Sì, è proprio così.
Lo spiega anche Bolden nel video prima di entrare nella Space Shuttle Experience al KSC.
Se digiti twang su google/youtube troverai molti link a riguardo.
Wikipedia dice così:
After the main engines start, but while the solid rocket boosters are still clamped to the pad, the offset thrust from the Shuttle’s three main engines causes the entire launch stack (boosters, tank and shuttle) to pitch down about 2 m at cockpit level. This motion is called the “nod”, or “twang” in NASA jargon. As the boosters flex back into their original shape, the launch stack pitches slowly back upright. This takes approximately six seconds. At the point when it is perfectly vertical, the boosters ignite and the launch commences.