This Month in Physics History

Of the many scientists who helped transform the space telescope from idea to reality, one of the most impactful—and underrecognized—was Nancy Grace Roman, remembered as the “mother of Hubble.” An internationally acclaimed astronomer in an era when few women were accepted in the field, Roman was tapped by a newly formed NASA in 1959 to serve as its very first Chief of Astronomy. By fostering connections between NASA and astronomy departments across the country, Roman is credited with establishing an ethos at NASA that major astronomy projects would be conducted for the benefit of the broader scientific community. In 1971, she convened a steering committee of NASA engineers and astronomers from around the country to design a space telescope that NASA could feasibly implement, along the way lobbying politicians and writing congressional testimony about the scientific value of such a project, even after funding was initially denied.

In 1977, three decades after the idea of a space telescope was first conceived, Congress at long last approved funding for what was then known as the “Large Telescope Project.” Designs for the telescope began in 1978, featuring a 7.8-foot, 1,825-pound primary mirror to collect light from objects in space, as well as several advanced instruments, including a wide-field camera, a high-resolution spectrograph, and a high-speed photometer.

HST’s launch date was pushed from 1983 to 1986 due to engineering challenges, and further delayed until 1990 in the wake of the Challenger disaster (see APS News, January 2021).

The setbacks did not end after HST was finally launched. After years of anticipation, the first images from HST—over 40 years and $1.5 billion in the making—appeared blurry and out of focus, a far cry from the crisp images expected from an instrument of this sophistication. The cause was later identified to be a spherical aberration: HST’s primary mirror had been ground too flat by a mere 2 microns, 1/50th the width of a human hair. The primary mirror was designed to bring 70% of a star’s light to the same focal point, but with this flaw it could only muster around 10%.

When news of this setback came to light, HST was heavily criticized in the media, lambasted in late night television sketches, and became the subject of a tense, high-profile congressional hearing over who was at fault for the flaw and how it should be fixed.

With HST’s fate and the space program’s reputation in jeopardy, disaster was averted thanks to two ingenious optical fixes. Work was already underway on a second-generation camera, WFPC2, to be later installed in a future servicing mission. Scientists realized that corrective optics could be implemented into this camera to compensate for the warped primary mirror. Separately, NASA scientists developed the COSTAR device—a set of corrective mirrors that could refocus the light paths of HST’s other instruments to properly focus their images, essentially acting as a pair of eyeglasses for the telescope.

In December 1993, a team of astronauts was ferried to HST to install the COSTAR device and replace HST’s original camera with WFPC2. Lasting 11 days and involving a record-breaking five spacewalks, it was one of the most technically complex missions NASA had undertaken to date. The risk paid off: The first images from the newly refurbished telescope to reach Earth later that month were crisp and clear, setting the tone for the jaw-dropping images that HST is now famed for.

Four subsequent servicing missions have kept HST operational for over 30 years, far exceeding the original expectation of 15 years.

While there is no set date for HST’s retirement, no further refurbishments are scheduled. Given the telescope’s aging hardware, the best estimates indicate that it will be brought back to Earth at some point during the 2030s.

It is perhaps fitting that the end of HST’s tenure in orbit coincides with the launch of the James Webb Space Telescope (JWST), sent into space on December 25, 2021 and currently undergoing calibration tests in preparation to begin data collection later this year. While not technically a successor of HST—JWST is primarily an infrared telescope, whereas HST observes the universe in visible and ultraviolet wavelengths—it was designed to push the boundaries in understanding that HST helped to establish. Among these include previously unaddressable questions surrounding “cosmic dawn” and the formation of the first stars as well as gaining further insight on phenomena such as the expanding universe, a concept first demonstrated a century ago by HST’s namesake, the legendary Edwin Hubble.

The author is a freelance writer in Stockholm, Sweden.

Further Reading:

“The Hubble Story.” NASA.gov

Chiasson, E. The Hubble Wars, 1994.