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Akatsuki Venus Climate Orbiter
Paolo
post Oct 27 2011, 05:53 PM
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this was posted earlier today (without any link or other references) on the NASAspaceflight forum:

QUOTE
Akatsuki was complete the oxidizer dump operations in Oct. 6, 12, 13th (each 6 min. 9min. 9min).

Three RCS burns are planned in Nov. 1, 10, 21th.
First two burn duration is 600 sec, delta-V is 90 m/s.
Third burn duration will be adjusted based on necessary delta-V.


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I'm one of the most durable and fervent advocates of space exploration, but my take is that we could do it robotically at far less cost and far greater quantity and quality of results.

James Van Allen
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Paolo
post Oct 28 2011, 05:13 AM
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a new pdf release by JAXA http://www.jaxa.jp/press/2011/10/20111026_sac_akatsuki.pdf


--------------------
I'm one of the most durable and fervent advocates of space exploration, but my take is that we could do it robotically at far less cost and far greater quantity and quality of results.

James Van Allen
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pandaneko
post Oct 28 2011, 10:30 AM
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QUOTE (Paolo @ Oct 28 2011, 02:13 PM) *



Thanks, Paolo

There is nothing we do not know on pages 1 to 3. These pages talk about history up until now. So, my translation starts with page 4 as follows.

page 4

3.Operation of oxidiser dumping

This was conducted on 6th, 12th, and 13th October 2011 for 6 minutes, 9 minutes, and 9 minutes respectively.

(There are two graphs here)

(with the graph on the left the vertical is temp and the horizontal is time in minute relative to the start of dumping of NTO)

(This graph is the temp history and)

red: fuel propellant valve temp
blue: oxidiser propellant valve temp
purple: oxidiser tank temp
green: injector temp

(with the graph on the right the vertical is acceleration in m/sxs and the horizontal is the measued value of acceleration)

(there are 4 zones from left to right and the are)

blue: test discharge (1 min)
red: 1st discharge (6 min)
green: 2nd discharge (9 min)
purple: 3rd discharge (9 min)

(top left character string says) : RCS settling (3 seconds)
(bottm righ string pointing to a sudden drop says) : end of discharge


Although power is supplied to the propellant valve on the fuel side while discharging operation is in progress there is no cooling by fuel available. Thus, it was feared that the temp of the fuel side propellant valve might exceed the allowed limit. Also, freezing of the OME injector was feared. However, we judged that discharging operation was feasible from the ground tests and analyses as long as we divide the operation into several times. It was confirmed that the discharging operation was completed at the 3rd time without exceeding the allowed temp limit.


The sudden drop in acceleration during the 3rd discharging operation indicatef that pressurising helium gas pushed through and discharging was complete as planned.

end of page 4 (and 2 more pages to go and they will follow tommorrow)

P
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rlorenz
post Oct 28 2011, 11:19 PM
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QUOTE (pandaneko @ Oct 28 2011, 05:30 AM) *
The sudden drop in acceleration during the 3rd discharging operation indicatef that pressurising helium gas pushed through and discharging was complete as planned.


Thanks again for these ongoing posts.

I'm wondering if this is a spaceflight first (dumping oxidiser this way) ?
I could imagine it may be - these are rather unusual circumstances.

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pandaneko
post Oct 29 2011, 10:25 AM
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QUOTE (Paolo @ Oct 28 2011, 02:13 PM) *


above for ease of reference

page 5

4.Considerations relating to orbit control by RCS


1. Maintaining the thermal balance in the thruster 's catalytic layers during the continuous firing

Main points of concern with the continuous firing of RCS and our current stance are as follows.

By adopting the orbit control attitude (+X pointing in the sun's direction) the +X side of the thruster will be in a thermally difficult state. However, analyses confirmed that the temp of the catalytic layers during the burn will be in an equiribruim state.



2. Temp rise of the propellant valve by the heat soakback (*) after the continuous firing

Although the temp of the thruster valve will increase by the heat soakback after the continuous firing it was confirmed that the rise will remain within the allowed temp range.

* This is a occurrence in which the temp of the propellant valve kept cooled by the supplied fuel will increase by the heat conducted from the hot burner after the continuous firing of the engine


3 Temp increase of various parts of the probe due to the attitude maintenance operation during the continuous firing

Orbit control attitude (+X sun pointing direction) will lead to temp increase in the various parts of the probe. However, we will change back to +Z sun pointing direction immediatelyy after the firing and it was confirmed that all parts of the probe will not exceed the allowed temp range.


Conclusion:

Based on the report of 30 September at the investigation meeting regarding the RCS continuous firing and records of similar burning in orbit by other satellites in addition to above further consideration as reported here we reached a conclusion that an orbit control firing by RCS will be conducted in November this year during a nearest sun approach.

end of page 5

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pandaneko
post Oct 30 2011, 09:43 AM
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QUOTE (Paolo @ Oct 28 2011, 02:13 PM) *


above for ease of reference

page 6


5.Orbit control plan at the nearest sun (I know that there is a special term for this, but I keep forgetting it and I am more comfortable with nearest sun, P) point

(There is a schematic and I will translate the character strings on it later. Main texts first)

Orbit control by the RCS engines at the nearest sun approach point



(1st control on 1 November) ΔV : 90m/s

(2nd contorl on 10 November) ΔV : 90m/s
(3rd control on 21 November) ΔV : approx. 70m/s

We will carry out the 3rd control by taking into account the result of ultra accurate measurement of orbits effected by earlier two controls (thrust direction and magnitude will be dependent on the errors due to the first two controls).


