Description of the payload

Stratollite is the trademark name of a tandem long duration balloon system given the technical name Variable Altitude Air Ballast Balloon System (VAABBS) developed by World View Enterprises. The system consists of a conventional zero-pressure balloon (ZPB) attached in tandem with an air ballast pumpkin super-pressure balloon (SPB) and a ladder which connects the ZPB to the gondola which is called the Stratocraft. This is an apparent modification of the Sky Anchor system first seen in the late 1960's. At left can be seen a scheme of its configuration (click for more details).

The ZPB is manufactured of custom-made UV light-resistant polyethylene with an approximate volume of 23.000 m3 and is inflated with Hydrogen or Helium. It provides initial and sustained lift for the system from launch to an altitude of about 75000 ft. The SPB located right below the ZPB is a pumpkin configuration which operates at a positive internal pressure in comparison to the external atmosphere and provides to the system a variable amount of effective ballast by pumping in or expelling out ambient air. It is composed of one or more compartments connected in series. By adding air to it the overall weight of the system increases thus making it descend, while venting air from it decreases the weight thus making the system ascend. The ZPB and the SPB are connected by a gimbal coupling both balloons, configured to rotate the SPB relative to the ZPB, where the SPB and the solar array are rigidly coupled with the ladder such that rotation of the SPB with the gimbal rotates the elongated ladder assembly and the solar array to a desired orientation. A special-built compressor provides air to the SPB and can be configured for providing a sufficient rate and volume of air at particular high altitudes in which the system will be flown. The particular design produces a moderate descent rate even at high altitudes where the air is thin and conventional compressors will not work. Rapid ascent is possible with SPB valve opening. Using this system, the ground operators can leverage different air currents at different flight levels to move the balloon towards an area of interest or to follow a more or less predetermined flight path.

Below the SPB is located the ladder assembly which connects the SPB balloon with the Stratocraft and also serves as support for the solar panel array, the hose which connects the compressor located in the stratocraft to the SPB (to pressurize it) and the parafoil which lands the stratocraft after the flight. The Solar power array is formed by a vertical train of one or more planar photovoltaic panels which are constantly turned toward the sun with a special pointing mechanism to gather maximum power during the day, charging batteries that are used for equipment and payloads at night. The length of the ladder is calculated to avoid shading from the balloons in order to provide sunlight to the solar array.

The Stratocraft is a tetrahedral structure that hangs at the end of the flight train and contains flight avionics, power systems, and a reconfigurable payload deck utilizing a modular open systems approach to host customer payloads. Currently, the Stratocraft can carry a payload mass of 50kg, provide 250W of continuous payload power, and 1000W instantaneous payload power. At the end of flight, the Stratocraft separates from the flight train and is remotely guided to a specified ground location. Landing pads located in the lower corners of the structure collapse upon landing to attenuate the impact and to protect the payload and onboard systems. It also includes bumpers which provide extra protection for the frame, in the event of rollover upon landing. The Stratocraft has azimuth pointing capability to maintain the vehicle pointing at the sun to maximize the efficiency of the solar array.

The Stratollite system can be scaled and configured simply for various missions and flight requirements: higher altitude and/or heavy lift missions with a higher capacity multi-stage compressor and larger volume SPB and ZPB.

Details of the balloon flight

Balloon launched on: 10/6/2021 at 16:10 utc
Launch site: Spaceport Tucson, Arizona, US  
Balloon launched by: World View Enterprises
Balloon manufacturer/size/composition: Stratollite - Variable Altitude Air Ballast Balloon System (VAABBS)  
Flight identification number: N137WV
End of flight (L for landing time, W for last contact, otherwise termination time): 10/6/2021 at (L) 17:30 utc
Balloon flight duration (d:days / h:hours / m:minutes): 2 h
Landing site: Cochise County, Arizona, US

The stratollite was launched from Space Port Tucson at 16:10 utc on October 6, 2021. The stratollite ascended to a maximum altitude of 56.400 feet -well below the nominal 70.000 ft of previous flights- but less than one hour after departure it started to loss altitude steadily, a clear indication of an early mission termination. It landed close to the San Pedro River in Cochise County, Arizona. Total flight time was less than two hours.

Next day the local press reported that a "World View high-altitude balloon test vehicle crashed east of Tucson" which forced the firm's CEO Ryan Hartman to make an statement on the incident:

"...The flight was terminated earlier than planned but there was no balloon crash. It was a normal termination of a flight where the balloon came down on parafoil as standard practice. This was not a part of the space tourism business recently announced so no humans were on board. This was the first time the new system was being evaluated, which proved successful for launch and ascension testing but not for a long-duration flight. Like all companies, testing and validation is a critical component of the development process. The feedback from today's test flight will provide valuable data to help inform and improve future iterations..."

External references

Images of the mission

The balloon being inflated (Image: Stephen Fleming) The stratollite ascending The stratollite ascending

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