Which construction technique is essential for the stability of a cluster rocket?

In the context of building a cluster rocket, the essential construction technique for ensuring stability is aligning the thrust vector with the rocket's center of mass. This concept is crucial because when multiple engines are clustered together, the combined force they generate needs to be directed through the center of mass to maintain stable flight. If the thrust vector is misaligned, it can create unwanted torques that can lead to instability and potential failure during ascent.

Ensuring the correct alignment of the thrust vector helps the rocket to fly straight and reduces the risk of rolling or pitching moments that could destabilize the flight path. This principle is fundamental to maintaining control of the rocket throughout its flight, making it a critical aspect of cluster rocket design.