Slow Orbit · Episode 4 · 18 min

The Life of the Hubble Space Telescope

Spherical aberration: when a mirror's edge and centre bring light to slightly different points, every star gets a soft halo. Hubble's mirror had it, by one fiftieth of the width of a hair. An idea written before the first rocket reached orbit, a mirror ground precisely wrong, astronauts who mended it by hand, and a grain of empty sky that held thousands of galaxies... Inside: a school bus with a mirror, fifteen sunrises a day, glasses for a telescope, the Pillars of Creation, a comet falling into Jupiter. James Webb will be mentioned too. Chapters: The idea · The bus with a mirror · The launch · The flaw · The repair · The deep field · The pillars · The visits · The long watch · Still there. Sources: NASA and Space Telescope Science Institute histories. Read by a synthetic voice; script written and fact-checked by the show's team.

The script

It is January, 1994. In a quiet room on Earth, a picture is slowly appearing on a screen.

A field of stars... and for the first time, each one is a sharp, clean point of light. Not a smudge. Not a blur. A point.

Someone in the room begins to laugh. Someone else is very quiet. After almost four years of waiting, the telescope can finally see.

Slow Orbit. Lecture four... the life of the Hubble Space Telescope.

This lecture is read by a synthetic voice. If these lectures keep you company at night, follow the show... it helps others find it.

Chapter one. The idea.

Why would anyone want to put a telescope in space?

Because the air is in the way.

Every star we see from the ground, we see through a deep ocean of moving air. The air shimmers and bends the light. It is why the stars twinkle... a lovely thing to watch on a summer night, and a terrible thing for an astronomer. The air also swallows whole colours of light that never reach the ground at all.

In 1946, an American astronomer named Lyman Spitzer wrote a short paper with a simple, bold suggestion. Put a telescope above the air. Let it look at the sky as the sky really is.

At the time, no rocket had yet reached orbit. The idea was a dream on paper.

It would take him most of his life to see it come true.

The telescope would carry the name of another astronomer... Edwin Hubble.

In the 1920s, from a mountain in California, Edwin Hubble showed that some of the faint, fuzzy patches in the night sky were not clouds inside our own galaxy at all. They were other galaxies... vast islands of stars, unimaginably far away. Then he found something stranger still. Almost all of them were moving away from us. The farther away, the faster.

The universe, it seemed, was growing.

He died in 1953. He never saw the telescope that bears his name. But the questions it would spend its life answering were, in a way, his questions.

Chapter two. The bus with a mirror.

Through the 1970s and the 1980s, the telescope slowly took shape.

It grew to about thirteen metres long... the size of a school bus... and it weighed about eleven tonnes. At its heart was a mirror two point four metres across, made of glass, polished and polished again for months, then coated with a layer of aluminium only a few hundred atoms thick.

Around the mirror, the builders placed cameras and instruments, and long, flat panels to catch the light of the Sun for power. Small spinning wheels inside would turn the whole telescope, slowly and precisely, toward any point in the sky. And it would have to hold still... more still than almost anything people had ever built... while it gathered the faint light of things billions of years away.

There were delays. There were costs. And then, in 1986, a disaster: the space shuttle Challenger was lost, and every shuttle on Earth was grounded.

The finished telescope waited in a clean room, in the dark, for four more years.

Chapter three. The launch.

On the twenty-fourth of April, 1990, the space shuttle Discovery rose from the coast of Florida, carrying the telescope folded inside its long cargo bay.

The next day, a robotic arm lifted it out, very slowly, and let it go.

There it was. Floating free, about six hundred kilometres above the Earth, its panels unfolding to the sunlight. It would circle the planet once every ninety-five minutes or so... about fifteen sunrises and fifteen sunsets every day... moving at more than seven kilometres every second, and yet, when it looked at a star, holding as steady as a stone.

The astronomers waited for the first pictures.

Chapter four. The flaw.

The first pictures came. And something was wrong.

They were better than pictures from the ground... but not nearly as sharp as they should have been. Every star had a soft, hazy halo around it, like a streetlamp seen through a fogged window.

Why?

Because the great mirror had been ground to the wrong shape.

The error was tiny. At its edge, the mirror was too flat by about two thousandths of a millimetre... around one fiftieth of the width of a human hair. But in a telescope, a mistake that small is enough. The light from the edge of the mirror and the light from its centre never quite met at the same point.

It was traced, in the end, to a testing instrument that had been set up wrongly while the mirror was being polished, years before. The mirror had been made very precisely... precisely wrong.

For a while, the telescope became a joke.

On the evening comedy shows, it was a punchline. Newspapers called it a costly mistake. It was easy to imagine it peering at the sky through a pair of glasses.

And that, in the end, was very nearly the answer.

Chapter five. The repair.

Because the mirror was wrong in a precise way, it could be corrected in a precise way... just as glasses correct an eye.

