Hubble's Impact on Human Spaceflight

Quick Facts

Astronauts spent a total of 57 days, 15 hours, 48 minutes, and 8 seconds in space on missions to Hubble.

An astronaut in a spacesuit holds aloft a tool resembling a pair of pliers in front of a device covered with wires and connectors. Earth is visible in the background.

Hubble's Servicing Mission 4 generated 116 new custom tools that astronauts used to service the observatory.

A silver, gold and blue device with cranks, levers, a hook and jaws for grasping.

Hubble was visited five times by astronauts.

Two astronauts float in the cargo bay in bright sunlight.

The longest servicing mission, Servicing Mission 4, lasted 12 days, 21 hours, and 37 minutes.

An astronaut with a power ratchet in one hand in front of Hubble. The shuttle cargo bay, gold carriers, and robotic arm are reflected in his visor.

Earth fills the background behind Hubble in its position in the space shuttle's cargo bay. Two astronauts work in the cargo bay, one partially obscured by the shuttle's robotic arm.

Missions to Hubble have brought new insight to our understanding of how humanity can function outside planet Earth. Astronauts C. Michael Foale (left) and Claude Nicollier (partially obscured by the space shuttle's robotic arm) hover above Space Shuttle Discovery's aft cargo bay during their spacewalk to perform servicing tasks on Hubble during Servicing Mission 3A in 1999.

NASA

The Hubble Space Telescope’s more than 30 years in orbit were punctuated by periodic visits from astronauts that kept the telescope functioning smoothly and equipped it with increasingly powerful instruments. These visits provided NASA with a unique opportunity: to observe men and women working together in space while developing ways to improve that experience —make it smoother, easier, and less dangerous.

The lessons learned from Hubble’s missions have gone on to influence human spaceflight and alter the way people work in the airless, gravity-free environment beyond our planet’s boundaries.

The Right Tool for the Job

There’s no popping out to the hardware store for a different tool when you’re on the job in space. Engineers, working closely with astronauts as they trained for and worked on Hubble, developed hundreds of custom tools. As astronauts put those tools to the test, the tools were revised and refined to work as best as possible under unique constraints, like bulky spacesuits, stiff gloves, an intensely hazardous environment, and the tendency for materials to float away when unattended. Tools had to be designed to prevent fatigue and to avoid wasting precious time to accomplish all the tasks of the mission.

For example, during the first servicing mission, astronauts found that a tool designed to work with electrical and cable connectors on the telescope was clumsy to use, so the tool was redesigned with that feedback for following missions. During Servicing Mission 3B, when astronauts had to swap out a power control unit with over 36 densely packed electrical connectors, all those revisions — including a final one specific to this job — paid off in the design of the High Torque Connector Tool, which proved to be up to the task.

One of the most famous tool developments for Hubble was the Pistol Grip Tool, first used on the second servicing mission. Today it is a standard tool for working on interfaces in space and is one of the workhorse tools on the International Space Station. The Pistol Grip Tool is very similar to a powered screwdriver with a few important alterations.

An astronaut holding the Pistol Grip Tool, which looks like an electric screwdriver. The astronaut's face is visible through his visor, he is smiling. He stands next to a large gold box with a bit of the Shuttle visible behind him.

Astronaut Claude Nicollier uses the Pistol Grip Tool on a storage enclosure during Hubble’s Servicing Mission 3A.

NASA

First, it’s incredibly programmable: Astronauts can pre-set the speed, number of turns, direction, and other features for each task. Secondly, it records information about the tasks it performs, like speed and torque, creating a record that becomes extremely useful later. For instance, if an astronaut working on the same part of Hubble later encountered a tough bolt, the torque could be checked against the record and adjusted accordingly.

The Mini Power Tool, a similar but faster, smaller device created to remove 111 tiny screws during the repair of the Space Telescope Imaging Spectrograph (STIS) during Servicing Mission 4, is also a candidate for use on future missions. The Fastener Capture Plate, built to keep those 111 very small screws from floating away and getting into places where they shouldn’t, was the model for a similar tool used in 2019 to repair a particle physics experiment module on the International Space Station.

An astronaut on the end of the robotic arm with numerous tools. The blue earth is in the background

Servicing Mission 3A astronaut Steven Smith retrieves the Pistol Grip Tool, which was developed to make servicing Hubble easier and is now a standard tool for space tasks.

NASA

Astronaut standing on the extended robotic arm. On the left there is Hubble, which the astronaut is touching as part of the repair.

Astronaut Mark C. Lee, on the end of the space shuttle's robotic arm, performs a patching task on Hubble's worn insulation. This was the final spacewalk of five performed by two teams during Servicing Mission 2 in 1997.

