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Dr David Maddison describes
high-altitude
Aerial Platforms
All air vehicles are limited by physics, some by imagination, all others are limited by fuel.
Chris Kelleher, inventor of Zephyr.
Special balloons and fixed-wing aircraft can act as long-endurance aerial
platforms for observation and communication. Known as high-altitude platform
stations/systems (HAPS), they fly above most planes but below satellites.
Weather, scientific and military balloons are similar; they also ascend to great
heights but do not necessarily stay there for a long time.
Image Source – Airbus 2023 – https://mediacentre.airbus.com/mediacentre/media?mediaId=604534
A
pplications for HAPS include communications, military or civilian
surveillance, scientific observations
and even amateur/hobbyist uses. They
are especially useful when a satellite
would take too long to organise or be
too expensive, as these applications
can often be effectively served by some
other type of platform located within
the Earth’s atmosphere.
HAPS are sometimes called ‘pseudo-
satellites’ or ‘atmospheric satellites’.
Such platforms are uncrewed and
fly at the highest possible aircraft altitudes or above. They are either special
aeroplanes designed for high-altitude
flying or lighter-than-air craft (a balloon or an airship) that rise due to
a buoyant gas like hydrogen (H2) or
helium (He).
The lowest practical orbital altitude
for a satellite is around 160km, while
the highest any aircraft can fly is 26km
(85,000ft) for the retired SR-71 ‘Blackbird’. The currently flying aircraft with
the highest maximum altitude is the
U2 surveillance plane at around 21km
(70,000ft) sustained, although the CIA
version of that same plane could cruise
at 22.7km (74,600ft).
By comparison, the Concorde could
cruise at a mere 18.3km (60,000ft)
above sea level.
Current commercial jets typically
fly at altitudes of 9-12.5km (30,000ft
to 41,000ft) with a maximum service
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ceiling of up to 13.1km (43,000ft).
That includes aircraft like the Airbus
A380, Boeing 787-8 and 787-9. Military jets such as the F-35A in service
with the RAAF have a service ceiling
of 15.2km (50,000ft).
This leaves a large gap from around
20km to 160km, unreachable by satellites due to too much atmospheric
drag, and aircraft due to a lack of lift
and oxygen to power their engines.
The Fédération Aéronautique Internationale (FAI) considers space to start at
the Kármán line, which is defined as
an altitude of 100km. However, there
is still too much air at that altitude for
satellites to realistically orbit.
The stratosphere is an area of the
atmosphere that starts at around 7km
at the poles, 10km at mid-latitudes
and 20km at the equator and extends
to an altitude of 50km (see Fig.2). This
is the area in which HAPS platforms
usually fly, most typically at around
20km (65,600ft).
Part of the region from 20km to
160km can be accessed by ‘aerostats’
such as balloons or airships. The
highest ever balloon flight was 53km
(173,900ft), by the BU60-1 in 2002.
Rockets can also access that region, but
they usually don’t stay there for long!
Why fly in or near the
stratosphere?
Fig.1: the US Air Force Project
Manhigh gondola from 1955-58.
Source: www.thisdayinaviation.
com/2-june-1957/screen-shot2018-06-01-at-11-53-55/
In the stratosphere, there is little or
no turbulence. The air is almost still,
so it provides a stable platform for
surveillance; it is ‘above the weather’.
Winds are minimal at around 20km up.
As the air is still, less structural mass
is required to deal with turbulence
and less engine power (for powered
Australia's electronics magazine
siliconchip.com.au
vehicles) is required to overcome it.
Because the air is so thin in the
stratosphere, it is difficult to generate
lift, so the aircraft has to be as light as
possible. That usually means limited
propulsive power, so they must fly
slowly. But as the air gets thinner with
altitude, the aircraft has to fly faster to
maintain sufficient lift. Studies find
the best balance for the lowest power
consumption to maintain lift and altitude is around 20km (65,600ft).
These light aircraft are naturally
fragile, and the limited power means
they take a long time to reach the target altitude.
They must take off and land under
calm conditions, which precludes
launches in places like the UK,
where it usually is too windy for such
launches.
Another consideration is that wherever a solar-powered HAPS aircraft
is launched, there must be enough
daylight hours for the solar panels to
charge batteries for night-time operation, precluding launches at the poles
in winter (for example).
Lighter-than-air HAPS aircraft
The first hydrogen balloon was
made in France in 1783 by Jacques
Charles and the Robert brothers.
The first crewed free-flight in a
lighter-than-air aircraft was an untethered hot air balloon invented by the
Montgolfier brothers and demonstrated in 1783. It was flown over Paris
by Pilâtre de Rozier and the Marquis
d’Arlandes.
Manned high-altitude balloons
were launched in the 1930s in pursuit of altitude records. For example, Explorer II ascended to 22,066m
(72,395ft) in 1935.
