Why were the MMU's used so little?

[banquo's_bumble_puppy]

I've always wondered whatever happened to the manned maneuvering unit that was used on a few shuttle missions. Many of us have seen the majestic photo of the astronaut strapped into an MMU floating above the Earth. Were they just to dangerous to use?

[Metricyard]

My guess is that NASA/the astronauts had no reason to use them.

[NEOWatcher]

My guess is that most of the EVA's were in close enough proximity to the craft that handholds and other traditional methods were good enough. It would seem to me that the MMU would cause more issues in being able to do the work that the EVA required.
They seem to be more suited to satellite repair or capture where the astronaut would need to be farther from the craft. And; we all know how little the shuttle was used in that capacity.

[novaderrik]

one of the coolest pieces of video footage from the shuttle program is of an astronaut using an MMU to go out and capture a satellite. this was back in the mid 80's before the Challenger accident, i believe... yeah, they could have just used the arm to do it, but they had that cool rocket pack and wanted to prove the concept.
it was just another one of those cool things that they developed for a specific purpose, only to have that purpose eliminated.

[Damburger]

Wikipedia said it was the Challenger accident.

After the accident, NASA looked into a whole bunch of safety things not directly related to the issue that had caused the loss of Challenger (e.g. disallowing centaur upper stages from flying on the shuttle). Unfortunately, one thing they did not look into was how they constantly ignored foam strikes on the orbiters...

[djellison]

Too expensive, too dangerous, and too difficult to use, the RMS's on Shuttle and Station worked out better for EVA work.

[KaiYeves]

Some things are just too cool to last.

[banquo's_bumble_puppy]

I think they were way too big as well....something on the order of the ones used in Star Trek: TMP would be cool....especially the countdown and firing of the emergency engine....one of the few "good" parts of the movie...

[The Jim]

My guess is that NASA/the astronauts had no reason to use them.

Bingo

[voyager_3]

Are there any of the MMU's in museums?

[ravens_cry]

A similar, but apparently simpler system is SAFER, that is Simplified Aid for EVA Rescue. But yes, if a spacesuit can be categorized as a mini spaceship, the MMU is a miniature spaceship, with an engine. Another idea you don't hear about much is the Rescue Ball. I plan to include a similar idea for a future science fiction story. Just pop a passenger in one of these and put them with the rest of the cargo in the Delicate Items cargo pod, without all the fuss and complication of a re-entry pod dedicated to passengers. It might also be an idea worth reviving in real life for private space flight. No need to fit a passenger for a full spacesuit or train them how to use it, just stuff them in one of these. Claustrophobia is optional.

[novaderrik]

A similar, but apparently simpler system is SAFER, that is Simplified Aid for EVA Rescue. But yes, if a spacesuit can be categorized as a mini spaceship, the MMU is a miniature spaceship, with an engine. Another idea you don't hear about much is the Rescue Ball. I plan to include a similar idea for a future science fiction story. Just pop a passenger in one of these and put them with the rest of the cargo in the Delicate Items cargo pod, without all the fuss and complication of a re-entry pod dedicated to passengers. It might also be an idea worth reviving in real life for private space flight. No need to fit a passenger for a full spacesuit or train them how to use it, just stuff them in one of these. Claustrophobia is optional.

SAFER? that's an acronym with an abbreviation inside it..

[ravens_cry]

SAFER? that's an acronym with an abbreviation inside it..

I bet they felt very clever when they came up with that one.

[joema]

I've always wondered whatever happened to the manned maneuvering unit that was used on a few shuttle missions...Were they just to dangerous to use?

Consider that a thruster malfunctioned nearly killed Neil Armstrong on Gemini 8. If a thruster sticks ON, it's not aways easy to determine which one. The vehicle (or MMU astronaut) is rapidly spinning up during that interval. The MMU had contingency procedures for that, but it was still risky.

When grabbing satellites the MMU-suited astronaut is exposed to sharp edges, moving massive objects, and he has limited visibility. A tethered EVA is dangerous enough when you have multiple cameras and eyes on you and you're physically attached to a stable platform. An MMU-type EVA has none of those.

If you picture a MMU-suited astronaut like a Apollo astronaut exploring with the Lunar Rover, the risk becomes more clear. He could always have a life support failure. He has a backup, but what if that fails or if he's too remote to reach in time before it's exhausted? With Apollo, the maximum distance allowed from the LM during rover trips was calculated on the return driving time if an astronaut's primary life support system failed and he was on the backup. With Apollo there was a 3rd backup -- an emergency "buddy" connection to his partner. With an MMU the astronaut is alone -- nobody to help him except the orbiter.

Also the MMU was designed and planned early in the shuttle program. This was before the capabilities of the Shuttle Remote Manipulator System (SRMS) were known and tested, and before the fine-positioning ability of the shuttle in space was validated.

For all they knew the orbiter and SRMS might not have the precision and delicacy to snag a satellite, or some satellites might be contaminated by the orbiter's hydrazine thrusters. If the satellite was spinning it might jeopardize the orbiter to try and grab it with the arm. An MMU astronaut using nitrogen thrusters might more delicately and flexibly approach and grab the satellite. He could also inspect the orbiter externally.

It turned out the orbiter and SRMS were much more precise than initially though. Likewise an MMU astronaut proved more unwieldy and less capable than initially thought, plus introduced significant risk. On STS-41-B, they nearly destroyed a satellite trying to grab it with by hand using the MMU.

Eventually all satellite grabbing was done by the SRMS, and orbiter inspection done by sensors on the arm, plus imaging from ISS.

[Glom]

SAFER? that's an acronym with an abbreviation inside it..

So is SLA.

And PHP.

[KaiYeves]

Are there any of the MMU's in museums?

There's one at the US Space and Rocket Center in Huntsville.

[Solfe]

Another idea you don't hear about much is the Rescue Ball.

I followed the link and had a good laugh at this line: "Crew members were to climb into the ball, assume a fetal position..."

Is it possible to get in to a Rescue Ball and not assume the fetal position? I don't think I could do it.

[ravens_cry]

I followed the link and had a good laugh at this line: "Crew members were to climb into the ball, assume a fetal position..."

Is it possible to get in to a Rescue Ball and not assume the fetal position? I don't think I could do it.

Looking at the size of the thing, I imagine not unless you were really tiny already. Here is a picture I Googled of someone getting zipped up inside one looking very bemused.The clear demonstration version in the astronautix entry I linked to earlier shows exactly how much room one would have. In short, not much.

[Ara Pacis]

IIRC, he's sitting cross-legged instead of the fetal position.

[JustAFriend]

Are there any of the MMU's in museums?

Prototypes are in the Smithsonian and the USAF Museum in Dayton.

[ravens_cry]

IIRC, he's sitting cross-legged instead of the fetal position.

Yes, and he is in Earth gravity. I guess if you really want to look all yoga in your spaceball, you can, but it is still a tight fit.