I'm back!


Hi folks,

I just posted a question to the forum, and decided I should re-introduce myself.

I’m back after 2 years. 2 years ago I was actively buying, selling, collecting, and repairing the classic series, and the 67/97 models. One day I was looking at my 42s and remembered how I always wanted an HP in my younger days, but never could afford one. I was in Junior High when the 35 came out. By the time I could afford one, the HP-11c was out. Later I bought a 42s, and still use it. Back in the day I had programmed part of the Space Shuttle ascent guidance system on the 42s. Yes, I am in fact, a rocket scientist.

Over a few months I collected a 35, 45, 65, 67, 97, and an 80. Never could find an affordable 55, 70 or the 91. To fund my hobby I learned to repair just about anything that typically goes wrong with these.

I even thought about starting a little side business repairing these, but I doubt I could earn a living off of it. But one never knows; I’ll probably get laid off soon, so the skill may come in handy.

Anyway, its good to see many of the same names here from 2 years ago. Hopefully I can contribute a bit, but I have to relearn a few things.


Dan W


Interesting !

I knew that 41CVs were used on the Space Shuttle program but you are implying the 42s was as well.

Some more questions if I may .

Do you have copies of your program you could share ? Or maybe they aren't publically available ? Do they still need or use calculators on the lates shuttle missions and if so which ones.




I used the 42s while designing a new shuttle ascent guidance algorithm called "TAL Droop". Getting time on the mainframe simulation was slow so I found it a lot easier to do all the prototype work on the 42s. Only after I verified the equations of motion, did I code it into the main simulation.

I also used the thermal printer to create a graph of the shuttle altitude. I'd end up with graphs about 6 inches long showing the altitude going up, then drooping down, then up again.

TAL Droop was a scenario where 2 SSMEs fail sometime soon after SRB sep. The T/W was so low that the vehicle would begin to loose altitude. After a while it would burn enough fuel to begin rising again. The altitude it drooped to was critical. If too low, thermal stress on the ET would cause the tank to explode. I had to predict that altitude well ahead of time so the crew would know to either ride it out hoping for a TAL landing, or get off the tank before it was too late and ditch.

I kept the program on the 42s for a few years, then I printed it, taped it to paper and photocopied it. I probably have it in my records somewhere.

Edited: 16 July 2009, 10:15 a.m.



Very interesting! I always wondered about the "single engine press to MECO" call and what were the crew's options if they didn't get to that point. Thanks for giving us a bit of insider history on that.

I found this recent paper that seems to describe what you mentioned in more detail for the potential Orion missions.


Edited: 16 July 2009, 2:19 p.m.


Hi Katie,

Yea the abort mode I developed was part of a larger activity to create "contingency aborts" that started after the Challenger disaster. We looked seriously at multiple SSME failures and wanted to keep the crew alive in the event of a ditch in the ocean. The bailout was created during this time. This is where they open the hatch and slide out on a pole. The pole was required because without it, the crewmember would probably hit the wing by just jumping out. A bailout was required because structural analysis showed that in the event of a ditch, whatever was in the payload bay would come through the cockpit when it hit the water.

By the way, I used your idler gear replacement idea on one HP-97 printer. Thanks! Worked like a charm.


Thanks. That's more than enough information for a non rocket scientist ! I suspect the maths/physics equations used in your program would go someway beyond my A Level Maths/Physics knowledge now long forgotten anyway.



Welcome back!

Is your potential near-term unemployment related to the winding-down and impending retirement of the STS, or just the general economy? (Obviously you may provide as much or little information on your personal situation as you like.)



I don't work for the space program any more. I left out of frustration with the inability to do long term planning, and I thought the space station was of little scientific value. They could have done so much more were it not for politics. I could go into a lot of detail here, but I'm not sure I want to get up on my soap box at the moment. I hope one day to go back. Space is my first love.


Dan, since you worked for NASA, did you ever see any of the listings or documentation for the programs that were written for the HP65's that were used in the Apollo-Soyuz Test Project? If not, do you know anyone that might have info on these? I've been trying to get that information for years (along with others), with no success. I even wrote Sol Liebergot, EECOM on Apollo 13, and he tried but came up short too.


Hi Don,

At the time I worked there I wasn't especially interested in the classic HP's. The Johnson Space Center has a great technical library. All of the records would be there on microfiche.

Once I was tasked to develop a precision lunar lander algorithm for a robotic explorer (which was canceled, like most of the really interesting stuff back then). At any rate I asked around JSC: Who knows how to land on the moon?

Guess what! No one did. The technology had been forgotten. This still amazes me, it is very possible to loose the knowledge to do things, like land on the moon, or build pyramids. Fortunately I had the library. I scrounged around in there for a week or so and dug up a bunch of Apollo technical documents, some of the original algorithm designs as far back as 1963. I am indebted to an engineer named George W. Cherry who did the initial design work.

So I am confident the documentation is there somewhere on microfiche. They were good about documenting everything. It may be hard to find though.

I've been gone long enough that I don't really have any contacts there now. Let me think about it. It may be very possible to get guest access too, if someone is in Clear Lake.


Thanks, Dan.

I did contact some library researcher at JSC a few years ago, and she checked some data base and couldn't find anything about those HP65 programs, but I'd bet there is something there, like you say, on microfiche. If I lived there, instead of Louisville KY, I'd go myself and try to find the info.

Yes, if you do find something, please let me know. Wow, today is the 40th anniversary of Apollo 11 liftoff. I was there, ten miles away in a post office parking lot in Titusville FL, with my super-8 movie camera. I transferred the film to DVD a few years ago and show it to all my math students. They love those old cars!


Have you uploaded it to Youtube?


I don't do youtube, or facebook, or twitter, or any of that kind of stuff. I'll leave all that for the younger generation.

The file on the dvd is big, 88 mb. The video clip is only about 3 or 4 minutes long, and it shows cars in the parking lot around where I was parked, and an Army helicopter that flew by right before launch. The actual launch pad was 10 miles away, but you can see the ignition and flames and liftoff. It's home movie quality, and I have no objections with sharing it with anyone who is interested, but I think it's too big to upload anywhere and I've never copied DVD's before, although I "think" my computer can do that.


Don, the free file sharing platforms like MegaUpload.com or RapidShare.com (free for the uploader and the occasional downloader, fee based for the downloader who wants maximum speed, like me) provide massive space. An 88MB file is of moderate size. You need some uploading power (most Internet lines have asymmetric bandwidth) or you must be patient while uploading. If you upload the file I can put it on my MegaUpload account so that it will not expire.


OK, thanks to Marcus, the video is uploaded here. You will need the DivX codec to view it, if you don't have that already.

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