performed by two CDSCC engineers on prime shift (exigencies at other times are handled by call-in or other CDSCC personnel). Currently, there is a single round-the-clock operator at CDSCC. The OMCS consists of an existing Current off-the-shelf (COTS) software shell with customized interfaces to each of the GRTS components. A series of window-like screens with mouse selection allows visibility and selectivity to any part of the RGRT from any of the nodes. The net result is a remote controlled automated site that can control an out-of-view F1 with minimal staffing.

Project Management Strategy

To achieve the very ambitious schedule constraint, maximum use of existing equipment was incorporated into the RGRT design. Essentially, all of the TT&C equipment was obtained from existing resources at GSFC. Redundancy in design was used throughout the GRTS to the extent that it was feasible and practical. Additionally, the TT&C equipment was identical to the existing equipment at CDSCC so that the training, repair, and logistics were already basically in pace. Mux/Demux units at either end of the Nascom lines were current COTS equipment each with automatic failover capability built in. The command validation units were a NASA in-house design and were customized for the TDRSS command signal structure. To receive and demodulate the GRO 32 kbs MA and SSA signals, a receiver developed from the TDRSS user RF Test Set (TURFTS) was used. It required modification to interface with the MA equipment and also some threshold extension to work at lower signal levels. Maximum use of existing Second TDRSS Ground Terminal (STGT) designs was made. The entire MA system and some additional RF components were brought from the same vendors. All of the remaining hardware, including the 10M S-band antenna and the 4.6M K-band antenna were procured externally using COTS designs.

The procurement strategy and process was very critical in attempting to meet the imposed schedule. The Raytheon Service Company (RSC) was used as the procurement agent for NASA. Technical support was provided by the AlliedSignal Technical Services Corporation. (ATSC) and NASA. The entire procurement process including specifications, solicitation, and negotiation was completed by January 1993. The 120-day delivery (or less) requirements was imposed on most vendors (except the MA) and the critical long-lead components were incentivized to ensure on-time delivery. Overall, this was a successful strategy. In the specific case of the MA equipment, it produced an early delivery which enabled the GRTS MA capability to be available 2 months ahead of the scheduled date. This was extremely significant in that it allowed testing of the MA capability prior to the F1 drift (drift is the moving of the F1 spacecraft from its nominal 171 degrees west location to the new 85 degrees east location). The 73-day trip started on November 29, 1993 and completed on February 9, 1994 and allowed GRTS to provide MA support to the GRO starting in late November and throughout the 73-day F1 drift. Monthly meetings between GRTS team and each of the more critical vendors allowed early detection/correction of schedule and technical problems. Numerous telecons were also helpful to work not only technical issues, but to make each vendor a part of the GRTS team. There were multiple occasions where this team relationship helped resolve thorny technical interface problems.

To further support the aggressive schedule, a transportation strategy was developed by RSC which had a goal of 169 hours of transit time from the vendor's dock to CDSCC. This goal was achieved for about 95-percent of the 434 pieces/53 tons of equipment shipped with essentially no damage except a 20-cent switch. This logistical success was primarily due to excellent RSC planning and coordination with ATSC and CDSCC.

Integration and Test

Another critical decision was made to meet the schedule and that was to perform the Integration and Test (I&T) totally at the CDSCC (versus doing it at GSFC). This had the potential of saving 3-4 months of schedule but it had high risk because of the geographic distance from GSFC and the various vendors. This was mitigated by increasing the skill and staffing of the integration team from GSFC and WSGT, having specific vendor support travel to CDSCC, and by the excellent CDSCC resident expertise. As problems arose during the I&T process, expert were brought in for resolution. Overall assessment of this remote I&T approach is judged as a definite success although somewhat stressful. Figure 3 shows the integration team at work assembling the 20M S-band antenna. Figure 4 shows the completed K- and S-band antennas and the associated transmitter buildings.

