Applying Newton’s Law of Cooling When The Target Keeps Changing Temperature, Such As In Stratospheric Ballooning Missions

Newton’s Law of Cooling describes how a “small” system, such as a thermometer, comes to thermal equilibrium with a “large” system, such as its environment, as a function of time. It is typically applied when the environment is in thermal equilibrium and the conditions are such that the thermal decay time for the thermometer is a constant. Neither of these conditions are met when measuring environmental (i.e. atmospheric) temperature using a thermometer mounted in a payload lofted into the stratosphere under weather balloons. In this situation the thermometer is in motion so it encounters layer after layer of atmosphere which differ in temperature, and the changing environmental conditions can influence the thermal decay time “constant” for the thermometer as well. We have used Newton’s Law of Cooling in spreadsheet-based computer simulations to explore how thermometer readings react under these conditions, to better-understand how logged temperature records from stratospheric balloon flights during both ascent (relatively slow) and descent (much faster, especially at altitude) are related to actual environmental temperatures at various altitudes

Techniques for Payload Stabilization for Improved Photography During Stratospheric Balloon Flights

Payload-box rotation and swing are perennial challenges to achieving high-quality photography (typically videography) during weather-balloon flights to “near-space” (AKA the stratosphere). Continuous camera motion can lead to blurred still photos, nearly-impossible-to-watch video footage, and precludes time-exposure photography required for most astronomical imaging even though altitudes are reached where the daytime sky appears black. Apparently-random payload rotation, persisting even at altitude, can often exceed servo rotation rates and frustrate attempts to do active camera pointing. Here we discuss mostly-passive payload stabilization strategies we, and our collaborators, have used to mitigate and dampen both swing and rotation of suspended payloads on high-altitude balloon missions, primarily on ascent. In particular, we stress the importance of avoiding single “main” lines and of firmly coupling the payload stack to, as opposed to intentionally trying to decouple (rotationally) from, the neck of the balloon. We discuss consequences these strategies have on stack weight and also on the location of the parachute, sometimes displacing it from its normal location hanging between the neck of the balloon and the payload stack. We expect these payload stabilization techniques will be of particular interest to balloonists planning to photograph the total solar eclipse of August 2017

Studying a Total Solar Eclipse in Multiple Wavelengths from a Near-Space Platform

The total solar eclipse of August 21, 2017, gave the high-altitude ballooning community an exceptional opportunity to study lighting conditions in the stratosphere during a total solar eclipse across multiple portions of the spectrum. Sensors on balloon platforms flown in Oregon and Nebraska measured changes in the sky’s overhead intensity at wavelengths ranging from 940 nm (Infrared A, also know as near infrared (NIR)) to 280 nm (Ultraviolet B, also called UVB) during partial eclipse and totality. The moon’s shadow was imaged in near infrared and the Earth’s horizon was imaged in thermal infrared, also known as far infrared (FIR). Intensity measurements at various wavelengths were made using Neulog Light, UVA, and UVB modules, as well using as a LED-based photometer (a Forest Mims design) to study the intensity of eight colors spanning the spectrum from 940 nm infrared to the violet/ultraviolet boundary (400 nm). A Mobius ActionCam was modified for recording NIR, while blocking visible light. A microcontroller/servo combination was use to trigger a Seek Reveal thermal camera for the horizon experiment. Preliminary analysis suggests that the sky’s overhead intensity shows no apparent effect based on wavelength – a somewhat unexpected result. Swinging of the photometer suggests that future measurements should incorporate a sun sensor. The NIR images of the Moon’s shadow are very clear – NIR light is more effective at penetrating the haze of the atmosphere than visible light. There is no evidence in the thermal imager of the eclipse shadow affecting the surface temperature of the Earth

Comparison of Risk Between Cropping Systems in Eastern Norway

The aim of this study was to compare production and policy risk of organic, integrated and conventional cropping systems in Norway. Experimental cropping system data (1991-1999) from eastern Norway were combined with budgeted data. Empirical distributions of total farm income for different cropping systems were estimated with a simulation model that uses a multivariate kernel density function to smooth the limited experimental data. Stochastic efficiency with respect to a function (SERF) was used to rank the cropping systems for farmers with various risk aversion levels. The results show that the organic system had the greatest net farm income variability, but the existing payment system and organic price premiums makes it the most economically viable alternative.organic, integrated and conventional crop farming, stochastic simulation, multivariate kernel estimator, risk aversion, stochastic efficiency with respect to a function, Crop Production/Industries, Risk and Uncertainty, Q12, C44,

Rotation Mitigation and OCCAMS + Tungsten Flight Termination for Eclipse Balloon Missions

