GNSS Constellations March On

March 25, 2015  - By
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This week nearly all the global navigation satellite systems will push their spatial presence one or two steps further, or higher, if they perform as scheduled. Rarely if ever has there been such a concentrated period of activity in the catapult category. Are we witnessing the real dawn of the multi-GNSS era? GPS, Galileo, BeiDou, and IRNSS all have positioned loaded rockets on the launching pad, destined to heave satnav payloads aloft. Only GLONASS seems stuck in stasis.

Leading the pack, as ever, GPS should send forth the ninth GPS Block IIF satellite (GPS IIF-9) on March 25 at 2:36 in the Eastern U.S. afternoon. Perhaps the event has already occurred by the time you read this.

The seventh and eighth Galileo satellites, Adam and Anastasia, are destined for a double date in space on March 27. After a four-hour flight into orbit 22,300 kilometers high, the duo will spring away from their Fregat fourth stage in opposite directions.

The launch of the fourth satellite for the Indian Regional Navigation Satellite System, scheduled for March 9 but postponed to replace a faulty onboard telemetry transmitter, will now take place on March 29. IRNSS-1D will pass the halfway point in India’s march to a seven-spacecraft regional constellation.

HTXK4 Credit: BeiDou

This philatelic first-day cover to commemorate an upcoming BeiDou launch indicates a specific date of March 31, 2015 (circled in red). Credit: BeiDou

There are indications that the first satellite in the BeiDou Phase 3 expansion may be launched by the end of March. Apparently, a BeiDou satellite has been shipped to the Xichang launch site, and tracking ships have left port for the open ocean. Also, a postal stamp first-day cover for the launch — a common Chinese practice — has been issued with a March 2015 inscription. The launch will likely be that of a medium Earth orbit satellite.

A GLONASS-M single-satellite launch from Plesetsk had been expected in the first quarter of this year, but has not materialized. A GLONASS-M triple-satellite launch from Baikonur is expected in the April/May 2015 timeframe. The Russian constellation’s orbit count now stands at 26, fully sufficient for global coverage.

As the Ides of March in 44 B.C. mark a turning point in Roman history, the transition from Republic to Empire, so might this week mark complete world domination. GPS is now ¾ down the last section of road that leads to the fully modernized Block III generation. Galileo will reach, numerically, 1/3 of the total number of satellites it needs for full operational capability, although there is some doubt about whether all satellites now in orbit can be counted as full integers. BeiDou will mark its 15th operational satellite, out of a planned total of 35, with the new philatelically commemorated rising. And, as mentioned, IRNSS will pass its halfway point this weekend.

Ironically, just as GNSS begins to show signs of approaching its apogee (similar to the dawning of Empire in the Augustan Era that followed Caesar’s assassination on the Ides of March), the world is starting to turn away from, or turn beyond, GNSS.

GNSS will remain at the core of our navigation and positioning technologies — as Roman values remain at the core of Western civilization. But we need to go now to multi-sensor approaches for several reasons:

  • some requisite positioning data, such as precise attitude, is not optimally derived solely from GNSS measurements;
  • despite their increasing numbers, GNSS satellites will never be ubiquitous enough to be visible in sufficient numbers everywhere;
  • threats such as jamming and interference will likely surmount all efforts at single-solution resilience to overcome GNSS vulnerability.

‘Twas ever thus. With rise come decline, with ripeness, decay. Sic transit Gloria.

About the Author:


Alan Cameron is editor-at-large of GPS World magazine, where he has worked since 2000.

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