Interesting read on navigating to the moon

I can see the directions now, "Second to the right, and straight on till morning."

screaming: "u-turn, u-turn, u-turn!"

Who needs GPS? You can see where it is right from here!

During the Apollo moon program, NASA only needed to use pi to 4 decimal places to navigate to the moon and back.

That was when I went to college, became an engineer and pushed around a slide rule. Slide rules made you think because you had to supply the position of the decimal point. As an example, for those not familiar with a slide rule, the position of the components were the same if you multiplied 2 x 3, 20 x 3, 200 x 3000, etc. Today of course young people are not very adept at many basic math skills.

Relatively full featured calculators made by Texas Instruments and HP came out in 1975.

IIRC the backup navigation computer was an HP hand calculator with a mag-stripe input for programming. The HP-65 was introduced in '74 so that wasn't it.

My dad studied electronics before WWII. He learned to reduce problems so that every step involved rotating the slide rule 180° (on it's major axis). I could never reduce problems to that.

Never used a "stick" slide rule more than a couple of times. In College getting my degree I always used a circular slide rule. I think I still have it in the attic somewhere. A museum relic by now....

Won’t be doing the algorithms…they’ll end up on Mars

Four-banger handheld calculators were just starting the tumultuous run from expensive curiousities to cheap throwaways when I was on my last Bell Labs co-op assignment in 1971. You could expect to pay hundreds of dollars for one that did nothing but My Dear Aunt Sally (multiply, divide, add, subtract). And as this was before the great inflation of the late Carter and early Reagan years, those hundreds corresponded to thousands today. None of my fellow MIT students had one.

The next year, 1972, HP brought out their first calculator--the HP-35. It had full scientific notation, fabulous accuracy, pleasing ergonomics that fit the hand and eyes well, keys with the labels embedded so they never wore off... And for $400 it seemed at the time a shockingly good buy. Still pretty pricey for an MIT student, and I only knew one fellow student who got one.

The next year, 1973, Texas Instruments entered the scientific calculator market with their SR-50 (Yes, Wikipedia says 1974--but I know better). To a student, it seemed a near functional equivalent to the HP-35 we all lusted for, and at less than half the price far more accessible. I bought one in late 1973. It had a few advantages over the HP-35, and several disadvantages--much less accurate arithmetic, for one, though few understood that, as a first glance it carried more digits. I think I paid about $170 for mine about October 1973. I'm dead sure I already owned it when I quit graduate school at MIT and drove west to take a job with Intel at the beginning of 1974.

You apparently weren't infected with the superior religion of RPN (Reverse Polish notation). I still have scar tissue.

Two points for me regarding Polish. Our small MIT fraternity had so many Polish speakers that the front line of our intramural hockey team could talk freely to each other in private on the rink. The one who was my roommate at times had only come across a little over a year before he entered MIT.

Now, back to RPN, it is worth mentioning that my next two (and last two) calculators were both HP. First an HP-65 (a programmable one that relied on mag strips for program memory), and then an HP-67, which was superior to all the others before it in a host of ways--not least that it discarded LED display with NiCd battery that chained you to your charger, in favor of LCD display with primary batteries that would last for many months of normal use, and would keep the program memory intact through years of neglect. I've now neglected mine for the most years ever. I need to stick in fresh batteries again and see whether it once again forgives me and remembers a program I had put in by 1983. First I need to check the replacement batteries, as they have been sitting in my drawer for many years also.

brings back a lot of memories. When HP brought out their HP-35, I had been doing engineering calculations for a living for about 12 years, first on the Apollo program and then for the DC-10 aircraft.

The company (Douglas Aircraft) had several Frieden and Marchant mechanical calculators in the group for our use, but I immediately lusted for the HP-35. However, the price was more than I made in a week before taxes and other deductions, so my lust went unrequited.

Finally, at the time HP introduced the HP-45 (a significant improvement on the HP-35, IMO), the company introduced a program where I could buy an HP through them and pay for it with six months of interest-free payroll deductions. With my extravagance spread out for so long, and also invisible to my wife, I jumped at the chance to get a HP-45, which DID turn out to be a really, really useful tool.

It's easy for ME to understand why one of the first Apps that I bought when I got a smartphone is a very nicely done emulator of the HP-45. (I still have the HP-45, but the batteries died permanently decades ago and then the charger also passed away after many additional years of keeping the HP functioning.)

