r by the time we get there.
Shall I detour, or put on a little more negative and wait for it to come
around to this side?"

"Better wait, I think. The farther away we stay from Jupiter and the
major satellites, the better."

"All x--it's on. Suppose we'd better start standing watches, in case
some of them show up?"

"No use," he dissented. "I've been afraid to put out our
electro-magnetic detectors, as they could surely trace them in use.
Without them, we couldn't spot an enemy ship even if we were looking
right at it, except by accident; since they won't be lighted up and
it's awfully hard to see anything out here, anyway. We probably won't
know they're within a million kilometers until they put a beam on us.
Barkovis says that this mirror will reflect any beam they can use, and
I've already got a set of photo-cells in circuit to ring an alarm at
the first flash off of our mirror plating. I'd like to get in the first
licks myself, but I haven't been able to dope out any way of doing it.
So you might as well sleep in your own room, as usual, and I'll camp
here right under the panel until we get to Ganymede. There's a couple
of little things I just thought of, though, that may help some; and
I'm going to do 'em right now."

Putting on his space-suit, he picked up a power drill and went out into
the bitter cold of the outer structure. There he attacked the inner
wall of their vessel, and the carefully established inter-wall vacuum
disappeared in a screaming hiss of air as the tempered point bit through
plate after plate.

"What's the idea, Steve?" Nadia asked, when he had re-entered the
control room. "Now you'll have all that pumping to do over again."

"Protection for the mirrors," he explained. "You see, they aren't
perfect reflectors. There's a little absorption, so that some stuff
comes through. Not much, of course; but enough to kill some of those
Titanians and almost enough to ruin their ship got through in about ten
minutes, and only one enemy was dealing it out. We can stand more than
they could, of course, but the mirror itself won't stand much more heat
than it was absorbing then. But with air in those spaces instead of
vacuum, and with the whole mass of the _Hope_, except this one lifeboat,
as cold as it is, I figure that there'll be enough conduction and
convection through them to keep the outer wall and the mirror cold--cool
enough, at least, to hold the mirror on for an hour. If only one ship
tackles