Under these circumstances, it is difficult to say to what extent a mutation is more likely totake place in space than on Earth. We may, however, state that the factor of cosmic radiation will not be multiplied by more than 40.
"When applied to any individual, this factor of 40 is negligible. After all, gentlemen, you do not propose to expose yourselves for the rest of your lives to this radiation, but only for some three years. We believe that millions of people would have to expose themselves in empty space for a lifetime before we scientists could confirm an increased number of mutations in succeeding generations.
"Now, you might like to know whether the nacelles of the Mars vessels might not be shielded to a point which would reduce the cosmic radiation density within them to that of the Earth's surface.
"The absorptive capacity of our atmosphere corresponds to that of a leaden wall some 40 inches thick. I need not tell you that anything even approximating such a thickness would render the Mars vessels incapable of fulfilling their functions. Anything thinner would be worse than useless, for as you have learned, the total radiation density at 60,000 feet is higher than in empty space by reason of the collisions between the atoms of the atmosphere and the particles. It is the atmospheric layers below this altitude which absorb the secondary radiation to an extent which reduces the total radiation density at sea level to less than that of empty space. Therefore a shield of a few centimeters of lead would only make matters worse and offer no protection whatsoever. It would simply increase the probability of collisions without being thick enough to absorb the secondary radiation.
"Thus, the thinnest wall remains the best, and the organic outer skins of your nacelles are favorable to the protective issue. The organic plastics of which the nacelles will be composed contain primarily hydrogen, carbon and oxygen atoms and are highly porous to the primary particles. Thus collisions, with their resulting secondary radiation, will be reduced to a minimum and the radiation density within will be no higher than in empty space, while metal walls of moderate thickness would increase it.
"In short, gentlemen, I believe that I can assure you that there is hardly any danger to which you will be called to expose yourselves that will be of less consequence than the cosmic rays, as infamous as they may be thought to be.
"There's no doubt in my mind that you risk yourselves and your posterity to a far greater extent each time you get into a motor car than you will be doing by exposing yourselves to cosmic rays in the nacelles of your space vessels."
Chapter 12 — The Great Space Lift
General Braden concentrated his personal attention on the organization of the ferry service which would freight Operation Mars up to the orbit of departure. Already he had reduced the rocket vessels which served Lunetta from 30 to 12. Those 18 ships which he assigned to Operation Mars were immediately sent to United Spacecraft for the necessary modifications, which included complete removal of the passenger accommodations and the relatively small cargo bays from the top stages. Fifteen of the vessels were equipped with cargo tanks for the hydrazine and nitric acid propellants of the Mars vessels. The other three ships were rebuilt with wide doors and large, roomy cargo spaces for the bulky components of the Mars vessels to be assembled in the orbit. United Spacecraft further completed 28 more Siriuses as propellant freighters exclusively, giving Braden a fleet of 43 tankers and three cargo vessels.
The ferry plan provided that each vessel should average a trip every ten days, and actually, the top stage of each ship required but 12 hours or so for a round trip. The problem of salvaging the booster stages, particularly the second stage, with its drop into the ocean a full thousand miles from the launching site, was complicated by reason of the three days required by the salvage steamer to get back to the base. There were, nonetheless, some seven days available for inspection, repairs and reassembly of the various stages to prepare each ship for its next departure. Experience with the Lunetta ferry system indicated that such a schedule could be safely complied with, and matters were so arranged that the 950 Mars ferry flights could be carried out within about eighth months, even if as many as six ships should be concurrently out of commission for major repairs.
Braden's plans were synchronized exactly with spacecrafts' delivery schedule for the components of the Mars vessels and with the assembly schedule for the orbit of departure.
Accordingly, a few cargo flights delivered a number of tank frames and tanks, followed by one of the nacelles for the passenger vessels. This cabin was to serve as a primitive shelter for the assembly gang during their labors in space. Working in space suits, the men assembled the frames and located the tanks within them, ready to receive propellants.
This permitted the propellant loading operation to begin without delay, during which the tankers pumped their hydrazine and nitric acid into the prepared receptacles of the as yet incomplete Mars vessels. Two tankers were to be launched simultaneously every 12 hours and to lay alongside the storage tanks which they would fill through their delivery hoses within the ten hours preceding the arrival of the next shipment. Then they were to uncouple their hoses and apply to themselves a brief decelerative thrust in order to reenter the elliptical plunging path whose perigee would touch the atmosphere after the ship had gone half around the Earth. After another half circle in extended gliding flight they would return to their point of departure. During the elapsed 12 hours, this point would have slowly advanced 180° by the Earth's rotation, and would hence again be below the orbit of departure.
The cargo vessels were intermittently to deliver the other Mars ship components as the fueling proceeded. The last movement was to be that of the landing craft, whose wide wings would already be awaiting them in the departure orbit. Using their own rocket motors atop Sirius-class booster stages, they would fly up to orbit to have their wings attached, and would themselves then be clamped to their mother ships in anticipation of the long voyage through space.
This was an enormous logistical effort, the greatest ever undertaken by the Space Forces. Establishing Lunetta had been child's play in comparison. But before Braden could begin it, he was faced with another important problem.
The plane of the orbit of departure lying, as it did, in the ecliptic, had eliminated Kahului as a practical base of operations for the ferry vessels, for the Hawaiian Islands are approximately in the latitude of the Tropic of Cancer. The latter represents the northernmost latitude attained by the orbit. Nor could more than one launching operation every 24 hours be carried out from Kahului, and this would have delayed the entire ferry operation. In addition, there was the matter of utilizing the maximum payload, and the location of Kahului was unsuited to this.
Braden therefore was forced to establish an entirely new base for the ferry vessels at Christmas Island, a huge atoll of more than 100 miles circumference rising from the Pacific to bare the ring of its palm-fronded islets 1,200 miles South of Hawaii. Since Christmas Island was almost exactly on the Equator, it was from there that the maximum peripheral velocity produced by the Earth's rotation could most effectively be utilized for ascent. At the Equator, this velocity is 464 meters per second, and since the direction of movement in the orbit of departure was identical, a velocity of 464 m/sec was no mean contribution to the required total velocity of 8,260 m/sec. In actuality, only 425 of those 464 meters per second would be saved, and this was because of the angle between the ecliptic and the Equator. Nevertheless, some six tons of propellants per trip would remain in the tanks of the ferry vessels over and above what would have been there had the trip been made from Kahului to Lunetta. Since the propellants were the same as those used in the Mars vessels, this represented a considerable net gain of available payload. Only by this gain had it been possible to reckon with but 950 flights for the whole ferry operations.