Akatsuki Update: Fuel Pressure Drop Likely Caused Insertion Failure

by Nicholos Wethington on December 11, 2010

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An image showing Venus from three of Akatsuki's different instruments, taken during a functions check of the probe. Akatsuki was 600,000 km (373,00 miles) from Venus when these images were taken. The red and blue are false color. From left to right: the ultraviolet imager (UVI), 1 micron camera (IR1) and long wave infrared camera (LIR). Image Credit: ISAS

While JAXA is still trying to get an exact handle on the problems that the Akatsuki probe sent to Venus encountered, there is a little bit of news leaking out. JAXA held a press conference last night, and the Yomiuri Shimbun newspaper has a brief recap of the conference. During some of the systems checks on the probe, it also took a few images of Venus, and many of the instruments on the probe appear to be working okay – it’s the engine that’s having the most problems.

Here’s what is known so far: Akatsuki’s engine did perform a burn to slow it down, but 152 seconds into the burn the fuel pressure dropped and the probe became unbalanced. Because the retrofiring of the rockets failed to slow down the probe enough for Venus to capture it, it was unable to enter into orbit around the planet, and then went into safe mode.

As to what caused the sudden drop in fuel, JAXA currently suspects that there is a damaged pipe or valve that reduced the flow of helium into the engine, but that is still speculative. As the engine burns propellant (Akatsuki uses a hydrazine/nitrogen tetroxide engine), helium flows into the tank to maintain the pressure. Something failed in the helium injection flow, and precipitated a drop in internal tank pressure, reducing the flow of propellant and causing the engines to stop burning.

The ceramic nozzle of the engine is also thought to have been damaged by the misfiring, which may make the task of trying to get the probe to Venus when the chance comes around again in six years a daunting one.

An image of Venus taken by Akatsuki's Ultraviolet imager (UVI) at the 365 nm wavelength, the color is artificial. Field of View: 12 deg x 12 deg Image Credit: ISAS

JAXA is planning on doing some tests on the ground to maybe come to a workaround of this problem. There seems to be plenty of fuel left, which is good news, but the damaged nozzle is not. Maybe they’ll call in some Hayabusa team members, and pull it through.

The Christian Science Monitor reported yesterday that there is some speculation that something may have struck the probe, though this most recent press conference from JAXA makes no mention of it.

Also, Emily Lakdawalla at The Planetary Society Blog reprinted some tweets translated from Japanese that summarize details from the press conference, as well as the Yomiuri Shimbun article.

Source: Yomiuri Shimbun, ISAS, the Planetary Society Blog,

Olaf December 11, 2010 at 8:52 AM

“something may have struck the probe…”

What is this evidence for that “something”?
I expect if “something struck the probe” then it makes it spinning.

Torbjorn Larsson OM December 12, 2010 at 8:07 AM

Well, it *was* spinning, but according to the PlanSoc timeline spinning up happened after Akatsuki autonomously switched to reaction wheel attitude control in response to the reaction (thruster) control failure, and of course eventually stabilized safe mode: can’t have rockets burn willy-nilly when going safe and for an indefinite time.

Torbjorn Larsson OM December 12, 2010 at 8:12 AM

I goofed (again, today): on better reading, it was safe mode that meant spinning up for stabilization.

hydrazine December 13, 2010 at 3:46 AM

Well, not necessarily. The probe weighs 320 kg (710 lb). If hit by a meteoroid the size of a pee the craft itself wouldn’t show much for the collision except a small hole or perhaps a damaged valve or a pipe. Maybe. It would be quite a bit of bad luck and I think it’s virtually impossible to confirm. That’s why I think this hypothesis is just someone speculating.

Regards,
/hydrazine

Manu December 12, 2010 at 6:32 AM

Do these images mean the spacecraft has stopped spinning?

Torbjorn Larsson OM December 12, 2010 at 8:09 AM

Someone (blogger, not JAXA AFAIU) mentioned aerocapture as possible (?) “last attempt” on the PlanSoc blog. Or is it PlanSO.oc blog now? :-D

Aqua December 12, 2010 at 8:44 AM

This ranks right up there with the biggest spaceflight bummer of the year…. dzzzz.

dwdeclare December 12, 2010 at 9:40 AM

“Pressure Drop Likely Caused Insertion Failure”…maybe Venus just isn’t pretty enough to keep Akatsuki’s pressure up.

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