Under the dome

Jan Michelsen, Cobham SATCOM, Denmark, looks at the vital role played by satellite communications in the global oil and gas industry.

Satcom antennas quietly perform a vital job for offshore operators, acting as the enabler of Internet on board platforms and vessels. But though they all look the same when high up on antenna platform, there’s a lot going on under the dome that makes it important to choose the right one.

Larger antennas with networks tailored to the user requirements are the mainstay of oilfield communications.

A VSAT antenna should point at 0.2° accuracy to a satellite, which is 36 000 km away from the surface of Earth. This takes precision engineering even on land, but at sea on a drill ship, FPSO or seismic vessel for example, a maritime stabilised VSAT antenna has to track the satellite from a platform moving through six degrees of motion. The engineering quality required to achieve this effectively is significant.

Inferior design, manufacturing or installation could potentially prevent an antenna from finding the satellite and keeping the connection, causing regular drops in service. Today, any loss of connectivity can be costly. Satcom is no longer just used for crew calling, office emails, or delivering electronic forms. IP connectivity delivered through VSAT is the foundation on which many exploration and production operations are based, and service interruption can prove incredibly costly. Operators work with complex drilling software providing live feeds to experts on land, deep collaboration and sharing solutions that bring engineers together when they are continents apart, and regulatory reporting commitments that must be met. So whilst satcom service providers strive to provide ‘Service Level Agreements’ up to 99.5% availability, antenna manufacturers continue to ensure their equipment can deliver the bits and bytes that are so depended on, regardless of the weather or environment.

Maximising antenna performance

With Ku-band or C-band VSAT, which are the most common form of satcom used in the oil and gas sector, users pay monthly flat rates for bandwidth, often with no data usage limits. It is therefore expected that they receive a maximum of uptime and availability of broadband service. The VSAT antenna is integral to achieving this.

RF Performance is the ‘Holy Grail’ in good antenna design. At grass roots, RF performance, (measured in G/T – antenna gain-to-noise-temperature measured in db Kelvin), is the ability to ‘listen’ to the satellite. On top of this is the size of the antenna reflector; the bigger the dish, the less power (and therefore cost) the satellite needs to hit the target and complete the link. Better performance means increased coverage area for the satellite service and better margins in rain or snow, which can have significant negative impact on satellite signal reception.

Antennas with larger reflectors, most often used by offshore oil and gas users, will generally have a higher G/T. Though there are physical limitations at play, it is possible to squeeze more performance from a smaller antenna, using an integrated approach to design and engineering that leverages every last ounce of performance and quality from both the receive and transmit components.

No one single component will boost antenna performance on its own. Instead of just focussing on increasing the reflector dish size, optimising the quality and interaction of all of the RF components is the best starting point, which only a few companies in the world master. By ensuring the best, most suitable components and integrating everything together perfectly, it is possible to maximise performance and therefore offer greater availability of service in all conditions on larger antennas, or to increase performance of smaller antennas to get closer to the performance benefits of bigger dishes.

In addition to precision internal engineering, even optimisations of the material of the radome can help. The glass-fibre lay-up of the antenna radome plays a role in performance because it is ‘in the way’ of the RF components inside and the satellite itself. The better the satellite signal gets through the radome, the ‘clearer’ the signal is, which contributes to better RF performance as a whole.

Simulating vessel motion

Whilst development is the platform for building high performing antennas, testing is vital to ensure they perform as expected. However it is unrealistic to be able to test each and every antenna in a live scenario on board a platform or vessel. For a start it would have to be installed (some antennas can be as big as 3.5 m), connected to a service, continuously monitored, then de-commissioned and removed once the testing is complete. All of this costs time and money. So Cobham SATCOM took a new approach to supplement live testing by building a testing and simulation facility in Denmark.

