A Grease Monkey In Space

Tom and Ray

Did you catch Tom and Ray's call with astronaut John Grunsfeld on Car Talk? If not, you can find Tom and Ray's old customer right here, hear about John's repairs to the Hubble Space Telescope, and check out photos of John at work... in space.

What did you think of Tom and Ray's advice? Should our hosts be next in line to repair the Hubble... or did John's training under Tom and Ray do the trick? Share you thoughts right here.

Researcher

When John first started the call, I envisioned that he was working on a motor cycle because their fasteners always seem to strip out the drive. One tool that seems to work quite well is an impact driver i.e. the driver turns when the end is hit with a hammer. The bolt or screw is driven axially as torque is applied. This tool will usually remove phillip head screws that have been torqued to spec on a motorcycle. So I think Tom and Ray need to demonstrate the use of the impact driver to John. I'll have to assume that the mass of the attached space vehicle is adequate to buck the impact of a 2# hammer.

Regarding the high loosening torque observed by John, the high vacuum in space plus the wide thermal cycles experienced by any space vehicle would cause any threads to semiweld themselves. Therefore, even if the fastener was torqued to spec on the ground, it would require more torque to remove in space after all adsorbed air and oil has vaporized into space from the threads. Also the vacuum of space would make it difficult to get WD-40 or Liquid Wrench to work as they would probably boil off before then wicked into the threads.

Keep us posted on any answers from NASA

Jim Waggoner

Cold-welding in a vacuum environment would be my guess as the cause of the sticky bolt. Keep in mind that satellites employing optical instruments are very sensitive to deposition of outgassing vapors from materials used in the fabrication of the satellite. As a result the rules are very strict as to what materials can be used. This rules out Loc-tite, for instance, as a way of keeping bolts from loosening. Lock washers are out also as they tend to generate fine metal shavings which are also undesirable. Nylock, as I recall, is also banned because of either vapors or particles from the Nylon. This leaves mechanical interferance as the preferred way to secure fasteners. (It's not the vibration in space one worries about; it's the vibration encountered getting there.) When metals are forced together in a vacuum, there is a tendency for the metals to stick together, a form of cold-welding. This has been a problem in the past with satellites such as the OSO (Orbiting Solar Observatory), which had a rotating body with a fixed solar-cell array which kept the observatories instruments pointed toward the sun. The bearings had a tendency to stick. It is possible that NASA has forgotten this early experience; witness the problems with the bearing failures on the current space station.

waterboy

Amazing insight. Just curious what the temperature extremes, sun vs shad might be and what was the probable temp of the bolt he was working on?

beachtracks

I think the extreme cold temperatures may be the key to why the bolts seize up. This is based on some very distant past experience rather than any engineering insight.

Years ago I was a powerplant mechanic in Michigan, part of a traveling repair crew that would go from one company power plant to another rebuilding boilers and steam turbines. The turbine covers were huge, the largest I recall being at the Palisades nuclear powerplant, 80 tons. To keep steam from leaking, the covers needed to be refitted very tightly. After honing the seating surfaces for a smooth fit (no gaskets), they were attached by lots of large, hollow center bolts. The hollow centers were important because that's where we'd insert big high temperature heating rods.

Every high school science student knows that metal expands when heated, but the physics of cylinder expansion is that this expansion occurs lengthwise, which has the effect of shrinking the cylinder's diameter slightly. Since bolts are cylinders, they lengthen and get slightly thinner as they heat up, and this can be used to advantage when tightening and loosening them.

So we'd hone the turbine cover's seating surface for a good fit, lower the cover in place, install the turbine cover bolts, insert the heating rods, heat the bolts to near glowing, and then (Tom & Ray will love this part) tighten the bolts with slug wrenches and sledge hammers.

Slug wrenches are big box end wrenches with giant squared off metal "handles" way too big to wrap your hand around but perfect for receiving the blows of a sledge hammer. That's right, you tighten the bolts by smacking the tar out of the wrench. When you get the bolt as tight as you can, you re-insert the heating rod, heat it up some more, and the bolt loosens slightly due to it's lengthwise expansion and diameter-wise contraction, allowing for more tightening by more beating on the slug wrench.

And here's the part possibly applicable to the Hubble sticky bolt issue... When those turbine cover bolts cool to their normal operating temperatures, they are tight! Really tight! We never had steam leakage problems because as the bolts cooled they would draw the two turbine cover seating surfaces together very, very tightly.

So... Could it be that bolts installed on the Hubble are warmer when installed than they are when removed? I would think in the very cold temps of space, those bolts would shrink lengthwise and fatten up diameter-wise after installation--a lot--thereby increasing the torque necessary to remove them.

Possible solution? I guess I didn't mention how we'd remove the turbine covers, but the process was the same in reverse. We'd insert the heating rods, heat the bolts to glowing, and slug them loose--righty tighty, lefty loosey. So maybe if NASA can figure a way to heat the bolts before trying to loosen them, the added elbow grease and temptation to beat on the bolts wouldn't be necessary. And maybe if before installing any replacement bolts they could be brought down to what their normal operating temperature will be, any change in length/diameter would have already taken place so it wouldn't later have the effect of tightening the bolts.

Dave Caylor
Kauai, Hawaii

greekfreek

i have a small 18 volt mikata impact wrench litium battery, small and compact which can drive or remove most anything. i have one just to work on cars with

oldschool

We don't need to wonder who will be next in line to repair Hubble, the last Hubble repair mission was the last Hubble repair mission.

Researcher

The temperature range I have seen mentioned is -100 to 125 degrees C (-150 to 250 degrees F). The work would probably have been done in the shuttle bay out of direct sunshine so the bolt would be fairly cool.

hallkbrdz

Very true... it's sad, but a reflection on just how pathetic our nation is becoming.

Once we could land on the Moon regularly. Now we won't be able to replace 70's technology with something much better to work in low earth orbit space. Orion - give me a break.

How the once mighty have fallen.

oldschool

I just finished a major paper on the current administrations review of the VSE. The Bush plan was not realistic and it smelled of politics. 400 billion plus to set-up on the moon and go to Mars,could we do it even if we could fund it?

gdzjuba

It's atomic force. I know that because I worked as a scientist in physics of solids and we used vacuum equipment in our laboratory.
Parts are typically made of none-rusting materials (like stainless steel) and are cleaned thoroughly before sending them to the outer of space. Space vacuum removes rest of the air and residues from all surfaces including fasteners. When 2 surfaces that are so clean come into close contact (the is no lubricant to separate them), they stick to each other by atomic force.
On the top of that if this contact lasts for a long time, atomic diffusion kicks (this takes years) in and parts are getting literally fused together by the process of atomic diffusion.
The remedy we used in our particle accelerator was special carbon-based lubricant that works in vacuum and does not give off gas