Rocket Lab USA Inc. is nearing an agreement to go public by merging with a special-purpose acquisition company, as a wave of such deals rolls on. Rocket Lab is in talks with Vector Acquisition Corporation (NasdaqCM:VACQ) about a deal that would value the U.S.-New Zealand startup at around $4.1 billion including debt, according to people familiar with the matter. The transaction could be finalized by Monday, assuming talks don't fall apart.