Re-entry
I got a bunch of video games for Christmas. They're all notable for one reason or another but the one that's been haunting me lately is called "re-entry an orbital simulator". It's a flight simulator developed by a solo developer recreating the American Mercury, Gemini, and Apollo space missions. I've always been interested in the engineering behind the space program and this game is my chance to learn what all those buttons do.
So far I've completed the Mercury training and I'm about half-way done learning the interior controls for the Gemini spacecraft.
It's interesting to see the engineering behind these spacecraft. The Mercury capsule was largely self-guided using 1960's technology, leaving the astronaut as little more than a passenger. Pilots were only responsible for monitoring and signaling the automated system and dealing with any emergencies, often by stepping through a paper checklist.
It's fun to know what each button and knob does but it's also fun to see all the redundancy built into the controls and guess the engineering reasons behind them. I suspect there was a good reason for the Mercury capsule to have 3 primary batteries, 2 backup batteries, and a third (called the isolated battery) to handle maneuvering. The electrical system was designed so you could remove or replace all the battery connections from the main bus using switches in the cockpit. Making all this work with 1960's technology and still be understandable is, in itself an interesting UI feat.
Most of the systems are routed through three-position fuses. Each fuse has two different ONs and one OFF. I'm not sure why they have redundancy in the shorted position but only a single open position. Is it because open circuits are less prone to failure? Are they less fatal to the mission? There isn't much feedback in some of these systems; how do you know that a fuse in position 1 has failed and should be switched to position 2?
Controls for blood pressure, suit temperature, and suit fans and fuses are found on the console along with the other cabin controls. How much was the astronaut plugged into the capsule? How easily could he get himself unplugged in an emergency? I seem to remember the first astronauts raising a fuss about having to wear rectal thermometers and diapers under their suits.
The mercury capsule has two separate fuel tanks for automatic RCS thrusters and manual thrusters. This seems to suggest the computer (the Automatic Stabilization Control System ASCS) wasn't trusted to not burn all the propellant during it's automatic attitude correction.
In both the Mercury and Gemini space capsules there's a DC and an AC electrical system. The AC is generated by inverters from the DC supply and is used to drive the fans and ASCS. This just seems crazy. Adding 250V lines to a oxygen pressurized spacecraft tempts disaster. Did they not have DC fans? Why did the digital computer require AC? Were they in a rush and had the mass allowance to just throw in another electrical system so they could re-use flight-tested hardware?
The game has an overwhelmingly positive rating on steam but I think it's because the only people who are playing it are massive space nerds like me and everyone else avoids a simulator where you're expected to sit in a cockpit among hundreds of buttons, knobs, and switches with strange acronyms. One of the reviewers said he hadn't played the game yet but was having a blast reading the manual. Each spacecraft comes with a 100+ page manual covering the various systems. You can see them here
So far I've gone through the Mercury training having launched, orbited, and landed the capsule and I'm working through the Gemini missions.
The Gemini spacecraft has an on-board computer that can be programmed (from tape!) and queried with a keypad. I don't know what happened between the two programs but the Gemini requires much more manual intervention. Each stage of orbital entry and retrograde burn is tracked by the computer which lights up a button but it's up to the astronaut to press it.
The flight controls are an order of magnitude more complex. I haven't gotten into changing the angle of inclination, orbital rendezvous, or orbital circulation but I suppose the extra controls let you do that.
I almost get the sense they were so proud of their new computer technology they included it even though it was kind of a pain. To compute your retro burn (essentially deciding when to de-orbit your spacecraft so you land in a particular spot on earth) you punch in 19 on the computer keypad and hit enter to get the time in seconds to retrograde. Then you program this number into an awkward facsimile of a digital clock, and load the re-entry program on the computer from tape - which takes 10 minutes and during which your computer is unavailable. When your digital clock runs out you know when to manually trigger the next stage of de-orbit. You can see this in action starting at 11:40 in this video
So far I'm really enjoying the game though it's still in early access and the graphics and effects are rough. I haven't blown up a spacecraft yet, it may not be possible in this early version of the simulator, but I accidentally ejected myself, didn't realize my temperatures sensors were off the scale (threatening a fire in my pure oxygen pressurized cabin), and I got trapped in space a few times when I messed up my retro burns.
I think I prefer the Mercury aesthetics over the Gemini.
Games like this and kerbal space program are fun to play in the dark before bed. In the quiet dark they become a meditative exercise of tracking fuel expenditure, battery, and oxygen use and watching clocks tick down to trigger events. I've somehow got 190 hours of playtime in KSP and I suspect I'll find this game equally absorbing if not as time intensive.
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