"But here we encounter a rather ugly difficulty. Our power plant has an overall efficiency of 30 % only. Thus 70 % of the solar energy from the reflector must be dissipated into space by the condenser. For the low exhaust steam temperature of 46 °C, the condensing surface must be double that of the reflector.
"You may argue that there'd be no particular problem in placing a condenser with twice as much surface as the reflector in the latter's shadow. The design of such a condenser would be elongated and extending to the rear, so that it would radiate heat not only directly away from the Sun, but also laterally. But that configuration would be rather bulky and unhandy, and we must not forget that the reflector with the condenser must be swivel-mounted so that, for any attitude of the ship in space, it can face the Sun directly.
"For all these reasons, we have decided to substitute mercury vapor for the more conventional steam. Such turbines are not a new departure and have the advantage of permitting higher admission temperatures to the turbine than steam and consequently the exhaust is hotter. That will give us a temperature of 120 °C in the condenser. This, of course, will make the surfaces radiate much more actively and we can get by with relatively compact condensers which will easily fit within the shadow of the reflector."
"Say, Dick," said Holt when Peyton stopped talking for a moment, "what about the electrical energy for radio communication? Have we got any figures on that?"
Peyton drew a deep breath and plunged on. "Here's the communication story.
According to the plan, we must consider three separate types of radio communication.
"The first type is for intership work. There's not much to that. It's short range stuff, not much different from the two-way command sets used between airplanes in formation. Each unit will use only a couple of watts and draws practically nothing from the mains.
"The second type is for middle distances of about 10 to 20,000 miles. It will be needed primarily for communication with the landing party when the space ships are circling Mars. Likewise, it will be useful for contact with Lunetta or terrestrial stations after return to Earth's orbit. We propose to equip three ships with transmitters for this middle distance service, and also one transmitter for each landing craft and ground vehicle. All vessels, landing craft and vehicles will of course have appropriate receivers.
These middle distance transmitters will draw about 5 kW each, and since the times during which they will transmit are short, the mains of the vessels will take care of it nicely.
"But the third and most problematical radio is for long, interplanetary ranges. These will be covered by the so-called High Duty Radio Sets, and these will have to be constructed as wholly separate structural entities, independent of the structures of the vessels. Two of the three cargo ships will each carry one of these sets. As a matter of fact, if the navigation should not be accurate enough to allow the Command of the expedition to effect notable savings in propellants, the Command may well be forced to abandon both these sets in the Martian satellite orbit, for we have been unable definitely to assign any portion of the payload of the passenger vessels to these radios.
"The idea is to erect a similar station on Earth with which they will communicate, although the boys are not yet quite sure of its configuration. It's not impossible that one exactly like those of the Mars vessels will operate from Lunetta's orbit… The range of these stations must suffice for two-way communication throughout the entire trip.
"As a matter of fact, this radio communication problem is giving us about as much trouble as any of them. You probably all know that we've been working with Old Man Lussigny, and he's running this show. I don't know as much about radio as I'd like to, considering how my problems tie in with it. Communication across hundreds of millions of kilometers apparently calls for concentrating the radio energy into a ray-pencil of small divergence. The radio boys are still pretty much puzzled over this. If they reduce their wavelength, the same size of directional antennas will give better concentration, but then they cannot build transmitters with enough output. On the other hand, longer wavelengths ease the transmitter problem, but require such large and cumbersome antennas that they give us acceleration troubles during power maneuvers. Right now, I'm still a little vague as to the outcome of this tail-chasing, but it seems quite definite that these High Duty Radio Sets will have to be separate from the ships, not only structurally, but as to sources of power."
Peyton had hardly closed his mouth after this speech than the door was flung open and Spencer burst in waving a newspaper. His usually solemn countenance was wreathed in smiles. "Hey! Read this!" he shouted joyously, "It's all in the papers! The Congress has voted us our whole two billion dollars! Boys, we're off in a cloud of dust! Cosmic dust, at that!"
Chapter 10 — How an Army of Technicians Works
All through 1981 and 1982 the key men of Operation Mars had been enmeshed in tremendous intricacies of problems and work, for the astronomers had set the date of departure at March 21, 1985, and there could be no tampering with it.
The assembly shops of United Spacecraft were filled with purposeful bustle. The three landing craft stood nearly completed in a wide, spacious, but low-roofed hangar, one behind the other. At first glance, they resembled enormous flying wings, but closer examination revealed individual peculiarities.
Their wings were very much swept back. Throughout their span of 153 meters they were exceptionally thin in section and had the familiar sharp leading edges which point to supersonics. Those leading edges were on hinges like the flapped trailing edges, except that they could not be depressed to the same extent. United Spacecraft had developed this expedient many years before and it was in use on the telescoping wings of the Sirius vessels. Its purpose was to improve the slow flight characteristics of the thin supersonic airfoils which, after descending through the sonic barrier, were unsuited for the lengthly subsonic glide and the ensuing landing. "Elevons," the well-known combination elevators and ailerons, were located at the trailing edges on the outboard ends of the wings.
The cylindrical hulls, almost insignificant beside the huge wings, protruded but little fore and aft of the central wing section. They were 22 meters long, 4.7 meters in diameter and sharp-nosed, while the afterbody terminated in the familiar flat base of rockets.
Behind this was a cruciform empennage, so tiny in comparison with the wings as to arouse curiosity concerning its purpose. In actuality, it was proposed to control the craft within the Martian atmosphere by means of the rudders atop the wings and with the elevons only.
The cruciform empennages with their own small control surfaces would serve when the wings had been shed on the surface of Mars. Then the landing craft would assume the guise of rockets pure and simple, and would launch themselves from a vertical position, standing on their stabilizing fins, in order to return wingless to the satellite orbit in which their mother ships awaited them.
One of the three boats had retractable skis, in contrast to her sisters' conventional tricycle landing gear.
Peyton and Spencer had scratched their heads for many a weary hour over the problem of landing these craft on Mars. Dr. Bergmann had said that he couldn't assure them that there was any place large enough, hard enough and smooth enough for a landing with wheels at the computed speed of 197 kilometers per hour. So they accepted Bergmann's suggestion that the first landing be made on skis in the snow-covered south polar region, and conveyed it to the Space Forces.
This suggestion, as appealing as it might appear at first blush, added no inconsiderable additional difficulties to the landing problem. Holt and Braden hesitated long before finally acceding to it, for it meant that the first echelon would be down in a region from which they could never return to the satellitic orbit under their own steam. This was because the satellitic orbit in the plane of the ecliptic could not be reached from that latitude. Hence, the first echelon after debarking would have to set out in their land vehicles towards the equator, in the hope of discovering a suitable landing area for the two remaining wheeled craft, or, if worse came to worst, preparing one. Such a surface voyage would most certainly face them with a passage through a zone of thaw and moisture, where the ground characteristics would be unknown. Holt and Braden's acceptance of this proposal made the enterprise of the first landing party an adventure upon whose outcome depended the success of the whole expedition, and which might bring all sorts of surprises.