Since the MA equipment was a clone of the STGT MA equipment, the original plan was to bring the GRTS MA equipment through STGT for final testing prior to shipping to CDSCC. This was the minimum risk approach but would have incurred an approximate 1-2 month schedule cost. Because we had previously run interface tests with the TURFTS receivers, and also had very successful acceptance tests on the MA equipment, the decision was made to ship directly to CDSCC with a staff of both GRTS and STGT personnel. Within a 2-week period after the MA equipment was on site, the first successful MA contact occurred-albeit a short 5-minute pass on October 5-but very significant because it would enable MA support to GRO during the entire drift period; the first operational MA contact occurred on December 6, 1993.

Training

Training of both the RGRT and ETGT operators and maintenance engineers was achieved by a combination of classroom presentations and their participation in the integration and testing process. By the time of drift in late November 1993, everyone was sufficiently trained to enable operational support to begin successfully. Extensive use of the NCC workstation allowed testing and software development/correction to be done in an extremely efficient manner in that all three nodes (RGRT, NCC, and ETGT) could participate in real time as testing progressed and minor software corrections could be made from the NCC and downloaded to their other node workstations. Major software updates used Internet from ATSC Columbia to CDSCC- a major benefit because the speed of transmission allowed new software to be infused daily as necessary.

Results of the Project

As of the date of this writing, F1 is on station at 85-degrees east longitude and GRTS is supplying approximately 20 contacts/day for a 17-percent absolute increase (relative to the 2-TDRS support, this is equivalent to a 28-percent relative increase). In addition to this success, the GRTS effort allowed the useful life extension of both F1 TDRS (launched in 1983 at a cost of $100 million and designed for a 10-year lifetime) and the GRO (launched in April 1991 at a $500 million cost with a potential 10-year lifetime) - a very significant return for a $12.1 million investment. The potential also exists to provide support to other missions as well as a useful location for future aging but still functional TDRS spacecraft. GRTS has demonstrated the concept of remote controlled automated ground stations and can be the prototype of other future designs. On the science side, hopefully, GRTS has a "black-hole" in its future.

Subcontractor Management

The success of the GRTS Project was due in no small part to the cooperation, dedication, and personal sacrifice of the many team members. The GRTS team was a group of individuals with significant specific skills that blended together with a single purpose - regardless of company affiliations and sometimes personal preference - to achieve a single purpose - namely, to make GRTS work and complete it on time and within budget. Each individual will be recognized in a forthcoming NASA award ceremony. A list of the corporate names from which these individuals came is as follows: Aerospace Engineering and Research Associates (AERA), AlliedSignal Technical Services Corporation (ATSC), Canberra Deep Space Communications Complex (CDSCC), Fred Herold and Associates (FHA), Government Systems Corporation (GTE), NASA/Jet Propulsion Laboratory, Loral AeroSys, NASA/Goddard Space Flight Center, RMS Technologies, Inc., Raytheon Service Company (RSC), Stanford Telecommunications (STel), TRW, UNISYS Corporation.

1995: Antarctic TDRS Ground Terminal

The Antarctic TDRS Project
Helicopters at McMurdo Base
Relay Station at Black Island
AlliedSignal Engineers at Black Island

The GRTS Project to install a TDRS Ground Terminal in Canberra, Australia was successfully completed on schedule and on budget. I was asked to form the Project Engineering Group to provide NASA, NOAA, the National Science Foundation, and other customers with Ground Terminal design and installation. Within six months we had 50 engineers working on a dozen projects including the Bermuda Radar Project, MILA/Bermuda Ground Station Re-engineering, the Shuttle Foward Link project, the X-Band sysem for JPL, FAISAT Digital Radios, LANDSAT Ground Station Design and Installation, and the LEO-T Automated Ground Station. But our first project was a continuation of GRTS to install a TDRS Ground Terminal at McMurdo Base in Antarctica. I selected Kevin Culin as the lead engineer on the project.

Introduction

ATSC engineers gear up for a trip to the coldest place on earth

Antarctica. . . it has the coldest climate of any continent, it is covered by 90 percent of the world's ice, and it has the strongest sustained westerly winds on Earth. Even so, Antarctica sounds downright inviting to a handful of engineers and technicians from the Engineering Department in Columbia, Md run by Jim Conrad.

