Deep Space exploration could be tricky in Future. To send an artificial satellite into deep space, any space agency not only need massive investments but they also need a tremendous amount of resources to keep the spacecraft going.

Recently, NASA’s Voyager 1, a human-made satellite, reached into interstellar space. This achievement is historical for human history as Voyager-1 is the first ever human-made satellite that crossed into interstellar space. Voyager 1 was launched in 1977, and just two years after, its twin “Voyager-2” was launched by NASA.

Voyager-1 is being operated on its own onboard energy power supply, having been gone far away from the Sun. Many space exploring spacecraft which covers long distance usually run on a ‘radioactive’ isotopes called Plutonium-238. It's an artificial element that we discovered as a byproduct of making nuclear weapons. And the bad news is NASA has been running out of it.

NASA turned the Voyager 1’s camera off after it took a historical picture of ‘Pale Blue Dot’ Earth from space on valentines in 1990. Turning off the camera would help Voyager 1 to save power so that it can cover more distance.

Back in the 1960s, NASA had SNAP (Solar for Nuclear auxiliary power) programme that developed, among other things, the radioisotope thermoelectric generator (RTG).

This small lump of decaying Plutonium-238 generates heat and power as it breaks down and it can power spacecraft for many decades in space. But NASA's been lacking Plutonium-238.

It’s not a problem when exploration is within our solar system as solar rays can power spacecraft for days and days. But, solar power isn’t enough when it comes to exploring space beyond the heliosphere.

NASA recently mentioned that they are planning to launch a spacecraft to Mars and this project will probably consume a third of all the remaining Plutonium-238 that NASA has left - 35 KGs.

“If the Energy Department's existing Pu-238 supply is used for next one or two missions, NASA would be forced to eliminate or delay future missions,” claimed Shelby S Oakley, director of acquisition and sourcing management at GAO

He added, "On a comet, operating at crazy distances, you can't land with solar panels the size of an Airbus wing.

A radioactive power supply is a totally enabling thing."

Why NASA lacking Pu-238?

Radioisotopes are powerful all-in-one fuel sources. As they decay and transform into new elements, they release impressive amounts of energy. Unfortunately, only 22 out of 2,900 known to humankind radioisotopes can power a deep space spacecraft, according to a 2009 study by the National Academies of Science.

There is only one radioisotope out of the 22 that have been identified, Plutonium-238, that is stable enough to work with. The other radioisotope emits dangerous radiation, and some do not release enough heat energy to warrant attention.

Is there any alternative to Plutonium-238?

Yes, power generators with the likes of batteries, fuel cells, solar power, and even nuclear reactors can substitute Pu-238.

But according to engineers, Pu-238 is way better than all of its substitutes for so many reasons.

Pu-238 is weightless compared to its alternatives. Less weight means spacecraft can cover more distance in less power consumption. That’s the main reason why Voyager-1 and Voyager-2 are still active after their launch in 1977 and 1979. Unfortunately, Voyager-1’s power will run out in 2025, and it’ll stop sending signals to earth, according to NASA.