8.17 The next five problems are based on the Messenger spacecraft launched from
Earth on August 3, 2002. After gravity-assist maneuvers around the earth, Venus,
and Mercury, Messenger is scheduled (at the time of this writing) to go into orbit
around Mercury on March 18, 2011. The radius and mass of Mercury are 2,440 km
and $3.3 \times 10^{23}$ kg, respectively. The orbit is designed to be highly elliptical, with
the altitude of closest approach (periapsis) of 200 km, and the altitude of farthest
distance (apoapsis) of 15,193 km. (Note: These are altitudes above the surface of
Mercury, not the distances from the center of the planet.) Calculate the period of
the Messenger orbit. Ignore the influence of the gravitational attraction of the sun
on the spacecraft orbit.
8.18 For the Messenger spacecraft in orbit about Mercury (see Prob. 8.17), calculate
the spacecraft's velocity at periapsis and at apoapsis.
8.19 For the Messenger spacecraft in orbit about Mercury (see Probs. 8.17 and 8.18),
calculate its angular momentum per unit mass.
8.20 What is the eccentricity of the Messenger's orbit about Mercury?
8.21 From the characteristics and properties of the orbit, some of which are given in
Prob. 8.17, it is not possible to extract the mass of the Messenger spacecraft. Why?