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Drones BetweenSatellite and EarthOne of the most significant military developments in the last 10 to 15 years hasbeen that of the unmanned aerial vehicle, which has evolved from the simpledrone with limited capability to today's sophisticated aircraft, which, for someroles, particularly Intelligence, Surveillance and Reconnaissance (ISR), is nowthe platform of choice.

Hugh Jameson

T he majority of drones download theproduct from their sensors by a line-of-sight datalink from a ground sta-

tion.This has the disadvantage of limitingthe range of the aircraft to that of thedatalink communication. This limitationcan be overcome by using another plat-form such as another drone or a mannedaircraft as a relay, but this solution has theobvious drawback of an increasedresource bill to support a single missionby a single platform. To achieve a trueBeyond Line of Sight (Blos) capabilityrequires the use of a satellite communi-cation (satcom) system.

A satcom-equipped drone will gener-ally carry a directional antenna that auto-matically tracks the satellite. The systemusually complements a conventional line-of-sight capability for mission controland product download as well as take-offand landing. It follows that the aircraftmust be capable of carrying the addition-al payload of the satcom equipment, andthat the airframe is capable of encom-

part of the Tier 1 Medium AltitudeEndurance programme, General Atom-ics Aeronautical Systems equipped aGnat 750 with a top-mounted pod con-taining a satcom payload as a test-of-con-cept platform. During the principaldemonstration in October 1993 the air-craft was launched from California andcontrolled by personnel in WashingtonDC. The system was designed, built andflown in only six months. A contract wassubsequently awarded in January 1994and 18 months later the system was flyingoperationally.

From these beginnings there is now anumber of drones that are flying opera-tionally with a satcom capability.

The largest of these is the RQ-4A/BGlobal Hawk, for which Northrop Grum-man is the prime contractor and whichhas an Integrated Communications Sys-tem (ICS) supplied by L-3 Communica-tions. This has an X-band (8 to 12.5 GHz)line-of-sight common datalink, a Ku-band(12.5 to 18 GHz) satellite communicationsystem and UHF (300 MHz to 3 GHz) C2satellite communication/line-of-sightlinks. Central to the ICS is the CommonAirborne Modem Assembly (Cama).

The Ku-band satcom system includesa 1.2-metre-diameter, three-axis, steer-able, parabolic dish antenna with auto-matic acquisition, a High-Power Amplifi-er (HPA), a High-Voltage Power Supply(HVPS) and a Satellite CommunicationsRadio Frequency Amplifier (SCRFA).

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The open nose compartmentof the General Atomics Altair

passing the satcom antenna. The telltalebulbous nose of some of the larger dronescurrently in use illustrates those that aresatcom equipped.

Communication capability with adrone must be constant (even if not used)throughout the flight for control and dur-ing the period its sensors are active. Thelatter may include video and, if it is to beused for targeting, particularly by aweapon carried by the platform itself,there can be no scope for delay in trans-mission, as this will increase the chance ofan unsuccessful strike or the risk of unac-ceptable collateral damage. This requiresadequate bandwidth and a permanentcommunication link. Any nation that isgoing to use satcom to control and receiveproduct from its drones must thereforeeither have sufficient access to militarysatcom or be prepared to pay the (consid-erable) sums required to provide the nec-essary commercial satellite time.

It follows that satcom-equippeddrones are likely to be limited to thosenations with this type of access.

In 1993, in response to an urgentrequirement from the US Air Force as

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The Cama, SCRFA, HVPS and HPA arelocated to port in the vehicle's forwardavionics bay, while the dish antenna isinstalled in the radome above the plat-form's nose. The system is compatiblewith Intelsat.

The UHF satcom portion of the inte-grated communication system, which isused for command and control of the air-craft, consists of a transceiver, a poweramplifier and a low-noise amplifier/diplexer and uses a 'batwing' antennathat is located on top of the enginenacelle. There is also an Inmarsat satcomcapability as a back-up command andcontrol facility, incorporating at least twointernal electronics units and using anexternal antenna that is mounted in aventral 'teardrop' radome.