Later this year, these brave and dedicated ATSC employees will take off for NASA's McMurdo ground station on Ross Island, Antarctica. Their mission is to stay warm while installing a Tracking and Data Relay Satellite (TDRS) system, which will enable the transfer of stored data from McMurdo to the White Sands Ground Terminal in New Mexico.

TDRS Spacecraft

The four TDRS satellites are the most sophisticated communications satellites in orbit today. They, along with the various ground terminals scattered around the world, provide a continuous communications and tracking system for the space shuttle, the Hubble Space Telescope, and other orbiting satellites. ATSC already manages, operates, and maintains the network, linking and controlling the TDRS satellites with Earth resources and users. Now, thanks to ATSC, the 40-year-old McMurdo ground station will be upgraded with the capability to use the TDRS satellites for data transfer.

"The TDRS satellites are in a geosynchronous orbit, which means they orbit parallel to the equator," explained Hugh Pickens, ATSC manager of the Project Engineering Group. "Since Antarctica is at the bottom of the world, it is extremely difficult for the McMurdo station to see the satellites through the troposphere since the TDRS satellites rise only a few degrees above the horizon," he added.

"Three years ago, NASA personnel went to McMurdo and proved that the TDRS satellites could be seen from there. This was the first step in a long line of events that eventually resulted in the National Science Foundation and NASA tasking ATSC to go to Antarctica," said Kevin Culin, ATSC McMurdo program manager.

Design of McMurdo TDRS System

Culin explained that ATSC's first job was to come up with a design for the new system. Then, during a six- to ten-week stay at McMurdo, ATSC engineers will install and upgrade the equipment. When the work is done, the new components will not only collect the data, but will provide a way of getting the data out of Antarctica.

"Currently, McMurdo gathers the data from orbiting satellites and stores them onto imaging tapes. Then, once per year, the tapes are loaded in limited quantities onto tankers or planes and shipped out. This is not an easy task. Strong winds, thick ice, and the distance make traveling to and from Antarctica difficult," Culin added.

With the upgrades to McMurdo, the tapes will be played through the new system, which will send the data directly to TDRS and on to White Sands. The data collection and dissemination that used to take a year will take approximately 48 hours. The new parts are also sturdy, hardy, and need only a limited power supply.

Installation

"An Antarctic winter can be very unpleasant," said Culin. "If something breaks, depending on the time of year, it could be months before it is fixed."

Redundancy has been incorporated into certain aspects of the new system to help eliminate down times at the station due to faulty equipment. Culin explained that the equipment must also run effectively and efficiently on wind generators and solar arrays. Fortunately, plans are currently in the works to upgrade to diesel generators. These will prevent the shut-down times that are occasionally necessary due to the weather problems.

"Much of our work will be done in the shelters," said Culin. "This is fortunate for us because during the time we are there, we will be experiencing a few days of total darkness and an average temperature of 0°F."

Culin explained that some of the equipment already at McMurdo will continue to be used with the new equipment. ATSC engineers will modify the existing antenna, repair the drive mechanism, and install the various signal and power cabling necessary for the equipment to be operational.

The ATSC engineers will be traveling back and forth between Ross Island, where the McMurdo station is located, to the uninhabited Black Island (the two are 22 miles apart). Neither site is ideal for viewing TDRS. On Black Island, Mt Erebus, a semi-active volcano, impedes visibility of both islands. The volcano is physically in the way of McMurdo seeing TDRS and obstructs visibility at Black Island with its constant spewing of dust. The trips back and forth are necessary in order to install microwave relays that will provide McMurdo a clear line of site to TDRS.

In striking contrast to Ross Island's ice, Black Island receives very little precipitation and has a climate more akin to a cold desert. Needless to say, the ATSC engineers and technicians going to Antarctica must be prepared. Culin said that each person must have a physical and dental exam before arriving at McMurdo. Medical facilities at the station are very limited and there are no dentists. The group must also attend three days of cold-weather survival training in New Zealand, which is the first stop on their trip to Antarctica.

Preperation for the Antarctic

"In addition to survival training, we will be briefed on how to conduct ourselves in Antarctica once we arrive," said Culin. "For example, we must be very careful not to disturb the seals, penguins, or other wildlife. In fact, vegetation in Antarctica, such as moss banks, are protected and we must take care not to step on anything. In addition, we must not disturb marked sites while we are wandering around, since many scientific experiments are being conducted in this area," he added.

