The journey of human flight began in 1903 with the Wright Brothers’ invention of the first successful airplane. Just over a decade later, in 1916, Robert Goddard launched the first liquid-fueled rocket, setting the stage for the advanced space technology we have today. Fast forward to 1965, when Soviet cosmonaut Alexei Leonov became the first person to perform a spacewalk, experiencing the vastness of Earth from space.
It wasn’t until the 1980s that astronauts could truly “fly” in space. To enhance mobility during spacewalks, NASA developed the Manned Maneuvering Unit (MMU), a large jetpack with thrusters that allowed astronauts to move freely around their spacecraft and space stations. Although the MMU’s design began in the early 1960s, it wasn’t used until 1984.
Spacewalks in the mid-1980s were still challenging, both mentally and physically. The spacesuits, necessary for survival, were stiff and resisted movement. The MMU aimed to provide astronauts with more freedom, reducing muscle strain during spacewalks.
The MMU was designed like a large backpack, attaching to the astronaut’s life support system. It had two aluminum tanks, each holding 9 kg of nitrogen, which powered 24 cold gas thrusters. These thrusters released small bursts of nitrogen to create thrust, similar to the system used in SpaceX’s Falcon 9 rocket for orientation during landing.
For the thrusters to function, nitrogen was stored at a high pressure of 4,500 psi, about 300 times the pressure of Earth’s atmosphere. However, as the nitrogen was used, the pressure decreased, reducing thrust over time.
The MMU had two joystick controllers: the left controlled movement in all directions, while the right managed rotational movements. This setup allowed astronauts to control their movements precisely, with enough propellant and battery life for a 6-hour spacewalk. The MMU could be quickly recharged and refilled, extending the spacewalk duration.
The first test flight of the MMU didn’t go as planned. Astronauts Bruce McCandless and Robert Stewart were tasked with testing the MMU. Before leaving the Space Shuttle, Robert encountered a problem when his communications cap’s chin strap broke, causing his microphone and headphones to float away. Concerned about mission control canceling the spacewalk, Robert decided to proceed despite the issue.
With his microphone displaced, Robert had to shout to communicate, which strained his throat. Additionally, his spacesuit’s cooling system malfunctioned, causing ice blockages. He attempted various solutions, including turning off the spacesuit fan and water pump, which only increased carbon dioxide levels in his helmet. Despite these challenges, Robert completed the spacewalk and returned to the shuttle.
Although the MMU provided incredible control and freedom, it was used for the last time in 1984. After the Challenger disaster, safety redesigns in the Shuttle program deemed the MMU an unnecessary risk. As spacewalks became easier and tethered spacewalks more common, the need for the MMU diminished.
Today, astronauts use a smaller version of the jetpack called “SAFER,” which acts as a life jacket in space. If an astronaut drifts away from the space station, SAFER can help them return safely. While the MMU didn’t reach its full potential, its legacy continues, and similar technology may reemerge as more people venture into space.
Research the evolution of spacewalks from Alexei Leonov’s first spacewalk in 1965 to the present day. Focus on technological advancements, challenges faced, and how these have been overcome. Prepare a presentation to share your findings with the class, highlighting key milestones and innovations.
Using the information from the article, design a modern version of the MMU. Consider current technological advancements and safety requirements. Create a detailed sketch or 3D model, and write a brief explanation of how your design improves upon the original MMU.
Participate in a class debate on the risks and benefits of untethered spacewalks using the MMU versus tethered spacewalks. Prepare arguments for both sides, considering safety, mobility, and mission objectives. Engage with your peers to explore different perspectives on space exploration safety.
In pairs, simulate a spacewalk communication challenge similar to Robert Stewart’s experience. One student will act as the astronaut with limited communication, while the other will be mission control. Use non-verbal cues and limited verbal communication to complete a simple task, then discuss the challenges faced and strategies used.
