Welcome to the I Can't Sleep podcast,
Where I help you drift off one fact at a time.
I'm your host,
Benjamin Boster,
And today's episode is about the Hubble Space Telescope.
The Hubble Space Telescope,
HST or Hubble,
Is a space telescope that was launched into low Earth orbit in 1990 and remains in operation.
It was not the first space telescope,
But it is one of the largest and most versatile,
Renowned as a vital research tool and as a public relations boon for astronomy.
The Hubble Space Telescope is named after astronomer Edwin Hubble and is one of NASA's great observatories.
The Space Telescope Science Institute selects Hubble's targets and processes the resulting data.
While the Goddard Space Flight Center controls the spacecraft.
Hubble features a 2.
4-meter,
Or 7-foot,
10-inch mirror,
And its five main instruments observe in the ultraviolet,
Visible,
And near-infrared regions of the electromagnetic spectrum.
Hubble's orbit outside the distortion of Earth's atmosphere allows it to capture extremely high-resolution images with substantially lower background light than ground-based telescopes.
It has recorded some of the most detailed visible light images,
Allowing a deep view into space.
Many Hubble observations have led to breakthroughs in astrophysics,
Such as determining the rate of expansion of the universe.
The Hubble Space Telescope was funded and built in the 1970s by NASA,
With contributions from the European Space Agency.
Its intended launch was in 1983,
But the project was beset by technical delays and budget problems.
Hubble was launched on STS-31 in 1990,
But its main mirror had been ground incorrectly,
Resulting in spherical aberration that compromised the telescope's capabilities.
The optics were corrected to their intended quality by a servicing mission,
STS-61,
In 1993.
Hubble is the only telescope designed to be maintained in space by astronauts.
Five space shuttle missions repaired,
Upgraded,
And replaced systems on the telescope,
Including all five of the main instruments.
The fifth mission was initially cancelled on safety grounds,
But NASA Administrator Michael D.
Griffin approved it.
The servicing mission was completed in 2009.
Hubble completed 30 years of operation in April 2020 and is predicted to last until 2030 to 2040.
Hubble is the visible light telescope in NASA's Great Observatories program.
Other parts of the spectrum are covered by the Compton Gamma-ray Observatory,
The Chandra X-ray Observatory,
And the Spitzer Space Telescope,
Which covers the infrared bands.
The mid-IR to visible band successor to the Hubble Telescope is the James Webb Space Telescope,
Which was launched on December 25,
2021,
With the Nancy Grace Roman Space Telescope due to follow in 2026.
In 1923,
Hermann Obert,
Considered a father of modern rocketry,
Along with Robert H.
Goddard and Konstantin Tsiolkovsky,
Published The Rocket into Planetary Space,
Which mentioned how a telescope could be propelled into Earth's orbit by a rocket.
The history of the Hubble Space Telescope can be traced to 1946,
To astronomer Lyman Spitzer's paper,
Astronomical Advantages of an Extraterrestrial Observatory.
In it,
He discussed the two main advantages that a space-based observatory would have over ground-based telescopes.
First,
The angular resolution,
The smallest separation at which objects can be clearly distinguished,
Will be limited only by diffraction,
Rather than by the turbulence in the atmosphere,
Which causes stars to twinkle,
Known to astronomers as seeing.
At that time,
Ground-based telescopes were limited to resolutions of 0.
5 to 1.
0 arcseconds,
Compared to a theoretical diffraction-limited resolution of about 0.
05 arcseconds.
For an optical telescope with a mirror 2.
5 meters,
Or 8 feet 2 inches in diameter,
Second,
A space-based telescope could observe infrared and ultraviolet light,
Which are strongly absorbed by the atmosphere of Earth.
Spitzer devoted much of his career to publishing for the development of a space telescope.
In 1962,
A report by the U.
S.
National Academy of Sciences recommended development of a space telescope as part of the space program.
And in 1965,
Spitzer was appointed as head of a committee given the task of defining scientific objectives for a large space telescope.
Also crucial was the work of Nancy Grace Roman,
The mother of Hubble.
Well before it became an official NASA project.
She gave public lectures touting the scientific value of the telescope.