NASA

A gold-colored device with a handle and a short, thin, forked protrusion. — The Lubricant Applicator was used to loosen door latch bolts on Hubble to make them easier to open. The forked applicator was aligned with the bolt and the astronaut would squeeze the trigger to apply the lubricant.
NASA/Michael Soluri

An astronaut in a spacesuit looks directly into the camera while holding a tool shaped like a long, thin drill. Part of Hubble is visible behind him and his helmet reflects the space shuttle bay. — Astronaut Steven Smith picks up the programmable Power Ratchet Tool (PRT) during the first spacewalk of Servicing Mission 2. Multiple combinations of torque, turns, and speed could be programmed into the tool before the spacewalk.
NASA

An astronaut in a spacesuit has a long tool that resembles a drill attached to his belt as he works on the Hubble space Telescope. Earth is visible in the background. — Astronaut Richard Linnehan has the Pistol Grip Tool at his side during his work on the Hubble Space Telescope's Power Control Unit during Servicing Mission 3B.
NASA

A roughly square-shaped tool with screws, two small holes in a clear window, and a loop-shaped appendage. — This Handrail Removal Tool was designed to help astronauts get past a handrail that was blocking access to a Space Telecope Imaging Spectroscope repair. The bolts of the handrail would be backed out through the two holes in the rubbery silicone window, trappping them so they would not re-engage or float away.
NASA/Michael Soluri

Using a robotic arm, an astronaut does maintenance work on Hubble. In the top third of the picture, Earth is seen in the background. — Astronaut Andrew Feustel carries the Pistol Grip Tool at his side and is locked onto the space shuttle's robotic arm with the Manipulator Foot Restraint as he performs work on the Hubble Space Telescope during Servicing Mission 4.
NASA

A silver-colored plate with holes and two loops that would fit over an astronaut's boots. — The Manipulator Foot Restraint secures the astronaut's boots to the space shuttle's robotic arm.
NASA/Michael Soluri

Train, Train, and Train Again

The Hubble servicing missions weren’t based on the premise of expecting the unexpected, but in taking as much of the unexpected out of the equation as possible. Intricate and precise replicas of Hubble and its components were built for use on the ground and in the water tanks at Johnson Space Center and Marshall Space Flight Center. Astronauts practiced with them constantly before missions, using what they learned to continuously redesign and refine both techniques and tools.

Clad in a spacesuit, an astroanut in an underwater tank pulls a tube from a replica of Hubble's bay doors. The labels "Bay A" and "Bay B" are visible on the doors. Two black-suited divers hover above him in the tank.

Monitored by scuba-equipped divers, astronaut C. Michael Foale practices a Servicing Mission 3A task with a Hubble Space Telescope mockup in a water tank at Johnson Space Center.

NASA

John Grunsfeld, an astronaut on three separate Hubble missions, recalled practicing every night for a year on a detailed replica of the Power Control Unit before replacing it on Servicing Mission 3B. “I wanted to know every connector personally, all the features of the keying of the circular connectors, the cable routing, even the pins and sockets of each connector (which I would have to inspect in orbit),” he wrote.

Astronauts struggled with some of Hubble’s doors on Servicing Mission 1, leading to the construction of simulated doors that future teams would practice on, learning not just the mechanics of how they opened and closed but how two astronauts should work together to operate them. Whenever astronauts encountered unexpected problems during the servicing missions — a given with Hubble enduring the wear and tear of its harsh space environment — they would be absolutely familiar with the components they were seeing and how they worked.

The replicas were also critical when the Hubble team decided to attempt repairs that were not previously envisioned, as on Servicing Mission 4, when astronauts made several key fixes that went far beyond swappable modules to opening up instruments and replacing internal components. Astronauts and engineers were able to work together on the replicas to revise tools and techniques that would make those repairs possible.

With so much training, servicing missions became almost choreography, with astronauts knowing exactly where to place their hands, turn their bodies, manipulate items, apply pressure, and so on, in precise conjunction with their spacewalking partner. Because nothing compared with the reality and complexities of a mission in space, if a spacewalk was scheduled for six hours, astronauts were sure to demonstrate that they could accomplish it in four and a half hours in the water tank.

Wearing bulky white spacesuit gloves and a gray shirt, astronaut Mike Massimino holds a small, drill-shaped tool and uses it to remove screws through a flat blue device covered with holes.

Astronaut Mike Massimino uses a version of the Mini Power Tool and the Fastener Capture Plate to practice on a replica of STIS while training for Servicing Mission 4.

NASA

Being able to test on the ground, test in the water tank, change your designs, go back in and do it again and again. Test, test, retest and train, train and retrain. That was the most fundamental process … what I think is the reason for all our success.

Frank Ceppolina

former associate director of NASA’s Satellite Servicing Capabilities Office

That degree of training, preparation, and development is expensive, and the associated price tag must also be carefully considered. Today’s missions may choose to invest in that long-term expense, while others decide to make their mission a one-and-done deal that ends when the technology wears out. But the success of Hubble’s servicing missions provided an important blueprint for the activities that led to effective and streamlined spacewalks.