The US Air Force’s Project Manhigh (Fig.1) was undertaken in 195558 and achieved the following altitudes for manned balloons. Manhigh I:
29,500m (96,800ft); Manhigh II: 30,942
m (101,516ft); and Manhigh III: 29,900
m (98,100ft).
In 1960, under the auspices of
the US Air Force Project Excelsior,
Joseph Kittinger skydived from a balloon at 31,300m (102,960ft), a record
not beaten until Felix Baumgartner’s
descent in 2012 from an estimated
39km (around 128,000ft).
Project Moby Dick
Project Moby Dick was a Cold War
era project of the USA to fly espionage
siliconchip.com.au
balloons with cameras over the then
Soviet Union. The Soviets protested
when they found the remains of one
in 1956.
Project Skyhook
Project Skyhook balloons were
launched by the United States Navy
Office of Naval Research from 1947
until the late 1950s, for atmospheric
research at very high altitudes. The
first such balloon carried a 29kg payload to 30km (100,000ft). About 1500
such balloons were launched. Some
highlights of this project are as follows.
In 1948, a three-balloon cluster was
launched.
In 1948 and 1953, Skyhook balloons
measured radiation in the atmosphere
between 27km (90,000ft) and 32km
(105,000ft).
In 1949, a manned launch took
place.
In 1954, two balloons with telescopes were launched to photograph
a solar eclipse from a high altitude.
In 1957, a 30cm telescope was
launched to photograph the sun, providing the sharpest photographs of the
sun taken to that date.
Project Genetrix
Project Genetrix, also known as
WS-119L, was a US program of the
1950s to send surveillance balloons
over China, Eastern Europe and the
Soviet Union. They flew at 9-18km
(30,000ft to 60,000ft).
Soviet surveillance balloons
The Soviets also had their own fleet
of surveillance balloons they sent
towards the West. Quoting from the
website at siliconchip.au/link/abl1:
...in 1956, the OKB-424 design
bureau — also known as the Dolgoprudny Automatics Design Bureau
(DKBA) — was established, especially
for the task of making new military
aerostats...
...The first task of OKB-424 was to
copy a US photo-reconnaissance balloon that had come down on Soviet
territory. Over the next 60 years,
DKBA produced around 20 types of
free-floating balloon envelopes, with
volumes ranging from 11,500 cubic
feet [326m3] to 21,190,000 cubic feet
[600,000m3], each of which could
carry various kinds of mission equipment.
The largest of them was the Ukolka
series of balloons from the 1960s,
Australia's electronics magazine
Fig.2: HAPS typically reside in
the upper part of the troposphere
or lower part of the stratosphere.
Original source: https://w.wiki/6doG
(author Kelvin Case, CC BY-SA 2.5)
August 2023 15
Cannon
Cosmic Ray Plates
Parachute
which had a capacity of 21,190,000
cubic feet and could lift a 660-pound
[300kg] payload to an altitude of
147,600 feet [45km].
Project Mogul
Radio Beacon
Gondola
Ballast
Project Mogul was a US program
conducted during 1947-1949 that
launched balloons carrying microphones to listen for the noises of
Soviet atomic blasts. When one of
these balloons went down, the result
was the “Roswell Incident”, which
was claimed to be a UFO. Since Project Mogul was highly classified at the
time, the object’s true nature was never
disclosed.
Project Strato-lab
Fig.3: Operation Stratomouse,
1955. The cannon was to sever the
payload at the end of the mission.
The temperature and pressure
inside the gondola were transmitted
via a radio beacon, and ballast
could be dropped or the payload
separated by radio control. Source:
https://academic.oup.com/milmed/
article/119/3/151/4933143
Fig.4: a Google Loon launch in New
Zealand in 2013. Source: https://w.
wiki/6dpb (CC BY 2.0).
Project Strato-lab was developed
from Project Skyhook (see above) and
ran from 1954 to the early 1960s. They
were manned balloons that contributed significantly to the space flight
program by measuring radiation at
altitude and testing pressure suits.
The maximum altitude achieved was
34.7km (113,740ft).
Operation Stratomouse (1955)
In 1955, the US Air Force undertook
a balloon flight program to determine
if primary cosmic rays, which are
strongly present at high altitudes, were
hazardous to humans. Mice were chosen as the experimental test subjects,
along with tissue cultures and cosmic
ray measuring equipment.
Helium balloons of 56,600m3 (Fig.3)
were constructed by a company
called Winzen Research (https://w.
wiki/6dpT), a pioneer in high-altitude
scientific balloons.
The balloons were made from
polyethylene and, uninflated on the
ground, were 76m long. Fully inflated
in the stratosphere, they had a diameter of 53m.
