"Jolly interesting, you know," mused Billingsley. "Then the swarms of meteors which return regularly on certain days belong to the elliptical brotherhood, et?"
Bergmann nodded.
"And how do they come into being?"
"We figure that the elliptical brotherhood, as you call them, are the wreckage of comets which may have come too close to the Sun and burst from the heat. When a swarm of such small particles following the same path — but considerably separated from one another — arrives at the inner regions of the solar system as they fly around the Sun, there are minor differences in the attraction exercised by the latter upon the nearer and more distant particles. This, and planetary gravity, produces small differences in their orbital periods which in time become cumulative. Thus the wreckage of the erstwhile comet is distributed along the orbit, and we see a swarm of shooting stars.
"It's not as bad as that," went on Bergmann. "The large tanks for the initial maneuver are but one tenth of an inch thick and can presumably be holed by meteors as small as the fifteenth magnitude, which are about one four-hundredth of an inch in diameter. The tanks are roughly the size of the nacelles, and of the same material. Fifteenth magnitude meteors are about one hundred times as frequent as those of the tenth magnitude, so we anticipate roughly one hundred punctures per year. By the time we jettison our presently empty tanks, they'll probably average 70 punctures apiece. We're far more concerned over the smaller tanks for later maneuvers, since they will be exposed to meteoric grain bombardment for a much longer time."
"It seems to me a jolly great miracle that we've a drop of fuel left…"
Bergmann smiled confidently. "You've heard of puncture-proofing, have you not? It was used in automobile tires as early as 1920 and in bulletproof aircraft fuel tanks before that. Our tanks contain a chemical which immediately flows to the tiniest wound and stanches it then and there. Nor is it often called upon to heal anything as large as a 0.50 caliber hole, as it used to do quite regularly when men fought airplanes. It will be 10,000 years before there's another puncture like Aldebaran's, you might remember."
"Really, Bergmann, you're the most accommodating and patient science fellow it's ever been my good fortune to travel to Mars with. They do have meteoric swarms if the tabloid journals are right," persisted Billingsley.
"They are relatively dense, to be sure," answered Bergmann, "but the nice thing about them is that we're on familiar terms and know where to expect them.
"Meteors may be classified as hyperbolic or elliptical. The hyperbolic type enter the solar system from elsewhere and when they enter the solar field of gravitation, they have an initial velocity which tends to increase the closer they approach to the Sun. When their distance from the Sun is equal to the distance of Mars's orbit, they are traveling more than 34.3 km/sec, and at the distance of Earth's orbit more than 42.1 km/sec, for they would have attained this velocity by solar gravity alone, even without any initial velocity.
"Such meteors are 'strangers' and they describe a hyperbola around the Sun and disappear for ever from the solar system, unless they fall into the Sun or onto a planet. We have no way of predicting their appearance, whether as to time or location, for they visit us but once and for a short time. It is assumed that 70 % of meteors are hyperbolic.
"Elliptical meteors must basically be slower than the figures I've quoted, and the whole situation is different. Like planets, they gravitate around the Sun in elliptical orbits which are frequently very eccentric. They cross Earth's orbit at regular intervals and this permits us to become relatively familiar with their paths. The track of this voyage avoids such paths by a safe margin, if our computations have been effective."
"Jolly interesting, you know," mused Billingsley. "Then the swarms of meteors which return regularly on certain days belong to the elliptical brotherhood, et?"
Bergmann nodded.
"And how do they come into being?"
"We figure that the elliptical brotherhood, as you call them, are the wreckage of comets which may have come too close to the Sun and burst from the heat. When a swarm of such small particles following the same path — but considerably separated from one another — arrives at the inner regions of the solar system as they fly around the Sun, there are minor differences in the attraction exercised by the latter upon the nearer and more distant particles. This, and planetary gravity, produces small differences in their orbital periods which in time become cumulative. Thus the wreckage of the erstwhile comet is distributed along the orbit, and we see a swarm of shooting stars.
Chapter 19 — The Approach Path to Mars
Ten days remained before the maneuver of adaptation to the satellite orbit around Mars, and the excitement among the crews waxed visibly. Their distance from the planetary goal had diminished to the paltry figure of 2.2 million kilometers and they could see him as a prominent half-disk, one third of the diameter of the Sun. The sunny side glowed intense orange-red and green, and even the naked eye could distinguish the white spot of the southern polar cap melting in the sunlight of the Martian Summer. The opposite half was shrouded in night, and its outline could be made out only when approached by a star which began to twinkle as its light passed through the Martian atmosphere. It would finally occult when it reached the invisible rim of the planet.
Not much more distant from it than the diameter of the Martian half-disk there was a softly glowing starlet whose relation to Mars visibly changed if observed for some time.
It was Phobos, Mars' inner moon, on its seven-and-a-half-hourly chase around the planet.
Double the distance away and on the opposite side of the luminous semi-disk was Deimos, the other and more distant moon. Inconspicuous against the fixed stars, it made a leisurely circuit of its lord and master in an exterior orbit requiring thirty hours for completion.
Hitherto the navigators had been content with a stellar parallax every 24 hours, but they now floated into the astrodomes every third hour and determined the apparent motion of the red planet against the fixed stars behind him. Two days remained before a corrective maneuver was scheduled to bring the convoy into a more exact elliptical path from which the actual hyperbolic approach to the planet might begin. Mars' solar orbit would then pass outside the aphelion of their improved ellipse and at exactly 8,800 kilometers from it. He was coming up behind them, overhauling them at the rate of 2.55 km/sec and bringing them subject to his gravitation. Then they would fall towards him in a hyperbola having its vertex about 1,000 km above the surface. 2,900 km before reaching this vertex, a propulsive maneuver was to reduce their velocity to that of the local orbital speed. The navigators figured that, if no such maneuver took place, they would shoot out into space again at an angle of exactly 106 degrees and 12 minutes of arc to the initial direction of approach.
Holt had instructed Bergmann to secure the big telescope through which he had been scrutinizing their rapidly approaching goal. It was fastened to the Goddard, and Lussigny's radio station likewise became a part of the Oberth after the last reports on Bergmann's observations had gone forth to Earth. The gravity cells were collapsed and hauled in; then Wiegand made a quick but thorough check that all was in readiness for the vital maneuvers. A full 24 hours before the signal was to be given, each ship was as much in readiness for it as human hands and eyes could make her.
The correction maneuvers had taken place without incident and the velocity of the squadron had been changed by 22 meters per second, exactly in the direction which the Chief Navigator figured would bring about the required 8,800 kilometers distance from the Martian orbit and provide proper timing with respect to the now rapidly approaching planet. Observations of Mars' disk in relation to fixed stars confirmed the correctness of the calculations and the outcome of the maneuver.