"Certainly," said Holt. "We met on the way up and he's waiting in the outer office."
"Hansen is outstanding among the Mars specialists," said the General. "He's probably the best in his field. Perhaps you don't know that he's the man who sparked the whole Mars expedition scheme, and he's here to go over the final details for his report to the President with the collaboration of our astronomers. You'd better have him sit in on your deliberations."
"And who's this Dr. Lussigny?" asked Holt. "What's his line?"
"He's MIT's top-notch radio and radar man. Professor Ashley sent him up for indoctrination and I understand that he's making some preliminary studies for the design of the radio gear for your expedition."
Riley opened the door to the next compartment and invited Hansen and Lussigny, who were waiting, to come in.
"Welcome to Lunetta, gentlemen" said he. "May I introduce Colonel Holt? He's almost on his way to Mars."
"You — well, I declare!" exclaimed the professor. "But it's wonderful luck to find you here! Colonel, we've got so much to talk about that it had better wait until later…"
"Gentlemen, I know that no food is served aboard the Sirius, so let's go into the mess room for breakfast," invited General Riley.
Together they made their way along an apparently unending passage which curved upwards before them, although they had no sensation of climbing as they walked. This was the long corridor through which the various compartments of the rim of Lunetta communicated. It was interrupted every 60 feet or so by an air-tight door of circular section. These doors permitted any 60 foot section of the ten composing Lunetta's rim to be hermetically sealed in the event that one of them might spring an air leak.
While they were breakfasting, Holt and Hansen decided that they would visit the observatory together.
"How far is it from Lunetta to the observatory?" asked Lussigny.
"It's about ten miles," said Riley. "It precedes us in the same orbit."
"Why so far?"
"Ten miles isn't very far in interstellar space," answered Riley. "We've found it the best practice to keep all the auxiliary stations of Lunetta pretty far apart for a variety of reasons. For one thing, the orbits are less liable to disturbance by reciprocal attraction, and it also tends to avoid collisions which might result from minor differences in the orbital data of the various auxiliary stations. Each station must be in possession of its own orbital data as the basis for a great variety of purposes. Here in the main station we require them, for example, in order to determine the arrival conditions for the ferries with absolute precision. Our military auxiliaries, which are located at very considerable distances, need their orbital data with extreme exactness for ballistic purposes. And the observatory needs them for astronomical measurement."
"Would there be any breach of military secrecy if you were to tell me how bombs are dropped from here to the Earth, General?" asked Lussigny.
"Of course there are one or two details that are top secret," answered Riley. "But the basic principle is quite simple and there's no reason whatever why you shouldn't know it.
There are two auxiliary stations flying in our orbit. One of them is 1,935 kilometers ahead and the other 1,935 kilometers astern of us. The one astern is the Bomb Bay and the one ahead is called the Control Station. When we bombed the Earth during the war, we really used rocket-powered missiles, which were fired from the Bomb Bay in the direction opposed to its rotation around the Earth. These missiles are gyro-controlled to maintain their set course during their short period of propulsion. Seen from the Earth, the rocket drive decreases the speed of the missile from the 7.07 kilometers per second which it had originally to 6.59 kilometers per second. This throws the missile into an elliptical path, the perigee of which is in the upper strata of the atmosphere after one half another circle around the Earth. The air drag gradually decelerates the missile, the tail of which is equipped with a special braking device. It then penetrates the lower atmospheric strata along a trajectory which is initially flat, but then grows steeper. Finally it falls onto the Earth.
In free flight, the missile requires nine minutes less than the hour the Bomb Bay does to half-circumnavigate the Earth, in order to reach the perigee of its semi-ellipse. This means that the Bomb Bay has lagged 26 degrees of arc behind the missile at the moment it enters the atmosphere. Even when it has entered on the decelerated trajectory, it still angularly precedes the Bomb Bay to a small extent. This is because the missile strikes the atmosphere at a considerably higher velocity than that of the Bomb Bay. Hence the Control Station is located some 3,870 kilometers ahead of the Bomb Bay in the same orbit so that the missiles can be easily seen from the Control Station while they are falling through the atmosphere, and may be guided to their targets by radio. The missiles are observed for this purpose with radar or powerful telescopes."
"It's not hard to understand that there can be no defense against that kind of attack," grunted Lussigny.
"The only effective one would be an attack on the Space Stations proper. During construction, we mounted quick-firing guns on Lunetta and her auxiliary stations because we always feared attacks form Russian space ships. But we fortunately succeeded in destroying their factories before they could get such ships into action. It wasn't until the war was over that we realized that it had been a matter of nip and tuck."
"You mentioned telescopes a few moments ago," said Lussigny, "with which the fall of the bombs was observed. How much detail of the Earth's surface can be recognized through them from as high as 1,000 miles?"
"Our new 100-inch reflector has good enough definition to let us distinguish two objects on Earth as little as 40 centimeters apart," answered Riley.
"Why then, you can make out individual people!" exclaimed Lussigny in amazement.
"No question about it. When we began to make observations during the last war, the Navy doubted whether we should be able to distinguish war ships. Not only could we distinguish them when weather and visibility were good, but we could make out their class and see the men on their weather decks."
"That's really incredible! What power do you use?"
"We can magnify up to 1,250 diameters. This brings the Earth 1,250 times as close as it appears to the naked eye, and we can see what goes on there as though we were 4,000 feet up instead of 1,000 miles."
"Why can't you step up your magnification?" asked Lussigny stubbornly. This brought Professor Hansen into the argument.
"Magnification is limited by the diameter of the telescope reflector," he said. "As General Riley just explained, the reflector up here has a resolving power corresponding to a distance of 40 centimeters on Earth. If we were to increase the magnification beyond 1,250 diameters, we'd magnify the diffraction patterns around the objects observed. That would simply blur the image without revealing any more detail. We'd have to double the diameter of the reflector in order to increase the resolving power from 40 cm to 20 cm.
Then we'd have a telescope as bulky as that on Mount Palomar. We simply haven't the means to produce anything like that, nor to freight it up here."
Lussigny wanted to know what the effect the atmosphere might have on observations, and Hansen continued. "We cannot, of course make any observations on zones covered by bad weather, but there's nothing like as much interference when the weather's good as is suffered by an Earth-bound astronomical telescope. This interference is quite serious.
When you're looking into the heavens from the bottom of our sea of air, that air is both within and immediately before your optical system. Slight irregularities of ambient temperature cause refraction of the light rays very close to your optical system and tend to make the whole image flicker. But if you are looking Earthwards from here, any disturbances in the air are far distant. They are practically negligible."