We’ve been working out the kinks in picokeystone extraction this week. We have one picokeystone out and mounted for synchrotron work — and it is beautiful! But it was a challenge — everything that could have gone wrong with it did. We machined the tunnels for the micropicklefork at 63 degrees, but found that at this angle we couldn’t easily insert the micropicklefork because it interfered with the microscope objective. We finally did it, and Dave pulled off the side blocks and put them in welled slides. The picokeystone is now mounted in a “TEM grid sandwich” for synchrotron analysis. It is super secure — Dave banged it around to see if it would move, and it is not budging!
We also found a mystery that we are still tracking down — there seems to be a systematic shift in the cuts between the first and second vertical cuts. This has happened twice now. At first we thought that it had to do with tension on the electronic cable plugged into the back of the micromanipulator, but we have now ruled that possibility out. One thing that led to some confusion was that we occasionally inadvertantly tripped the laser safety system (which we now know works great!) — this leads to a small but subtle shift in the coordinate system of the micromanipulator, so everytime this happens we have to rezero the needle. But this is not the cause of the shift. This has not led to any loss of the picokeystones, but we do need to understand it, so Zack is trying to reproduce the problem now on the keystoning system in the Stardust lab (where the cometary samples are handled).
Yesterday Ron and I made new fiducial marks on the flight tray so that we can do scanning much better and faster than we had before. Basically, in each of the six positions that the tray can be placed for scanning, we will have three fiducial marks, so that we can compensate for any translations and rotations that they tray may acquire when being remounted on the tray. It was really great to see the tray again in person — like seeing an old friend. To the naked eye it looks amazingly clean — it is hard to believe that it was seven years and space and travelled billions of miles! It is also extremely sobering to look at this object and realize that it would take $200 million to get another one. We have a very heavy responsibility in handling it.
We also figured out how to make the extractions go much much faster on the “pico undercuts”, which were the most time-consuming step. We were going slowly to reduce “twanging” on the long arm, but realized that this is not necessary when the needle is well below the surface, so we could accelerate to a higher speed in these phases. We also started to use a “sawtooth” motion rather than a straight in and out motion, and this works great. It’s one of those things — why didn’t we think of this a year ago?!
We have also realized how useful it will be to make fiducial marks on the picokeystone itself. We will implement this and practice it in Berkeley next week.
For the last couple of days it has felt as if every time we turn around something said “Gotcha!” But this is good, and is really what we want — to work out the kinks on the flight spare rather than on the real thing. Although we didn’t get as many blanks done this week as we had hoped, we did learn a huge amount. This is a new challenge to us in three ways. First, we have to work under the restrictions of the Cosmic Dust Lab, which is a horizontal laminar flow tunnel, so neither we nor any part of us (that is, hands, arms, heads) can be upstream of the microscope at any time. Second, we are doing the extractions directly from the tray, so unlike working with a track in a tile we can’t move it around, rotate it, etc., but just work with it as is, and move the micromanipulators to accommodate. This can be tricky. Needle alignment is also challenging over the tray. Finally, these are incredibly precious samples, so we can’t afford to lose even one of them. So we’re just being very careful, and we won’t go to the next steps until we’re really confident that we won’t lose any precious tracks.
We’re headed back to Berkeley this evening, then back here to Houston on the 28th. Stay tuned!
First — a “picoblock” held in microtweezers after having been pulled off of the side of the picokeystone by Dave.
Second — The first picokeystone mounted in the “TEM grid” sandwich. The “pico” part of the picokeystone is the almost invisible bit on the top of the keystone. It is 70 microns thick.