The smooth operation of communications satellites can be influenced by solar weather. Mimic this effect on a smaller scale in the classroom with a simple demonstration.
It’s the final of the 2014 football World Cup, the score is tied and there is no time left on the clock. Fans all over the world hold their breath, but suddenly all the TV sets in Europe go black! What can cause this to happen?
Let’s start from the beginning. How is it possible to watch, almost in real time, an event taking place thousands of kilometres away? The answer orbits above our heads: satellites.
Since the launch of Telstarw1 in 1962, satellite communication has continued to grow. Today, even when news or sport events are taking place just a few kilometres from a TV studio, the camera signals are probably being transmitted using a satellite in geostationary orbitw2 (this means that the satellite orbits Earth at the same speed as Earth rotates, so it stays above the same position on Earth). For you to watch the final of the World Cup in Rio de Janeiro while sitting at home in Europe, a number of satellites have to work together. However, the environment far above Earth’s surface is harsh: there is no atmosphere, lots of cosmic radiation, and extreme temperature variations between sunlight and shadow. Telecommunication satellites contain state-of-the-art technology to cope with these extreme conditions, but a sneaky enemy can still threaten the operation of a satellite: the solar wind.
The solar wind is a stream of charged particles, mainly electrons and protons, that are released from the very hot corona, the upper atmosphere of the Sun. The particles escape the Sun's gravity because of their high kinetic energyw3. This stream of particles reaching Earth varies in density, temperature and speed, depending on time and longitude.
When these particles approach Earth, they can have various effects: from spectacular aurorae to great geomagnetic storms. As geostationary satellites are near the edge of Earth’s protective magnetism, they can be exposed to these storms.
The effect of the solar wind on telecommunications is a modern issue that can trigger students’ interest in space technology and space weather. But how can we mimic it in the classroom? How can we simulate the solar wind?
The Fun Fly Stick toy (figure 1) is a portable wand-like version of the Van de Graaff generator. When switched on, a belt moves inside the Fun Fly Stick and a static charge builds on the wand. Instead of the metal dome of the Van de Graaff generator, the charge accumulates on a cardboard tube. Cardboard has a high electrical resistivity but becomes a conductor when subjected to high-voltage electricity. Furthermore, it discharges more slowly than metal, so the shocking discharge sensation is eliminated.
We can safely use this toy to simulate solar wind by placing a large needle or thin metal axle on the end of the control tube (figure 2). Positive electrostatic charges formed on the cardboard tube are concentrated at the tip of the needle and so ionise the air nearby. Negative ions in the air will rush towards the needle tip and positive ions will move away due to electrostatic repulsion. The movement of these ions creates a form of an ‘electric wind’ or, for the purpose of our simulation, a ‘solar wind’.
To demonstrate the effect of the laboratory-made solar wind, we can just use a test screwdriver. Ask your students to imagine that the simple electrical circuit built into this screwdriver (usually including a battery supply and a red LED) is part of the electronic equipment of an orbiting satellite transmitting their favourite TV show. What will happen if we turn on the generator and come close (about 1 metre or less) to the test screwdriver? The red LED starts glowing (figure 3), and as the stick approaches the screwdriver it glows more and more brightlyw4! The electric circuit starts to overload. What could be the effects of a solar storm on the electronic circuits of a satellite?
As well as overloading and possibly damaging the electronic circuits in a satellite, the solar wind could disrupt the live streaming of the World Cup final. To show this experimentally, we first have to observe that electromagnetic waves can carry usable information. To do this, we propose a modified version of the experiment described by Bernardelli, 2010 (figure 4).
Instead of using a laser pointer and a photo-diode, we use a LED flashlight (torch) and a small solar panelw5. In this way, we reduce the distance that the sound is transmitted but make a stronger impression on the students: most of them consider a laser beam to be something special, but by using a normal flashlight, we can focus on the science behind the phenomenon.
The flashlight batteries provide a strong but constant direct current (DC) to the LEDs. As a result, the LEDs glow with a fixed brightness. When the mp3 player is turned on, it adds a weak but fluctuating electrical signal to the constant current from the battery. The LEDs flicker in sync with the output from the player. The stronger battery current of the flashlight is added to the weaker signal from the player (the capacitor protects the player from being overheated by the input DC). These fluctuations are picked up by the solar panel and are converted into electrical pulses that are turned back into sound by the speaker. This whole process is amplitude modulation (AM). It is the same principle used for transmitting AM radio signals.
With the screwdriver demonstration above, we showed that the solar wind could overload and probably damage a subtle electronic circuit on board a telecommunications satellite. To repeat our classroom simulation without ruining equipment, we designed and built a simple electronic circuit (box 2).
The circuit is in fact a switch triggered by the charges on the cardboard tube of the Fun Fly Stick. When the stick approaches the circuit, the induced electric charge turns on the relay and interrupts transmissionw6: according to our scenario, the solar wind has just hit a satellite and the transmission of the World Cup final has stopped. As soon as you turn off the charge, the relay turns off too, and the transmission resumes: the damage experienced by the satellite is negligible and reversible.
The concepts of space weather and satellite technology are not part of the curriculum, at least not in Greece. However, space-related topics can increase students’ interest in science (Spencer & Hulbert, 2006). An obvious problem for teachers is how to demonstrate effects of this scale and intensity in a classroom. In this article, we hope to convince you that all it takes is a toy and some basic skills in constructing a simple electronic circuit.