Akatsuki Venus Climate Orbiter Options

[pandaneko]

(page 51)

B.8 Examples of gas supply system in long duration flight with 2 liquid propellant system

(please refer to original schematics for this page"

(a) Hayabusa

Stainless diaphragm is installed so that propellant is supplied to the engine without fail on touch-down. As a result we could prevent the flow of oxidiser vapour in the piping system.

(with the piping schematic for Hayabusa top left character string is "fuel system" and top right "oxidiser system", corresponding lower ones are fuel tank and oxidiser tank) (String with an arrow is "stainless diaphragm"

( HTV

Manned mission requirement meant that valves are installed in cascade and a buffer tank is also installed in order to alleviate the pressure rise in the gas supply piping system. As a result, the flow of fuel vapour in the system is prevented.

(schematic captions are similar here, and an arrow starts from "buffer tank", also valves 1 and 2, 3, and 4 are indicated below buffer tank, above fuel tank.)

(end of page 51)

[pandaneko]

(page 52)

B.8 Examples ofgas supply system in long duration flight with 2 liquid propulsion system (continuation)

© Cassini (NASA Saturn space probe)

Source ：T. J. Barber, R. T. Cowley, “Initial Cassini Propulsion System IN- Flight Characterization”, AIAA 2002-4152

Many pyro-valves are installed in order to prevent oxidiser vapour flow in the piping system


(d) Messenger (NASA Mercury space probe)

Source ： San Wiley, Katie Domer,“Design and Development of the Messenger Propulsion Sytem”, AIAA 2003-5078

Separate piping is arranged for fuel and oxidiser distribution in order to prevent propellant vapours migrating in the piping system.

(end of page 52)

[pandaneko]

(page 53)

B.8 Examples of gas supply piping system in long duration flight using 2 liquid propellant system (continuation)

(e) NEAR (NASA asteroid space probe)


Source ： S. Wiley, G. Herbert, L.Mosner,“Design and Development of the NEAR Propulsion Sytem”, AIAA 95-2977

CV- and V- valves are arranged so as to prevent flow of oxidiser vapour in the piping system

(f) Mars Observer (NASA Mars space probe)

Source ： Carl S. Guernsey, “Propulsion Lessons Learned from the Loss of Mars Observer”, AIAA 2001-3630

CV-valves and pyro-valves are placed to prevent oxidiser vapour flow in the piping system.

Most convincing cause of failure is said to be that oxidiser at the cold portion of the gas supply system caused condensation and liquefaction and this flew into the fuel side when the pyro-valve was opened, leading to explosive reaction.

(end of page 53)

[pandaneko]

(page 54, main text portion only)

C.1 Current understanding of OME status analysis

Phenomena inside a burner are complex and there are many models. However, we need further efforts in trying to model "cooling" before we can quantitatively discuss absolute values. Naturally, analysis of stress distribution and destruction probability is useful in discussing burner's structural strength and heat resistance. However, even then, we need further efforts before we can discuss values of quantitave and non-quantitative aspects.

We have been following two research themes as per below as our long term projects even before Akatsuki was designed. We are hoping that the burn data we obtained thanks to the failure of Akatsuki outside the designed range of parameters will be useful in increasing the accuracy of our burn analysis model.

Burn analysis

We analyse steady state of burn inside a burner. At this point in time we are satisfied that our model can reproduce test results more or less faithfully by giving it a film cooling (FC) vanishing point. Our next long term projects will be about modelling FC and non-steady state analysis.

Strength analysis

Here, we try to evaluate the destruction probability by analysing the thermal stress inside the burner using burner temp. distiribution obtained in tests burns and burn analysis.

(end of text portion of page 54)

(schematics' translation will have to follow tommorrow as I am not exactly sure how to translate this at the moment. Some characters, even blown up, are illegible, P)

[pandaneko]

(page 54, schematics translation, or rather my understanding of them, only)

(there are two parts, I think, top and bottom and the top schematic seems to be a CG from CFD simulation and there are 6 boxed characters, boxes 1.2. and 3 from left to right above boxes 4.5. and 6 in the same order. Each box is aparently is a model and the character for it is placed at the bottom. There are other characters relating to the model name hovering above it, which I will place after the model name)

box 1: secondary microglobular model- secondary crush, microglobules
box 2: vapourisation model- N2H4 gas, N2H4 liquid drop, N2O4 gas, N2O4 liquid drop
box 3: thermal analysis model:
box 4: primary globular model- N2H4 injector mouth, N2O4 injector mouth, N2O4 liquid drop, N2H4 liquid drop, and an additional character with this box reads "virtual liquid membrane fan" with an arrow

box 5: film cooling liquid membrane vanishing point model (formation of formulae for experiments)
box 6: burn or combustion model- burn gas, N2H4 gas, N2O4 gas, vapour phase burn

(here above, I must say I do not know what they are talking about, P)

