Iridium and GPS revisited: A new PNT solution on the horizon?

How many times have you heard of a nearly 20-year-old space constellation being modified with a new technology? It almost never happens.

I will never forget when the general slid the sensitive Iridium folder across my desk; I knew from his facial expression that he was not happy. The folder contained a controversial civilian plan to de-orbit the entire multi-billion dollar Iridium communications satellite constellation less than a year after it was launched.

Fortunately, the folder also contained a proposed military, U.S. government (USG) and joint civilian proposal to sustain the constellation, with the only caveats being that a buyer be found and that the military and/or USG provide “indemnity” (insurance policy) for the Iridium constellation if it were to be utilized by the USG and our Allies, especially during wartime. At the time I was serving as the deputy chief scientist at Air Force Space Command headquarters. Our job was to determine the technical feasibility of both proposals and make a recommendation.

Iridium satellites

Replica of Iridium satellite. (Photo courtesy of Iridium)

Launched in 1998 by Motorola, Iridium is a satellite communications constellation that is a “technological marvel,” as John Bloom writes in his new book about Iridium, Eccentric Orbits. Additionally, Iridium was and remains a capability sorely needed by the USG that in many ways revolutionized global communications — unfortunately, just not in the manner or time frame Motorola originally envisioned.

Indeed, eventually not 66 or 77, or even 88, Iridium satellites would be launched, as you will read in many places. Rather, a total of 95 Iridium satellites have been launched to date, which should give the constellation the name Americium, since 95 is the atomic number for the element americium. But I digress.

The problem with Iridium was not technical or even space-related. Motorola, which developed the technology and launched the constellation into low Earth orbit (LEO) — an amazing feat in so many respects — totally missed the correct marketing strategy. Motorola developed Iridium as a quick (five-year lifetime) money-making capability and profit center when in fact it proved to be a much longer term project. Today, there are Iridium satellites that are fully expected to be on orbit and fully functioning for more than 20 years.

The original Iridium satellite was — and still is — a technological marvel that broke almost all the so-called rules for manufacturing spacecraft:

• The satellites were built without any fully space qualified or certified parts.
• The satellites were not built in a clean room.
• The satellites were built “horizontally” on a moving assembly line, like automobiles, versus vertically, individually and historically as a stationery static device. The moving assembly line produced a satellite every five days by a little-known company that eventually became part of Lockheed Martin (LMCO).
• The satellites were launched by nearly every space-faring nation that had a launch capability at the time.
• The original Iridium satellites were built for a projected lifetime of five years — that was more than 18 years ago. The current Iridium constellation of 66-plus satellites (remember, 95 have been launched) has exceeded its projected lifetime by nearly 400 percent, and is still going strong.

In 2010, Iridium Communications entered into a long-term agreement with Boeing for maintenance, operations and support of the satellite network. Boeing operates the constellation and provides support for Iridium’s satellite control system (SCS).

Recently, the corporation that owns Iridium announced a global space-based capability that promises to compliment GPS and other PNT constellations.

How many times have you heard of an almost 20-year-old space constellation being modified with a new technology? It almost never happens.

The constellation’s legacy

Amazingly, the only reason the Iridium constellation still exists today, in several respects, is due to the intervention of the USG and a major program that suffered a production failure. Originally Motorola contracted for an additional hosted payload that just never came to fruition. The nameless company developed an Iridium test program, on which it failed to deliver. This “major glitch” caused a weight and balance problem for the Iridium satellites, which Danny Stamp, an Iridium program engineer, solved at the time by recommending a quick fix: adding an additional fuel load of the same weight as the failed payload to the satellite. It was a simple fix just to get the satellites launched on time that no one thought much about at the time. However, the result was a key component — remaining or residual fuel — that ensures the satellites are still in orbit, and can be maneuvered and working properly today.

As I mentioned earlier, one of the major reasons the entire Iridium constellation was not de-orbited was because the USG decided it was a necessary tactical capability during wartime for our warfighters, as well as being an amazing R&R tool for morale purposes. (The Iridium system enabled conversations with loved ones back home.)

Add to that a civilian plan put together by some true visionaries, individuals such as Dan Colussy and corporate partners such as Boeing, that were able to purchase the entire constellation for pennies on the dollar, and you have an incredible success story.

