NVS-01: Indigenously developed Rubidium atomic clock used for the first time in 2G navigation satellite

Vibha Sharma

Chandigarh, May 29

The Indian Space Research Organisation (ISRO) today successfully launched second generation navigation satellite NVS-01 using a GSLV rocket with a cryogenic upper stage. Carrying navigation payloads L1, L5 and S bands, the NVS-01 has been designed by scientists using an indigenously developed Rubidium atomic clock “for the first time”, according to reports.

Scientists earlier depended upon the imported ones to determine date and location—one of the primary roles/features of any satellite. The atomic clock has been developed by Ahmedabad-based Space Applications Centre.

According to ISRO, “just a handful of countries possess the technology”.

NVS-01 aims to provide accurate and real-time navigation with signals designed to provide user position accurate to better than 20 metres and timing accuracy better than 50 nanoseconds.

What is Rubidium?

Flashback to chemistry lessons and Periodic Table—Rubidium is an element with symbol ‘Rb’ and atomic number ’37’. The very soft, whitish-grey/silverish solid is similar to potassium. It is the second most electropositive metal and ignites spontaneously in air. If it ignites, the moderately toxic element can also cause thermal burns while over-exposure can result in skin and eye burns, according to the available information.

Because of its chemical properties, it is also used in locating and imaging brain tumors. Rubidium is said to be ideal for monitoring ischemia, a condition where blood flow is obstructed through the main coronary arteries. Its radioactive isotope is a valuable tool for identifying myocardial ischemia in Positron Emission Tomography (PET) imaging, say scientists.

Discovered by German chemists Robert Bunsen and Gustav Kirchhoff in 1861, the element derives its name from the Latin word ‘rubidus’, which means deep red—the colour of its emission spectrum.

Its compounds also have electronic applications due to the ability to conduct electricity. Rb is used in the manufacture of photocells as well. Though itis not a known nutrient for living organisms, its ions have properties and charge similar to potassium ions.

Why atomic clocks?

Atomic clock is a clock that measures time by monitoring the resonant frequency of atoms. It isused onboard GPS satellites that orbit the Earth by combining a quartz crystal oscillator with an ensemble of atoms to achieve greater stability, according to the NASA website.

“Most modern clocks, from wristwatches to those used on satellites, keep time using a quartz crystal oscillator. These devices take advantage of the fact that quartz crystals vibrate at a precise frequency when voltage is applied to them. The vibrations of the crystal act like the pendulum of a grandfather clock, ticking off how much time has passed.

“To know the spacecraft’s position within a meter, navigators need clocks with precision time resolution, clocks that can measure billionths of a second.

“Navigators also need clocks that are extremely stable. By space navigation standards, quartz crystal clocks aren’t very stable. After only an hour, even the best-performing quartz oscillators can be off by a nanosecond (one billionth of a second). After six weeks, they may be off by a full millisecond (one thousandth of a second), or a distance error of 185 miles (300 kilometers). That would have a huge impact on measuring the position of a fast-moving spacecraft,” it states.

According to various research papers on the subject, the Rubidium atomic clock is the “workhorse” of any satellite navigation system of which GPS is the key.

They are said to be better than other atomic clocks because they are low in weight, easy to build and the cost factor.

Rubidium, incidentally, is the 16th most abundant element in the earth’s crust and producing RB atomic clocks is relatively inexpensive—perhaps among thereasons for its wideusein military applications for communications, electronic warfare, command and control, navigation etc.

Because of the colour, at times Rb compounds/salts are also used in fireworks and add purple hues to glass and ceramics.