The Hubble Space Telescope, one of the most successful and most beloved science experiments of all time, is 25 years old this week. But its lifetime has been full of drama. It ended up launching seven years late in April 1990, costing significantly more than expected. When NASA engineers first turned it on, its images were blurry, caused by a flaw introduced in manufacturing its primary mirror. The telescope and the space agency that launched it were redeemed when seven astronauts flew onboard the space shuttle Endeavour in 1993 to install a new camera and a package to fix the instrument’s optics. That visit was followed by four more shuttle servicing missions to upgrade and repair the observatory, allowing it to remain a cutting-edge tool for astronomy for a quarter century and counting.
 
In wonderful interviews with Scientific American, scientists, engineers and astronauts who worked on Hubble recall its ups and downs. Edited excerpts appear below.
 
The optimistic early years
David Leckrone, former senior project scientist for Hubble at NASA Goddard Space Flight Center in Maryland:
I started working on Hubble in 1976 and I worked on it until in 2009, basically my whole career. When I came onboard, Hubble was supposed to fly in 1983. Those were the heady days when we were all optimistic. We thought this thing could be done in a certain amount of time and could be done cheaply, which was a big part of our early problems.
 
John Troeltzsch, senior program manager at Ball Aerospace & Technologies Corp., which built seven Hubble instruments over the years:
I was in my mid-20s in the 1980s, an aerospace engineer. Hubble was the coolest concept—it was state of the art at the time. You had phones still plugged into the wall with cords then. There were no computers controlling the machines that we used to build the hardware; it was done by machinists. We were still doing drawings by hand.
 
Story Musgrave, former NASA astronaut and astronaut lead on the Hubble project:
At the astronaut office starting in 1975 we identified every possible failure on the telescope and came up with the tools and procedures to fix it. As the design matured, my procedures matured; I had prototypes and mock-ups.
 
Delays and threats of cancellation
Leckrone:
Before 1983 there was just dogged belief that we could bring this thing in for $400 million. But that was founded on the certainty that if we exceeded that amount of money, Congress would cancel the mission. That’s why there were very draconian discussions of throwing away some of the instruments. And without the instruments you can’t do the science. We were very much worried, very much angry, because the leadership of the project wouldn’t face the reality of what needed to be done. Finally, they decided we either needed to fish or cut bait, and they decided to fish.
 
In 1983 NASA said we’re going to give you a substantially larger budget, get you new, fresh-blood managers, and we’re going to reset and start down a different path. And that helped a great deal. Then we were optimistic we could make a launch in 1986, but unfortunately in January of ‘86 the Challenger disaster happened. We were designed hand-in-glove to work with the shuttle and the shuttle was designed hand-in-glove to carry the telescope. The wonderful aspect of that was that we were going to be able to service Hubble in space, and replace and repair instruments. But the downside was being locked in with the shuttle program when the shuttle had its own serious problems.
 
Launch
Leckrone:
I was at the Cape and it was thrilling. Challenger was fresh in our minds, so as that thing lifted off the pad, we were all just absolutely holding our breath. The shuttle’s got this huge wonderful telescope in it, so you just can’t imagine a catastrophe. The glorious, wonderful moment was when it was finally up.
 
Troeltzsch:
The day of launch was a very long day, very exciting. Many things stick in my mind—one is driving to Goddard that morning. That day there were so many cars that we were just parking on the streets. It was very festive—it was a spring morning, sunny, and there was this air of anticipation in the air.
 
Spherical aberration
Leckrone:
NASA had promised the press that they could be present when we brought down the first images. The first images came down and they were not very much better than a ground-based image that we were showing for comparison. It seemed strange at the time but most of us thought, well the telescope just needs to be focused. There were many knobs you could twist to get it properly aligned. Unfortunately no matter what we tried we could not get it focused. It became obvious that we had basic spherical aberration [a flaw in the geometry of the mirror]. It was a complete shock to everybody and a huge, huge embarrassment.
 
Robert Brown, senior scientist at the Space Telescope Science Institute in Maryland, the scientific operations center for Hubble, and former Hubble project scientist:
There was a backlash. [Maryland Sen.] Barbara Mikulski famously called it a “techno-turkey.” A number of astronomers who were at the peaks of their careers decided to do something else rather than wait around for a possibly fixed telescope.
 
Finding a fix
Brown:
People at PerkinElmer who built the mirror went back and reconstructed what went on in the testing and found that a little measuring rod that was supposed to be part of their optical testing had been inserted in their device backwards, and that led to polishing the mirror perfectly to prescription, except that the test was wrong—they introduced spherical aberration to get a good image out of bad test equipment.
 
