One of the reasons why rockets are staged is to deal with the issue of expansion ratio (upper stage engines have bigger expansion ratios). Also there is the trade-off between thrust and specific impulse, Isp. A rocket needs thrust to get off the launch pad and to overcome atmospheric drag. However once the vehicle is high enough in the atmosphere, a larger Isp is more desireable. The Saturn V's first stage used F-1 engines that had a high thrust but a modest Isp. The second and third stages used J-2 engines that had excellent Isp but reduced thrust. If you look at old motion pictures of the Saturn V in flight, you can see the F-1 rocket plumes over expanding as the vehicle gains altitude (they were optimized for zero altitude). The over expansion actually gets in the vehicle's boundary layer and is half way up the vehicle when the fist stage reaches Main Engine Cut Off (MECO). Supposably the Soviet N-1 rocket was tapered to keep that from happening.
Gary
Space/Science » in reply to re: pleated rocket nozzle.
Rocket staging
The whole thread (44 posts)
- Mike Griffin's road map to Mars
- I think rocket technology is about as good as it's going to get
- Other good points
- I agree
- The 30+ years hasn't been a complete waist.
- re: I agree
- Could the shuttles be redesigned?
- I agree