Craig,
What happened to Starliner is (probably) what they claim. The gains were not
wrong. It was the wrong burn mode and used the fuel that was expected for that
mode. This is pretty standard and no this is not a forgotten lesson.
ian
--
Ian M Garcia
From: Craig Fink<mailto:webegood@xxxxxxxxx>
Sent: Saturday, December 21, 2019 11:40 AM
To: arocket@xxxxxxxxxxxxx<mailto:arocket@xxxxxxxxxxxxx>
Subject: [AR] Re: LEO radiation shielding
Speaking of Control Systems, fresh out of College, with my first real job
working GN&C on Space Shuttle I was assigned to help with the On-Orbit post
flight report for STS-1 and STS-2. One of the problems these first few flights
was in attitude control, the gains were wrong resulting in excessive fuel
usage. Essentially, banging back an forth from positive limit to negative
limit, hosing out propellant. Things haven't changed much in 40 years with
Starliner as the NASA administrator is talking about the problem.
https://youtu.be/NpQlxN4xbKM?t=85
Here he's saying the attitude tried to maintain "to precise" an attitude
window, which isn't the problem, it's the gains were wrong. The precise
tolerance just means it takes much less time to get from the +side to the
-side, so it hosed fuel out faster. But even with a very loose attitude
window, if the gains are wrong, it's going to be banging back and forth
(+-+-+-+-+-+ firings) from one limit to the other.
--
Craig Fink
WeBeGood@xxxxxxxxx