The Spacecraft Control Toolbox (SCT) helps design control systems and attitude estimators, analyze station-keeping requirements, generate fuel and pointing budgets, and analyze spacecraft dynamics. The SCT provides a comprehensive set of over five hundred functions including:

  • Attitude dynamics modeling including flexible and multi-body spacecraft
  • Orbit dynamics analysis and simulation
  • Spacecraft control system design and analysis
  • Attitude estimation
  • Ephemeris calculation
  • Environmental modeling including atmospheric, gravitational, and magnetic field
  • Pointing and propellant budgeting
  • Spacecraft visualization
  • Extensive database of useful parameters

Princeton Satellite Systems (PSS), in cooperation with Innovation Chain, has made a number of these functions available for general use through the NASA Tech Briefs Model and Simulation Exchange website. The "Jacchia 1970 Atmospheric Model" and the "Keplerian Elements to Radius and Velocity Vectors Model" are two of the SCT functions available.

The Jacchia 1970 Atmospheric Model computes the atmospheric density using Jacchia's 1970 model as presented in "Models of the Earth's Atmosphere (90-2500 km)," NASA Publication SP-8021. Users enter the desired orbital location (latitude, longitude, and altitude), date, and time, as well as the geomagnetic and solar flux conditions. The model calculates the atmospheric density at that location. The model also outputs the atmospheric temperature, mean molecular mass, and number densities of nitrogen (N2), helium (He), and oxygen (O and O2). It is valid for altitudes between 90 km and 2500 km.

You can use the results of this model to calculate atmospheric drag forces and torque on a particular spacecraft. These values allow you to size actuators and generate fuel budget. The Spacecraft Control Toolbox provides a number of additional functions to simplify these calculations. You also can perform combined altitude and orbit simulations with environmental disturbances to verify the performance of your control systems.

The "Keplerian Elements to Radius and Velocity Vectors Model" is one of the many conversion utilities in the SCT. To use it, you enter the Keplerian orbital elements of a satellite and the function converts these elements into orbital radius and velocity vectors in the Earth-Centered-Inertial (ECI) frame. A complementary function performs the reverse conversion. These utility functions, along with the many others available in the Spacecraft Control Toolbox, enable users, even non-specialists, to quickly and easily convert between the various coordinate systems that astrodynamicists and attitude control engineers use.

The models presented on the NASA Tech Briefs Model and Simulation Exchange are a sample of the full functionality of the SCT. The complete toolbox enables you to design and test control systems in hours, instead of days or weeks. Among the other sophisticated models in the toolbox is a topological tree multi-body model.

This work was performed by employees at Princeton Satellite Systems. For more information on the Spacecraft Control Toolbox, contact Derek Surka at This email address is being protected from spambots. You need JavaScript enabled to view it., or visit the PSS web site at www.psatellite.com.

NASA Tech Briefs Magazine

This article first appeared in the March, 2001 issue of NASA Tech Briefs Magazine.

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