Julio and Matt discuss the MMU and way more. Matt interviews Bruce McCandless III about his new book Wonders All Around: The Incredible True Story of Astronaut Bruce McCandless II and the First Untethered Flight in Space

Neil deGrasse Tyson

Bruce McCandless III has published poems, stories, and essays. He is also the author of the novels Sour Lake and The Black Book of Cyrenaica, as well as a modern fairy tale for pre-teens called Beatrice and the Basilisk.

Most recently, Bruce is the author of the biography Wonders All Around: The Incredible True Story of Astronaut Bruce McCandless II and the First Free Flight in Space, scheduled for release in July of 2021. No science required! Wonders All Around is first and foremost a relationship story about a family caught up in a father's ambitions, disappointments, and struggle for professional redemption.

Richard Branson became the second oldest person to ever go to space, the first to do it on his own spaceship!!!

The Manned Maneuvering Unit (MMU) is an astronaut propulsion unit that was used by NASA on three Space Shuttle missions in 1984.

STS-41-B untethered extravehicular spacewalks at a distance from the shuttle.

Second mission STS-41-C, astronauts James van Hoften and George Nelson attempted to use the MMU to capture the Solar Maximum Mission satellite and to bring it into the orbiter's payload bay for repairs and servicing. The plan was to use an astronaut-piloted MMU to grapple the SMM with the Trunion Pin Attachment Device (TPAD) mounted between the hand controllers of the MMU, null its rotation rates, and allow the Shuttle to bring it into the Shuttle's payload bay for storage. Three attempts to grapple the satellite using the TPAD failed. The TPAD jaws could not lock onto Solar Max because of an obstructing grommet on the satellite not included in the blueprints for the satellite. This led to an improvised plan which nearly ended the satellite's mission. The improvisation had the MMU astronaut use his hands to grab hold of an SMM solar array and null the rates by a push from MMU's thrusters. Instead, this attempt induced higher rates and in multiple axes; the satellite was tumbling out of control and quickly losing battery life. SMM Operations Control Center engineers shut down all non-essential SMM subsystems and with a bit of luck were able to recover the SMM minutes before total failure. The ground support engineers then stabilized the satellite and nulled its rotation rates for capture with the orbiter's robotic arm, the Shuttle Remote Manipulator System (SRMS). This proved to be a much better plan. Their successful work increased the lifespan of the satellite.

The third MMU MMU was used in practice to retrieve a pair of faulty communications satellites, Westar VI and Palapa B2.

Following the third mission, the unit was retired from use.

A smaller successor, the Simplified Aid For EVA Rescue (SAFER), was first flown in 1994, and is intended for emergency use only

1949 Concept by BIS - H.E. ROSS and R.A Smith

The Von Braun Bottle suit of the 1950s functions as a hybrid of a space suit and a one-person spacecraft

1965 The Hand-Held Maneuvering Unit was the EVA "zip" gun used by Ed White on the Gemini 4 mission in 1965. The hand-held gun held several pounds of nitrogen, and allowed limited movement around the Gemini spacecraft. It was also used by astronaut Michael Collins on the Gemini 10 mission in 1966

1966 - Astronaut Maneuvering Unit (AMU) was designed by the U.S. Air Force, which was planning to use the Gemini spacecraft as part of the Manned Orbiting Laboratory (MOL). The AMU was a backpack using hydrogen peroxide as the fuel. The total delta-v capability of the AMU was about 250 feet per second (76.2 meters per second), roughly three times that of the MMU. The astronaut would strap on the AMU like a backpack, and maneuver around using two hand controllers like that of the later MMU. Because of the fuel, which came out as a hot gas, the astronaut's suit had to be modified with the addition of woven metal "pants" made of Chromel-R metal cloth.

NASA chief astronaut Deke Slayton later speculated in his autobiography that the AMU may have been developed for the MOL program because the Air Force "thought they might have the chance to inspect somebody else's satellites

This was planned to be tested during Project Gemini on an EVA by Eugene Cernan on Gemini 9A on June 5, 1966. However, the test had to be cancelled because Cernan, tired and overheated, sweated so profusely that his helmet visor fogged before he could get to the AMU mounted on the back of the spacecraft.

There was no real need for self-contained astronaut EVA flight in the Apollo and Skylab programs, the idea had to wait for the advent of the Space Shuttle program, though several manoeuvring device designs were tested inside Skylab.

In 1973, the Automatically Stabilized Maneuvering Unit (ASMU) was test-flown aboard Skylab during the Skylab 3 and 4 missions. Tested inside of the orbiting laboratory, it used nitrogen gas allowing both unsuited and suited testing of the unit. The Skylab AMU was the closest to the Shuttle MMU, but was not used outside the spacecraft because the EVAs were conducted with the astronauts attached to life support umbilicals, and to prevent damage to the delicate solar arrays on the Apollo Telescope Mount.

Foot Controlled Maneuvering Unit (FCMU) was tested within Skylab. The purpose of it was to free the astronaut's hands. It was propelled by cold, high-pressure nitrogen gas located in a tank on the back. It was tested both suited and unsuited.

The MMU was used on three Shuttle missions in 1984.

It was first tested on February 7 during mission STS-41-B by astronauts Bruce McCandless II and Robert L. Stewart.

