Comprehensive investigations of gravitationally-bound systems based on data from ground- and space-based missions offer the best opportunities to study a range of objects in our Galaxy. Current strategies for measuring the orbits of TNOs are expensive and require years of observations. Simultaneous ground- and space-based observations at L2, however, offer a unique opportunity to determine their orbits by taking advantage of the distance between L2 and Earth, resulting in instantaneous parallax measurements, which I show yields reliable orbit-determinations with little observational expense. Beyond the solar system, the current population of hot Jupiters serves as a unique laboratory for studying exoplanets, but their existence presents a challenge to current theories of planet formation and evolution. HD 217107 b was one of the first exoplanets detected using RVs, and is one of few eccentric hot Jupiters, enabling me to explore the possibility of detecting its orbital precession due to general relativistic effects. KELT-24 was independently discovered by two groups in 2019, with each reporting best-fit stellar parameters that were notably inconsistent. I present three independent analyses of the KELT-24 system that incorporate a broad range of photometric and spectroscopic data. My analyses not only increase the fidelity of our understanding of the KELT-24 system, but also serve as a blueprint for future stellar modeling in global analyses of exoplanet systems. Stellar mass is a fundamental parameter, yet relatively few stars have had their masses precisely measured. Using Gaia astrometry, I present a new statistical approach to establish a Mass-Magnitude relation applicable to >30 million stars in the Gaia catalog. I also present a dynamical mass estimate of the nearby white dwarf Stein 2051 B, which is in a wide orbit with the red dwarf Stein 2051 A. By combining precise RVs of Stein 2051 A with calibrated absolute astrometry from Hipparcos and Gaia, I measure the three-dimensional acceleration of Stein 2051 A and directly constrain the masses of both stars, as well as the orbit of the Stein 2051 binary system.