National Geographic : 1964 Mar
that lengthen the launch window from minutes to hours. But let's not venture too far into the maze of orbital mechanics. Essentially the mission begins as I have described it. There is one other vital factor involved: plane error, or the differ ence in the planes of the two orbits. This error must be corrected. But diagrams tell that story best, and I refer you to the excellent illustra tions on pages 366-7. There you can see the problem and its solution. Now let's assume that the hunter is nearing the hunted. Ground stations have been tracking both, and the information needed for pre cise maneuvering has been passed to Gemini. When the craft are about 250 miles apart, Gemini's radar picks up Agena. Computers tell the astronauts how far they are from the target and what course corrections to make. They fire rockets, moving up, down, or laterally, at times in creasing or decreasing their speed. If a large correction is required, they may flash a signal to Agena, and it will maneuver obediently. Part of the chase may occur on the night side of earth. Then strob oscopic beacons flash on Agena; the astronauts see them as intermittent lights moving among the stars. They take sightings on the beacons and keep changing the direction of their flight until the winking lights seem to be stationary in relation to the stars. That means they have drawn a direct bead on the target, now dead ahead. Spacecraft Join While Traveling 17,500 Miles an Hour So Gemini closes in. Crewmen see their quarry clearly when two to 20 miles away, depending upon the time of day. Should it be night, floodlights illuminate Agena's docking collar. Flick-firing his maneu vering engines, powered by propellants similar to those used in Titan II, the Gemini commander eases his craft's nose into the collar. Latches trip and hold the vehicles firmly together, a bond that will not be broken until the astronauts trigger a release mechanism. Now, if the men wish, they can rotate the Agena-Gemini combination and fire Agena's engines to venture farther out into space. Joining two vehicles together while both travel 17,500 miles an hour may seem difficult in the extreme, but it is only the relative speed be tween the two that is of concern. Have you ever seen two speeding automobiles play a game of "bumper tag?" One inches up on the rear of the other and playfully nudges it. This is a popular game among some teen-age drivers, and I deplore it, but it is not difficult. Similarly, when Gemini scores its tag, it will be moving only 11/2 feet per second faster than Agena, a difference of little more than one mile an hour. Visibility for the docking maneuver does not seem to be a problem, even though in space there is no air to scatter, diffuse, and soften light. All four Mercury astronauts placed in orbit saw the Atlas clearly after it separated from the capsule. Observing the booster for some time as it drifted away, they felt their judgment of its distance from them was DARING GEMINI ASTRONAUT FLOATS WEIGHTLESS, A THISTLEDOWN IN THE VASTNESS OF SPACE OPENING THE HATCH of his spacecraft, the tethered explorer ventures out alone into the deadly void. Pack on his thigh contains enough oxygen for a 20-minute sortie. Design of the pressure suit ensures that it will not balloon out in the vacuum of space, lest it impair the man's mobility. To determine the problems repairmen might face in servicing manned space stations, Gemini pilots may eventually go outside their ship, as this astronaut is doing, and perform experimental tasks. The astronaut himself becomes a satellite traveling 17,500 miles an hour. But, without air resist ance, he has no sensation of speed. Small round jets on the nose of the Gemini capsule stabilize the craft during re-entry. Maneuver-control jets on the fore section of the white retro-module control Gemini's attitude in orbit. 369 PAINTINGBY DAVIS MELTZER© N.G.S.