Mercury, the smallest and hottest planet in the system. Burl remembered that it was one of the two worlds that they knew for sure had a Sun-tap station on it. He went down the hatch to carry the news to the landing crew. Haines, Burl discovered, had already heard the new plan on the intercom from Lockhart. As soon as Burl joined them, the four men, including Ferrati and Boulton, went into a planning session. The problem of Mercury was a hard one. As Ferrati remarked, "It would have been better to tackle this one last instead of taking it on first." "Yes, but on the other hand," was Haines's comment, "Mercury's station is probably one of the most important--located as it is, so close to the Sun. With ideal conditions for steady, undiverted concentration of solar power, it must be the primary station in the system." "The problem boils down--and I do mean 'boils'--to heat," Boulton laughed. "Mercury rotates on its axis only once a year--its year being only eighty-eight of our days long. This means that just as the Moon presents only one side to the Earth, Mercury always presents the same hemisphere to the Sun. On the Sun side, therefore, there is always day. The Sun appears to be fixed in the sky. Naturally, we assume the Sun-tap station will be on that sunny side. And the heat must be terrific." "Matter of fact," said Haines dryly, "the records show the heat in the center of the Sun side reaches 770° Fahrenheit. Enough to keep tin and lead molten." "The problem is how to reach the station over such a boiling landscape," summed up Burl. "It seems to me that the absence of an atmosphere could answer part of the problem." Haines nodded. "Let's get to work on a plan of action, men. We've got a few days to get our equipment laid out." Those few days passed quickly enough. When several possible schemes had been outlined, the men made lists of the types of equipment that might be used with each. Then, putting on pressurized space suits and carrying air tanks, they left the inner sphere and worked through the cargo space surrounding it within the outer frame of the spaceship. There had originally been air here, but now they found most of it was gone, thinned out from infinitely tiny leaks in the outer shell caused by the constant bombardment of microscopic bits of meteoric dust. They located each piece of equipment and moved it into position for easy handling. The ship came to its halting point, where the repulsion against the Sun finally braked it against the gravitational pull of the Sun. Then, by increasing the selective pull of the approaching planet Mercury, they moved off in that direction. Mercury was changing in appearance. As they neared it from the outer side, its lighted half swung away from their view, and what they saw was a constantly narrowing crescent, growing larger even as it narrowed. Finally the hour came when they swung up close, coming in on the eternally sunless, night side of the little planet.