(Bottom half is as follows)

box 1: measured temp. distribution during test burn (there is a photo just underneath it)
box 2: thermal analysis (arrow is pointed to this from above)
box 3: stress analysis (arrow is pointed to this from above)

(after this, there is a strange looking structure and just underneath it)

box 4: stress distribution (no arrow as such)
box 5: destruction probability evaluation (and this box is pointed at with an arrow)

(after this there are 2 circled numbers + a note)

1st circled number: evaluating in unit of elementary volume (volume standard destruction probability)
2nd circled number: evaluating in unit of elemental area (area standard destruction probability)

NOTE: strength depends on surface processing methods

(end of schematics on page 54)

[pandaneko]

(page 55)

C.2 Observation of breakage of the broken burner

Here, we show the results of our surface observation of the burner which was destroyed during test burn (part 1). As a result, we confirmed the existence of the breakage starting point and did not find any clear material fault around it, indicating that the breakage was not due to a simple manufacturing error.

(there are 4 photos which are numbered as follows)

a) low resolution photo
material surface of the observed spot
c) blow up of the region around starting point
d) blow up of the region around starting point

(end of page 55)

[pandaneko]

(page 56)

C.3 History of accerleration and angular velocity during the latter half of VOI-1

Here, we looked at the effects suffered by OME.

In order to compare test burn data with that from the 1st investigation meeting we carry the latter as follows.

(no need for translation, except perhaps that; )

left vertical axis is angular velocity (deg/s) and right vertical is acceleration (m/s/s), horizontal is the time line relative to OME start taken at zero second.

On the graph itself, blue is angular velocity around X axis, red Y axis, yellow around Z axis. Solid line is accerleration.

(end of page 56)

[pandaneko]

(page 57)

C.4 Propulsion characteristics of the broken burner

Here, we compared the estimated (from acceleration telemetry data) propulsive power with that measued during the test burn (part 1) after thruster nozzle breakage.

Behaviour during VOI-1 (telemetry data);

• 152 seconds after the start of burn a step like power fall is observed, and after that 2 more step like power changes are observed.

Behaviour during test burn (part 1)；

• In this test burn we also observed a step like power drop as was observed at the time of breakage during VOI-1

• In other examples of breakage there was a case where cracks opened up along the circumferential direction. If burn were to continue with this kind of breakage it might develop further, suggestive of the power change observed during VOI-1

(after this there are 2 graphs and one photo)

graph 1: VOI-1 propulsion (estimated from acceleration) (vertical is power (N) and horizontal is time line as with page 56)

(there is a character string astriding both graph 1 and graph 2 (both lines pointed at with an arrow from this string) and it says;)

propulsion after VOI-1 step change and that of test burn upon breakage are more or less in agreenment

graph 2: Shorter nozzled burner was used in test burn (part 1), leading to smaller steady propulsion (time line is real)

(caption pointing to the vertical precipitation reads;)

emergency stop was enforced in ground test

photo: Crack example at nozzle breakage (almost half the circumference) (fluorescent immersion defect search with another broken burner, broken in another test burn)

Therefore, we can explain the behaviour of power after 152 seconds of VOI-1 start as resulting from burner breakage.

(end of page 57)

[pandaneko]

(page 58)

C.4 Propulsion characteristics of the damaged burner (continuation)

Here below, we show photos of the flight model burner and the burner which was damaged during part 1 of our test burn and the comparison of propulsion characteristics before and after the damage.

As for the lateral propulsion we conducted computer fluid dynamics (CFD) estimates using the shape data of the damaged burner. The result was more or less in unison with the lateral propulsion estimated from the telemetry data of the X-axis angular velocity measured at the time of mulfunction during VOI-1.

(here after, there is a computer output, entitled;)

Estimation of the lateral propulsion of the damaged burner (example of CFD results)

1st display: vertical is pressure (Pa) and pressure distribution is horizontal
2nd display: vertical is Mach number and horizontal is Mach number distribution
3rd display: vertical flow (m/s) speed and horizontal is flow vector


photo 1: that of the burner that actually flew
photo 2: that of the burner which was damaged during part 1 of the test burns


Propulsion characteristics of the flight model and damaged burners

(here, I use my table concept, 4 rows and 5 columns)

R1C2 and 3 combined: Flight model burner
R1C4 and 5 combined: Burner after the damage during test burn (part 1)

R2C2: At the time of VOI-1 start
R2C3: after 152 seconds of OME burn in VOI-1
R2C4: test burn data
R2C5: estimation from CFD

(Here below, I attempt to create the rest of the table, in the same order, vertical and horizontal, and I need to put a slash between entries, I think)

Propulsive power (N): 476 / 300 / 315 / 307


Lateral propulsive power (N): 0 / 5〜20 / （no available data） / 14

(end of page 58)

[pandaneko]

(page 59)

C.5 Looking at reducing re-ignition impacts

We are currently conducting re-ignition experiments using a damaged burner with a view to igniting OME once again