After obtaining clean bills of health, survival and "etiquette" training, and their gear (each person is allowed to take 75 pounds of baggage with them; parkas, boots, and other warm clothing could weight as much as 40 pounds), the engineers will board a cargo plane to begin their ten-hour flight to Antarctica. Culin was told that the headwinds are so strong that the plane could run out of fuel while going against them and be forced to turn back.

"If this happens, we will just wait for another day!" said Culin.

When the plane finally arrives at McMurdo, it will land using snow skis on the permanent ice runway at Williams Field. A bus will then take them to the station. By this time, the equipment should have already arrived and the group will begin the long and painstaking task of installing and testing the station's new components. When their jobs are done, the ATSC engineers come home, leaving the equipment to be remotely operated from White Sands.

Autonomous Station

"This aspect is what makes McMurdo more challenging than other ground station projects ATSC has completed," said Pickens. "Unlike MILA in Florida, the Bermuda tracking station, or STGT at White Sands, PEG's two TDRS ground terminals, GRTS and McMurdo, are both unmanned. However, unlike GRTS, the station at Black Island will be totally inaccessible during much of the year so it must be totally autonomous and reliable, with remote control design elements not totally unlike those of an autonomous spacecraft."

Sure, the trip means time away from home and a lot of hard work. But Culin said he is looking forward to it as an adventure.

The Challenge

Systems Integration, and Project Management, the challenge of designing, building, and installing Ground Stations such as McMurdo are challenges that PEG Engineers and Project Managers like Kevin accept," added Pickens.

"We will be sleeping on bunks in one large dorm-like room," Culin said. "We have also been told that our food and water will be limited since supplies are shipped to McMurdo only occasionally. I know when people read this story, they will probably pity us! But I think we are very lucky. We are not only assisting NASA and the National Science Foundation with a very worthwhile project, but the trip will also give us the unique opportunity to explore the wonders of one of the most remote areas of the world," he added.

"If ATSC expects to become a Center of Excellence for systems engineering, systems integration, and project management, the challenge of designing, building, and installing Ground Stations such as McMurdo, AGNS, Landsat, and GRTS," added Pickens. "These are challenges that PEG Engineers like Kevin Culin, Peter Miitch, Joe Valvano, and Ed Richards accept."

1998: NOAA Fairbanks Autonomous Ground Station

In 1998, AlliedSignal Technical Services (ATSC) installed three fully autonomous 13-meter satellite tracking systems for the Integrated Program Office of the National Oceanic and Atmospheric Administration (NOAA) at the Command and Data Acquisition Station near Fairbanks, Alaska. These systems track and command NOAA Polar Orbiting Weather Satellites and Defense Meteorological Satellites and download weather data from them. These systems are huge. Blow up the photo by clicking on it and note the scale by looking at the pickup truck next to the antenna on the left.
Exhibit 1. Sample Ground Station Automation Display
Exhibit 2. Scrollable Event Log
Exhibit 3. Antenna Control Interface
Exhibit 4. STOL Procedure
Exhibit 5. Pass Selection Window
Peter Militch was the lead engineer on the NOAA Fairbanks Autonomous Ground Station shown here debugging the Ground Terminal Automation software on site.

Technical Paper presented at the International Telemetering Conference in 1999

by Hugh Pickens, Peter Militch, and Mike Anderson

Abstract

In 1998, AlliedSignal Technical Services (ATSC) installed three fully autonomous 13-meter satellite tracking systems for the Integrated Program Office of the National Oceanic and Atmospheric Administration (NOAA) at the Command and Data Acquisition Station near Fairbanks, Alaska. These systems track and command NOAA Polar Orbiting Weather Satellites and Defense Meteorological Satellites and download weather data from them.

Each tracking system operates for extended periods of time with little intervention other than periodic scheduling contacts. Schedule execution initiates equipment configuration, including establishing the RF communications link to the satellite. Station autonomy is achieved through use of a robust scheduler that permits remote users and the System Administrator to request pass activities for any of the supported missions. Spacecraft in the mission set are scheduled for normal operations according to the priority they have been assigned. Once the scheduler resolves conflicts, it builds a human-readable control script that executes all required support activities. Pass adds or deletes generate new schedule scripts and can be performed in seconds.