After it was approved,
She became the program scientist,
Setting up the steering committee in charge of making astronomer needs feasible to implement,
And writing testimony to Congress throughout the 1970s to advocate continued funding of the telescope.
Her work as project scientist helped set the standards for NASA's operation of large scientific projects.
Space-based astronomy had begun on a very small scale following World War II,
As scientists made use of developments that had taken place in rocket technology.
The first ultraviolet spectrum of the Sun was obtained in 1946,
And NASA launched the Orbiting Solar Observatory,
OSO,
To obtain UV,
X-ray,
And gamma-ray spectra in 1962.
An orbiting solar telescope was launched in 1962 by the United Kingdom as part of the Ariel program.
And in 1966,
NASA launched the first orbiting astronomical observatory mission.
AOA-1's battery failed after three days,
Terminating the mission.
It was followed by Orbiting Astronomical Observatory 2,
Which carried out ultraviolet observations of stars and galaxies from its launch in 1968 until 1972,
Well beyond its original planned lifetime of one year.
The OSO and AOA missions demonstrated the important role space-based observations could play in astronomy.
In 1968,
NASA developed firm plans for a space-based reflecting telescope with a mirror of 3 meters,
Or 9.
8 feet in diameter,
Known provisionally as the Large Orbiting Telescope,
Or Large Space Telescope,
LST,
With a launch dated for 1979.
These plans emphasized the need for crewed maintenance missions to the telescope to ensure such a costly program had a lengthy working life,
And the concurrent development of plans for the reusable space shuttle indicated that the technology to allow this was soon to become available.
The continuing success of the OAO program encouraged increasingly strong consensus within the astronomical community that the LST should be a major goal.
In 1970,
NASA established two committees,
One to plan the engineering side of the Space Telescope project,
And the other to determine the scientific goals of the mission.
Once these had been established,
The next hurdle for NASA was to obtain funding for the instrument,
Which would be far more costly than any Earth-based telescope.
The U.
S.
Congress questioned many aspects of the proposed budget for the telescope and forced cuts in the budget for the planning stages,
Which at the time consisted of very detailed studies of potential instruments and hardware for the telescope.
In 1974,
Public spending cuts led to Congress deleting all funding for the telescope project.
In 1977,
Then NASA Administrator James C.
Fletcher proposed to token $5 million for Hubble in NASA's budget.
Then NASA Associate Administrator for Space Science,
Noel Hinners,
Instead cut all funding for Hubble,
Gambling that this would galvanize the scientific community into fighting for full funding.
The political ploy worked.
In response to Hubble being zeroed out of NASA's budget,
A nationwide lobbying effort was coordinated among astronomers.
Many astronomers met congressmen and senators in person,
And large-scale letter-writing campaigns were organized.
The National Academy of Sciences published a report emphasizing the need for a space telescope,
And eventually the Senate agreed to half the budget that had originally been approved by Congress.
The funding issues led to a reduction in the scale of the project,
With the proposed mirror diameter reduced from 3 m to 2.
4 m,
Both to cut costs and to allow a more compact and effective configuration for the telescope hardware.
A proposed precursor 1.
5 meters,
Or 4 feet 11 inches,
Space telescope to test the systems to be used on the main satellite was dropped.
And budgetary concerns also prompted collaboration with the European Space Agency,
ESA.
ESA agreed to provide funding and supply one of the first generation instruments for the telescope,
As well as the solar cells that would power it,
And staff to work on the telescope in the United States.
A return for European astronomers being guaranteed at least 15% of the observing time on the telescope.
Congress eventually approved funding of $36 million for 1978,
And the design of the LST began in earnest,
Aiming for a launch date of 1983.
In 1983,
The telescope was named after Edwin Hubble,
Who confirmed one of the greatest scientific discoveries of the 20th century,
Made by Georges Lemaître,
That the universe is expanding.
Once the Space Telescope project had been given the go-ahead,
Work on the program was divided among many institutions.
Marshall Space Flight Center,
MSFC,
Was given responsibility for the design,
Development,
And construction of the telescope,
While Goddard Space Flight Center was given overall control of the scientific instruments and ground control center for the mission.
