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Akatsuki Venus Climate Orbiter
Paolo
post Oct 6 2011, 04:28 PM
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for something different, an interesting paper presented today at EPSC: In-flight observations performed by Akatsuki/IR2
note also Emily's tweet:

QUOTE
Akatsuki performed first near-0-phase observations of Venus, found phase curve does not match models


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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.

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elakdawalla
post Oct 6 2011, 05:43 PM
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With the benefit of more than 140 characters I'll add that the phase curve had this odd double-humped shape near 0 phase that I don't recall ever seeing before in a phase curve, but admittedly I really haven't seen phase curves for anything but airless bodies.


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pandaneko
post Oct 8 2011, 09:31 AM
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QUOTE (Paolo @ Oct 1 2011, 06:40 PM) *
and here is the usual very detailed release (Japanese PDF only) about the two September firings.


Above for ease of reference

Page 10

3.4 OME test firings result (1/3)

We conducted test firings as planned on 7th and 14th of September. Each firing was about 2 and 5 seconds in duration.

(after this there are two graphs side by side)

(left graph is about accerleration (vertical axis in m/sxs) and the horizontal axis is time in second relative to OME firing start)
(wtih this graph (and also one on the right) the 1st firing is in depicted in red and the 2nd firing is in blue)

(leftmost character says:) RCS settling
(characters to the right and from top down are:) 1st firing and 2nd firing

(right graph is about Doppler monitoring (vertical axis is the increment in velocity in line of sight in m/s) and the time axis is the same relative lapse of time)

(characters here are top down and they read:) RCS settling, 1st firing, 2nd firing

We observed almost the same phenomena both in acceralation and Doppler monitoring during the two in-orbit firing tests.

• Priort to OME firings we fired 4 RCS thrusters for 3 seconds (total of about 70N) and as a result the RCS settling which moves propellant in the tank to the exit port side was carried out normally.

• The acceralation subsequently obtained by OME firings was about 1/9 of our estimation and the proplusive power was about 40N (We accepted these values as reasonable and reliable as the acceralation obtained during RCS operation was in agreenment with our estimation)

• Also, the line of sight increment in velocity as obtained from our Doppler monitoring was in agreenment with the acceralation data.

Therefore, we concluded from the telemetry data that OME propulsive power was significantly less than our initial expectation.

End of page 10
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pandaneko
post Oct 9 2011, 08:54 AM
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QUOTE (Paolo @ Oct 1 2011, 06:40 PM) *
and here


above for ease of reference

page 11

3.4 OME test firings result (2/3)

(there are two graphs here, sandwitching a schematic)

(caption for the graph on left is:)

Temperature of each section of the propulsive system during the 1st firing

Vetical axis says: OME propellant valve temp and fuel piping temp in deg C
Horizontal axis is time in min relative to OME start

(colour coding is as follows)

blue: OME propellant valve temp (oxidiser side)
red: OME propellant valve temp (fuel side)
pale brown: OME injector temp
pale green: OME piping temp (fuel side)

(With this and also with the right hand graph the dark vertical line nearest to the vertical axis denotes the start of OME firing)

(caption for the schematic is:)

piping system around OME

(and the crossed square at top right is smile.gif oxidiser system
(and the crossed square at top left is smile.gif fuel system

(caption for the graph on right is smile.gif

Fuel piping temp (analysis and measured) at the timne of 1st test firing

vertical axis is temp in deg C and horizontal is time in min relative to OME start

(dotted red line is smile.gif fuel piping (analysis based on 1/9 of propellant flow)
(thick solid green line is smile.gif fuel piping
(thin solid green line is smile.gif fuel piping (analysis with normal flow rate)

During the engine firing tests we monitored the status of the propellant supply system as follows.

• Valve status monitoring during the firings returned normal value.

• History of the temp of each section of the propulsive system during OME firings was in agreenment with our expectation (by detecting temp decrease due to the 20℃ propellant flow) and showed similar tendency both on 7th and 14th September (see graph on left)

• We conducted propellant flow rate sensitivity analysis with temp drop against the temp history of each section of the propellant supply system. We noted that the piping temp simulation with the assumed normal flow rate was in quantitative agreenment with the history of the piping temp in orbit. We therefore concluded that the propellant supply amount during the firings was more or less normal (see graph on right)

From above observations we conclude that the supply of propellant during the engine test firings was normal.

End of page 11
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pandaneko
post Oct 13 2011, 09:22 AM
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QUOTE (Paolo @ Oct 1 2011, 06:40 PM) *
and here is the usual very detailed release (Japanese PDF only)


above for ease of reference

page 12

3.4 OME test firings result (3/3)

Evaluating the propulsive power generated by the test firings

In what follows we will try to estimate the force of the gas burning in free space pushing the bottom of Akatsuki by assuming that OME destruction continued to progress, leading to the total loss of the burner and that the bottom of Akatsuki is now planar.

