Solar system — eleven planets

The brief

An exhibition wanted a full solar system hanging from its ceiling — the Sun, the planets and Saturn with rings — printed from planetary texture maps and able to hold air for weeks without a blower. A hanging set is a different problem from a standing one, because there is nobody at floor level to top anything up.

The no-blower condition is what makes the set sealed rather than inflated on demand. A blower-fed sphere has to have a hose running to it, and a hose running to a sphere hanging over an exhibition floor is both visible and something to route and protect. Sealing the spheres removes the hose and moves the problem to pressure loss.

The client's other requirement was that the set look like a set. Eleven spheres printed individually and checked individually would each be correct and still fail together, because a system reads as one only when the pieces were tuned against each other.

Design

Each body was mapped from a texture onto gore panels so the print has no distortion at the poles. Gore panels are the standard way to build a sphere from flat fabric, and they converge at the top and bottom — exactly where a printed texture stretches and smears unless the mapping accounts for it.

The colour across the set was tuned so the pieces read together on a ceiling. This is the decision the set is judged on. Real planetary colour is not a coherent scheme — the palette across the solar system runs from grey to rust to pale yellow — and eleven accurate spheres hanging together look mismatched rather than accurate.

Saturn's ring is a separate flat chamber rather than part of the sphere. A ring built into the sphere would have to be inflated through the same volume and would pull the ball out of shape where they joined. Separating it means the ring holds its own pressure and the sphere stays round.

Sizes were scaled to read as a system from the floor rather than to true relative scale. A true-scale solar system is almost entirely empty space and one very large sphere; what an exhibition needs is a set where the relationships are recognisable at a glance from underneath.

Build

The spheres are sewn gore panels with a top valve, hanging loops and a sealed inflation port. The loops are sewn into the panel seams rather than patched onto the surface, because a patch carrying the whole weight of a sphere in a ceiling rig is the one place on this build where the load concentrates.

Sealed spheres lose a little air over weeks, so each has a top-up valve reachable from a ladder. That valve is the concession the sealed design makes, and it is deliberately placed so a maintenance visit is a ladder and a minute rather than a scaffold and a rigging job.

The print is on PVC fabric, which is what allows a texture map to be reproduced at this size without the panels drifting out of register across a three-metre gore.

Test inflation

All eleven pieces were inflated together on the factory floor and colour-checked side by side. This is the step that cannot be done any other way. A sphere checked on its own always looks correct; the question only appears when it is lying next to the other ten, and by then the print is already on the fabric.

The test also confirms the rings. Saturn's ring has to sit level on the sphere rather than slicing through it at an angle, and that is a seam-alignment question only visible when the ring and the sphere are both inflated.

It was the last check before the set was packed into a single crate, which is the shape the client wanted the shipment in: one consignment, one unpacking, and no piece arriving separately after the ceiling rig was already booked.

Installation

The client hung the set from a truss grid using the loops we sewed in. We supplied the loop positions and the load each one takes rather than a rigging plan for their ceiling, because their ceiling was not ours to design — but the loops had to be specified so their riggers could plan the grid around them.

Nothing on site needs power. The spheres were inflated to pressure in the factory, and the only site work is hanging and, weeks later, topping up through the valves. For an exhibition running for a season, that is the difference between a display that needs a technician and one that needs a ladder.

Result

It shipped as one consignment and hung as a system. The colour check is the reason: pieces tuned against each other on the factory floor arrive at the ceiling as a set rather than as a collection.

The valves were used, as expected. A sealed sphere over a long exhibition does lose pressure, and designing on the assumption of a ladder and a minute per top-up is what kept the display looking right for the whole run.

What we took from it

The lesson is that a set is a different design problem from an object. Every individual piece here could have been right and the display still could have looked wrong, because the thing being judged was the relationship between the eleven — which means the colour decision has to be made across the set, not on each sphere.

The second is about sealed construction. Removing the blower does not remove the maintenance; it moves it from a continuous process to an occasional one, and that only works if the occasional visit is easy. Where the top-up valve is placed decides whether the sealed spec is practical or a promise.