Statistics – Applications
Scientific paper
Dec 1996
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996esasp.392..305s&link_type=abstract
Environment Modelling for Space-based Applications, Symposium Proceedings (ESA SP-392). ESTEC Noordwijk, 18-20 September 1996. E
Statistics
Applications
Scientific paper
NASA has specified that the Marshall Engineering Thermosphere (MET) model is to be used in the design, development, and testing phases of the ISS. The neutral atmosphere parameter that affects the ISS the most is the mass density. Although the MET model is based on density values calculated from the orbital decay histories of satellites, the key parameter for calculating the mass density is the temperature structure above 90 kilometers altitude, particularly the exospheric temperature. The exospheric temperature is highly dependent on the 81-day average 10.7-cm solar radio noise flux, the daily value of the 10.7-cm solar flux and the 3-hourly average geomagnetic index, ap. In this study the MET model is used to compute total mass density from 250 to 450 km altitude using the available 47 years (1947-1993) daily values for the 10.7-cm solar flux and the 3-hourly (8 per day) average value of the geomagnetic index, ap. A description of the MET model and examples of the neutral atmospheric density applicable to the ISS microgravity experiment requirements are presented. One of the microgravity experiment requirements is that one micro-g cannot be exceeded at the ISS internal payload location for 6 periods of not less than 30 consecutive days per year. The atmospheric drag acceleration is only one of the factors that can contribute to the residual accelerations on the ISS. Other causes include mechanical noise, crew disturbances, and uncertainties in the Control Moment Gyros (CMG) capability to control attitude and torques. In this study, under simplifying assumptions, the critical ambient neutral density required to produce one micro-g on the ISS is estimated using an atmospheric drag acceleration equation. Examples are presented for the critical density versus altitude, and for the critical density that is exceeded at least once per month and at least once per orbit during periods of low and high solar activity
Adelfang S. I.
Smith Edgar O.
Smith Robert E.
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