Space jetpacks exist, though they don’t work quite as you’d see in the movies. So when, on 12 February 1984, the astronaut Bruce McCandless went free-flying 40 metres (131 feet) away from the Orbiter – farther than anyone had ever been from the safety of their ship – it was a considerable achievement. It was made possible using NASA’s Manned Maneuvering Unit (MMU), a nitrogen jet-propelled backpack that is the most practical answer to science fiction’s idea of a working jetpack.
Fully loaded with gaseous nitrogen propellant, the MMU weighs a hefty 148 kilograms (326 pounds). It comprises two aluminium tanks with Kevlar filament wrappings to protect them from punctures and improve strength. Each tank is loaded with 5.9 kilograms (13 pounds) of nitrogen under 20.7 kilopascals of pressure, which is enough propellant for six hours’ worth of extra-vehicular activity (EVA).
Each tank feeds an individual system of thrusters through to a combination of 24 nozzles, three on each of the eight corners of the MMU. The astronaut uses their fingertips to manipulate the individual controllers, the right-hand controller rotating the MMU for roll, pitch and yaw, the left-hand controller pushing the MMU forward, back, up, down, left and right.
On one of the shuttle missions following McCandless’s ground-breaking EVA flight in November 1984, astronauts Joseph Allen and Dale Gardner were able to use the revolutionary MMU to capture two rogue communication satellites which had faulty propulsion modules, then bring them back to the Orbiter to be returned to Earth.
More recent developments in jetpack technology have resulted in SAFER, the Simplified Aid for EVA Rescue. This is a smaller unit than the MMU and works as a safety device for use on the International Space Station (ISS). In the event of an ISS crew member working on the structure drifting away without hope of retrieval, they can use this device to return to the station.
It fits over the life support system of a spacesuit (the EMU) and has a control module and display that moves from the bottom of the SAFER to the front during operation. It has a similar build to the MMU, with gaseous nitrogen expelled from 24 nozzles that can propel the user with a similar manoeuvrability. But because it only holds 1.4 kilograms (three pounds) of propellant, it can’t manage the same velocity change as the MMU.
The pros and cons of anyone working in space is that you, as well as any other object, have no apparent weight. This can be great when you need to lift heavy objects around, like the 148-kilogram (326-pound) MMU, but only when you’re secured to something with much greater mass than the object you’re trying to shift. Newton’s third law of motion states that for every action there must be an equal and opposite reaction, so the average 80-kilogram (176-pound) astronaut trying to manually push the MMU around, without standing on the Orbiter, will only succeed in pushing themselves away at a much greater velocity than they can move the MMU.