We now want to tackle the problem of solving the equation of rocket motion Eq. ( 1.1.7). As will be seen in Sect. 2.1, even for many simple cases it can be solved only by numerical methods. Since this is not the objective of this book, we will treat only those important cases that can be analyzed analytically. This will give rise to an important characteristic quantity the so-called “delta-v budget”. Its relevance will be explored in Sect. 2.4.1.