Author Topic: When NASA meets Murphy's Law  (Read 1768 times)

Offline 12oh2alarm

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When NASA meets Murphy's Law
« on: May 21, 2016, 04:28:44 AM »
Some lesser known anomalies with the Hubble Space Telescope:



Especially the last one is an instance of Murphy's Law "If it jams, force it. If it breaks, it needed replacement anyway."
« Last Edit: May 21, 2016, 04:36:21 AM by 12oh2alarm »

Offline ka9q

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Re: When NASA meets Murphy's Law
« Reply #1 on: May 21, 2016, 04:57:27 AM »
Tinker toys. I love it. A classic engineering war story.

Offline bknight

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Re: When NASA meets Murphy's Law
« Reply #2 on: May 21, 2016, 05:56:07 PM »
What comes to mind is what may happen the next time a part malfunctions and we have to result to a robot that has been programmed to do a specific procure and one of those "something goes bump in the night moments." Will the engineers be able to reconfigure in real time, instead of explaining to a more versatile astronaut? 
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Offline ka9q

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Re: When NASA meets Murphy's Law
« Reply #3 on: May 24, 2016, 06:05:06 AM »
An astronaut probably wouldn't have been helpful in fixing Hubble's cable problem, though he might have determined the problem more quickly through simple visual inspection.

Even if an astronaut had been able to cut the cable and splice in a longer one, the engineering fix that was actually performed was far simpler and just as effective: merely avoid swinging the antenna through the problem area. It becomes an operational constraint just like avoiding gimbal lock on a 3-gimbal platform.

And then there are all the other issues involved in astronaut repair: the accessibility of the spacecraft orbit (the shuttle could only reach low altitudes), the exorbitant cost of shuttle missions (one of the main reason the program was ended), the difficulty of doing any kind of unanticipated repair work while wearing a pressure suit, the vastly increased safety requirements associated with human space flight, etc, etc.

Quite frankly, although the on-orbit servicing of the Hubble is frequently held up as an example of the versatility of the shuttle, I strongly suspect it would have been cheaper to just build a half dozen Hubbles and launch them on expendables as replacements as needed. HR Haddon's comment in Contact ("First rule in government spending: why build one when you can have two at twice the price?") is a bit too cynical; in actual fact, you can almost always negotiate a considerably lower cost per unit when you commit to several rather than just one. Not only is the NRE (non-recurrent engineering) cost amortized over more units, but there's almost always a manufacturing learning curve that brings down the variable costs of additional units.
« Last Edit: May 24, 2016, 06:07:09 AM by ka9q »

Offline bknight

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Re: When NASA meets Murphy's Law
« Reply #4 on: May 24, 2016, 08:12:40 AM »
An astronaut probably wouldn't have been helpful in fixing Hubble's cable problem, though he might have determined the problem more quickly through simple visual inspection.

Even if an astronaut had been able to cut the cable and splice in a longer one, the engineering fix that was actually performed was far simpler and just as effective: merely avoid swinging the antenna through the problem area. It becomes an operational constraint just like avoiding gimbal lock on a 3-gimbal platform.

And then there are all the other issues involved in astronaut repair: the accessibility of the spacecraft orbit (the shuttle could only reach low altitudes), the exorbitant cost of shuttle missions (one of the main reason the program was ended), the difficulty of doing any kind of unanticipated repair work while wearing a pressure suit, the vastly increased safety requirements associated with human space flight, etc, etc.

Quite frankly, although the on-orbit servicing of the Hubble is frequently held up as an example of the versatility of the shuttle, I strongly suspect it would have been cheaper to just build a half dozen Hubbles and launch them on expendables as replacements as needed. HR Haddon's comment in Contact ("First rule in government spending: why build one when you can have two at twice the price?") is a bit too cynical; in actual fact, you can almost always negotiate a considerably lower cost per unit when you commit to several rather than just one. Not only is the NRE (non-recurrent engineering) cost amortized over more units, but there's almost always a manufacturing learning curve that brings down the variable costs of additional units.
I'm referring to replacement of broken/worn parts, not work around procedures.
Truth needs no defense.  Nobody can take those footsteps I made on the surface of the moon away from me.
Eugene Cernan

Offline ka9q

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Re: When NASA meets Murphy's Law
« Reply #5 on: May 24, 2016, 10:07:20 PM »
That's what I meant about buying a bunch of ground spares and launching them as needed.

Offline bknight

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Re: When NASA meets Murphy's Law
« Reply #6 on: May 25, 2016, 08:23:10 AM »
That's what I meant about buying a bunch of ground spares and launching them as needed.
I'm not sure that would be a cheaper program, but since we really don't have a manned vehicle currently to do repairs, it may be the only way to keep it going.
Truth needs no defense.  Nobody can take those footsteps I made on the surface of the moon away from me.
Eugene Cernan