sure. The trouble lay in our lack of
effective tests for the _Magellan's_ drive. We thought we knew just what
it would do, but after all, the problems of space are intricate. It
turned out that it did not act so effectively against the Sun as had
been calculated. Either that, or the Sun's pull was stronger at this
proximity than registered on our instruments. Chasing after Venus, after
coming back to its orbit, could be done, but it would prove
time-consuming and difficult to plan. What we are doing instead is
altering our schedule."

"But then there's no other place to go from here but Mercury. Is that
what the new plan is?" Burl asked him.

Russ nodded. "Mercury is coming around this side of the Sun. By the time
we have braked, we will be closer to its orbit than to that of Venus. So
we shall proceed inward toward it and make our first planetfall there."

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 deg. 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