GPS III satellites have been a promised evolution for GPS capabilities for almost a decade. Initially planned for a 2014 debut, GPS III satellites are currently scheduled to launch in December. Last month, Lockheed Martin's second GPS III satellite, the GPS III SV02 (GPS III Space Vehicle 02), was shipped to Cape Canaveral in preparation for an expected 2019 launch. These are the final stages of a years-long effort to bring GPS III satellites into service.
But how will engineers on the ground manage these new satellites in space?
In 2010, Raytheon won a contract to develop the next generation of GPS control segment to enable more advanced satellite launches. In this article, we'll take a look at the current state of operational control and what Raytheon has developed to enable GPS III satellites to meet their full potential.
What Is a GPS Control Segment? An Intro to the OCS
The GPS control segment monitors, controls, and corrects the GPS satellite constellation.
The current GPS control segment, the Operational Control Segment (OCS) shown below, provides Command and Control (C2) capabilities for GPS Block II satellites.
GPS OCS system. Image courtesy of GPS.gov
Consisting of the Architecture Evolution Plan Operational Control System (AEP) to control operational satellites and the Launch/Early Orbit, Anomaly Resolution and Disposal Operations (LADO) to control non-operational satellites, OCS tracks satellite launch, provides initial testing once the satellites are in orbit, controls and moves the orbiting satellites in and out of position as needed and provides general maintenance of the satellite constellation. Orbits are tracked via a network of monitoring stations around the world. Commands and corrections are sent by four dedicated ground stations at Cape Canaveral, Ascension, Diego Garcia, and Kwajalein.
From the initial GPS satellite launch in the late 1990s, the OCS has gone through a number of upgrades to stay current with improving satellite functionality and to maintain and control the constellation. With the launch of GPS III satellites, the OCS is being replaced with Raytheon's Next-Generation Operational Control System, referred to as OCX.
OCS vs OCX
OCX will double the accuracy of the GPS Position, Navigation, and Timing (PNT) signal, upgrade security against cyber attacks, and increase the number of satellites that can be controlled.
Although the OCX is primarily a software development effort, new GPS receivers will be installed at the globally-distributed monitoring stations to monitor all GPS signals. All four ground antennas with uplink capabilities will be upgraded and hardened against cyber attacks. OCX is backward-compatible and will be able to integrate new capabilities and signals as they become available. OCX will also enable current GPS IIR-M and IIF satellites to reach full functionality.
GPS OCX System. Photo by US Air Force
GPS OCX Components
OCX consists of:
- The Master Control Station (MCS) at Schriever Air Force Base (AFB) in Colorado
- An alternate MCS at Vandenberg AFB in California
- Advanced monitor stations at remote sites around the world:
- 6 sites in the US Air Force Satellite Control Network (AFSCN) controlled by the 50th Space Wing
- 11 sites co-located at National Geospatial Intelligence Agency (NGA) sites including in England, Argentina, Ecuador, Bahrain, Australia, and Washington, DC.
- Upgraded legacy ground antennas located at Cape Canaveral, Ascension Island, Diego Garcia, and Kwajalein Atoll
Additionally, OCX will include:
- A GPS system simulator: For software development and testing ground assets
- A standardized space trainer: a dedicated operator training system
The OCX Program
OCX will provide all control segment support for GPS Block IIR, GPS Block IIR-M, GPS Block IIF and GPS Block III satellites. It has been in development since 2008 and will be delivered in three phases, or blocks.
Block 0, the Launch and Control System (LCS), includes a cyber-secure ground system, computing systems, operations center workstations, and mission application software. The LCS Launch and Early Orbit (LEO) operations supports the GPS III launch and initial testing once in orbit. Also included is a subset of the Block 1 functionality to provide some hardware, software and cybersecurity. Initially scheduled to be delivered in 2016, program delays resulted in LCS being delivered in the Fall of 2017, with the US Air Force accepting delivery in November 2017.
Block 1 provides support for both legacy and modernized satellites. The supported signals will include:
- Civil signals (L1 C/A),
- Military signals (L1P(Y), L2P(Y))
- Modernized civil signal (L2C) and
- Aviation safety-of-flight signal (L5).
Basic control will also be provided for modernized military M-code signals (L1M and L2M ), and the globally compatible signal (L1C). Block 1 is scheduled for delivery in 2021.
Block 2, will be delivered concurrently with Block 1 and includes advanced control for the international L1C signal as well as the modernized Military Code signals.
Raytheon rendering of a satellite. Image used courtesy of Raytheon.
Both OCS and OCX will operate until a fully functional OCX is delivered and takes control of the GPS constellation, currently scheduled for 2023. To make sure there are no gaps in support, the current OCS is being upgraded as a contingency plan so the modernized signals are supported until OCX is fully operational. Plans call for the OSC AEP to be updated with new software, with hardware upgrades for the worldwide GPS ground facilities.
The GPS III Contingency Ops (COps) will allow the OCS AEP to support orbiting GPS III satellites. With COps upgrades, OCS will be able to operate GPS III PNT and Nuclear Detonation Detection System (NDS) payloads as well as maintain limited test M-Code capability until OCX Block 1 is delivered. OCX Block 0 is still required for GPS III launch, major anomaly, and disposal capabilities. Besides controlling GPS III satellites, COps will also continue support for all the GPS IIR, IIR-M and IIF satellites in the legacy constellation.
The M-Code Early Use (MCEU) will accelerate M-code deployment to currently orbiting GPS IIR-M and GPS IIF satellites and the GPS III satellites. M-code is an advanced signal designed to improve security, anti-jamming and anti-spoofing for military GPS signals for U.S. and allied armed forces.
The new signals and security functions of the GPS III satellites require an upgraded ground control segment. When fully functional, the OCX will support all existing GPS II and GPS III satellites in the GPS constellation.
You can see one of Raytheon's promotional video on the OCX program below: