|The NASA Glory rocket being loaded for launch|
Photo from NASA
A video of the launch is about half way down this WWW page. It is worth watching for several reasons, the saddest one being the problem at the end. It has narration, the stage 1 separation comes at about 1:45, and at 2 minutes into the mission, all systems nominal. The tape skips ahead to 5 minutes at 2:40 into the tape and the narrators indicate that the vehicle velocity is not correct and that it is likely that the fairing had not separated. In researching this, I found a site called "Space Launch Report" that appears to track space launches around the world.
Rockets work because of Newton's Third Law of Motion. Mass accelerates through the rocket engine and out of the rocket with a certain velocity and at a certain overpressure at the exit plane (overpressure is the difference between the pressure of the gas and local atmospheric pressure). In response, the thrust force is applied to the engine in the opposite direction. A calculation of thrust has two terms: the first is the mass flux times the velocity, and the second is the overpressure times the area. Thrust changes continuously throughout a launch because the mass flux and velocity of the gas change, and because the overpressure changes as the rocket rises higher and higher into thin atmosphere.
It is easy to envision the overpressure change by watching the change of shape of the exhaust plume as the rocket rises (as shown on the two images above). Near the surface of the earth, the plume tends to be fairly "straight," whereas it flares out in a very pronounced manner as the rocket rises into the near vacuum of space. You can see this change in plume shape on the video of the Gloria launch referenced above, worth going back for a second look!
In my next blog, I'll discuss how this rocket technology is relevant to volcanic eruptions, and particularly, to the eruption of Mount St. Helens in 1980.