Stack rotation is a nemesis for many ballooning experiments, especially photography when trying to keep a specific target in view such as the Moon’s shadow (or the Sun itself) on eclipse flights. Ascending weather balloons tend to slow or even stop rotating once in the stratosphere and out of most cross winds. However payload stacks can continue to rotate with respect to the balloon right up to burst, especially if attached to the balloon neck by just a single main line. Our passive “rotation mitigation” device attaches directly to the neck of the balloon and runs four parallel lines separated by 6 inches from the balloon neck down to the payload stack, significantly diminishing stack rotation with respect to the balloon, especially at high altitudes. This arrangement complicates the placement of the parachute, but we have successfully deployed parachutes from a hook on the side of the upper-most payload box. This also complicates the placement of a flight-termination line-cutter, be that Montana’s “OCCAMS” razor cutter or something like a Tungsten hot-wire cutter. We have developed a compact payload box to enclose both an OCCAMS razor cutter and a Tungsten hot-wire cutter, both of which can independently release the multiple lines of our rotation mitigation device. We can fire the OCCAMS by XBee commands relayed through our RFD 900 payload, as an alternative to the Iridium text-message system. The Tungsten cutter can be fired by XBee command, by timer, or by autonomous GPS-sensor-based decision making

Improving the “Active Heading Control Platform” (CHAD) for Active Experiment Pointing During Stratospheric Balloon Flights

Payloads carried into the stratosphere using weather balloons typically spin and sway during ascent, limiting the types of experiments that can be performed. This project aimed to improve the functionality and performance of the Arduino-controlled active anti-rotation camera platform called CHAD (Controlled Heading Automation Device) that was reported upon at AHAC 2016 by Andrew Kruger from Wilbur Wright College in Chicago. The CHAD device senses its orientation using a magnetometer and an inertial measurement unit, then counters rotation by turning its main shaft with a stepper motor so as to hold fixed the absolute heading of the attached experiment (such as a video camera). The goals of this project were to make CHAD more low-temperature tolerant, to add the capability to adjust the heading in flight by radio command, and to add on-board logging of sensor data, stepper motor commands, actual orientation (independent from what the stepper motor was told to do), and all radio communications. This log was valuable for post-flight analysis if the unit did not hold its heading as effectively as desired. Some thermal issues were identified and addressed. The stepper motor was found to be powerful enough to control the heading of a full video-telemetry system, not just a bare video camera. The implementation of an in-flight-reset command proved valuable. A shaft-rotation encoder was added to assist in knowing orientation independently from the stepper motor commands. Although significant progress has been made, in-flight performance of the modified CHAD device remains somewhat inconsistent in stratospheric conditions

University of Minnesota – Twin Cities Modifications to the Montana State University Telemetry System for Stratospheric Eclipse Ballooning

On August 21, 2017, the path of totality of a solar eclipse swept across the continental United States from Oregon to South Carolina. Our team, flying weather balloons near Grand Island, Nebraska, was able to live stream the shadow of the moon from the stratosphere to the ground. The team was able to track our balloons with high accuracy due to new payload software and hardware implemented on the still image telemetry platform developed by the Montana Space Grant. In addition, the modified system allowed the team to relay commands and receive information from individual payloads attached to our balloons, giving live telemetry and control from a new GUI-based ground station control application. Although the eclipse is now over, the system will still be a powerful and useful tool for the University of Minnesota stratospheric ballooning team. The platform could be used for any other application needing real-time, ground-based communication to various payloads on a balloon gondola

Development of a Multi-Cut Payload for use in Stratospheric Ballooning Missions

The ability to cut strings (AKA lines) during stratospheric ballooning missions has a wide variety of uses including, but not limited to, (a) flight termination (i.e. cutting payloads away from the main balloon), (b) cutting away excess lift balloon(s) to slow ascent rate (and possibly achieve float), (c) cutting away ballast weights to slow descent rate or increase ascent rate, (d) cutting away burst balloon(s) on descent to avoid parachute entanglement, and (e) cutting away payloads which are intended to return to the ground independently, for experimental purposes. We report on the development of a “multi-cut” payload box that uses an Arduino microcontroller that can control the cutting of multiple strings in arbitrary order at arbitrary points during a mission, expanding our options for stratospheric ballooning operations. For example, this device may be used during the solar eclipse of August 2017 to drop a timed-series of independently-recovered Geiger counter payloads from a stratospheric balloon stack to characterize changes to the Pfotzer maximum as the Moon’s shadow passes

Using Thermocouple, Thermistor, and Digital Sensors to Characterize the Thermal Wake Below Ascending Weather Balloons

In this paper we present additional results from our on-going research effort to characterize the thermal wake that trails below ascending latex weather balloons on flights into the stratosphere; a wake which interferes with the ability of temperature sensors in payload boxes hanging from the balloon (and hence enveloped by the wake) to correctly measure the ambient temperature of the atmosphere through which the balloon is ascending. A “wake boom” is used to measure temperature variations up to 1.5 m horizontally from varying distances directly below the neck of the balloon. Results to date agree with the literature that especially above the tropopause the thermal wake is warmer than the ambient air during daytime ascents, due to solar radiation warming the balloon skin, but colder than ambient air during night-time ascents, due to adiabatic cooling of the gas inside the balloon (which also occurs in the daytime, but is smaller than the daytime warming effect). In particular we report on thermal wake characterization using (Neulog) thermocouple sensors, as compared to (HOBO) thermistors and (Arduino-logged) DS18B20 digital temperature sensors. We also present additional results from X-shaped 2-dimensional wake booms or “X-Booms” which allow us to compare wake temperatures on the sun side versus the shade side of the balloon, looking for asymmetries in the horizontal temperature profile