Author Topic: Back up system for the MMU  (Read 1042 times)

Online SkipMorrow

Back up system for the MMU
« on: 12/23/2017 12:09 PM »
RIP Bruce McCandless. Your picture of you testing the MMU was amazing! But I was wondering, what was the backup plan if the MMU failed while he was so far away from the shuttle? Probably try to move the shuttle closer to him??? Is that even possible?

Online DaveS

  • Shuttle program observer
  • Senior Member
  • *****
  • Posts: 7795
  • Sweden
  • Liked: 322
  • Likes Given: 13
Re: Back up system for the MMU
« Reply #1 on: 12/23/2017 12:11 PM »
RIP Bruce McCandless. Your picture of you testing the MMU was amazing! But I was wondering, what was the backup plan if the MMU failed while he was so far away from the shuttle? Probably try to move the shuttle closer to him??? Is that even possible?
That was the plan. And why do you think it wouldn't be possible?
"For Sardines, space is no problem!"
-1996 Astronaut class slogan

"We're rolling in the wrong direction but for the right reasons"
-USA engineer about the rollback of Discovery prior to the STS-114 Return To Flight mission

Online SkipMorrow

Re: Back up system for the MMU
« Reply #2 on: 12/23/2017 12:15 PM »
I guess I thought it would be hard to move the shuttle to catch up with someone floating away. But now that I think about it, I guess that isn't much harder than docking with the ISS. Silly me.

Online DaveS

  • Shuttle program observer
  • Senior Member
  • *****
  • Posts: 7795
  • Sweden
  • Liked: 322
  • Likes Given: 13
Re: Back up system for the MMU
« Reply #3 on: 12/23/2017 12:22 PM »
I guess I thought it would be hard to move the shuttle to catch up with someone floating away. But now that I think about it, I guess that isn't much harder than docking with the ISS. Silly me.
That's exactly why the MMU was retired after Challenger. Whatever the MMU could do, the orbiter could it at least 10x better. The MMU was developed when the actual controlability/maneuverability of the orbiter was still unknown. As the program went on they found that orbiter was far more maneuverable than initially thought and the MMU was deemed unnecessary. I think it even was on STS-41B that an Manipulator Foot Restraint (MFR) came loose and drifted away. They just moved the orbiter over to it and Bob Stewart just grabbed it when it was close enough and re-stowed in the payload bay. No need for the MMU.
"For Sardines, space is no problem!"
-1996 Astronaut class slogan

"We're rolling in the wrong direction but for the right reasons"
-USA engineer about the rollback of Discovery prior to the STS-114 Return To Flight mission

Offline Hog

  • Full Member
  • ****
  • Posts: 1130
  • Woodstock
  • Liked: 277
  • Likes Given: 614
Re: Back up system for the MMU
« Reply #4 on: 12/24/2017 12:08 AM »
I guess I thought it would be hard to move the shuttle to catch up with someone floating away. But now that I think about it, I guess that isn't much harder than docking with the ISS. Silly me.
That's exactly why the MMU was retired after Challenger. Whatever the MMU could do, the orbiter could it at least 10x better. The MMU was developed when the actual controlability/maneuverability of the orbiter was still unknown. As the program went on they found that orbiter was far more maneuverable than initially thought and the MMU was deemed unnecessary. I think it even was on STS-41B that an Manipulator Foot Restraint (MFR) came loose and drifted away. They just moved the orbiter over to it and Bob Stewart just grabbed it when it was close enough and re-stowed in the payload bay. No need for the MMU.
No need for SAFER then?    There was risk management concerns after STS-51L, MMU was deemed too dangerous, in addition to your points.  The risk averse culture was born.
Paul