The systems can be configured to support CCSDS and TDM telemetry processing, but the units installed at Fairbanks required only telemetry and command through-put capabilities. Received telemetry data is buffered on disk-storage for immediate, post-pass playback, and also on tape for long-term archiving purposes. The system can autonomously support up to 20 spacecraft with 5 different configuration setups each. L-Band, S-Band and X-Band frequencies are supported.

Key Words

Satellite tracking station, satellite ground station, satellite ground system, satellite ground terminal, ground segment, spacecraft commanding, autonomous, monitor and control, scheduling

System Overview

Each system includes a 13-meter elevation over azimuth antenna with a 7 degree tilt and dual polarization auto-tracking feeds. .The G/T is 19 dB/ÆK at L-Band, 23 dB/K at S-Band and 34 dB/ÆK at X-Band. Transmitter EIRP is 68 dBW. The system supports a 1750 to 2120 MHz uplink band. The receive bands are 1670 to 1710 MHz, 2200 to 2400 MHz and 7.6 to 8.4 Ghz. The L/S-Band RF subsystem employs a polarization diversity feed with optimal ratio combining and supports FM, PM, BPSK and QPSK modulation types with up to 5 MBps data rates. The X-Band feed provides switchable polarization selection and sufficient bandwidth to accommodate current and future high-rate, remote sensing satellites.

Communications links between the antenna and the operations building for the L-Band, S-Band and X-Band signals, command and command verification data, equipment monitor and control, and timing signals are over a fiber optic link.

Each system includes five strings of dual receivers and diversity combiners for L/S-Band signal processing. The receivers are configured with dual band tuners to cover the required L and S-Band frequency ranges. Diversity combiners assure excellent performance for all combinations of RHCP, LHCP or linear signal conditions. Discrete bit synchronizers are provided, permitting operations personnel to rapidly configure the complete receive processing subsystem manually should the need arise. A failure of any receiver or bit synchronizer can be easily remedied by substituting a spare unit.

Dual tracking receivers are located in the antenna pedestal. Two receivers provide the required auto-tracking performance for all receive signal conditions. These receivers are Datron Universal Track Receivers.. L/S-Band transmit capability is provided by a solid state transmitter, offering high reliability and simplicity of operations.

The command verification subsystem consists of a directional coupler at the output of the transmitter to sample any transmitted signals. The sampled signal is mixed down to 230 MHz at the antenna. This signal is received and demodulated by a VME form-factor receiver for return to the operations building. A signal generator is used as an exciter for both L-Band and S-Band operations. The generator includes a built-in PRN generator for system loop-back performance testing.

A digital recorder simultaneously records data from all five receive channels. Both tape and disk storage is used. The disk allows rapid queuing of data for playback in either the forward or reverse direction. Real-time and playback telemetry, and real-time commands, are routed to and from the individual systems automatically under schedule control.

The central feature of this system is that all the equipment described above is monitored and controlled from a low-cost, high performance workstation. This workstation and the ground station automation software it executes provide for both local or remote monitor and control capability, and for fully automated antenna operations. The remainder of this paper explains what the ground station automation software does and how it works.

Ground Station Automation Overview

The monitor and control package used to automate the ground station is the Epoch 2000 COTS software package from Integral Systems. The software provides all required ground equipment monitor and control capabilities. All configuration data is managed in an Oracle ground station automation data base.

The data base allows the ground station to be configured for new satellites and new missions without extensive software modifications. The station automation software runs on a Unix Administrative Workstation. The workstation is a Pentium PC running at 200 MHz, with 128 Mbytes of memory, 2 Gbytes of hard disk storage, plus keyboard, mouse, and a 20" color monitor.

Manual Control Mode

Manual control mode provides complete local monitor and control capabilities through a graphical user interface shown in Exhibit 1. All of the hardware reconfiguration capabilities which can be accomplished via equipment front panel switches can be accomplished directly at the Administrative Workstation, providing a central point of management for the entire system. There are several different mechanisms for reconfiguring the hardware using the ground station automation software directives. First of all, control directives can be manually typed in directly on the user input line which appears in the header of every display page on the workstation.