An altitude of 40km (131,500ft) was
reached on one of the flights, with
flight durations of up to 26 hours. For
a fascinating full account of this project, see https://academic.oup.com/
milmed/article/119/3/151/4933143
Google Project Loon
Project Loon (https://x.company/
projects/loon/) was a project of Google’s parent company, Alphabet, to use
HAPS balloons (Fig.4) at an altitude
of 18-25km (59,000-82,000ft) to provide internet access in remote areas.
Manoeuvring was to be achieved by
altitude control to move the balloons
into layers with different wind directions.
One test balloon achieved a flight
duration of 312 days in 2020. The balloons used were Raven Aerostar Super
Pressure Balloons (see below) composed of polyethylene about 0.076mm
thick. They were around 15m across
and 12m tall. They also carried an
electronics box weighing 10kg plus a
100W solar panel. The project was terminated in January 2021 due to a lack
of profitability.
Aerostar
Aerostar (https://aerostar.com/
products/balloons-airships) is a
US manufacturer of high-altitude,
long-duration stratospheric balloons
(Fig.5), some of which are steerable,
such as the Thunderhead model. The
Thunderhead exploits different wind
directions at different altitudes to provide directional control.
Aerostar was previously associated
with Google and their Project Loon,
now discontinued, despite making
significant technical advances.
Sceye
Fig.5: an Aerostar super pressure balloon at launch with the payload in the
foreground. Note the solar panels. Source: https://aerostar.com/products/
balloons-airships/super-pressure-balloons
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Australia's electronics magazine
Sceye (www.sceye.com) is a Swiss
company (also with offices in Roswell, New Mexico, USA) developing
an airship (Fig.7) for applications such
as broadband delivery, atmospheric
monitoring, agricultural monitoring
and security surveillance (eg, border
protection).
It uses a hull fabric of unspecified
composition that is said to be five times
stronger and 1500 times more gastight, UV-resistant and ozone resistant
than existing materials. Its advanced
lithium sulfur batteries have an energy
siliconchip.com.au
Helium or hydrogen for balloons?
Fig.6: the Czech Stratosyst Skyrider
can stay aloft for weeks or more.
Source: www.stratosyst.com
Helium is extremely expensive for balloons, and the supply is very limited.
Hydrogen is cheap and of unlimited supply, but flammable. Hydrogen is not
considered suitable for human flight in balloons or airships ever since the
Hindenburg disaster. Still, it can be used in uncrewed balloons, provided proper
safety precautions are taken during filling.
Hydrogen is typically used in weather balloons, including those launched by
Australia’s Bureau of Meteorology (BoM). Nevertheless, many organisations
still prefer to use helium, even for unscrewed balloons.
Our recent report on the Australian International Airshow in Avalon
Airport (May 2023; siliconchip.au/
Article/15773) included mention of
the Sierra Nevada Corporation (www.
sncorp.com) developing an LTA-HAPS
(lighter-than-air higher altitude platform station) for long-term ISR (Intelligence, Surveillance, Reconnaissance)
for military missions. It is designed to
fly for up to 60 days at 23km (75,000ft)
with a 50kg payload.
To do this, they partnered with
balloon maker World View Enterprises (https://worldview.space/), as
described in the news article found
at: siliconchip.au/link/abl2
World View Enterprises use their
balloons for remote sensing with what
they call a Stratollite (Fig.8), a portmanteau of stratosphere and satellite.
A Stratollite flies at 15-23km (49,00075,000ft) and can be launched as a
constellation. These tandem balloons
have an upper balloon containing
helium or much cheaper hydrogen,
and beneath that, a ballast balloon for
altitude control.
Winds often blow in different directions at different altitudes, so by varying its altitude, it is possible to have a
limited ability to control the position.
Technically, this type of balloon is
known as a ‘variable altitude air ballast
balloon system’ (VAABBS). The lifting
balloon is known as a zero-pressure
Fig.7: a Sceye airship climbing. It can
reach 20km altitude and is expected
to go into commercial operations in
around one year. Source: www.sceye.
com
Fig.8: the Stratollite can alter its course by varying its buoyancy and thus
altitude. Source: World View.
density greater than 400Wh/kg. An
ultra-thin laminated solar cell ‘cape’
covers much of the airship’s surface
that is 50-85% lighter than conventional solar cells.
One such airship was launched in
New Mexico in June 2022; it took two
hours to ascend into the stratosphere
and then maintained its position for
24 hours. Commercial operations from
20km (65,600ft) up are expected in
about 9-15 months.
Stratosyst
Stratosyst (www.stratosyst.com)
is a startup company from the Czech
Republic developing the Skyrider
HAPS.
It is expected to take a payload of
12kg, have a power supply that can
deliver up to 5kW, fly at an altitude of
20km and have a mission duration of
weeks to months (see Fig.6).