The test area is a three-storey extension to the HQ building in Lyngby (11 km north of Copenhagen), and was implemented solely for the purpose of improving development resources for the design of new antenna systems. Critical to the success of the new testing facility and the SAILOR 900 VSAT – the first antenna development programme it supported – was obtaining real vessel data that could be used to simulate real-life conditions at sea, on land.

Onshore testing facility in Denmark can simulate almost any vessel type for extended antenna trials.

Special measurement equipment that records vessel attitude data in regards to heading, roll, pitch, yaw, acceleration, position, temperature and random vibrations etc., was deployed on different kinds of vessels from 20 - 300 m. This data is fed into the multi-axis hydraulic motion testing and simulation platform that replicates exactly the movement of any vessel. Using real vessel motion and conditions, whilst connected to a live satellite, provides a realistic long-term testing ground. This testing supports live sea trials of new antenna designs, and enables a huge amount of data to be acquired in a relatively short period. With at-sea testing only, costs can spiral and time to market is contingent on the co-operation of the owner of the vessel used for testing. With ‘live’ on land testing though, the development process is enhanced, as well as being more efficient.

End users see these benefits

Simulated antenna testing is a complicated process, not least because pointing at the satellite from inside a building is obviously a challenge. However, the investment and effort in setting up the test and simulation facility enables antennas to be ‘sea-trialled’ at will. Different ship profiles can be loaded easily, resulting in an extended testing regime, without going near a drop of water. This is an important factor considering the limitations antenna manufacturers face on carrying out live testing during antenna development. Additional facilities in the test area include a set of vibration equipment and a special chamber for highly accelerated lifetime testing (HALT), which ensure that the antenna could be designed to exceed performance and reliability requirements within the harsh maritime environment.

As a result of this approach to antenna development, and specifically testing, Cobham SATCOM can provide antennas that work ‘out of the box’. The SAILOR 900 VSAT for instance requires no evaluation, planning, procurement or installation of RF components. The system is shipped from the factory ready to install. This removes the need for labour-intensive testing and balancing of the antenna on-board vessels, as live testing of the antenna during production ensures it will work on any Ku-band service, anywhere. The importance of this cannot be understated; it really is a step change in the world of maritime VSAT, and though the antenna is not designed for use on oil and gas platforms, its relevance to the offshore and seismic vessel fleets is high.

Special technology development

For antennas used on drill ships or FPSOs, the goal is not necessarily to make them ready to go straight out of the box. The high bandwidth requirements, and critical nature of IP communications on board, call for more complex networks capable of handling multiple LANs, user groups and high-end specialist applications. This is where a custom approach is preferable to the use of off-the-shelf products, as antennas have to be more integrated with specific network design for each project. This makes every network different, so it is important to develop a flexible antenna technology architecture. An example of this kind of high-end development is a new switchable antenna, which can operate on both Ku and C-band networks.

The RF part of an antenna consists of the electronics and mechanical support components that make sure it can connect to a satellite, and then transmit and receive data that the VSAT modem transforms into Internet traffic. The receiving part consists of the feed horn and reflector dish, and behind these, the LNBs (low-noise block down converter). A global antenna system would carry two LNBs to be able to seamlessly receive from satellites using cross-polarisation (x-pol) and co-polarisation (co-pol). In order to manage two such multi-frequency band LNBs, the antenna also needs additional electronics. These ‘receive’ electronics communicate directly with the ground station equipment. The transmit part is mainly the Block Up Converter, or BUC, which is defined in Watt of power; the standard in 1 m VSAT antennas is 8 W, while larger antennas, e.g. 1.5 m and 2.4 m, are often supplied with BUC of up to 25 or 400 W.

The switchable feed antenna (Sea Tel 9711 IMA) is generally deployed in high-end, customised VSAT networks for large, specialist vessels such as cruise ships, research ships, jack-up rigs and FPSOs. Its ability to switch between C- and Ku-band without degradation of service, offers much needed flexibility and redundancy for service providers and users. It enables better availability of service in high-precipitation regions such as the tropics or the Arctic.

