The story of the Hubble Space Telescope

June 09, 2022

With the JWST about to take centre stage in the quest for new images of deep space, we thought it is also a good time to look back at the history and achievements of the Hubble Space Telescope.

Construction started on the Hubble in the late 1970's and it was originally due to launch on the Space Shuttle in the 1983. Continual rescheduling, mainly surrounding construction of the primary mirror, delayed the launch until September 1986. However, this launch date was delayed due to the grounding of the shuttle fleet following the Challenger disaster earlier that year.

It eventually launched aboard the space shuttle Discovery on 24th April 1990, and very soon thereafter, a major problem became apparent.

Flawed Mirror Fault

Scientists expected to see pin sharp images of deep space objects, but instead they got pixelated, blurry images - something had gone terribly wrong! After much analysis it was concluded that the primary mirror had been polished to the wrong shape, and although the error was measured in nanometres, the affect on Hubble's performance was catastrophic.

The very future of NASA depended on their ability to come up with a way to fix the problem. Since the mirror was now in orbit 400 miles above the Earth, the challenge was immense. The Hubble had been designed to be serviced by Astronauts, and this did offer a faint hope of recovery, but NASA still had to come up with a way to resolve the fault without having to replace or alter the mirror.

Just as it seemed the problem may be insurmountable, an engineer came up with an idea inspired by a flip down shower head in his hotel room!! He proposed that a set of mirrors placed in the light path at a particular point would correct the aberration - and it worked.

 One of Hubble's most famous pictures - the Eagle Nebula.

Credit: NASA, ESA, and the Hubble Heritage Team (STScI/AURA)

Features of the Hubble

The Hubble is a cassegrain telescope of the Ritchey–Chrétien variety and features a 2.4 m (7 ft 10 in) mirror, and its main instruments observe in the ultraviolet, visible and near-infrared regions of the electromagnetic spectrum. 

Because it orbits outside of Earth's atmosphere, it can capture ultra-high resolution pictures. Images from the Hubble have led to numerous advances in our understanding of Astrophysics, including the expansion of our universe and discovery of the earliest galaxies.

Credit: NASA

 Achievements of the Hubble

It is fair to say that the Hubble is one of the single most important scientific instruments ever, and it has led to some of the most ground breaking discoveries in science. Here are some of it's achievements:

• The age of the universe - Prior to Hubble scientists had estimated the age of the universe at between 10 and 20 billion years. By measuring Cepheid Variable Stars - stars that pulse at a constant rate - scientists have remodelled the universe and refined it's age to 13.7 billion years.
• Deep Space objects - Hubble has discovered literally thousands of objects that were not visible to ground based telescopes. In this video astronomers have put together the largest and most comprehensive "history book" of galaxies into one single image, using 16 years' worth of observations from NASA's Hubble Space Telescope.

• Exoplanets - our never ending search for habitable planets outside of our solar system has received a massive boost from observations using the Hubble.

What will happen to Hubble

Now that the James Webb Space Telescope is about to enter full operation, inevitably some focus will shift to this even more spectacular instrument, but the Hubble will continue operation until at least 2030 and perhaps to 2040. Since the dangers of a completely uncontrolled re-entry are too great, the current plan is too either soft capture the Hubble and return it to Earth or boost it to a higher orbit.

Hubble Fast Facts

• Launch date - 24th April 1990
• Launch Vehicle - STS31 (Discovery)
• Launch Mass - 11,110kg
• Dimensions - 13.2m x 4.2m
• Orbit distance - 335 miles average
• Orbit inclination - 28.47 deg
• Hubble races through its orbit at about 17,000 miles per hour (27,000 kph), completing an orbit about every 95 minutes. That means it sees 15 sunrises every day. 
• While Hubble is speeding around Earth, it can lock onto a target without deviating more than 7/1000th of an arcsecond, or about the width of a human hair seen at a distance of one mile. 
• Hubble has travelled over 4 billion miles (6 billion km) over its more than three decades in space. 
• Hubble has no thrusters. To change pointing direction, it uses Newton’s third law ― every action has an equal and opposite reaction. Hubble spins internal wheels weighing about 100 lbs (45 kg). When spun in a clockwise direction, the spacecraft itself will turn counter clockwise. The spacecraft turns at about the speed of a minute hand on a clock, taking about 15 minutes to turn 90 degrees. 
• Thanks to its technology and position above the atmosphere, Hubble can see astronomical objects with an angular size of 0.05 arcsecond, which is like seeing a pair of fireflies in Tokyo that are less than 10 feet (3 m) apart from Washington, D.C. 

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