"You will notice that the mirror does not revolve with the wheel; instead, a photoelectric cell controls a mechanism which keeps it constantly directed at the Sun. Of course, this could not be done unless the rotation of the wheel was kept in the ecliptic.
However, you must not confuse the plane in which the wheel rotates with the plane of Lunetta's orbit around the Earth, for the latter is at right angles to the ecliptic, as I already told you."
"What's the connection between the mirror and the spokes of the wheel?" asked Lussigny a bit confused.
"Ah, yes. Sorry I digressed from your last question. Those spokes are used as condensers for the exhaust steam of the turbine, and here we run into one of the more interesting anomalies. Despite the general belief that interstellar space is extremely frigid, it is very difficult indeed to achieve satisfactory cooling. There is, of course, no air, so we cannot resort to air cooling and are restricted entirely to radiation cooling. The turbine expands its steam down to 46 degrees Centigrade, and we're obliged to cool our condenser with what little radiant heat is still given off at that temperature. Even for the miserable 35 kilowatts that the generator puts out, we have to have 1,790 square feet of cooling surface, and the spokes are the condenser tubes. Since their combined length equals 1,300 feet and their diameter is 5.3 inches, they provide exactly the amount of radiating surface necessary."
"But how does it happen that these tubes are not heated by radiation from the sun?"
"That's quite simple," said Holt. "They're always shaded by the rim, because it rotates in the plane of the ecliptic."
Lussigny's curiosity was still unappeased, and he went on with his questioning.
"That is certainly cleverly thought out, but tell me, just how the water gets back into the boiler from the tubes?"
"Simplest thing in — or out — of the world," said Holt. "It condenses on the inner walls of the tubes and runs outwards towards the rim by the centrifugal force brought into play by the rotation of Lunetta around the hub. There's a collector ring connecting the outer ends of the condenser spokes. From this ring, an electric pump feeds the condensate back to the boiler through one of the spokes reserved for that purpose."
"That's really wonderful! And now, what are the two thick spokes?"
"They're actually elevator shafts, if you can call a little car in which a man can ride- but which goes neither up nor down — an elevator. As a matter of fact, when you're riding in one, you feel like you're going down when you're moving towards the rim. Lunetta's rotation around her hub produces, as I think I told you, the effect of gravity in the rim.
Anyhow, the crew can move between the hub and the rim in these elevators. But look, we're making fast."
The man in the space suit was now close to Sirius. At the end of the steel cable which he dragged behind him was a coupling device to be shackled to a fitting at the ship's nose.
The man disappeared from the view of those at the portholes and could be heard moving around and connecting the shackle. Then he appeared in front of the entrance door of the passenger cabin.
Prior to this, the ship's mechanic had pulled himself down the ladder and was waiting near the door. He touched a switch button as the man in the space suit approached the outer door of the airlock, opening the latter. The man in the space suit drew himself in and the mechanic pressed another switch button after closing the outer door. There was a hissing sound which Holt described to Lussigny as the airlock being pressurized. Then the inner door was opened and the stranger drew himself in. After removing his transparent helmet and greeting the passengers with a cheery "Hello, folks!" he pulled himself along the ladder into the pilot's compartment. There was a slight jerk.
"That's the winch taking hold," said Holt. "Lunetta has a little electric winch which is now winding in the cable the man just brought over and made fast on our nose."
Slowly, Sirius began to turn and the great wheel which was Lunetta disappeared from view, coming into sight again a few moments later. Its enormous, rotating circumference drew closer and closer to the portholes. Then there was a mild jar, followed by a soundas of a skidding auto tire. Sirius began to turn about her central axis.
When the mechanic opened the outer door without closing the inner one, there was no change of pressure, nor cracking in the ears of the passengers.
"That's the end and object of the contact maneuvers," said Holt. "We can now see
how Lunetta looks from the inside."
Chapter 3 — Interstellar Stop-Off
The Central Station of Lunetta was an elongated cylindrical space about 30 feet in diameter and 40 feet long and almost empty. Holt floated into its barrel-like interior through a door that opened in the mooring cone. At the apex of the mooring cone was a hand wheel that locked Sirius' nose against the hermetic seal. Between the point of the cone and the opposite end of the station was a meshed shield of wire, behind which stood the turbogenerator.
In the center of the space was a sign reading "Welcome to Lunetta. Arriving personnel please report to Room 21 without delay."
There was a hand-rope leading to the door of one of the elevator shafts and Holt, Hansen and Lussigny held their luggage in their left hands as they pulled their bodies along this rope. Lussigny was having quite a bit of trouble, unaccustomed as he was to the weightlessness. With his luggage in one hand, he failed to pull himself exactly parallel to the rope, so that when he let go of it to get another grip, he found himself floating away and bumping into the wall. He then attempted to seize it with his left hand, thus relinquishing his grasp on his luggage. Before he knew it, the suitcase had escaped and floated away. Lussigny and his equipment were apparently hopelessly separated, despite the former's frantic wriggling, punctuated by mirth.
"Hold it! Here comes help" laughed Holt, pushing his own luggage against the wall of the cylinder where it remained, held by centrifugal force. Then Holt launched himself across the center with a powerful thrust, gripping the floating Lussigny as he passed.
Together, they impinged lightly on the opposite wall, where Holt instructed Lussigny to make a similar leap back and then to hold on.
"I'll get that obstreperous suitcase of yours!" he said, laughing. They then entered the cage.
"Now watch out," said Holt, grasping a pair of hand grips. "As soon as we move, you'll feel a push into the corner. This is a combined effect of the increasing centrifugal acceleration floorwards and the sideways acceleration which brings us up to the peripheral speed of the ring."
When the car stopped at what seemed the bottom, the old feeling of weight was restored, although it was definitely weaker than down on Earth. They found that they could both stand and walk, but Holt was the only one of the three who didn't tend to leap lightly from the floor at each step when they first arrived.
Holt immediately reported to Major General Riley, commanding Lunetta.
"I'm very happy to meet our Mars-man," said the General. "General Braden has radioed us to offer you every facility we have. What's your program?"
"My most important mission is to visit the observatory and to ask various questions about Mars of Dr. Bergmann and his assistants. After that, I'd like to discuss some of the astronomical measurement problems that are of vital importance to our planning work."
"Do you know that Professor Hansen from the Mount Palomar Observatory is to arrive?" asked the General.