Program suited for studying planetary orbit missions including mapping and flyby components. Sample data included for geosynchronous station drift cycle study. Venus radar mapping strategy, frozen orbit about Mars, and repeat ground trace orbit. Written in FORTRAN.
[Show abstract][Hide abstract] ABSTRACT: An extensive calibration of semi-empirical atmospheric density models (JR-71, MSIS-86, MSISE-90, TD-88) was carried out, by analyzing the orbital decay of nine spherical satellites in the 200-1500 km altitude range. The orbital decay data used spanned a full solar activity cycle (1987-1999). The drag coefficients obtained by fitting the observed semimaior axis evolution with a high accuracy orbit propagator were compared with those estimated by theoretical analysis. MSIS-86 and MSISE-90, practically identical above 200 km, resulted to be the best models to compute air density below 400 km, in low solar activity conditions. However, JR-71 seemed more precise at greater altitudes and/or solar activity. TD-88 gave quite mixed results, but generally closer to JR-71. The intrinsic accuracy of JR-71, MSIS-86 and MSISE-90 was generally better than 20%, often better than 15% and, sometimes, close to 10%. But at altitudes greater than 400 km this picture resulted progressively degraded. A better drag coefficient theory and dedicated laboratory measurements will be needed to investigate in detail the deficiencies of the current models and improve the knowledge of the earth atmosphere with satellite drag analysis.
[Show abstract][Hide abstract] ABSTRACT: The external tank is currently the only non-reusable portion of the National Space Transportation System. The tank has 98% of the energy required to be placed in orbit at the point it is jettisoned. The purpose of this study is to develop techniques which would transform this throw-away item into a source of construction material at low earth orbit. A simulation is developed to verify the reduction timelines and peak power requirements for manual and automated reduction. The required tools to accomplish the tasks of initial cutting, product transport, spray on foam insulation removal, and product storage are developed. A trade study is conducted to determine the proposed method of power generation. Orbit models are developed to predict the orbital decay of the facility and its annual fuel requirements. A thermal model is developed and the thermal impacts of on-orbit salvage are investigated for three scenarios. A probabilistic cost model is developed and life cycle costs are projected based upon reducing four tanks per year. It is shown that more than 52,000 lbs of readily usable construction material in the form of I-beams and plate can be salvaged annually, and is cost competitive compared to equivalent products launched from earth.
[Show abstract][Hide abstract] ABSTRACT: Planetary Observer High Accuracy Orbit Prediction Program (POHOP), an
existing numerical integrator, was modified with the solar and lunar
formulae developed by T.C. Van Flandern and K.F. Pulkkinen to provide
the accuracy required to evaluate long-term orbit characteristics of
objects on the geosynchronous region. The orbit of a 1000 kg class
spacecraft is numerically integrated over 50 years using both the
original and the more accurate solar and lunar ephemerides methods.
Results of this study demonstrate that, over the long term, for an
object located in the geosynchronous region, the more accurate solar and
lunar ephemerides effects on the objects's position are significantly
different than using the current POHOP ephemeris.
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