※ These orbit changes are carried out in order to reunite with Venus after 2015.


※ There is a possibility that our orbit control plan may be altered depending on the assessment taking place from now on.

(the schematic title says): Relative positions between the probe, Venus and the earth at the time of Akatsuki orbital controls

(the unit, both vertical and horizontal, is 10 to the power of 8km)
(outer circle is earth, inner circle is Akatsuki and in between is the Venus orbit)

(2 characters around 9:00 are): top is Sept 2011 and bottom is test firing

(bottom character on Venus orbit is): Nov 2011

(on earth orbit at 1 O'clock is): Nov 2011 (and at around 3:00 on the same earth orbit is ): Sept 2011

(at around 4:30 on Akatsuki orbit is): nearesst sun orbit control

end of page 6

P


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pandaneko
post Oct 31 2011, 10:01 AM
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QUOTE (Paolo @ Oct 28 2011, 02:13 PM) *


above for ease of reference

page 7

6.Summary of this report

1.Akatsuki's current health and operational plan from now

All insturments on board are healthy and the satellite is circulating around the Sun

From the in-orbit firing of the OME conducted in September this year (2011) we judged that OME will not be able to produce an effective propulsion required for further orbit controls and that any further orbit control will have to be achieved by the RCS engines

Dumping of unrequired oxidiser was conducted in October this year in order to reduce the satellite mass and this operation was confirmed to be a success from telemetry data, all aprts of the satellite not exceeding the allowed limit in temp.

2. Nearest sun approach orbit control

Orbit control by RCS engines is planned for November this year as the satellite makes a nearest approach to the Sun.

We investigated the risks involved in the orbit control by RCS and it has been confirmed that there is a good scope for safe operation.

Orbit control will be divided into three parts, each taking place on 1, 10, and 21 November and depending on our further consideration and the outcome of controls the orbit control plan may change.

end of page 7 and end of this particular report

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Paolo
post Oct 31 2011, 10:18 AM
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thanks Pandaneko, very informative, as always!


--------------------
I'm one of the most durable and fervent advocates of space exploration, but my take is that we could do it robotically at far less cost and far greater quantity and quality of results.

James Van Allen
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antipode
post Oct 31 2011, 10:24 AM
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If the Japanese pull this off it will be another 'snatching victory from the jaws of defeat' performance. They seem to do their best when their missions are in deep doodoo! smile.gif

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pandaneko
post Nov 1 2011, 09:27 AM
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This morning I was surprised to find that there is to be a news coverage of Akatsuki during this evening's 7 O'clock TV news. It is only half an hour to go. This sort of coverage is very rare here. As far as I can recall about the only TV coverage for even Hayabusa was at the time of its disintegration...

So, I am intrigued.

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pandaneko
post Nov 2 2011, 08:30 AM
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QUOTE (pandaneko @ Nov 1 2011, 06:27 PM) *
a news coverage of Akatsuki during this evening's 7 O'clock TV news.


I watched this TV news last night. A few things.

1. Although I am used to seeing graphs all neatly compiled for reports in the course of my translation this was the first time that I had seen a raw graphical output for Akatsuki. It was a horizontal line of about a foot in length and the delta V gain bit was a short (an inch or so) straight line at an angle, about 30 degrees, I would say. These magnitudes are judged relative to human size seen in the control room. It was pleaseing to see this output. It was like having a freshly baked bread right in front of me!

2. The intro said "a new (after the failure) period of a few days against the originally planned 30 hours circulation period" and at this point my brain went "???". I had all along viewed the current operation as a cosmetic excercise and in any event I was under the impression when I was translating for the new orbit that it was going to be anything from a few weeks to a few months.

As far as I am wishfully concerened "a few days" is 3 days and that is 72 hours. Does this not mean that I might be able to watch some lightenings as I had hoped to watch? I love lightenings, celestial or otherwise.

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Paolo
post Nov 2 2011, 09:02 AM
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here is a short release (in Japanese) on yesterday's burn
http://www.isas.jaxa.jp/j/topics/topics/2011/1101.shtml


--------------------
I'm one of the most durable and fervent advocates of space exploration, but my take is that we could do it robotically at far less cost and far greater quantity and quality of results.

James Van Allen
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pandaneko
post Nov 2 2011, 09:33 AM
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QUOTE (Paolo @ Nov 2 2011, 06:02 PM) *
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

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pandaneko
post Nov 9 2011, 09:51 AM
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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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rlorenz
post Nov 9 2011, 12:52 PM
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QUOTE (pandaneko @ Nov 9 2011, 04:51 AM) *
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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