MSFC commissioned the optics company Perkin Elmer to design and build the Optical Telescope Assembly,
OTA,
And fine guidance sensors for the space telescope.
Lockheed was commissioned to construct and integrate the spacecraft in which the telescope would be housed.
Optically,
The HST is a cassegrain reflector of Ritchie-Cration design,
As are most large professional telescopes.
This design,
With two hyperbolic mirrors,
Is known for good imaging performance over a wide field of view.
With the disadvantage that the mirrors have shapes that are hard to fabricate and test.
The mirror and optical systems of the telescope determine the final performance,
And they were designed to exacting specifications.
Perkin Elmer,
PE,
Intended to use custom-built and extremely sophisticated computer-controlled polishing machines to grind the mirror to the required shape.
However,
In case their cutting-edge technology ran into difficulties,
NASA demanded that PE subcontract to Kodak to construct a backup mirror using traditional mirror polishing techniques.
Construction of the Perkin Elmer mirror began in 1979,
Starting with a blank manufactured by Corning from their ultra-low expansion glass.
Mirror polishing continued until May 1981.
Doubts continue to be expressed about Perkin Elmer's competence on a project of this importance,
As their budget and timescale for producing the rest of the OTA continue to inflate.
In response to a schedule described as unsettled and changing daily,
NASA postponed the launch date of the telescope until April 1985.
Perkin-Elmer's schedules continued to slip at a rate of about one month per quarter,
And at times,
Delays reached one day for each day of work.
NASA was forced to postpone the launch date until March,
And then September 1986.
By this time,
The total project budget had risen to $1.
175 billion.
The spacecraft in which the telescope and instruments were to be housed was another major engineering challenge.
It would have to withstand frequent passages from direct sunlight into the darkness of Earth's shadow,
Which would cause major changes in temperature,
While being stable enough to allow extremely accurate pointing of the telescope.
While construction of the spacecraft in which the telescope and instruments would be housed proceeded somewhat more smoothly than the construction of the OTA,
Lockheed experienced some budget and schedule slippage.
And by the summer 1985,
Construction of the spacecraft was 30% over budget and three months behind schedule.
An MSFC report said Lockheed tended to rely on NASA directions rather than take their own initiative in the construction.
During a delay in 1986,
The telescope was kept in a clean room,
Powered up and purged with nitrogen until a launch could be rescheduled.
This costly situation,
About $6 million a month,
Pushed the overall costs of the project higher.
However,
This delay allowed time for engineers to perform extensive tests,
Swap out a possibly failure-prone battery,
And make other improvements.
Furthermore,
The ground software needed to control Hubble was not ready in 1986,
And was barely ready by the 1990 launch.
Following the resumption of shuttle flights,
Space Shuttle Discovery successfully launched Hubble on April 24,
1990,
As part of the STS-31 mission.
NASA Administrator Sean O'Keefe decided all future shuttle missions had to be able to reach the safe haven of the International Space Station should in-flight problems develop.
As no shuttles were capable of reaching both HST and the space station during the same mission,
Future manned service missions were cancelled.
In January 2004,
O'Keefe said he would review his decision to cancel the final servicing mission to HST due to public outcry and requests from Congress for NASA to look for a way to save it.
The National Academy of Sciences convened an official panel,
Which recommended in July 2004,
That the HST should be preserved despite the apparent risks.
The nomination in April 2005 of a new NASA administrator,
Michael D.
Griffin,
Changed the situation.
As Griffin stated he would consider a crude servicing mission.
Soon after his appointment,
Griffin authorized Goddard to proceed with preparations for a crewed Hubble maintenance flight,
Saying he would make the final decision after the next two shuttle missions.
In October 2006,
Griffin gave the final go-ahead,
And the 11-day mission by Atlantis was scheduled for October 2008.
Hubble's main data handling unit failed in September 2008,
Halting all reporting of scientific data until its backup was brought online on October 25,
2008.
Since a failure of the backup unit would leave the HST helpless,
The service mission was postponed to incorporate a replacement for the primary unit.
Servicing mission 4SM4,
Flown by Atlantis in May 2009,
Was the last scheduled shuttle mission for HST.
