Space Forum / Shuttle / March 2007

Several reasons. I've been thinking about it overnight to try to rank
them and right now this is the best I have:

1) Human error is the cause of 80% of aviation accidents and this pattern
is continuing in spaceflight. Out of five fatal accidents (Apollo 1,
Soyuz 1 and 11, STS-51L and 107), human error was a primary cause of all
but Soyuz 11. Compared to this cause, all other causes are secondary (and
therefore, all the safety features designed into spacecraft are likewise
secondary). It's just that in spaceflight, much more of the
responsibility falls on those on the ground rather than the flight crew:
in the four spacecraft accidents caused by human error, the error was the
decision to proceed with a launch or ground test despite indications of
an unsafe condition. There is no reason to believe that Orion will be
immune to this.

2) All spacecraft have design flaws; unlike aviation, we have not gone
through enough design generations to weed them out. The staleness of the
current US experience base due to the long gap between design generations
increases the likelihood of a flaw in Orion. And Orion already has one
obvious flaw, common to all current and historical capsules: the
necessity of jettisoning critical parts of the spacecraft during the
window between deorbit and entry interface. This design flaw was a
contributing cause to the Soyuz 11 mishap and the primary cause of two
close calls (Soyuz 5 and TM-5). It just doesn't get widely recognized as
a flaw per se because it hasn't killed an American (yet).

3) Orion's projected flight rate is so low that I believe reusability
will prove to be non-viable. That means a big hit to component
reliability since Orion's systems will never get out of the "infant
mortality" part of the "bathtub curve."

There are other reasons but after ranking them, I think the above three
capture the "first-order" effects and a good bit of the second-order.

Yes, but look at how many flights it has had since its last fatal failure.

=?ISO-8859-15?Q?Andr=E9,_PE1PQX?= <pe1pqx_geenviagra@planet.nl> wrote in
news:mn.3aab7d73c8e3df37.58901@planet.nl:

I did.

Years aren't relevant, flights are.

Soyuz has two fatal accidents in 95 flights (1 in 47.5) and four fatalities
in 228[*] person-trips (1 in 57). Soyuz has had 85 safe landings since the
last fatal accident.

The space shuttle has had two fatal accidents in 117 flights (1 in 58.5)
and fourteen fatalities in 698 person-trips (1 in 49.9). It had 87 safe
landings between the 51L and 107 accidents.

Within the wide statistical uncertainty imposed by the small sample sizes,
those numbers are essentially identical - they're all "one in fifty", give
or take. (The other statistician's rule-of-thumb comes into play as well:
if a single accident for either vehicle is enough to change the rankings,
it's a tie.) I worded my statement as I did partly to be needlessly
provocative and partly because "tied for first" is still equivalent to "has
best record."

[*] - this is the only number I'm not certain of - it may be 225 but I
don't have my spreadsheet handy.

You forget, NASA isn't re-doing Apollo sorties. Their plan is to build
a moonbase beginning with Landing No.1. That, most decidedly, will be
useful for follow-on Mars operations. So will any sorties from the
Moonbase that later astronauts make for exploration missions. That
will really help pave the way for how to explore Mars.

Besides, if Mars is the real expedition and the moon is the weekend
camping trip, then we are currently just doing jaunts around the
block.

Brian