Out of the shadows

Just a few years ago the idea of a robot combat aircraft was little more than a glint in the eye of the most forward thinking military scientist.

While remotely operated drones used for reconnaissance have been around for some time the autonomous, unmanned combat air vehicle (UCAV) has remained in that shadowy area where military secrecy and the whispered rumours of science-fiction geeks make the truth hard to find.

But now the veil of secrecy is beginning to slip and, in both the US and here in the UK, the use of robotic combat aircraft is fast becoming a reality of modern warfare.

Under a £124m MoD contract announced late last year, UK engineers have begun work on the development of a prototype unmanned air vehicle (UAV) that could pave the way for a new generation of autonomous, stealthy aircraft and ultimately spell the end for human bomber pilots.

Headed by BAE systems, the aim of the portentous-sounding Taranis project (named after the Celtic god of thunder), is to build and fly a technology demonstrator that will autonomously travel long distances deep into enemy territory and sneak past sophisticated air-defence systems. It will, says Chris Clarkson, BAE’s technical director of autonomous systems and future capability, ‘demonstrate the maturity of some of the key technologies required for a deep-strike UCAV’.

The four-year project also involves Rolls-Royce, which is developing the propulsion system; Smiths Aerospace, which is working on the flight electronics and Qinetiq, which is developing the autonomous flight control alongside BAE. Ground testing of Taranis will take place in early 2009 and the first flight trials are expected a year later in Woomera, Australia.

After that, if the project achieves its aims, it is up to the MoD to decide whether deep-strike UCAVs will form a part of its future air capability.

Some aspects of Taranis’ design are still to be finalised while other details are closely guarded but the finished vehicle is expected to borrow heavily from earlier BAE UAV projects such as Raven, Corax and Herti.

While the precise dimensions of Taranis are under wraps, the aircraft is expected to be around the same size as a BAE Hawk jet [these are 12.4m long]. This would make it one of the biggest UCAVs yet developed, although it is possible that a full production version of such a vehicle would be bigger still given the payload it might be expected to carry.

So what would a deep-strike UCAV be capable of? While suggesting it would fulfill a similar role to the Tornado, BAE was otherwise tight-lipped.

So The Engineer consulted renowned UAV expert, Bristol University’s Dr Thomas Richardson, who was happy to indulge in some informed speculation.

Based on the few glimpses that BAE has allowed of the Taranis design, Richardson said it looks like it would be used to carry out stealthy, ground-attack missions, possibly involving air-defence targets, in the initial phases of a military operation. He said on route to the theatre of operations he would expect Taranis to cruise at an altitude of up to 35,000ft before flying low in the final stages of attack to avoid radar detection.

Given this, Richardson said the performance of the aircraft will probably depend on stealth, rather than speed. ‘I expect that Taranis will not be capable of supersonic flight and will probably have an upper limit of Mach 0.8.’

He added that he does not expect the aircraft to be particularly manoeuvrable. ‘The role for Taranis will depend on it remaining unobserved and it is unlikely, especially at this stage, that they are considering rapid manoeuvring in order to avoid air or ground threats.’

Despite the emphasis on stealth, performance is still an issue and BAE’s Clarkson said one of the tricks in the design process will be striking a balance between these two characteristics. ‘You want it to have a low signature but you still want it to be able to reach these in-depth targets — you still have to have the performance capability and it’s got to be flyable. One aspect of this sort of generation of vehicles is the lack of a vertical fin, so the ability to control the vehicle is particularly important,’ he said.

One of the biggest keys to Taranis’ stealthiness will be its autonomous operation. While most production UAVs now in use are remotely operated Taranis, said Clarkson, will operate with an unprecedented degree of autonomy. ‘It needs to have intelligence in its mission systems to allow it to route round threats and take evasive action if it needs to do so, without having to have a human involved.’

Thus, while human operators will be called upon if the vehicle has gone off-course, or to authorise weapons deployment, its communications back to base will otherwise be kept to a bare minimum, helping the aircraft to remain hidden from enemy eyes. ‘If you’re on a sensitive mission, every time you communicate back with base, that’s when the enemy will spot you. You only want to be communicating those times that you have to,’ he said.

The autonomous operation draws heavily on work carried out by BAE on Raven, Corax and Herti. ‘Raven and Corax demonstrated the ability to start with a mouse click and end with a mouse click — and upload new missions to the vehicle. You can ask it to loiter, you can tell it to do things during the mission if you need to but equally if it lost communications it would continue to do its mission,’ said Clarkson.

Explaining the operation of Herti’s autonomous system, Clarkson said that the vehicle is programmed with a 3D corridor, a time constraint as to when it has to be exiting that corridor, and a 3D box when it gets to the target area that it can fly within. ‘It can do what it likes as long as it doesn’t go outside that corridor,’ he said.

