Build a rocket, boys (and girls)

Features editor

A chilly Cornish afternoon this week saw the first full-scale test of the rocket that will propel Bloodhound SSC and its anciliary equipment. Stuart Nathan took his earplugs along

Bloodhound’s rocket in the team’s latest simulation video (see below)

Most of my visits to Cornwall over the years have been for holidays, so it was odd to revist the roads around Newquay for this week’s test of the hybrid rocket designed to propel Bloodhound SSC over 1000mph in 2014. A grim, grey chilly day —not unlike many of my Cornish holidays, to be honest — brought me and many others to the surreal landscape of green, flattened half-cylinders that is the Aerohub, next to RAF St Mawgan, where the test was to be carried out.

Each of these structures is a hardened air-shelter (HAS), a reinforced hangar originally designed to keep aircraft safe in case of a bombing attack. Cavernous, cold and concrete-floored, they are utilitarian structures which can’t have seen anything like this week’s event.

It was clear to see just how much Bloodhound has captured the imagination of the country. The place was packed out with over 200 hundred guests — sponsors, suppliers and donors; members of the Bloodhound supporters’ ‘1K Club’; media from all corners of the world; local dignitaries and lots of schoolchildren. Invited from local junior schools, the kids were busily building, testing and racing dragsters powered by compressed air from an upright bicycle-pump, and the hiss, whizz and crack of the model cars on their metal racetrack was a constant background to the events of the day.

It marked out one of the most notable aspects of the Bloodhound project, its educational programme. Built in at Bloodhound’s inception as part of the Ministry of Defence’s quid pro quo for lending the project its jet engine (a Rolls-Royce EJ200 unit that would normally be found in a Eurofighter Typhoon), it has brought in schoolchildren and students of all ages, from primary schools to post-graduate students.

This is one of the things that makes the atmosphere around Bloodhound so different from that of its predecessor, Thrust SSC, which I covered back in 1996. Despite having many team members in common and the truly daunting target of the sound barrier, Thrust had a slight whiff of the shed about it. There was an emphasis on tried-and-tested technology; the car was mainly developed old-school style using models in wind tunnels, with minimal use of computational fluid dynamics. The engines were old, rescued from a scapped F4 Phantom fighter-bomber. There was very little new technology on board, and what there was, was mostly in the form of sensors and telemetry.

It’s a very different story for Bloodhound, even when it’s decamped to a bunch of oversized sheds in the Cornish countryside. Bloodhound is bright and shiny and packed with equipment and technologies on the very cutting edge of innovation. The Cosworth F1 engine which powers the rocket’s oxidiser pump is the one which is currently in the Marussia team’s Grand Prix cars. The jet engine is the latest model from one of the world’s most advanced fighter aircraft. The smooth curves of the car display the extensive use of CFD. And the rocket is like nothing else that’s ever been fired.

The Bloodhound rocket test set-up: the rocket itself is on the left of the blastwall in the centre of the picture, with the HTP tank, pump, gearbox and F1 engine on the right

The excitement of the schoolchildren, inventing and building on the hoof, and the way they are welcomed and included by all of the Bloodhound team, is a real indication of the spirit that surrounds the project.

At the focus of the event was driver Andy Green, RAF wing commander, the first and only person to have broken the sound barrier at ground level, and a man who exudes such an aura of coolness and unflappability that he manages to seem six inches taller than everyone else in a room even when he isn’t. Before acting as a presenter for the rocket test itself, Green was busily trying to give the impression that any result would be a good one.

‘We’re the first to do this kind of testing in public since the days of the Apollo Programme, and this is the first time that we’ve tested the whole rocket configuration, with the F1 engine, gearbox and pump supplying the oxidiser to the rocket,’ he said. ‘And we don’t know what’ll happen. This is front-line, experimental engineering.  We could crack the rocket casing. We could blow the rocket nozzle out of the end. The whole thing could explode. But that’ll give us valuable data that we can start to build on. This is the start of a process that takes us up to the desert in South Africa.’

Andy Green
Radiating coolness, Bloodhound driver Andy Green

The rocket itself is unusual. Rather than being a solid fuel firework like the Space Shuttle’s booster rockets or fuelled by liquified oxygen and hydrogen like most heavy launchers, it’s a hybrid. Its fuel is a solid synthetic rubber, similar to that used in aircraft tyres, and it won’t burn unless it’s heated about 600°C in the presence of oxygen. To achieve that, an oxidising agent — high-test hydrogen peroxide — is pumped at high pressure into the fuel grain through a catalyst pack consisting of 80 layers of silver oxide-plated wires. The silver makes the peroxide break down into water and oxygen, and this releases enough energy to heat the breakdown products to over 1000°C. When they hit the fuel, it starts to burn, generating the thrust needed to propel the car into the record books. The power of the rocket can be controlled by varying the pressure at which the oxidiser is fed into the rocket, which makes it more controllable than a solid fuel rocket and safer than a liquid-fuelled one.

‘The only comparable technology around at the moment is the hybrid that Virgin Galactic is going to use, but theirs is a bit different from ours,’ Green said. ‘Our hydrogen peroxide is quite safe to use – you could swim in it, and you’d come out a bit paler than when you went in but it wouldn’t kill you. Virgin is using nitrous oxide and that will kill you, but it’s more powerful than peroxide and they need more thrust than we do — they’ve got to almost go into orbit, we’ve just got to go pretty quickly across 12 miles of desert.’

