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Teledyne TSS heads north to get the truth on gyro performance

Theoretical calculations are one thing, reality is another. When it came to proving the performance of the Orion Inertial Navigation System in northern latitudes, the engineering team at Teledyne TSS realised that there could be no substitute for trials on Europe’s northernmost tip.

The International Maritime Organisation requires gyro compass manufacturers to verify their products’ ability to precisely identify true north while at latitudes of 70 deg North or South. This ability to measure the horizontal component of the earth’s rotation can be performed by gyros with mechanical spinning wheels as well as by compasses that are entirely solid state. In most cases these abilities can be demonstrated to the IMO’s satisfaction by simulation yet, as everyone in manufacturing will know, simulation is not the same as reality. With the increase of oil exploration and shipping in polar regions, the designers at Teledyne TSS in Watford, UK, wanted to be confident that the real performance of the Orion Inertial Navigation System (INS) would justify their claims when they are addressing these markets.

It was for this reason that last July, Simon Jordan and Tim Hopper drove away from the Teledyne TSS factory in a specially adapted Volkswagen Transporter van*. They were leaving Watford at 51 deg North and heading for the North Cape of Norway where, at latitude 71 deg North they would see whether the TSS claims and calculations for the Orion had been correct. They knew how the performance of the gyro would deteriorate the as they travelled north further north they travelled but the question was would it behave as expected?

The van had been fitted with two external GPS antennas and separate batteries to provide a dedicated power supply for the hardware to be tested. Central to this was a carefully calibrated base plate with a turntable upon which was mounted the Orion INS. This was supported by a Teledyne TSS Meridian Surveyor gyrocompass, a SGB 2000 gyro, which is also manufactured by Teledyne TSS and a high specification Litef LSR 85 military gyro compass, all of which were precisely bolted to the base plate.*

After crossing the North Sea to Esbjerg in Denmark and then by ferry to Helsingborg, the van was driven north through a rain swept Sweden and up the Finnmark Road before entering Norway. If they had been expecting a deserted and lonely drive, Simon and Tim were disappointed because they soon discovered that the North Cape of Norway is an extremely popular summer destination for European caravanners and recreational vehicle drivers.* Cruising at leisurely speeds, the holidaymakers’ objectives were markedly different from those of the gyro scientists for whom the journey became a trial of patience. Even cyclists were encountered in large numbers along the way and when cycling in the road tunnels without lights they proved to be as big a hazard as the herds of reindeer* that Tim and Simon would meet idling in the middle of the road. When they arrived at the Norwegian border the customs inspectors initially assumed that they were fishermen and were puzzled by their lack of rods and gear. They became even more intrigued when they saw the plethora of gyro technology fixed inside the van. Its function was, however, never explained to them as they proved quite content to know that they were testing GPS equipment that was a technology with which they were perfectly familiar.

The nearest airport to the North Cape is at the town of Alta and is where Simon and Tim eventually arrived safely to meet two more colleagues from Teledyne TSS; Paul Ryrie and Steve Cowls *who had flown in from the UK. With 24 hours of daylight, the concept of early morning depends upon reference to clocks, but that was when the four left their hotel in Alta the next day and drove the remaining 150 miles to the North Cape of Norway.* This required four hours on a good tarmac road including a passage through the world’s deepest road tunnel to Nord Kapp Island before they came to a halt beside the road in a wide and open valley.

The tests that followed were the outcome of considerable thought and planning and required the repeated creation of baselines against which the performance of the Orion could be compared. Despite the many thousands of pounds worth of gyroscope technology in the van, one of the most important pieces of equipment that they had brought proved to be a folding bicycle that enabled them to ride away into the distance armed with a handheld GPS receiver enabled with EGNOS.* All four party members took it in turns to pedal into the wilderness from where they would radio their precise coordinates. To create baselines that were as long as possible, the team rode as far as visibility would permit and being a clear and sunny, if chilly, day this proved to be between one and two kilometres.

A precisely calibrated mirror had been secured to the back of the Orion which, mounted on the turntable, had been aligned with its reading of true north. A theodolite had been set up some two meters behind the van from where, by focusing on the mirror, it was possible to take that reading of true north and relate it to the bearing it took from the distant yellow GPS receiver which was visible through the theodolite’s telescope.* In this way it proved possible to move the Orion through an accurate and well-defined angle to verify that it was giving the right answer. This process was repeated some 15 times and other bearings were taken from distant landmarks such as road signs and telegraph poles that had been plotted as waypoints during the approach drive.

The Orion was allowed to settle on eight different headings for 20 minutes. The spread between the achieved final headings is driven by the quality of the ring laser gyros used. This was found to be 0.3º, which meets the specification of 0.1º sec lat. The mean heading error is mainly due to the quality of the GPS baseline. This was within 0.03º.

At the end of one day of careful measurement the expedition was voted a success with the performance of the Orion exceeding everyone’s expectations. It was, furthermore, seen as an endorsement of the mathematics and software that the team had been using to calculate the performance of Teledyne TSS gyros in the factory in Watford. It was satisfying that Orion performed within specification so the team is now convinced of the value of field testing their products. As two volunteer drivers flown-in for the task returned to Watford with the van, the team travelled home making plans to venture further north in 2009 to the island of Svalbard where even more Teledyne TSS products can be scientifically appraised.

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