3.1.2 Raven Aerostar
Raven Aerostar has the capability to make any balloon type. It provides envelopes
and other systems as required for NASA, DOD, corporations and institutions. The
balloons can be different in film and thickness. In recent years, there has been a
big demand for balloons used for accessing the internet in remote locations. For
example, the balloons manufactured for Loon are quite different from those used
by NASA for large scientific payloads.
The balloon envelopes used by the Loon project are based on the Raven Aerostar
Super-Pressure Balloon. These balloons employ polyethylene plastic that is about
75 μm (0.0030 in) thick. They are filled with helium and are 12 m (39 ft) tall and
15 m (49 ft) across, fully inflated. They carry a custom air pump system known as
the “Croce” that pumps in or expels air in order to ballast the balloon and control
its altitude. A small box weighing 10 kg (22 lb) that hangs underneath the inflated
envelope contains each balloon’s electronic equipment. This box contains circuit
boards that control the system, radio antennas and a Ubiquiti Networks “Rocket
M2” radio to communicate with other balloons and with internet antennas on the
ground, plus batteries to store solar power so the systems can function during the
night. Each balloon’s electronics are powered by an array of solar panels that sit
between the envelope and the hardware. In full Sun, the panels produce 100 watts
of power. This is sufficient to keep the unit running while also charging a battery
for use at night. A Raven Aerostar Payload Recovery Parachute is attached to the
payload for a controlled descent, landing, and payload recovery. In the case of an
unexpected failure, the chute deploys automatically. When taken out of service, a
balloon is guided to a hopefully easily reached location and the helium is vented.
The balloons typically have a maximum life of approximately 100 days, although
Loon claims that its tweaked design can enable them to stay aloft for closer to 200
days. Their record is 223 days.
The envelopes made for NASA’s scientific missions are considerably larger
than those for Loon. They have gone through modifications and testing over
decades. The improvements could only be made following analysis and testing of
existing film, in order to fully understand the materials stress levels under different
loads and pressures, and degradation caused by temperature changes and exposure
to ultraviolet radiation, X-rays and cosmic rays. Furthermore, the improved films
can perform differently for different balloon design parameters. NASA puts the
manufacturer’s films through three stages of testing before they are flight ready,
including quality control tests at the Balloon Research and Development Lab of
the Wallops Flight Facility. While the balloons will experience temperatures of
around –76°F in flight, the films will be subjected to –130°F in the laboratory.
For example, after Stratofilm-430 was tested in the lab it was used to produce a
NASA zero-pressure balloon. This was a three-layer co-extruded film that used
the same resins as Stratofilm-420. Compared to traditional zero-pressure balloon
3.1 Balloon Envelopes 31
Raven Aerostar has the capability to make any balloon type. It provides envelopes
and other systems as required for NASA, DOD, corporations and institutions. The
balloons can be different in film and thickness. In recent years, there has been a
big demand for balloons used for accessing the internet in remote locations. For
example, the balloons manufactured for Loon are quite different from those used
by NASA for large scientific payloads.
The balloon envelopes used by the Loon project are based on the Raven Aerostar
Super-Pressure Balloon. These balloons employ polyethylene plastic that is about
75 μm (0.0030 in) thick. They are filled with helium and are 12 m (39 ft) tall and
15 m (49 ft) across, fully inflated. They carry a custom air pump system known as
the “Croce” that pumps in or expels air in order to ballast the balloon and control
its altitude. A small box weighing 10 kg (22 lb) that hangs underneath the inflated
envelope contains each balloon’s electronic equipment. This box contains circuit
boards that control the system, radio antennas and a Ubiquiti Networks “Rocket
M2” radio to communicate with other balloons and with internet antennas on the
ground, plus batteries to store solar power so the systems can function during the
night. Each balloon’s electronics are powered by an array of solar panels that sit
between the envelope and the hardware. In full Sun, the panels produce 100 watts
of power. This is sufficient to keep the unit running while also charging a battery
for use at night. A Raven Aerostar Payload Recovery Parachute is attached to the
payload for a controlled descent, landing, and payload recovery. In the case of an
unexpected failure, the chute deploys automatically. When taken out of service, a
balloon is guided to a hopefully easily reached location and the helium is vented.
The balloons typically have a maximum life of approximately 100 days, although
Loon claims that its tweaked design can enable them to stay aloft for closer to 200
days. Their record is 223 days.
The envelopes made for NASA’s scientific missions are considerably larger
than those for Loon. They have gone through modifications and testing over
decades. The improvements could only be made following analysis and testing of
existing film, in order to fully understand the materials stress levels under different
loads and pressures, and degradation caused by temperature changes and exposure
to ultraviolet radiation, X-rays and cosmic rays. Furthermore, the improved films
can perform differently for different balloon design parameters. NASA puts the
manufacturer’s films through three stages of testing before they are flight ready,
including quality control tests at the Balloon Research and Development Lab of
the Wallops Flight Facility. While the balloons will experience temperatures of
around –76°F in flight, the films will be subjected to –130°F in the laboratory.
For example, after Stratofilm-430 was tested in the lab it was used to produce a
NASA zero-pressure balloon. This was a three-layer co-extruded film that used
the same resins as Stratofilm-420. Compared to traditional zero-pressure balloon
3.1 Balloon Envelopes 31