Cobham SATCOM engineers designed a method for making automatic band switching possible, on already installed Sea Tel 9797B and now on the Sea Tel 9711 IMA for new installs. The Sea Tel 97IMA Ku Switchable Feed Upgrade Kit adds a permanently installed Ku-band feed along with a moveable sub-reflector, which swings into position on an electric motor when switching is initiated either manually or by remote access. The Ku-band feed illuminates the sub-reflector, which bounces the signal down to the main reflector. The process requires high precision, achieved through the use of a precision mechanical stop and limit switches, to ensure no loss of signal or degradation of service.

Prior to the development of this new technology, switching between bands on the Sea Tel 9797B or Sea Tel 9711 IMA required a trained technician to manually change feeds, connect the wave guide plumbing, change wiring and re-balance the antenna – all of which takes at least half a day. Without the need for human intervention, and considering that a vessel may change VSAT bands semi-regularly, the new solution will provide significant cost savings during the lifetime of the antenna, whilst increasing the amount of opportunities when the switching capability can be implemented to ensure availability of VSAT services.

High throughput satellites

Though not always in the limelight, it is important not to underestimate the development efforts made by satcom antenna manufacturers. Whereas innovative new features like automatic switching help to reduce costs and improve efficiency for specific challenges, recently developed antennas are also the enabler of forthcoming satellite communications services that will, over the coming years, be adopted by oilfield users.

Based on a new generation of high throughput satellites (HTS), these new services are being classed as the next generation of satcom at sea. HTS services will be based on Ka or Ku-band VSAT, which though offering potential for much higher data throughput than older Ku-band and C-band VSAT, does suffer from some drawbacks. Ka-band is often described as being susceptible to rain-fade, which is where precipitation can cause distortion of the signal, causing drops in services. However, newer technology like the latest adaptive coding and modulation (ACM) in the modem and teleport can improve matters. Inmarsat’s Global Xpress HTS satellites also use ACM, and complement this with FleetBroadband on L-band. Operating on the L-band, FleetBroadband offers the highest level of redundancy and also has the added benefit of providing near global coverage.

In order for operators to make the most of FleetBroadband Xtra and Fleet Xpress (the maritime services of Global Xpress), they will need two systems, and it is once again here that technology is the key. The Cobham SATCOM’s flagship antenna for the service is the SAILOR 100 GX. It features a new Ka-band feed, but the system is built on the same technology platform as the SAILOR 900 VSAT (Ku-band). So users can be assured that it is a mature product and that it can operate in the harshest conditions.

A key aspect though, is how it integrates with the Cobham SATCOM SAILOR FleetBroadband user terminals. It is this integration between Ka-band and L-band systems that will provide full availability of IP connectivity globally and in bad weather, which are two vital aspects of Global Xpress. SAILOR 100 GX ships with the new SAILOR Ka-band antenna controller and the SAILOR GX Modem Unit (GMU), which works seamlessly with SAILOR 500 and 250 FleetBroadband systems and out-of-band management, to ensure that when the Ka-band part of the service is not available, switch-over to the fall-back is seamless (managed by the Network Service Device).

The antenna features advanced demodulation and tracking receiver technology that enables it to find and verify the right satellite in less than a second. This feature, tried and tested in the benchmark SAILOR FleetBroadband systems for years, ensures quick satellite acquisition at start-up, and re-acquisition of the satellite in case of temporary blockage after bad weather or poor signal strength.

With HTS forthcoming and maritime VSAT antenna development at a very mature stage, the outlook for satcom in the oilfield is bright. There are still challenges to overcome, but as long as development continues, antenna manufacturers will continue to support exploration and production to evolve and become more connected, whatever the weather and wherever the action is.

Adapted by David Bizley

Read the article online at: https://www.oilfieldtechnology.com/digital-oilfield/28042015/under-the-dome/