Online the_other_Doug

  • Senior Member
  • *****
  • Posts: 2610
  • Minneapolis, MN
  • Liked: 1627
  • Likes Given: 2930
Re: Back up system for the MMU
« Reply #5 on: 12/24/2017 01:32 AM »
I guess I thought it would be hard to move the shuttle to catch up with someone floating away. But now that I think about it, I guess that isn't much harder than docking with the ISS. Silly me.
That's exactly why the MMU was retired after Challenger. Whatever the MMU could do, the orbiter could it at least 10x better. The MMU was developed when the actual controlability/maneuverability of the orbiter was still unknown. As the program went on they found that orbiter was far more maneuverable than initially thought and the MMU was deemed unnecessary. I think it even was on STS-41B that an Manipulator Foot Restraint (MFR) came loose and drifted away. They just moved the orbiter over to it and Bob Stewart just grabbed it when it was close enough and re-stowed in the payload bay. No need for the MMU.
No need for SAFER then?    There was risk management concerns after STS-51L, MMU was deemed too dangerous, in addition to your points.  The risk averse culture was born.

SAFER is more for ISS EVAs.  You could maneuver the Shuttle around to grab someone drifting away.  You can't move the ISS in the same way, or nearly as quickly as would be needful.
-Doug  (With my shield, not yet upon it)

Online obi-wan

  • Full Member
  • **
  • Posts: 266
  • Liked: 579
  • Likes Given: 5
Re: Back up system for the MMU
« Reply #6 on: 12/24/2017 05:02 AM »
The MMU development process was accelerated prior to the first shuttle flight out of concern for the potential need for a tile repair capability. It was retired because the GN2 pressure tanks were operated beyond their original design pressures, and were certified for only ten pressurization cycles once filled to the higher pressures. Several cycles were used for each pre-launch checkout, so the units hit end-of-life after a few flights. NASA studied it and decided tearing them down to install new pressure tanks was about the same cost as building new ones. Given the conclusion that an MMU-based tile repair was as likely to cause new damage as it was to fix prior damage, as well as the abilities of the orbiter for direct retrieval, it was decided to retire the MMUs.

Offline Zed_Noir

  • Senior Member
  • *****
  • Posts: 2271
  • Canada
  • Liked: 293
  • Likes Given: 476
Re: Back up system for the MMU
« Reply #7 on: 12/24/2017 07:21 PM »
Slightly OT. But think it is not worth starting another thread.

Will someone in the near future field something similar to the MMU? Specifically a maneuver unit operating with a spacesuit.

Offline Bob Shaw

  • Full Member
  • ****
  • Posts: 995
  • Liked: 379
  • Likes Given: 348
Re: Back up system for the MMU
« Reply #8 on: 12/24/2017 07:44 PM »
Slightly OT. But think it is not worth starting another thread.

Will someone in the near future field something similar to the MMU? Specifically a maneuver unit operating with a spacesuit.

It is called SAFER.

Offline dbaker

  • Full Member
  • *
  • Posts: 114
  • Liked: 3
  • Likes Given: 0
Re: Back up system for the MMU
« Reply #9 on: 12/30/2017 02:17 PM »
The primary mode for an MMU backup was to carry two (only two flight versions were ever built) so that the second could be used, by the second EVA crewmember, to go off and retrieve an untethered and stranded astronaut. If all the energy available for delta-V was focused through a single translation axis (almost impossible to contrive!) the MMU/astronaut would be 1.5 km away within one minute.

Offline Jim

  • Night Gator
  • Senior Member
  • *****
  • Posts: 31557
  • Cape Canaveral Spaceport
  • Liked: 9908
  • Likes Given: 309
Re: Back up system for the MMU
« Reply #10 on: 12/30/2017 09:10 PM »
The primary mode for an MMU backup was to carry two (only two flight versions were ever built) so that the second could be used, by the second EVA crewmember, to go off and retrieve an untethered and stranded astronaut. If all the energy available for delta-V was focused through a single translation axis (almost impossible to contrive!) the MMU/astronaut would be 1.5 km away within one minute.

no, it was orbiter maneuvering as the primary mode.

MMU testing on 41-C post Solar Max capture was limited due to low RCS propellent levels.

Tags: