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Case Study 4: A Goddard Rocket Study

Excerpt

Yes, it is rocket science; although simplified here, it is adequately rich. The objective is to schedule thrust (e.g., change thrust with time) to maximize the altitude a rocket can achieve. You could have full thrust until the fuel burns out, and then let the rocket coast up until gravity pulls it back. But this plan makes the rocket go fast in the lower altitude where the air resistance is high and wastes energy. A better plan to minimize the impact of air resistance is to move slowly in the low altitudes and then full throttle to fast speed in the high altitudes. But moving slow in the low altitudes, in the high gravitational field, means wasting fuel to fight gravity. In a limit of not enough thrust to overcome gravity, the rocket never rises; it burns all its fuel on the launch pad. This optimization is known as the “Goddard problem” in honor of rocket scientist Robert Goddard.

Yes, it is rocket science; although simplified here, it is adequately rich. The objective is to schedule thrust (e.g., change thrust with time) to maximize the altitude a rocket can achieve. You could have full thrust until the fuel burns out, and then let the rocket coast up until gravity pulls it back. But this plan makes the rocket go fast in the lower altitude where the air resistance is high and wastes energy. A better plan to minimize the impact of air resistance is to move slowly in the low altitudes and then full throttle to fast speed in the high altitudes. But moving slow in the low altitudes, in the high gravitational field, means wasting fuel to fight gravity. In a limit of not enough thrust to overcome gravity, the rocket never rises; it burns all its fuel on the launch pad. This optimization is known as the “Goddard problem” in honor of rocket scientist Robert Goddard.

39.1The Process and Analysis
39.2Pre-Assignment Note
39.3Exercises
39.1The Process and Analysis
39.2Pre-Assignment Note
39.3Exercises
Topics: Rockets

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