Back in 2010, we were sad to hear that JAXA’s Akatsuki orbiter experienced a malfunction during its attempt to insert itself into orbit around Venus. A planned twelve minute engine burn ended prematurely after about only three minutes, the result of salt formation causing a fault in a check valve. You might expect that that would have spelled the end to the mission, and Akatsuki would have spent eternity orbiting the Sun. Fortunately, JAXA would get a second chance to try their insertion effort again, but they’d have to wait nearly five years for both the craft and Venus to be in the right places for the attempt.
Orbit control test and maneuvers were conducted in 2011, and then again in 2015, setting the stage for an orbit insertion attempt. Tests showed that Akatsuki’s Orbital Maneuver Engine (OME), its main engine, couldn’t provide the thrust needed for the second insertion attempt. Hope fell to the craft’s attitude-adjustment engines.
65 kg of oxidizer fuel that would have been used by the no-longer-functional main engine was dumped to lighten the craft and allow it to be more maneuverable. In December, 2015, exactly five years after the first attempt to make orbit, four of the spacecraft’s secondary attitude control thrusters burned for 20 minutes and 33 seconds, slowing the spacecraft enough to be captured by Venus’s gravitational hold. The attempt was a success. Akatsuki entered Venusian orbit and began to conduct its mission objectives.
The final orbit is much further (between 4,000 km and 370,000 km versus the planned 300 km to 80,00 km) from our sister planet than originally planned. Instead of orbiting Venus once every 30 hours, Akatsuki orbits once every 9 days.
So, while not exactly as planned, Akatsuki is still able to conduct great science. Akatsuki has already observed an interesting atmospheric gravity wave, peered through the clouds in infrared to reveal an equatorial jet, and sent back stunning images of our closest planetary neighbor.
You can stay up-to-date with Akatsuki at JAXA’s English language version of their project page.