World View Enterprises
(2012 – present)
siliconchip.com.au
Australia's electronics magazine
balloon (ZPB), while the ballast balloon (one or two) are super-pressure
balloons (SPBs).
Beneath the ballast balloon is a
‘ladder’ that contains solar panels to
charge the batteries. Beneath that is
the gondola or “Stratocraft”.
The ZPB is made of UV-resistant
polyethylene with a volume of about
23,000m3. The SPB beneath it has
a pumpkin shape and operates at a
higher pressure than the surrounding
atmosphere. Its pressure is varied to
alter buoyancy and thus altitude by a
compressor in the Stratocraft.
The concept of using both a lifting
balloon and a ballast balloon (one or
more) or tandem balloon originates in
the “Sky Anchor” system developed
by Texas A&M University in 1976.
The orientation of the ladder can
be changed to ensure the solar panels
have maximum exposure to the sun;
the orientation of the Stratocraft can
also be altered to suit requirements.
The Stratocraft can carry a payload of
50kg. Continuous power of 250W and
instantaneous power of up to 1000W
are available.
At the end of a flight, the Stratocraft separates from the structure and
August 2023 17
Figs.9 & 10: the human-powered AeroVironment Gossamer
Penguin (left) and 2kW AeroVironment Solar Challenger
(above). They and their predecessors pioneered techniques of
lightweight construction, low drag and solar power that were
later used in HAPS aircraft. Source: www.nasa.gov/centers/
armstrong/news/FactSheets/FS-054-DFRC.html
descends via a steerable parachute,
guided to a designated landing location.
Stratollites have sensor packages
that can photograph the surface with
a 5cm/pixel resolution (5cm GSD) vs
25cm GSD for a commercial satellite.
Plus, they can take infrared imagery,
radar imagery and RF signals can be
received and processed. Word View
has an online portal for customers to
examine the data that has been collected.
World View is also developing nearspace tourism and has produced a
pressurised gondola (with restroom!)
with the intention of launching at
various locations around the world,
including Australia.
Passengers will be taken to 30km
(100,000ft) and flights are expected
to take place from 2024 – see https://
worldview.space/space-tourism/
on human-powered aircraft turned out
to be valuable research put towards
building HAPS aircraft.
An athlete such as a Tour de France
contender can sustain a continuous power output of a few hundred
watts for several hours, so that is how
much power is available for sustained
human-powered flight. A HAPS aircraft such as the Zephyr (see below)
uses around 100-200W of power to
cruise, so it’s arguably more efficient
than early human-power aircraft.
HAPS aircraft have the advantage
that they don’t have to carry the weight
or volume of a human, although the
battery, motor and other electronics
might come close to that.
Some milestones were:
● 1974: NASA Sunrise II was the
first radio-controlled solar-powered
aircraft.
● 1977: the first human-powered
flight in the AeroVironment GossaHeavier-than-air
mer Condor. Its empty weight was
HAPS aircraft
31.75kg. Similar ultralight construcHAPS aircraft must be lightweight, tion techniques were later used on
have very low drag and fly with lit- HAPS aircraft.
tle power. Those parameters are
● 1979: the AeroVironment Gosall also requirements for human- samer Albatross became the first
powered flight; hence, the past work human-powered aircraft to cross the
English Channel with an empty weight
of 32kg.
● 1980: the AeroVironment Gossamer Penguin (Fig.9) was the first
solar-powered aircraft capable of carrying a human with an empty weight
of 30.8kg.
● 1981: the AeroVironment Solar
Challenger (Fig.10) was the first
solar-powered aircraft to cross the
English Channel with an empty weight
of 90kg.
NASA ERAST program
The NASA Environmental Research
Aircraft and Sensor Technology
(ERAST) program that ended in 2003
produced UAVs that could perform
long-duration science missions at
18km (60,000ft) and above. Among
other vehicles, it resulted in the solar
or fuel-cell-powered Pathfinder, Centurion and Helios aircraft (see Fig.11).
NASA Pathfinder
(first flight 1995)
The NASA Pathfinder by AeroVironment (see Fig.12) was the first aircraft
built under NASA’s ERAST Program to
develop long-duration, high-altitude
aircraft for science missions.
Fig.12: the solar-powered NASA Pathfinder over Hawaii Fig.13: the NASA Centurion first flew in 1998. Source: www.
on the 28th of August, 1997. Source: www.dfrc.nasa.gov/ nasa.gov/centers/armstrong/news/FactSheets/FS-056-DFRC.
Gallery/Photo/Pathfinder/HTML/EC97-44287-2.html
html
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Australia's electronics magazine
siliconchip.com.au
Fig.11: the planform evolution
of the NASA solar-powered
aircraft designed under the
Environmental Research Aircraft
and Sensor Technology (ERAST)
program. Original source:
https://w.wiki/6doD
In 1995, it set an official record
altitude for solar-powered aircraft of
15.4km (50,567ft). It also set an unofficial altitude record of 21.8km (71,500ft)
and had a ground speed of 24-40km/h.
