Nozomi in perspective, Revisiting the causes of failure Options

[pandaneko]

http://www.mext.go.jp/b_menu/shingi/uchuu/...ts/04061101.pdf

Above pdf file will be translated for aspiring students in aeronautics, control engineering etc. so that in future lay people like me will be able to enjoy planetary scenes and events without worrying about failures.

The overall title is "Looking into the causes of failure and trying to find the right measures to take for the future with respect to the 18th scientific satellite (PLANET-B ) not inserted into Mars orbit as planned" and it is dated 21 May 2004.

This file is very much detailed at 1.1 megabytes and the number of pages is about 40, I think. In addition, I will be translating 3 more files after this particular file. They will be;

1. ISAS file with views and comments on the failure
2. Another ISAS file, a newsletter written out in a series of 4 individual letters.
3. JAXA file, which is a press release and it is a very concise document with just sufficient details.

Re concise link making I tried a few times, but I simply failed and all the links will be fully pasted out as required.

Pandaneko

[pandaneko]

http://www.mext.go.jp/b_menu/shingi/uchuu/...ts/04061101.pdf

above for ease of reference

page 27


Ⅳ．For the future

１．For the future of fuel supply system

(1) Measures to be taken in selecting the valves

From the mulfunction of this time we can point out two major issues relating to the selection of valves for Nozomi. These are the fact that we made a design change to the valve which had an ample track record of going on board in space and also the verification methodology of that valve. We show measures to be taken in relation to these two issues as follows.

1) About design changes

The valve we are talking about as developping a mulfunction is LV2. Originally, this valve made by a certain US manufacturer with ample flight records was changed at the request of the then Institute of Space and Astronautical Sciences (ISAS) to include a status monitor (LVDT) for monitoring of valve opening and closing.

This LVDT was added to the existing valve to ensure reliable operation of LV2. It meant that the valve with enough track records but lacking the monitoring function was changed to include LVDT as a post desgin alteration.

As for this change of design, since it was made by a specialist US manufacturer based on existing design with track records we thought, at the time of decision making, that the risk involved was small enough, but we now think that our study at that time was not satisfactory.

At this time, given the structure of Nozomi, we had to introduce a design alteration to LV2, but we think that inherent risks involved in desgin altered componets must be treated adequately.


2) About the verification methodology

Most of space use valves are imported from overseas and in some cases detailed structural indormation and availability of technical information is limited. It is vital to establish high reliability with these products. With Nozomi we did conduct LV2 verification and evaluation as shown below, but we now think that it was not enough.

With Nozomi verification tests were conducted as shown on tables II-2-2 and II-2-3. We also requested the US manufacturer for similar verification and in Japan we conducted an independent study on the NTO vapour arising from the oxidiser. We conducted an even harsher test of sealing NTO liquid inside a valve for keeping and for action tests, thereby verifying the durability of the valve against NTO environment and confirmation of its health.

This particular test was conducted so as to verify that LV2 had durability against NTO and lasted only for two months equivalent length. In that sense it was, strictly speaking, not an accelerating test approapriate for Nozomi's operational lifetime (one year had been assumed)


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The number of valving actions during the accerleratin test is important from the viewpoint of verifying the influence of that number affecting the condition of the sliding part of the valve. In our case this time it was less than 10 cycles of opening and closing that were tested in the oxidiser environment and we cannot deny the possibility of it being inadequate for taking into consideration the possibility of fletching wears etc.

From all these reasons mentioned as above we should have paid a lot more attention to the issue of conditions in which verification is sought. Valves in particular have wide areas of concern relating to electricals, materials, fluid dynamics etc and we should be closely working with specialists in these areas both inside and outside our organisation in order to check if proposed verification methods are adequate for our purpose.

With imported valves we may think of, as a means to further improve on the adequacy evaluation technique, an early detection of valve deteriolation from the changes appearing in the current wave profile imprinted (or imposed?, P) on the valve. Clearly, we should be spending a lot more on strengthening our verification stance.


end of page 27

P