Space is hard. Justifying Rocket Lab's stock price may be harder.Rocket Lab (RKLB 4.68%) stock is taking investors on another roller-coaster ride Monday morning. First spiking past 7% in the opening minutes, the stock began losing steam almost immediately, falling into the red before 10 a.m. before finding its footing and rising again.As of 10:45 a.m. ET, Rocket Lab stock is up 2%.Why did Rocket Lab stock pop?Investors enjoying today's ride can thank two investment banks, Morgan Stanley and Citigroup, for t ...