(after this there are two simple graphics side by side)

(the caption between the two graphics reads) : OME burner damaged at the throat section

(the captions for the lefthand graphic read) :

OME damaged at the throat section, approx. 350 N of propulsive power is assumed

(the captions for the righthand graphic read) :

OME burner is completely lost.

We estimate the propulsive power to be approx. 50 N by assuming the burning gas expanding in an ideal isotropic entropy flow.

In reality, actual flow and the burning state must be more complicated. However, we are satisfied at the measured propulsive power if we also assume that test firings led to further OME damage and OME not functioning as a burner.

We therefore think that switching from OME to RCS will be more efficient if we compare accerlation abilities per unit mass of the fuel (specific impulse) .

End of page 12
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pandaneko
post Oct 14 2011, 09:57 AM
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QUOTE (Paolo @ Oct 1 2011, 06:40 PM) *
and here


above for ease of reference

page 13

3.5 Orbit control method from now based on the test firings

We have, from the aruguements put forward up until the last page, following understandings.

• We will not be able to obtain specific impulse required for the orbit control using the damaged OME burner.


• We have done our best, based on our ground tests, to alleviate the ignition schocks. However, we now think that the burner damage continued to progress further.

From these understandings we think it only proper to carry out further operation based on the following policy.


• Any further orbit control for the purpose of Venus reunion and subsequent orbit insertion attempt will be made using the single liquid RCS engines (hydragine fuel only).


• We will jettison all of the oxidiser by mid October to reduce useless mass in order to meet the nearest sun approach orbit control in November.



• We should note that all of our further operation will be based on the understanding that the fuel side high pressure gas supply line's reverse flow stop valve continues to mulfunction and also that a tiny amount of pusher gas supply is still being maintained.

end of page 13


(I have no information yet of oxidiser jettisonning. P)
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pandaneko
post Oct 15 2011, 09:15 AM
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QUOTE (Paolo @ Oct 1 2011, 06:40 PM) *
and here


above just for ease of referencing

4. Discussing nearest sun orbit control

4. 1 Operation by jettisoning the oxidiser


As seen in the previous section it is now thought approapriate to carry out orbit control operation by the RCS engines ( Plan 2 in Sec 2.2 Trade-offs in Venus reunion orbit control)

In order to carry out an effective orbit control by the RCS (4.1.2) it is vital to lose unrequired oxidiser to reduce the probe mass.

With oxidiser jettisoning operation we need to be careful because;

injector might freeze as we inject liquid oxidiser into vaccum

temperature of each section of the probe members including the propellant valves might exceed the allowed limits

With these in mind we have conducted ground test experiments (left schematic bellow: for example 3 seconds injection at an interval of 60 seconds was made three times) and thermal analysis (right schematic bellow: for example 600 seconds continuous injection) in order to come up with a safe method for jettisoning the oxidiser.

We will from now on obtain orbital data and through these data will carry out oxidiser jettisoning operation in early to mid October this year.

(there are two schematics after this)

(Lefthand schematic's caption says) : Temp history of each section of the injector (ground test example) (vertical is temp in deg C and horizontal is time in second)

Jettisoning period : 60 seconds
Jettisoning duration per each jettisoning : 3 seconds

in red : reverse (or rear) side of the injector
in green : injector's injection face
in blue : Akatsuki's measurement points equivalent

(Righthand schematic's caption says) : Temp history of sections around OME as the oxidiser is jettisoned (thermal analysis example) (vertical is temp in deg C and horizontal time in minute)

Oxidiser jettisoning : 600 seconds (this refers to the period as indicated on the graph by the short horizontal line with two arrow heads)

in red : OME propellant valve temp (fuel side)
in green : OME injector temp
in blue : OME propellant temp (oxidiser side)

end of page 14

P
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Paolo
post Oct 15 2011, 09:55 AM
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thanks Pandaneko. this confirms what I suspected: that oxidiser will be jettisoned through the OME injectors


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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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pandaneko
post Oct 16 2011, 09:46 AM
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QUOTE (Paolo @ Oct 1 2011, 06:40 PM) *
and here


above for ease of reference

page 15

4.2 Discussions for the long duration firing of the RCS engines

RCS is a single liquid thruster and obtains its propulsive power by gassifying the fuel by catalytic decomposition. We therefore looked at various points of concern during the long duration firing such as;

power decrease and/or unstable power generation through catalyser damage and deteriolation
power decrease and/or unstable power generation through burn loss of the catalyser supporting system

⇒ RCSs on board Akatsuki have been used on various science satellites with proven record of reliability

With Akatsuki it is expected that cumulative firing length will be some 4,000 seconds (continous burn is at the most 2,000 seconds). Against this we have achieved in QT tests on ground a maximum of 23,000 seconds cumulative burn (6,000 seconds continous) and we are satisfied that the burn pressure was normal and there has been no report of catalyser deteriolation.

