The Need for SPEED

In the midst of an experiment in early 1908, the German physicist Hans Geiger was perplexed: his new device that was supposed to count charged particles from a radioactive source, was doing so, even in the absence of a source. Where were these particles coming from? When scientists launched a balloon with Hans’ device into space a few years later, they observed the particle count steadily increasing with altitude, leading them to conclude that these particles, mysteriously enough, came from outer space. In the early 1950s, the flurry of excitement surrounding this discovery was still alive, and inspired the young physicist Van Allen to launch Geiger counters on whatever means of ascending from the ground he could find.

When the United States launched their first satellite in 1958, the Explorer I, it carried a Geiger counter built by Dr. Van Allen as its payload, which is the main functional unit of a satellite. As Explorer I looped the earth, live count measurements showed an unexpected pattern: The counts suddenly went high in certain regions of space, leading to the first major discovery of the infant space era, the aptly named “Van Allen” radiation belts. Encircling the earth in the form of a giant doughnut replete with protons and electrons, the Van Allen belts are the subject of study of several space missions today.

What, you might ask, is keeping the charged particles trapped within the doughnut? The answer, it turns out, has to do with Earth’s magnetic field lines, which too, are doughnut shaped.

We’ve all learnt in high school that a moving charged particle, when injected at an angle along a set of parallel magnetic field lines, executes a circular motion around the field lines, while at the same time moving along it. The charged particles in the Van Allen belts undergo a similar motion, save for two important differences: the field lines are curved and their density is not the same – it’s much higher at the Earth’s magnetic poles.

 

This visualization, created using actual data from the Relativistic Electron-Proton Telescopes (REPT) on NASA’s Van Allen Probes, shows the doughnut shaped inner and outer Van Allen belts, filled with charged particles.
This visualization, created using actual data from the Relativistic Electron-Proton Telescopes (REPT) on NASA’s Van Allen Probes, shows the doughnut-shaped inner and outer Van Allen belts, filled with charged particles.        IMAGE: NASA http://ipy.gsfc.nasa.gov/vis/a010000/a011200/a011212/

 

When a charged particle in the belt moves towards the poles, it feels a stronger magnetic field, which makes it reverse it direction and move towards the other pole, where it repeats this behavior. This endless loop of particles bouncing back and forth is what keeps these charged particles trapped.

The behaviour, as you might have guessed, isn’t this simple. There are particles which free themselves from this trap and also new particles getting trapped all the time, due to various phenomena.

A good example of particles escaping the Van Allen belts is the majestic aurora occasionally seen in the night sky near the polar regions. As the principal mission of the IIT Madras Student Satellite Project (IITMSAT), we are interested in one particular cause of the escape: the interaction of charged particles with electromagnetic (EM) waves produced on the earth.

EM waves are produced due to a variety of phenomena. Of particular interest to us is a particular type of low-frequency wave thought to be produced in the days leading to an earthquake at its epicenter. It turns out that these waves match the frequency of gyration (rotation of the charged particle around the field line) of the charged particles in the Van Allen belts, providing a favourable condition for the energy of the wave to be transferred to the particle. When this occurs, the particle now has enough energy to push against the repulsive magnetic field at the poles, and drops out of the Van Allen belts into low Earth orbits – orbits at an altitude of 500–800 km from the Earth’s surface – where it can be detected. All of this occurs in a very small instant of time after an EM wave is produced, and thus, what we really see is a sudden “burst” of particles in space. IITMSAT’s payload is built to detect precisely this burst, allowing us to predict expected seismic activity at a particular location on the ground.

To better understand this phenomenon, we built a computer model last year to simulate the interaction of an EM wave with the Van Allen belts and to study the nature of the charged particles that are precipitated. Thus, we know how much precipitation to expect in the low Earth orbits and the energy of the charged particles that IITMSAT’s payload will see when in orbit. The Space Based Proton Electron Energy Detector (SPEED), IITMSAT’s payload, which has been in development for nearly three years now, is steadily reaching completion.