Troeltzsch:
It was 21 months from when we started to when we delivered the finished COSTAR [an instrument package to compensate for Hubble’s flawed optics] to Goddard. Typically that would be about a four-year job. The fix was beautiful and eloquent, but so wicked complicated. The light entering the instrument aperture is really a three-dimensional wave. COSTAR would capture that wave, fix it, then put it into the same [aperture] hole that it was supposed to go into originally. The mirrors had to be ground very, very precisely to a very difficult shape—basically the shape of a potato chip. And then you have to position these mirrors very precisely to a tenth of a millimeter, and then the mirrors have to be stable as Hubble goes around the Earth and it warms and cools.
 
Repair crew to the rescue
Musgrave:
I did three of the five spacewalks. I first saw the telescope through the air, getting bigger and bigger as it got nearer to the shuttle. She’s a very big telescope. When we start to catch up, that tells you, hey, it’s your moment now, here she comes. Then you grab it. When you go out, it’s a nice, serene, quiet dance—you just do the dance. There’s no nervousness and there’s no pressure. You do what you’ve got to do and you accept victory or defeat. It’s not exhausting; you’re not even tired.
 
Troeltzsch:
I’m watching the TV and there’s an astronaut holding COSTAR, drifting across the shuttle bay—it was so cool. I thought, “I just touched that thing.” They plugged it in, hooked up the cable and that’s when we did our job. We turned it on and made sure it worked. Imagine if we had set out to fix Hubble and we had not fixed it? It would have been horrible. There was just this incredible relief and satisfaction that it worked.
 
Science results
Leckrone:
It was in late December 1993 when we started collecting new data. We were so relieved and so happy. And in January there was a big meeting for the American Astronomical Society, so the scientists hustled to get their data reduced and interpreted scientifically so they could present it at that meeting. We had so many great papers that showed the kind of scientific data we had expected all along.
 
Brown:
At that point we were seeing the sky clearly for the first time in human history. No matter where you pointed the telescope, it seemed you saw something that was different, that you hadn’t seen before.
 
Comet Shoemaker–Levy 9 smashes into Jupiter
Leckrone:
July of ‘94 was when 21 fragments of Comet Shoemaker–Levy 9 crashed into Jupiter. It put on a wonderful show for about a week and it captured the attention of the whole world. The Hubble images of that were just glorious. You could see organic molecules being generated, for example, as the gas of Jupiter’s atmosphere heated up.
 
Mario Livio, senior astrophysicist at the Space Telescope Science Institute:
The Shoemakers and the Levys were here, having a press conference in the auditorium, but we were downstairs looking at the screen. We didn’t know if we would see anything. But we did see this plume, like a mushroom cloud. It was amazing. That’s a moment that I vividly remember.
 
Hubble’s Deep Field
Livio:
Bob Williams was the director of the Space Telescope Science Institute and he was thinking of using some “director discretionary time” to do something big. He convened a committee of experts that were supposed to suggest what the telescope would do. All kinds of options were discussed and then the option that remained was: Why don’t you just blast one area of sky for 10 days and see what happens? It wasn’t clear exactly what we’d see.
 
Leckrone:
They started at that blank space and when all was said and done there were thousands of galaxies there that had never been seen before. Some of them emitted their light nine billion years ago. What was terrific about this was that there were papers published just prior to Hubble’s launch that said we wouldn’t be able to do that, that galaxies that distant would just be amorphous blobs that would fade into the background.
 
Four more servicing missions
Livio:
The other servicing missions were perhaps not as intense as the first one, but each one had its own important moments. In particular, the last one in 2009 was when the mission was originally canceled following the Columbia shuttle disaster and then it was reinstated by NASA Administrator Mike Griffin. We knew this would be probably the last servicing mission so this was very, very important. They installed two new instruments and repaired two existing ones.
 
Andrew Feustel, NASA astronaut who conducted three spacewalks during the final mission to Hubble in 2009:
This was my first mission to space and so as a rookie to have had that opportunity to be selected for such a prestigious mission was a privilege and an honor. We trained for over three years for this mission and I spent roughly 300 hours in a spacesuit underwater practicing all the work I would do in space. Each time I see a new image from the telescope, it’s amazing to know you’ve got a part in the history of what the telescope is proving.
 
Still on top
Troeltzsch:
Every year the Space Telescope Science Institute puts out a call for Hubble proposals. Every year something like five or six times more people ask to use it than can ever possibly use it. The science it’s doing is competitively selected from astronomers throughout the world.
 
Livio:
There has been almost no scientific experiment that has done as much as Hubble has done in terms of inspiring the public, making them really feel these are big discoveries, making people appreciate our place in the cosmos. Hubble images appear now everywhere, and I mean everywhere. They are in films, TV programs, mentioned in all kinds of places. Hubble images have inspired at least two pieces of contemporary music that I am aware of, and have appeared in late-night TV shows. When you get into the pop culture like that you know you’ve really made it.
 
Brown:
God willing, it will go on doing its wonderful thing indefinitely into the future. The past 25 years are wonderful proof that nothing limits the ingenuity of people to use a very capable instrument to do new things.
 
Feustel:
This will probably be the most important scientific instrument that humans have ever built. I think the nation, and the world, really, should be proud.