Akatsuki Venus Climate Orbiter Options

[Paolo]

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

[Paolo]

here is a short release (in Japanese) on yesterday's burn
http://www.isas.jaxa.jp/j/topics/topics/2011/1101.shtml

[pandaneko]

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

[pandaneko]

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

[rlorenz]

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.

[pandaneko]

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