Akatsuki returns from the dead
[This article was originally published in Boulder Weekly on January 19th, 2017.]
It is Dec. 7, 2015. We’re in Sagamihara, Japan, a little southwest of Tokyo. On a clear day like today, you can just make out the silhouette of Mount Fuji in the distance. We are standing outside of the control room of the Japanese Aerospace eXploration Agency (JAXA), watching as a spacecraft named Akatsuki is preparing for its arrival at Venus.
Success here means the beginning of a promising collaboration between JAXA and NASA scientists — mostly between JAXA and Boulder scientists, since four of the eight scientists chosen by NASA to work with the Japanese on this ground-breaking mission are based in Boulder. The team includes myself, along with Mark Bullock, Kandis Lea Jessup and Eliot Young, all from the Southwest Research Institute.
“That chart on the far screen shows the speed of the spacecraft relative to the Earth,” says Takehiko Satoh, current project scientist of the mission. “If the pointer reaches at least 80 percent of the target, that means we have made it into orbit.”
An announcement is made. The pointer begins to climb. The tune from the Mountain Climber game in The Price is Right pops into my head. You know, the game where the little pickax-wielding mountain climber ascends one step for every dollar you’ve missed the target price by. If you miss by too much, the little climber hikes past the summit and falls to his death. This time, I do not want to hear the music stop. I’m rooting for the little climber to make it all the way to the top.
Everyone in the control room looks very nervous. This is not surprising, they have all been here before. Five years ago to the day, in fact, when things did not go very well at all.
On Dec. 7, 2010, we were following the proceedings via Twitter from 6,000 miles away. The Akatsuki Twitter feed had announced the successful start of the orbit insertion burn. The time for the end of the burn came and went, but no new information was released. Hours went by in tweetless silence. Akatsuki’s faint signal was finally detected, but all was not well. Akatsuki was spinning in an orientation that it was programmed to assume when problems are detected, a condition called “safe mode.”
The engineers eventually determined that a single valve on the fuel line had failed. This caused the rocket exhaust to heat the ceramic rocket nozzle. The nozzle soon cracked, which caused the spacecraft to spin like a garden sprinkler. The spacecraft computer recognized that this was a “bad thing” and stopped the burn before things got even worse. This quick reaction saved the spacecraft, but it meant that Akatsuki would not be captured into orbit. Venus was quickly fading in the rear-view mirror.
“The orbit insertion failure was shocking and sad, but there was a thin sliver of hope,” says Ralph Lorenz of the Applied Physics Laboratory at Johns Hopkins University. “Having followed spacecraft systems failures closely over the years, I knew that JAXA has been tenacious and ingenious in devising recoveries from failures.”
The engineers discovered that Akatsuki would, after orbiting the Sun for five years in lonely silence, come close enough to Venus to try to enter orbit again. How can that be helpful, since the main rocket engine had been destroyed? In addition to the main rocket, spacecraft also carry several low-thrust rockets for fine adjustments in control and pointing. These were still operational. However, they were never intended to be fired as long as would be necessary to get into orbit.
No spacecraft had ever attempted to achieve orbit in this way before. Why would it? It would be like fighting a house fire with a garden hose instead of the high pressure water from a hydrant. But on Dec. 7, 2015, because Akatsuki’s hydrant is broken, that is essentially what’s being attempted in a last-ditch effort to help the spacecraft achieve its goals.
Akatsuki’s primary goal is to explain why the atmosphere of Venus whirls around the planet at speeds approaching those of the Shinkansen “bullet trains” for which Japan is famous. A hundred years ago, we would forecast the weather on Earth by measuring the wind speeds only at the surface. These forecasts were very poor. Today, we also release weather balloons, to measure the wind speeds at many altitudes, improving our picture of the current atmospheric condition.
By taking pictures of Venus at several different wavelengths from the ultraviolet to the infrared, Akatsuki can measure winds at different altitudes by tracking how cloud features move in the images. If they can explain the workings of an atmosphere as unusual as Venus — especially with regard to greenhouse warming and the effects of clouds on planetary temperature — the Akatsuki team hopes also to better understand our own atmosphere.
Back in the control room, things are going well. The curve climbs with agonizing slowness to 80 percent and beyond, actually reaching 105 percent before the rockets stopped. There is brief applause and a few handshakes after the program manager formally announces that the burn was executed successfully and Akatsuki is in orbit. Then everyone quickly and dutifully returns to their work.
Akatsuki has now been in orbit for more than a year, and a new chapter in history is being written by this successful American-Japanese scientific collaboration. Investigators on both sides of the Pacific now pour over the images, yearning to understand what they can, to help us learn about the unusual atmosphere of Venus.
Kevin McGouldrick is a Research Scientist at the University of Colorado-Boulder’s Laboratory for Atmospheric and Space Physics, and a NASA participating scientist in residence in Japan with the Akatsuki mission to Venus.
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