Blogging

GNSS – GPS, GLONASS, Galileo, & Compass – What’s in the Air

The Global Navigation Satellite System – GNSS – has developers and manufacturers working at full stretch to develop new satellite systems that will launch to beam new, improved signals: good news indeed for a multitude of diverse GPS-dependent users, not least marine navigators.

Unfortunately there is a risk that the GNSS, even with its huge capability, may not extend quickly enough to meet the demands of an ever-expanding consumer market, fired by a growing global dependency on SatNav. Thus there is the specter of a world that might become a victim of its own early GNSS success.

First, a look at the navigational revolution that began with the ubiquitous Global Positioning System itself, familiarly known as GPS, a component senior member of the GNSS family.

GPS

The U.S. Air Force was mandated in 1973 to operate a system of navigational satellites which it named the ‘Navstar Global Positioning System’, later to become known familiarly as ‘GPS’.

The first satellites were superseded by a program of ‘Block ll’ GPS launches that began in 1989, culminating in a fully operational system by 1995 that presently makes up the constellation of 24 Medium Earth Operating (MEO) satellites that are the necessary minimum to provide worldwide coverage.

GPS can thus be seen to be a comparatively elderly system, as maximum on-orbit satellite life is estimated at about 20 years.

GLONASS

GNSS – GPS, GLONASS, Galileo

The Russian satellite system is of much the same vintage as GPS, having been largely neglected following the collapse of the national economy, but since 2001 the system has been restored gradually, with six new satellites launched in 2008. It is expected that GLONASS system accuracy and availability for public use will be comparable to that of GPS in future.

GLONASS is therefore seen as the next system according to analysts, as it now has a full constellation flying, although its signals are complex to utilize in present-day global positioning receivers, since they do not correspond exactly to the GPS frequency.

Galileo

After gathering dust on the European Commission’s shelves until January 2010, the first major contracts for the Galileo GNSS were placed for the manufacture of 14 of a planned 32-strong constellation beginning from July 2012.

GNSS Prospects for the Future – A Summing Up of What’s Likely to be Up

By 2020 there may be as many as 117 MEO navigation satellites (GPS, GLONASS, Galieo and Compass) according to a paper, “Economics, Shipping, and Aids to Navigation” by Admiral Sir Jeremy de Halpert and Dr Sally Basker that was presented jointly at the Capetown IALA Conference in March 2010. The authors foresee GNSS satellites in orbit by that date which will deliver multi-frequency open-access services, with sub-10 meter accuracy and wide availability.

Until then there remains just a shadow of doubt that the aging GPS system, though supplemented by GLONASS, (whose robustness is unproven) will be able to cope until the new dawn of Galileo and Compass breaks in the GNSS sky.

Understanding the Solar Cycle

The solar cycle is sometimes called the solar magnetic activity cycle or the sunspot cycle.

Definition of a Solar Cycle

A solar cycle is the time period from solar minimum to solar minimum, as measured by sunspots. Every 11.1 years on average, the sun reverses polarity and sunspots move from mid-latitudes toward the equator over the course of a cycle. For example, a new solar cycle (number 24) began January 4, 2008, as a new sunspot appeared on the sun that was at a higher latitude and opposite polarity of the sunspots that preceded it. The sunspot that signaled the start of the new solar cycle was labeled number 10,981 and the leading half of the sunspot showed negative polarity.

gps

In the gray image, sunspots from the previous solar cycle, number 23, can still be seen near the equator of the sun. The solar cycle is usually referred to as lasting 11 years (although it can vary a year or two in either direction), but occasionally the solar cycle is referred to as a 22-year cycle, in regards to the polarity returning to what it was previously as the sun’s magnetic poles reverse again.

Understanding Sunspots

Sunspots, which are dark, cool, active regions on the sun that tend to occur in clusters, generally have two main locations of opposite polarity. The half that leads the spot across the sun is called the preceding and usually is a bit closer to the sun’s equator also. The other half is called the following spot. It is these two sections that swap polarities when a new solar cycle begins. It is also this opposite polarity region that causes violent flares and prominences that can leap up from the sun, snapping off and hurtling themselves toward Earth.

The Butterfly Diagram

When a new solar cycle begins, sunspots start forming at higher latitudes in both the north and south hemispheres, farther from the equator. This is the solar minimum, when there are fewer spots and therefore less activity on the sun. Over the course of the cycle the sunspot number and solar activity will increase as the spots more closer to the equator. This time of more solar storms is called solar maximum. As the activity slowly dies down, the sunspots continue to move toward the equator and taper off in numbers until solar minimum is reached again. A diagram of the positions of the sunspots on the sun looks a bit like a butterfly flying to the left, as the outstretched wings mark the furthest north and south reaches of sunspots. The movement of the sunspots from mid-latitudes toward the equator is known as Sporer’s Law.

Maunder Minimum

Astronomers of old noticed a strange event between 1645 and 1715. Fewer sunports were seen on the sun, with the periods of solar maximum being much quieter than years that came before and after.