Exhibit 1 shows theSample Ground Station Automation Display.

In general, for every equipment control state and system configuration option there is a corresponding control directive. A directive is simply an ASCII keyword which tells the system how to reconfigure a given item of equipment. The control directive definitions and configuration options are defined through the ground station automation database utility, which is bundled with the standard automation software package. This allows new hardware and new configurations to be added with a minimum of software impact.

The ground station automation software provides an input line for control directives, as well as tabular and graphical displays for monitoring station status and the station event log. Directives may also be issued via user-programmable function keys and user-definable "hot" buttons, reducing the typing required to a single keystroke or mouse click. Directives may also be issued by dragging the mouse through a series of hierarchical menus organized by system and subsystem.

On input, the ground station automation software checks each directive for proper syntax, keyword, and arguments. The directive is then decoded and issued to the hardware for execution .

As each directive is input and processed, the software writes it into the station log. The station log contains a time-sequential list of all significant station activity, including hardware equipment configuration changes, operational mode changes, system status and event messages, and alarm/event messages. Each log entry is stamped with station time (as received via the time code reader in the Admin Workstation) and message source (e.g., hardware component, software process). The user interface (see below) supplies a view window into the station log which can be scrolled backwards and forwards in time, providing the operators with complete visibility into all of the significant station activities. Exhibit 2 provides a sample display.

Exhibit 2 shows the Scrollable Event Log.

All of the equipment status information, as well as the configuration of the software itself, may be monitored and controlled via the ground station automation software on the Administrative Workstation. The M&C user interface provides full adherence to OSF Motif open systems standards. Our interface follows industry standard design principles to ensure ease of use.

The equipment status parameters themselves can be displayed in a variety of formats, including ASCII text, graphs, polar plots, bar charts, and gauges. A set of pre-defined display pages is available to users, and users can easily define their own custom pages. Exhibit 3 provides a sample display for manual antenna control and monitoring.

Exhibit 3 shows the Antenna Control Interface.

The Administrative Workstation supports multiple simultaneous local and remote login's via the SUN Solaris operating system and X-Windows so that multiple workstations can be used to support operations, both locally at the Fairbanks site and remotely at SOCC and/or other sites. Each login is a separate X client, running its own copy of the X-Windows Administrative Interface.

Local Automated Mode

The ground station automation software provides a built-in procedure language which can provide fully automatic local operations. In Local Automated Mode, the system operation is conceptually the same as in Local Manual Mode, with the addition of one key element: STOL (System Test And Operations Language). STOL is an interpreted procedure language hat supports features such as: procedure flow control such as DO-WHILE, IF-THEN-ELSE, and GOTO, calls to other STOL procedures, directives to the automation software processes, including directives to configure ground equipment, directives to send spacecraft commands, arithmetic, logical, and string expressions, calls to built-in functions, calls to execute UNIX scripts or start software processes, relative and absolute time tags. Exhibit 4 provides a sample STOL procedure. This high-level language allows automation of all Fairbanks hardware and software configuration operations.

Exhibit 4 shows the STOL Procedure.

STOL is an existing component of the ground station automation software package. Fully automatic local operations are provided simply by writing procedures for each of the routine operational activities, such as pre-pass setup, real-time pass processing, post-pass termination, and offline troubleshooting/diagnostics. The appropriate procedure may then be invoked by typing in its name, selecting it from a menu list, pressing a designated function key, or clicking on a hot button.

Remote Automated Mode

The automated ground station provides a complete, built-in scheduling system which supports fully-automated operations from a remote site (e.g., SOCC). Key features of the scheduling system include: automatic allocation of antenna coverage across multiple missions, automatic conflict resolution, automatic pre-pass, pass, and post-pass reconfiguration according to pre-defined database specifications, automatic ingest and propagation of orbital elements and automatic generation and selection of candidate passes for coverage. The scheduler supports up to 20 different simultaneous missions (satellites), each with up to 5 different pre-defined configuration options for support requirements.