In 1998, it was modified into the
Pathfinder Plus (more on that later). It
had a wingspan of 29.5m. It weighed
252kg and could carry a payload of
45kg. Endurance was 14-15 hours with
2-5 hours on battery power.
NASA Pathfinder Plus
(first flight 1998)
The AeroVironment Pathfinder Plus
is a modification of the Pathfinder that
climbed to 24.4km (80,206t) altitude in
1998. It was the second NASA ERAST
aircraft with a wingspan of 36.3m, a
Fig.14: the NASA Helios in its HP01
high-altitude configuration. Source:
www.nasa.gov/pdf/64317main_helios.
pdf
siliconchip.com.au
weight of 315kg and a payload of up
to 67.5kg.
The solar array produced up to
31kW at high noon in summer. It had
14 electric motors of 1.5kW each and
flew at around 27-34km/h. Like the
original Pathfinder, its endurance was
14-15 hours with 2-5 hours on battery
power alone.
In 2002, it was involved in atmospheric satellite tests from 20km
(65,600ft), transmitting HDTV and
3G signals. Only 1W of transmission
power was required.
NASA Centurion
(first flight 1998)
The NASA AeroVironment Centurion (Fig.13) first flew in 1998 and
Fig.15: this dramatic image
demonstrates the fragility of this type
of aircraft as it disintegrates and falls
into the Pacific Ocean. Source: www.
nasa.gov/pdf/64317main_helios.pdf
Australia's electronics magazine
was the third ERAST aircraft. It was
designed to fly to 30.5km (100,000ft),
although no official altitude attainment was recorded. It had a wingspan
of 63m, weighed 529kg and could carry
a payload of 45-270kg. Its endurance
was, once again, 14-15 hours with
2-5 hours powered by its lithium battery alone.
NASA Helios
(flights in 1999 – 2003)
The NASA Helios (Fig.14) was the
fourth aircraft of the ERAST program
and a modification of the Centurion.
A 12m wing section was added to
the Centurion for a new wingspan of
75.3m. In 2001, it achieved a world
record for sustained horizontal flight
by a winged aircraft of 29.524km
(96,863ft).
It had two possible configurations.
HP01 was optimised for altitude and
used solar cells and a battery to power
14 motors. HP03 was optimised for
endurance and used solar cells, a
battery and a fuel cell to power 10
motors. The HP01 weighed 600kg
empty weight and could carry a payload of 329kg.
It was lost in a dramatic accident
in 2003 – see Fig.15. You can read the
accident investigation report at www.
nasa.gov/pdf/64317main_helios.pdf
Solar Impulse 1 (2009)
Solar Impulse 1 by André Borschberg
August 2023 19
Fig.16: an artist’s impression of the
Titan Aerospace Solara 50. Source:
https://w.wiki/6doE
and Bertrand Piccard of Switzerland
first flew in 2009. As the name suggests, it was solar powered and used
LiPo batteries so it could continue flying at night. In 2010, they took it for a
manned flight over a complete night/
day cycle (26 hours).
Solar Impulse 2 (2015 – 2016)
Solar Impulse 2, also by André
Borschberg and Bertrand Piccard,
completed a manned circumnavigation of the world in 2015-16, although
it involved 16 stops (17 stages).
Titan Aerospace Solara
50 concept (2015)
Titan Aerospace was a US company
that existed from 2013-14 before being
acquired by Google. Google planned to
use the Solara 50 (Fig.16) and subsequent models as atmospheric satellites
to deliver services such as internet,
real-time Earth images, voice, navigation and mapping.
The aircraft was expected to fly at
around 20km (66,600ft) and spend
five years continuously in the air. It
had a 50m wingspan, was 15m long
and could carry a payload of 32kg.
The ground area to be serviced was
expected to be 17,800km2.
Fig.17: an illustration of one aircraft from the DAP concept. It has a wingspan of
39m, a wing area of 64m2 and a gross weight of 192kg. Source: www.nasa.gov/
sites/default/files/thumbnails/image/niac_engblom_phii.png
Unfortunately, the aircraft crashed
due to structural failure early on its
maiden flight in 2015, and Google shut
down the company in 2016.
Dual-Aircraft Platform (DAP)
concept (2015)
This is a very unusual idea from
Embry-Riddle Aeronautical University. It involves two powered aircraft
tethered together that take off from a
runway and ascend to around 60,000ft
using both solar and battery power.
The lead aircraft is called SAIL, while
the towed aircraft is called BOARD
(Fig.17).