(after this there are two graphs and one image and I will deal with these before translating the concluding remarks)

(Caption of the first graph is) : History of internal burn pressure during 6,000 seconds continuous firing tests (QT) (example of result)

(vertical axis here is the burn pressure and the horizontal is time in second. Caption on the graph itself says "constant burn pressure")

(the small entry on the right is an image and its caption says: "RCS catalyser (image))


(caption of the second graph says) : History of the propellant valve temp (analysis) around the time of RCS continuous burn for 2,000 seconds

(Upper curve caption is) : Sun side propellant valve
(Lower curve caption is) : Opposite Sun side propellant valve

(Vertical here is RCS thruster propellant valve temp and the horizontal is time in minute)

(the zone indicated by the two-way arrows is the duration of continuous burn)

Looking at temps of RCS and surrounding areas

• RCS is designed to be capable of long duration firings (as stated above) and the probe itself is hadly thermally affected by the burn

• We also looked at the possibility of RCS temp increase by the heat soakback after burn (propellant valves in particular) exceeding the allowed value

⇒ We are now satisfied through thermal analyses that temps such as the propellant valve temp will remain within the allowed values even after RCS continusous firings

end of page 15

Paolo, if I may, do you know what went wrong with Nozomi? I did look into JAXA archive and did not find anything, as I remember it now. I and my colleagues at that time were very much intereted in the British Beagle and thought Nozomi as a backup for what we had in mind. I remember one of them shouting to me to say "No hope for Nozomi!" and that was that.

I have remained too busy for the next 10 years or more to ask why...

P
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Paolo
post Oct 16 2011, 10:00 AM
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pandaneko,
I don't have the original references at hand now, but here are some sentences from the forthcoming "Robotic Exploration of the Solar System - part 3" book:

QUOTE
In Nozomi’s case, a latching valve in the pressurization system of the oxidizer suffered a malfunction that caused the engine to burn a non-optimal mixture of more fuel and less oxidizer than required. As a result, Nozomi was left with a velocity shortfall of 100 m/s. If ISAS had been in communication with the spacecraft, it could have ordered an immediate follow-on burn to compensate, but contact was not established until 12 hours later, and by that time the engine could not recover the trajectory and still fly a nominal mission.


QUOTE
At the end of April 2002, Nozomi ceased to issue telemetry, apparently after a power supply malfunction. The cause was never determined, but could have had something to do with the massive solar flare that completely saturated solar proton monitors. Engineers soon found that they could not perform attitude maneuvers or course corrections. It was inferred that the loss of the power supply must have also switched off the hydrazine tank heaters, causing the fuel to freeze.


QUOTE
After 2 months, however, it proved possible to restore the beacon. Japanese controllers then employed a clever trick in which they reprogrammed the on/off status of the beacon as a means of producing the telemetry required to gain some understanding of the health of the spacecraft.


QUOTE
engineers had still to determine how to regain use of the power supply, as this would be essential for orbit insertion and for scientific operations. With Nozomi finally heading for its target, disaster struck again with contact being lost on 8 July 2003 and never re-established. The reason for this failure was never determined.


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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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pandaneko
post Oct 17 2011, 09:00 AM
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QUOTE (Paolo @ Oct 1 2011, 06:40 PM) *
and here


above just for ease of reference only

Paolo, thanks. Interesting, valve failure and power down. Hopefully, I may find something in ISAS archive. Anyway,

page 16

4.3 Orbit plan from now on

(immediately after this there are two schematics)

(caption with the left schematic says): solar orbits (sun circulating orbit) (current orbits) Relative positions of the probe, Venus and the earth (and these are indicated by the circles, from the innermost (probe) to the outermost (Earth))

(caption for the large arrow in the middle is): Insertion into Venus circulating orbit

(here, I must tell you that I am not familiar with the expression for circulating around something, just going around in general as opposed to something more specific like sun synchronous orbiting)

(caption for the right schematic is): Akatsuki circulating orbit (image)

(caption near Venus lower down says): (original plan) Venus circulating orbit with 30 hour period


• We are plannning to conduct orbit control in the first half of November 2011 using the RCS engines in order to meet up with Venus in 2015. With this operation the probe will be subjected to thermal environment well beyond the design conditions and we will be forced to operate the probe beyond its original design lifetime, and we will be taking every precaution. Re-insertion into Venus orbit will be carried out in 2015 and beyond.



