Earth’s ‘second moon’ target of proposed mission

The Earth’s “second moon” is the target of an innovative concept for a space mission. The proposal – put forward by a researcher in Italy – would see a light and cheap-to-launch satellite travel to the near-Earth asteroid, Cruithne. Among…

The Earth’s “second moon” is the target of an innovative concept for a space mission. The proposal – put forward by a researcher in Italy – would see a light and cheap-to-launch satellite travel to the near-Earth asteroid, Cruithne. Among the novel features of the mission is the idea of having two independent “nano platforms” that can be deployed to conduct scientific surveys once the satellite has reached its destination.

Also known as asteroid 3753, Cruithne is a five-kilometre-wide near-Earth object (NEO). While presenting no risk of colliding with us, the asteroid is locked in a 1:1 mean motion resonance with the Earth. This means that the two bodies take approximately the same time to complete an orbit of the Sun, so they appear as if they are chasing each other. Viewed from Earth, Cruithne is seen to weave a bean-shaped path, coming closest at a distance of 12,500,000 kilometres away – a habit that has lent it the nickname of the Earth’s “second moon”.

Relic of the early solar system

Cruithne is of great scientific interest. As with many small asteroids, its composition should still preserve its original chemical make-up – unaltered by high internal pressures and temperatures – which could tell us more about how the solar system formed. For the purposes of a visiting survey satellite, however, Cruithne’s large orbital inclination presents a particular challenge to reaching it, one that certainly tests the mettle of any proposed space mission. “The [new] study proposes a novel mission approach for the survey of near-Earth asteroids based on small and flexible satellites,” says paper author Pierpaolo Pergola, an aerospace engineer from the University of Pisa.

The efficiency of the mission comes primarily from making use of an electric ion-propulsion system. This would use power generated from solar arrays to produce and accelerate high-temperature plasma in two thrusters – which would enable the craft to travel at high speeds while using relatively small amounts of fuel for a space mission of this type. By saving in propellants, launch costs are lowered and mass can instead be allocated to a greater payload. “This is especially convenient for a high-total-impulse mission,” says Pergola, explaining that in a classical chemical-propulsion system – with more conventional trajectories – one would need more fuel.

The proposed payload in this case would be two subsidiary nano-platforms, which could be deployed at the destination to conduct detailed surveys. Pergola explains that the ideal candidate for this would be 2U CubeSats (with dimensions of 20 × 10 × 10 cm), the miniaturized research platforms that have brought affordable research opportunities in recent years. Despite their size, CubeSats can achieve a range of applications – such as employing accelerometers, mass spectrometers or particle probes – while still being lighter together with the mother satellite than one single expansive and less manoeuvrable probe. With the main spacecraft acting as a telecommunications relay to Earth, and as a radiation shield during space travel, the mission design overcomes two of the exiting hazards that are associated with using CubeSats for deep-space applications.

No need to slingshot

Furthermore, as the mission would go straight from Earth to Cruithne without having to slingshot around anything else en route, such a mission would save on transit time and complexity while offering a highly flexible launch window. In total, the spacecraft is expected to weigh around 100 kg and would be expected to reach Cruithne in around 320 days. Such a survey mission could potentially help pave the way to subsequent robotic landing missions, human explorations or even asteroid-mining endeavours, claims Pergola.

While this interesting mission proposal certainly seems to have potential, a trip to Cruithne may not be quite “written in the stars” as yet. “For the time being, [this] is a proof of concept,” explains Pergola, who reports having received positive feedback on the principle from colleagues. He adds: “I’m aware that there is a growing interest worldwide toward applications of the CubeSat standard in more exotic missions, like [this] one.”

As yet, however, Pergola does not have a clear picture of all the expenses involved in such a mission.

The proposed mission is reported in Advances in Space Research.