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Submarines and Space: Creating an Antenna in the Sky by In Dr. AHMAD FAIZAL MOHD ZAIN F.A.S.c. SEVERAL questions can be asked: How can an antenna exist in space Why do we need an antenna in the sky above What has a submarine got to do with space Is "space, the final frontier" Trekkies or fans of the Star Trek TV series that debuted in 1966, would be familiar with this cliche. Space has intrigued humanity since the creation of man on earth. Man has looked to the skies searching for answers as to his origins. With naked eyes, man is able to see two of the brightest objects; the sun and the moon. Ancient Greeks and Arabs had studied the night sky looking for celestial objects. Aided by the telescope, invented by Lipperhey and made famous by Galileo in the early 17th century, man is able to look deeper into space. With modem technologies, space is just an instrument away. When people talk about space, they almost always think about outer space. However, closer to home, we have what is termed as near space. This starts about 20 km above the earth in the stratosphere, to the edge of the thermosphere for about 100 km. This region contains small concentrations of neutral and ionised particles, and an abundance of electrons. esfiJotmg Electrons, as being amongst the lightest atomic particles, would be found at even higher levels, up to more than 600 km. These particles are generated by solar radiation, in the form of x-rays, gamma rays, ultraviolet, and infrared- rays, that reach the earth. These radiations knock the electrons out of the neutral molecules. Being lighter, they rise until a point where gravity takes over, and form, a cloud of electrons. This part of the earth's atmosphere is called the ionosphere because it consists of ions and electrons. It is a well known fact that the depth of penetration of an electromagnetic wave depends on its frequency and the conductivity of the media. This is known as the skin depth effect. The lower the frequency of an electromagnetic wave, the deeper it penetrates seawater. That is why things deep or in the ocean look red because it is of a lower frequency than blue light. A submersible vehicle like a submarine, it has to surface to communicate with the outside world, either via satellite or high frequency waves (HF). How can it be submerged and stay stealthy, if it wants to communicate The obvious solution is to use a very low frequency radio carrier. The downside is that it needs a very big antenna. For the submarine to communicate at a depth of about 7 to 10 meters in seawater, the frequency would have to be about I kHz. To radiate efficiently, a simple half-wave dipole antenna would have to be 150 km long, at a minimum height of 75 kin above the earth! The answer to this problem can be found in the abundance of electrons in the ionosphere. This layer of electrons can be periodically agitated by using very high power radio transmitters operating at around 3 to 6 MHz. Vertical radiation is obtained by using directional antenna. By pulsing the transmitters on and off, the electrons will be heated and cooled in tandem with the frequency of pulsing. This action will in turn radiate electromagnetic waves at the pulsing frequency. If the pulsing is done at a much lower frequency of about 1 to 10 kHz or in the ELF/ VLF (extremely low frequency or very low frequency) band, an electromagnetic wave
of that frequency is generated in the sky above. This action is similar to an antenna that radiates electromagnetic waves when it is excited by a time varying current at its terminal. Hence, no physical antenna is required. This generation of ELF or VLF waves was been carried out near Fairbanks, Alaska, where the author had the opportunity to work with the Office of Naval Research, U.S. Department of Defense in the mid-80's. The high powered transmitter facility to heat and cool the ionosphere was run by the University of California, Los Angeles, the Geophysical Institute at Fairbanks, Alaska, and the Pennsylvania State University. The ELF/VLF waves generated were detected as far away as Prince Edward Island, Canada. The advantage of this system is that there is no necessity to have a ground based ELF / VLF antenna which had to have lengths in the region of 100's of kilometers. Another recent development in near space research is the prediction or detection of tsunamis caused by a massive earthquake. The changes in the earth's surface crust or lithosphere would cause the electrons in Prof. In Dr. Ahmad Faizal Mohd. Zain, F.A.Sc. is now at Universiti <strong>Malaysia</strong> Pahang. He was instrumental in running both the ionosonde and GPS receivers at the Wireless and Radio Science Centre at Batu Pahat, before his transfer to Pahang. He was also involved in the first <strong>Malaysia</strong>n microsatellite program from its inception. the ionosphere above to be agitated. The changes in electron concentration can be detected using various means. A relatively cheap and popular means is by using a dual-frequency GPS receiver that can measure the number of electrons in the path of the GPS satellites. By detecting changes in electron concentration, the disturbances can indicate the presence of an earthquake. An added phenomena is that the disturbance occurs before the onset of the real earthquake and hence allows predictions to be made. Research is on-going on how to deter- mine the exact time and magnitude of the actual earthquake. Another ground-based instrument to measure the concentration of electrons in the ionosphere is the ionosonde. This is basically a HF radar with the antenna directed vertically overhead. The reflected waves allow the height of reflection and electron density to be determined. Again, eminent earthquakes and pre-earthquake phenomena cause changes to the electron concentration which can be detected. Space science is an intriguing subject and allows a better understanding of the earth using scientific technologies. Being a multidisciplinary subject, it allows experts and professionals alike to look above to appreciate what happens below. GLOBAL BROADCAST SYSTEM SHF COMMERCIAL UHF FLTSAT UNMANNED AIR VEHICLE #UAV) UHF OTCIXS BGIXS Voice EHF (M LSiARI cut r CJTFI GMCiXS (RR(3 Celiuisr) .tTIDS1Lknk1G Link IINILE AIF t HF Voico - TTY r MF/HF UHF SSIXS TADtX$ A TADI.XS 8) TRAP OTCIXS Voice EMF (MILSTAR) SHF GCCS! US CtNC
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