Propulsion - Orbital Mechanics (page 3 of 6)
The trajectory the space craft will follow is shown below:
Figure 3:
Homhann
Transfer Duration of 138 Days
The space craft will approach a Venusian orbit of 40,000 km. At this point the probe module will be jettisoned from the craft towards its atmospheric entry point. The probe will land along the equator of Venus. The spacecraft, now containing the satellite and the thruster module will execute a burn in order to bring the satellite to a circular Venusian orbit of 18,615 km. The orbital period will be one third of an Earth day or approximately 28,000 seconds. This will allow for a thrice daily data transmission back to Earth.
The spacecraft (before jettisoning the probe) will arrive at a velocity relative to Venus of 2,872 m/s. The jettisoning the probe will alter the velocity of the craft; that will be neglected at this point. We assume that the spacecraft, after jettisoning, will have a velocity relative to Venus of 2,872 m/s. It so happens that this velocity is sufficient to generate an elliptical orbit around the planet. In order to sustain a circular orbit of 18,600 km, a speed of 4,177 m/s is required. This will require a burn of the thrusters to at apogee to degrade the orbit and another at perigee to stabilize it at the lower altitude. The Δv to degrade the orbit is -599 m/s and the Δv required to stabilize the circular orbit is 1822 m/s. Aside from station keeping, no other burns should be required.