There are two basic inputs into the scheduling process: Orbital elements and pass coverage requests. The orbital elements can be hand entered in any of approximately one dozen different coordinate systems including both the NORAD standard used by DMSP and the NASA IIRV standard used by NOAA. The system can also be configured to automatically ingest NORAD or IIRV types from a remote server. The input frequency, propagation interval, remote server domain name, and pathname for the element files are user-reconfigurable via the database.

The retrieved elements are then be propagated automatically to determine the contact information (e.g., start time, stop time, max el, etc.) for all possible passes for each mission supported. This propagation is performed by OASYS (Orbit Analysis System), which is a COTS package for general orbit support provided by Integral Systems. The orbital analysis software provides a full spectrum of orbit analysis capabilities, including: orbit determination, high-fidelity numerical orbit propagation, NORAD SGP-4 semi-analytic orbit propagation, generation of satellite and station geometry reports (e.g., position, velocity, subpoint, range, Doppler, etc.), generation of satellite and station event reports (e.g., AOS, LOS) and orbit maneuver planning

The outputs from the orbital analysis software processing consist of sets of tracking elements for each satellite mission defined in the database. These are automatically downloaded to the antenna controller during the pre-pass configuration processing at the start of each pass. This guarantees that the antenna controller always has the freshest elements available for antenna pre-positioning and open loop track operations.

Exhibit 5 shows the Pass Selection Window.

The orbital analysis software also outputs a complete set of candidate pass parameters for all of the supported satellites. This information is used to drive the Pass Selection window, which is the mechanism for getting the other primary input to the scheduling process; namely, the user's pass coverage requests. The Pass Selection window shown in Exhibit 5 is accessible locally at the Admin Workstation or remotely (e.g., at SOCC) via X-Windows. It lists all of the potential passes for all the satellite missions defined in the data base in chronological order, along with the predicted time of Acquisition of Signal (AOS), Loss of Signal (LOS), and maximum elevation.

The software allows the user to request coverage for single or multiple passes with a click of the mouse. To request coverage, the user simply highlights the desired contacts with the mouse and clicks the "Submit" button. Schedule requests are then automatically generated for those passes and satellites. The user may optionally specify one of up to 5 pre-defined pass configurations for each satellite's passes for non-nominal or special coverage requests; else, the default configuration for each satellite is used automatically.

Schedule requests are nominally submitted over a 7 day cycle (the cycle is reconfigurable via the database). Multiple requests may be submitted at essentially any point in the cycle. Then, at a user-configurable time interval (default 7 days), the software automatically invokes the schedule generation process. This process first builds a timeline of requested passes. The process input consists of all schedule requests, schedule related database parameters, and the satellite orbital information prepared by the orbital analysis software.

Each of up to 20 satellites has a unique priority, as assigned by the ground station administrator in the database. Conflict resolution is then performed on the requests in a strict-priority basis - that is, the highest priority satellite gets all of its pass requests, followed by the next highest, and so on. The end result is a conflict-free set of passes for all the satellites which can be accommodated given the current contact geometry.

Schedule Execution

Once conflict resolution has been performed, two output files are created: a Schedule Summary File and a Weekly Schedule File. The Schedule Summary File is a concise ASCII description of the weekly schedule, listing all passes and their associated parameters. The Weekly Schedule is also an ASCII file containing STOL-compatible constructs which can be executed directly by the ground station automation software. This file contains everything necessary to execute automatically for an entire week, including calls to a standard library of STOL procedures. The procedure library encapsulates frequently performed functions, e.g., standard ground equipment setup, pre-pass configuration sequences, etc. Most of the weekly schedule directives are calls to procedures in the STOL procedure library - the same STOL library procedures used in the Local Automated Mode described previously. Thus, the weekly schedule is more concerned with 'what to do', leaving the 'how' to procedures in the library. This allows implementation details of a particular function, e.g., pre-pass setup, to be encapsulated within a procedure. Any changes to how that function should be performed can then be made in the procedure, without affecting the rest of the system.

