I have had the opportunity as a Rocket Scientist to work on three different Kill Vehicles: THAAD, Raytheon, and GMD.
One thing really stands out: They are all very different.
Of the three, the Boeing Kill Vehicle stands out as being extremely reliable.
There are reasons for this.
One of the basics is that when you design a complicated piece of machinery, you can make it easy to fix. A large percentage of Design Engineers (including me) think that their design is the best “Because I designed it”. It will never need fixing, so you will not need to design it so it can be repaired. This is an incorrect assumption, but this is how Design Engineers think.
In fact, though, we really need to relate not to IF it needs fixing, to WHEN it needs fixing. Can you disassemble it? Can you test it? Can you fix it?
Example: The Raytheon Kill Vehicle was not readily repairable. It had a rats-nest of tubes on the manifold, where you could only fix something if you took the whole thing apart. You could not get a wrench in there. If there was a leak, you could not fix it, you needed to take the whole thing back to the factory and disassemble the whole thing. Then, when you reassemble it, you really don’t know if you fixed the thing, or if you initiated a new leak somewhere else.
Where this becomes a problem is when you are ready to fly, and you hear a leak somewhere. You cannot easily find the leak source, and you cannot get a wrench in there to tighten the B-nut. So you hear a leak, and you are under pressure to fly out. Changing out the KV will take about two or three weeks to replace the KV. A quick decision is made to fly, with the leak, as soon as you can, before you lose your fuel. The missile flies, but when the KV flies out into space, it runs out of fuel. The FRACAS System records that the KV was hissing before takeoff, a decision was made to fly, and it ran out of fuel. The whole mission failed.
If you work on the Raytheon FRACAS System, the Failure Reporting Analysis and Corrective Action System will always give you hints about how a failure occurred. The idea is not to spank the engineer, but how to avoid another failure in the future. Unknown to many people, the same failure keeps on occurring again and again. Sometimes it causes the failure, sometimes not, but it is always there.
If you become familiar with Kill Vehicles, enough so you can compare them, it would be astonishing how different they are. Some have good points, some have bad points.
The comparison leads the Engineer to WISH for something, but he doesn’t know what. Usually, the Engineer cannot compare Kill Vehicles because each one is made by someone else.
But what happens if you have a large wish list, and you see everything you want when you look at the Boeing Kill Vehicle?
Initially, you can see that they have deleted a lot of unnecessary hardware. The design is much simpler. It is easy to fix (An Engineering Technician’s dream). It seems that the hardware functions properly. The KV is functional.
I did the FMECA for the Boeing KV. That means that I analyzed each piece of the Boeing KV. I was amazed how simple it was. I came up with a list of Single Point Failures (SPF) and the associated Mitigation. The Boeing KV Design compensated for potential failures very nicely. The problem I had was why was the Boeing KV ignored?
There was an urban tale about an Engineer who stole KV secrets and brought the secrets with him when he moved. Then Boeing bought the other company, and Boeing then became responsible for the actions of that engineer. Boeing was told that they could not provide a KV. So, it sat on the shelf for many years. It was even there when Darleen Druyun (one of the smartest women I ever met) was on duty at Boeing.
So, we tried to resurrect the Boeing KV because of its inherent Reliability and Performance. But we did not do that. It has sat on the shelf anyhow, even though it is far superior to anything else.