Write a short essay exploring the legacy of the MMU and its impact on current and future spacewalk technologies. Consider how the lessons learned from the MMU have influenced modern equipment like SAFER and speculate on future innovations in astronaut mobility.
This episode of Primal Space is sponsored by BetterHelp. In 1903, the Wright Brothers invented the world’s first successful airplane. Just 13 years later, Robert Goddard launched the world’s first liquid-fueled rocket, a technology that would develop into the incredible machines we have today. Fast forward to 1965 when Soviet cosmonaut Alexei Leonov became the first human to float freely in space. Protected by nothing other than a rope and a spacesuit, Alexei experienced the scale of the Earth in a way that no one ever had before.
But it wasn’t until two decades later that humans would really fly in space. In order to give astronauts more mobility during spacewalks, NASA developed a new machine called the MMU, or manned maneuvering unit. This was essentially a giant jetpack with onboard thrusters, which would allow astronauts to easily move around their spacecraft and future space stations. Early designs of the MMU were in development since the early 1960s, expecting to be used during the Gemini missions. But it wasn’t until 1984 that the jetpack was first used to fly an astronaut in space.
Even by the mid-1980s, spacewalks were no easy task. The mental and physical challenges required to do an 8-hour spacewalk were enormous. The spacesuits required to keep them alive were incredibly stiff. Since they were inflated like a big balloon, it created a lot of resistance against their movements. So while the jetpack wouldn’t make spacewalks an easy task, the idea was to give the astronauts more freedom and allow them to move without straining their muscles.
The jetpack itself was shaped like a large backpack, which would attach to the life support system on the astronaut’s spacesuit. It featured two large aluminum tanks, each containing 9 kg of nitrogen. This nitrogen would be used as the propellant for the 24 thrusters placed around the jetpack. These were cold gas thrusters that would simply let out tiny bursts of nitrogen to produce thrust. As the nitrogen was released from the tank, it would expand and shoot out through the nozzle of the thruster, producing a small amount of thrust and moving the astronaut. This is essentially the same system used on SpaceX’s Falcon 9 rocket, where a series of cold gas nitrogen thrusters are used to orient the rocket as it comes in for a landing.
In order for these cold gas thrusters to work, the nitrogen needs to be stored at incredibly high pressures. In the jetpack, the nitrogen was stored at 4,500 psi, around 300 times the pressure of the air we breathe here on Earth. But these thrusters had one drawback. As the gas was used up, the pressure in the tanks would decrease, gradually reducing the thrust with each firing.
The jetpack featured two joystick controllers on each arm. The one on the left would control the up-down, left-right, forward, and backward movements. The one on the right would control the rotational movement of yaw, pitch, and roll. With this, the astronauts could accelerate at a rate of 0.1 m/s², giving them really precise control over their movements. When doing a spacewalk, the jetpacks had enough propellant and battery life to last up to 6 hours. But thanks to the jetpack’s design, it could be recharged and refilled very quickly by another crew member, allowing the spacewalk to continue for another 6 hours.
So, the jetpack seemed like an amazing new tool for the astronauts to have. But on the very first test flight, things didn’t go to plan. The astronauts who would be testing the jetpack were Bruce McCandless and Robert Stewart. This was to be a very simple spacewalk to test out the jetpack’s functionality. But the problems started for Robert before he even left the Space Shuttle. While in the airlock, Robert followed the normal procedure of yawning to equalize the pressure between his ears and the atmosphere in his spacesuit. But in doing so, the chin strap on his communications cap broke and sent his microphone and headphones floating up to his head. He didn’t want mission control to know about this problem in case they canceled the spacewalk. So, he talked it over with Bruce and the crew inside the Space Shuttle and decided to go for it.
