Emily Lakdawalla • Jul 02, 2011
Latest report from Akatsuki failure review board
JAXA held a press conference on June 30 about the latest report from the review board that is charged with finding out what exactly caused Akatsuki's failure to enter orbit at Venus, and what that implies for the possibility of Akatsuki to try again when it returns to Venus in 2015 or 2016. The report can be found here (in Japanese) -- all 61 pages of it. The Japan Broadcasting Corporation posted this brief summary of the report:
Reverse fuel flow clogs valve in Akatsuki failure
Japan's aerospace agency says an experiment has supported its assumption that a clogged valve in a pipe linked to a fuel tank caused the failure of the Akatsuki probe to enter orbit around Venus.
The Japan Aerospace Exploration Agency earlier analyzed data sent from the Venus probe, which failed in December of last year. The agency concluded that a valve linked to a fuel tank is presumed to have become clogged up, resulting in an insufficient fuel supply to the engine.
It had conducted experiments on the ground to support its theory since March. It says oxidizer that boosts fuel combustion ran back and came into contact with fuel. This triggered a chemical reaction that caused crystals to form, clogging the valve.
The valve is designed to prevent the reverse flow of oxidizer. But the chemical is believed to have seeped in despite materials in place that should have blocked leaks.
The agency says it plans to conduct an engine thrust test in space this fall to study the possibility of another attempt to place the Akatsuki probe in Venus orbit in the next fly-by in 6 years.
Thursday, June 30, 2011 10:01 +0900 (JST)
Twitter user @ hee913758 posted via Twitter a bit more detail gleaned from the report. They're planning to conduct a test of the orbit entry rocket in September. If it's found to work, they'll try again to use the main motor to go into Venus orbit. If the orbit entry motor doesn't work, they've come up with a typical JAXA creative workaround to save a seemingly unsalvagable mission: they'll dump all their oxidizer to reduce their mass and then attempt to enter orbit using only their reaction control system. Obviously this would shorten the lifetime of the in-orbit mission substantially, but better something than nothing!
When JAXA had designed Akatsuki, they had taken it into account that the oxidizer might leak through the valve. But actually, the large amount of oxidizer seeped (rather than LEAKED) through the polymer of the seal which fills in the crack of the valve.
Vaporized fuel (not liquid) + oxidizer -> crystal (blockage of the valve) [ 6N2H4 + 3N2O4 -> 4NH4NO3 (ammonium nitrate) + 2N2H4 + 3N2 ]
The oxidizer seeped through the valve -> ran back -> mixed w/ vaporized fuel at around the fuel valve -> crystallized by chemical reaction.
And it's also highly possible that the nozzle would be broken because the fuel supply had been blocked -> abnormal combustion -> the nozzle had heated up and damaged.
JAXA is going to conduct Akatsuki's thruster (OME) test in space in September 2011. If OME works, -> [Venus] re-entry in Nov.2015. If OME is broken -> dump all the oxidizer to lighten the weight so that it can speed down effciently. And try to re-enter other Venus orbit by RCS(Reaction Control System) in Nov.2015.
That's all. Thank you. ..I can't help thinking it's all because they didn't have enough budget. ..Re-entry by RCS..they never give up...
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