Date: Mon, 29 Dec 1997 21:06:59 GMT Server: NCSA/1.5 Content-type: text/html Last-modified: Mon, 25 Aug 1997 18:44:43 GMT Content-length: 15791 Integral Systems OASYS

OASYS


System Overview

OASYS is a workstation-based software tool for spacecraft orbit analysis. Its principal functions are:

Orbit Determination
Ephemeris Propagation
Maneuver Planning

OASYS provides end-to-end support for spacecraft orbit determination and control. With OASYS, you can manage a single spacecraft or a fleet in any earth orbit, including Low Earth, Geosynchronous, and Molniya-type orbits.

In a typical operational environment, OASYS is used to estimate the spacecraft state from tracking data, to propagate a high precision ephemeris to predict the future spacecraft state, and to compute thrust parameters to maneuver the spacecraft into a desired orbit. Other functions, such as Attitude Determination and Fuel Accounting, can be provided as spacecraft-specific options in OASYS.

The system provides a state-of-the-art graphical user interface. The software is interactive and fully integrated, making it much easier to learn and use than batch-oriented orbit packages. In fact, most OASYS sessions can be accomplished using only the mouse, with no keystrokes required. Using option menus, for example, you can instantly display orbital elements in a variety of user-specified coordinate frames (including Cartesian, Keplerian, Geodetic, Brouwer-Mean, and Equinoctial) and engineering units (both Metric and English).

OASYS may be hosted on any UNIX workstation under X-Windows/Motif compatible window managers. The software runs faster than traditional orbit packages because its modern numerical algorithms are optimized for earth orbits. And since OASYS is workstation-based, it is available for a fraction of the cost of systems based on mainframes and mini-computers.

The OASYS software is database driven, so you can easily add new spacecraft or new ground stations. The database includes:

Astronomical/Geophysical Constants
Ranging Station Locations
Antenna and Station Biases
Spacecraft Parameters
Thruster Characteristics

These parameters are modifiable using the OASYS on-line editor or a commercial relational (SQL) database management system.


Orbit Determination

The Orbit Determination module provides an orbit fix which best fits a set of input measurements. Most standard measurement types, including phasemeter, range, turn-around range, range rate, azimuth, and elevation, are already supported. Other measurement types can be easily accommodated by modifying the OASYS measurement model.

Once the measurements are ingested, the software calculates the associated orbit. The measurements may be pre-filtered (automatically or manually). The resulting set of good measurements is fed through a statistical estimation algorithm which computes an orbit that is the best fit to the measurement set. The software then computes and displays the measurement residuals.

An Orbit Determination state dialog is also provided which allows you to analyze the statistics associated with the fit. The state dialog provides initial and final statistical estimates for:

Dynamic States (Orbital Elements)
Dynamic Biases (Solar Pressure and Drag Coefficients)
Measurement Biases
Measurement Noise

The final orbit fit is stored for future reference and transferred automatically to the Ephemeris Propagation routines.


Ephemeris Propagation

The Ephemeris Propagation software forecasts the spacecraft position over time on the basis of initial state estimates obtained from Orbit Determination or user input. The propagator uses an adaptive numerical integrator which is optimized for earth-orbit calculations. This variable step/variable order algorithm determines step size based on the dynamics of the orbit and a user-specified error tolerance, resulting in faster and more accurate propagations. Brouwer-Lyddane, Kepler, and NORAD semi-analytic propagators are also available.

You can do a short run of a few orbits to get a quick set of event predicts, or a long run of months (or years) to study long-term stability. Propagations can even be run backward in time, allowing you to back propagate the state to evaluate measurement residuals or thruster performance after maneuvers.

The force model is database-driven and consists of the following components:

N x M Spherical Harmonic Geopotential
Solar and Lunar Point Mass
Solar Pressure
Atmospheric Drag
Thrust/Impulse

The memory resident output ephemeris is immediately available to other software functions, including Maneuver Planning and Plots/Reports.


Maneuver Planning

The OASYS Maneuver Planning software provides a unique graphical interface for planning and implementing spacecraft maneuvers. There are three basic steps to the process:

Select a Thruster Configuration
Select a Maneuver Type
Define a Maneuver Target or Delta

The graphical approach to maneuver planning has two advantages: it is easy to use, and the graphical display provides an intuitively obvious interpretation of both the pre-maneuver state and the post-maneuver state.

OASYS supports general cross-track (change inclination, ascending node) and along track (change semi-major axis) maneuvers. The graphical planner for geosynchronous spacecraft operates on drift, eccentricity, and inclination. The software automatically posts a plot of the spacecraft's predicted trajectory and current box limits. You can then click on the plot and define a new trajectory using the mouse. Once you are satisfied with the trajectory, a click of the mouse will save it to disk as the post-maneuver state. The required burn times for the selected thruster set are computed automatically.


Plots and Reports

OASYS provides a complete set of data output products, including:

Ground Track Plot showing spacecraft nadir ground track and station contact circles on a world map
Cartesian and Polar Plots for trending spacecraft orbit data and consumables
Ephemeris Reports providing the orbital elements at user-specified intervals
Predicted Tracking Files for station antenna pre-positioning and real-time control
Event Report specifying the time of orbital/station events such as perigee/apogee, node crossings, sun/eclipse transitions, and spacecraft rise/set

The contents and formats of the output products can be customized on-line via the OASYS menus. An integrated set of conversion routines allows both program inputs and outputs to be expressed in Metric and English engineering units as well as a variety of coordinate frames.


Screen Shots

Click on the examples below for some OASYS screen shots:

Main Menu
Ephemeris Services Menu
Orbit Determination Menu
Measurement Edit Plot
Maneuver Services Menu
Station Keeping Menu
Drift Maneuver Planner
Ground Track Plot

Update Sources for Orbital Information

SEC NEOS Celestial
F10.7cm Solar Flux Polar Motion & UTC Corrections NORAD Two-Line Elements

NORAD Two-Line Elements can also be obtained from the NASA Orbital Information Group (OIG) BBS. They provide shuttle elements and data for most objects in the USSPACECOM catalogue. Telnet to oig1.gsfc.nasa.gov and login as oig with password goddard1. After going through a simple registration process you can download the data you desire.

The latest ASCII Database Files (.adb) [updated monthly] are available for download from the ISI anonymous ftp site.

polar_mo.adb -Version 2/Version 3 - Polar Motion and UTC Corrections
et_ut.adb - Version 2/Version 3 - Table Of Leap Seconds


Additional Information

For further information on OASYS features, prices, and support, contact Steve Carchedi at the address below, or email him directly.


Integral Systems, Inc.* 5000 Philadelphia Way* Suite A* Lanham MD 20706-4417 USA
Phone: (301) 731-4233* Fax: (301) 731-9606
contact sales * contact webmaster


The following are trademarks or registered trademarks:

OASYS - Integral Systems, Inc.
UNIX - UNIX Systems Laboratories, Inc.
X-Windows - Massachusetts Institute of Technology
Motif - The Open Software Foundation, Inc.