US Air Force Global Hawks are eithercontrolled from Beale AFB in Californiaor from a deployed AN/MSQ-131 GlobalHawk Ground Segment (produced byRaytheon), consisting of a four-personRD-2A Mission Control Element and atwo-person RD-2B Launch and RecoveryElement, each housed in a transportabletactical shelter complete with power andenvironmental units.A single ground seg-ment can control up to three air vehiclessimultaneously. Either the Ku-band or theUHF systems can be used. The sensorproduct can also be made available toothers with suitable communications andreception equipment.

A derivate of the RQ-4B, known asEuro Hawk, is being procured by Ger-many with the first delivery planned in2010. The RQ-4B is also the basis forNorthrop Grumman's solution for theUS Navy's Bams (Broad Area MaritimeSurveillance) programme, for which low-rate initial production is planned for USfiscal year 2011 and initial operationalcapability in 2014. In both cases the inte-grated communication system is likely tobe upgraded,although few details of whatthis might entail are available at presentexcept for the general desire for smaller,lighter, cheaper, more capable equip-ment. It is likely that the Bams satcomwill include an Advanced ExtremelyHigh Frequency (AEHF) capability, asthe follow-on to the current US Depart-ment of Defense Milstar system is theplanned AEHF constellation, the firstlaunch of which is scheduled for 2008.

The AEHF will provide ten times thecapability of its predecessor.

The other principal American familyof satcom-capable drones is the GA-ASIPredator and its variants RQ-1A, MQ-1B, MQ-1C Sky Warrior, MQ-9 ReaperPredator B and Mariner (although, as theGeneral Atomics photograph in our titleindicates, a Gnat was used for initial tests

ations Center at Nellis Air Force Base inNevada.

There are a number of differentGround Control Stations (GCS) for thePredator, all provided by GA-ASI, usingthe satcom datalink to control the drone.A standard station has pilot and payloadoperator stations, each with multi-func-tion workstations with data exploitation,mission planning and search and rescuecontrol capabilities. The Multi AircraftControl variant, in service with the US AirForce, allows control of four aircraft fromone ground station. The crew consists ofone pilot and four sensor operators. Thepilot can dynamically select which aircraftis under direct control, while the sensoroperators maintain continuous control ofsensors; they can control the drone withpoint-and-click commands.

The Portable Ground Control Stationis a suitcase-portable equipment setweighing less than 45 kg. It enables theoperator to exercise complete control,including launch and recovery and sensorcontrol. Two such portable stationsmounted in a Hummer (HMMWV) formthe High Mobility GCS, which is current-ly in use by the US Army.

In mid-2007 General Atomicsannounced that it had successfully tri-alled a new generation ’cockpit’, theenhancements of which include: an opti-mised crew station design with intuitivecontrols and information displays, touch-screen technology, anthropometric con-siderations such as adjustable displays,controls,and ergonomic seating, fused sit-uational awareness data providing a com-mon operating picture on a single display,improved synthetic video with graphicaloverlays, a 120° field-of-view with terrainavoidance and threats/special-use airspace embedded into 3D graphics andhigh-definition video feeds.

In all cases the ground stations requirea Ku-band satellite terminal to providecommunication with the drone. L-3 Com-munications provides alternatives accord-ing to the requirement. At the larger endof the scale is the company’s trailer-mounted 6.2-metre Tri-band Trans-portable Earth Terminal, which providesC, Ku and X-band communication.At theother end is the AN/TSC-160 2.4-metre

The bulbous nose of the Global Hawk houses the satcom antenna. The UHF satcombatwing antenna can be seen on top of the engine nacelle. (Northrop Grumman)

The Gnat 750 with a top-mounted podcontaining a satcom payload first flewas a test-of-concept platform in 1993.(GA-ASI)

This cutawaydrawing shows thedisposition of theGlobal Hawk’sprinciple sensors,including the L-3CommunicationsUHF satellitecommunicationsaerial installed onthe top of theengine fairing.(NorthropGrumman)

back in 1993). They also use a Ku-bandsatcom datalink. The on-board packageconsists of a 75-cm-diameter three-axissteerable, parabolic dish antenna plus aSignal Processor Modem Assembly(SPMA). The antenna is mounted cen-trally in the bulbous nose of the aircraftwith the SPMA behind and to starboard.As with the Global Hawk, there seems tobe no alternate UHF satcom system.Line-of-sight communications are pro-vided by a C-Band datalink.

