attraction between even a big ship like the Tricorn and a tiny, tiny satellite such as Deimos isn't enough to matter; all that matters is getting the very considerable mass of the ship shoved free.

The second gentle shove, the one that kept up and never went away, was the ship's own main drive-onetenth of a standard gee. The Tricorn is a constantboost ship; she doesn't dillydally around with economical orbits and weeks and months in free fall. She goes very fast indeed ... because even 0.1 gee adds up awfully fast.

But one-tenth gee is not enough to make comfortable passengers who have been used to more. As soon as the Captain had set her on her course, he started to spin her and kept it up until the centrifugal force and the boost added up (in vector addition, of course) to exactly the surface gravitation of Mars (or 37 percent of a standard gee) at the locus of the first-class staterooms.

But the floors will not be quite level until we approach Earth, because the inside of the ship had been constructed so that the floors would feel perfectly level when the spin and the boost added up to exactly one standard gravity-or Earth-Normal.

Maybe this isn't too clear. Well, it wasn't too clear to me, in school; I didn't see exactly how it worked out until (later) I had a chance to see the controls used to put spin on the ship and how the centrifugal force was calculated. Just remember that the Tricorn- and her sisters, the Trice and the Triad and the Triangulum and the Tricolor are enormous cylinders. The thrust is straight along the main axis; it has to be. Centrifugal force pushes away from the main axis- how else? The two forces add up to make the ship's "artificial gravity" in passenger country-but, since one force (the boost) is kept constant and the other (the spin) can be varied, there can be only one rate of spin

which will add in with the boost to make those floors perfectly level.

For the Tricorn the spin that will produce level floors and exactly one Earth gravity in passenger country is 5.42 revolutions per minute-I know because the Captain told me so....nd I checked his arithmetic and he was right. The floor of our cabin is just over thirty meters from the main axis of the ship, so it all comes out even.

As soon as they had the floor back under us and had announced the "all clear" I unstrapped me and hurried out. I wanted a quick look at the ship; I didn't even wait to unpack.

There's a fortune awaiting the man who invents a really good deodorizer for a spaceship. That's the one thing you can't fail to notice.

Oh, they try, I grant them that. The air goes through precipitators each time it is cycled; it is washed, it is perfumed, a precise fraction of ozone is added, and the new oxygen that is put in after the carbon dioxide is distilled out is as pure as a baby's mind; it has to be, for it is newly released as a by-product of the photosynthesis of living plants. That air is so pure that it really ought to be voted a medal by the Society for the Suppression of Evil Thoughts.

Besides that, a simply amazing amount of the crew's time is put into cleaning, polishing, washing, sterilizing-oh, they try!

But nevertheless, even a new, extra-fare luxury liner like the Tricorn simply reeks of human sweat and ancient sin, with undefinable overtones of organic decay and unfortunate accidents and matters best forgotten. Once I was with Daddy when a Martian tomb was being unsealed-and I found out why xenoarchaeologists always have gas masks handy. But a spaceship smells even worse than that tomb.

It does no good to complain to the purser. He'll listen with professional sympathy and send a crewman around to spray your stateroom with something which (I suspect) merely deadens your nose for a while. But his sympathy is not real, because the poor man simply cannot smell anything wrong himself. He has lived in ships for years; it is literally impossible for him to smell the unmistakable reek of a ship that has been lived in-and, besides, he knows that the air is pure; the ship's instruments show it. None of the professional spacers can smell it.

But the purser and all of them are quite used to having passengers complain about the "unbearable stench"-so they pretend sympathy and go through the motions of correcting the matter.

Not that I complained. I was looking forward to having this ship eating out of my hand, and you don't accomplish that sort of coup by becoming known first thing as a complainer. But other first-timers did, and I certainly understood why-in fact I began to have a glimmer of a doubt about my ambitions to become skipper of an explorer ship.

But- Well, in about two days it seemed to me that they had managed to clean up the ship quite a bit, and shortly thereafter I stopped thinking about it. I began to understand why the ship's crew can't smell the things the passengers complain about. Their nervous systems simply cancel out the old familiar stinks-like a cybernetic skywatch canceling out and ignoring any object whose predicted orbit has previously been programmed into the machine.

But the odor is still there. I suspect that it sinks right into polished metal and can never be removed, short of scrapping the ship and melting it down. Thank goodness the human nervous system is endlessly adaptable.

But my own nervous system didn't seem too adaptable during that first hasty tour of the Tricorn; it is a good thing that I had not eaten much breakfast and had refrained from drinking anything. My stomach did give me a couple of bad moments, but I told it sternly that I was busy-I was very anxious to look over the ship; I simply didn't have time to cater to the weaknesses to which flesh is heir.

Well, the Tricorn is lovely all right-every bit as nice as the travel folders say that she is... except for that dreadful ship's odor. Her ballroom is gorgeous and so big that you can see that the floor curves to match the ship... only it is not curved when you walk across it. It is level, too-it is the only room in the ship where they jack up the floor to match perfectly with whatever spin is on the ship. There is a lounge with a simulated sky of outer space, or it can be switched to blue sky and fleecy clouds. Some old biddies were already in there, gabbling.

The dining saloon is every bit as fancy, but it seemed hardly big enough-which reminded me of the warning in the travel brochure about first and second tables, so I rushed back to our cabin to urge Uncle Tom to make reservations for us quickly before all the best tables were filled.

He wasn't there. I took a quick look in all the rooms and didn't find him-but I found Clark in my room, just closing one of my bags!

"What are you doing?" I demanded.

He jumped and then looked perfectly blank. "I was just looking to see if you had any nausea pills." He said woodenly.

"Well, don't dig into my things! You know better." I came up and felt his cheek; he wasn't feverish. "I don't have any. But I noticed where the surgeon's office is. If you are feeling ill, I'll take you straight there and let him dose you."

He pulled away. "Aw, I'm all right-now."

"Clark Fries, you listerj to me. If you-" But he wasn't listening; he slid past me, ducked into his own room and closed the door; I heard the lock click.

I closed the bag he had opened-and noticed something. It was the bag the inspector had been just about to search when Clark had pulled that silly stunt about "happy dust."

My younger brother never does anything without a reason. Never.

His reasons may be, and often are, inscrutable to others. But if you just dig deeply enough, you will always find that his mind is never a random-choice machine, doing things pointlessly. It is as logical as a calculator-and about as cold.