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Airspace safety review a study of the aircraft hazards from an 80 k w transmitter- webster
1. A Study of the Aircraft Hazards from an 80kW
Transmitter, Model Development and Analysis
Canberra Deep Space Communication Complex
Neil Webster,
Radiation Safety Officer, CASS
ARPS Conference – Adelaide, October 2010
2. Introduction
Today we will cover:
• Some Background
CSIRO Astronomy & Space Science. ARPS Conference, Adelaide October 2010
• Development of the Model
• Applying the Model and Analysis of the Results
• Briefly discuss the Outcomes
• Highlight some future Research and Analysis Work.
3. 34m Beam Waveguide Antenna
CSIRO Astronomy & Space Science. ARPS Conference, Adelaide October 2010
4. New High-Power Transmitter
• When introducing a new Transmitter there are a number of
Radiation Safety requirements to evaluate and demonstrate
compliance against.
• These include:
• Personnel Safety (on Ground)
• Public Safety on surrounding terrain
• Aircraft Safety
Here we are considering the Aircraft Safety aspect
CSIRO Astronomy & Space Science. ARPS Conference, Adelaide October 2010
5. Aircraft Safety Evaluation Considerations
• There are two considerations to evaluate for Aircraft Safety:
• Is it Safe for the Aircraft?
• Aircraft use complex avionics equipment to fly and operate the
aircraft safely. Modern aircraft incorporate fly-by-wire technologies
and computer-controlled avionics systems in addition to the
increasing use of composite materials in the aircraft’s structure.
• These systems are susceptible to electronic interference,
particularly from High Intensity Radiated Fields (HIRF).
• Safe for the passengers and crew in the Aircraft?
• RF Radiation Standards exist for the RF exposure to members of
the public. If the power density is sufficiently high, even a very
short exposure time-averaged will exceed the maximum exposure
limit.
CSIRO Astronomy & Space Science. ARPS Conference, Adelaide October 2010
6. Relevant Safety Standards
• Aircraft Design Standards
• These Standards refer to levels of Power Flux Density which an
aircraft has been tested to withstand without adversely affecting
the aircraft’s electrical and electronic systems.
• US – FAA incorporated RTCA DO-160
• EU – Eurocae ED614
• Australia – CASA adopted the US requirements.
• Human Exposure Standard
• Refers to the maximum exposure limits for Public and occupational
exposure to RF Radiation.
• ARPANSA Radiation Protection Standard No 3.
CSIRO Astronomy & Space Science. ARPS Conference, Adelaide October 2010
7. Understanding the Problem.
• Size of the Fresnel Zone
• The fresnel zone (2D2/λ) of the 34m antenna at X-Band is 51,156m
• Volume of Space of interest
• Aircraft typically fly between 5,000’ and 50,000’ in our region of
interest.
• Antenna pointing limitations
• Restricted to a minimum of 10 degrees elevation.
• Power Density of the Antenna/transmitter
• The on-axis power density within the fresnel zone
• Consider Transmitters from 2 or more Antennas.
• It is possible that 2 antennas could point to the same point in space
and their fields combine.
CSIRO Astronomy & Space Science. ARPS Conference, Adelaide October 2010
8. Development of the Model
• Initially created a 3-D Matrix of 80km * 80km * 30km, which to
provide acceptable resolution (10-15m) would mean
approximately 60 billion data points.
• This was reduced to a 2-D plane of 80km * 30km in specific
directions of interest.
• As the existing site aviation reference point is in the centre of
the site, geo-spatial offsets were applied from the actual
antenna location and the reference point to accurately
reference and display the volume of airspace.
• The power Density / field strength was calculated for each data
point in the matrix and displayed.
• Model was enhanced to allow multiple antennas, field
summation and Monte-Carlo Analysis of the transmit frequency.
CSIRO Astronomy & Space Science. ARPS Conference, Adelaide October 2010
9. Calculating Power Density
CSIRO Astronomy & Space Science. ARPS Conference, Adelaide October 2010
The power density values of this analysis were determined by a number of
complex calculations. The calculation shown below was derived from an
adaption by Dan Bathker (Jet Propulsion Laboratory in the US) from the classic
Bickmore & Hansen research publication “Antenna Power Densities in the
Fresnel Region”.
10*
))*2(*40(
)*)(**((
*
793458.299
*2
*8
1*14.13 2
2
illum
effeff
Watts
MHz
eff
D
ADDP
f
D
r
CosPD
Where:
PD = Power Density in W/M2
P = Power in W
D = Antenna Diameter
Deff = Antenna Effective Diameter
Dillum = Antenna illuminated Diameter
Aeff = Antenna Effective Aperture
As this formula provides power density in W/M2 the answer needs to be
converted into field strength (V/m) in order to compare against the Aircraft
safety standards. Applying Poynting’s theorem provides an approximation of the
result, with a caution that the field being evaluated is in the radiating near-field.
10. On-Axis E-Field Strength.
CSIRO Astronomy & Space Science. ARPS Conference, Adelaide October 2010
Here we can clearly see the on-axis power density (field strength) oscillations in
the near field region of the antenna. Note that we have not yet reached the
point where power density reduces at the rate of 1/r2.
11. Applying the Peak Value
CSIRO Astronomy & Space Science. ARPS Conference, Adelaide October 2010
To evaluate the hazards we applied the peak value up to the distance to the
peak. This takes into account the differing spatial fields encountered across
the entire aperture of the antenna.
12. The Result in 2-D.
CSIRO Astronomy & Space Science. ARPS Conference, Adelaide October 2010
13. Analysis of the Results.
• In order to compare the results for the human exposure case,
an understanding of the time in which a person may be
exposed to the field from the antenna and the dimensions of the
field is required.
• Aircraft flight operating manuals were consulted to obtain
aircraft groundspeeds for different flight configuration, which
were then applied to calculate the time a person would remain
in the field of the antenna. The methodology from the Standard
was applied to obtain the maximum allowable time-averaged
power density.
• A direct comparison of the results and the HIRF Standards was
made after converting the results to Field strength (V/m).
CSIRO Astronomy & Space Science. ARPS Conference, Adelaide October 2010
14. Outcomes from the Analysis
• Analysis of the human exposure case found that the safety
levels for the aircraft would also provide protection for the
aircraft occupants.
• Analysis of the HIRF environment created by the 80kW
transmitter against aircraft safety levels has identified that a
method of airspace management surrounding CDSCC needs to
be developed.
• A Technical Report was written which covers all the existing
transmitters in addition to the proposed 80kW transmitter. This
report will be included as an attachment to the Airspace
Change Proposal to be submitted to the Civil Aviation Safety
Authority.
CSIRO Astronomy & Space Science. ARPS Conference, Adelaide October 2010
15. Further Research and Analysis
• Research the aircraft operating environment surrounding the
complex and compare the proposed antenna operating
geometry and transmitter utilization to determine a risk/ impact
analysis.
• Consider undertaking physical measurements on-axis at low
power to further verify the model.
• Consider investigating further the use of time-averaging for
human exposure to microwave frequencies at 10-20 second
exposures.
• Consider looking at the research from the EU funded HIRF-SE
project. Standards development, composite aircraft shielding,
etc.
CSIRO Astronomy & Space Science. ARPS Conference, Adelaide October 2010
