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Akatsuki Venus Climate Orbiter
Explorer1
post Sep 17 2011, 04:58 AM
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Yeah, I guessed as much; one would need an actual heat-shield to do aerocapture.
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Paolo
post Sep 18 2011, 09:47 PM
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If I understand correctly the google translation of this Mainichi article (in Japanese), Akatsuki could enter an elliptical Venus orbit using the RCS with a period between one week and 90 days. Pandaneko can you confirm?
I wonder: what science could be accomplished on such a distant orbit? and would it be stable? I guess it would get large solar perturbations...


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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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pandaneko
post Sep 19 2011, 11:39 AM
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Yes, what the paper says is as follows.

1. It is no longer possible to insert Akatsuki into the planned orbit.

2. If they use RCS the orbit will be 90 days elliptic. Original plan was 30 hours per rotation.

3. In order to try November 2015 inerstion attempt they will have to fire the engine for 400 seconds in November this year.
They have not yet decided which engine to use and the decision will be made by the end of this month.

4. Akatsuki was developped to observbe super rotation at the cost of JPY 250 times 10 to the power of 8.

5. The only consolation is that all of the deviecs for observation are OK and healthy.

6. If they use RCS then it will take 72 times longer per rotation and the maximum distance will be 10 times further away.
They are therefore looking at optimum observational conditions for their devices.

This means I paid about 2 Macs worth of tax money for Akatsuki. I am willing to pay more.

P
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Paolo
post Oct 1 2011, 07:10 AM
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it's going to be RCS in the end... sad.gif
http://www.jaxa.jp/projects/sat/planet_c/index_e.html


--------------------
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 1 2011, 09:17 AM
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QUOTE (Paolo @ Oct 1 2011, 04:10 PM) *


Thanks, Paolo. Today's Asahi newspaper here says the same thing. In addition, it says the total mass of whatever is to be jetissoned is 64kg. It does not say oxidiser or fuel or both.

P
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pandaneko
post Oct 1 2011, 09:26 AM
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QUOTE (pandaneko @ Oct 1 2011, 06:17 PM) *
Thanks, Paolo. Today's Asahi newspaper here says the same thing. In addition, it says the total mass of whatever is to be jetissoned is 64kg. It does not say oxidiser or fuel or both.

P


Another newspaper here says it is the oxidiser and it is going to be jetissoned some time this month.

P
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Paolo
post Oct 1 2011, 09:29 AM
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QUOTE (pandaneko @ Oct 1 2011, 11:17 AM) *
Today's Asahi newspaper here says the same thing.


thanks for the info Pandaneko. do you have a link?


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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 1 2011, 09:40 AM
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and here is the usual very detailed release (Japanese PDF only) about the two September firings. as I understand it, the nozzle must have broken off and the engine is only providing 50 N of thrust instead of 350 N.
given the propulsion system plumbing schemes. only oxidiser will have to be vented overboard (hydrazine for the RCS comes from the very same tank as hydrazine for the OME). I guess the simplest way of venting oxidiser will be through the OME


--------------------
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 1 2011, 10:16 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. as I understand it, the nozzle must have broken off and the engine is only providing 50 N of thrust instead of 350 N.
given the propulsion system plumbing schemes. only oxidiser will have to be vented overboard (hydrazine for the RCS comes from the very same tank as hydrazine for the OME). I guess the simplest way of venting oxidiser will be through the OME


Thanks, Paolo

I will start translating the new document from tommorrow on. Links to local papers will be useless, I think, as they are all in Japanese. There are papers in English here, such as;

The Japan Times
The Asahi Evening News
The Mainichi Daily
The Daily Yomiuri (not sure if this really exists, but I am 90% certain that it does)

P
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Paolo
post Oct 1 2011, 10:22 AM
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QUOTE (pandaneko @ Oct 1 2011, 12:16 PM) *
I will start translating the new document from tommorrow on.


thanks. I didn't dare to ask wink.gif
I think you can skip the first pages, which seem to just repeat thing we already know about the missed orbit insertion, clogged valve etc.


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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 2 2011, 09:49 AM
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QUOTE (Paolo @ Oct 1 2011, 07:22 PM) *
thanks. I didn't dare to ask wink.gif
I think you can skip the first pages, which seem to just repeat thing we already know about the missed orbit insertion, clogged valve etc.


Yes, I agree completely. However, we want to know contents list, at least. That is shown below.

Contents list

1. Events up until now. Discussing orbit control with the nearest approaches to sun

2. Summary up to the third meeting

2.1 Understanding the phenomena during VOI-1
2.2 Trade offs in operating for Venus reunion

3. Discussions for re-firing of OME

3.1 Searching for conditions for mitigating the re-firing shocks
3.2 Mitigating the re-firing shocks using the damaged burner
3.3 Rehearsing for orbital test firings
3.4 Results of OME firings
3.5 Orbiting after test firings

4. (I have lost the character string that ought to be here, or perhaps it was not there in the first place)

4.1 Operating by jettisoning the oxidiser
4.2 Discussing the long duration firing of RCS
4.3 Orbit plans from now on

5. Scheduling for nearest to sun approach orbit control

6. Summary of this report

End of contents list page

I think I will start with 2.2. from tommorrow.

P
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pandaneko
post Oct 3 2011, 12:46 PM
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Page 6:

2.2 Trade offs in Venus reunion operation

We reported at the third meeting that we will be carrying out test firings in orbit in order to verify the in orbit status of OME . Our plan was such that we will be choosing one of the following two options based on the result of these test firings and carry out the required orbital change in November 2011 at the time of nearest sun approach.


