The Hubble Space Telescope: ‘It’s a terrific comeback story’

gathered crowd to watch. On it was to appear the first ever image from Hubble, Nasa’s powerful, sparkling space telescope. That, at least, was the plan. Plenty of the astronomers wanted this event – called, in the business, first light – to be held away from the media gaze. But the press had been invited and arrived in numbers. Together they waited. And then it arrived: the first picture of the heavens from the most impressive space telescope ever built, one that promised a revolution in our understanding of the universe.

It was May 1990 and the $1.5bn Hubble had been in orbit for a month. In the room at Nasa’s Goddard Space Flight Centre in Maryland, everyone stared at the image.

“Some eyebrows went up,” says David Leckrone, a senior scientist who worked on Hubble from 1976 until his retirement in 2009. “It was supposed to be a picture of a binary star, a pair of stars. But it was just sort of a fuzzy blur.” Someone piped up: “It’s OK, isn’t it? That’s how it’s supposed to look?” Those in the know drew breath. That was not how it was supposed to look.

This Friday, it will be 25 years since the space shuttle Discovery lifted the 11-tonne telescope into space. The size of a bus, Hubble began circling Earth as Tim Berners-Lee wrote the first page of the World Wide Web, and the England football team were preparing for the World Cup in Italy. After a near- disastrous start, Hubble came to define our view of the cosmos.

Hubble was named after Edwin Hubble, the US astronomer who discovered in the 1920s that the universe is expanding. Much of the science that the telescope did built on his work. But its origins can be traced back to the German scientist Hermann Oberth who enthused about blasting telescopes into space. It was Lyman Spitzer, a Princeton astrophysicist, who made the proposal convincing. High above the distorting blanket of Earth’s atmosphere, a space telescope could perform science far beyond the reach of ground telescopes, he argued. His ideas appeared in a 1969 report. Lyman was an extraordinary intellect. He won the backing of fellow scientists, and ultimately the US Congress.

Leckrone joined the US space agency the year that Pitzer’s report came out, and moved to the fledgling Hubble project seven years later. The telescope was designed to fit inside the payload bay of Nasa’s new fleet of space shuttles. Astronauts would drop the telescope into orbit, then fly back on occasional service missions, using the shuttle’s robotic arm to grab hold of the telescope and retrieve it.

Nasa hoped to launch Hubble in 1983, but the schedule slipped. The team was about ready in 1986 when Nasa suffered one of the greatest blows in its history. On 28 January that year, the space shuttle Challenger disintegrated over the Atlantic Ocean, killing its crew of seven. The disaster grounded the shuttle fleet for the best part of three years. Without the shuttle, Hubble could not fly. The engineers made use of the delay. When Hubble finally reached the launchpad, seven years late, confidence was high.

Steven Hawley, a former astronaut and astronomy professor at Kansas University, operated the shuttle’s robotic arm that put Hubble in orbit. When the crew was about to start the procedure, he thought of all of the people who had devoted much of their careers to the dream of a large telescope in space. “Everyone was dependent on us executing that last step properly,” says Hawley. The deployment went well. Hubble floated free and the shuttle backed away. Onboard, astronauts captured some breathtaking footage: the telescope apparently suspended as the Earth rolled beneath.

Nasa engineers spent several weeks checking out Hubble’s systems before taking their first picture. The image was a huge disappointment, but Leckrone stayed optimistic. They could adjust Hubble in countless ways from Earth. A few weeks’ work and they would have it working properly, he thought. “Then, some weeks went by and nothing we did made the image much better. Suddenly the mood became very morose,” he says.

The lowest point came one afternoon at Goddard. The various technical teams had gathered for their regular status meeting. One by one, they stood up and gave verbal updates: the computer people, the thermal team, the power group. Then it was time for the optics team. They were still trying to get good images, but so far had got nowhere. Then another voice broke in from the back of the room. It was Chris Burrows, an optics specialist. “There was an edge of anger in his voice,” says Leckrone. “He said: ‘You’ve got half a wave of spherical aberration and there is nothing you can do about it”. The room fell silent.

Hubble’s 2.4m primary mirror was the product of exquisite workmanship, but the curvature of the mirror was not quite right around the edges. The fault meant that images from the mirror would always be blurred because light rays bouncing off the surface were not properly focused. None of the adjustments that could be made from Earth could correct the problem.

