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Constellation Management


THORpex Application

This page shows a simulation using stratospheric balloons to achieve THORpex objectives. THORpex is a loose acronym for "The Hemispheric Observing system Research and Predictability Experiment". This simulation demonstrates a possible targeting test mission scenario that takes advantage of trajectory control for observations. The goal is to obtain multiple dropsonde samples in regions of high sensitivity for 2- to 10-day weather forecasts in the western U.S. This region of high sensitivity is the Pacific Ocean in Northern Hemisphere winter.

In this simulation, the Red trajectory shows an uncontrolled balloon floating at 35 km. The Green trajectory represents a "simple control" balloon at 35 km whose trajectory is being controlled by a StratoSail® BGS at 20 km. The objective of the simple trajectory control algorithm for the Green balloon is to maintain 45°-north longitude at all times. Thus, if the balloon is south of 45°, the BGS pushes the balloon north if possible, and vice versa. The Blue trajectory shows a balloon at 35 km with the same 20-km StratoSail® BGS as the green balloon. However, the Blue balloon uses a sophisticated trajectory control algorithm. At various times throughout the flight, the Blue balloon is commanded to maintain latitude or to move toward or away from the center of an observed vortex. Control actions are taken based on the structure of the wind field at the time the control decision is made. No forecast information is utilized.

This simulation begins at November 1, 2000 and ends on March 1, 2001, 120 days in duration. Only 15 days of the trajectories (starting from December 1, 2000) are shown for clarity. The arrows on the trajectories indicate direction of travel and are spaced at 6-hour intervals to demonstrate locations of possible sonde drops. Real stratospheric winds from the time of the flight are used for calculating balloon trajectories.

The table below gives the number of sonde observations in the region of interest over the 120 days of simulation.


Number of Sonde Drops in High-Sensitivity Region
Uncontrolled (Red)
Simple Control (45°) (Green)
Sophisticated (Blue)



These simulations demonstrate the effectiveness of trajectory control capabilities for targeted balloon observations.




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