William W. Vaughan

NASA Marshall Engineering Thermosphere model — 1999 version (MET-99) and implications for satellite lifetime predictions

Abstract The use of thermospheric density models in the prediction of atmospheric drag (the major perturbation for orbiting spacecraft) is of great importance. Issues associated with these predictions include lifetime estimates, orbit determination and tracking, attitude dynamics, and re-entry prediction. Logistics planning through attitude control requirements and re-boost planning are also influenced by future orbital altitude density estimates. The MET-99 model and its predecessors were developed to provide the inputs needed to address these issues. The sensitivity of the future estimation of solar activity, and thus thermospheric density and the prediction of a satellites lifetime, to the selection of Solar Cycle 23 minimum other than the conventionally identified mathematical minimum is shown. This can produce about 25 percent error in predicted satellite lifetime for a typical low Earth orbit example.

The NASA Marshall solar activity model for use in predicting satellite lifetime

Abstract A principal source of uncertainty in estimating future orbital altitude densities for predicting satellite orbital lifetimes is the solar extreme ultraviolet (EUV) heat input values to use in the atmospheric model. The observed 10.7-cm solar radio flux (not adjusted to 1 AU) is used as a proxy for this most significant input, which is not otherwise available. A statistical technique was developed to estimate the future 13-month Zurich smoothed solar radio flux and geomagnetic index values. A principal application of this model is as an input to thermospheric density models used for satellite lifetime predictions.

Development of NASA Technical Standards Program Relative to Enhancing Engineering Capabilities

The enhancement of engineering capabilities is an important aspect of any organization; especially those engaged in aerospace development activities. Technical Standards are one of the key elements of this endeavor. The NASA Technical Standards Program was formed in 1997 in response to the NASA Administrator’s directive to develop an Agencywide Technical Standards Program. The Program’s principal objective involved the converting Center‐unique technical standards into Agency wide standards and the adoption/endorsement of non‐Government technical standards in lieu of government standards. In the process of these actions, the potential for further enhancement of the Agency’s engineering capabilities was noted relative to value of being able to access Agencywide the necessary full‐text technical standards, standards update notifications, and integration of lessons learned with technical standards, all available to the user from one Website. This was accomplished and is now being enhanced based on feedbacks f...

Space weather, Earth's neutral upper atmosphere (thermosphere), and spacecraft orbital lifetime/dynamics

Accurate prediction of a spacecraft/satellite orbital lifetime, insertion altitude, reboost requirements, and mission performance is mainly the result of the integrated effect from knowledge of the atmospheric density, space weather (solar/geomagnetic), and timeline of vehicle characteristics. Each of these elements is dependent upon a model developed to provide the inputs necessary for the use of an orbital lifetime prediction program. This paper will address relative influences of these elements with emphasis on solar/geomagnetic activity, atmospheric density, and drag coefficient associated with the model products used to predict orbital lifetime and related spacecraft/satellite design and operational conditions. Issues associated with the potential for improvement of the lifetime prediction model input elements will be discussed with regard to their relative contributions to improving orbital lifetime and performance predictions.

NASA Technical Standards Program and Implications for Lessons Learned and Technical Standard Integration

The National Aeronautics and Space Agency consists of fourteen Facilities throughout the United States. They are organized to support the Agencys principal Enterprises: (1) Space Science, (2) Earth Science, (3) Aerospace Technology, (4) Human Exploration and Development of Space, and (5) Biological and Physical Research. Technical Standards are important to the activities of each Enterprise and have been an integral part in the development and operation of NASA Programs and Projects since the Agency was established in 1959. However, for years each Center was responsible for its own standards development and selection of non-NASA technical standards that met the needs of Programs and Projects for which they were responsible. There were few Agencywide applicable Technical Standards, mainly those in area of safety. Department of Defense Standards and Specifications were the foundation and main source for Technical Standards used by the Agency. This process existed until about 1997 when NASA embarked on a Program to convert NASAs Center-developed Technical Standards into Agencywide endorsed NASA Preferred Technical Standards. In addition, action was taken regarding the formal adoption of non-NASA Technical Standards (DOD, SAE, ASTM, ASME, IEEE, etc.) as NASA Preferred Technical Standards.

Updated Terrestrial Environment Guidelines for Aerospace Vehicle Development

NASA recently released extensively revised and updated guidelines and information on terrestrial environments (land, water, and atmosphere). The guidelines are applicable in developing design requirements and specifications for aerospace vehicles, payloads, and associated ground support equipment operating in specific geographic regions. The document, “Terrestrial Environment (Climatic) Criteria Guidelines for Use in Aerospace Vehicle Development, 2008 Revision” (NASA/TM-2008-215633), has been updated periodically since its initial publication in 1964. The latest version includes a broad scope of information about the terrestrial environment, though spaceflight systems development and test centers are the primary geographic areas encompassed in the document.

Date estimated for maximum of Solar Cycle 23

The Suns activity follows an approximately 11-year cycle. For the current cycle, number 23, the minimum, or low point in the Suns activity occurred in May 1996. Maximum—the peak of the Suns activity—is expected to occur in May 2000, according to NASAs Marshall Solar Activity Future Estimate (MSAFE) Model. Our ability to identify the start and approximate profile of a new solar cycle, and to produce viable, consistent, and timely estimates of its behavior, is considerably important since the space environment and associated geophysical effects are all, to one degree or another, affected by aspects of the Suns activity. Early identification of the magnitude and projected time of minimum (and maximum) amplitude of a new cycle occupies many researchers, especially as the peaks and valleys of the Suns activity near. Identification of the date and minimum amplitude is particularly important because it is used in models that predict future levels of solar activity as related to spacecraft orbital lifetime predictions, flare frequency, number and severity of geomagnetic storms, and radiation and ionospheric models.

Access to atmospheric data reaches new heights

The newly updated Global Reference Atmospheric Model (GRAM-95) provides complete geographical, altitude, and monthly variations of atmospheric temperature, pressure, density, and winds for the troposphere, stratosphere, mesosphere, and thermosphere. The model can also simulate spatial and temporal perturbations in these atmospheric state parameters. Estimates are included for atmospheric concentrations of water vapor, ozone, nitrous oxide, carbon monoxide, methane, carbon dioxide, nitrogen, molecular oxygen, atomic oxygen, argon, and helium below 90 km and nitrogen, molecular oxygen, atomic oxygen, argon, helium, and hydrogen above 90 km. Other features include a new variable-scale perturbation model and a pressure perturbation model.