The result is one of the most successful — certainly the largest and most well known — satellite communication constellations ever flown. Plus, as I mentioned earlier, Iridium has proposed a brand-new capability that, if it comes to fruition, has the potential be a huge boon for GPS by serving as a key global PNT augmentation.

The way ahead

Just last week, Iridium announced that it is proposing, or has developed, in conjunction with other companies, an augmentation or compliment to GPS. Reuters quoted the CEO of Iridium Communications, Matthew Desch as saying the new technology used chips that were the size of a postage stamp, and could ultimately be integrated into other devices, heavy machinery, automobiles and the power grid.

The system, known as STL or Iridium Satellite Time and Location System, transmits signals via Iridium’s satellite constellation, delivering codes to ground positions that are independently authenticated, Reuters reported.

Both Iridium and the private firm Satelles said STL as a system has been demonstrated in military, academic and commercial applications. The Reuters article didn’t provide specific details on the exact nature of the devices or any launch customers. (Satelles and Boeing entered into a patent and technology license agreement for STL in 2013).

Iridium NEXT, Iridium’s next-generation global satellite constellation, will support the STL solution. Iridium NEXT is scheduled for completion by late 2017. Along with supporting the current Iridium constellation, Boeing is under contract from prime contractor Thales Alenia Space to provide system integration and testing support for Iridium NEXT.

So, while STL is far from concrete, it makes for an interesting possibility that Iridium is proposing or has apparently built an on-orbit satellite augmentation to GPS, and PNT in general. My government inquires brought the to-be-expected, “We can neither confirm or deny” response. As far as Iridium and Satelles are concerned, I suppose it is a wait-and-see proposal.

Still, it is good to see company internal R&D funding being used to further support our global PNT infrastructure. Now that the word is out, we can look for more details on the horizon. So stay tuned. By the way, many of you may remember that this is not the first time Iridium has gone down this path; perhaps this time it will actually work.

Yes, sometimes 18 years ago seems just like yesterday.

Note: You can read about Iridium as a GPS augmentation solution in “Iridium/GPS Carrier Phase Positioning and Fault Detection Over Wide Areas, a paper by M. Joerger, J. Neale and B. Pervan presented at ION GNSS 2009. It is available for download per ION’s current download policies.

Abstract: The iGPS high-integrity precision navigation system combines carrier-phase ranging measurements from GPS and low-Earth orbit Iridium telecommunication satellites. Large geometry variations generated by fast moving Iridium spacecraft enable the rapid floating estimation of cycle ambiguities. Augmentation of GPS with Iridium satellites also guarantees signal redundancy, which enables fault-detection using carrier phase Receiver Autonomous Integrity Monitoring (RAIM). Over short time periods, the temporal correlation of measurement error sources can be exploited to establish reliable error models, hence relaxing requirements on differential corrections.

In this paper, a new ionospheric error model is derived to account for Iridium satellite signals crossing large sections of the sky within short periods of time. Then, a fixed-interval positioning and cycle ambiguity estimation algorithm is introduced to process Iridium and GPS code and carrier-phase observations. A residual-based carrier phase RAIM detection algorithm is described and evaluated against single-satellite step and ramp-type faults of all magnitudes and start-times. Finally, a sensitivity analysis focused on ionosphere-related system design variables (ionospheric error model parameters, code-carrier divergence, single and dual-frequency implementations) explores the potential of iGPS to fulfill some of the most stringent navigation integrity requirements with coverage at continental scales.

ION Joint Navigation Conference

The highly anticipated and always rewarding Institute of Navigation Joint Navigation Conference (ION JNC) kicks off this week, June 6-9, at the Convention Center in Dayton, Ohio, and at Wright Paterson Air Force Base.

There are the expected technical and joint presentations, along with a classified day (U.S. only) and a Warrior Panel. It all sounds like a great time and an educational experience. Be sure to visit the National Museum of the U.S. Air Force, including the website where you can take a virtual tour; it is an amazing venue. Also take time to visit the Wright Brothers exhibits in the “Birthplace of Aviation” while you are there.

Wright Brothers 1901 Wind Tunnel on display in the Early Years Gallery at the National Museum of the United States Air Force. (Photo: U.S. Air Force)

ION always puts on a great event. I hope many of you are there to participate.

Until next time, happy navigating, and remember: GPS is brought to you free of charge, courtesy of the United States Air Force.