In order to detect charged particles, SPEED uses materials known as scintillators, which fluoresce when a charged particle strikes them. A charged particle that travels through a scintillator knocks off electrons from its atoms, leaving a void. When electrons from a higher energy state drop down to replace the knocked off electrons, they lose energy in the form of blue light.

 

This sequence of images illustrates how an electromagnetic wave can cause a particle in the Van Allen belts to escape, so that it can be detected in the low Earth orbits.
This sequence of images illustrates how an electromagnetic wave can cause a particle in the Van Allen belts to escape, so that it can be detected in the low Earth orbits.     CREDIT: NASA, http://www.nasa.gov/vision/universe/solarsystem/space_lightning.html

 

In SPEED, this blue light enters “wavelength shifting” (WLS) fibers, which cover the scintillator surface. The WLS fibers convert this blue light into green light, which is then transported along the length of the fiber to devices known as Photomultiplier Tubes (PMTs). The PMTs then convert the light into an electrical signal which is amplified and fed into an electronics system that processes the signal and returns information on the energy and the type of the incident particle.

SPEED’s development over the last three years has been an interesting journey, with the design undergoing several critical modifications as our understanding of the phenomenon evolved over time. After several iterations, we now have a complete structural prototype of SPEED that is designed to meet the strict Polar Satellite Launch Vehicle (PSLV) conditions. This allows us to put together our scintillator modules into one compact package and finally test them all at once.

 

These images show the bottom view (left) and the top view (right) of the SPEED payload. Only the top scintillator is visible in the top view image. CREDIT: The IIT Madras Student Satellite Project.
These images show the bottom view (left) and the top view (right) of the SPEED payload. Only the top scintillator is visible in the top view image. CREDIT: The IIT Madras Student Satellite Project.

 

The IIT Madras Space Center is currently being built at the Electrical Engineering Department, which will house several test equipment, in addition to a clean room that will help accelerate our experiments in the next few months. With parallel developments on developing the instruments and understanding the phenomenon, we are making headway in building a satellite whose scientific mission, if successful, is bound to have a definitive impact on the way we understand the Van Allen belts’ mysterious phenomena.

A BRIEF HISTORY

The IITMSAT Project was created by a group of enthusiastic first-year undergraduate students in 2009, with the aim of launching a satellite with a socially relevant scientific mission. The initial funding for IITMSAT was in the form of an “innovative student’s project” grant, provided by the Industrial Consultancy and Sponsored Research (ICSR) unit of IIT Madras. For about a year, the team experimented with the feasibility of several possible payloads that could be flown on IITMSAT, and developed an organizational structure for the satellite by dividing it into seven subsystems: the communication subsystem, the electrical power subsystem, the payload, the attitude determination and control subsystem, to name a few.

The idea of flying a high-energy-particle-detector was finalized after a discussion with scientists at ISRO’s satellite center in 2010, and this eventually led to the SPEED payload that stands today. As of now, we have a group of about 25 dedicated undergraduates working on various aspects of SPEED and the rest of the satellite, while certain specific units have been converted into Masters projects with the aid of faculty members.

Over the years, the IITMSAT has greatly benefited from collaboration with several institutes in India and abroad. SPEED’s initial development was carried out in the form of internships at ISRO’s satellite center, Tata Institute of Fundamental Research (TIFR), Mumbai and Indian Institute of Space Science and Technology (IIST), Thiruvananthapuram. In order to develop certain units of the satellite’s subsystems, our team members worked at York University, Canada and EPFL, Switzerland, which have prior experience in nano-satellite development. In this regard, we have also received recognition and useful feedback at several conferences, the most recent of which was the 5th Japanese Nano-satellite Symposium at Tokyo, in November 2013.

The funding for IITMSAT comes from different sources, of which our Institute and alumni have been the major ones. A significant portion of these funds is being used to construct the IIT Madras Space Center. We aim to complete the project in 2015.

FURTHER INFORMATION:

IITMSAT’s official website: www.iitmsat.iitm.ac.in

A non-technical overview of the IITMSAT project, ”Unveiling the Aurora: IITMSAT,” is available at http://t5e.iitm.ac.in/2013/08/unveiling-the-aurora-iitmsat/.

For further information, please contact Nithin Sivadas at astronithin@gmail.com.