Akatsuki Venus Climate Orbiter |
Akatsuki Venus Climate Orbiter |
Mar 13 2010, 11:29 AM
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#501
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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 |
I thought it was time to start a separate thread on this mission, launching soon
some good medium-resolution images of the spacecraft are available on JAXA digital archives http://jda.jaxa.jp/jda/p3_e.php?time=N&...mp;mission=4066 |
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Nov 2 2011, 09:02 AM
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#502
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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 |
here is a short release (in Japanese) on yesterday's burn
http://www.isas.jaxa.jp/j/topics/topics/2011/1101.shtml |
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Nov 2 2011, 09:33 AM
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#503
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Member Group: Members Posts: 817 Joined: 17-April 10 From: Kamakura, Japan Member No.: 5323 |
here is a short release (in Japanese) on yesterday's burn http://www.isas.jaxa.jp/j/topics/topics/2011/1101.shtml Thanks, Paolo The press release reads as follows. "About the orbit control of Akatsuki during the nearest sun approach 1st of the orbit control by RCS was conducted for some 10 minutes from 13:22 on 1 November (JST). We will be analysing the telemetry data to reflect the finding with the 2nd orbit control firing planned for 10 November." end of presss release P |
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Nov 9 2011, 09:51 AM
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#504
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Member Group: Members Posts: 817 Joined: 17-April 10 From: Kamakura, Japan Member No.: 5323 |
I know that people will laugh at me for all sorts of reasons.
However, I will say this for record! We should forget about dual liquid engines for orbital operation and instead use smaller single liquid attitude control engines for all orbital operations including orbit insertion. Instead of having half a dozen smaller engines why not have a dozen of them? I have not heard of a single case of these attitude controlers going out of control. I am saying all this because of a simple fact that larger and more complex engines seem to fail without fail! Pandaneko |
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Nov 9 2011, 12:52 PM
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#505
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Member Group: Members Posts: 613 Joined: 23-February 07 From: Occasionally in Columbia, MD Member No.: 1764 |
We should forget about dual liquid engines for orbital operation and instead use smaller single liquid attitude control engines for all orbital operations including orbit insertion. Instead of having half a dozen smaller engines why not have a dozen of them? I have not heard of a single case of these attitude controlers going out of control. I am saying all this because of a simple fact that larger and more complex engines seem to fail without fail! Well, this is exactly the trade that any system design has to make.... unfortunately such decisions have to be made on very incomplete data : larger engines do not always fail, and small monopropellant thrusters are not immune to failure either. Consider the following : 1. you'd need 20 (not an extra 6) small 20N thrusters to give you the thrust of the biprop engine. Even if the individual failure rate of these engines is lower than the biprop, there are now 20 of them to go wrong (e.g. a valve stick 'on') 2. the specific impulse of the monoprop is less (and small thrusters are also less efficient than a large one). Via the rocket equation, this can have a huge impact on the vehicle mass. 3. the root cause of the Akatsuki failure (viz poor helium flow through the check valve on the fuel-side pressurization) might have caused enough underperfomance of a monopropellant system to prevent orbit insertion anyway. So what you suggest makes sense, and engineers do it when they can get away without a big engine, but missions typically demand the performance that only a biprop can give. |
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Nov 9 2011, 01:19 PM
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#506
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Member Group: Members Posts: 817 Joined: 17-April 10 From: Kamakura, Japan Member No.: 5323 |
Well, this is exactly the trade that any system design has to make.... and engineers do it when they can get away without a big engine, but missions typically demand the performance that only a biprop can give. Thanks, Ralph I have been frustrated a lot. I want to see lots and lots of different facets of our other planets. I probably have another 25 years and these satellites keep failing. I wish they launched at least one satellite every year. Yes, trade-offs..., yes, and thanks again for further thoughts. Pandaneko |
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