- Tom -

Wouldn’t it be just a straight line of sight situation?

The moon is 2160 miles in diameter so to land at a precise location on the lit side requires some form of precise navigation. The back side is never visible from earth, so any exploration there would likely also require some form of external navigation. I’m not an expert on radio communications, but I would think the moon itself would block backside communications.

Since the moon is in motion with respect to earth that won't work. If we shot a rocket at a particular spot on the moon and went in a straight line the moon would be long gone by the time that the rocket got to what it thought was it's target.

Recalculating ...

Recalculating ...

Recalculating ...

My wife and I still use our HP-15C calculators. The HP-15C was so popular that HP came out with an emulator app for the iPhone. That is still a great calculator.

Take a slight right after the third Dunkin' Donuts.

Still have both my HP-55 and HP-15C calculators. Also got the Hewlett Packard HP-15C iPhone app and a Windows HP-15C app (produced by Vicinno Soft LLC) that was available for a while at the Microsoft Store. Ditched my slide rule in the mid 70s for the HP-55. As long as we are talking old tech, I still have a couple of IMSAI 8080 computers in the basement.
Mark

I've been looking for a 15C, but the secondhand values are ridiculous. Best I could do for older calculators was a 20S, which is noteworthy for being one of two HP calculators that in the late 80s was NOT using RPN.

The "G" had 32 KB Memory (Non-Expandable) and was graphing capable. Batteries are still available (AAA). I have the case but no manual although it is available online (600+ pages) Works fine, I just prefer my 15C.

Make an offer if interested.

...while I would be interested, finances took a huge hit prior to the holidays. Sadly, it would sit around like most the calculators I have here. I rely on a scientific calculator app for the few calculations I need to do, though I'm rather partial to my TI graphing calculator emulator for Android with a TI-89 Titanium ROM installed.

Sorry. I just had to say it. Actually, a very interesting read. Makes you wonder how we ever succeeded with the voyage so long ago

Above I asserted that my second HP calculator was an HP-67. Possibly it was, but if so I went on and got an HP-41CV.

That is the one that had LCD display, and was thus able to dispense with NiCd batteries keeping one chained to the charger. It had an odd choice of cells--alkaline type N.

I left a program in the calculator when I left one employer in 1983 which not only survived until I came back in 1987, but continued to survive, even though as I stopped using it I often let the batteries run out.

If I let the batteries run out, often the calculator would not turn on after replacing them. I learned to wait half an hour, and up until my previous battery change in 2013 it still remembered that program.

This time waiting half an hour was not enough. Neither was an hour, but three hours was enough to get it to turn on. However all programs seem to be gone. Pity, but I've forgotten how to run them, anyway.

It is still a fine handheld calculator. Maybe I'll stop putting minor side calculations into Excel and use the HP-41CV instead. I did that for years after I had a PC on my desk.

I was a huge fan of HP calculators ever since I was an engineering student in the mid/late 70s. I had quite a few over the years, but the one I remember most was the HP-41CX, the last in the line of the 41 series. As I recall the 41s were the first to have a full alphanumeric display. Made programming much easier since you didn't have to remember/look up the row/column key labels that had been the norm up until the 41.

But the coolest thing about the 41s was called "synthetic programming". I had no idea it existed until a very geeky engineer I worked with at the time told me about it. Basically, it was a bug in the firmware that allowed you to get into the system memory area and do things you weren't supposed to be able to do (including locking it solid, which I fortunately never did). I promptly went out and bought a book about it - books were about the only option available pre-internet - and wasted far too many hours playing with it. The bug was present in the very first 41Cs that came off the line. HP could have easily fixed it on later models, but wisely left it intact since it quickly developed a large cult following.

One of my memories from the early sixties is the evening we invited several of my Apollo program colleagues to dinner at our apartment.

At that time there was no real data on the characteristics of the moon's surface, so NASA had a project called the Ranger program that was intended to crash into the surface to obtain data. They had just had a launch a couple of days earlier that went off-course and was going to miss the moon by a LONG ways.

When my colleagues were leaving after dinner that night, they opened the door of our apartment to be greeted by the sight of a full moon, a glowing orb just above the horizon. One of my colleagues turned to another and said, "Look at that target, Dave! Look at THAT! With a target like that, how could they miss? HOW COULD THEY MISS ???"

Sixty years later, my wife and I still joke about that night.

- Tom -