How the Hubble Telescope Works

### How the Hubble Telescope Works

The Hubble Space Telescope (HST) has fundamentally transformed our understanding of the universe since its launch in 1990. Perched about 547 kilometers (340 miles) above the Earth, beyond the distortion of the atmosphere, Hubble provides a clear and unhindered view of distant stars, galaxies, and other celestial phenomena. But how exactly does this marvel of modern engineering work? This article dives into the key components, principles, and operations that make HST an unparalleled instrument in the field of astronomy.

#### Historical Context and Mission Goals

The idea for the Hubble Space Telescope dates back to the 1940s, though it wasn’t until the 1970s that plans started to take shape for what would become one of NASA’s most successful scientific endeavors. Named after the astronomer Edwin Hubble, the telescope’s primary mission goals are to explore the universe’s structure, the formation of galaxies and stars, the properties of planets within our solar system, and more generally, to answer foundational questions about our place in the cosmos.

#### Components of the Hubble Space Telescope

Understanding how Hubble works begins with a breakdown of its main components.

1. The Optical Telescope Assembly (OTA) :
– Primary Mirror : The heart of the Hubble, the primary mirror is 2.4 meters (7.9 feet) in diameter. It collects light from celestial objects and reflects it onto the secondary mirror.
– Secondary Mirror : This smaller mirror, positioned above the primary mirror, reflects light again, directing it down into the main instruments.

2. The Scientific Instruments :
Hubble is equipped with a suite of cutting-edge scientific instruments, each specialized for different types of observations:
– Wide Field Camera 3 (WFC3) : This camera captures high-resolution images across three different ranges of the electromagnetic spectrum: ultraviolet, visible, and near-infrared.
– Advanced Camera for Surveys (ACS) : Optimized for survey-style observations, it can capture large regions of space in great detail.
– Cosmic Origins Spectrograph (COS) : Designed to study the spectra of ultraviolet light from celestial sources, revealing information about their composition, temperature, density, and motion.
– Space Telescope Imaging Spectrograph (STIS) : These combined imaging and spectroscopy capabilities allow for a detailed examination of chemical compositions and physical properties.
– Near Infrared Camera and Multi-Object Spectrometer (NICMOS) : Though it is no longer operational, NICMOS was critical for infrared observations before the WFC3 took over this role.

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3. The Support Systems :
– Pointing Control System : Accuracy in space is paramount, and Hubble’s precision pointing system uses gyroscopes and fine guidance sensors to maintain an exact orientation. This system allows the telescope to lock onto a target with an accuracy of 0.007 arcseconds.
– Data Handling Systems : Hubble is equipped with computer systems that control observations, store data, and transmit this information back to Earth. The data is relayed via the Tracking and Data Relay Satellite System (TDRSS).

#### The Principles Behind Hubble’s Functioning

Hubble’s operation hinges on several fundamental principles of physics and engineering:

1. Reflection and Refraction :
As previously mentioned, Hubble relies on its primary and secondary mirrors to capture and focus light. These mirrors are coated with a thin layer of aluminum, followed by a protective layer of magnesium fluoride, which increases reflectivity and reduces scattering.

2. Spectroscopy :
Spectroscopy is crucial for identifying the chemical makeup of observed objects. By splitting light into its constituent colors (spectrum), instruments like COS and STIS can identify unique signatures that correspond to specific elements and molecules.

3. Electromagnetic Spectrum :
Hubble observes a wide range of the electromagnetic spectrum, from ultraviolet to near-infrared. This capability allows it to detect phenomena that are invisible to the naked eye and even some ground-based observatories that are limited by atmospheric interference.

#### The Operations: How Hubble Conducts Observations

1. Mission Planning and Target Selection :
Before Hubble can conduct an observation, scientists on Earth must determine its targets. Proposals for observation time come from astronomers worldwide, and these proposals are rigorously vetted and scheduled.

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2. Pointing and Stability :
Once a target is selected, Hubble’s high-precision gyroscopes and fine guidance sensors work together to point the telescope in the desired direction. Hubble orbits Earth at about 27,300 kilometers per hour (17,000 miles per hour), completing an orbit roughly every 97 minutes. Despite this rapid movement, its pointing system allows it to focus steadily on distant objects for extended periods.

3. Data Collection :
As light from a celestial object enters the telescope and is focused by the mirrors, it is directed to the appropriate scientific instrument. Depending on the requirements of the observation, the instrument might capture images, analyze spectra, or even measure polarizations.

4. Data Transmission and Processing :
The collected data is sent to Earth via the TDRSS network. This information is stored, processed, and calibrated at the Space Telescope Science Institute (STScI) in Baltimore, Maryland. The processed data is then made available to astronomers and the public, contributing to countless scientific discoveries.

#### Achievements and Contributions

Since its launch, Hubble has revolutionized our understanding of the universe. Some of its most significant contributions include:

– The Age of the Universe : By observing variable stars in distant galaxies, Hubble helped refine the age of the universe to approximately 13.8 billion years.
– Dark Energy : Hubble’s observations of distant supernovae provided key evidence for the existence of dark energy, a mysterious force driving the acceleration of the universe’s expansion.
– Exoplanet Atmospheres : Hubble has been instrumental in characterizing the atmospheres of planets orbiting other stars, detecting water vapor, methane, and other molecules.
– Deep Field Images : The Hubble Deep Field and its successors (Ultra Deep Field, Extreme Deep Field) have revealed a universe teeming with galaxies, each at different stages of evolution, considerably expanding our knowledge of cosmology and galaxy formation.

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#### Challenges and Maintenance

Hubble’s journey hasn’t been entirely smooth. Immediately after its launch, a flaw in the primary mirror’s curvature was discovered, causing blurred images. This issue was famously corrected in 1993 by a servicing mission that installed the Corrective Optics Space Telescope Axial Replacement (COSTAR), effectively giving Hubble “glasses” and restoring its observational clarity.

Five servicing missions conducted by astronauts aboard the Space Shuttle have upgraded Hubble’s systems, replaced old instruments with new ones, and ensured its continued operation. The last of these missions took place in 2009, and since then, Hubble has continued to produce stunning images and valuable scientific data.

### Looking Forward

While Hubble’s successor, the James Webb Space Telescope (JWST), is poised to take the front lines in astronomical research with its advanced capabilities, Hubble’s legacy will endure. Together, these observatories will offer complementary views, with Hubble focusing on ultraviolet and visible

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