The crewmen soon shifted their eyes to the display. The ship could be captured only because it was registered on Titan. Ensign Yagisawa couldn't understand why the enemy would assault this base. Chief Zanak said, without averting his eyes from the display.
"I noticed that there was something strange about its behavior. It repeatedly made unnecessary corrections to its orbit, then I noticed that it emitted something a few minutes ago. It wasn't very big, a tank or something. It may be less than two meters long, possibly a nuclear bomb. You had better scan it as soon as possible."
The black face of the commander turned red.
"Send Valhalla an emergency call. There is a strong possibility that this base would be bombed from orbit. As for its future course, send its registry number and tell them to scan it for themselves."
The communication officer excitedly asked him.
"Shall I send it in cipher ?"
"You need not. It is urgent."
Suddenly the headquarters became noisy, but Yagisawa couldn't grasp the situation. He asked Zanak in a low voice.
"I cannot understand...why would they aim at a minor base like this. Do they intend to attack the weakest point for propaganda ?"
"You might not think so, but this base is an important strategic foothold."
"Do you mean this railroad? It is certainly useful to project metal resources, but there are many similar facilities on the moon. They are more efficient than this and there are more military bases."
"Here are resources that the moon doesn't have."
"What resources? The only things Mars has in abundance are ice and dry ice."
"What is ice made of?"
"Water. Or do you mean that it's made from hydrogen and oxygen ?"
Yagisawa stopped talking. Hydrogen fuel and deuterium were important strategic materials. It was true that there was an inexhaustible supply on Earth, but they exist at the bottom of a deep gravity well and dense atmosphere. It was impractical to supply them for vessels in the space. In comparison, there were several places that could supply a large quantity of cheap hydrogen and deuterium to space. They were the satellites of the outer planets. Air Space Force is at war with them.
"How about the private railroad ? The capacity of the Pavonis Line is larger than that of this railroad, isn't it ?"
"The problem is what position will the Martian City Alliance take. Presently Mars has taken neither side on this war. It is commonly believed that Mars will remain a bystander. If the Olympia railroad was destroyed, they will bluff the Martians next. They will demand that no munitions be supplied to ASF or they will conduct bomb indiscriminate. That could be very effective. Unlike the earth, Mars has little atmosphere. Cities on Mars are very vulnerable on this point. If this base was destroyed, we can certainly compensate for it, but in fact the damage would be considerable."
"But..."
Yagisawa was still unconvinced and he went on asking.
"I don't think that the bombardment from the ship would be effective. The bomb must be small so not as to be detected. It will have no boosters for propulsion. Then it won't be able to change course and dive. The object that separated from that ship must come in horizontally, like our approach course. So they must detonate above this caldera. But I don't think that it could do much damage to the railroad because here is almost no air.
Even if the crew were injured by radioactive contamination, the base itself would not suffer much damage. If it comes in as a low altitude as possible, even a tiny error in the course will result in it crashing into a mountain around the caldera."
"It comes straight to the railroad tunnel and explodes, the damage will be considerable. It will make this line unusable for more than one year."
"Is that possible ?"
Yagisawa asked him in surprise. While the pre-approach track is designed to be wide, the diameter of the entrance of this tunnel was no more than two hundred meters. And the deeper it goes, the narrower the tunnel becomes. He couldn't believe that a bomb which has no propulsion could be shot deeply into the tunnel.
"And...the ship moved a little strangely, but it didn't make any great orbital shift. If they wanted the bomb to come along like our approaching course, the ship would have to take an orbit with an angle of inclination is nineteen degrees. But it took the course to dock at a private station. Its orbit is directly above the equator with an angle of inclination of zero degree. Silian line, Pavonis line and the private station are in synchro... no, anyway they are just above the equator."
"It wasn't on the docking course before it separated from the bomb."
Zanak said slowly. A new point lit on the display. It must be the bomb. It was indeed on the approach to Olympia railroad. Zanak said quietly to Yagisawa who was in blank surprise.
"It is between the autumnal equinox and the winter solstice on Mars. In the Northern hemisphere. The axis of Mars has a twenty-five degrees' inclination and the summit of Mt. Olympus is 19 degrees North latitude. We don't need to do the detailed calculation. Remember the course that we took. The sun right over our heads when we were in the opposite side of Mars. And it was going backwards. We can say, in other words, that the midnight approach to the Olympia line is essentially to the ecliptic.
Further, while the ship is registered on Titan, it must have come from somewhere in the asteroid. It may be from Ceres or possibly from Vesta."
"From Ceres."
The commander added in a subdued voice. Zanak continued.
"Didn't I tell you ? Ceres is now slightly below the ecliptic plane. It is possible, if all going well, to throw a bomb directly along the economical course from Ceres into the approach to the Olympia line. It pretends to approach the station above the equator. After it kills its inter-planetary speed and before it enters orbit around Mars, it would be the ideal time to launch the bomb. At that time, it would be easy to shift course.
In addition, the topographical map of the Olympia line is open to the public. In the early stages of development many private shuttles used this line. For a smart bomb this will be like having a high-way."
"All hands are to take refuge in the lowest block of the base in ten minutes."
The commander spoke to a microphone.
"This base will be bombed twenty minutes later. The fleets on orbit cannot prevent this bombing. But it will do only a minor damage on this base itself. You need not be too worried."
Damn it.... Someone in the headquarters groaned out. Yagisawa urged Zanak to leave. But Zanak silently stared at the display. He walked to the commander, who was still standing in front of the console, and said.
"Give me a chance. I'll try to down it."
Out of habit, the commander cast an indignant glance at him.