With his microphone now halfway up his face, Robert had to shout at the top of his voice every time he communicated with mission control. All of this shouting, paired with the dry pure oxygen atmosphere inside his helmet, made his throat incredibly sore. But if he dipped his chin to reach his drink straw, his headset would come loose, making communication almost impossible. Despite this, he continued on with the spacewalk, testing the jetpack and flying almost 100 meters away from the Space Shuttle. This is when he discovered his next problem. The sublimator in his spacesuit, which chilled the cooling water, became blocked with ice. Following his safety checklist, he turned the temperature control to cold, which spread more water around his suit, using his body temperature to melt the ice. This immediately made it feel like he had just jumped into the Atlantic Ocean, so he quickly turned it back up to the normal temperature.
Now out of ideas, he turned off the spacesuit fan and water pump, hoping that the ice would turn from a solid straight into a gas and disappear into the vacuum of space. All this did, though, was cause the carbon dioxide levels in his helmet to rise, causing his breathing to deepen, forcing him to turn the fan back on. Robert dealt with several ice blockages throughout his spacewalk before finally coming back to the Space Shuttle and ending the spacewalk. Despite this being one of the toughest spacewalks in the history of spaceflight, Robert went out two days later to perform another one using the jetpack. With a bit of tape to secure his communications cap, he experienced a flawless flight. Many astronauts that used the jetpack on future missions found it to be a dream to fly. The level of control it offered astronauts was incredible, but sadly, it wasn’t used for much longer.
At the end of 1984, the jetpack was used for the final time. Following the Challenger disaster, many parts of the Shuttle program had to be redesigned for safety, and the jetpack was considered to be an unnecessary risk. As the Shuttle itself continued to develop, spacewalks became easier. And with NASA putting more training into tethered spacewalks, the need for the jetpack had disappeared. But its legacy lives on. Now, astronauts wear a slimmed-down version of the jetpack called ‘safer’. This smaller jetpack is essentially the astronaut’s life jacket. If an astronaut ever found themselves floating off into space, they could use this jetpack for a short period of time to help them get back to the space station. And although the jetpack never lived out its full potential as a flying machine, it’s amazing to see how things like this could make a return in the future when we have more and more people in space.
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Spacewalk – An activity where an astronaut moves outside a spacecraft in space to perform tasks or experiments. – During the spacewalk, the astronauts repaired the damaged solar panels on the International Space Station.
Astronauts – Trained individuals who travel into space to conduct scientific research and exploration. – The astronauts aboard the spacecraft conducted experiments to study the effects of microgravity on plant growth.
Nitrogen – A chemical element with the symbol N, commonly used in spacecraft systems for pressurization and as a component of life support systems. – The spacecraft’s life support system uses nitrogen to maintain a breathable atmosphere for the crew.
Thrusters – Small engines on a spacecraft used to control its orientation and make minor adjustments to its trajectory. – The spacecraft’s thrusters fired briefly to adjust its orbit for docking with the space station.
Pressure – The force exerted by a fluid or gas per unit area, crucial in maintaining the structural integrity of spacecraft and spacesuits. – Engineers carefully monitor the pressure inside the spacecraft to ensure the safety of the astronauts.
Mobility – The ability of astronauts to move and perform tasks efficiently in the microgravity environment of space. – The new spacesuit design enhances mobility, allowing astronauts to conduct more complex repairs during spacewalks.
Spacecraft – A vehicle designed for travel or operation in outer space, used for exploration, research, or transportation. – The spacecraft successfully entered Mars’ orbit, marking a significant milestone in the mission.
Cooling – The process of removing excess heat from spacecraft systems to maintain optimal operating temperatures. – The spacecraft’s cooling system is essential for preventing overheating of electronic components.
Technology – The application of scientific knowledge for practical purposes, especially in the design and operation of spacecraft and related systems. – Advances in propulsion technology have significantly reduced travel time to distant planets.
Legacy – The long-lasting impact or contribution of a particular mission, technology, or individual in the field of space exploration. – The legacy of the Apollo missions continues to inspire new generations of scientists and engineers.
