The traffic between the Earth and the space station takes place through rocket-powered space ships, like those described in general in the first part of this book. It may complete the picture to envision such a trip at least in broad outlines:
The space ship is readied on the Earth. We enter the command room, a small chamber in the interior of the fuselage where the pilot and passengers stay. The door is locked airtight from the inside. We must lie down in hammocks. Several control actions by the pilot, a slight tremor in the vehicle and in the next moment we feel as heavy as lead, almost painfully the cords of the hammocks are pressed against the body, breathing is labored, lifting an arm is a test of strength: the ascent has begun. The propulsion system is working, lifting us up at an acceleration of 30 m/sec2, and causing us to feel an increase of our weight to four times its normal value. It would have been impossible to remain standing upright under this load.
It does not take long before the feeling of increased gravity stops for a moment, only to start again immediately. The pilot explains that he has just jettisoned the first rocket stage, which is now spent, and started the second stage. Soon, new controlling actions follow: as explained by the pilot, we have already attained the necessary highest climbing velocity; for this reason, the vehicle was rotated by 90°, allowing the propulsion system to act now in a horizontal direction in order to accelerate us to the necessary orbital velocity.
Very soon, we have attained this velocity. Only some minutes have elapsed since launch; however, it seems endless to us, [given] that we had to put up with the strenuous state of elevated gravity. The pressure on us is gradually diminishing. First we feel a pleasant relief; then, however, an oppressive fear: we believe we are falling, crashing into the depths. The brave pilot attempts to calm us: he has slowly turned the propulsion system off. Our motion takes place now only by virtue of our own kinetic force, and what was sensed as free fall is nothing other than the feeling of weightlessness, something that we must get used to whether we like it or not. Easier said than done; but since we have no other choice, we finally succeed.
In the meantime, the pilot has acutely observed with his instruments and consulted his tables and travel curves. Several times the propulsion system was restarted for a short time: small orbital corrections had to be made. Now the destination is reached. We put on space suits, the air is vented from the command room, the door is opened. Ahead of us at some distance we see something strange, glittering in the pure sunlight like medallions, standing out starkly in the deep black, starfilled sky: the space station (Figure 94).
Figure 94. The complete space station with its 3 units, seen through the door of a space ship. In the background-35,900 km distant-is the Earth. The center of its circumferential circle is that point of the Earth's surface on the equator over which the space station continually hovers (see Pages 107109). As assumed in this case, the space station is on the meridian of Berlin, approximately above the southern tip of Cameroon.
However, we have little time to marvel. Our pilot pushes away and floats toward the space station. We follow him, but not with very comfortable feelings: an abyss of almost 36,000 km gapes to the Earth! For the return trip, we note that our vehicle is equipped with wings. These were carried on board in a detached condition during the ascent and have now been attached, a job presenting no difficulties due to the existing weightlessness.
We reenter the command room of the space ship; the door is closed; the room is pressurized. At first the propulsion system begins to work at a very low thrust: a slight feeling of gravity becomes noticeable. We must again lie down in the hammocks. Then, little by little more thrusters are switched on by the pilot, causing the sensation of gravity to increase to higher and higher levels. We feel it this time to be even heavier than before, after we had been unaccustomed to gravity over a longer period. The propulsion system now works at full force, and in a horizontal but opposite direction from before; our orbital velocity and consequently the centrifugal force, which had sustained us during the stay in the space station, must be decreased significantly to such a degree that we are freely falling in an elliptical orbit towards the Earth. A weightless state exists again during this part of the return trip.
In the meantime, we have come considerably closer to the Earth. Gradually, we are now entering into its atmosphere. Already, the air drag makes itself felt. The most difficult part of this trip is beginning: the landing. Now by means of air drag, we have to brake our travel velocity-which has risen during our fall to Earth up to around 12 times the velocity of a projectile so gradually that no overheating occurs during the landing as a result of atmospheric friction.
As a precautionary measure, we have all buckled up. The pilot is very busy controlling the wings and parachutes, continuously determining the position of the vehicle, measuring the air pressure and outside temperature, and performing other activities. For several hours, we orbit our planet at breakneck speed: in the beginning, it is a headdown flight at an altitude of approximately 75 km; later, with a continual decrease of the velocity, we approach the Earth more and more in a long spiral and, as a result, arrive in deeper, denser layers of air; gradually, the terrestrial feeling of gravity appears again, and our flight transitions into a normal gliding flight. As in a breakneck race, the Earth's surface rushes by underneath: in only half hours, entire oceans are crossed, continents traversed. Nevertheless, the flight becomes slower and slower and we come closer to the ground, finally splashing down into the sea near a harbor.