Drones between satellite and earth.

Author:Jameson, Hush
Position:Drone satcom
 
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One of the most significant military developments in the last 10 to 15 years has been that of the unmanned aerial vehicle, which has evolved from the simple drone with limited capability to today's sophisticated aircraft, which, for some roles, particularly Intelligence, Surveillance and Reconnaissance (ISR), is now the platform of choice.

The majority of drones download the product from their sensors by a line-of-sight datalink from a ground station. This has the disadvantage of limiting the range of the aircraft to that of the datalink communication. This limitation can be overcome by using another platform such as another drone or a manned aircraft as a relay, but this solution has the obvious drawback of an increased resource bill to support a single mission by a single platform. To achieve a true Beyond Line of Sight (Blos) capability requires the use of a satellite communication (satcom) system.

A satcom-equipped drone will generally carry a directional antenna that automatically tracks the satellite. The system usually complements a conventional line-of-sight capability for mission control and product download as well as take-off and landing. It follows that the aircraft must be capable of carrying the additional payload of the satcom equipment, and that the airframe is capable of encompassing the satcom antenna. The telltale bulbous nose of some of the larger drones currently in use illustrates those that are satcom equipped.

Communication capability with a drone must be constant (even if not used) throughout the flight for control and during the period its sensors are active. The latter may include video and, if it is to be used for targeting, particularly by a weapon carried by the platform itself, there can be no scope for delay in transmission, as this will increase the chance of an unsuccessful strike or the risk of unacceptable collateral damage. This requires adequate bandwidth and a permanent communication link. Any nation that is going to use satcom to control and receive product from its drones must therefore either have sufficient access to military satcom or be prepared to pay the (considerable) sums required to provide the necessary commercial satellite time.

It follows that satcom-equipped drones are likely to be limited to those nations with this type of access.

In 1993, in response to an urgent requirement from the US Air Force as part of the Tier 1 Medium Altitude Endurance programme, General Atomics Aeronautical Systems equipped a Gnat 750 with a top-mounted pod containing a satcom payload as a test-of-concept platform. During the principal demonstration in October 1993 the aircraft was launched from California and controlled by personnel in Washington DC. The system was designed, built and flown in only six months. A contract was subsequently awarded in January 1994 and 18 months later the system was flying operationally.

From these beginnings there is now a number of drones that are flying operationally with a satcom capability.

The largest of these is the RQ-4A/B Global Hawk, for which Northrop Grumman is the prime contractor and which has an Integrated Communications System (ICS) supplied by L-3 Communications. This has an X-band (8 to 12.5 GHz) line-of-sight common datalink, a Ku-band (12.5 to 18 GHz) satellite communication system and UHF (300 MHz to 3 GHz) C2 satellite communication/line-of-sight links. Central to the ICS is the Common Airborne Modern Assembly (Cama).

The Ku-band satcom system includes a 1.2-metre-diameter, three-axis, steer-able, parabolic dish antenna with...

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