Projects

This section highlights the projects that I have worked on since leaving UCSB. Due to IP restrictions, some of the details are intentionally kept vague. My graduate/postdoc projects can be found here, and my undergraduate projects can be found here. I go into more detail in those sections.

Improved Humidity Solar Shield

Overview: At WindBorne Systems, air temperature and humidity are gathered on an instrument package known as the "dangly." It is called so, because it dangles 10 meters below the weather balloon in order to avoid the thermal boundary layer of the balloon. To further increase accuracy, the dangly circuit board, which contains the humidity sensor, is shielded from direct sunlight. Direct sunlight on the sensor can cause spurious readings because it can cause uneven heating and the humidity readings are temperature dependent. Furthermore, error is exponential with temperature.

When I came to WindBorne Systems in June 2025, the dangly was housed in a shield folded out of aluminized mylar. This shield was effective for preventing uneven solar heating, but despite the aluminum's high reflectivity, it still resulted in significant solar heating (20°C+). This is because aluminum is a poor infrared emitter. Consequently, a large amount of humidity data was rejected.

To improve dangly performance, WindBorne Systems redesigned the dangly and a goal was to minimize/eliminate solar heating on the humidity sensor and simplify the assembly of the dangly.

Contribution: My primary contribution was the new solar shield. While the final design is very simple, its development was nontrivial.

Despite the recent progress in radiative cooling, finding a commercially available, easily processable, low-cost material with very high solar reflectivity and high infrared emittance proved challenging. The material needed to be whiter than conventional white paint. Eventually, I found a polymer material with all the right properties; it is commonly used for non-thermal applications.

In all, I flight tested about 30 different shield designs. The designs tested different materials and configurations to vary things like convection, Earth infrared absorption, and manufacturability as well. I even tested a couple of designs that achieved daytime sub-ambient cooling. This is especially impressive at altitude, because of the large amounts of infrared radiation from the Earth's surface. Ground systems generally do not have to deal with this. Ultimately, for manufacturing reasons, we used a design that has a small amount of solar heating (~5°C).

In the end I contributed the following:

A new dangly solar shield design.
The tooling for attaching the new sensor shield to the dangly; I made a custom jig to staple on the shield.
New packaging to store the dangly prior to deployment. The new packaging keeps the ambient temperature probe straighter and reduces system weight on takeoff.
I also conducted several tests to test various ambient temperature probe placements. The new placements could reduce solar bias by 0.25-0.5°C. Further testing is needed.

Results:

A solar shield with significantly lower solar bias.
An easy to assemble shield. Thousands built and flown.

Comparison of the different dangly designs. On the left is old design. The dangly board is housed inside a solar shield folded out of aluminized mylar (A). The ambient thermistor is at the end of 0.5 m long wire (B). A channel (C) in the shield allows air to flow over the humidity sensor on the dangly board. The dangly dangles at the end of a 10 m wire (D). The right is the new design. The new design has a new circuit board and the solar shield is made out of a very white polymer (E) that I repurposed for thermal applications. It is stapled (F) onto the circuit board.

WindBorne Systems

WindBorne Systems is a climate tech start up based in Redwood City. It operates the world's largest weather balloon constellation and sells weather balloon data and AI powered weather forecasts. A core technology of theirs is the global sounding balloon (GSB). Unlike traditional weather balloons, which can only up and down once (i.e., two soundings), GSBs can do multiple soundings and operate for several days. Some have even operated for hundreds of days. GSBs gather altitude, pressure, wind speed, air temperature, and humidity data.

A rare tandem launch of two GSBs in July 2025. Left panel shows two GSBs on the launch rigs. Right panel shows the GSBs in flight. The envelope (A) contains the hydrogen (or in some cases helium) gas. At the top of the envelope is a vent. The main unit (B) contains the communication equipment, processors, ballast, and the "dangly." The dangly measures ambient air temperature and humidity and drops 10 m below the main unit later in flight. To go up and down, the balloons vent gas and release a ballast made out of glass beads.

Improved Infrared Heat Harvesting

Overview: In the winter of 2025-2026, WindBorne Systems' balloon constellation was largely concentrated in the northern hemisphere and it needed to gather a large amount of data to fulfill some data contracts; however, many of the balloon flights, especially the stratospheric flights, suffered from communication issues due to the cold affecting the modems. Temperatures in the stratosphere, could dip below -80°C and were routinely below -60°C. The long nights reduced solar charging, which made running resistive heaters infeasible. A passive solution was needed.

The ground is a good source of passive heating. On average, the Earth surface radiates about 250 watts per square meter of infrared heat. For comparison, about 1000 watts per square meter of sunlight reaches the Earth surface from the Sun. Early designs used a reflector made out of folded aluminized mylar to reflect the Earth infrared onto the modem.

Contribution: I significantly improved the performance of the harvester.

Upon further analysis (with analytical specular view factor calculations), I found that the existing design did not harvest much Earth infrared. Simply increasing the size of the harvester would greatly improve the performance. With my analysis, I found a size that maximized heating without being excessively large.

I then flight tested several variations of the harvester. The resulting design reminded people of the Luxor pyramid in Las Vegas and was called "Luxor." It is made of two pieces dual-sided aluminized mylar.