The System: Ground Control Readied for GPS III

October 1, 2013  - By 0 Comments

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Raytheon Company reached several milestones recently in its development of the GPS Next -Generation Operational Control System (GPS OCX). Lockheed Martin’s GPS III Non-flight Satellite Testbed (GNST) — a full-sized, functional satellite prototype currently residing at Cape Canaveral Air Force Station — successfully established remote connectivity and communicated with OCX during pre-flight tests.

GNST proved that it could connect with and receive commands from Raytheon’s Launch and Check Out System (LCS), a part of OCX that supports the satellite and mitigates risks prior to launch. The GNST received commands from Lockheed Martin’s Launch and Checkout Capability (LCC) node in Newtown, Pennsylvania via the OCX servers at Raytheon’s facility in Aurora, Colorado; the system then returned satellite telemetry to the control station. The tests mirror launch and early orbit testing planned for all flight vehicles.

“While we have connected OCX with ground-based simulators before, these tests were the first time that OCX and a GPS III satellite have actually communicated,” said Keoki Jackson, vice president for Lockheed Martin’s Navigation Systems mission area.

Ahead of Schedule. Raytheon received Interim Authorization to Test (IATT) security certification from the U.S. Air Force for OCX LCS four months ahead of schedule. The company received a one-year certification with no liens, meaning the government does not require any changes.

“Typically, IATT certification is given for six-month increments,” said Matthew Gilligan, Raytheon’s GPS OCX program manager and a vice president in Raytheon’s Intelligence, Information, and Services business. “The LCS one-year accreditation speaks to the quality of the information assurance design and threat protection.” The IATT not only includes the LCS, but also Lockheed Martin’s GPS III satellite support systems, Exercise and Rehearsal Training Tool, and Upload Generation Tool.

OCX is being developed in two blocks. There are seven iterations in Block 1 and one in Block 2. LCS is the fifth Iteration of Block 1; it successfully completed Critical Design Review in June 2013.

Early Orbit Exercises. Lockheed Martin and Raytheon also completed the third of five planned launch and early orbit exercises to demonstrate launch readiness of GPS III and OCX.

Exercise 3 demonstrated space-ground communications; first acquisition and transfer orbit sequences; orbit-raising maneuver planning and execution; and basic anomaly detection and resolution capabilities. In addition, the industry and Air Force GPS Directorate teams jointly executed mission planning activities, such as orbit determination and the generation of upload command files.

Two additional readiness exercises and six 24/7 launch rehearsals are planned before launch of the first GPS III satellite. The first flight GPS III space vehicle (SV-01) is expected to be available for launch in 2014, and launched by the U.S. Air Force in 2015.

Exelis Encryptors. Exelis delivered the first three of a planned 14 ground-based encryptors to Raytheon Company for OCX. Designed to automatically code and decode GPS signals, encryptors facilitate the exchange of user information by securely transmitting navigation payload data between the OCX ground station and the orbiting constellation of satellites.

Delivery followed successful thermal, electromagnetic interference and security verification testing. Exelis provides critical elements of software in the navigation processing subsystem that will enable controllers to better understand the exact position of GPS satellites. This helps ensure accurate navigation information is securely broadcast to users. In addition to encryptors, Exelis is building high-precision receivers for use in GPS ground monitoring stations and satellite signal simulators for testing purposes.

Exelis is also on contract with Lockheed Martin to provide the payloads for the GPS III satellites.


Fire_engine_galileoEurope Tests Galileo Public Regulated Service

European Union member states began their independent testing of the Public Regulated Service (PRS) broadcast by the four Galileo navigation satellites in orbit. Transmitted on two frequency bands with enhanced protection, PRS offers a highly accurate positioning and timing service, with access strictly restricted to authorized users, such as government defense, security, and emergency services.

PRS access was initially considered for Galileo’s Full Operational Capability phase, but it has been enabled in 2013 in response to the strong interest of member states in this service. To allow early access to PRS during the current phase, the European Commission and ESA began the joint project PRS Participants To IOV (PPTI) in July 2012.

ESA ensured the availability of several tools developed under ESA contracts, including test receivers and other qualification equipment. ESA’s PRS Laboratory, based at the Agency’s ESTEC technical centre in Noordwijk, the Netherlands, provided training, demonstrations and sample data.

“Belgium, France, Italy, and the UK have now performed independent PRS acquisition and positioning tests. In parallel, ESA, through collaboration with Dutch and Italian authorities, is conducting PRS fixed and mobile validation in several locations in the Netherlands and Italy,” said Miguel Manteiga Bautista, head of ESA’s Galileo Security Office.

The PRS tests have demonstrated a current autonomous positioning accuracy of less than 10 meters when in the correct geometrical configuration. This is an impressive result considering the small number of Galileo satellites in orbit and the limited ground infrastructure so far deployed.

Italy has developed its own PRS receiver, and tests have confirmed the feasibility of independent PRS receiver development and verification based on specifications provided by ESA.

“The PPTI project is still ongoing to test more advanced functionalities this coming autumn and to run the first aeronautical PRS tests in collaboration with the Dutch authorities. Other member states have also expressed their willingness to join the IOV PRS experimentation campaigns soon,“ concluded Miguel Manteiga.

The project is a first step to ensure use of the PRS as soon as it becomes operational. It will be complemented by PRS pilot projects, focused on PRS applications, which are currently under definition in a common effort between European agencies.

The United States has submitted a request to be able to use Galileo’s PRS. Other non-EU countries have also expressed a desire to be associated with the program.


System Briefs

Way to Go GAO, Part II. The Air Force should come up with better cost estimates and options for new GPS satellites, according to a September 9 report from the U.S. Government Accountability Office (GAO). The GAO was responding to an Air Force study on lower-cost space solutions for GPS.

“More information on key cost drivers and cost estimates, and broader input from stakeholders would help guide future investment decisions,” the GAO concluded. Specifically, the key cost drivers include dual-launch capability, navigation satellites (smaller GPS-type satellites yet to be developed), and a nuclear detection capability.”

New Birds by Fall. Galileo satellite-builder OHB AG said it should know by late September whether tests of the first Full Operational Capability (FOC) Galileo satellites are proceeding well enough to permit their delivery later this year. The first FOC satellite began testing at ESA’s European Space Research and Technology Centre in May, and the second arrived August 9.

The OHB satellites either “bear a strong resemblance” or “are identical” to the four in-orbit validation spacecraft now in medium-Earth orbit, depending on the source. However, the on-board power of the OHB spacecraft exceeds that of the validation satellites built by a different manufacturer. According to one source, Galileo managers made the modification in part to enable Galileo’s encrypted Public Regulated Service signal to overcome a signal frequency overlap issue with China’s BeiDou constellation.

Alan Cameron

About the Author:

Alan Cameron is editor-in-chief and publisher of GPS World magazine, where he has worked since 2000. He also writes the monthly GNSS System Design e-mail newsletter and the Wide Awake blog.

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