The UAE’s Rashid rover may be on an arduous journey to the Moon but the complex route has helped its lander to save fuel.
Hakuto-R Mission 1 lander’s lunar voyage began on December 11, with arrival expected at the end of April.
Instead of having to fire thrusters and burn more propellant, it will travel further into deep space and use the Sun’s gravity to push itself back to Earth.
It will then slingshot around the Earth, allowing the planet’s gravity to propel the spacecraft towards the Moon.
The private Japanese lander's route is an example of low-energy transfer, different to conventional and direct transfers that take only three to six days.
Nasa’s Apollo missions, for example, took a direct route to the Moon, as did the agency’s Lunar Reconnaissance Orbiter, which took four and a half days to reach orbit.
And while these get a spacecraft faster to its destination, there are more companies now choosing a low-energy transfer for other benefits.
Reduces cost of fuel
Ispace, the company that built the Japanese lander, said the route would help save on fuel and also cut down the spacecraft's weight.
“The reason why we took this strategy is to reduce the mass of the spacecraft and that leads to a reduced cost of launch,” Takeshi Hakamada, founder and chief executive of ispace, told The National.
“We can utilise the gravity of the Sun to accelerate our spacecraft without using propellant.”
But using this route also means the lander will travel as far as 1.5 million km from Earth at its farthest point — roughly four times the distance between Earth and the Moon.
The lander has already travelled that far and will continue to perform a series of manoeuvres before it reaches lunar orbit.
Once there, it will attempt a landing.
Missions that have used similar routes
Ispace is not the first organisation to use a low-energy transfer to the Moon.
Nasa’s Capstone mission — a miniature satellite that was launched in June — also took five months to reach lunar orbit.
It too used gravitational assistance from the Sun and then the Earth to propel itself towards the Moon.
“Assisted by the Sun’s gravity, it will reach a distance of 963,000 miles (1.54 million km) from Earth — more than three times the distance between Earth and the Moon — before being pulled back towards the Earth-Moon system,” Nasa said in a statement before the mission was launched.
“This sinuous track — called a ballistic lunar [low-energy] transfer — follows dynamic gravitational contours in deep space.”
South Korea’s first lunar probe, the Korean Pathfinder Lunar Orbiter, took four months to reach the Moon’s orbit.
It was launched in August and arrived in December.
Nasa also used this long journey in 2011 when it launched the Gravity Recovery and Interior Laboratory towards the Moon in September, which reached orbit almost four months later.
How will the lander communicate while in deep space?
Ispace has a mission control in Tokyo that it uses to communicate with and track the lander.
But the company needs large ground satellites to be able to send and receive signals from the spacecraft.
It is using the European Space Agency tracking station network, called Estrack, to establish communication links.
The network is a global system of ground stations that use large deep space antennas located in New Norcia, Western Australia, Cebreros, Spain and Malargue, Argentina.
Two smaller antennas are also located in Kourou, French Guiana. The commercial Goonhilly Earth Station in the UK, as part of the ‘Estrack extended network’, will also provide support.
This means the lander will be able to communicate with mission control throughout its journey and during its operations on the lunar surface.