Path: csiph.com!eternal-september.org!feeder.eternal-september.org!news.eternal-september.org!.POSTED!not-for-mail From: Keith Thompson Newsgroups: comp.lang.c Subject: Re: Mars lander crash Date: Fri, 09 Dec 2016 16:49:04 -0800 Organization: None to speak of Lines: 52 Message-ID: References: Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Injection-Info: mx02.eternal-september.org; posting-host="d3e5cee4cb06db8dd070f0b5a238435d"; logging-data="9985"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX1/Zlziov2YiM+1/lpiKlcQj" User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/23.1 (gnu/linux) Cancel-Lock: sha1:bF1IUXzOI90+NCLv72B2k9rit2M= sha1:n3LJx7YvHKTeZgaEV+jaE9GU+x4= Xref: csiph.com comp.lang.c:98639 ram@zedat.fu-berlin.de (Stefan Ram) writes: > ram@zedat.fu-berlin.de (Stefan Ram) writes: >>In 2004 clock speeds suddenly stopped to grow. The single-threaded >>free lunch was over. That's why Microsoft now prefers C++ over C# >>again. > > Here is a recent wording. Reportedly, "the explanation". > > »But shortly after the parachute deployed, > Schiaparelli's IMU [Inertial Measurement Unit] reached > saturation (maximum inertia) --- and the IMU reported at > saturation for longer than the navigation system expected.« > > . »Saturation« is not overflow. It might mean another means > of handling very large values: one does not "wrap around" or > throw exceptions, but replaces them by the largest value > still representable. > > But the wording is quite vague. What is "inertia"? Do they > mean "acceleration"? > > »When the navigation system got wind of the IMU's wacky > output, it decided that meant the spacecraft had > "an estimated altitude that was negative"«. > > This really sounds strange. There was nothing "wacky", it > sounds as if the IMU was just doing its job and reporting > correct data. It doesn't sound like that to me. The article says that the IMU was reporting unexpected data; how do you conclude that it was reporting correct data? > And it really sounds like a programming error. I don't think we can conclude that, at least not from the information we've seen here. > "The acceleration is large for a long time, so we must be > below the ground.", why should this implication be assumed? You're assuming "maximum inertia" means "large acceleration". I don't think that assumption is justified. The phrase "maximum inertia" doesn't make much sense (possibly a misinterpretation by a reporter?), but I'm very hesitant to make *any* assumptions about what was actually meant. -- Keith Thompson (The_Other_Keith) kst-u@mib.org Working, but not speaking, for JetHead Development, Inc. "We must do something. This is something. Therefore, we must do this." -- Antony Jay and Jonathan Lynn, "Yes Minister"