Flying Rockets

Over the past ten years, more than 170 major rockets have been flown from the Geophysical Institute's Poker Flat rocket range, north of Fairbanks. Each of these was an "unguided" rocket, meaning that once it left the ground no further guidance control was possible.

Despite the lack of in-flight guidance, it is possible to fly the rockets several hundred miles into the atmosphere and still have them hit a target only a few miles across, some distance downrange. Downrange from Poker Flat is to the north or east.

Most of the rockets have two stages. The first stage motor lifts the rocket from the ground and gets it well underway. Its fuel being spent after a few seconds, this first motor falls away and lands within a few miles of the launch site. The second-stage rocket with its attached payload coasts upward for about twenty seconds, and then it fires for a few more seconds to give the velocity needed to lift the payload up into the high atmosphere.

The launch crews use a steerable launcher to aim the rockets, one that can be aimed with a precision of one-tenth of a degree. Once the first-stage rocket motor is fired, the rocket moves a few inches or feet before flying freely on its own.

Before launching a rocket, the crew carefully measures the winds by means of anemometers spaced along a 200-foot tower at the site and radar-tracked balloons flown to altitudes above 20,000 feet. The winds are critical because a rocket drifts with the wind when its motors are coasting and it cocks over into the wind when they are firing. Thus, the crew must know the wind at all altitudes and must set the launcher according to complex formulas based upon the wind direction and speed.

Adjustment for the wind sometimes requires setting the launcher direction up or down by one or two degrees, or right or left up to twenty degrees, from the direction it would be aimed were there no wind. When the winds are strong or highly variable, the launch team waits for a better day.