There was now no further use for the great propellant containers from which had been drawn the power for the departure maneuver and the ensuing corrections. They must be jettisoned in order to save weight during the coming maneuver of adaptation to the circum-Martian orbit. Preparations for abandoning them included forcing all residual propellants into the reserve tanks.
This done, the engineers in space suits emerged from the nacelles and broke the connections to the propellant pumps, then unscrewed the helium lines which pressurized the tanks. Finally they pulled the plugs and interrupted the electrical connections to the quantity gauges and remote-indicating thermometers in the control room.
There were other useless loads besides the empty tanks to be dispensed with. The superfluous storage batteries provided for steering during the extra long initial maneuvers were now useless, since the smaller regular bank of batteries would be adequate for the coming shorter propulsion periods. Spent food containers, broken tools and instruments and similar accumulated debris was to be eliminated. Carried along as useless ballast, it would cause waste of propellants. Packed in what might be called sidereal garbage cans, the debris was bolted to the tank retainers to be jettisoned. Then the engineers reentered the nacelles.
Flywheels were started to bring the vessels into slow rotation around their longitudinal axes. Then the closing of electrical circuits detonated explosive bolts holding the outer arms of the tank retainers to their center pieces. The centrifugal force generated by the rotation then flung the arms with their great silver globes out into space, where they continued to recede slowly into the infinite distance. There could now be no danger of their interfering with the coming maneuver of adaptation. Holt ordered his convoy into echelon with an interval between ships of some 1,000 feet, with instructions that their captains should keep station with the utmost accuracy, using the four rotatable steering jets only.
Events now came in such rapid succession, almost taking away the breath of the Mars crews after the weary boredom of their months in space.
The apparent diameter of Mars two days before the maneuver of retardation had been equivalent to about twice that of the Sun, and twenty-four hours later it had increased to nearly quadruple. Now, just four hours before the vertex of the hyperbola was to be passed, the enormous multicolored disk, more than half of which was brightly illuminated, subtended an arc of vision of over seven degrees, or fourteen times the angle subtended by the Sun. The now compact flotilla of space ships was only 55,000 kilometers from the center of Mars's enormous sphere.
All navigators lay strapped into their astrodomes, recording the times of occultation behind Mars of various stars and reporting results to Holt immediately by radio telephone as he and his Chief Navigator, Hal Royer, studied the flight path chart in the navigation room of the Polaris. As Royer read positions from the tables with each incoming report, Holt would mark the spot on the chart with a round-headed, colored pin. Thus he could keep track of any small divergences of the convoy from the prescribed track's thick red line. Holt was well content, for the many careful observations of star occultations were now bearing fruit, proving the last correction maneuver to be accurate. There was no reason to anticipate any unforeseen alteration of the flight path by extraneous or unpredicted factors.
Two hours and fifteen minutes remained before they would reach the hyperbolic vertex where they were to convert their precipitous drop into a definite circular orbit. In the meantime, their velocity relative to Mars bad increased from 2.55 kilometers per second to 3.1 km/sec and the rapid increase of the disk of Mars in their eyes impressively confirmed it. The distance to Mars' center was 27,500 km, and almost three-quarters of the great sphere was bright with sunlight.
There was a brilliant star close to the inky edge of Mars' nocturnal side, sliding rapidly towards the planet. Instead of disappearing behind the somber edge it remained visible on the night-steeped face of the planet, and passed across the orange-red deserts, finally moving off into the world of stars with increasing pace. It was Phobos, the fast-moving inner satellite of Mars, crossing their course! Field glasses revealed that the 10 kilometer sphere was misshapen in contrast to the perfected rotundity of larger heavenly bodies.
At X minus 85 minutes, their distance from the center of Mars had been clipped down to 13,750 kilometers and their relative velocity had risen to 3.57 km/sec. Mars himself, with his glowing red, white and green shadings, subtended a full 30 degrees of angular vision in the eyes of the tense crewmen.
Holt now gave the order to turn the ships to the attitude for the maneuvers. Royer selected two fixed stars on which the directional 'scopes of the new Sperry instruments were bracketed. Then the desired relative attitude of each vessel to this system of reference was set, and when the control gyros had leveled themselves, the flywheels were started. Ponderously, the ships gyrated in space until their rocket motors faced in the direction of flight. There was no disturbance of their orderly echelon. Within minutes Holt received the reports that each ship occupied the proper attitude and was ready to apply thrust.
At X minus twenty-three minutes and sixteen seconds, their relative velocity had mounted to 4.37 km/sec, they were but 6,875 km from Mars' center, and the planet's colored surface seemed to rotate with ever-increasing speed. This evidenced that they would not crash perpendicularly upon his surface, but were racing towards him tangentially in a graceful sweep which would permit them to use his gravity to convert their movement into the satellite path which was their objective.
No more than 3,500 km separated them from the planet's surface at X minus eleven minutes! His entire surface was bathed in brilliant sunlight.
The maneuver of retardation which would swing them into the orbit of a satellite around Mars was to be simultaneous for all ships, unlike the maneuver of departure, for it was not desired that there should be the slightest divergence between them when the maneuver was completed. Minor differences in angle or speed would have been much more difficult to correct in an orbit than during the long, elliptical interstellar passage.
The Space Forces had developed a technique for simultaneity during the ferry operations, when it had been found desirable to launch two Sinus ships in a time interval of but a few seconds toward the assembly operations going on in the orbit of departure.
The technique used a flagship as "master." Other ships were "slaved" to her angular attitude. This was done by automatic, continuous registry of the flagship's angle in relation to her three control gyros and impressing the three error angles upon three continuously emitted tones which modulated a radio carrier wave. A fourth tone conveyed the acceleration factor of the flagship. Thus any special attitude of the flagship and her acceleration would be reflected in the pitch of the tones emitted by her radio transmitter.
On the slave vessel, the corresponding four tones were generated, and comparison of the pitches of these four tones with those emitted by the flagship indicated whether the slave ship deviated in spatial angularity and in acceleration from the master. If one tone varied in pitch, it produced a beat with that of the flagship. This beat induced a corrective signal in the automatic control equipment of the erring vessel, and her angle or thrust was corrected until the beat disappeared.