On the relatively few occasions the aircraft will need to talk to the outside world, it will use a communications system that is also being developed with stealth in mind. Clarkson declined to reveal the specifics of this system but said many of the design challenges are focused on keeping the radar cross-section low by ensuring nothing protrudes from the body of the aircraft.

‘You can’t have lots of aerials sticking out — the key technologies here are how you integrate the antennae in the vehicle, in a way that you don’t have protuberances that would give it a high radar signature.’ He added that BAE has already demonstrated the required technology ‘on the bench’ but this is the first time it will be brought together on a flying vehicle.

A critical element of any military communications system is how the data is collected and packaged before being sent back to base. To meet this challenge, Clarkson said Taranis will use BAE’s ICE image collection and exploitation technology. Previously tested on Herti, Raven and the BAE autonomous underwater vehicle Talisman, this autonomously collects and distributes high-quality images using specially-developed image compression technologies. According to a recent BAE announcement, the technology is being further developed so that it can form part of an onboard auto-routing capability and threat-avoidance system, and provide an automatic target-recognition capability.

As to how how images are acquired by Taranis, Richardson suggested the system is likely to use existing, off-the-shelf components.

‘It is very unlikely that they would develop bespoke solutions in terms of sensing technologies given both the timescales and the budget involved,’ he said, adding that sensors used might include synthetic aperture radar (SAR) and/or infra-red (IR).

BAE will not discuss the weapons payload that will be carried by Taranis. Some reports have suggested the vehicle may be equipped with directed energy weapons but Richardson thinks this unlikely. ‘I would suggest that it will be designed to carry conventional weapons, probably stowed within the vehicle,’ he said.

He added that the stealth requirements of the design mean it will be undesirable to have weapons mounted on pods outside the vehicle and any weapons are likely to be stored internally. However, the challenges of safely releasing internally stored weapons are considerable. ‘Weapon release from internal weapons bays is an ongoing area of research aimed at the safe, reliable release of weapons into the air flow. Modelling and testing of weapons release is an ongoing engineering challenge,’ added Richardson.

The development and integration of the propulsion system, which some reports have suggested may be based on Rolls-Royce Adour engine, is also governed by stealth considerations. ‘You don’t want to be throwing a lot of energy overboard so that IR missiles can see the vehicle. You have some very difficult propulsion integration things to do. You haven’t got the freedom you have with conventional aircraft,’ Richardson said.

Here, Clarkson’s team is drawing heavily on the lessons learned with Nightjar, a six-year BAE project, which concluded earlier this month. Carried out at BAE’s Warton site in Lancashire, the Nightjar project centred around a testbody specially designed to have a low radar signature, so that technologies fitted to it could be analysed without the body itself figuring in the test results. During these tests Nightjar provided vital data on air-induction systems (intake and ducts) performance.

As well as developing the on-board technology, another important aim of the Taranis project is to demonstrate the ease with which such a vehicle could be manufactured.

Again, this side of the project will borrow from previous forays into the world of UAV production and is likely to draw particularly heavily on rapid prototyping techniques initially investigated during the Raven project. ‘We’re looking at composite technologies that don’t need the enormous great autoclaves that we need for today’s composites,’ said Clarkson.

Richardson said such an approach would reduce infrastructure costs and lead times as well as bring other benefits. ‘Given the tight timescale, rapid prototyping would be highly desirable as well as damage-tolerant, light-weight stealthy materials, all of which would lend themselves towards composite materials.’

Ease of manufacture is likely to be further enhanced by the mix-and-match approach employed by BAE’s UCAV developers. ‘Rather than reinventing the wheel — the same flight control system would be used in Raven, Corax and Herti and they all have the same fuel systems and the same electric actuation systems, so you don’t have to come up with a new set of actuators for each system,’ said Clarkson.

He believes this approach, which enabled BAE to take Raven, Corax and Herti from concept to development in just 10 months, was one of the major factors in securing the MoD contract for Taranis.

Despite the corners that can be cut using the latest manufacturing techniques, a production UCAV based on the Taranis model will not be cheap. Indeed, according to Richardson, the cost of any production vehicle is likely to be close to that of an existing strike aircraft (about £25m). Instead, he claims, its potential to reduce troop losses is likely to be the biggest selling point for the MoD.

‘It is often thought that UAVs would be cheaper. However, in this role the platform still needs to be able to carry the same payload as well as having an increased level of autonomy compared to that of existing strike platforms.

‘The benefit of UCAVs such as Taranis is not in terms of cost but predominantly in their potential to be able to reduce the risk to military personnel.’

Beyond its potential as a future aircraft, Taranis is also extremely important in developing the UK’s general level of autonomous vehicle expertise.

Richardson said while it is possible to learn a lot about autonomy using computer simulations, there is no substitute for the experience gained by developing the real thing. ‘This is a really exciting time in the aircraft industry where UAVs are just beginning to demonstrate what they are capable of.

‘This is the next logical step in UAV development within the UK and it will be fascinating to see how Taranis develops.’