Akatsuki Venus Climate Orbiter |
Akatsuki Venus Climate Orbiter |
Sep 8 2011, 10:02 AM
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#466
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Member Group: Members Posts: 817 Joined: 17-April 10 From: Kamakura, Japan Member No.: 5323 |
JAXA HP is saying;
OME was fired for 2 seconds at 11:50 (JST) on 7 September as planned in order to establish quantitatively external disturbances (such as lateral propulsion) and the telemetry data is now being analysed. The 20 seconds firing planned for 14th will be used to verify the attitue control logic system. P |
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Sep 9 2011, 11:43 AM
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#467
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Senior Member Group: Members Posts: 1729 Joined: 3-August 06 From: 43° 35' 53" N 1° 26' 35" E Member No.: 1004 |
Pandaneko, can you confirm the Google translation of today's JAXA release that the measured acceleration was less than expected?
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Sep 9 2011, 02:00 PM
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#468
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Member Group: Members Posts: 817 Joined: 17-April 10 From: Kamakura, Japan Member No.: 5323 |
Pandaneko, can you confirm the Google translation of today's JAXA release that the measured acceleration was less than expected? Yes, I confirm that the measued acceleration was less than expected. As a result the planned firing of 20 seconds on 14th will be shortened to 4 seconds in order to re-check the status of OME. Apparently, there is no change to Akatsuki after the first firing. What does all this mean? Someting fell off again before the first firing? Oxidiser leak? Perhaps, helium, less of it remaining? P |
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Sep 9 2011, 02:31 PM
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#469
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Senior Member Group: Members Posts: 1729 Joined: 3-August 06 From: 43° 35' 53" N 1° 26' 35" E Member No.: 1004 |
if the "bell" of the thruster is physically damaged, gases would not expand the way they should, which could explain the "loss of acceleration"
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Sep 10 2011, 12:34 PM
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#470
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Senior Member Group: Members Posts: 1729 Joined: 3-August 06 From: 43° 35' 53" N 1° 26' 35" E Member No.: 1004 |
according to the NASAspaceflight forum the engine provided only 13 p.c. of the expected thrust. very bad news...
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Sep 10 2011, 12:53 PM
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#471
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Member Group: Members Posts: 817 Joined: 17-April 10 From: Kamakura, Japan Member No.: 5323 |
Yes, I confirm that the measued acceleration was less than expected. As a result the planned firing of 20 seconds on 14th will be shortened to 4 seconds in order to re-check the status of OME. My apologies. Next firing will be "about" 5 seconds, not 4 seconds. P |
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Sep 11 2011, 02:18 PM
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#472
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Member Group: Members Posts: 817 Joined: 17-April 10 From: Kamakura, Japan Member No.: 5323 |
I am no longer sure if Akatsuki will be able to be of any use because today's Yomiuri newspaper says;
"the propulsion measued at the first firing was one ninth of the expected value" I do not know how much fuel there still is left, but my gut feeling is that Akatsuki will run out of fuel. Sad... P |
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Sep 11 2011, 03:46 PM
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#473
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Senior Member Group: Members Posts: 1729 Joined: 3-August 06 From: 43° 35' 53" N 1° 26' 35" E Member No.: 1004 |
they can still make it to venus using the RCS thrusters, but the mission will be shorter
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Sep 15 2011, 01:24 PM
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#474
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Member Group: Members Posts: 817 Joined: 17-April 10 From: Kamakura, Japan Member No.: 5323 |
re second firing test on 14th, same as the 1st, propulsion less than expected (no value given in today's JAXA release). JAXA will think about what to do next based on these lower values.
They may announce something more concrete. P |
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Sep 16 2011, 02:33 AM
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#475
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Merciless Robot Group: Admin Posts: 8783 Joined: 8-December 05 From: Los Angeles Member No.: 602 |
...thanks for the update, Pandaneko.
The (possibly) good news here is that the engine is still capable of generating at least SOME delta-V, so instead of merely jettisoning it & relying entirely on the RCS some productive maneuvers seem possible at first glance. Big unknown here is whether the thrust vector is still aligned properly (thinking nozzle damage here) or perhaps even stable & predictable. -------------------- A few will take this knowledge and use this power of a dream realized as a force for change, an impetus for further discovery to make less ancient dreams real.
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Sep 16 2011, 05:20 AM
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#476
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Member Group: Members Posts: 214 Joined: 30-December 05 Member No.: 628 |
I recall contingency plans to jettison excess oxidizer, but I believe that fuel not burned in the main engine can be burned in the RCS. (The engineering details are far from clear to me, because chemically speaking oxidizer should either be required or not required, regardless of what engine is being used.) If however, the excess fuel is somehow usable by the RCS then the question becomes where it can be used most efficiently in terms of changing the course of the spacecraft. If the OME is 87% less efficient that originally planned, then unless the RCS is even less efficient that that, it probably doesn't make sense to burn any of the remaining fuel in the OME.
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Sep 16 2011, 05:31 AM
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#477
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Senior Member Group: Members Posts: 1729 Joined: 3-August 06 From: 43° 35' 53" N 1° 26' 35" E Member No.: 1004 |
the OME is a bi-propellant thruster, i.e. it generates gas by the spontaneous combustion of two liquids (hydrazine fuel and nitrogen tetroxide oxidizer).
RCS thrusters are mono-propellant thrusters, i.e. they generate gas by decomposing hydrazine on a catalyst bead. Think of your car's catalyser: that is a remote relative of this technology. This is why RCS thrusters need no oxidizer. Edit: the OME nominally provides 500 N of thrust, and should now provide about 1/9th of that, i.e. about 55 N. There are two families of RCS: one providing 23 N and the other 3 N (for roll attitude control only, probably not usable for trajectory control). I am not sure that using the OME would be a good idea. it would probably use too much hydrazine to provide too little thrust (I don't have info on the fuel consumption of the different thrusters but I assume that that of the OME would be larger than that of the RCS) |
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Sep 16 2011, 12:39 PM
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#478
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Senior Member Group: Members Posts: 1729 Joined: 3-August 06 From: 43° 35' 53" N 1° 26' 35" E Member No.: 1004 |
A Mainichi Daily News release: Venus probe unlikely to enter orbit fit for atmospheric observation
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Sep 16 2011, 10:41 PM
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#479
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Senior Member Group: Members Posts: 2079 Joined: 13-February 10 From: Ontario Member No.: 5221 |
Am I right to assume that aerobraking, Magellan style, isn't plausible, if worst comes to worst and the engine is kaput?
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Sep 16 2011, 11:06 PM
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#480
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Member Group: Members Posts: 540 Joined: 17-November 05 From: Oklahoma Member No.: 557 |
Magellan was already in orbit, and very gradually lowered that orbit a bit at a time with atmospheric friction that was within tolerable limits. To bleed off enough speed all at once to make orbital insertion at the rate Akasuki is going - no, you would be fried. BUT ... if you could manage to get into an orbit with the thrusters, then I don't know, you might look into using aerobraking to get into a lower and more favorable orbit.
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