Purpose of the flight and payload description

The Thunderhead Balloon System is a steerable multipurpose platform developed by Raven Aerostar for stratospheric missions of long duration, with navigational capabilities and the ability of performing persistent flight over areas of interest. The balloons can be flown individually or in constellations to support a wide range of requeriments including intelligence, surveillance, and reconnaissance; serve as an alternative to satellite communications or make surveys of ground, marine and environmental objectives.

The heart of the system is a superpressure balloon to which is attached a gondola containing the payload, flight systems and solar panels.

The balloon is a pumpkin-shaped superpressure model made of polyethylene in several sizes with a volume varying from 64.000 cubic feet to 400.000 cubic feet and altitudes of flight of between 50 and 65 kft for the smaller ones and between 75 and 92 kft for the bigger ones. This is well above commercial jetliners and weather phenomena. Both models can carry a payload of up to 125 pounds. To inflate the balloon is used helium and once it reach float altitude it expands and pressurises acquiring the final pumpkin shape. Inside the main balloon there is a smaller one called "balloonet" which serves as ballast and is the heart of the Thunderhead steering system: air is introduced into it using a special built pump permitting the balloon to modify its weight for ascent or descent. Although is not possible to directly control course or speed, these altitude changes allows the balloon to take advantage of different wind patterns at different altitudes for navigation. The balloon is also equipped with a valve at the top which is used to introduce helium during inflation and to vent helium during flight. The average flight duration can range from a few days to two months.

The instrumented gondola is attached directly below the balloon. Is composed of lightweight materials, may vary in size and can be rectangular shaped or truncated pyramid shaped. The upper part of the gondola houses in an insulated compartment the avionics and the elements that are part of the command and control system: ADS-B Out transponder for localization by nearby planes and Air Traffic controllers; RF-based systems for LOS (Line Of Sight) communications; Iridium-based system for BLOS (Beyond Line Of Sight) communications; GPS aided inertial navigation systems for real time positioning and Iridium backhaul as datalink for control and command of the payload. On the sides of this compartment are mounted the solar panels which varies in size according to power requeriments. They provide energy to the whole system during the day while charging onboard batteries for nighttime operations. Protruding ends of the booms on which are mounted the panels also serve to mount GPS and Iridium antennas. In some cases an additional payload compartment is located directly below the instrumented gondola with size and shape specially adapted for the mission requirements. If necessary, insulating panels can be added on the sides to protect onboard equipment and help to counteract the extremes temperatures of the stratosphere. A packed parachute is attached between the bottom of the balloon and the top of the gondola to allow a safe descent of the equipment at mission's end. In some cases, crush pads are fixed to the bottom of the gondola to absorb the shock of the landing.

Thunderhead systems are highly versatile with minimal space requirements for ground operation, so they can be launched by semi-manual means or using specially developed mobile platforms from almost anywhere, including small airfields, open terrain, or even from any vessel in open sea.

Video of launch operations

Details of the balloon flight

Balloon launched on: 7/27/2021 at 13:50 utc
Launch site: Raven Innovation Campus, Baltic, South Dakota, US  
Balloon launched by: Raven Aerostar
Balloon manufacturer/size/composition: Superpressure balloon with internal ballonet  
Flight identification number: HBAL562
End of flight (L for landing time, W for last contact, otherwise termination time): 7/28/2021 at 23:50 utc
Balloon flight duration (F: time at float only, otherwise total flight time in d:days / h:hours or m:minutes - ): 34 h
Landing site: SSE of Merriman, Nebraska, US

The objective of the flight was to expose to cosmic radiation at altitude a device called RadPC (Radiation Tolerant Computer System) developed at the Department of Electrical & Computer Engineering of the Montana State University. This development is critical for astronauts relying on computing systems in space, where cosmic radiation is a real concern. This is why NASA is supporting tests of radiation-tolerant computing systems on suborbital vehicles, and eventually on the Moon.

The two flights on Thunderhead balloon systems performed on July 27 and September 22, 2021 from Raven's Innovation Campus near Baltic (SD) served as tests for the RadPC technology in advance of planned lunar testing as part of NASA's Artemis program. The goal is to make sure the computing system could withstand the high-energy radiation particles emitted by the Sun and other celestial bodies. The innovation behind RadPC is it's hability to replace failed processors in real time through its redundant core processing system. It includes multiple cores on a single chip, allowing the system to switch from a failed core to a working core. RadPC also includes background memory scrubbing and error correction codes to further ensure its performance and fault-recovery capabilities. Over the course of the two flights the balloon reached altitudes up to 75,000 feet and provided a total of over 80 hours of flight time, enabling researchers to test the computing technology against more than 3,000 injected system faults; the RadPC recovered from all of them successfully.

Different iterations of the RadPC system has been tested in two rocket flights in 2014 and 2016 and a four hour balloon flight in 2019. The team's two recent flights of RadPC on Raven Aerostar's Thunderhead System balloon represented a culmination of the previous suborbital tests, with an improved payload design informed by the data gathered on previous flights. Data obtained from all flight tests will enable preparation for the upcoming lunar mission.

The flight was made possible with funding from NASA's Flight Opportunities program, part of the agency's Space Technology Mission Directorate (STMD).

External references

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