Interest in weapon-carrying UAVs is growing as aircrew losses become unacceptable. But are they feasible?

Paul Lewis/ST LOUIS

Unmanned combat air vehicles (UCAVS) promise to be as pivotal a development in aerial warfare as stealth technology - but their potential has still to be proven.

Accordingly, much attention is focused on the UCAV advanced technology demonstration (ATD) being conducted jointly by the US Defense Advanced Research Projects Agency (DARPA) and the US Air Force, and a parallel effort now under way with the US Navy.

The ground-breaking ATD entered its second phase with the roll-out of Boeing's UCAV demonstrator system, comprising the X-45 air vehicle, its storage container and reconfigurable mission control station. The first of two X-45s is due to make its first flight from Edwards AFB, California, in the second quarter.

The UCAV effort is intended to demonstrate an affordable unmanned weapon system capable of undertaking high-risk, "first-day-of-the-war" missions while removing the pilot from harm's way. Suppression of enemy air defenses (SEAD) is seen as the most demanding mission. Precision strike is another potential role.

The parallel naval unmanned combat air vehicle (UCAV-N) demonstration adds surveillance to the mission envelope and focuses on the unique requirements of shipboard operation.

Affordability is the paramount requirement, and the operational UCAV must be cheap to produce, operate and maintain. DARPA has set a target acquisition cost of less than a third of the $30 million sticker price of the USAF's future Joint Strike Fighter, while simultaneously achieving operational and support cost savings of around 75% over today's Lockheed Martin F-16CJ manned SEAD aircraft.

DARPA has management responsibility for the first two UCAV ATD phases, with the USAir Force Research Laboratory (AFRL) providing technical support. The programme lays out a series of tests and a graduation exercise which, if accomplished successfully, could lead to a USAF-led risk reduction (RR) and operational evaluation (OE) phase. This would serve as the stepping stone to an engineering and manufacturing development (EMD) effort that could lead to the fielding of an operational UCAV as early as 2010.

The programme began with development of a concept of operations, from which the demonstrator system design was derived. The operational UCAV will be capable of being stored in a purpose-designed container for up to 10 years, but will be transportable to a theatre of operations at 24h notice. Six containerised vehicles at a time will be transported in a Boeing C-17, along with the mission control system and magazines containing the weapons.

Software update and mission plans will be downloaded into the UCAV while it is still stored, and operator training will be entirely synthetic. Once the vehicle is removed from its container, wings will be attached and magazines loaded using the same equipment, to reduce the logistics requirement.

Mission control will be split between two operators: one responsible for the vehicle during taxiing, take-off and landing; the other taking over to conduct the mission. Whereas it takes two people to fly one Predator unmanned air vehicle (UAV), increased vehicle autonomy will allow one operator to control up to four UCAVs.

The exact split between vehicle autonomy and "man-in-the-loop" control will be determined by the demonstration. Development of secure and robust line-of-sight and beyond-line-of-sight command and control (C2) links are a key element of the programme, but ultimately it will be a "political decision" as to how much autonomy is allowed, says AFRL.

The man is expected to remain in the loop for target identification and weapon release authorisation, says Dave Lanham, head of the UAV focus area at AFRL's Air Vehicles directorate. "Rule number one" if contact is lost, he says, is that the UCAV must know what to do, whether it is to loiter until the link is restored, continue with the mission or return to base.

A "seamless" C2 network should make it possible to locate the UCAV mission control station anywhere: at a command headquarters, on a ship, on an aircraft such as the Airborne Warning and Control System (AWACS), or Joint Surveillance Target Attack Radar System. These are operational issues that will be resolved after the demonstration.

Much will hinge on the success of the $131 million second phase of the UCAV technology demonstration, to which Boeing is contributing $21 million. The initial block of testing is due to wrap up this year, and is focused on flying the first X-45 demonstrator, including validating single-vehicle C2, mission software and contingency handling. Block 1 will also serve to define the requirements for follow-on Block 2 testing.

With a second identical X-45 demonstrator due to join the programme next year, testers will begin to explore co-ordinated operations in a multi-vehicle environment. The two demonstrators, along with a piloted Lockheed T-33 fitted with X-45 avionics and acting as a "surrogate UCAV", will be used for interoperability testing, including ingress and egress from the target area, and co-operating with other aircraft in an airbase traffic pattern.

Block 2 will include a series of SEAD-type exercises in which a single air vehicle will detect a ground emitter, manoeuvre to shoot a simulated synthetic-aperture radar (SAR) target image, and transmit the picture back to mission control which will then authorise the UCAV to take lethal action.

This block of testing will culminate in a single armed X-45 actually attacking a representative radar target: "This will allow us to say we understand the technical feasibility to do a pre-emptive destructive mission," explains Col Mike Leahy, DARPA project manager.

While SEAD is the focus of the ATD, it is envisioned UCAV mission capabilities will quickly broaden out to include striking other high-value targets, as well as electronic warfare. The operational UCAV will have an unrefuelled radius of action of 1,100km (600nm) carrying a full load of weapons. The vehicle can also self-deploy 5,500km with the addition of external and weapon-bay fuel tanks. In a separate study, AFRL is looking at inflight refuelling of UCAVs as an option.

Boeing has designed its 6.8t gross-weight UCAV around two internal weapon bays with a maximum payload of up to 1.4t. One of theX-45's bays is currently occupied by a test avionics pallet. A wide range of existing and future weapon types has been studied, and the UCAV is capable of accommodating either 225kg (500lb) Joint Direct Attack Munitions or 115kg Small Smart Bombs.

