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Japan Releases AKATSUKI's Pictures of Venus (discovery.com)

Posted by samzenpus on from the worth-a-thousand-words dept.

astroengine writes: The Japanese space agency JAXA has released a confirmation that their Venus mission Akatsuki did indeed enter orbit at Venus on Dec. 7 (JST) — releasing unprocessed images of the Venusian atmosphere as it entered orbit. The spacecraft is currently in a highly-elliptical 13-day, 14-hour orbit around the planet, coming within 400 kilometers (248 miles) at its closest point and reaching 440,000 kilometers (243,400 miles) away at its farthest. This mission has just become the most unlikely success story of 2015 after "missing" its intended Venus orbit way back in 2010.

5 of 44 comments (clear)

  1. As for why... by Rei · · Score: 5, Informative

    ... all of this trouble happened, the Planetary Society blog had a nice detailed writeup a while back. The "short" of it? Akatsuki has a new type of primary thruster based on ceramics to withstand the heat rather than exotic materials like dicilicide-lined niobium as are normally used on these sorts of small hypergolic thrusters; they wanted to prove the new technology. You generally run thrusters a bit fuel-rich and inject it in such a manner as to try limit combustion near the chamber and nozzle walls to keep the temperature down. Well, the pressurant valve to the fuel tank didn't open all the way (they think it corroded) but the oxidizer pressure valve opened all the way. So the burn kept getting more and more oxidizer rich, meaning hotter chamber and nozzle walls way past the design limits, until they cracked and the nozzle simply flew off.

    The only reason they were able to salvage this was because another unusual choice they did: to save mass, they implemented a more complicated hydrazine (fuel) feed system, allowing them to use the same hydrazine suppy for the main engine as for the small monopropellant RCS thrusters (tiny, low-efficiency maneuvering thrusters). Because they did this, they were able to take the fuel that was planned for the main engine and route it instead to the RCS engines. While they're less efficient and much lower thrust, they had enough excess fuel to pull off the maneuver (after first making the craft lighter by dumping the now-unneeded oxidizer, of course!)

    --
    Nothing says 'welcome to the neighborhood' like a gunny sack full of dead squirrels.
    1. Re:As for why... by Anonymous Coward · · Score: 2, Informative

      Hydrazine does burn hotter with oxidizer (thus faster exhaust gases, better efficiency), yes.

      (Incidentally, oxygen would not be the oxidizer of choice for a deep-space mission, since it will boil off -- dinitrogen tetroxide is the usual choice to go with hydrazine. Liquid at room temperature, with ignition on contact. Also horribly toxic.)

    2. Re:As for why... by Brett+Buck · · Score: 4, Informative

      Nice summary! I would note that the ability to interconnect the bipropellant hydrazine supply to the monopropellant engines is not an "unusual choice", it's common bordering on ubiquitous. Pretty much in order to provide this option as a backup.And it has been used in exactly this way (for more-or-less the same reason) in the very recent past.

    3. Re:As for why... by Rei · · Score: 3, Informative

      I can think of a couple examples of spacecraft where it's been used that way (the Planetary Society's writeup mentions MESSENGER and MRO), but not many. Most of the designs I've seen use separate systems, for simplicity and supposedly extra reliability (the irony here being that the lack of separation on the systems is what saved Akatsuki). Cassini, for example has fully independent systems - like Akatsuki its main engine is hydrazine/N2O4 and its RCS is monoprop hydrazine, but the RCS has its own separate tank.

      --
      Nothing says 'welcome to the neighborhood' like a gunny sack full of dead squirrels.
  2. Re:Jebediah Approves by Fire_Wraith · · Score: 4, Informative

    Not to the original, but here's a link to the image of the series of maneuvers they had to do to get into orbit, over five years:
    http://goo.gl/ONZpns

    Full article here: http://gizmodo.com/tonight-is-...