SM-4 installed the replacement data handling unit,
Repaired the ACS and STIS systems,
Installed improved nickel-hydrogen batteries,
And replaced other components,
Including all six gyroscopes.
SM-4 also installed two new observation instruments,
Wide Field Camera 3 and the Cosmic Origin Spectrograph,
And the Soft Capture and Rendezvous System,
Which will enable the future rendezvous,
Capture,
And safe disposal of Hubble by either a crewed or robotic mission.
Except for the ACS's high-resolution channel,
Which could not be repaired and was disabled.
The work accomplished during SM4 rendered the telescope fully functional.
Hubble has helped resolve some long-standing problems in astronomy,
While also raising new questions.
Some results have required new theories to explain them.
Among its primary mission targets was to measure distances to Cepheid variable stars more accurately than ever before,
And thus constrain the value of the Hubble constant,
The measure of the rate at which the universe is expanding,
Which is also related to its age.
Before the launch of HST,
Estimates of the Hubble constant typically had errors of up to 50%.
But Hubble measurements of Cepheid variables in the Virgo cluster and other distant galaxy clusters provided a measured value with an accuracy of plus or minus 10%,
Which is consistent with other more accurate measurements made since Hubble's launch using other techniques.
Thanks.
The estimated age of the universe is now 13.
7 billion years.
Astronomers from the High-Z Supernova Search Team and the Supernova Cosmology Project used ground-based telescopes and HST to observe distant supernovae and uncovered evidence that,
Far from decelerating under the influence of gravity,
The expansion of the universe is instead accelerating.
The cause of this acceleration remains poorly understood.
The term used for the currently unknown cause is dark energy,
Signifying that it is dark,
Unable to be directly seen and detected to our current scientific instruments.
The high-resolution spectra and images provided by the HST have been especially well suited to establishing the prevalence of black holes in the center of nearby galaxies.
While it had been hypothesized in the early 1960s that black holes would be found at the centers of some galaxies,
And astronomers in the 1980s identified a number of good black hole candidates,
Work conducted with Hubble shows that black holes are probably common to the centers of all galaxies.
A unique window on the universe enabled by Hubble are the Hubble Deep Field,
Hubble Ultra Deep Field,
And Hubble Extreme Deep Field images.
Which used Hubble's unmatched sensitivity at visible wavelengths to create images of small patches of sky that are the deepest ever obtained at optical wavelengths.
The images reveal galaxies billions of light years away,
Thereby providing information about the early universe,
And have accordingly generated a wealth of scientific papers.
The collision of comet Shoemaker-Levy 9 with Jupiter in 1994 was fortuitously timed for astronomers,
Coming just a few months after servicing Mission 1 had restored Hubble's optical performance.
Hubble images of the planet were sharper than any taken since the passage of Voyager 2 in 1979.
And were crucial in studying the dynamics of the collision of a large comet with Jupiter,
An event believed to occur once every few centuries.
In March 2015,
Researchers announced that measurements of aurorae around Ganymede,
One of Jupiter's moons,
Revealed that it has a subsurface ocean.
Using Hubble to study the motion of its aurorae.
The researchers determined that a large saltwater ocean was helping to suppress the interaction between Jupiter's magnetic field and that of Ganymede.
The ocean is estimated to be 100 kilometers or 60 miles deep,
Trapped beneath a 150 kilometer or 90 mile ice crust.
HST uses gyroscopes to detect and measure any rotations so it can stabilize itself in orbit and point accurately and steadily at astronomical targets.
HST has six of these rate sensing gyroscopes installed.
Three gyroscopes are normally required for operation.
Observations are still possible with two or one,
But the area of sky that can be viewed would be somewhat restricted,
And observations requiring very accurate pointing are more difficult.
Hubble orbits the Earth in the extremely tenuous upper atmosphere,
And over time its orbit decays due to drag.
If not reboosted,
It will re-enter the Earth's atmosphere within some decades,
With the exact date depending on how active the Sun is and its impact on the upper atmosphere.
If Hubble were to descend in a completely uncontrolled re-entry,
Parts of the main mirror and its support structure would probably survive.
