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

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.

34m Beam Waveguide Antenna

CSIRO Astronomy & Space Science. ARPS Conference, Adelaide October 2010

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

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

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

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

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

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

effeffWatts

MHz

eff

DADDP

f

DrCosPD

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.

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.

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.

The Result in 2-D.

CSIRO Astronomy & Space Science. ARPS Conference, Adelaide October 2010

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

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

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

Questions?

CSIRO Astronomy & Space Science. ARPS Conference, Adelaide October 2010

Thank you

CSIRO Astronomy & Space Science Neil WebsterRadiation Safety Officer

Phone: 02 6201 7825Email: Neil.Webster@csiro.au