"Dropping a weapon is not central to the demonstration, it's just icing on the cake. What's important is everything that leads up to being able to approve the release of the weapon," says Richard Alldredge, Boeing Phantom Works UCAV programme manager. Critical to this is the ability to reliably transmit real-time data between the UCAV and the ground station, such as target identification, location, designation and weapons authorisation, as well as being able to conduct follow-up bomb damage assessment.

Another Block 2 man-in-the-loop test objective is to demonstrate the C2 of multiple autonomous air vehicles by a single mission controller using a ground simulation laboratory in Seattle. "A combination of these events will get us to a graduation exercise," says Leahy.

Seamless path

The yet-to-be-funded follow-on RR and OE phase is pencilled in to begin around the middle of next year and to continue into 2005, at which juncture a decision is scheduled to be taken on launching into full EMD. "We've laid out a seamless path that could take us all the way through," says Leahy. The emphasis in the next phase will be on assessment of the UCAV's military utility and operational value, and it will include the addition of a more production-representative prototype by the end of 2003.

It is probable the third UCAV will incorporate low-observable (LO) features, including composite substructures. The first two demonstrators, while retaining the outer mould lines of a stealthy vehicle, are of metallic construction and include no LO treatment. "The third vehicle is the key in demonstrating the affordability of this system," notes Alldredge.

The intention is to equip the third vehicle with a more production-representative sensor suite to aid decision-making. One of the aims of the UCAV demonstration is to determine the correct balance between on- and off-board sensors. "The less the better," says AFRL's Lanham, as the greater the number of sensors carried, the more complex, heavy and costly the air vehicle will then become.

The sensor suite will include an SAR. This could leverage the USAF's investment in the Northrop Grumman/Raytheon Multi-Platform Radar Technology Insertion Programme, under which a family of modular and scalable active-array antennas will be developed. The SAR could be accommodated in one of the UCAV's two mission bays.

There are also plans to incorporate the emitter location system developed under DARPA's Advanced Tactical Targeting Technology programme. This uses a network of receivers on manned and unmanned aircraft to determine and share the location of emitters.

While the third UCAV prototype will likely retain the X-45's 7,000lb- (31kN) class Honeywell F124 powerplant, this will not be the choice of engine for a future operational vehicle. The in-service UCAV would require an engine providing high transonic performance at altitudes above 35,000ft (11,000m). DARPA and Boeing are looking at a number of General Electric and Pratt & Whitney options including the modification of an existing commercial core.

"By Phase 4 we'll be ready to go into a traditional acquisition EMD phase. We believe we can understand and be ready to go in by 2005, and that will allow us to have some form of initial operational capability by the 2010 timeframe, but we do not have any current funding, so it may or may not happen," cautions Leahy.

Shipboard operations

The UCAV-N programme, which is running about a year behind the air force effort, is structured differently. Because the UCAV demonstration will cover many technologies common to both programmes, DARPA plans to focus on the unique requirements of the naval mission, particularly shipboard operation.

"We do not intend to repeat things done in the UCAV programme that are identical or similar to UCAV-N," says DARPA programme manager William Scheuren. At the same time, the USN believes its operating environment is sufficiently different to warrant a separate demonstration. "We want to leverage the USAF UCAV, but this is not necessarily 'son of UCAV'," he says. "We want this to be a naval system - if it's completely different [to the UCAV], that's okay."

DARPA hopes that, by not repeating work performed under the UCAV programme, it will be able to fly competing demonstrators that Boeing and Northrop Grumman are working on under 15-month feasibility studies: "This is patterned after what we did in Phase 1 [of the UCAV programme]. It's taking what we've already learned in the first phase of the air force programme and applying that to the unique challenges of a shipboard environment," says Leahy.

Whereas DARPA and the USAF downselected to one UCAV design for demonstration, and mapped out a programme leading to development and deployment of that vehicle (an approach already used for the Northrop Grumman Global Hawk UAV), the UCAV-N programme does not lead directly to development of one or other of the competing designs. "At the end of the demonstration phase there is a 'clean break' and we hand the programme over to the service with two contractors," says Scheuren.

In addition, at the end of the current feasibility study phase, the USN will have the option of proceeding with its own flight demonstration or joining the DARPA/USAF programme in its planned third phase starting in fiscal year 2002.

Having started later than the air force effort, the UCAV-N programme is on "a fast track", says Scheuren. Northrop Grumman plans to roll out a flyable model of its UCAV-N demonstrator early this year. This will be used to perform trial catapult "shots" and arrester "traps" on a simulated carrier deck at the US Naval Weapons Center, China Lake, California.

DARPA said the UCAV-N should be ship-based, not specifying carrier-based, although "it looks like it will be [carrier-based]," Scheuren says. This poses unique challenges: "The carrier is a very confined and structured operating arena, and it will be a major challenge to fit [the UCAV-N] into that environment." Scheuren believes the naval mission is more challenging for a UCAV in areas ranging from the concept of operations to the air vehicle design. For example, adding the surveillance mission, equally weighted with SEAD and strike, needs good loiter performance.

The biggest challenge, and one not faced to the same degree by the air force programme, is gaining the acceptance of the manned aircraft community. While land-based UCAVs must operate with manned aircraft, they will not necessarily replace them, though each carrier-based UCAV-N will displace a manned aircraft from the space-constrained flightdeck of a carrier.

"UCAVs are going to have to earn their way on to the deck of a carrier, because something is going to have to come off," the USN says. "They will have to be at least as survivable as manned aircraft and have similar or better combat effectiveness. That's a tall order," says Scheuren.

Additional reporting by Stewart Penney and Graham Warwick

Source: Flight International