A satellite describes a circular orbit at an altitude of $19110 \mathrm{km}$ above the surace of the eaarth. Determine $(a)$ the increase in speed required at point $A$ for the satellite to achieve the escene velocity and enter a parabolic orbit, (b) the decrease in speed required at point $A$ for the satellite to enter an elliptic orbit with a minimum altitude of $6370 \mathrm{km},(c)$ the eccentricity $\varepsilon$ of the elliptic orbit.