At first glance, the capsules for the Millennium Wheel look fairly conventional. In fact, nobody has ever built anything like them before – and the problems were unprecedented, too.
It will be the ride of a lifetime – of the millennium, even. For the thousands of people eager to see seven counties from a height of 130 m, stepping into a capsule on the Millennium Wheel will be the start of a unique viewing experience.

But for the residents of a tiny village on the outskirts of Grenoble in southern France, where the capsules were manufactured, the first part of the experience at least is becoming rather familiar. As many as 150 volunteers of all ages have spent hours stepping in and out of the capsules, human guinea pigs in one of the many tests the architects insisted on as they struggled to perfect the design of the passenger capsules.

The wheel’s architects, husband-and-wife team David Marks and Julia Barfield, knew that the capsule design would be crucial to the wheel’s successful operation. The brief was a tough one: the passenger capsules needed to be fully enclosed, comfortable and suitable for sitting in or walking around to take in the views while remaining level. As the wheel turns constantly at 0.26 m/s, the capsules would also have to allow passengers to step in and out of them while the wheel revolved. There were no precedents on which the architects could base their design – nothing like it had been built before.

The architects’ solution is 32 transparent eggs measuring 8 × 4 m and capable of carrying 25 passengers at a time. They are divided into three sections: a top one housing the lighting above a suspended ceiling; a middle section where passengers will sit, and a bottom section beneath the floor of the passenger compartment, which contains the air-conditioning system and the motors that keep the capsule level. The capsules are built around a steel skeleton.

The support comes from two ring beams that surround the glazed passenger compartment, which are connected to the wheel by triangular support brackets welded to the outside face of the wheel’s rim. The remainder of the frame consists of glazing bars and supports for the doors.

Surprisingly, the capsule form has changed very little from the early concept sketches to the final design. “Their aerodynamic form was determined by the need to minimise the effects of high winds on the wheel,” says Marks.

The original design was for 60 passenger capsules, with space for 16 passengers in each, clustered around the wheel’s circumference. Following boarding tests in France using a full size mock-up, however, it was found that the capsules could accommodate 25 people. The scheme was changed to allow for 32 capsules. This would increase the space between the cars and improve the view for their occupants.

From the beginning, the architects realised that the design would require some specialist expertise. Nic Bailey, an industrial designer and naval architect, joined the team and led the development of the capsule’s design – initially with Ove Arup & Partners and subsequently with Sigma, the capsules’ French manufacturer.

The first problem the team had to solve resulted from the unique location of the capsules on the very outside of the wheel. On a traditional Ferris wheel, the passenger gondolas hang below the wheel so that gravity keeps the capsules level. By placing the capsules outside the wheel’s circumference, however, their centre of gravity is much higher, so they are more likely to tip over if the passengers move around.

The team therefore decided to control the movement of the capsules using an electric motor. This drives two toothed rings set within the two circular ring beams around the capsule. The levelling system adjusts each capsule’s position according to two factors: the position of the capsule on the circuit and any imbalance caused by passengers walking around inside.

The next challenge for the design team was the glazing. The design was crucial if the passengers were to enjoy the view in safety. The capsules’ elliptical geometry meant that glazing panels had to be curved much more than would be used for car windscreens, for example, but had to retain the same level of visual clarity.

“We sourced glass manufacturers all over Europe,” says Marks. “We investigated different methods of forming the double curve and explored the limits of technology to achieve this degree of double curvature without loss of optical clarity.”

The final solution, specifically developed for the project, was to bend three sheets of glass together and discard the sheet closest to the mould. To ensure passenger safety, the glazing panels were formed from two sheets of 6 mm float glass sandwiched around a layer of polyvinylbutyral foil. This can withstand the weight of six people/m2 per square metre.

As a final safety measure, the glass was glued into the capsule’s steel frame with retention patches.

Two air-conditioning units hidden beneath the capsule floor provide cooling during summer and heating in winter. Air is injected into the passenger compartment around the perimeter of the capsule next to the glazing. “With 25% fresh air, this should stop condensation forming on the glass,” says Marks.

At night, light levels were critical if passengers were to feel safe yet still be able to see out. During boarding and disembarkation, the capsule will be lit from two white fluorescent lights concealed in the overhead ceiling panel.

As the doors close and the capsule leaves the boarding platform, the white light dims and four dark blue fluorescent lights come on. Marks says the level of blue light will be high enough for people to feel secure among strangers, but low enough to avoid distracting reflections on the inside of the glass. Viewed from across the river, each capsule will have “a faint blue glow”, says Marks.

The lights are operated from two on-board computers that, as well as controlling the level of light, are pre-programmed to operate the air-conditioning, open the capsule doors, play pre-recorded messages and commentaries and monitor the capsule’s positioning and stability.

In the event of a fire, the computers can switch off the air-conditioning, open the capsule’s roof vents and alert the operator.

Finding an appropriate manufacturer to develop a prototype and then make the capsules was a major task. There were no obvious candidates for a product that had never been built before.

The design team visited more than 20 companies in the UK and Europe. Boat builders, monorail manufacturers, theme park developers, light aircraft producers, car makers – and even model steam train manufacturers – were all visited before cable-car manufacturer Sigma was selected.

Planning permission for the wheel was granted on the basis that it would be taken down after five years. This seems a shame given the amount of work that has gone into its creation. But Marks is keen to point out that the wheel has been designed to last 50 years and is suitable for wind conditions as far north as Newcastle upon Tyne.

All any potential site needs is a view.