Knowledge Nugget | SpaceX’s latest launch raises a question: What powers satellites?

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Let’s understand the nuclear-powered satellite and what powers the satellites in space.

1. The satellite, called BOHR (Betavoltaic Orbital High-Reliability), was developed by Florida-based company City Labs and lifted off on July 7 aboard a SpaceX Falcon 9 rocket as part of the company’s Transporter-17 rideshare mission from Vandenberg Space Force Base in California.

2. BOHR is a demonstration mission designed to test City Labs’ proprietary NanoTritium betavoltaic micropower source in space for the first time.

3. NanoTritium generates electricity by using the beta particles released during the radioactive decay of tritium, a radioactive form of hydrogen. Those particles are converted directly into electrical energy using a semiconductor device.

Tritium

Tritium is a radioactive isotope of hydrogen. Isotopes are atoms with the same number of protons but different numbers of neutrons. Tritium has same number of protons and electrons as hydrogen but has 2 neutrons, whereas regular hydrogen does not have any.

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Tritium is produced naturally from interactions of cosmic rays with gases in the upper atmosphere, and is also a by-product of nuclear reactors. It is present in our Pressurized Heavy Water Reactors (PHWRs).

Like all radioactive isotopes, tritium decays. As it decays, it emits beta radiation. As tritium decays, it changes to helium.

4. The technology differs from the radioisotope thermoelectric generators used on NASA spacecraft such as the Voyager probes, which generate power from heat emitted by decaying plutonium.

5. Although BOHR still depends on solar panels for its primary spacecraft operations, the mission is intended to demonstrate how betavoltaic power systems could eventually support spacecraft operating in environments where sunlight is scarce.

6. City Labs believes the technology could one day power missions to permanently shadowed regions of the Moon, including craters near the lunar south pole that receive little or no direct sunlight.

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What powers satellites in Space?

7. According to NASA, “a spacecraft generally gets its energy from at least one of three power sources: the Sun, batteries or unstable atoms.” The instruments mounted on the spacecraft for various tasks need electricity supply to function.

8. A reliable source of power supply is the sun. According to the European Space Agency (ESA), “the Sun provides around 1.4 kilowatts of power per square metre in Earth orbit – a bountiful resource that spacecraft designers do their very best to take advantage of. This is why the majority of spacecraft incorporate wing-like solar arrays or else have them layered across their hull.

9. Today most satellites rely on advanced solar cells with an efficiency around 30% and on Li-ion batteries. When the distance to the Sun becomes too large, i.e. typically beyond Jupiter, then the solar flux can no longer be used effectively and nuclear sources are the only option left.”

10. Also, the efficiency of the Photovoltaic cells is reduced by heating from the Sun and radiation damage during a satellite’s lifetime. This means that solar arrays have to be of a significant size to deliver useful power levels. This is one of the reasons for exploring an alternative source of supplying power to the spacecraft.

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BEYOND THE NUGGET: Voyager 1

1. On April 17, engineers at NASA’s Jet Propulsion Laboratory (JPL) in Southern California shut down one of its long-running science instruments aboard Voyager 1 called the Low-Energy Charged Particles experiment, or LECP, as the spacecraft ran critically low on power.

2. Voyager 1 had run out of power to operate all of its systems. The spacecraft is equipped with a radioisotope thermoelectric generator that utilises the heat generated by decaying plutonium and transforms it into electric power. The energy level, however, has declined gradually since the probes were launched; about 4 watts disappear every year.

3. Without such steps, nuclear-powered spacecraft risk triggering an automatic fault protection system that could shut down multiple components at once, making recovery far more difficult.

An illustration of the trajectories of Voyager 1 and Voyager 2. (Image credit: NASA/JPL-Caltech)

4. Launched in 1977, Voyager 1 is one of the most important space missions ever undertaken. It was originally sent to study the outer planets, including Jupiter and Saturn, but it went far beyond its initial goal. Today, it is the most distant human-made object in space, travelling through interstellar space at high speed.

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5. Voyager 2 was launched on August 20, 1977, two weeks before the September 5 Voyager 1 takeoff. Voyager 1 and Voyager 2 are identical spacecraft. Each of them is equipped with instruments to carry out 10 different experiments

6. The most interesting discoveries made by Voyager 1 included the finding that Io, one of Jupiter’s moons, was geologically active. The spacecraft noted the presence of at least eight active volcanoes “spewing material into space, making it one of the most (if not the most) geologically active planetary bodies in the solar system,” another report by NASA said.

Post Read Question

Consider the following statements:

1. Tritium is a radioactive isobar of hydrogen.

2. NanoTritium generates electricity by using the beta particles.

3. A radioisotope thermoelectric generator utilises the heat generated by decaying plutonium and transforms it into electric power.

Which of the statements given above is/are correct?

(a) 1 and 2 only

(b) 2 and 3 only

(c) 1 and 3 only

(d) 1, 2 and 3

Answer Key

(b)

(Sources: The legacy of the Voyager mission, Why Nasa shut down a key Voyager 1 instrument after 49 years, SpaceX launches world’s first commercial nuclear-powered satellite, Nasa, Esa, Isro)

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