The US Air Force controls many of itsPredator flights from the Predator Oper-

Deployable Multi-Channel Satcom(DMCS), which can be transported intransit cases.

A significant segment of the groundelement of American drone systems – i.e.in their use by those at the sharp end –has been the development of theRemotely Operated Video EnhancedReceiver (Rover). Now in its 3rd version(Rover III) and made by L-3 Communi-cations, the Rover is a portable receive-only terminal that displays sensor datafrom a number of airborne platforms,including drones. It consists of Ku-bandand C-band omni-directional antennas, areceiver and a display, which is standard-ising on the DRS Hammerhead Multi-Role Terminal (MRT). It provides real-time full-motion video from the airbornesensor, which dramatically improves sur-veillance and targeting at the tacticallevel. Over 2000 Rover III systems haveso far been delivered to US-based cus-tomers with another 1000 on order. Inaddition, Australia, Canada, Britain andNorway are all known to have purchasedthe system, and other nations may havehad systems passed on to them by Amer-ican authorities.

An upgraded version, the Rover 4, isexpected to be ready for production at theend of 2007.This will add an S-band capa-bility and will also allow image metadata

to be passed as well as the images them-selves, which is important for targeting.

In the pipeline is the Rover 5, a new-generation concept that is being devel-oped with US National Security Agency(NSA) participation.A hand-held system,its weight will be reduced from twelve toless than five pounds and it will provideboth receive and transmit capabilities,enabling the user to control the sensorsdirectly.Theoretically it could also be usedto control the drone, but this is unlikely tohappen in the near term, especially with aplatform the size of the Predator.

At present there is some discussionbetween the US Army and Air Force overfuture control of the Predator pro-gramme, and this will affect any possibleupgrades. The MQ-1C Sky Warrior isunder development for the US Army andit is possible that this variant will have anX-band satcom capability and beequipped with a Multi-Role CommonData Link.

The dominant US military satcom fre-quency bands for the next decade will bethe X and Ka bands, principally becauseof the Wideband Gapfiller Satellite(WGS) constellation, the first (of five) ofwhich was launched on 10 October of thisyear.Boeing reported that it had receivedthe first signals from the WGS (nowcalled the Wideband Global Satcom)

satellite the following day. These fiveWGS satellites will each provide eight X- and ten Ka-band spot beams, full earthX-band cover and X-to-Ka and Ka-to-Xcross-banding. A digital ’channeliser‘divides the uplink bandwidth into nearly1900 independently routable 2.6 MHzsub-channels, providing any-coverage-to-any-coverage connectivity.

Depending on the mix of ground termi-nals, data rates and modulation schemesemployed, each satellite can support datatransmission rates ranging from 2.4 Gbpsto more than 3.6 Gbps, a dramaticimprovement over the current DSCS IIIsatellite support of up to 0.25 Gbps.

X-band satcom is likely to becomeincreasingly used in satcom-on-the-moveprogrammes, which are important to theUS Army's future command and controlconcepts and an integral part of pro-grammes such as the Warfighter Informa-tion Network - Tactical (Win-T). It would

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A Predator operatorcontrolling theaircraft via satellitelink from a groundcontrol stationbased at Balad inIraq. Interestingly,the operator’sshoulder badgedisplays an armedPredator to clearlyboast the ‘musclefactor’ with thefollowing motto:«We’re not drones,we fire back».(General Atomics)

The new-generationPredator ’cockpit‘which was trialledby General Atomicsin mid-2007. Itaims at providingincreased ergo-nomics, particularlythrough touchscreens and fusedsituational aware-ness data.(General Atomics)

The L-3 Communications-West AN/TSC-160 2.4-metre Deployable Multi-Channel Satcom (DMCS) antenna is aunit that can be transported in transitcases. (L-3 Communications)

therefore be attractive to the US Armyfor its major drone systems to have an X-band capability.

Once the discussions over programmecontrol have been finalised it is likely thatthe development for all Predators will bealong the Sky Warrior X-band route.

General Atomics is also offering acompetitor for the Bams contract in theform of a Predator variant known as theMariner.This would seem to be followingthe same developmental path as thatenvisaged for the Sky Warrior, in that it isbeing offered with X-/Ka-Band Wide-band and Inmarsat UHF DemandAssigned Multiple Access (Dama) nar-rowband satcom capability.

