Why so Little Launch Reliability?
The key to improving any dynamic system is first to carefully describe what wrong, define why it went wrong, and then make adjustments to designs and procedures according to what we’ve learned — not according to our preconceptions or expectations.
In many cases, only later do we realize how first impressions fail to tell me the whole story. For example, the decision to launch STS51 in 28 degree weather in itself wasn’t the main cause of the accident (the last flight of the Challenger space shuttle). It was doomed at least as much by wind shear and an SRB design flaw that could have easily failed even on a much warmer day. Evidence of the design problem was obvious long before Jan, 1986. The fact that this hadn’t yet lead to an accident blinded NASA to the danger they faced.
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Mostly we fight the last war. We do this because that’s the war we know how to fight. To fight a new war we haven’t yet imagined requires us to envision an endless set of possibilities — and we’re simply no good at this beyond a rudimentary step or two. Most often we feel the need to witness a significant failure before we’ll take a problem seriously enough to fight any war at all.
In fighting the last war, we’ve worked really hard at launch vehicle (LV) reliability. Watching a vehicle explode off the pad is a visceral experience garnering all sorts of effort. Yet overall launch failure rates are pretty much unchanged the last 40 years. Still to this day, for example, 10-15% of all launch failures are due to faulty separation mechanisms, not LVs. A separation failure happens far from sight and simply does not seem as important – so it doesn’t receive enough attention. (It also doesn’t help that among satellite owners and LV operators neither is fully responsible for separation mechanism performance).
Right this second there are more commercial airline flights airborne than all launches to orbit in the 50 year history of the space age. If we had a similar level of experience in space launches, today we’d have a much better success rate. For now we build mostly customized vehicle/payload combinations, which simply is not enough experience to discover the lion’s share of design and operational weaknesses.
Human nature is perhaps the greatest stumbling block in the equation — driven home to me just today in a terrific reminder.
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I’d been waiting for some adhesive to set in an experimental solar heating system panel under construction as a hobby project. With light winds in mind I turned the heavy end of a table-size plastic sheet to the west (into the typical wind direction for a sunny day in New England). If a gust came along, it wasn’t likely to pick up this end — so I figured.
While running a few time-killing jobs around the yard I noticed how leaves were being pushed to the west end of our pool and remarked to myself how odd it was to see any sort of breeze gusting out of the east on such a sunny day.
A minute later I heard …
BAM, CRASH, THUMP, SCRAPE
I’d had plenty of time to recognize the folly of my ways and yet it took my solar panel flipping onto the deck for me to realize how my routine preventative measures against the wind were entirely backwards — even with plenty of evidence to the contrary clearly in hand.
My ongoing experience was not linked to my routine thinking. Both were happening at the same time. Yet it took an accident to gel the connection and reveal the discord.
(BTW, the panel was fine — and I decided to call this a test of its structural integrity in addition to a lesson on weather-related negligence).
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In a control room, the weather go-no-go decision can be tricky. Yet the even bigger problem is learning how to recognize when any circumstance might be trying to interrupt a cozy expectation of any sort. The group inertia of a control room is much worse than my backyard experience and can be overcome mostly via people piping up when something doesn’t feel right.
Even then, with so little flight experience to date, there’s no saying that anyone will notice a gaping hole in a design or procedure until after something goes terribly wrong.
