I still can't comprehend how the scientists and engineers managed to launch STS 1 (test flight) with two astronauts in 1981 - without doing a prior test launch with no astronauts inside (like SpaceX).. Absolutely incredible. I don't know what it is about the Shuttle, but the aesthetics are just really nice. The safety, of course, is a different question, but it still has a special place in my heart.
They did a lot of static testing of both the SRBs, external tank, and main engines before the first flight. This NASA slide deck gives a pretty good overview:
After all of that they were probably confident enough in the individual pieces working well individually that they were also decently confident that they'd all work well together during the STS-1. Although STS-1 through STS4 had ejection seats installed for both crew members, just in case. Perhaps the thinking was that if anything was going to go wrong, it would happen below 80k feet where the ejection seats would still be usable.
"–Up to 20 tons of payload capacity on re-entry
•1,693,500 lbs returned to earth*"
I always find myself laughing when propaganda material like this mixes units for the benefit of sounding more impressive. Capacity of 20 tons, yet they switch to pounds to get a larger number. 1,693,500lbs is only 846.75 tons, which just doesn't sound nearly as impressive.
The test pilots were pushing for no unmanned flights, and famously insisted that the Shuttle's landing gear control be a fully manual control that could not be activated remotely. This ensured the continuing relevance of the astronaut corps, since unmanned Shuttle flights weren't possible. An unmanned flight such as the one Buran later did was what the engineers wanted, but wasn't possible for what boiled down to office politics reasons.
This reminds me an old video by Scott Manley of an abort procedure of the Space Shuttle that never was tried in real life. (He used a model in the Kerbal Space Program.) "Space Shuttle RTLS Abort Challenge - Without The Manual" https://www.youtube.com/watch?v=Iwn3kk-q1YU
Unlike many of his videos which are made using KSP, this RTLS Abort Challenge video was made using Orbiter 2016 Space Flight Simulator from UCL http://orbit.medphys.ucl.ac.uk/
Brining Comic Book Guy level of pedanticism, the thing that stood out the most for me was that the space shuttle in the sim had a glass cockpit with full colour displays.
The shuttle cockpit upgrades didn’t take place until late-1990s/early-2000s, and before then, it was just green text on CRTs.
Regardless, it’s amazing to see what people can achieve with enough interest and time.
The STS 62A polar orbit mission was scheduled to take place in 1986, so the model used in the sim doesn’t correlate to what the shuttle capabilities were at the time.
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The Space Shuttle was a vehicle designed to do many things, and in a deal with the US Military it was redesigned to make it able to perform a very specific secret mission. The redesign radically changed the Shuttle from the early concepts to the actual design which we saw fly, but, before the shuttle even flew the secret mission had been abandoned.
It wasn’t a “deal” with the US military, NASA crammed it down their throat. The redesign only became necessary when NASA got congress to cancel the Air Force launch program to force their payloads on the Shuttle.
Sidenote: IMO these STS space suits were far better looking than the oompa loompa version that SpaceX has devised. In the name of minimalism, they've created something that looks like a bad hollywood low-budget scifi film (including the purely decorative bridge to the space capsule and the touch screen cockpit). It's personal opinion/taste but I can't help but look at how beautiful and professional it was back in the day. Also, traveling to the SpaceX rocket in Tesla Model X is one of the tackiest things I've seen.
I don't know about orbiter but FlightGear uses JSBsim for flight dynamics modeling which can be very accurate and was even used at NASA.
You are correct that as space is not the primary use case for FG the shuttle developers had to start from scratch on many things.