Upon completion the new schedule is logically appended to the old schedule, ensuring continuous operations with no gaps at the overlaps (the append is "logical" rather than physical to keep the cumulative schedule file from growing arbitrarily large). Once the schedule is created, it may be inspected through a dedicated schedule display window (either locally or remotely via X-Windows). The schedule window also allows authorized users to manually modify the schedule in several ways, including: addition of new passes in the gaps between the scheduled passes, cancellation of a scheduled pass and modification of pass parameters (start and stop times, specified database configuration). These capabilities are provided to support non-routine operations and anomalies and are not necessary in normal automated operations.

Schedule execution is normally be continuous and automatic, requiring no operator intervention. The system transitions autonomously between satellites and passes. A typical pass scenario is as follows (all times and events are reconfigurable):

At two minutes prior to the start of a pass, the weekly schedule issues directives to bring up a new stream configured for that pass. As part of this operation, a database flat file is read into memory that contains all parameter values for the spacecraft and selected configuration option. A new log file is also opened, which contains all events for the pass. At T-1 minute, a STOL procedure is invoked to point the antenna. Software invoked by this procedure makes use of the antenna mask parameters stored in the database, so that antenna elevation is maintained at or above the mask. The system then configures all of the equipment and the data communications paths per the database specification. If a database parameter indicates that uplink commanding is required, then at T-1 minute a STOL procedure turns on the transmitter and begin sweep acquisition which continues until spacecraft transponder lock is detected Once the satellite crosses the predicted elevation masking point, the Antenna Subsystem begins automatic tracking. At AOS, the system begins downlink archiving on the digital recorder. At LOS, the system ceases irradiating, terminates the recorder session, reconfigures the equipment to standby mode, and closes out the contact log. For emergency situations, the ground station automation software provides the system administrator with a method for suspending the current schedule, and running an unscheduled pass. This can be done through the standard user interface. Through this interface, an administrator can view schedule directives being executed, pause a schedule, bring up a new satellite database and reconfigure ground equipment, run part or all of other STOL procedures, enter directives manually at the keyboard, and resume a schedule at any point. Again, this can be accomplished either locally at the Admin Workstation or remotely via X-Windows.

References

  • European Space Agency. "European Weather Satellite Moves Closer to United States" February 24, 1993
  • Wikipedia. Gamma Ray Observatory. Retrieved February 14, 2014
  • Wikipedia. TDRS Spacecraft. Retrieved February 14, 2014
  • GRTS - The Experience of a Lifetime by Frank Stocklin. NASA. Goddard Space Flight Center. Code 530. 1994.
  • ATSC engineers gear up for a trip to the coldest place on earth. AlliedSignal Update. April, 1995.
  • NOAA Fairbanks Autonomous Ground Station by Hugh Pickens, Peter Militch, and Mike Anderson. Technical Paper presented at the International Telemetering Conference in 1999

About the Author

Hugh Pickens

Hugh Pickens (Po-Hi '67) is a physicist who has explored for oil in the Amazon jungle, crossed the empty quarter of Saudi Arabia, and built satellite control stations for Goddard Space Flight Center all over the world. Retired in 1999, Pickens and his wife moved from Baltimore back to his hometown of Ponca City, Oklahoma in 2005 where he cultivates his square foot garden, mows nine acres of lawn, writes about local history and photographs events at the Poncan Theatre and Ponca Playhouse.

Since 2001 Pickens has edited and published “Peace Corps Online,” serving over one million monthly pageviews. His other writing includes contributing over 1,500 stories to “Slashdot: News for Nerds,” and articles for Wikipedia, “Ponca City, We Love You”, and Peace Corps Worldwide.

Articles about Ponca City

Other Writing

Updates to the Web Site

This web page is frequently updated so check back periodically to see the latest information added to this article or subscribe to the rss feed for this article. If you have any information or insights that you would like to see added to this report please contact Hugh Pickens by email at hughpickens AT gmail DOT com.

Copyright

The material in this article is licensed under under the Creative Commons under an Attribution-Noncommercial-Share Alike 2.0 Generic license. Except for short, fair use excerpts, the material on this article cannot be used for commercial purposes without permission of Hugh Pickens. Attribution for use of any material from this article must be provided to Hugh Pickens and if used on the web a link must be provided to http://hughpickens.com.

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