By Squadron Leader Clarry Briese
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Air
Power Development Centre
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SPACE
is already very important to the Air Force and is becoming
more so as we procure systems that are increasingly reliant
on space for precision navigation, surveillance, weather information
and communications.
But as well as using space systems, the future Air Force could
operate near-space platforms that give cost-effective “space-like”
capabilities to complement other platforms.
Near-space is the region between 65,000 feet and about 325,000
feet (100km).
This is above the altitude used by most aircraft and below
the lowest sustainable satellite orbit, which is at about
150km. With present technology, near-space platforms can operate
up to about 120,000 feet.
Conditions in near-space are harsh. The temperature ranges
from -59 degrees Celsius at 65,000 feet to -23 degrees Celsius
at 120,000 feet.
The atmospheric pressure is very low. Most of the near-space
platforms would be made of composites and synthetic materials.
The materials must be specially engineered to resist degradation
by the very strong ultraviolet radiation in the region.
Near-space is above most of the weather that we observe, and
also above the jet-stream winds – the average wind speed
from 65,000 to 80,000 feet is less than 20 knots. These platforms
operate below the charged particle layers of the ionosphere
that can interfere with radio frequency communications and
navigation signals.
Most near-space platform designs are solar-powered balloons
and airships, although winged aircraft using solar power and
hydrogen fuel cells are also being trialled.
The simplest platforms are free-floating balloons that drift
with the wind. Steered “free-floaters” are more
complex and have some ability to manoeuvre but cannot stay
in one location. Finally, manoeuvring vehicles under development
will be able to launch, travel to a specified point, and remain
there for between one week and many months.
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In
the future, near-space aircraft may be used for surveillance
and communications.
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Photo
illustration by PTE John Wellfare
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The
near-space platform is just a means to carry a payload that
is similar to an air or space system payload.
Compared to space systems, near-space platforms can offer
persistent coverage without the high launch costs of satellites.
Payload costs are also reduced due to the shorter lifetime
required of components, and the lower power and resolution
demands from operating four to ten times lower than a Low
Earth Orbit (LEO) satellite. Near-space platforms are also
responsive, able to be launched in shorter time for a particular
campaign.
However, small, responsive tactical satellites (TACSATs) are
being developed. Satellites can also legally overfly any area,
whereas in peacetime, near-space platforms will be limited
to flying above friendly or international airspace. Therefore,
only satellites can conduct some strategic tasks.
In a recent US Air Force experiment, a free-floating balloon
with a radio repeater increased the range of forward air controllers’
line-of-sight radios from 10 miles to over 400 miles.
The same system could help Australian aircraft operating at
low altitude, or tactically deployed ground personnel, in
a wide variety of roles. Surveillance and reconnaissance near-space
platforms won’t replace satellites, Wedgetail or Global
Hawk, but they could be used to cue those sensors and provide
communications network relays.
Manoeuvring near-space vehicles with a mixed payload could
loiter over an area of operations providing continuous surveillance,
reconnaissance, electronic intelligence, and communications.
The important point to note is that near-space platforms are
not “better” or “worse” than satellites,
aircraft, or UAVs, but they offer an interesting mix of characteristics
that may allow them to fill capability gaps.
Squadron
Leader Clarry Briese is Staff Officer - Space at the Air Power
Development Centre
