Talk:Manned Maneuvering Unit

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That gives me an idea: How fast could you get spinning in circles with constant thrust in space? You wouldn't have any resistance to slow down. :D

Your rotation would be limited by your body's ability to hold itself together - enough centripetal force and it will fly apart. I supposed that if you were in a superstrong suit that could withstand any force you would then be limited by general relativity. :P Thomasdelbert 16:53, 2 February 2006 (UTC)

That's a good question because that's an obvious failure mode: stuck thruster causes uncontrolled spinning. A similar problem actually happened on Gemini 8, which nearly killed Neil Armstrong. In that case the Gemini vehicle reached about one revolution per second, which caused so much G force that the astronauts nearly blacked out before regaining control. This possibility was discussed extensively for the MMU and NASA added sufficient safeguards to prevent or limit the problem.

To attempt answering the specific question, the MMU had about 80 ft/second of delta-v capability. If completely expended solely in pitch, yaw or roll, the astronaut would rotate about his center of mass very rapidly.

From a translational (straight line) standpoint, the total kinetic energy available is given by:

KE = 1/2*m*v^2, where:

KE = kinetic energy (joules)

m = mass (kg), assume about 276 kg (MMU+suit+PLSS+astronaut)

v = velocity (m/s), 24.38 m/s (80 ft/sec)

KE = 82,025 joules

So the question is if 82,025 joules were expended rotationally, how fast would he spin. Unfortunately this depends on some unknowns, including how far from the center of mass are the thrusters. Maybe someone more familiar with physics could do the calculation. However he'd likely be rotating so fast he'd "red out" from centrifugal force pushing blood to his head. Then he'd just keep spinning forever, even after thruster propellent was exhausted. Joema 20:33, 2 February 2006 (UTC)

Contents 1 Not used any more? 2 Strela crane 3 Do you sit on it? 4 Zip gun gas?

[edit] Not used any more?

Decent article, but missing one major explanation: why hasnt the MMU been used since 1984? I'm assuming its nasas paranoia about safety, and they no longer like astronauts not being tethered to the shuttle, but does anyone know this for sure / any details? Modest Genius 02:14, 29 January 2006 (UTC)

I agree, the biggest question I have after reading the article is also why has it not been used since 1984. Good article otherwise. Canderra 04:07, 29 January 2006 (UTC)

It -is- used. EVAs are the only way that new components of the International Space Station can be assembled, for example. Pictures of NASA astronauts sporting MMU packs are available online dating from 2001 to 2004 proving this. The article is false in stating that the MMU hasn't been used since Challenger. Needs fixing.

The article is absolutely correct. The MMU has not been used since 1984. There are no pictures showing an astronaut wearing an MMU in space since 1984. Look all you want, you'll never find an image of an MMU-suited astronaut working on the International Space Station (ISS). You may be thinking about the much smaller SAFER unit, which is totally different from the MMU. ISS assembly is by the SRMS (Space Station Manipulator System), or by tethered astronauts, or by astronauts riding the SRMS. It is not by free flying astronauts using either MMU or SAFER. Joema 21:13, 29 January 2006 (UTC)

From a 1991 report [1]:

Yet the MMU has not been used since 1984. There are several reasons for this. First, most extravehicular activities were effective without use of the MMU. Tethers, safety grips, hand bars, and other restraints allowed astronauts to work in the open cargo bay. Furthermore, the maneuverability of the Space Shuttle itself and the utility of the shuttle's robotic manipulator arm had proved capable of rescuing satellites-the primary function for which the MMU had been designed. The orbiter could be piloted with such accuracy that on mission 41-B, for example, commander Vance D. Brand piloted the Challenger into position so that McCandless on the manipulator arm could grab a foot restraint that had broken loose and floated away from the orbiter. On flight 41-C, the MMU failed to achieve mechanical mating to the Solar Max satellite, but the orbiter and manipulator arm recovered the satellite. On the Discovery mission, 51-A, commander Henry W. Hartsfield operated the remote manipulator arm to knock ice off a waste-water port, the ice being a reentry hazard. This sort of contingency was a potential MMU activity, but the manipulator arm solved the problem.

Another reason for lack of use of the MMU was the Challenger accident. In January 1986 the Challenger exploded 73 seconds after launch. The crew of seven, the spacecraft, and the payload were lost. That accident initially prompted a suspension of space flights that lasted into September 1988. The accident and resulting investigations also prompted new safety rules that would require expensive changes to the existing MMU, changes pending both a customer and a mission for the MMU. Still another reason for not using the MMU has been the lack of a new user with adequate funding and appropriate mission. Finally, since the Space Station is still under discussion, the Space Shuttle remains the main space human flight program of the United States. The MMU is not necessary to its operations.

I hope this more fully answers the question. (Actually, I think the original inquirer accessed the article moments before I added the brief explanation.) Today's astronaut rules do not permit a US astronaut to operate without two tether devices, so that one may be attached at all times. The "arm" and future "hand" on the space station are intended to replace the need for many EVA tasks. There simply isn't a need for an MMU at present, and it's difficult to justify using today's failsafe rules. --Dhartung | Talk 22:02, 29 January 2006 (UTC)

So yeah, its a safety thing. Thanks for the clarification and edit Modest Genius 22:57, 30 January 2006 (UTC)

Wasn't the MMU used during the opening ceremonies of the 1984 Los Angeles Olympics, or was that another jetpack contraption? -- Jalabi99 20:50, 7 February 2006 (UTC)

[edit] Strela crane

The Russian SPK section references a Strela crane, but the article linked to Strela does not make sense as it links to an armnament similar to a bazooka, not a tool used for space walks. Is there another use of the term "strela"? Can somebody please verify this, and either correct it, strike it out, or link to an article that describes a strela crane that would make sense to use for a spacewalk? ==Thomasdelbert 23:11, 29 January 2006 (UTC)

[edit] Do you sit on it?

Is it like a chair, do you sit in it? All the pics of it look like some ugly space chair.

[edit] Zip gun gas?

The article claims oxygen. However, I seem to recall Michael Collins saying he plugged the gas supply into a nitrogen connector outside the spacecraft. —The preceding unsigned comment was added by 205.175.225.22 (talk) 16:29, 7 February 2007 (UTC).