(here, two photos sandwiching a larger arrow)

Left photo: burner after nozzle damage

Larger arrow reads: cases occurred where thrusters were totally lost immediately upon re-ignition

Right photo: burner which developped further damage upon re-ignition (we confirmed an existence of a penetrating crack using immersion defects serach test)




We therefore think that the burner may not withstand the impact upon re-ignition. At the time of this reporting we do not know the state of the damaged burner in orbit (such as a penetrating crack etc)

Looking at reducing the re-ignition impact

Our current view, upon examining the re-ignition impacts, is that by starting oxidiser injection earlier (100 to 200 milliseconds) there is a possibility that impacts may be reduced. We are now discussing the operation including that of carrying out this manuever on the real burner in flight.

(end of page 59)

[pandaneko]

(page 58)

C.4 Propulsion characteristics of the damaged burner (continuation)

As for the lateral propulsion we conducted computer fluid dynamics (CFD) estimates using the shape data of the damaged burner. The result was more or less in unison with the lateral propulsion estimated from the telemetry data of the X-axis angular velocity measured at the time of mulfunction during VOI-1.

Here, I forgot to translate a small thing. With angular velocity we are supposed to refer to section C.3. Thus, angular velocity above should be "angular velocity (see section C.3)"

Also, I forgot to translate the graph on page 59. The vertical axis is the propulsion (N). The horizontal axis is the time or duration of oxidiser pre injection in milliseconds. The slanted caption inside the graph says "possibility of reducing re-ignition impacts"

Two more pages to go! Actually, the last two pages are rather interesting.

P

[pandaneko]

(page 60)

C.6 Looking at the possibility of realising continuous burn of OME

It is thought that during VOI-1 the closure of CV-F led to O/F ratio going out of the design range and this resulted in OME being affected (damage likely)


Therefore, we are now talking about maintaining the right O/F ratio even under the restriction of CV-F closure. This takes into account the next nearest approach to sun and we are currently conducting test burns with blowing down on fuel and oxidiser tanks.

During part 1 of the manuever test burns there was no change (damage?, P) in the burner and the burn was completed normally.


All this means that we will be operating outside the planned operational range of O/F ratio and we are now discussing if we can go ahaed with its execution.

(there is one large graph)

(Left vertical scale is oxidiser tank pressure (MPa))
(Horizontal is fuel tank pressure (MPa))
(Top horizontal is O/F ratio)

(Square on the graph (inside the graph, upper right) is flight plan range)
(Dotted lines: result of blow down operation preparatory test)
(Yellow band sandwiched between dotted lines: range which is expected during orbital manuever)

(there are two character sets on the graph with arrows pointing from them)

(top set reads) "conditions at the start of preliminary (or, preparatory,P) operation of blow down test"

(bottom set reads) "conditions at the end of blow down operation test"
(please note there is no preliminary or preparatory here, P)

(end of page 60)

[pandaneko]

(page 61) ( final page of this 3rd Akatsuki report)

C.7 Looking at the method whereby oxidiser may be jettisoned

If we find orbital re-insertion by OME is not possible, we will then have to turn to insertion by RCS. Since RCS is a one liquid engine we will need to reduce the craft's inertial mass by jettisoning oxidiser.

We are currently conducting preliminary experiments in order to come up with approapriate methods ( of freeze prevention etc) of oxidiser purge

Here below, we show an example from temp. changes at various points on OME during such preliminary tests.

(with the graph on the left, vertical is temp. (deg C) and horizontal is time)
(arrowed peaks are "injection")

(with the photo points of temp. measurement are indicated by A, B, and C, and these are reflected on the graph, of course, P)

(main text continues as follows)

In this example, we see that oxidiser purge may be possible without it freezing if we use pulse injection of duration less than 1 second. However, we will continue with our experiments in view of the possibility that the burner is totally damaged.

As for the contribution by oxidiser purge to the propulsive power the resulting specific impulse, even in the ideal case of perfect expansion, will be in the order of a few tens of seconds and its contribution to delta V is thought to be minimal.

(end of page 61!)

[pandaneko]

I learnt just now from a local newspaper that Akatsuki will fire its OME for 2 seconds on 7th this month to see what it is like. This will be followed by 20 seconds firing on 14th while attidue is maintained by smaller thrusters. This is meant to move Akatsuki through a distance of 5,000 km.

If all these are OK, then OME will be used again in November this year for insertion in 2015.

I also learnt a few weeks ago and this really is pleasant and surprising news to me, at least, that Hatsune Miku is flying with Akatsuki, possibly with 2 more vocaloids because media seem to be talking about 3 metal plates fixed as some kind of supporting structure on Akatsuki!

P

[Paolo]

according to Akatsuki_JAXA tweets, people is cheering at the Sagamihara operation center. It looks like the first engine firing was successful (just how successful remains to be seen..)