"Let's ask Dad."

Hazel stopped them at the hatch to the control room. "He's at the computer. What's the complaint?"

"Hazel, the reflecting foil we've been salvaging - is it on the jettison list?"

"Certainly. We'll pick up some more on Mars for the trip back. Why?"

"A radar corner - that's why!" They explained the plan. She nodded. "A long chance, but it makes sense. See here, wire everything we jettison to the bikes. We might get it all back."

"Sure thing!" The twins got busy. While Pollux gathered to­gether the bunches of bicycles, all but a few in good repair and brave with new paint. Castor constructed a curious geometrical toy. With 8-gauge wire, aluminium foil, and sticky tape he made a giant square of foil, edged and held flat with wire. This he bisected at right angles with a second square. The two squares he again bisected at the remaining possible right angle with a third square. The result was eight shiny right-angled corners facing among them in all possible directions - a radar reflector. Each corner would bounce radar waves directly back to source, a principle easily illustrated with a rubber ball and any room or box corner. The final result was to step up the effectiveness or radar from an inverse fourth-power law to an inverse square law - in theory, at least. In practice it would be somewhat less than perfectly efficient but the radar response of the assembly would be increased enormously. A mass so tagged would stand out on a radar screen like a candle in a cave.

This flimsy giant kite Castor anchored to the ball of bicycles and other jetsam with an odd bit of string. No stronger link was necessary; out here no vagrant wind would blow it away, no one would cut it loose. "Pol," he said, "go bang on the port and tell 'em we're ready."

Pollux walked forward and did so, rapping on the quartz first to attract his grandmother's attention, then tapping code to report. While he was gone Castor attached a piece of paper reading:

NOT FOR SALVAGE

This cargo is in free transit by intention. The undersigned owner intends to recover it and warns all parties not to claim it as abandoned. U.P. Rev. Stat. # 193401

Roger Stone, Master

P.Y. Rolling Stone, Luna

When Pollux came back he said, "Hazel says go ahead but take it easy."

"Of course." Castor untwisted the single wire that held the ungainly mass to the ship, then stood back and watched it. It did not move. He reached out and gave it the gentlest shove with his little finger, then continued watching. Slowly, slowly it separated from the ship. He wished to disturb its orbit as little as possible, to make it easy to find. The petty vector he had placed on it - an inch a minute was his guess - would act for all the days from there to Mars; he wanted the final sum to remain small.

Pollux twisted around and picked out the winking gleam of the War God. "Will the jet be clear of it when we swing ship?" he asked anxiously.

"Quit worrying. I already figured that."

The maneuver to he performed was of the simplest - point to point in space in a region which could be treated as free of gravity strain since the two ships were practically the same distance from the Sun and Mars was too far away to matter. There were four simple steps: cancellation of the slight vector difference between the two ships (the relative speed with which the War God was puffing away), acceleration toward the War God, transit of the space between them, deceleration to match orbits and lie dead in space relative to each other on arrival.

Steps one and two would be combined by vector addition; step three was simply waiting time. The operation would be two maneuvers, two blasts on the jet.

But step three, the time it would take to reach the War God, could be enormously cut down by lavish use of reactive mass. Had time been no object they could have, as Hazel put it, closed the gap 'by throwing rocks off the stern." There was an infinite number of choices, each requiring different amounts of reactive mass. One choice would have saved the bicycles and their per­sonal possessions - but it would have stretched the transit time out to over two weeks.

This was a doctor's emergency call - Roger Stone elected to jettison.

But he did not tell the twins this and he did not require them to work a ballistic. He did not care to let them know of the choice between sacrificing their capital or letting strangers wait for medical attention. After all, he reflected, the twins were pretty young.

Eleven hours from blast time the Stone hung in space close by the War God. The ships were still plunging toward Mars at some sixteen miles per second; relative to each other they were stationary - except that the liner continued her stately rotation, end over end. Dr. Stone, her small figure encumbered not only with space suit, pressure bottles, radio, suit jet, and life lines, but also with a Santa Claus pack of surgical supplies, stood with her husband on the side of the Stone nearest the liner. Not knowing exactly what she might need she had taken all that she believed could be spared from the stock of their own craft -drugs, antibiotics, instruments, supplies.

The others had been kissed good-by inside and told to stay there. Lowell had cried and tried to keep his mother from enter­ing the lock. He had not been told what was going on, but the emotions of the others were contagious.

Roger Stone was saying anxiously, "Now see here, the minute you have this under control, back you come - you hear?"

She shook her head. "I'll see you on Mars, dearest."

"No indeed! You -"

"No, Roger. I might act as a carrier. We can't risk it."

"You might act as a carrier corning back to us on Mars, too. Don't you ever expect to come back?"

She ignored the rhetorical question. "On Mars there will be hospitals. But I can't risk a family epidemic in space."

"Edith I've a good mind to refuse to-"

"They're ready for me, dear. See?"

Over their heads, two hundred yards away, a passenger lock on the rotation axis of the mighty ship had opened; two small figures spilled silently out, flipped neatly to boot contact, stood on the ship's side, their heads pointing 'down' at Mr. and Mrs Stone. Roger Stone called into his microphone, "War God!"

"WarGod aye aye!"

" Are you ready?"

"Whenever you are."

"Stand by for transfer."

Acting Captain Rowley had proposed sending a man over to conduct Dr. Stone across the gap. She had refused, not wishing to have anyone from the infected ship in contact with the Rolling Stone. Now she said, "Are my lines free for running, Roger?"

"Yes, dearest." He had bent several lines together, one end to her waist, the other to a padeye.

"Will you do my boots, dear?"

He kneeled and unzipped her magnetic boots without speak­ing, his voice having become uncertain. He straightened and she put her arms around him. They embraced awkwardly, hampered by the suits, hampered by the extra back pack she carried. "Adios, my darling," she said softly. "Take care of the children."

"Edith! Take care of yourself!"

"Yes, dear. Steady me now."

He slipped his hands to her hips; she stepped out of the boots, was now held against the ship only by his hands.

"Ready! One! Two!" They crouched down together. "Three!" She jumped straight away from the ship, her lines snaking after her. For long, long seconds she sailed straight out over his head, closing the gap between her and the liner. Presently it became evident that she had not leapt quite straight; her husband got ready to haul her back in.