The Secret to Hubble's Success
A technological tour of the Hubble Space Telescope from 1990 to today
By Jason Treat, Anna Scalamogna, and Eve Conant
The Hubble Space Telescope, which has allowed us to peer into the depths of space, celebrates its 25th anniversary on April 24. A remarkable source of scientific research, the telescope has snapped more than 570,000 pictures across the electromagnetic spectrum, from ultraviolet to infrared. What's the key to its success? Hubble has been flexible, adaptable, and expandable. There have been five servicing missions to the telescope since its launch in 1990, and each one has led to more advancements and improvements.
1990 | Launch
Hubble launched in 1990 with five primary instruments designed to capture images from space and transmit them back to Earth.
1. Wide Field and Planetary Camera (WFPC)
This instrument was composed of two cameras: the wide field camera, which had a large aperture to capture wider views, and the planetary camera, which had a higher resolution capable of more detailed observations.
2. Goddard High Resolution Spectrograph (GHRS)
This spectrograph separated and measured wavelengths of electromagnetic radiation so that their different properties, such as temperature, motion, and composition, could be analyzed.
3. Faint Object Spectrograph (FOS)
This spectrograph, like the GHRS, separated and measured wavelengths of electromagnetic radiation so that its different properties, such as temperature, motion, and composition could be analyzed. While the GHRS was able to analyze very fine spectral detail, the FOS could examine fainter objects across a much wider spectral range.
4. High Speed Photometer (HSP)
This instrument measured the brightness and oscillation of light emitted by distant objects.
5. Faint Object Camera (FOC)
The original telephoto lens for Hubble was capable of capturing images in exceedingly high resolution. Extremely sensitive, it could detect the faintest of celestial objects, including individual stars in distant star clusters.
Hubble's Fine Guidance Sensors (FGS) locate distant "guide stars" with high precision and calculate their relation to the telescope's astronomical target. This information gives Hubble operators a reference to make sure the telescope is pointed in the right direction. The FGS also provides high-resolution observations of distant stars.
Distorted images captured by the Hubble Space Telescope shortly after launch were caused by a small flaw—called a spherical aberration—in the telescope's primary mirror.
That small defect in the curvature of the mirror, about one-fiftieth the thickness of a sheet of paper, led to fuzzy images like the one seen below.
A perfectly calibrated mirror focuses light on the telescope’s instruments.
A spherical aberration causes the image to become distorted.
Sources: NASA, ESA, and the COSTAR Team
1993 | Servicing Mission 1
After multiple space walks totaling 35 hours and 28 minutes, two teams of astronauts completed the first servicing of the Hubble Space Telescope.
A key aim of this first servicing mission was to install corrective optics to compensate for the telescope’s defective mirror.
Fixing the flawed mirror required the removal of the High Speed Photometer. A package of corrective optics, Corrective Optics Space Telescope Axial Replacement (COSTAR), was installed to refocus the errant reflected light. COSTAR also corrected the imagery for the other onboard instruments.
The original Wide Field and Planetary Camera was replaced during this mission as well. The new instrument, Wide Field Planetary Camera 2 (WFPC2), featured significantly improved ultraviolet detection and corrective optics. Later, all instruments would include this technology, leading to the eventual obsolescence of COSTAR.
1997 | Servicing Mission 2
Four years later, NASA launched a second servicing mission to replace two instruments and perform further repairs.
The Near Infrared Camera and Multi-Object Spectrometer (NICMOS) stretched Hubble’s range into the infrared and replaced the Faint Object Spectrograph. After a malfunction in 1999, the NICMOS was inoperable for four years until it was repaired during Servicing Mission 3.
The Space Telescope Imaging Spectrograph (STIS) separates light into its component parts. STIS is used for many observations, most notably as Hubble’s main black hole hunter.
1999 | Servicing Mission 3A
When three of Hubble’s six gyroscopes failed, a planned servicing mission was split into two discrete missions. Servicing Mission 3A was launched six months ahead of schedule to address the gyroscope issue.
The mission became more urgent on November 13, 1999, when a fourth gyroscope failed. Without at least three gyroscopes, Hubble entered "safe" mode, becoming inoperable.
During this eight-day mission all six gyroscopes and one of the Fine Guidance Sensors were replaced. Astronauts installed a new computer that was 20 times faster and had 6 times more memory than the telescope’s older model.
2002 | Servicing Mission 3B
The next mission included the installation of the Advanced Camera for Surveys (ACS), enabling the telescope to capture the most distant image of our universe, called the Hubble Ultra Deep Field.
The Near Infrared Camera and Multi-Object Spectrometer (NICMOS), which had been inoperable since 1999, was fitted with a new cooling system, restoring Hubble’s infrared range.
The telescope’s solar array panels were also replaced with smaller, more efficient panels capable of producing 20 percent more power.
2009 | Servicing Mission 4
Two failed instruments, the Space Telescope Imaging Spectrograph (STIS) and the Advanced Camera for Surveys (ACS), were brought back to life by the first repairs ever conducted during a space walk.
Astronauts also installed the Cosmic Origins Spectrograph (COS), allowing Hubble to peer deeper into the universe’s ultraviolet range, where the hottest and most active objects in the cosmos can be detected. COS studies large-scale structures in the universe and the evolution of galaxies.
The Wide Field Camera 3 (WFC3) replaced its earlier version, the WFPC2, providing broad-spectrum coverage, from ultraviolet to infrared. WFC3 includes two cameras: UVIS (ultraviolet and visible) and IR (infrared).
The Hubble Space Telescope has expanded our knowledge of the universe immeasurably. The images it has captured—of spiral galaxies, the birth and death of stars, stellar jets, supernovae, and thousands of other celestial phenomena—will continue to inspire and illuminate even after its expected replacement by the James Webb Space Telescope in 2018.
Sources: Zolt Levay, Space Telescope Science Institute; NASA