The Hubble project was managed by Nasa’s Marshall Space Flight Centre in Huntsville, Alabama. Some Marshall scientists had heard Burrows speak that afternoon. After the meeting, they gathered in a small office to take stock. As Leckrone walked in he heard Jean Olivier, Hubble’s chief engineer, in downbeat mood. “Break out the hemlock, boys,” Olivier said.

The situation was bleak, but not as hopeless as Olivier had feared. An optics specialist called John Trauger at Nasa’s Jet Propulsion Lab in California had shown Hubble’s first blurry image to Marjorie and Aden Meinel, a married couple who ranked among the world’s best telescope designers. They happened to be on sabbatical at JPL and knocked on Trauger’s door when they heard Hubble’s first images had arrived. It took Aden a matter of minutes to diagnose spherical aberration.

Some weeks later, Trauger was at a meeting of the Optical Society when he bumped into Aden Meinel in the buffet queue. They got chatting. Almost in passing, Meinel delivered a bombshell. He knew how to fix the problem.

Trauger was building a copy of Hubble’s Wide Field and Planetary Camera, as a backup. Inside the camera were a series of coin-sized mirrors that reflected light from Hubble’s primary mirror into the camera’s detector. Meinel worked out that curving each of those small mirrors in precisely the right way would cancel out the distortion of the primary mirror.

The space shuttle flew its first service mission to Hubble in 1993. The crew replaced the telescope’s main camera with Trauger’s modified version, and fitted a second device to correct Hubble’s other scientific instruments. Back on Earth, the team pointed the telescope at a patch of space strewn with stars and waited for pictures.

“When the first image came down, it was extraordinarily beautiful,” says Leckrone. “From that point on, every place we pointed Hubble in the sky, there was something new and remarkable. It’s a terrific comeback story.”

Astronauts repaired the orbiting observatory on five separate missions. Stabilising gyros broke, solar panels and a power unit were replaced, and new instruments added. “With every mission, we tried to extend Hubble’s lifetime and increase its scientific productivity,” says Mike Weiss, former programme director. The last servicing mission was in 2009, but without the shuttle, no more are planned. Nasa’s calculation is that Hubble’s instruments will pack up in a year or two. At some point, it will be brought down. Most of it will burn up in the atmosphere, but parts will rain down into the Pacific.

Hubble has taken more than a million pictures. It has revealed regions of space where newborn stars are surrounded by flat discs of dust, the building material for planets of other solar systems. Its images reveal thousands of galaxies. The faintest light we see left those galaxies when the universe was a mere 500m years into its 13.8bn-year existence.

Though Hubble is nearing the end of its life, its pictures and raw data will keep scientists busy. “Hubble has provided the last couple of generations with awe-inspiring images and tonnes of scientific data, and it’s going to continue providing that for decades to come,” says Weiss. “It has far exceeded our expectations. It’s been the thrill of a lifetime.”
Hubble’s big brother

Hubble should not fall from the sky until its successor is in orbit. Nasa’s James Webb Space Telescope (JWST) is earmarked for launch in 2018, seven years later than originally planned. The telescope will blast off aboard an Ariane 5 rocket from the European spaceport near Kourou in French Guiana. Its final destination lies about a million miles from Earth, in the opposite direction to the sun.

Named after Nasa’s chief administrator during the Apollo programme, the JWST has a primary mirror more than five times larger than Hubble’s. The mirror is made up from 18 hexagonal panels which fold up for launch. Once deployed in orbit, the huge mirror should allow the JWST to see much fainter objects than Hubble.

A giant sunshield the size of a tennis court separates the JWST into two sections. The warm, sun-facing side carries solar panels to provide power for the telescope’s instruments. The side facing away from the sun is kept cool, and operates at a temperature of -220C.

Unlike Hubble, the JWST is an infra-red observatory. That gives the telescope the ability to look further back in time than Hubble. Because the expansion of the universe is accelerating, ancient galaxies are hurtling away from us at enormous speed. As they recede, the light they emit is stretched to longer wavelengths, making them appear more red, or “redshifted”. By making observations in the infra-red, the JWST will search for the most far-flung objects: the first stars and galaxies that formed after the big bang.

Planet-hunting telescopes have spotted about 2,000 candidate worlds beyond our solar system. The JWST will watch some of these planets as they cross the faces of their stars. Light coming from the planets, or through their atmospheres, can reveal changes in seasons on the ground, weather patterns and potentially even signs of vegetation.