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Sunday, October 3, 1999 Published at 16:57 GMT 17:57 UK


Window on the world

The cupola design has been fully tested on computer

By Alun Lewis of BBC Science

It is one of the costliest windows ever constructed.

But then it is going into one of the most expensive pieces of real estate known, and will give the best view of our planet and the heavens when the International Space Station (ISS) nears completion in three year's time.

A consortium of European engineers working for the European Space Agency (Esa) is designing and building a two-metre-diameter, seven-paned dome or cupola that will give astronauts working on the orbiting science laboratory an unparalleled view of the station itself, the stars and, perhaps most importantly, their home planet.

"You can't imagine, unless you've been into space yourself, how vital it is to be able to see "home" with your naked eye - rather than through a camera and TV screen" says experienced NASA astronaut Marco Runco. "It keeps you sane."

BBC Science Correspondent Sue Nelson: "The Earth from space is a magnificent view"
Apart from the obvious psychological advantages, there are two other practical reasons for including this large porthole in the space station's specification, according to Alan Thirkettle, head of Esa's Modules Division.

"The glass will be ground flat and optically perfect allowing scientists take as many photographs as they like of the views. It'll be like having their own private Hubble space telescope. It will also give the crew members a perfect view of the robot arms that move around the outside of the station conducting routine repairs and maintenance.

"A good view with both human eyes makes working the robot arms much easier and more natural."

[ image: The mock-up impresses astronauts Pedro Duque and Mario Runco]
The mock-up impresses astronauts Pedro Duque and Mario Runco

Useful though it is, the glass dome with its six individual windows spaced round the circumference of the dome and one on top, poses several engineering challenges.

The fused silica glass is not unusual but for the first time space technologists will use four layers to create a 100 mm thick pane for each window. That is one more than used on Nasa's space shuttles or high-flying Concorde.

"The two middle layers resist the huge force of the pressurised interior," explains Alan Thirkettle, "and the inner layer protects them both from the boots of astronauts floating in zero gravity and loose tools."

[ image: Even typing can be a problem in microgravity]
Even typing can be a problem in microgravity
The outer layer protects the window from space debris - a tiny piece of metal from an old satellite travelling at 18 kilometres a second has far more energy than a rifle bullet.

The service crews will use this viewing room to control the robot arms and will be spared dangerous space walks.

"We've had to design a control panel for the exterior robot arms that can be moved around from one side of the cupola to the other so that it's in the right place according to which part of the station is being worked on," says Marianne Torner, and ergonomics expert working at Lindholmen Developments of Sweden.

"Using both human eyes gives a sense of distance and depth which you don't get from flat two-dimensional TV screens. And we've also provided a natural body restraint that stops the astronauts from drifting away from the joystick controller when they push against it.

"Even typing commands on the lap top computer key board can be tricky when you slowly drift away with keystroke."

[ image: It will give astronauts a perfect view of home]
It will give astronauts a perfect view of home

All images by Lindholmen Development, Research & Development Dept

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