At about 60,000ft (18.3km), the two
aircraft separate by around 1km and
utilise the difference in wind speeds
at the two locations in an analogous
manner to kite surfing (Fig.18). The
SAIL aircraft provides lift for both aircraft, while the BOARD aircraft provides directional control, like a keel.
The propeller can be used as a wind
turbine to recharge batteries under
certain conditions, and missions of up
to several months or years are thought
possible. However, it has yet to be
flight tested. For more information, see
the video titled “DAP Configuration”
at https://youtu.be/fidiDPaLWWw
Facebook Aquila (2016 – 2018)
Facebook Aquila, developed by
Ascenta in the UK, was a HAPS
intended to provide Internet access
in remote areas (see Fig.19). It was
designed as a flying wing about the
size of a Boeing 737, with a wingspan
of 43m, but weighed just 399kg.
It was to fly at 27km (90,000ft)
during the day, dropping to 18km
(60,000ft) at night. The planned endurance was three months, to provide
internet access to an 80km radius
below the flight path. The project was
cancelled in 2018.
Airbus Zephyr (2001 – present)
Zephyr is a solar electric HAPS platform that uses solar during the day
Fig.20 (left): the Airbus Zephyr. Source: https://mediacentre.airbus.com/mediacentre/media?mediaId=604534
Fig.21 (right): the Zephyr 8/S in flight, presumably soon after launch, during 2021 tests in the United USA to demonstrate
wireless broadband service delivery. It undertook 18 daytime flights. Source: https://mediacentre.airbus.com/
mediacentre/media?mediaId=557935
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Silicon Chip
Australia's electronics magazine
siliconchip.com.au
Fig.18: the dual-aircraft platform (DAP) aerodynamic concept, analogous to
kite-boarding. Source: www.nasa.gov/sites/default/files/thumbnails/image/
engblom_sail_board.jpg
Fig.19: the Facebook Aquila drone
in flight. Source: Meta – http://
siliconchip.au/link/ablk
and batteries at night – see Fig.20.
The Zephyr was initially conceived
and designed by Chris Kelleher for
QuinetiQ around 2001 (QuinetiQ
is an offshoot of the UK Ministry of
Defence).
In 2013, the project was sold to Airbus Defence and Space and is now
under the Airbus business unit AALTO
HAPS (www.aaltohaps.com).
Zephyr went through a series of
models, and in 2004, the Zephyr 4 was
demonstrated in Australia. In 2010,
the Zephyr 7 achieved a flight duration record of 14 days, 22 minutes and
eight seconds, which was longer than
any other unrefuelled aircraft flight
at that time. It flew as high as 21.5km
(71,000ft).
In 2018, a Zephyr 8/S broke another
record with a flight of 25 days, 23 hours
replacing 250 terrestrial mobile phone
towers and providing coverage over a
7500km2 area. Other possible applications include military reconnaissance,
communications relay and environmental monitoring.
Zephyr is optimised for operations
at around 20km, the ideal balance
between power required for propulsion and altitude. At this altitude, the
line-of-sight (LOS) is about 500km,
so a radio reception area of 1000km
diameter could be established (eg,
using UHF).
Zephyr can travel up to 1852km
(1000nmi) if it is not kept on station
in one area. It takes about eight hours
to ascend to its usual altitude of 20km
and, due to its highly efficient aerodynamics, it takes about 24 hours to
descend from that altitude.
and 57 minutes. In 2022, a Zephyr 8/S
was lost due to a mechanical failure
after flying for 64 days.
The Zephyr 8/S (Fig.21) has a wingspan of 25m, weighs 62-65kg, has a
service ceiling of 23km (76,000ft), a
rated endurance of 624 hours (26 days)
and can carry a 5kg payload. Another
variant, the Zephyr T, has a wingspan
of 32m, weighs 145kg and can carry a
payload of 20kg.
The Zephyr can be used for various
HAPS applications. One example is
surveillance with the Airbus OPAZ
Earth observation payload. OPAZ
has an electro-optical (EO) sensor
that provides an 18cm resolution and
an infrared sensor for night and day
operations.
It can also be used as a ‘mobile
phone tower in the sky’ (Fig.22),
Fig.22: the ‘mobile phone tower in the sky’ concept for Zephyr. Coverage is expected over an area of 7500km2, equivalent
to 250 ground towers. D2D is short for direct-to-device. Original source: www.aaltohaps.com/mobile-connectivity
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Australia's electronics magazine
August 2023 21
Fig.23: an artist’s concept of the Stratospheric Technologies aircraft, to be
launched from a balloon and then use a plasma engine to stay aloft. Source:
https://stratospherictechnologies.com/technology
Fig.24: the Hawk30 (in 2020, renamed
Sunglider), a product of HAPSMobile.
