Hubble Space Telescope: Searching the Sky
Hubble Space Telescope: Searching the Sky
The Hubble Space Telescope has inspired and drawn people into astronomy and space studies more than any other astronautical advancement in the past 20 years. During NASA's tumultuous history since the mid-80s, the Hubble Space Telescope is one of the notable advancements during a time of budget cuts, monetary stress and mission failures.
The major quest for a space-based telescope began in 1966, when NASA launched the Orbiting Astronomical Observatory (OAO). An immediate failure due to power subsystem failure, NASA launched OAO-2. OAO-2 successfully stared into space during 1968-1972, outliving NASA scientist expectations and proving an extra-terrestrial telescope was feasible.
In 1974, lobbying began to fund a NASA-led space-based telescope. The National Academy of Sciences advocated the space telescope, along with astronomers across the United States. The 1977 Congress proposed and approved a budget of $36 million dollars for the telescope, and it was dubbed the ?Hubble Space Telescope? after Edwin Hubble. The target launch date was scheduled for 1983 and engineering began in earnest.
The engineering of the Hubble Telescope was a multi-agency effort. Lockheed was awarded a contract to design the on-orbit housing for the telescope. The Marshall Space Flight Center was responsible for design, development and overall construction. Marshall Space Flight Center contracted Perkin-Elmer to design and construct the Optical Telescope Assembly and guidance sensors. The Goddard Space Flight Center was responsible for ground-control of the telescope and on-board instruments.
Delays in the construction of the mirror for the telescope and the housing assembly caused the engineering completion of the Hubble to slip to 1986. Meanwhile, the budget for the program over-inflated to a staggering $1.18 billion dollars. When 1986 began, launch was imminent. Then, the disaster of the Challenger caused the US space program to come to screeching halt. The Hubble Telescope was stored for four years until launches resumed, raising the cost of the total program to $2.5 billion dollars. The original instruments launched on the Hubble Telescope were the Wide Field and Planetary Camera (WF/PC), Goddard High Resolution Spectrograph (GHRS), High Speed Photometer (HSP), Faint Object Camera (FOC) and the Faint Object Spectrograph (FOS).
The Hubble Space Telescope was launched on April 24, 1990 with STS-31. Initial images revealed a significant flaw in the design of the primary mirror, and spherical aberrations were discovered that caused poor image quality. The Jet Propulsion Laboratory was charged with discovering why the flaw occurred, and they found that poor management enacted by Perkin-Elmer in which the company ignored pre-launch test results that indicated the spherical aberration of the lens.
A plan immediately began to form to correct the aberration of the primary mirror. During STS-61, the high speed photometer was sacrificed to make room for the "Corrective Optics Space Telescope Axial Replacement" (COSTAR). In December 1993, astronauts embarked for the next few months on five service extra-vehicular activities (EVAs) to install COSTAR. The mission was a complete success and proved that astronauts were capable of performing very delicate on-orbit work. Congress and US astronomers were thrilled.
At the same time, the International Space Station (ISS) was just taking form on orbit. Doubts rose about whether or not astronauts could connect elements of the space station during EVAs. The success of STS-61 and repair of the Hubble Space Telescope proved this a possibility and fueled further development of the ISS. It also proved that the Hubble Space Telescope was a long term solution to the question of a space-based telescope. Parts such as gyroscopes and rate sensor units could be replaced to effectively extend the life of the payload.
Four more servicing missions were performed on the Hubble Space Telescope between 1997 and 2009. Throughout these missions, the previous measurement instruments on-board were replaced with newer ones. Today, the Hubble Space Telescope has a Wide Field Camera (WFC3), a Cosmic Origins Spectrograph (COS), an Advanced Camera for Surveys (ACS), Space Telescope Imagine Spectrograph (STIS) and Near Infrared Camera and Multi-Object Spectrometer (NICMOS).
The WFC3 is the third version of the Wide Field Camera series, and it presents a very high resolution camera that can see near-ultraviolet, visible and near-infrared light. It is being used to study dark matter and the remotest galaxies in the universe.
The COS replaced COSTAR after the new astronomy instruments built in accounted for the spherical error of the primary mirror and COSTAR was no longer needed. COS separates light from small cosmic objects (i.e. stars) into identifiable wavelengths that reveal composition and motion. With this tool, extremely faint objects can be analyzed for temperature, chemical composition and even motion in the universe.
The ACS detects visible light and is used to study extremely distant objects in the universe. It also aids in mapping dark matter. The ACS provides astronomers with insight into the formation of galaxies and star clusters. It also doubled Hubble?s field of view.
The STIS has been dubbed the ?black hole hunter? on-board the Hubble Space Telescope. It detects ultraviolet, visible and near-infrared light and serves the opposite purpose of COS. STIS can map enormous galaxies and large sources of light.
NICMOS serves Hubble by detecting distant infrared light emitted by cosmic objects. It provides a ?heat map? of the universe. This unique function of NICMOS allows astronomers to discover hidden objects in the galaxy because it effectively sees through cosmic dust.
Finally, the Fine Guidance Sensors (FGS) function much like star sensors and allow the Hubble to focus on guide stars for fine distance measurement and calibration.
Other on-board systems on the Hubble Space Telescope keep the fine-tuned instrument functioning. The Hubble Space Telescope contains six gyroscopes, which allow the telescope to maintain healthy attitude determination (payload?s position in X, Y and Z axis). The Hubble also has an extensive thermal control system consisting of specially designed layers around the primary mirror and thermal blankets. The on-board computer commanding system is the Science Instrument Command and Data Handling unit (SIC&DH). This instrument controls the scientific instruments and also controls data flow from the payload to the ground site at Goddard Space Flight Center and Space Telescope Science Institute.
Like all good things, the Hubble Space Telescope will ultimately come to an operational halt and de-orbit. Right now, its operational date is anticipated to end during 2014-2019, and it will likely de-orbit in 2019. The NASA community hopes to robotically assist the Hubble through the atmosphere and into the ocean, where its remains can be recovered and displayed. The future replacement for the Hubble Space Telescope is the James Webb Space Telescope (JWST). JWST is scheduled to launch in 2014 and it will orbit much higher than the Hubble Space Telescope at 1.5 million kilometers above Earth. In comparison, the Hubble orbits at low-earth orbit, at around 550 km.
The Hubble Space Telescope has brought a revolution to modern astronomy. The Hubble Space Telescope discovered the acceleration of the galactic expansion and has contributing to over 8000 professional papers since its inception. The telescope has also led to research surrounding gamma ray bursts and proto-planetary disks. Hubble Space Telescope has also refined the galaxy?s age measurement and fueled the development of the ISS with successful EVA servicing missions. For astronomers, the Hubble Space Telescope has delivered some of the most breath-taking images of far away galaxies and nebulas, inspiring future astronomical work.
Hubble Telescope Resources