• Since we will be using less powerful RCS engines instead of a healthy OME our current prediction indicates that the probe will be flying in an orbit whose furthest position from Venus is much higher than originally planned. The latest capacity of the RCS engines will be updated by the data to be gained from our operation in orbit control from now on.


• Orbit life expectancy, nearest and furthest positions, and period of the probe will be variable from now on depending on the results of orbit changes and the health of the probe. We will be taking the best options in choosing the right orbit inclination angle (I know there is a better expression, P) and we are also looking at the possibility of orbit insertion after meeting up with Venus a couple of times.

In any event we will be guiding the probe into the best orbit in order to comply with the requests from the science community who wish to maximise the return from this mission.

end of page 16

P
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pandaneko
post Oct 18 2011, 09:52 AM
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QUOTE (Paolo @ Oct 1 2011, 06:40 PM) *
and here


above for ease of reference

P17

5. Schedule for orbit control with respect to the nearest sun approach

(this is a flow chart page and the top scale refers to the months, from August (8) to November (11))

(starting block says) : 1st and 2nd test firings on 14th and 17th September (this year, 2011)

(question box say): Can OME be used?

(NO is given a caption which says): orbit control by RCS

(dotted line refers to OME, not adopted)

(the oblong bottom box says): discharging the oxidiser in early to mid October

(box after this oblong box says): rehearsal in late October

(last box says): nearest sun orbit control in early November

end of page 17

page 18 (last page of this document)

6. Summary of this 4th investigation report

1. Following actions/notes have been taken for the future orbit control, including the ground tests with OME


• Re-igniting the damaged burner may well lead to further damage due to ignition schocks

破損した燃焼器に再着火すると,着火衝撃により破損が進行する可能性がある.
• From results obtained during the experiments for the ignition schock characteristics we were able to identify possibile conditions for use on the probe in orbit in order to reduce ignition impacts and thus made a plan for test firings desgined to decide whether or not we will be able to use the OME.



2. These test firings in orbit were made on 14th and 17th of September and we arrived at the following conclusions.



• OME propulsion was only 40N or thereabout and we will not eb able to obtain the specific impulse required for further control in orbit.


• OME burner is thought to have been further damaged and we must not make use of it any further.


• For any further orbital control we will have to be content with the RCS engines and with them we will still aim for Venus reunion and subsequent orbital insertion.


• Since RCS is of only single liquid type we will discard all of the oxidiser.



3. Plan for future operation including Venus reunion and orbit insertion



• After discarding the oxidiser we will carry out the nearest sun orbit control operation in early November.


• For the reunion with Venus and orbit insertion thereafter we will be closely working with the science community in trying to decide the best orbit and orbit insertion method based on the result of the nearest sun approach operation of this time and future health of the probe, and the results of the RCS firings.

end of page 18 and end of the report


Paolo

I searched around last night, not inside JAXA nor ISAS, but in the general world of the internet, for further Nozomi failure information. I am satisfied that there are (amazingly) ISAS and JAXA documents, not as quite detailed as those on Akatsuki, but sufficiently informative.

Do you think these will be of any use at this late stage for light readings? If so, where might I upload them to? I could not find any trace of a suitable platform inside Mars. Not a lot, perhaps 20 to 30 pages as I will have to devide these 3 single and seperate documents into manegeable size for a day's translation.

P



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Paolo
post Oct 18 2011, 11:15 AM
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Pandaneko, just to stress once more how useful your posts are.
concerning Akatsuki, we are now past mid-October, but I have yet to see any news on the oxidiser dump
concerning Nozomi: documents would be interesting, from an historical point of view, thanks. take your time, anyway, and don't stress you too much!


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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 19 2011, 05:20 AM
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I have got my answer from Akatsuki_JAXA tweets + google translate:

QUOTE
Last week the dumping operation from Sagamihara [oxidant], finished successfully. Akatsuki should lean a little longer.


--------------------
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 19 2011, 09:28 AM
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QUOTE (Paolo @ Oct 18 2011, 08:15 PM) *
take your time, anyway, and don't stress you too much!


Thanks, Paolo

I did another search today. Would you believe it? I found a proper and very detailed report on the failure of Nozomi, a final report made to the Space Activities Commission (SAC). It no longer belongs to JAXA and is archived elsewhere. No wonder I did not find anything of this sort inside JAXA or ISAS. This report, from the quick glance I made, is about 85 pages long. I may turn out to be wrong, but one of the pages I had a quick glance towards the end of this report seemed to have that page number.

I will start a fresh thread soon inside Mars and start translation. I am feeling sorry and sympathetic towards the poor Nozomi.

P
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