Holt, lying full length upon his couch, groaned as the almost unbearable load of the acceleration descended upon him. His breath labored as the menacing hand of the accelerometer crept past 3.2 g. The speed indicator and the altimeter hands hurried around their dials and the cabin was filled with the muffled growling of the rocket exhaust. Still the accelerometer needle climbed… 5g… 6g… 7g… Holt was pushed into the supporting cushions almost viciously. It was as though every organ in his body had turned to lead. The acceleration rose to 8g.
Another luminous sign flared up on the ceiling: "Caution! Dropping first stage!"
There was an instant of relief from the dreadful pressure and the menacing accelerometer hand dropped back to 1.3g. Then the deep booming set up once more and the accelerometer increased to 1.8g. It continued slowly to the higher figures again, renewing the torture with which acceleration besets the human frame. The burning time of the second stage was 124 seconds, during which the acceleration once more reached 8g.
"Caution! Dropping second stage!" shone at the passengers from the ceiling sign; then came a moment of respite. But the experience was repeated as soon as the acceleration diminished to 1.3g. With a howl, the third stage combustion exerted its push upon the now tiny core of the erstwhile enormous rocket. There was a clicking sound and the accelerometer climbed again to 1.5g. Gone was the second stage which had brought them to the speed at which they could carry on towards Lunetta with the power packaged in the tip of the rocket. Vibration increased, for their own, undetachable rocket plant was thundering and roaring a scant fifteen feet below the floor of their cabin. It was the third and last stage of acceleration. It was 84 seconds since the second stage had been jettisoned.
"Caution! Cut-off!" glared from the ceiling.
The accelerometer began to descend from 2.5g, the almost mercifully low figure which this time was its maximum. The cruel pressure melted, slowly at first, and then it was gone.
Holt closed his eyes for a moment. He had just come through that horrible second at the end of the acceleration ordeal, when the agony is over and the peculiar sensation of weightlessness begins. All people and all things in a rocket ship coasting through space are weightless, or seem to be, and this offers a feeling of release second to none. But the transition from the agonies of acceleration to the joys of weightlessness is ever accompanied by a dark moment of spiritual terror which besets everyone, no matter how often they have been through it. He released his belt and found himself floating unsupported above his couch. Beyond the thick glass of his deadlight he could see the black sky with its stars projected in unnatural brilliance. Their Earth-familiar twinkle was gone.
Soon the sliding hatch in the ceiling opened and an officer who might be the copilot emerged head first, pulling himself along with his hands and with one foot hooked around the ladder rail, so as to remain parallel to the wall. Arriving at the bottom, he flicked himself into an upright position.
"Gentlemen," he said, "Those of you on your first trip to Lunetta may want to hear some details about our path of ascent, our present flight condition, and the maneuvers we shall undertake.
"Our vessel, Sinus, is the flagship of the Lunetta Ferry squadron. We reach a maximum velocity of 8,260 meters per second in ascent, in a direction horizontal to the Earth's surface. This is attained in three consecutive but separate propulsion periods.
"During the first period, lasting 84 seconds, the vessel is given a velocity of 2,350 meters per second by the first booster stage. The rocket motor of the first stage develops a thrust of 12,800 metric tons. During the 84 seconds of operation it consumes some 4,800 tons of propellants. While the angle of ascent is vertical at the beginning, the gyro gear gradually tilts it until, at the moment when the propellants of the first booster are exhausted, the ship has an angle of elevation with respect to the plane of the horizon of slightly more than 20 degrees. At the end of the propulsion period of the first booster, the ship has attained an altitude of approximately 40 kilometers above the Earth's surface and has made good a horizontal distance of some 50 kilometers from the launching platform.
"Shortly before the exhaustion of the first booster propellants, acceleration is diminished by throttling their admission to the motor, and this diminished acceleration permits the second booster stage to break free of the almost exhausted first booster stage by its own power.
"The second booster exerts a thrust of 1,600 tons, and as soon as it begins this, the first booster drops off. The latter is then decelerated by a large, specially designed parachute and descends to Earth supported by it. The second booster stage works for 124 seconds and consumes about 700 tons of propellants during this time, at the end of which the ship has attained a velocity of 6,420 meters per second, has climbed to 64 kilometers above the Earth and has reached a horizontal distance of 534 kilometers from the launching site. The gyroscopic steering gear has continued to tilt the angle of the ship during the operation of the second stage, so that the angle of elevation of the flight path to the plane of the horizon is only 2.5 degrees at the end of its combustion period.
"After the second booster is exhausted, the power plant of the third and final stage effects its release from the second stage in the same manner that the second stage is released form the first booster. The second stage, like the first, is decelerated by a parachute and descends to Earth.
"The thrust of the third stage rocket motor is but 200 tons and this thrust lasts for 84 seconds. During this period, the ship is brought up to her maximum velocity of 8,260 meters per second, after consuming 58.8 tons of propellants. This only partially exhausts the tankage of 83 tons, leaving a very considerable supply of propellants still available after ascent has been completed. This reserve is required for the maneuver of adaptation, which I shall shortly describe, as also for the return trip to Earth. There is still left a very considerable margin of safety as to propellants.
"During the propulsion period of the third stage, the ship rises to an altitude of 102 kilometers and at combustion cutoff has covered a horizontal distance from the launching site of about 1,135 kilometers. The angle of elevation of the flight path at combustion cutoff of the third stage is almost exactly zero. When referred to the plane of the horizon at the launching site, this angle is slightly negative, although with respect to the surface of the Earth directly below the rocket ship it is practically horizontal. This is due to the curvature of the Earth, which makes a spirit level, just below the momentary position of the ship, lie at an angle to a level at the launching site.
"When the third stage is moving horizontally at a rate of 8,260 meters per second, and is at an altitude of 102 kilometers above the ground, it is some 410 meters per second faster than the orbital velocity at that altitude. Were its speed exactly that of the orbital velocity, centrifugal force would balance its weight exactly and it would continue to orbit around the Earth at the altitude of 108 kilometers. But since the velocity imparted to the ship by the third stage is somewhat above the orbital velocity, centrifugal force is greater than the attraction of gravity and the ship recedes from the Earth.
"Our initial speed of 8,260 meters per second was selected in order that we might proceed along an elliptical path, the apogee of which is at 1,730 kilometers from the Earth's surface. This is the altitude at which Lunetta circles the Earth at the orbital speed corresponding to that altitude, namely 7,070 meters per second. We, however, lose a certain amount of our speed as a result of our climb to that altitude, so that our velocity will be but 6,610 meters per second at the time we intercept Lunetta's orbit. Thus we shall have to carry out a so-called "adaptation maneuver" in order to increase our velocity by the amount it lacks, to equal that of Lunetta. This is 460 meters per second. We fly unpropelled for a period of 50 minutes and 54 second after final combustion cutoff. At the end of this period we shall arrive at a point of tangency with Lunetta's orbit. The adaptation maneuver will begin at the end of this period and will require us to run our rocket motor for about 15 seconds. Until then, you gentlemen may do as you wish.