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 12

2) Building in of LV2

We had debated about whether we should carry LV2 on Nozmi and our conclusion was that we should do so from the viewpoint of preventing a massive reverse flow of oxidiser vapour. LV2 is placed in the propulsive system at the downstream side of the regulator after the forking out of fuel and oxidiser pipes and between the check valve CV2 and the oxidiser tank (schematic II-1-1). Its function is to prevent the mixing of fuel and oxidiser at the gas side of the system.

With this particular propulsive system we are employing a dual redundancy system of accident prevention together with the CV2 placed in the upstream. This dual redundant system with LV2 and CV2 does not mean we did not have confidence in any of these valves. Rather, it was employed to increase reliability to an even higher stage against the reverse flow of vapour which might lead to a fatal accident, damaging the probe.

During the development stage of Nozomi in 1994 an accident occurred to a US Mars probe (Mars Observer) and it was lost. Its cause was estimated to be an accidental mixing of oxidiser and fuel vapours in the gas system pipeline. Reverse vapour flow is likely to lead to a total loss of a satellite and this point was also taken into consideration.


3) Adding LVDT

About whether we should install a valve status monitor LVDT with the LV2 our conclusion was that LVDT constituted an important source of information for the steady operation of LV2, reducing the pressure on the operating team and the possibility of human errors.

In the case of Nozomi, on the other hand, there was a factor of influence at the time of valve selection arising from the merger and acquisition of the US valve manufacturer in that it meant the addition of LVDT to a valve without a status monitor but with an ample proven record of operation.

Generally speaking the reliability evaluation of a design change to an operationally proven part has not been established just as in the case of newly developped parts. However, our judgement was that this was going to be based on an operationally proven valve and the design change was going to be introduced by a reliablbe US manufacturer and consequently the risks involved in this design change were small enough. For this reason we selected the LV2 with LVDT added to it.

As shown in the table II-2-1 the risk of valve mulfunction after the desing change was thought to be similar to that of operationally proven valves.

end of page 12

P

表Ⅱ－２－１に示すように、バルブ開閉ができなくなるリスクでは、改造品といえども、そのリスクは搭載実績品と同様であると判断されていた。