GPS System Segments - Understanding GPS: Principles and Applications - page 88

The 2SOPS supports all crew-action required operations of the GPS constella-
tion, including daily uploading of navigation information to the satellites and moni-
toring, diagnosis, reconfiguration, and stationkeeping of all satellites in the GPS
constellation. Spacecraft prelaunch, launch, and insertion operations are performed
by a different ground control system under the command of the First Space Opera-
tions Squadron (1SOPS), also located at Schriever AFB. If a given SV is determined
to be incapable of normal operations, the satellite commanding is transferred to
1SOPS for anomaly resolution or test monitoring.

3.3.1 Current Configuration
At the time of this writing, the CS configuration consisted of dual MCSs, six monitor
stations, and four ground antennas (see Figure 3.15). The MCS data processing soft-
ware, hosted on an IBM mainframe under the Multiple Virtual Storage operating
system, commands and controls the CS with multiple high-definition textual dis-
plays. The monitor stations and ground antennas are unmanned and are operated
remotely from the active MCS. The monitor stations' and ground antennas' data
processing software, hosted on Sun workstations under the UNIX operating system,
communicate with the MCS using transmission control processing/Internet process-
ing (TCP/IP) communication protocols. The MCS also has numerous internal and
external communication links. The majority of these links use the IBM's System
Network Architecture communication protocol. There are plans to transition all of
these links to TCP/IP.
The CS configuration is in transition. Two major upgrades are in development:
the Legacy Accuracy Improvement Initiative (L-AII) and the Architecture Evolution
Plan (AEP). The L-AII upgrade adds up to 14 NGA monitor stations. Therefore,
there can be a total of 20 Air Force and NGA monitoring stations within the CS.
These additional NGA stations will provide the CS with continuous L-band tracking
coverage of the constellation. (The current six monitor station configuration can
have satellite L-band coverage outages of up to 2 hours.) The AEP upgrade replaces

Schriever

Cape Canaveral

Ascension

Kwajalien

Hawaii

Diego Garcia

Ground antenna (GA)

Monitor station (MS)

Figure 3.15 Geographic distribution of CS facilities.