Engineers designed small corrective mirrors, shaped to cancel out the error exactly, and a new main camera with the correction built inside. Then they began to plan something that had never been done before: a full repair of a telescope in orbit, by hand.

In December 1993, the space shuttle Endeavour rose to meet the telescope. The ship's name was taken from the vessel of James Cook, the eighteenth-century explorer of the Pacific.

The astronauts caught the telescope with the robotic arm, and drew it gently into the cargo bay.

Then, over five long spacewalks, working in pairs, they took it apart and put it back together.

They worked slowly, in bulky suits and thick gloves, tethered to the ship, with the Earth turning beneath them... oceans, deserts, the lights of cities at night. Each bolt was planned. Each movement was practised for months on the ground, in great tanks of water.

They replaced the main camera. They fitted the corrective mirrors. They changed the solar panels and the spinning wheels inside.

And then they set the telescope free again, and went home.

A few weeks later, in January 1994, the new pictures came down.

A field of stars, and each one a sharp, clean point of light.

Chapter six. The deep field.

In December 1995, the director of the telescope's science institute made an unusual choice.

He pointed the telescope at a tiny patch of sky near the handle of the Big Dipper... a patch that looked, from the ground, almost completely empty. A patch about as large as a grain of sand held at arm's length.

And for about ten days, it simply stared.

Many astronomers thought it was a waste. What could there be to see, in a place where there was nothing?

The answer came slowly, as the faint light gathered, frame after frame.

In that tiny, dark patch of sky, there were around three thousand galaxies.

Spirals and smudges and glowing ovals. Some of them so far away that their light had been travelling for most of the age of the universe. Each one, a city of stars. And all of it, in a space the size of a grain of sand.

Nine years later, the telescope did it again, in another dark patch of sky, for even longer. This time, it found around ten thousand.

Chapter seven. The pillars.

In 1995, the telescope turned toward a cloud of gas and dust in the constellation of the Serpent, called the Eagle Nebula, thousands of light years away.

What it saw there has become one of the best-known pictures ever taken.

Three great dark towers of dust and gas, rising out of a glowing haze... like the fingers of a hand, or the columns of a ruined temple. Light-years tall. At their tips, new stars are forming, hidden inside the dust. Around them, the light of young, hot stars is slowly wearing the towers away.

People gave them a name: the Pillars of Creation.

The telescope kept looking.

It watched, in the summer of 1994, as the fragments of a broken comet named Shoemaker-Levy 9 fell, one after another, into Jupiter, leaving dark bruises in the clouds larger than the Earth.

It measured the light of distant exploding stars, and helped to show that the growth of the universe is not slowing down, as everyone expected... but speeding up.

It helped to measure the age of the universe itself... about thirteen point eight billion years.

It looked at the air of planets around other stars. It found small moons around Pluto. It watched storms on Saturn and the seasons on Mars.

Chapter eight. The visits.

Again and again, astronauts came back.

In 1997. In 1999. In 2002. Each time, they brought new cameras and new instruments, and replaced worn parts... like caretakers visiting an old lighthouse.

Then, in 2003, the shuttle Columbia was lost on its way home, with all seven of its crew. Afterward, the last visit to the telescope was cancelled. It seemed the telescope would be left to grow old alone.

But scientists, engineers and many people who simply loved its pictures asked for one more visit. And the decision was changed.

In May 2009, the shuttle Atlantis climbed to the telescope one last time.

Over five spacewalks, the astronauts installed two new instruments, repaired two others that had failed... work never meant to be done in space, with hundreds of tiny screws... and gave the telescope new batteries, new gyroscopes, and new life.

When they let it go, it was the most capable it had ever been.

No one has visited it since.

Chapter nine. The long watch.

So what is the telescope doing now, tonight?

It is still circling the Earth, once every hour and a half or so, as it has for more than thirty years. It has made well over a million observations. The scientists who use its pictures have written many thousands of studies.

It is growing old. Some of its gyroscopes, the spinning wheels that help it point, have worn out, and since 2024 it has been working with just one, slowly and carefully, turning a little more patiently than before. Its orbit is sinking, very gradually, as the thinnest traces of air at that height brush against it.

One day, perhaps in the 2030s, it will come down. Engineers are already thinking about how to guide it safely home.

And far away, beyond the Moon, a younger telescope... named after James Webb... now looks at the universe in a different colour of light. But that is a story for another night.

Chapter ten. Still there.

On a clear evening, just after sunset, the telescope can sometimes be seen from the ground... a small, steady point of light, moving quietly across the sky, catching the last of the sunlight high above the darkening Earth.

It does not twinkle. It does not blink. It slides from one side of the sky to the other in a few minutes, and fades into the Earth's shadow.

It began as an idea on paper, written before any rocket had reached orbit. It was mocked, and mended, and visited again and again. It looked into a grain of empty sky and found thousands of galaxies.

And somewhere above, right now, it is holding perfectly still... gathering the light of a star, one sharp, clean point of light.

Slow Orbit... and the slow orbit goes on.

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