“ ‘One may well ask why this life form has never been observed before. First, it is doubtless confined to the Asteroid Belt, the density of matter being too low elsewhere. We have established that it is poisoned by water and free oxygen, so no spores could survive on any planet man has yet visited, even if they did drift there. Second, if a meteorite covered with such barnacles does strike an atmosphere, the surface vaporization as it falls will destroy all evidence. Third, even if barnacle-crusted meteorites have been seen from spaceships, they look superficially like any other stony objects. No one has captured them for closer examination.’ ”

He paused to drink water from a squeeze bottle. “Hear, hear,” murmured Bull, pretending the captain stood behind a lectern.

“That’s why the unmanned probe ships never were found,” said Helledahl. “They may well have been seen, more or less on their predicted orbits, but they weren’t recognized.”

Langnes nodded. “Of course. That comes next in the report. Then I go on to say: ‘The reason that radio transmission ceased in the first place is equally obvious. Silicon components are built into the boom, as part of a transistor system. The barnacles ate them.

“ ‘The observed increase in internal irradiation is due to the plating of heavy metals laid down by the barnacles. First, the static charges and the ferromagnetic atoms interfere with the powerful external magnetic fields which are generated to divert ions from the ship. Second, primary cosmic rays coming through that same plating produce showers of secondary particles.

“ ‘Some question may be raised as to the explosive growth rate of barnacles on our hull, even after all the silicon available in our external apparatus had been consumed. The answer involves consideration of vectors. The ordinary member of the Asteroid Belt, be it large or small, travels in an orbit roughly parallel to the orbits of all other members. There are close approaches and occasional collisions, but on the whole, the particles are thinly scattered by Terrestrial standards, isolated from each other. Our ship, however, is slanting across those same orbits, thus exposing itself to a veritable rain of bodies, ranging in size from microscopic to sand granular. Even a single spore, coming in contact with our hull, could multiply indefinitely.’ ”

“That means we’re picking up mass all the time,” groaned Bull. “Which means we’ll accelerate slower and get home even later than I’d feared.”

“Do you think we’ll get home at all?” fretted Helledahl. “We can expect the interference with our radiation shield, and the accumulation of heavy atoms, to get worse all the time. Nobody will ever be able to cross the Belt!”

“Oh, yes, they will,” said Captain Langnes. “Ships must simply be redesigned. The magnetic screens must be differently heterodyned, to compensate. The radio booms must be enclosed in protective material. Or perhaps—”

“I know,” said Bull in great weariness. “Perhaps antifouling paint can be developed. Or spaceships can be careened, God help us. Oh, yes. All I care about is how we personally get home. I can’t modify our own magnetic generators. I haven’t the parts or the tools, even if I knew precisely how. We’ll spin on and on, the radiation worse every hour, till—”