Hurtling around the planet Venus is Japan's Akatsuki space probe. The Venus probe — also known as the Venus Climate Orbiter (VCO) and PLANET-C — was sent to study the erratic atmospheric environment of the second planet away from Earth in the solar system and was meant to spend two years there. However, the Venus climate orbiter didn't get there without encountering some mission-critical issues. At one point, suffering from a complete engine burn-out, it was flung out of the orbit of Venus and sent flying around the Sun instead.
But its team of dedicated engineers wasn't about to abandon their beloved Akatsuki spacecraft that just because of some lousy critical engine failure, though. Using their wits alongside the technology still available aboard PLANET-C, they decided to postpone the Venus mission and send the Japanese space probe slingshotting around the Sun instead. After five whole years of "sleep mode" hibernation, the probe was in the proper place to attempt another Venus orbit.
Despite the longer time than expected, the Venus space probe was able to make it back to Venus safe and sound in 2015 — escaping the clutches of the Sun and boosting itself back to its original destination. It took a few extra years, but the story of Akatsuki — which means "dawn" in Japanese — is an inspiring one of scientific patience, determination, and the resilience required in space exploration.
Salt Deposits Likely Jammed The Probe's Valves
Akatsuki's main engine experienced a total failure, causing it to stray far from its orbital destination — but what caused it to fail? A well-tested engine on a $300 million dollar mission isn't expected to just give up and die out of nowhere. Looking into the issue, scientists deduced that the most likely reason is due to a valve jam caused by salt deposits. Sticking between the helium tank and the fuel tank, combustion temperatures soared through the roof, or, in this case, the engine combustion chamber.
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It Totally Missed Its Target But Didn't Have Enough Fuel To Return To Earth
On its first try, Akatsuki encountered engine issues — shutting down the spacecraft and completely failing its mission. When the spacecraft went to enter Venus's orbit, its main engine fizzled out, causing the craft to go shooting into space. However, its team of scientists and engineers weren't ready to call the $300 million mission a total flop. Because it didn't have the resources to return to Earth, scientists allowed it to continue its path towards the Sun, then put it into sleep mode. Akatsuki then rested in its orbit until it got another chance to propel itself towards Venus.
It Remained In Hibernation Until It Could Make Another Shot At Venus
In order to keep Akatsuki functional after its five-year orbit around the Sun, it needed to preserve its battery life. The probe was only designed to last for four and a half years, meaning that its batteries would be dead by the time it was able to make another shot for its destination. To keep Akatsuki alive, the engineers put the probe to sleep — literally into safe mode while it remained unused. Waking up from its slumber to launch towards the small, hot planet, it was alive and well after its hibernation — its batteries ready to go for at least two more years.
Its Main Engine Was Totally Dead So It Used Thrusters To Propel Itself Back To Venus
The reason why the Akatsuki probe missed its mark is due to the failure of its main engine. Engines don't just come back to life in deep space — when they're dead, they're useless. Needless to say, Akatsuki's main engine has been long dead — so scientists had to find a way to propel the probe without it. Instead of relying on the main engine, Akatsuki used its thrusters to shoot itself away from the Sun and back into the orbit of Venus. After five years, to the day, the time was right — Akatsuki launched itself towards Venus and successfully entered the planet's orbit.Overall, the boost to send Akatsuki into orbit only took about 20 minutes, but required just the right positioning, which is why it had taken five years for the time to be right for another attempt.
Its Reliance On Solar Power Makes Being In The Shadow Of Venus An Engineering Risk
Escaping a near-failed mission, Akatsuki returned to Venus after five years to continue where it left off. As of 2018, its orbit is now much more elliptical than intended, which presents some engineering risks. Because of the wide orbit, the probe rests in the shadow of Venus each day.
Designed to siphon energy from solar power, the lack of sunlight forces Akatsuki to use its batteries. Its batteries were only made to last for four and a half years, and it can only be without solar power for 90 minutes tops before it has to switch to using them. Without the Sun, the lifespan of the probe has been shortened to two years.
In general this is good news, but there is one thing to be slightly concerned about: the equatorial orbit necessarily has Akatsuki in Venus' shadow for some part of each day, which robs it of solar power and requires it to rely on batteries. Hirose said that the spacecraft cannot be permitted to be in shadow for longer than 90 minutes. Small changes in shape and orientation of the orbit can cause large differences in time spent in eclipse. They didn't discuss this in any further detail so I will assume unless told otherwise that the orbit that they are currently in poses no current danger to the spacecraft. Over the two-year nominal mission, the orbit inclination will increase to 25 degrees.
It Launched Alongside IKAROS - The First Spacecraft To Use A Solar Sail In Interplanetary Space
Akatsuki didn't go flying off into space by itself. The probe launched alongside an experimental spacecraft on a mission to test solar sail technology — the first attempt of its kind. The spacecraft, under the acronym and nickname IKAROS, was also destined for Venus. IKAROS gathered solar power through its sail and harnessed it for use as its main method of maneuvering around space. While IKAROS arrived at Venus in 2010, its partner Akatsuki fizzled out, losing control of orbital entry and parting ways with its solar friend.