The engineers who make ZTF discoveries happen

We highlight members of the incredible team of engineers who work day and night to make sure ZTF never misses a transient.

Date: March 11, 2022

Roger Smith

ZTF camera lead

After stellar performance since its commissioning back in 2017, ZTF had to be taken out of service in Dec 2021 due to a cryo-cooler malfunction. Since then, my team and I have performed multiple fixes and tests, but let us start from the beginning.

The CCDs in the ZTF camera are cooled to about 170K and this process is achieved without liquid nitrogen but rather by employing two cryocoolers (made by Polycod. These work much like a domestic refrigerator, but to get to much lower temperature, a 3 m long counter-flow heat exchanger is coiled up behind the cold-head and the refrigerant used is a proprietary mixture of liquid propane and gaseous ethane, methane and Argon. Compression to ~375 psi heat the refrigerant which is returned to room temperature by forced air flowing across the heat exchanger preceding a holding tank where oil from the seals is collected and returned to the inlet side.

A charcoal adsorber captures residual oil vapor, but after years of operation, a small amount of this oil makes it into the supply lines, and subsequently to the cold head where it freezes and degrades performance. We have procedures to replace the charcoal adsorber, to change the lines for clean ones, and to warm the system to unblock the capillary tube but by November last year, these measured no longer worked, so we were forced to bring the instrument back on campus, disassemble it and replace the cold heads.

Read more

David Hale

Software engineer at Caltech Optical Observatories

My primary role in the recent ZTF work was to manipulate the Kuka filter exchanger robot arm, check for proper filter alignment, and verify operation of the filter exchanger system after the instrument was reinstalled. I also contributed to pulling of cooling lines, checking for leaks, and troubleshooting of telemetry sensors.

During my off hours I race APBA outboard and inboard hydroplanes and during the off-season of racing I rebuild my own engines. I only burn petrol for racing as I commute to Caltech in a Porsche 914 that I converted to electric in 2009.

Reed Riddle

ZTF software lead

We noted back in October that the ZTF cooling system was having issues. The roboti software system of ZTF (ROS) was able to keep operating and taking science observations, and informing us about the condition of the cooling system, but eventually the system had to go back to campus for refurbishment. When it returned, I helped to support the reinstallation by keeping the sensor monitoring system running and Rich Dekany, Jennifer Milburn, and I worked on getting a rough focus position for ZTF, which had shifted significantly. I then reconfigured ZTF for the new rough focus, ran the automated instrument alignment system to dial in the focus, tip, and tilt position, and then released ZTF to science operations. That lasted for one night, and then we had the second return due to the zeolite contamination. We went through the same process when ZTF returned to Palomar, with Rich once again helping with the rough focus positioning. ZTF was put back into science operations at 2:30am and ROS continued to operate the system normally until another issue required another dissasembly.

Beyond ZTF, I work on many robotic instruments, including the first automated adaptive optics system, Robo-AO, which is what the ZTF robotic software is based on. I also enjoy working on various auto and home projects, and spend as much time as I can with my wife and our little ones.

Rishi Pahuja

Mechanical Engineer at Caltech Optical Observtories

I joined Caltech in November last year and one of the first assignments at my job was the repair of ZTF instrument. My primary responsibilities include disassembling and re-installation of the instrument at Palomar. I am also responsible for troubleshooting and ensuring smooth functioning of the shutter. The unpredictable shutter failure events were eventually identified to be caused by a partially failed solder joint. Because the failure was intermittent and inconspicuous, we adopted method of elimination to systematically rule out mechanical (sensors, belt tension, shaft alignment) and software (servo speed and travel) related parameters. We will continue to monitor and aim to identify system repeatability to make better decisions on the inventory of spares, preventive and corrective maintenance schemes and schedule, enhanced signal monitoring and fault diagnostics, and any design modifications.

In my free time I like to paint impressionist and landscape subjects in oil and acrylic. I recently moved from Seattle and exploring hiking trails in SoCal.

Alexandre Delacroix

Mechanical Engineer at Caltech Optical Observatory

When the ZTF instrument arrived at Cahill, we opened the crate and loaded the camera on the fixture in the clean room. We started by disassembling ZTF and cleaning the window and the vaccum interface board (VIB) using a special vacuum cleaner adaptor to pick up the zeolite pellets lodged in the interstices. After the zeolite pellets immediately visible got picked up, we loaded the cryostat holding the CCDs and the VIB on a turnover fixture. Rocking the cryostat from side to side, up to about 80 deg above horizontal and back to level exposed additional pellets that we removed. We rotated the cryostat 90 deg about the vertical axis and repeated the operation until no more pellets showed up.We repeated the procedure multiple time to ensure we have picked everything and decided not to remove the VIB as this would have take additional time (minimum a day).

My personal project is finding the origin and nature of UAP/UFOs. I am also an active research team member of The Harvards’s Galileo project.