The System: IRNSS Signal Close up

September 1, 2013  - By and

IRNSS Signal Close up

By Richard Langley, Steffen Thoelert, and Michael Meurer

The spectrum of signals from IRNSS-1A, the first satellite in the Indian Regional Navigation Satellite System, as recorded by German Aerospace Center researchers in late July, appears to be consistent with a combination of BPSK(1) and BOC(5,2) modulation.

Figure 1 shows that, centered at 1176.45 MHz, the signal has a single symmetrical main lobe and a number of side lobes characteristic of the signal structure that the Indian Space Research Organization (ISRO) announced would be used for IRNSS transmissions in the L-band. Figure 2 shows the corresponding IQ constellation diagram. Further analysis will be required to sleuth additional signal details as ISRO, so far, has not publicly released an IRNSS interface control document describing the signal structure in detail.

Figure 1. Spectrum of IRNSS-1A L5 signal.

Figure 1. Spectrum of IRNSS-1A L5 signal.

Figure 2. IQ constellation diagram of IRNSS-1A L5 signal.

Figure 2. IQ constellation diagram of IRNSS-1A L5 signal.

The German scientists caution that “this is a very early snapshot of the current signal transmission and probably both the signal power and the signal quality will change and possibly improve during the in-orbit-testing phase of the satellite’s operation.

Extra Life for IIRs, IIR-Ms

U.S. Air Force engineers are testing on-orbit a technique to extend the life of the 19 GPS IIR and IIR-M satellites on orbit, roughly 60 percent of the current contellation.

A new charging method may reduce the rate of satellite battery degradation, thereby extending satellite operational life. If the technique passes the test, the initiative could add a combined 20 years to the life of the satellites — saving the Air Force tens of millions of dollars in the process.

Gen. William Shelton, commander of Air Force Space Command, credits Capt. Jacob Hempen of the Air Force’s 2nd Space Operations Squadron for the job. Capt. Hempen says in turn that Warren Hwang of the Aerospace Corporation originated the idea.

When satellite solar panels are directly exposed to the Sun, they charge satellite batteries while continuing to power other operations onboard the space vehicle. When the satellite passes  into the Sun’s shadow behind the Earth, it runs on batteries. The batteries can be re- charged at variable rates. When some of the batteries are powered above a certain rate threshold, they can overheat, accelerating their natural rate of decay.

Lowering battery charging rates could still enable the satellites to perform well while minimizing the rate of degradation. Hitting the optimum number called for some finely-honed calculations.

The satellites were built by Lockheed Martin Space Systems, and the oldest still in operation was launched in 1997.

They had an intial design life of eight years, which many have now well outlasted. If the technique proves out and is carefully applied across the board, it could conceivably fill in replenishment gaps equivalent more than two additional spacecraft — conceivably as much hundreds of millions of dollars in build and launch costs, postponed. In today’s budget environment, a postponement can be construed as equivalent to outright savings.

System Briefs

GLONASS Partial Make-Good. Russia will launch two GLONASS satellites later this year to make up for the loss of three satellites in the July 2 Proton rocket explosion. The first is scheduled for the beginning of September, and the second at the end of October. Both will rise aboard Soyuz carrier rockets, which have proven more reliable than the Protons. A constellation of 29 GLONASS satellites is now in orbit, with 24 spacecraft in operation, three spares, one in maintenance, and one in test flight phase.

Meanwhile, plans to reduce GLONASS funding have alarmed at least some deputies of the Duma, the Russian state legislative body. Government officials have floated a plan to reduce funding of the space program in 2014 by 11.7 billion rubles ($355 million), by 13.5 billion rubles in 2015, and by 40 billion rubles in 2016. The federal space program of Russia for 2006-2015 already lacks 10.5 billion rubles funding, and this year there has been a 2.3-billion-ruble additional reduction in R&D. A Duma committee chairperson warned that this trend will “lead to the loss of confidence of the international community in the GLONASS system and, consequently, to a reduction in its use globally. Russia will lose a strategic global instrument of political and economic prestige.” The Duma has recommended that the government maintain funding of federal space programs.

Galileo Satellites’ Trial By Noise. The first Galileo Full Operational Capability (FOC) satellite successfully completed acoustic testing in July, part of a full-scale test campaign at ESA’s ESTEC Test Centre in Noordwijk, the Netherlands.

The satellite was placed in the Large European Acoustic Facility (LEAF), effectively the largest sound system in Europe. A quartet of noise horns embedded in a wall of the 11 x 9 x 16.4 meter test chamber generated an acoustic noise level of 140.7 decibels, about the same noise as standing 25 meters from a jet taking off, and intended to simulate the extreme environment experienced by a satellite atop a rocket about to fire itself off the launch pad.

A second FOC satellite arrived at ESTEC on 9 August from manufacturer OHB in Bremen, Germany. It will undergo a similar acoustic testing and then a System Compatibility Test Campaign will linking it with the Galileo Control Centres in Germany and Italy and ground user receivers as if it were already in orbit.

A total of 14 FOC satellites are being produced and then tested at ESTEC as an integral part of their path to orbit. A second work order of eight satellites has been given to OHB.

GPS III Pathfinder. On July 19, Lockheed Martin delivered a full-sized, functional prototype of the next-generation GPS satellite to Cape Canaveral Air Force Station to test facilities and pre-launch processes in advance of the arrival of the first GPS III flight satellite.

The GPS III Non-Flight Satellite Testbed (GNST) paves the way for the first flight GPS III satellite, expected to arrive at the Cape in 2014, ready for launch by in 2015.

An innovative investment by the Air Force under the original GPS III development contract, the GNST has helped to identify and resolve development issues prior to integration and test of the first GPS III flight space vehicle (SV-01).

Following the Air Force’s rigorous “back-to-basics” acquisition approach, the GNST has gone through the development, test and production process for the GPS III program first, significantly reducing risk for the flight vehicles, improving production predictability, increasing mission assurance and lowering overall program costs.

Lockheed Martin is currently under contract for production of the first four GPS III satellites (SV 01–04), and has received advanced procurement funding for long-lead components for the fifth, sixth, seventh and eighth satellites (SV 05–08).

GNSS Industry Survey. Here are the results of two questions asked about government and industry from the 2013 GNSS STATE OF THE INDUSTRY SURVEY.

Is government committed to private industry in a time of drastic budget cuts? For more results from the 2013 GNSS STATE OF THE INDUSTRY SURVEY.

Is government committed to private industry in a time of drastic budget cuts?

Is industry actively making its concerns known to government?

Is industry actively making its concerns known to government?


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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 Design & Test e-Newsletter and the Wide Awake blog.

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