25 years of the Hubble Space Telescope

The Hubble Space Telescope — a joint venture between NASA and the European Space Agency (ESA) — was launched in its orbit 552 km above Earth on April 24, 1990 by the space shuttle Discovery. It has provided breathtaking images, produced fundamental discoveries and brought about a paradigm shift in our understanding of the universe. Hubble has unlocked the wonders of the universe and “placed our world into a context of 100 billion stars in 100 billion galaxies.”

If the spotting of the Hubble variable number one, or V1 star in 1923 in the neighbouring Andromeda galaxy permanently altered the course of modern astronomy, the Hubble Telescope has done it even more dramatically.

The Hubble, which has so far travelled more than 3 billion miles, has made more than 1.2 million observations since 1990 by completing an orbit around the Earth every 97 minutes at a speed of about 8 km per second.

A household name today, it was an instrument that “much of the astronomical community didn’t want!” Worse, it almost turned out to be a dud soon after the launch.

Catastrophic

The bad news came a few weeks after its launch. The very first image taken by it was fuzzy. The primary mirror of the telescope had a flaw called spherical aberration.

“We put a telescope in space and it could hardly see. I felt terrible. I felt like a dog wouldn’t take a bone from me,” Jean Olivier, former Hubble chief engineer told Nature.

“They’ve had 10 years to put this together. They’ve spent $2.8bn to be able to get it right and now we find that the Hubble Telescope’s got a cataract,” Barbara Mikulski roared at the time,” The Independent recalled in a recent article. Ms. Mikulski was a senior U.S. senator who fought hard to get NASA the funding for the development of the telescope.

Though there was no way to rectify the problem from the Earth, scientists found a way to fix it — placing “small and carefully designed mirrors in front” of the original Hubble instruments, much like placing eyeglasses to restore the vision.

In December 1993, seven astronauts spacewalked from the shuttle Endeavour to fix the telescope in space, a mission that was never attempted before. Only the first image from the corrected telescope could tell if the problem was indeed rectified.

“We were all huddled around a little screen, waiting for the first image to come down. It probably only took five seconds but it seemed like six hours.

“First we saw a little dot in the centre, but it was a really well-focused dot. And then we saw the faint stars. You just knew, right then, that we had nailed it. The trouble with Hubble was over,” Edward Weiler, former Hubble chief engineer told Nature.

And months after it was repaired, the Hubble recorded the first major celestial event — the comet Shoemaker-Levy 9 breaking into fragments and plunging into Jupiter.

The 1993 mission to fix the spherical aberration problem was only the first of the five missions to service the instrument. Subsequent servicing missions to repair the telescope and to upgrade it occurred in February 1997, December 1999, March 2002 and May 2009.

During the 1997 service mission, a spectrograph and an infrared camera were added to the telescope. In 1999, an emergency mission was undertaken to repair three of the six gyroscopes. Gyroscopes keep the telescope pointing correctly. The 2002 mission was to replace a camera and solar panels and finally the 2009 mission was to install a new spectrograph and camera (Wide Field Camera 3). Since its launch, astronauts have also replaced the mechanical tape recorders with solid-state memory drives, and upgraded the solar arrays.

With its higher resolution and larger field of view, the Wide Field Camera 3 provides the telescope greater power to image the Universe. Today, the Hubble Telescope has the ability to see in multiple wavelengths — near-infrared, visible light and near-ultraviolet.

To mark the 25th anniversary of the launch of the Hubble Space Telescope, a snapshot of the famous “Pillars of Creation” in the Eagle Nebula was taken last year. The first time the “Pillars of Creation” was snapped was in 1995. Hubble’s instruments that have been upgraded during the 19 years after the original image was taken helped astronomers see more details in the image than was previously possible.