LUMINARY was never completely bug free. Allan told me about a fascinating series of events that could have easily prevented the first moon landing and might have caused disaster. Allan was the principal designer of the LM’s descent guidance program which steered the LM by gimballing and throttling the descent engine. Whenever the computer commanded the engine to increase or decrease thrust, the engine (and LM) reacted after a short time lag. Allan’s descent program needed a routine to accurately estimate the new thrust level, which could be accomplished by reading the “delta-V” (change in velocity) measured by the LM’s accelerometers. He wrote a short routine that took into consideration, i.e., compensated for, the engine’s lag time, which TRW’s “interface control document”, full of useful information for the programmers, said was 0.3 seconds. It took 0.3 seconds for the LM’s descent engine to achieve whatever thrust level the computer might request. The final version of the thrust routine, which was put into the LM, was written by Allan’s friend Don Eyles. Eyles was sufficiently enthusiastic about the programming challenge that he found a way of writing it which required compensating for only 0.2 of the 0.3 seconds. The IBM 360 simulator showed Eyles’ program worked beautifully. His routine was aboard Apollos 11 and 12 which landed successfully. However, telemetry transmitted during the landings later showed something to be very wrong. The engines were surging up and down in thrust level, and were barely stable. A guy at Johnson Space Center called Allan and informed him that the LM’s engine was not a 0.3-second-lag engine after all. It had been improved some time before Apollo 11′s launch such as to lower the lag time to only 0.075 seconds. Correction of this item in the interface control document had simply been overlooked. Once this discrepancy was discovered, theIBM 360 simulator was reprogrammed to properly simulate the actual, faster engine. Running on the simulator, Don Eyle’s thrust program, with the 0.2-second compensation, exhibited the surging that had occurred on the real flights. But here’s the most interesting fact: the simulator also showed that had Allan Klumpp chose to “correct” Don Eyles’ program by compensating for the full 0.3 seconds that was printed in the document, the LM would have been unstable and Apollo 11 would never have been able to land. By pure luck, Don Eyles was creative enough to write the thrust routine in a way that kept the LM just inside the stability envelope and allowed successful landings!

Full post at tech-archive.net’s sci.space.history archive.

I just ran across this little requirement in signing up for a service that I’m now nervous about using:

Username: 3+ lowercase letters and numbers, starting with a letter.
Password: 8+ Alpha Numeric characters & must include – 1 uppercase, 1 lowercase, and a number.
Special Characters are not accepted!

No special characters?!? I haven’t been this annoyed since I figured out my database IDE couldn’t handle a schema password with an @ in the name.

• I really hope at some point they come out with the iPatch.
• The iPad is an iPhone I can’t fit in my pocket and can’t use to make phone calls.
• The iPad is an expensive, but lighter and shinier, netbook where I have to pay extra for an hardware keyboard and comparable storage.
• The iPad has access to the Apps store, so I can run iPhone apps without having to squint at them.
• Maybe the iBookstore can force Amazon to start supporting epub?
• I’d get one over the Kindle DX at a similar price. I don’t know about Kindle 2.0 at its current price point.
• Unlike the iPhone, I could use it for extended reading. One also assumes the Amazon Kindle app will still work.
• iWork apps are kind of cool. Could use it for presentations at work.
• I love the data plan pricing, particularly the pre-pay option.
• I kind of wonder about the whole 250MB plan. That could be fine on the iPhone, but I suspect people would use video on this more frequently.
• Might have been an awkward design at 16:9, but I was a little surprised at the 4:3-ish screen ratio. Oh well, it’s not a TV.
• Games will be prettier, faster, and more involving, but I’d need to pick one up to see whether the size would be awkward for a handheld.

I like this gadget, but I just can’t see where it would improve my life in the age of the iPhone and netbooks. I’ve already got light-enough computing in a form factor that’s been around forever, and I’ve got good-enough ubiquitous data access.

But, that all being said, it’s one step closer to that future of computerized houses, touchpads, and jetpacks I’ve been hoping for since I was a kid, so I appreciate it for that.

Update: Almost forgot…if it’s running the iPhone OS, I’m guessing no Flash. Maybe more pressure to adopt some HTML5 alternatives?

Update, redux: I’m getting slightly irritated by the sheer number of blog posts I’ve read lauding the iPad as high-tech at a cheap price. Really? At the base level, it’s a 1GHz processor, 16GB of flash storage, 1024×768 multi-touchscreen, and Wireless-N. It’s not delivering high-tech…it’s delivering good-enough tech in a better form factor than we’ve been used to. That’s called design, and Apple does that regularly.

BTW, I have figured out an awesome use for the iPad in my life: A computer my mom would regularly use. She’s not a big fan of mice, or touchpads, or the pointy cursor, but a large touchscreen would be awesome for her. Now, if AT&T would actually deliver 3G to Reidsville, NC, getting her on the Internet would be easy. As it is, we’d have to get cable or DSL and a wireless router in her house.

The processor is more than fast enough to run software written in capitalistic programming languages like C++, but the majority of the user interface is written in slow left-wing languages like Python. – Errata Security: Why the OLPC promotes terrorism

I mostly program in ColdFusion at work. I like to think of it as a feudal language.

Link courtesy of Global Nerdy.

Link courtesy of TheCrumb.com.

The article is a good tutorial on the CFEclipse plugin for the Eclipse IDE, which I use for ColdFusion coding at work. (Eclipse and I have come to a pause in our struggle and are trying to normalize relations to avoid future conflict.) I had been ignoring the snippet feature for a while, since I didn’t see a lot of time savings with it, but Jim’s article convinced me to use it again.

Anyway, if you want more about ColdFusion, check out TheCrumb.com.

So, software for mobile phones that allows third-party applications? Sounds like a direct shot at OS X on the iPhone. I wonder if Apple will get their SDK out there a little earlier now? (Too bad they didn’t work together. That would have been interesting.)

Link courtesy of Planet Intertwingly.

I HAS A <var> ITZ …

Declare a variable. Note the following:

• Every variable is an array.
• ITZ … has been reserved for future usage and should not be used (except possibly for initialization of single-element arrays)
• At present, all arrays are heterogeneous (they can have different types of values in them). This may change in the future!

All values are typed, and the types are:

• NUMBAR (signed integer, at least 32 bits wide)
• YARN (string)
• ARRAY (contains NUMBARs and/or YARNs and/or ARRAYs)

Currently the interpreter and/or compiler does type checking at compile and/or runtime. This may get nailed down to one or the other in future recommendations.

There is also a .NET compiler.

I’m going to be lucky if I can get through the day without typing CAN HAS or KTHXBYE into my code.

Update: Good examples of code.

Link courtesy of Boing Boing. Title courtesy of PawSense.