Source: NASA / Carla Thomas
During ascent and descent, it is vulnerable to bad weather because of its
light structure, so the weather must
be carefully monitored (this applies
to all HAPS).
duration of several months. It can provide a phone service area 200km in
diameter for use by smartphones and
IoT devices.
It is envisaged to use it in areas with
no existing coverage, such as islands
or remote areas, for natural disaster
relief or to provide communications
links for drones.
The Sunglider is a development
of the NASA Pathfinder and NASA
Helios. In 2020, a demonstration flight
lasted for 20 hours and reached 19.1km
(62,500ft). Its operational altitude is
intended to be 20km.
Stratospheric Technologies
(2016 – present)
Stratospheric Technologies (web:
https://stratospherictechnologies.
com/overview) is developing a HAPS
(Fig.23) that is launched by balloon
and then released at an altitude of
around 30km (98,000ft). After that,
it is powered by plasma engines that
derive their power from solar panels
and ascends to 35km (115,000ft).
We don’t have specific details of the
plasma engines, but Fig.25 shows how
atmosphere-breathing electric propulsion works. Electric power ionises
atmospheric gases and then accelerates them to generate thrust.
At night, the platform gradually
glides down to around 20km; when
it becomes light again, the panels can
again produce power for the engines so
it can ascend. The plasma propulsion
system is unaffected by low air density and is said to be the first plasma
propulsion system that operates in the
atmosphere. When the platform needs
to return to Earth for maintenance, it
glides to a landing area.
The company says that potential
use cases for the platform include telecommunications, weather forecasting,
imaging and surveillance, including
civil and military applications.
It is not in commercial use at the
moment. For more details, see the
video titled “Stratospheric Technologies” at https://youtu.be/4D1TAV_aocc
Hawk30/Sunglider
(2018 – present)
The Hawk30, renamed Sunglider in
2020, is a product of the Japanese company HAPSMobile (website: www.
hapsmobile.com/en/) – see Fig.24. It
has a wingspan of 78m, a cruise speed
of 110km/h and is designed for a flight
Kraus Hamdani Aerospace
Kraus Hamdani Aerospace (also
called KHA; https://krausaerospace.
com/) has developed the K1000ULE
Rev-P 4.8m wingspan drone, demonstrating a powered flight duration of
26 hours so far. However, this drone
is designed to fly like a glider or bird
and extend its mission time using
thermals.
Fig.25: how atmosphere-breathing electric propulsion works. Original source: https://w.wiki/6doF (CC BY-SA 4.0).
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Australia's electronics magazine
siliconchip.com.au
This aircraft is not strictly a HAPS
as it is only intended to fly to 6.1km
(20,000ft) to perform various observation and communication functions.
Balloons of uncertain origin
and purpose
Mysterious balloons over the United
States were in the news recently. One
was ultimately shot down by US Air
Force planes. Fig.26 shows one of
these balloons from a US Department
of Defense U-2 high-altitude reconnaissance aircraft. While parts of the
balloon were recovered, at the time of
publishing, the origin and purpose of
these balloons are not known for certain. The Chinese government said it
was a civilian weather balloon that
was blown off course.
BAE Systems PHASA-35
(2020 – present)
Promoted as having the “wingspan
of a 737 and weight of a motorcycle”,
and being able to carry a 15kg payload,
the BAE Systems PHASA-35 (www.
baesystems.com/en/product/phasa-35)
is described as a high-altitude long-endurance (HALE) unmanned aerial system (UAS). It is solar-powered and can
operate over an area of interest for several months – see Fig.27.
It provides a persistent, stable platform for monitoring, surveillance,
communications and security for
military and civil applications. It can
also be used in disaster situations, for
agricultural monitoring, environment
monitoring, Earth observations and
border monitoring.
It can potentially deliver 5G communications in a disaster or remote
area. Its wingspan is 35m; it weighs
150kg and flies at 20km (65,600ft). It
can also be used as part of a constellation of identical aircraft.
For more information, see the video
titled “PHASA-35 - Persistent High
Altitude Solar Aircraft” at https://
youtu.be/Z7NE-rcDtGs
What to do if you find a downed weather balloon
If you find a weather balloon, it should be considered dangerous if it is still
inflated, even partially, as it likely contains flammable hydrogen. The advice
from the BoM is to call the Fire Brigade.
Secondly, it will have a radiosonde. The BoM says these can be disposed of
in regular household garbage or recycling; you do not need to return them. We
suggest a better use. You can use and reprogram the radiosondes for amateur
radio purposes, including tracking any balloons you may launch (subject to
appropriate laws).
That balloon has likely been for a journey into HAPS territory; they typically
achieve 16-35km altitude, according to the BoM.