0.OME test firings in orbit

Several test firings were to verify the status of OME and confirm our ability to control attitude during OME firings.

OME:Orbital main engine (2 liquids and class 500N)
RCS: Attitude control system (1 liquid and class 23N4)

Option1: where we can use both OME and RCS

Step 1.Nearest sun approach orbital control:

around Nov 2011 or June 2012

Step 2.Venus reunion manouver (4 day orbit):

around Nov 2015 (Venus reunion)

Step 3.Insertion into observational orbit (from 4 day orbit to 30 hours orbit):

around Nov 2011 or June 2012


Option 2: where we cannot use OME

We will carry out delta V using only RCS engines

Step 1.Jettisoning of oxdiser:

(during Oct 2011 as reported in the press)

2.Nearest to Sun approach (NSA) orbit control:

just before nearest sun orbital control

3.Venus orbit reunion manouever:

after Nov 2011 at NSA position and around Nov 2015 (Venus reunion)

end of page 6

P
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pandaneko
post Oct 4 2011, 12:29 PM
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Page 7

3. Discussions for OME refiring

3.1 Searching for conditions for mitigating ignition shocks

We estimated that OME had been broken at the time of VOI-1 in December last year. Therefore, we carried out tests and experiments with a view to understanding OME behaviour upon reignition in order to insert the probe into originally planned orbit.

(after this there are two photos horizontally (as it were) and in between them a large arrow with a character string in it)

Caption for the left photo says;

Burner after nozzle breakage (existence of through cracks confirmed by penetration flow detection method)

Character string in the arrow says;

cases occurred where thruster is wholly lost immediately upon ignition

Caption for the right photo says;

Burner whose breakage continued after re-ignition

Given continued breakage upon re-ignition we searched for conditions in which ignition shocks are mitigated.


What we found quantitatively is that re-ignition shocks can be mitigated if we inject oxidiser slightly ahead of fuel injection and by keeping fuel temp at a relatively high level before injection. These findings that we should not inject fuel and oxidiser simultaneously were realistically the best operational option we could find from our ground tests for Okatsuki in orbit.

In carrying out our experiments we first constructed a metal thruster whose parametric performance we could monitor with high accuracy and then applying the found conditions to ceramic thrusters.

Best re-ignition schock mitigating conditions we found from our 195 ground tests are as follows.

OME injector temp: higher than 150 deg C

OME fuel valve temp: 65 to 74 deg C *
OME piping temp: 57~68 deg C*
Oxidiser pre-emptive injection by: 100~400ms

*: Too high temps also leading to re-ignition schoks

end of page 7

P
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pandaneko
post Oct 5 2011, 08:40 AM
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QUOTE (Paolo @ Oct 1 2011, 06:40 PM) *
and here is the usual very detailed release


Page 8

3.2 Ignition schock mitigated burn tests using damaged burners

We used thus obtained optimum conditions for ignition schock mitigation and carried out multiple burn tests using damaged burners. In view of next operational phase we conducted repeated short duration re-ignition tests.

Examples of continued or progressing damage or damage propagation

(hereafter there are three photos horizontally, from left to right. Please, for ease of reference, look at above link to see actual photos)

Caption for the leftmost photo says;

(initial state) burner damaged near the throat

Caption for the first arrow says;

re-ignition

there are cases where damage progressed

Caption for the middle photo says;

burner whose damage progressed

Caption for the second arrow says;

re-ignition after damage progression

there are cases where total loss occurred

Caption for the right photo says;

totally damaged burner

From these tests we observed that even using mitigation conditions we still had cases where damage still continued to propagate. Given these test results and our desire to insert the probe into the desirable orbit using OME we decided that we should conduct in-orbit ignition tests by giving due considerations to the mitigation conditions and using probe's OME and decide whether we might be able to make use of OME as desired.

end of page 8

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pandaneko
post Oct 6 2011, 09:37 AM
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QUOTE (Paolo @ Oct 1 2011, 06:40 PM) *
and here is the usual very detailed release


Above for ease of reference

Page 9

3.3 In-orbit test firing rehearsal

In order to satisfy ground obtained conditions for mitigating ignition schoks we, in addition to temp control using heaters, changed the probe attitude (solar array angle) so that these conditions are met in orbit.

What is shown below is the comparison between the control parameters required of the probe and the prediction and in-orbit resulting values. As a result we were able to confirm that we will be able to satisfy these conditions for mitigation in orbit.

(after this there are three entries, something on the left and a graph on the right and these are followed by a table at the bottom. A lot of captions are stuck on top of another for the first entries and my translation are as follows)

Control parameters required of the probe (lefthand entry, P)

(captions are from top to bottom)

Fuel supply pressure
Oxidiser supply pressure
Fuel cut-off valve action timing
Oxidiser cut-off valve action timing
OME piping temp (fuel side)
OME piping temp (oxidiser side)
OME propellant valve temp (fuel side)
OME propellant valve temp (oxidiser side)
OME injector temp

Comparison of predicted values and in-orbit measurements for rehearsal (righthand entry, P)

(captions from top to bottm are;)

OME injector temp in-orbit measurement
OME propellant valve temp in-orbit measurement
OME piping temp in-orbit measurement
Analysis: OME injector temp
Analysis: OME propellant valve temp
Analysis: OME piping temp

(These are colour coded and being colour language blind I am simply ignoring to translate these different colours. Above reference should help, P)

(table is translated on CX RX basis)

C1R1: Temperature (perhaps, this was not here?)
C2R1: Required value
C3R1: Result of in-orbit rehearsal

C1R2: OME injector temp
C1R3: OME propellant valve temp
C1R4: OME piping temp

End of page 9

P

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