Expanding NASA’s Knowledgebase

Hubble’s servicing missions provided many opportunities to increase or refine the knowledge NASA had about how things work in space. Knowledge and skills related to rendezvousing and docking with another object in orbit translated to other missions with the ISS and Russia’s MIR, and Soyuz spacecraft. One of the areas where Hubble was particularly helpful was in providing analysis of the vibrations from jets firing. The vibrations and the frequencies at which they resonate can damage or even tear interacting spacecraft apart if they aren’t just right. Those investigations are critical for every spacecraft, current and future, and the analysis performed for Hubble servicing missions helped improve those studies.

Another area where Hubble stood out was the degree of human interaction with the telescope and its components. Astronauts actively grasped and at times even struggled with the telescope, gripping onto parts like handrails. These actions called attention to the importance of items like glove checks, during which astronauts will take time to make sure that their gloves are undamaged. By checking their gloves during one servicing mission, astronauts found yellow paint was flaking off Hubble’s handrails, which could possibly contaminate the telescope’s components during the mission. Astronauts would eventually install covers over the guardrails to solve the issue.

Frequent visits to the telescope also provided a treasure trove of knowledge about how components stand up to a lot of unattended time in space. The cracking of Hubble’s insulating blankets, for example, led NASA to seriously study the conditions affecting the blankets in space at a molecular level. This drove NASA engineers to develop better versions that were later installed on Hubble.

A window on the space shuttle Atlantis frames Hubble. One of Hubble's solar panels and the shuttle's robotic arm are visible through the window, and a blue, cloud-covered Earth fills the background behind the telescope.

A window on the space shuttle Atlantis frames Hubble as astronaut Megan McArthur uses the shuttle's robotic arm to grab the telescope in preparation for the final servicing mission. From its perch 326 miles above Earth, the famed space telescope has tracked celestial objects across the universe.

NASA

With Earth in the background, an astronaut works on Hubble and is reflected in the shiny surface of the telescope. Below him, the space shuttle's metallic, red-colored Flight Support System helps hold the telescope in position, and the newly removed Wide Field Planetary Camera 1 is stowed temporarily nearby.

Hubble is mounted on the Flight Support System (copper in color) in this image from Servicing Mission 1. Astronaut F. Story Musgrave is working on the telescope above it.

NASA

Robotic servicing missions are on the calendar for the future, but in some ways Hubble was a pioneer in robotic servicing as well. The Flight Support System developed for the shuttle’s cargo bay was a turntable device similar to a "Lazy Susan” that could rotate and tilt once Hubble was berthed to it to assist with servicing tasks. The shuttle’s robotic arm was equipped with a device called a Manipulator Foot Restraint, which let astronauts lock their boots into a secure platform with a lean, podium-like attachment for securing items like tools. Astronauts could then be moved via the robotic arm around and above the shuttle’s payload bay, where the telescope rested, and be oriented in the ideal way to access the telescope while keeping their hands free. While these activities on Hubble required a human at all times, the marriage of such robotics with human repair tasks was an early step toward potentially turning certain tasks over to robots.

Earth is visible in the background as an astronaut attached to the shuttle's robotic arm is moved toward the top of the Hubble telescope. Another astronaut works in the shuttle bay below.

Positioned on the space shuttle's robotic arm with the Manipulator Foot Restraint, astronaut F. Story Musgrave works on Hubble against the background of a serene Earth during Servicing Mission 1. Astronaut Jeffrey Hoffman performs tasks in the shuttle’s cargo bay.

NASA

From launch through five servicing missions, the Hubble Space Telescope has always been a shining example of what humanity can accomplish in space. Thanks to Hubble, we have refined our techniques for operating in a weightless environment, learned how to accomplish once-unthinkable tasks, and found we can rise above adversity to reach even further than we imagined. As people set their sights on the Moon and Mars, Hubble has helped pave the way for the next chapter in human exploration of the cosmos.

Learn More About Hubble Servicing Missions

Servicing Mission 1
The first opportunity to conduct planned maintenance on the telescope. Astronauts installed new instruments, including equipment that counteracted the flaw in Hubble's primary mirror.
Servicing Mission 2
The second servicing mission extended the range of wavelengths Hubble can see with the installation of two new instruments and increased the observatory's efficiency and performance.
Servicing Mission 3A
What was originally a mission of preventive maintenance turned more urgent when the fourth of Hubble's six gyros failed. Hubble entered a state of dormancy called safe mode while the telescope awaited repairs.
Servicing Mission 3B
During SM3B, astronauts replaced Hubble's solar panels and installed the Advanced Camera for Surveys, which took the place of Hubble's Faint Object Camera, the telescope's last original instrument.
Servicing Mission 4
The Hubble Space Telescope was reborn with Servicing Mission 4 (SM4). The fifth and final serving mission left the observatory at the peak of its scientific capability, and prepared it for many years of further scientific discovery.