You can view the video by Australia’s Peter Parker, VK3YE, titled “A mystery
package from a mystery sender” at https://youtu.be/_-cwbIiinkA
Also check out “Repurposing Vaisala RS41 radiosondes for amateur radio
high-altitude balloon tracking” by 0xfeed at siliconchip.au/link/ablg
Fig.26: “A U.S. Air Force pilot looked down at the suspected Chinese
surveillance balloon as it hovered over the Central Continental United
States February 3, 2023” – from US DoD. Source: www.dvidshub.net/
image/7644960/u-2-pilot-over-central-continental-united-states
Fig.27: BAE Systems’ PHASA-35. Source: www.baesystems.com/en/product/
phasa-35
Tethered drones
While not strictly speaking HAPS,
tethered drones such as quadcopters
and multi-rotor drones can provide
persistent aerial observation, surveillance, reconnaissance and communications at altitudes up to a few
hundred meters. Tethering a drone
involves connecting a power and
data cable from a ground station to
a drone.
siliconchip.com.au
Fig.28: launching a
tethered Teledyne FLIR
Skyranger drone. Source:
www.flir.fr/news/pressreleases/flir-acquirestethered-drone-assetsand-technology-fromaria-insights/
Australia's electronics magazine
August 2023 23
The flight duration is then limited
only by the power available and how
long the drone can last before requiring a motor overhaul etc. Existing
drones, including consumer types, can
be converted to tethered operation.
However, dedicated tethered drones
are available, designed for particular
commercial or military applications
(see Fig.28).
Tethering can be done from a stationary position, a moving vehicle
such as a ship at sea, a land vehicle
or even a person carrying the ground
station in their hands or, more likely,
in a backpack.
One potential use for a tethered
drone is for aerial filming in areas
subject to commercial airspace restrictions, where untethered drones can’t
be used; for example, near airports.
One example is the LIFELINE tethering system (www.lifeline-drone.
com) that works with consumer DJI
drones like the Phantom 4 Series V1
& V2, Mavic Pro, Mavic 2 Pro, Zoom
& Enterprise, Inspire 1, and Inspire 2.
UAVOS Inc.
We can’t tell you too much about the
UAVOS product as our Malwarebytes
software warns us not to visit their
website at the time of writing. However, you can safely view the video
titled “HAPS (High Altitude Pseudo
Satellite) by UAVOS” at https://youtu.
be/1YsloiRVEzs
PICO balloons
PICO balloons are a form of amateur HAPS that anyone with an amateur radio license can participate in.
We first mentioned these balloons in
the February 2015 issue (“Reach for
the Sky”, siliconchip.au/Series/281).
They are basically standard helium-
filled Mylar party balloons that you
can buy at any party supply shop carrying a tiny transmitter, solar panel
and GPS module. The payload can
weigh 13g or less but relays the balloon’s position using weak signal protocols such as JT9, JT65 and WSPR at
10-25mW.
These balloons can stay aloft for
Wind direction varies with altitude
The wind speed and direction usually change with altitude, not only in the
stratosphere but at any height – see Fig.29. By altering the altitude of a
balloon, it is possible to achieve some directional control. Smart software and
information from weather resources can help a lighter-than-air HAPS platform
stay on station.
many weeks and even circumnavigate
the Earth several times, see:
• https://picospace.net/
• www.picoballoons.net
Balloon tracking website
You can track amateur balloons at
https://amateur.sondehub.org/
If you want to track scientific and
weather balloons such as from the
BoM, check out:
• siliconchip.au/link/able
• siliconchip.au/link/ablf
Links and videos
● “B-Line to Space: The Scientific Balloon Story”: https://youtu.be/
sPQ-tMoAHkY
● “China’s Balloon: One Question
NO ONE Is Asking!”: https://youtu.be/
eeAFCclFXUY
● More about the Chinese balloon
over the USA: https://stratocat.com.
ar/2023-03-e.htm
● L.E. Epley (1990) “A system architecture for long duration free floating
flight for military applications”: www.
osti.gov/biblio/6525013
● “Stratosphere: The Uncharted
Territory in Networks | Halim
Yanikomeroglu | IEEE YP Ottawa
| 14Mar2023”: https://youtu.be/
XyGGQoCt5M0
● A website about Stratospheric
balloons: https://stratocat.com.ar/
indexe.html
● Information about high-altitude
balloons: farleyflightaerospacellc.
SC
space/FFA.html
Distance to the horizon by altitude
To indicate the desirability of using
HAPS, this table shows the distance
to the horizon as a function of altitude.
Theoretically, a radio beam could reach
the horizon from a HAPS at the indicated
altitude.
Altitude Distance to the horizon
1km 113km
5km 252km
10km 357km
15km 438km
20km 505km
25km 565km
30km 619km
Fig.29: how a balloon can control its direction of travel by varying its
altitude.
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50km 800km
160km 1438km
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