NASA was the most concerned with the thrust oscillation happening near and on depletion of the first stage fuel, roughly 105-115 seconds into the flight after liftoff and just before first stage separation (see Ares I-X Mission Profile below), as it was shown by the computer modeling and early design analyses of the Ares 1 rocket.
This so-called thrust oscillation occurs as solid fuel in the first stage depletes, leaving a long, empty shell that takes on the characteristics of an organ pipe, and resonates at frequencies between 12 and 14 hertz. The second stage of the rocket and the Orion spacecraft atop it would naturally dampen the resulting pressure pulses, which would essentially jackhammer the astronauts and make it nigh impossible for them to read console displays and respond accordingly during that only roughly 5 seconds long, but crucial interval of the ascent phase.
This was not ideal, so NASA engineers looked into many possible ways to mitigate this thrust oscillation at that time (probably matching the time of that "We are working on it ..." reply that you got). Some of the proposed solutions included tuned mass damper around first stage parachutes (active tuned mass or harmonic absorbers / dampers), reaction control system (a spring-and-damper ring separating the first and second stage of the rocket), active pulse RCS (Reaction Control System, actuators acting like shock absorbers and added to the bell-shaped aft skirt at the bottom of the rocket), and so on:
Engineers were also looking to use a passive "compliance structure", a spring-loaded ring detuning the stack by softening the interface between the first and upper stages, while preserving lateral stability in the Ares 1 design concept. Proposals are described in more detail in this Ares I Thrust Oscillation mitigation options head into trade study from April 29, 2008.
This concept was expected to reduce the G-forces by vibrations on the astronauts from about 0.7 G’s to 0.25 G’s (on top of 4 G’s from acceleration at that stage of the ascent). Needless to say, all this would add significant costs to designing and constructing Ares 1 first stage, stage engine, first and second interstage, and the crew module (MPCV, Multi-Purpose Crew Vehicle) adapter.
The Orion Multi-Purpose Crew Vehicle (MPCV). The MPCV includes both crew and service modules, and a MPCV adaptor.
All this was happening around the times of announced budget cuts for the next fiscal years, so they started looking at other, cheaper solutions. And good that they did, too.
NASA turned to the Human Factors Division, among them their asst. chief Human Performance, Brent R. Beutter and people from the NASA Ames Vibration Lab. They have fast realized the vibrations were limited to a rather narrow frequency range between 12 and 14 Hz. This lead them to the idea of strobing crew displays, tuned to the frequency of launch vehicle's in-flight vibrations as detected by accelerometers attached to the chairs.
Oscillating display tested with vibrations of up to 0.5 G’s, by Brent R. Beutter, NASA asst. chief Human Performance and Brent
Rose, Gizmodo stuff. Video of this demonstration is available on YouTube.
A few cheap and cheerful circuits later, the flight displays was perfectly legible even at predicted vibration acceleration up to 0.7 G’s.
Each operator was asked to locate the highlighted (magenta) box in a
display consisting of a six-by-six matrix of boxes, read and process
the contents of the middle row of digits, and then make a
two-alternative forced-choice (2AFC) based on the row's content.
Task error rates in the main condition, shown below, suggest that
vibration levels above 0.3 g (0-to-peak) may meaningfully compromise
the processing of alphanumeric symbology in the currently anticipated
Orion display viewing conditions, particularly if the font size is
small.
Source: NASA Ames Human Vibration Laboratory Research
And this is the story of how NASA solved a multi-hundred-million dollars problem for maybe a few ten thousand bucks.
