The semimajor axis of Mars orbit is about 1.52 astronomical units (au), where an au is the Earth's average distance from the Sun, meaning the semimajor axis of Earth's orbit is 1 au. To go from Earth to Mars and use the least energy from rocket fuel, the orbit has a semimajor axis of 1.26 au and an eccentricity of about 0.21. Starting at Earth's orbit, to follow this path we give the spacecraft an orbital velocity of 40 km/s. Which of the following describes this best? It arrives at Mars orbit at the same moment that Mars is there, and must speed up to go into an orbit next to Mars or else drop back into perihelion (closest to the Sun) at Earth's orbit. It arrives at Mars orbit at the same moment that Mars is there, and must slow down to go into an orbit next to Mars or else drop back into perihelion (closest to the Sun) at Earth's orbit. It flys past Mars on its trajectory unless it is braked by accelerating toward the Sun. It which leaves Earth when Mars is nearly closest to Earth and traverses the smallest distance possible, nearly straight out along the Sun-Earth-Mars line. It arrives at Mars with exactly the same velocity as Mars has in its orbit, so the two are naturally in lock step and only a little adjustment is necessary to go into orbit around Mars.
The semimajor axis of Mars orbit is about 1.52 astronomical units (au), where an au is the Earth's average distance from the Sun, meaning the semimajor axis of Earth's orbit is 1 au. To go from Earth to Mars and use the least energy from rocket fuel, the orbit has a semimajor axis of 1.26 au and an eccentricity of about 0.21. Starting at Earth's orbit, to follow this path we give the spacecraft an orbital velocity of 40 km/s. Which of the following describes this best?
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It arrives at Mars orbit at the same moment that Mars is there, and must speed up to go into an orbit next to Mars or else drop back into perihelion (closest to the Sun) at Earth's orbit. |
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It arrives at Mars orbit at the same moment that Mars is there, and must slow down to go into an orbit next to Mars or else drop back into perihelion (closest to the Sun) at Earth's orbit. |
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It flys past Mars on its trajectory unless it is braked by accelerating toward the Sun. It which leaves Earth when Mars is nearly closest to Earth and traverses the smallest distance possible, nearly straight out along the Sun-Earth-Mars line. |
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It arrives at Mars with exactly the same velocity as Mars has in its orbit, so the two are naturally in lock step and only a little adjustment is necessary to go into orbit around Mars. |
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