Working with inclined orbits: Creating a viable solution

by Staff Reporter | March 11th, 2012

 

Koen Williams, strategic marketing director, government and IP trunking

Are satellite operators alive to the challenges of managing a satellite in an inclined orbit? Koen Williams, strategic marketing director, government and IP trunking, Newtec says, “Satellite operators will lose a section of their customers, such as DTH providers, who require constant throughput. The empty bandwidth needs to be filled up as quickly as possible with customers that can deal with fluctuating bandwidth. Hence the bandwidth is offered at 50% lower prices. But instead of keeping the satellite alive for just 10/11 years, the life of the satellite can be extended to 15 years when putting it in an inclined orbit. This gives the satellite operator four to five years of extra revenues.

“Keeping the satellite in its slot and putting it in an inclined orbit could also be a strategic choice by the satellite operators. They want to keep the satellite slot (and not lose it to other companies as competition for orbital slots is fierce above some regions) until they have a satellite ready to replace the older satellite in the same slot. And if the launch of the replacement satellite fails, the satellite providers still have some buffer until the next launch.

“The fluctuating throughput that comes along with inclined orbit satellites tends to frighten away providers that need to transport Committed Information Rates (CIR) services over these satellites. At Newtec , we offer FlexACM, the option to provide both variable as fixed rate throughput in DVB-S2 ACM (Adaptive Modulation and Coding) to fulfill SLA requirements. By bringing fixed rates and CIR to ACM, we at Newtec address the service providers in point-to-multipoint configurations providing constant throughput at optimal availability in the most efficient way.”

Keeping the satellite in its slot and putting it in an inclined orbit could also be a strategic choice by the satellite operators. They want to keep the satellite slot (and not lose it to other companies as competition for orbital slots is fierce above some regions) until they have a satellite ready to replace the older satellite in the same slot.

More about inclined orbits

Government agencies and service providers are increasingly using inclined orbit satellites for the transmission of data for all their applications and service. The driving factor behind the transition towards inclined orbit birds is an OPEX consideration. The inclined satellites provide a good alternative to reduce the bandwidth cost by half. Another driver is the need to source bandwidth over regions where satellite capacity is scarce.

In order to extend the life of a satellite, some satellite operators decide to put the satellite in an inclined orbit. The switch to inclined orbit operation has repercussions on the availability of the services as the satellite footprint shifts in a predictable and continuous pattern.

Therefore it is essential to implement technology to optimise the throughput over inclined orbit satellites. This is necessary to increase margins, keep OPEX under control and to support government missions independent of the location around the globe.

Option to go inclined

Inclined orbit satellites can be defined by the fact that they exhibit an angle other than zero degrees with the equatorial plane. At the end of a satellite’s life, when station-keeping fuel is running low, there is the option to “go inclined”. Station-keeping is performed in two directions, east-west and north-south. Since the Equator runs in an east-west direction, with many adjacent satellites, east-west station-keeping is mandatory. The north-south station-keeping can be abandoned with the result that the satellites in inclined orbit start to make a figure of eight pattern. On the ground this could be experienced by having a weaker signal or lesser throughput during parts of the day when it is off axis. Most inclined orbit satellites operate up to six degrees, but in some extreme cases, some satellites can go up to 15 degrees.

Satellite operators have different drivers to put satellites into and to keep in an inclined orbit.

• Extend the life of older satellites

• Opportunity to extend revenues

• Risk mitigation to keep the orbital slot until replacement

For service providers and government agencies, on the other hand, the inclined orbit satellites give the opportunity to drive down bandwidth (OPEX) costs.

In the exercise of keeping OPEX under control or increasing margins and revenues, government agencies and service providers tend to migrate their services to inclined orbit satellites. Due to the link degrading conditions of these satellites (resulting in less throughput) the bandwidth is offered at up to a 70% lower price than normal transponders over the same area.

Communication lines over the satellite need to be available at all times to exchange mission critical information and to keep customer satisfaction at a high level. However, the footprint shift which comes naturally with inclined orbit satellites results in a periodic reduction of throughput and could cause link losses and packet drops if the correct technology is not implemented. Receiving conditions could drop as much as 6 dB, which means that a low modulation scheme and increased error correction has to be used. Other effects that occur through inclined orbit operations are degraded cross-polarisation performance, an increased range variation, range rate and Doppler shift.

Application Note: Newtec

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