Japan’s Akatsuki Reaches Venus . . . At Last

Engineers executed an innovative contingency plan to save the Akatsuki spacecraft and place it in orbit around our sister planet.

Triumph is never sweeter than when following defeat. On Sunday, December 6th, at 23:51 Universal Time, the Japanese Aerospace Exploration Agency's (JAXA) Venus Climate Orbiter Akatsuki burned four tiny reaction-control thrusters for more than 20 minutes to insert the spacecraft into Venusian orbit. The success came five years to the day after a main engine failure in 2010 caused the spacecraft to fly past Venus instead of going into orbit, leaving scientists and engineers to puzzle out a way to salvage the mission.

JAXA Mission Control

Elation in mission control at the Japanese Aerospace Exploration Agency following Akatsuki's orbital insertion.

Launched atop an H-IIA rocket from Tanegashima Space Center in Japan on May 20, 2010, Akatsuki (meaning "dawn" in Japanese) is JAXA's first mission to the planet Venus.

Venus from Akatsuki

The Ultraviolet Imager aboard Akatsuki captured this image of Venus's swirling atmosphere on December 7th from an altitude of 72,000 kilometers.

The six instruments aboard the Akatsuki spacecraft will probe Venus’s atmosphere, measuring its rotation and convection.Researchers also hope to detect evidence for Venusian lightning using a high-speed imager aboard the spacecraft. Viewing across radio, infrared, visible and ultraviolet wavelengths, the payload will also record heat radiated from the Venusian surface and may spot active volcanoes if they exist. A series of radio occultation experiments will also allow researchers to probe the depths of the Venusian atmosphere as the spacecraft makes successive passes behind the planet as seen from Earth.

In addition to the science payload, JAXA also teamed up with the Planetary Society to carry to Venus more than 260,000 people’s names and messages printed on aluminum plates aboard the spacecraft.

If At First You Don’t Succeed . . .

Akatsuki spacecraft's orbit

This diagram shows Akatsuki's hibernation orbit around the Sun (green) with respect to Earth's (blue) and Venus's (red) orbits, before its reunion with Venus on December 6, 2015.

The spacecraft ran into trouble on December 6, 2010, when its main engine failed to execute a planned 12-minute burn to enter orbit around Venus. The spacecraft emerged from radio blackout behind Venus in safe mode, having only burned its engines for 152 seconds before shutting down. Later telemetry analysis showed a pressure drop caused by a faulty check valve in the main engine, which resulted in burning an oxidizer-rich mixture beyond normal limits. The failure overheated and destroyed much of the main engine.

With its main means of propulsion ruined, Akatsuki flew past Venus and entered solar orbit, and scientists and engineers scrambled to recover the mission. They came up with an innovative solution: burn its four reaction control thrusters for over 20 minutes — much longer than before — at the next available opportunity to enter orbit around Venus. Engineers tested a series of shorter burns in 2011 to show that this attempt was indeed possible. The spacecraft was then placed in hibernation mode to extend its life.

A Space Milestone for JAXA

Akatsuki's orbit

This diagram shows Akatsuki's current (green) and future (purple) orbits. The additional engine burn planned for spring 2016 will reduce the farthest distance of the spacecraft from Venus.

Akatsuki’s successful orbital insertion marks a milestone for JAXA: it’s the first time the space agency has put a spacecraft in orbit around another planet. In 2003 JAXA's first attempt, the Nozomi mission to Mars, failed to orbit achieve orbit. Another mission, a successful solar sail demonstrator named IKAROS that deployed along with Akatsuki, was a Venus flyby mission only. And JAXA’s Hayabusa 2 sample return mission flew by Earth just last week en route to asteroid 162173 Ryugu in July 2018.

The 2015 orbital insertion places Akatsuki in a slightly wider-ranging orbit than originally intended. The planned track would have carried the spacecraft around Venus every 30 hours, with a closest approach of 300 km. This week’s burn placed Akatsuki in a 13.6-day elliptical orbit that brings it as close as 400 km to the surface. Next March, JAXA is planning a series of engine burns that should shrink Akatsuki’s elliptical orbit to a period of 9 days.

A brief press release from JAXA today reports the burn went as planned, and the spacecraft is in good health and in its expected orbit.

Space is hard, and the successful recovery of the Akatsuki mission highlights the resourcefulness of JAXA engineers. Congrats to the team on a remarkable feat to contemplate this holiday season, as Venus shines high in the east of Earth’s dawn skies. Watch for some great science out of the Akatsuki mission to come in 2016.

2 thoughts on “Japan’s Akatsuki Reaches Venus . . . At Last

  1. Anthony BarreiroAnthony Barreiro

    This is a great technical achievement, although I understand that the scientific value of the mission will be modest — the orbit is farther from Venus than originally planned, the instruments have degraded significantly during five years orbiting the Sun, and during this time ESA’s Venus Express orbiter already sent back solid data on Venus’s atmosphere and surface, including recently announced compelling evidence for volcanic activity. Still, it’s great that the JAXA team were able to salvage the mission.

    Akatsuki also serves as a demonstration of the superiority of robotic planetary exploration over human missions. If Akatsuki had been lost completely, it would have been a disappointment, but also a learning opportunity for future spacecraft design. As it was, Akatsuki could be placed in hibernation for a second attempt at orbital insertion after five years! If this had been a human mission, it would have been a disaster. A human crew would not have survived for five years waiting for a second chance. I suppose the advocates of human space flight would argue that a human mission would have much more functional redundancy, reserve life support, and the planned capacity to return to Earth. But all these things equal weight that has to be lifted off the Earth, as well as money that won’t be spent on robots. It makes a lot more sense to me to keep sending lots of robots to the other planets, rather than to invest limited resources into human spaceflight that has, at best, a long term prospect of success. Plus, robots get do-overs.

    1. LeoM

      On the contrary, this demonstrates one of the big weaknesses of robotic planetary missions. Several light-minutes from Earth, a critical manoeuvre has to be performed without any possibility to interrupt it if things go wrong. With humans present the poor burn parameters could be recognised in real time and quite probably the burn aborted before the engine is destroyed.
      But anyway this is a case of comparing apples and oranges. There are widely different rationales for robotic and human space exploration. And nobody will be sending humans to Venus any time soon!

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