Tribology in Outer Space

[MolaKule]

In 1995 the Galileo Spacecraft attained an orbit around Jupiter.

Previously in 1991 it failed to fully deploy its 16 ft/ high gain umbrella antenna.

ps://trs.jpl.nasa.gov/handle/2014/32404 and click "ViewOpen."

In three full sentences or less, explain why the umbrella antenna failed to deploy.

This Question of The Day is open to all members.

 

[dkryan]

As a longtime avid reader and subscriber to Aviation Week and Space Techology, I remember it came down to two simple things: lubrication and transport.

Galileo was stored for much longer than anyone imagined and they ended up transporting it across the U.S. via truck rather than via air.

I don’t recall why the method of transport was an issue but I do recall they never replaced the original lubricant in the antennae ribs and that likely resulted in a partial deployment of the antenna.

 

[bulwnkl]

I don’t know what happened. Did the lube respond poorly to the extremely high-radiation environment? I’d have thought NASA would’ve figured that out well before then, but IDK.

 

[MasterSolenoid]

I heard the lubrication boiled off because of the vacuum of outer-space.
NASA then went on to invent Dry-Lubricants.

 

[wpod]

Too cold, too hot or space itself.

 

[Kestas]

One thing that you lose in space that you have on earth is an absorbed air layer, which acts as a lubricant. Lack of this layer results in cold welds. One of the first failures with satellites was the Sputnik. It was a simple transmitter that was designed to go beep-beep-beep. Unfortunately the relay switch cold welded and all they got was a long continuous beeeeeeeeeep that was detected by doppler effect.

This is why they minimize the number of moving parts for satellite applications.

I believe one of the few viable lubricants for space application are molybdenum disulfide and Krytox.

 

[MolaKule]

I don’t know what happened. Did the lube respond poorly to the extremely high-radiation environment? I’d have thought NASA would’ve figured that out well before then, but IDK.

The answer is in the NASA paper I linked.


ps://trs.jpl.nasa.gov/handle/2014/32404 and click "ViewOpen."

 

[OilReport99]

Copy + Paste

The testing also showed that with an atmosphere present to continue to react with the bare titanium as it was worn by sliding contact, the friction coefficient never exceeded 0,35. However, once a pin’s drylube was damaged by operation in air and then operated in a vacuum, the surfaces started to gall and produce coefficients of friction in excess of 1.0,

??

 

[Skippy722]

The ceramic coating on the ends of the pins was damaged during the 4 shipping trips, testing, and launch exposing raw titanium. In atmosphere, oxides/contamination allowed it to operate satisfactorily, but those oxides don’t form in the vacuum of space. The upper stage of the rocket naturally induced vibrations to the satellite causing further damage to the pins, and without an atmosphere to cause more oxides to form the titanium galled effectively seizing the pins in place.

 

[MolaKule]

Wow, you guys are "On it!" Well done!

An Interesting Summary:

The antenna was built in Florida and shipped 2500 miles to JPL in California, and then shipped back to Florida's NASA KSC.

Galileo's launch was delayed in 1989 following the Challenger disaster so it and the antenna was shipped back to JPL, and then back to NASA KSC travelling over 10,000 miles total in Earth's atmosphere.

The high contact stresses on V-groove pin-socket interfaces destroyed the integrity of the solid lubricant film on the pins causing cold welding between the pins and sockets.

The solid coating was MoS2 and has a higher wear and degradation rate in air than in a vacuum. The titanium pins readily formed an oxide coating in air, so in air testing did not detect the change in friction coefficients.

The functional tests were performed in vacuum and not in air. so functional testing did not detect this failure mode.

The postmortem reported concluded, "The test conditions were not adequate for finding this problem, indicating that just a functional test in vacuum is not always appropriate."

Thanks for all who read this most interesting report and for submitting answers.

 

[John Done]

On September 21, 2003, after 14 years of flight and 8 years of exploration of the Jupiter system, the Galileo mission was completed. The device was sent into the atmosphere of Jupiter at a speed of about 50 km / s in order to avoid the possibility of introducing microorganisms from Earth to the satellites of Jupiter. It was destroyed in the upper atmosphere.