The Interstellar Boundary Explorer (IBEX) is a Small Explorers (SMEX) mission that will provide the first globalviews of the Sun's interstellar boundaries (see McComas et al.1,2,3). For a spacecraft in a low-Earth orbit, attempts tostudy this region would be drowned out by the Earth's magnetosphere, so developing these global images requires ahigh-energy orbit that puts the spacecraft beyond the magnetosphere for the majority of the time. Scheduled tolaunch in the fall of 2008, IBEX is the first Pegasus-class spacecraft to achieve such a high energy orbit, using aninnovative ascent profile that efficiently combines the performance of the Pegasus launch vehicle, an additionalsolid rocket motor, and the spacecraft's hydrazine propulsion system. The Pegasus launch vehicle will target a 200km circular orbit, and 22 seconds after Pegasus separation IBEX will fire its own solid rocket motor to boost apogee.A series of hydrazine burns then finishes the job, raising both apogee and perigee to a 7000 x 319,000 km altitudeorbit.This paper begins with the initial daunting problem of finding the performance to reach a high enough orbit andsteps through a series of innovations that led to a final design that could reach such an orbit with performance tospare. This ascent approach and mission orbit also present several unique challenges, such as the potential for solareclipses lasting longer than 10 hours and lunar orbit perturbations that can reduce the orbit perigee to below thesurface of the Earth. This paper discusses how those challenges were addressed, and also discusses how the IBEXascent approach could be applied to future high-apogee – or even Earth escape – missions.
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