Space Mission Profiles: The Hubble Space Telescope
By Dr. Gary L. Deel, Ph.D., J.D.
Faculty Director, School of Business, American Military University
The Hubble Space Telescope was launched in 1990 and remains one of the largest and most versatile telescopes that scientists have ever deployed for studying the cosmos. It sports a suite of scientific instruments for studying the cosmos.
The mission of Hubble is to help scientists understand the universe better through observations in the visible, infrared, and ultraviolet spectrums. Hubble cost NASA approximately $1.5 billion in 1990, which is nearly twice that amount in 2020 dollars.
Technical Details of the Hubble Space Telescope
The Hubble Space Telescope is 13.2 meters long and weighs almost 12,000 kilograms. The diameter of the telescope is 2.4 meters, and the focal length is 57.6 meters.
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The main truss structure is a little over five meters long and is made of graphite-epoxy. All in all, the spacecraft is about the size of a school bus, and it was carried into orbit by Space Shuttle Discovery.
The orbit of Hubble is almost perfectly spherical, with a perigee of 537 kilometers and an apogee of 540.9 kilometers. The inclination of the orbit is 28.47 degrees, and the orbital period is 95.42 minutes.
Hubble has both high-gain and low-gain antennas on board to communicate with mission control on Earth. It relays its communications through NASA’s Tracking and Data Relay Satellite (TDRS) network in S-band radiofrequency. Hubble receives commands from the Space Telescope Operations Control Center (STOCC).
Hubble gets its power from two 25-foot long solar arrays, which have been upgraded three different times since its launch. The spacecraft uses about 2,100 watts of power, and the power coming from the solar panels is managed by a power control unit.
When needed, power is distributed to the spacecraft’s systems through four power distribution units. Excess power is stored in Hubble’s six 32-volt nickel-hydrogen batteries.
To prevent temperature fluctuations from compromising the integrity of Hubble’s systems, the spacecraft is protected by an aluminum outer shell with multi-layer insulation underneath the shell. This insulation is made of metal foils that prevent radiation from reaching the inner components. Hubble also has radiators that allow it to evacuate excess heat when needed.
Hubble does not have a propulsion system, so it is not able to change its altitude or orbital dynamics. It is only able to change its attitude through its Pointing Control System (PCS). There are five types of sensors in Hubble’s PCS: coarse sun sensors, magnetic field sensors, gyroscopes, fixed head star trackers, and fine guidance sensors.
Hubble relies on the PCS to maintain its stable orbit. Once its sensors determine the spacecraft’s attitude, actuators — which include both reaction wheel assemblies and magnetic torquers — are used to physically turn the telescope to the desired attitude.
In terms of changing Hubble’s orientation, all commands come from the flight operations team at the Goddard Space Flight Center, which works 24 hours a day to monitor and direct the telescope. Commands to Hubble are sent through the TDRS network.
Hubble relies on the Science Instrument Command & Data Handling Unit (SI C&DH) to manage all of the data that it collects in its operations. The SI C&DH uses redundant components, including a NASA Standard Spacecraft Computer, interface circuit boards, central processing units, and memory and communication peripherals.
Hubble Needed Some Additional Work After Its 1990 Launch
After Hubble was launched in 1990, the first images taken by its cameras revealed a serious problem with the telescope’s ability to focus and provide the clarity and detail that was expected based on design specs. After thorough diagnostics, engineers deduced that the reason for this problem was that the primary mirror had been polished to the wrong shape.
Near the edges of the mirror, the shape was off by as much as 2,200 nanometers. This mistake caused severe spherical aberration, a problem where light reflecting off the outside edges of a mirror are focused on a different point than the light reflected in the center. An investigation determined that this error was caused by an incorrectly assembled mirror calibration tool used during the grinding and polishing stages.
Unfortunately, replacement of the flawed mirror in space was not possible, and returning Hubble to Earth for refit would have been too expensive. To fix the error, engineers designed new optics for the cameras and instruments on Hubble that had the exact same error gradient that the existing mirror had, but in the inverse fashion.
This strategy allowed the errors in the mirror and the errors in the optics to cancel each other out, and render clear, undistorted images. Fortunately, this mission was successful.
Hubble Has Provided Extraordinary Images That Revolutionized Our Knowledge of Space
Ever since its repair, the Hubble Space Telescope has returned extraordinary images from deep space that have revolutionized our understanding of the cosmos. Hubble’s data has been the source of more 13,000 published scientific journal articles since the telescope began its operation.
One small example of Hubble’s profound impact on our knowledge of the universe is the publication of the Hubble Deep Fields, a collection of images that Hubble took of swaths of the night sky that were once thought to be empty and boring. After days of exposure, these deep field images revealed that the regions of space which appear “empty” to the naked eye are in fact teeming with thousands upon thousands of galaxies, far too distant and dim to detect without the aid of precision instruments like Hubble.
Hubble’s Orbit Is Beginning to Decay, But It Needs Financial Support to Continue Its Function
Sadly, Hubble’s orbit is slowly decaying due to atmospheric drag. If the telescope is not boosted it will eventually burn up in Earth’s atmosphere in the mid-2020s. Although newer and more advanced telescopes, such as the James Webb Space Telescope (JWST), are currently in development, there is still much that Hubble could accomplish in the years ahead.
But in order to continue its intended function, the Hubble Space Telescope needs to be re-boosted and maintained in its current orbit. This work will require NASA funding, which is in limited supply at present.
Hubble will need our support if it is to survive the next decades. So I encourage readers to write their Senators and Representatives and tell them that Hubble should not be allowed to die before it has exhausted its full potential.
About the Author
Dr. Gary Deel is a Faculty Director with the School of Business at American Military University. He holds a J.D. in Law and a Ph.D. in Hospitality/Business Management. Gary teaches human resources and employment law classes for American Military University, the University of Central Florida, Colorado State University and others.