Tether testing with Vishaal

As part of our NASA-funded STI project, Vishaal came back out again for another few months in the lab. Covid prevented him from coming in the summer, but he was able to spend the fall with us. After successful runs at relatively warm temperature last summer, we were ready to start going colder.  Or so we thought...  

Upon closer inspection we realized the pump in our custom circulating fluid chiller was leaking. After taking it completely apart (a pretty big feat in itself) we found that some seals were cracked and a spring broken. A bit of delay, but hey, now we know how to replace a seal on a pump. Always good to acquire some real world skills.

While we were at it, we decided to do some reorganization so that the chiller flow control valves were attached to the back wall and not hanging off the front of the rig. RTDs were installed to monitor temperature along the fluid path.

We also worked with colleagues at WHOI on a die that allows pretensioning of the tether before freezing the ice around it. Our addition was to add tubing and valves to pull a vacuum on ice samples and flood from the bottom. The final sample assembly is one long bar that fits into the cryostat. The notched square tube allows us to load the assembly without touching the ice. 

An optical meter measures signal loss during shearing of the tethers. Vishaal splices the ends of the tether. 

Here is the whole set up in the new lab. Ain't it pretty?

During Vishaal's last week we decided to push the envelope and go all the way down to Europa surface temperatures (~100K). For this, we took the chiller out of the system and instead went to directly pumping liquid nitrogen into the cryostat. First we pre-chilled by pouring LN all over everything.

Ideally we pump only enough LN to cool the cryostat and it comes out as a gas. But occasionally the LN just poured right through....

It was frosty in there!!  But we held 100K steady for the whole test. A great end to a successful series of experiments!