Green’s remarks about the safety of peroxide were somewhat belied by the fuelling process, with engineers clad in clumsy green chemical hazard suits transferring a tonne of peroxide into the rocket’s stainless steel oxidiser tank from a long double-line of blue plastic canisters using a long lance and pump.

Presiding rocket prodigy Daniel Jubb — immaculate in a blue three-piece suit, his trademark handlebar moustache maginificently waxed, pointed and curled — also wasn’t displaying any signs of nerves. Over the past three years, Jubb has used CFD to model the flow of peroxide into the catalyst pack, its breakdown, the path of the hot oxygen and steam into the rocket fuel grain and the development of the flame as the fuel burns, and has designed the cross-section of the hollow along the middle of the fuel cylinder into a rounded star shape, intended to stabilise the development and propogation of the flame as the rocket burns. With this test running with the highest pressure peroxide that the team had attempted so far, the way that the fuel grain would burn was one of the big unknowns.

Daniel Jubb (right) and his amazing moustache inspect the rocket HAS

The rocket itself was waiting in another HAS with Jubb’s team and engineers from Cosworth swarming over it. The October chill meant that the F1 engine had to be periodically warmed up with an electric blanket, while Jubb decided that an igniter pack would be used to start the rocket itself — under working conditions, the hot gases from the catalyst pack would be sufficient to start ignition.

With the rocket HAS cleared, the Cosworth team blipped the throttle on the engine a few times before handing over to the rocket control team, seated at the back of the guest audience like the sound crew at a rock concert. We in the audience watched their computer displays projected onto a big screen, along with live video of the rocket itself, as Andy Green talked us through the final stages of the test; the rhythmic barking of the engine clearly audible through two sets of concrete walls and several yards of grass.

Once control had been handed over, the crew opened the throttle on the engine and the needle indicating oxidiser pressure swung over. The messy flame of the igniter pack gave way to a long, narrow tongue of fire and the roar of the rocket caused a perceptible shudder in the concrete floor of our building. During the ten-second burn, a row of diamond-shaped shock waves were clearly visible in the rocket plume, an indicator of smooth fuel combustion; Jubb’s painstaking CFD had worked, to the obvious delight of his team, some of whom had marked the occasion by donning false moustaches.

Shock diamonds are clearly visible in the rocket plume

As the roar died away and the rocket plume diminished, flames continued to roil from the back of the rocket tube. ‘Well, clearly I’m going to have to have a word with the engineers,’ Green said drily. ‘Nobody told me my arse would be on fire at the end of this.’

The test appeared to have destroyed the team’s thermal imaging camera (although this was later rectified by the time-honoured method of switching it off and switching it on again), but the test had been a success. With the F1 engine running at 16,600 rpm, the oxidiser had exited the pump at a pressure of 820psi, and the rocket had generated 14,200lb of thrust — enough to break Thrust SSC’s landspeed record, but not enough to break through 1000mph, said chief engineer Mark Chapman.

However, he stressed that this was merely a first, low-power test; for its full-power runs, the engine will need to pressurise the oxidiser to 1100psi, to generate over 25,000lb of thrust, with a burn of around 20 seconds – twice as much power, for twice as long, as this test. ‘This is a great first step, but we’ve got at least 30 more static firings like this to develop the system up to full power,’ Chapman said.

The equipment which supplies high-test peroxide to the rocket, with the stainless steel HTP tank in the foreground

The flames following the test also didn’t concern Chapman. ‘It’s not a problem,’ he said. ‘It could be some peroxide remaining in the tube — we flush it with nitrogen after the burn, but that might not have completed.’

The road to South Africa’s Hakskeen Pan, where the record attempt will take place, is still a long one. The car itself is still under construction, and should be ready for its first tests, at an airfield in the UK, early next year. Initial runs will be at about 200mph and will help test systems such as Bloodhound’s air brakes, Chapman said.

‘We have two huge air brakes on either side of the car,’ he explained. ‘They’re mechanically linked together so that they open at the same time and rate, and they should work like the air brakes on a fighter jet. But we’ll deploy these at 800mph and at ground level — that’s completely different from the way an aircraft operates. We’ll start testing them at low speeds and work up.’

The trials will also test how the F1 engine responds to its unaccustomed environment. It’s mounted the opposite way around to its racing-car orientation, which affects how the lubricants flow around the engine. ‘We won’t run in the UK with the rocket, but we’ll do tests just pumping water to see how it copes with the acceleration and deceleration,’ Chapman said.

After that, it’s off to South Africa for an initial series of runs where the goal will be to break the existing record, which will also test out the turnaround team whose job will be to remove and replace the rocket, refill the oxidiser tank, refuel the F1 engine and physically turn the car around within an hour. Bloodhound will then return to its Bristol base where it will be stripped down, inspected, and any new parts necessary will be fabricated and installed. That takes the project up to 2014, when the team will return to the desert and begin a second series of runs, with the Sound Barrier as a starting point.

‘It’ll be cramped, very noisy, and there could be a lot of vibration,’ Green said. ‘And the G-forces will change very rapidly from +2 to -3. I’ll have to make some quick decisions on how much rocket power to use, depending on headwinds and tailwinds and so on. It won’t be particularly comfortable,’ he added. ‘But apart from that, it should be quite straightforward.’