Two months later, during mission STS-41-C, astronauts James van Hoften and George Nelson attempted to use the MMU to capture the Solar Maximum Mission satellite and to bring it into the orbiter's payload bay for repairs and servicing. The plan was to use an astronaut-piloted MMU to grapple the SMM with the Trunion Pin Attachment Device (TPAD) mounted between the hand controllers of the MMU, null its rotation rates, and allow the Shuttle to bring it into the Shuttle's payload bay for stowage. Three attempts to grapple the satellite using the TPAD failed. The TPAD jaws could not lock onto Solar Max because of an obstructing grommet on the satellite not included in the blueprints for the satellite. This led to an improvised plan which nearly ended the satellite's mission. The improvisation had the MMU astronaut use his hands to grab hold of an SMM solar array and null the rates by a push from MMU's thrusters. Instead, this attempt induced higher rates and in multiple axes; the satellite was tumbling out of control and quickly losing battery life. SMM Operations Control Center engineers shut down all non-essential SMM subsystems and with a bit of luck were able to recover the SMM minutes before total failure. The ground support engineers then stabilized the satellite and nulled its rotation rates for capture with the orbiter's robotic arm, the Shuttle Remote Manipulator System (SRMS). This proved to be a much better plan. Their successful work increased the lifespan of the satellite.

The final MMU mission was STS-51-A, which flew in November 1984. The propulsion unit was used to retrieve two communication satellites, Westar VI and Palapa B2, that did not reach their proper orbits because of faulty propulsion modules. Astronauts Joseph P. Allen and Dale Gardner captured the two satellites and brought them into the Orbiter payload bay for storage and return to Earth

After a safety review following the Space Shuttle Challenger disaster, the MMU was judged too risky for further use and it was found many activities planned for the MMU could be done effectively with manipulator arms or traditional tethered EVAs

NASA also discontinued using the Shuttle for commercial satellite contracts, and the military discontinued the use of the Shuttle, eliminating the main potential uses. Although the MMU was envisioned as a natural aid for constructing the International Space Station, with its retirement, NASA developed different tethered spacewalk approaches.

The two operational, flown flight units MMU #2 and #3 were stored by NASA in a clean room at Lockheed in Denver through 1998.

NASA transferred flight article #3 to the National Air and Space Museum in 1998, which now hangs suspended in the hall above the Space Shuttle Discovery.

Flight article #2 is on display at the U.S. Space & Rocket Center in Huntsville, Alabama. As of 2017,

MMU #1 is on display in the Space Vehicle Mockup Facility at Johnson Space Center.

The former Soviet Union also used a cosmonaut propulsion system on flights to the space station Mir. The SPK (or UMK, UPMK) was larger than the Space Shuttle MMU, contained oxygen instead of nitrogen and was attached to a safety tether. Despite the tether, the SPK allowed the cosmonaut, wearing the self-contained Orlan spacesuit, to "fly around" the orbiting complex, allowing access to areas nearly impossible to access otherwise. Though tested on Mir in 1990, the cosmonauts preferred using the Strela crane (equivalent to the Mobile Servicing System). The SPK, which was left attached to the outside to the Kvant-2 module, was destroyed when Mir re-entered the atmosphere after decommissioning.

The 21KS system is a completely new design for Orlan-DMA spacesuit not using a safety tether, but air-jet engines. This system was similar to MMU. It was automatically stabilized, used 6 degrees of freedom, weighed less than 180 kg, had a delta-v of 30 m/s, practical speed of 1 m/s, and an emergency mode that allows for rotational acceleration of 8°/s per second

SAFER is designed to be used as a self-rescue device if in spite of precautions such as tethers, safety grips, and the robot arm an EVA crewmember gets separated and no vehicles can provide rescue capability.

SAFER is worn by every ISS crewmember using an Extravehicular Mobility Unit.

SAFER was co-invented by former astronauts Joseph Kerwin, Paul Cottingham and Ted Christian under a Lockheed contract to NASA for Space Station Freedom.

SAFER was the design solution to the Shuttle Program's requirement to provide a means of self rescue should an EVA crewmember become untethered during an EVA

SAFER was first flown on STS-64 September 9, 1994, where an untethered flight test was performed first by astronaut Mark Lee and then Carl Meade. Both astronauts flew the SAFER up and around the Shuttle's Robotic Arm along with a demonstration test of the SAFER's automatic attitude hold feature. This feature arrests uncontrolled rotation of a detached crewmember expected in an accidental separation. SAFER has a mass of approximately 83 lb (38 kg) and can provide a total change in velocity (delta-v) of at least 10 ft/s (3 m/s).[4] It was also tested during flight STS-92 when astronauts Peter Wisoff and Michael López-Alegría performed test maneuvers, flying up to 50 feet (15 m) while remaining tethered to the spacecraft.[5]

Complications

The left side latch on the SAFER unit became unlatched during an EVA by astronaut Piers Sellers on STS-121 while testing shuttle repair techniques. The latch had been inadvertently bumped and moved to the unlatch position. As a precaution, Mike Fossum tethered it to him and the spacewalk continued.[8] In subsequent spacewalks, the latches were secured with Kapton tape, a space-rated form of adhesive tape, to prevent the latches from inadvertently opening.