Britain has acquired four Predator Bsduring the course of 2007, together with anassociated ground station package, havinghad personnel (1115 Flight) stationed atNellis AFB since 2004 gaining operationalexperience as pilots and controllers.

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Italy also procured five Predators in2004, with a ground station made byMeteor (now Galileo). Although theoriginal aircraft were not equipped withsatcom, they were due to be upgraded in2006, but it is not clear whether this hasbeen achieved.

Israel makes considerable use ofdrones, and so it is not surprising that sat-com-equipped platforms have beendeveloped there as well.

The Malat division of Israeli Aero-space Industries produces the Heronfamily. This includes the Heron 1 and theHeron TP, the latter (and much larger)first appearing at the Paris Air Show in2007. Each has the telltale bulbous noseto accommodate IAI's EL/K-1891 fullduplex X- or Ku-band satcom antenna.This is offered with either a 25 � 10 cmplanar array or an 80-cm-diameter dish,both on a dual axis stabilised pedestal.The EL/K-1891 provides a data rate of upto 128 Kbps.

The Heron airframe is also the basisfor the EADS Eagle 1. This is being pro-cured to meet a French Air Force require-ment for a medium-altitude long-endurance system known as the Sidm(Système Interimaire de Drone Male).The French Air Force order is for 24 airvehicles and 25 GCS.The satcom solutionselected by EADS for the system isuncertain, although it might be based onAstrium's Master airborne satellite ter-

It is worth noting that the Watchkeep-er programme, which will use a derivativeof the Hermes 450, will not be equippedwith a beyond-line-of-sight system.

Ruag of Switzerland unveiled itsSuper Ranger shortly before the ParisAir Show in 2007. The drone was shownwith the option of a nose-mounted Ku-band satcom capability, with possibly aUHF backup. Later the same year, how-ever,Armada was told by a company rep-resentative at DSEi that it was unlikelythis route would be pursued.

The Russian Zond and Chinese ASN-207 and WZ-2000 UAVs are also satcom-equipped – they have the telltale bulbousnose – but no information is available onwhat these systems might be.

What of the future? As drones becomemore ubiquitous there may be wider use ofsatcom. However, the need to operate abeyond-line-of-sight system is likely to belimited to a small number of countries.

In the view of Al Modrovsky of L-3Communications-West, the future devel-

The L-3 Communications-West trailer-mounted 6.2-metre Tri-band Transportable EarthTerminal providing C, Ku and X-band communication. (L-3 Communications-West)

While their respective manufacturers are shy about the systems they embark, the Elbit Hermes 900 and IAI Heron TP presented at the2007 Paris Air Show could do little to hide their satellite communication capability. (Armada/EHB)

This model of theSukhoi Zond-2 project,in addition to whatappears to be an earlywarning aerial mountedon the spine of thefuselage, also suggeststhe presence of asatellite communicationsuite under a glider-likecanopy. (Armada/EHB)

opment of drone satcom will revolvearound a reduction in size and weight andimprovements in capability. Modems aredecreasing in size at rate akin to 'Moore'sLaw' for computers: «What was once in abox is now on a card, and soon singlemodems will be able to handle multiplewaveforms simultaneously». While thisreduces some payload, there is only limit-ed scope for reducing the size of a satcomantenna, once the aperture size hasreached the minimum. The wide use ofelectronically steered antennas canreduce the size, but at present these areprohibitively expensive. Additionallythey have lower effective gain, requiremore satellite resources and thereforealso cost proportionally more in satellitelease rates when commercial satellitesare being used. a

minal also believed to be fitted on theBritish Nimrod MRA4.

Some of the Elbit Hermes family,notably the 900 and 1500, are also satcomequipped. Although no information isavailable about the systems used, theymay be related to the Globalight broad-band system produced through a jointventure between Elbit and Gilat SatelliteNetworks. At DefExpo 2006 theyannounced a maritime derivative of theElbit Globalight 2 terminal, intended toprovide wideband Satcom connectivityto ships. It connects the users to an IP net-work, supporting simultaneous exchangeof voice, video and data. The terminalutilises advanced Vsat technology (GillatSkyedge) and a 3-axis stabilized trackingantenna. Such an antenna could be equal-ly applicable to a drone.

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