Manned Maneuvering Unit: Difference between revisions - Wikipedia

m

Line 1:

{{Short description|NASA astronaut propulsion unit}}

{{Use American English|date=January 2014}}▼

{{Use American English|date=March 2021}}

{{Use mdy dates|date=March 2021}}

{{more footnotes|date=February 2011}}

[[Image:Bruce McCandless II during EVA in 1984.jpg|thumb|right|280px|U.S. astronaut [[Bruce McCandless II|Bruce McCandless]] uses a Manned Maneuvering Unit during the 1984 [[STS-41-B]] mission]]

The '''Manned Maneuvering Unit''' ('''MMU''') is an [[Astronaut Propulsion Unit|astronaut propulsion unit]] that was used by [[NASA]] on three [[Space Shuttle]] missions in 1984. The MMU allowed the [[astronauts]] to perform untethered [[Extravehicular activity|extravehicular]] spacewalks at a distance from the shuttle. The 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.

==Overview==

Line 8 ⟶ 13:

To adapt to astronauts with different arm lengths, controller arms could be adjusted over a range of approximately 13 centimetres. The MMU was small enough to be maneuvered with ease around and within complex structures. With a full propellant load, its mass was 148 kilograms (326 pounds).

Gaseous [[nitrogen]] was used as the propellant for the MMU. Two aluminium tanks with [[Kevlar]] wrappings contained 5.9 kilograms of nitrogen each, enough propellant for a six-hour [[Extravehicular activity]] (EVA) depending on the amount of maneuvering done. TypicalThe MMUtwo velocitypropellent capabilitytanks had an initial charge on the ground prior to the mission allowing for [[Delta-v]] of 110 to 130 ft/sec. The tanks could be recharged in orbit to a minimum equivalent [[Delta-v]] of 72 ft/sec. For a nominal mass, translational acceleration was about0.3±0.05 80ft/sec² feetand perrotational secondacceleration (25was m10.0±3.0 deg/s)sec².<ref>https://ntrs.nasa.gov/api/citations/19790008382/downloads/19790008382.pdf {{Bare URL PDF|date=August 2024}}</ref>

There were 24 nozzle thrusters placed at different locations on the MMU. To operate the propulsion system, the astronaut used their fingertips to manipulate hand controllers at the ends of the MMU's two arms. The right controller produced rotational [[acceleration]] for roll, pitch, and yaw. The left controller produced translational acceleration for moving forward-back, up-down, and left-right. Coordination of the two controllers produced intricate movements in the unit. Once a desired orientation was achieved, the astronaut could engage an automatic attitude-hold function that maintained the inertial attitude of the unit in flight. This freed both hands for work.

Line 15 ⟶ 20:

[[File:Robert L. Stewart, hanging above the Earth - DF-SC-84-10569.jpg|thumbnail|Robert L. Stewart]]

In 1966, the [[US Air Force]] developed an Astronaut Maneuvering Unit (AMU), a self-contained rocket pack very similar to the MMU. 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. Astronauts did not learn how to work during EVA without tiring until the final [[Gemini 12]] mission, but no AMU was carried on that flight. Since there was no real need for self-contained astronaut EVA flight in the [[Apollo program|Apollo]] and [[Skylab]] programs, the idea had to wait for the advent of the [[Space Shuttle]] program, though several maneuvering device designs were tested inside Skylab.

===Active use in space===

[[File:Capturing the Solar Maximum Mission satellite.jpg|thumb|SMM being captured, 1984]]

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 (astronaut)|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 stowage and return to Earth.

[[Image:STS-51-A Westar 6 retrieval.jpg|thumbnail|Dale Gardner retrieves Westar 6.]]

===Retirement===

After a safety review following the [[Space Shuttle Challenger disaster|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.<ref>{{cite web

Line 28 ⟶ 37:

| date=1998

| publisher=[[NASA]]

| accessdateaccess-date=2014-10-14}}</ref> 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 #No. 2 and #No. 3 were stored by NASA in a clean room at Lockheed Martin in Denver through 1998. NASA transferred flight article #No. 3 to the [[National Air and Space Museum]] in 1998, which now hangs suspended in the hall above the Space Shuttle Discovery in the [[Steven F. Udvar-Hazy Center|Udvar-Hazy Center]] annex.<ref>{{cite web

| url=http://www.collectspace.com/news/news-102004a.html#102004

| title=Smithsonian opening space history hangar

| date=2004-10-20

| publisher=[[collectSPACE]]

| accessdateaccess-date=2014-10-14}}</ref><ref>{{cite web

| url=https://airandspace.si.edu/collection-objects/manned-maneuvering-unit-mmu?object=/nasm_A20010176000

| title=Manned Maneuvering Unit (MMU)

| publisher=Smithsonian's National Air and Space Museum Home Page

| accessdateaccess-date=2016-072022-01-21}}</ref> Flight article #No. 2 is on display at the [[U.S. Space & Rocket Center]] in Huntsville, Alabama. As of 2017, MMU #No. 1 is on display in the [[Space Vehicle Mockup Facility]] at Johnson Space Center.

==See also==

* [[Single-person spacecraft]]

* [[Astronaut_propulsion_unitAstronaut propulsion unit#Soviet_SPKSoviet SPK|Soviet SPK]]

==References==

{{Include-NASA}}

{{reflistReflist|1}}

==External links==

Line 66 ⟶ 75:

| author=Jonathan Malory

| date=2013-10-09

| archiveurlarchive-url=https://web.archive.org/web/20131009064800/http://www.spacetravel.org/space-travel/interactivespacesuit.html

| archivedatearchive-date=2013-10-09

| url-status=dead}}

* {{cite webencyclopedia

|url = http://www.astronautix.com/craft/shulemmu.htm

|title = Shuttle MMU

|date = 2011-11-17

|workencyclopedia = Encyclopedia Astronautica

|url-status = dead

|archiveurlarchive-url = https://web.archive.org/web/20090504004428/http://www.astronautix.com/craft/shulemmu.htm

|archivedatearchive-date = 2009-05-04

}}

* {{cite web

| url=http://www.lockheedmartin.com/us/100years/stories/mmu.html

| title=Manned Maneuvering Unit (MMU)

| work=Lockheed Martin}}| date=March 28, 2018

}}

{{space suit}}

{{Authority control}}

▲{{Use American English|date=January 2014}}

[[Category:Human spaceflight]]