Space Station Solar Equipment Showing Damage

bhmit1 writes "The latest space walk has turned up some bad news for the problematic solar panels: metal shavings. From the article: "The rotary joint, 10 feet in diameter, has experienced intermittent vibrations and power spikes for nearly two months. Space station managers were hoping a thermal cover or bolt might be hanging up the mechanism. That would have been relatively easy to fix, so they were disheartened when Daniel Tani radioed down that metal shavings were everywhere. 'It's quite clear that it's metal-to-metal grating or something, and it's widespread,' Tani said.""

Comments

that's not metal-on-metal grating

[jollyreaper]

That's not metal-on-metal grating in the bearings, that's just some sick bastard playing Yoko Ono.

Will a replacement fix it?

[_merlin]

I noted that they intend to fit a replacement joint, and are limiting the travel of the solar panel(s) in the mean time. My question is, do they know what the source of the problem actually is? Is it a manufacturing defect, damage or wear and tear in the currently fitted joint? If it is, replacing it is a reasonable solution. But if it isn't - i.e. if there's a design or operational problem - replacing it will just be a temporary band-aid, and the same thing will happen again sooner or later.

Re:Will a replacement fix it?

[mha]

So how would you propose these things are done? I mean, things that no one's ever done before, and which you can't really simulate?

An anecdote from my days of working for a huge German company (240000 employees) at Oracle (first job after university): I was part of the 32-64bit porting team. The question came up, are customers going to need additional or larger hard drives for the 64bit version of Oracle?

The answer from the Germans: Well, you've got the source code. Examine all structures in the code that end up on disk and count the bytes. (we know how many Bytes an "int" takes up on 32 vs. 64bit, etc.)

The answer from the Americans: Well, you've got the source code there. Just compile it and see what happens!

You know, while the German approach (I *am* German) sounds a lot more "scientific" and exact I would say the American way was not just better, but the only one that actually WORKS outside a simulated computer environment with a limited number of known-in-advance factors.

So again, how would YOU go about discovering the unknown? *I* would do just what NASA does, and what humans have done for millenia: Try, fail and try again, never approaching any ideal solution but something that works for now, until the next unforeseen thing happens.

Of course, in the western world everything that even LOOKS like risk has to be eliminated: from hot coffee to horses with tourists on them going any faster than a slow walk (I'll NEVER go on any tourist expedition on a horse in the US again, in Germany my friends who've never been on a horse before were forced to "survive" gallop several times in a 2 hour tour - and did so with relative ease).

One hell of a gear box

[BadHaggis]

The SARJ, 10.5 ft in diameter and 40 inches long, will maintain the solar arrays in an optimal orientation to the sun while the entire space station orbits the Earth once every 90 minutes. Drive motors in the SARJ will move the arrays through 360 degrees of motion at four degrees per minute. The joints must rotate the arrays smoothly without imparting vibrations to the laboratories and habitation modules on the station that would impact microgravity-processing activities. At the same time, 60 kW of power at 160 volts and multiple data channels are carried across each joint by copper "roll rings" contained within. From: Google Cached Lockeed Martin Article on the Panels.

The joints in question are huge and as this article points out any vibrations back into the ISS could cause problems with other equipment or experiments. Additionally power is transferred back to the ISS through copper rings in the unit itself. Any metal which provides a better circuit path than the copper would cause the power spikes.

Opening this thing up would be something like trying to rebuild an Automatic Transmission, then add the complexity of doing this in micro-gravity. It would probably be easier for NASA to send up a complete replacement instead of trying clean out all of the metal shavings and replace the parts that are damaged.

Re:Towing in space

[Rei]

These *were* designed to run for many rotations. The design specs for the SARJ (Solar Alpha Rotary Joint) were that the 10.5'x2.5', 2,500lb structure would rotate at 4 degrees per minute without imparting vibration to the laboratories that would mess up the microgravity experiments, for a minimum of 15 years. They also have to transfer 60kW of power at 160V while rotating through a "roll ring". These were the design specs, and they were engineered around that; this break was not supposed to happen. That's why this is considered an anomalous event. It's not a case of an insufficient design goal.

One thing that a lot of people don't realize is that there's still a tremendous amount of stuff that we don't know about living and operating things in space. It's deceptively similar to our world; just picturing it being like an Earth where you can't breathe and you can have enough velocity to fall in a circle simply doesn't cut it.

Example: TSS-1R. Space Shuttle Columbia deployed this as part of NASA's series of experiments with orbital tethers (for "hanging" craft from other craft and for raising and lowering orbits). When the tether was 19.7km out of the desired 20.7km deployed, it snapped. Evidence suggested arcing and burning in the tether. Why? The tether was at -3500VDC compared to the orbiter, with no current flowing through it. A minor defect in the tether's insulation left the conductive core exposed to space. Unexpected trapped gas in the insulation bubbled out in the vaccuum of space. This gas created a path for conduction to the orbiter, creating a plasma arc that burned away at the tether until the remaining strands failed under the strain.

In hindsight, it's easy to look at this and say, "Oh, we should have had a short-detection system." However, hindsight is 20-20. We've learned a great deal from past experiences, which unfortunately means that systems have to get more complicated. For example: where does the heat from running the drive motor for the arrays go? Why, it goes all over the place! It took an entire design study just to figure out where it would be going and what to do with it. Now picture unexpected current draws (creating more heat) from the metal shavings thrown into the mix, and what that will do for heat load, or what the metal shavings themselves could get into or allow to conduct unexpectedly. Things get tricky fast.

Too many people seem too eager to see a "finished product" in space. It's important that things like the ISS be seen foremost as learning experiences. In this case, I'm sure we'll see the same thing.