Rainbow Mars by Larry Niven Read Free Book Online

tracked down Miya afterward and asked her.
    â€œHanny, it’s a wonderful notion. You know what synchronous orbit is? It’s where we put the weather satellites.”
    â€œNo.”
    â€œUm. Suppose you’re orbiting just outside the atmosphere. You go ’round the Earth in an hour and a half, right? Higher, it’s a bigger circle and you’d move slower. Takes longer. As high as the Moon, it takes almost a month to go around. Right?”
    â€œRight.”
    â€œSomewhere in between is where it takes just twenty-four hours. For the Earth it’s 35,700 km up. That’s synchronous orbit. The Earth is spinning as fast as you’re moving, so you stay above the same point.”
    â€œOkay.”
    â€œI take a coil of good strong rope. I set it moving above the equator with its center of mass at synchronous orbit. Now the coil stays just over a point on the equator, right?”
    â€œRight.”
    â€œNow I reel the rope out until one end is on the ground and the other end is way out there for balance.”
    â€œThat’s your orbital tower?”
    â€œRight. Now I run an elevator up and down the rope. I use it to lift cargo for the price of electric current plus any profit I can get away with. If I go past the synchronous point and then let something slide up along the rope, it’ll fly off the far end with enough velocity to reach the asteroids.”
    â€œIt’s a tree, but it’s hanging from the sky? ”
    â€œYes, exactly!”
    Svetz rubbed his eyes. He said, “That would cost … I can’t imagine what it would cost. And you think you’ve found such a thing?”
    â€œHanny, what made you say it was a tree?”
    â€œIt … reminded me of a redwood. It went up and never seemed to stop.”
    â€œLike Yggdrasil! Like the world-tree from Norse legend!”
    â€œBut no tree could be strong enough! Steel wouldn’t be strong enough—”
    â€œNo, Hanny, hold on. An orbital tower has to be strong, right? If you build it around Mars, you get high rotation and a lower mass, much lower, so it doesn’t have to be as long or as strong. Picture it a hundred thousand klicks long, and the only thing strong enough is still carbon crystal fibers or fullerine tubules, and those are carbon too.
    â€œI think you were right. We can’t make such a thing, we don’t have anything to make it out of, so why can’t it be a tree? Life is carbon based. Trees are good at manipulating carbon. And if we had seeds, we would go to the planets for nothing more than electricity!”
    Svetz, Miya, Zeera, and most of the techs slept on air cots in the Center while a composite team of Sky Domains and History Bureau wrote instructions for the probes on archaic Mars.
    In the morning they were back in the small extension cage.
    *   *   *
    Gravity shifted. They floated toward each other, bumped skewed, and pulled themselves around. The clothing they stripped off kept floating back like intrusive ghosts. They made a game of batting garments away.
    â€œHanny! How many times do we have to do this before I’m a virgin again?”
    Svetz laughed. “I’ve never gotten less hungry on any trip.”
    And later he asked, “Are we going for a record this time?”
    â€œMmm. Duration? Number? Intensity?”
    â€œNot unless I get some rest.”
    â€œSomeday I’m going to get you in a bed.”
    Svetz didn’t answer. Miya asked, “What’s the matter?”
    â€œI had this notion once. Miya, we’re going back to before time travel was even a concept. Once it was fantasy, fairy-tale stuff. In the late Industrial Age, Thorne and Tipler and some other top mathematicians showed that time travel was theoretically possible and did some designs. The Institute for Temporal Research came out of those. What if everything we collect from before plus-thirty Atomic Era is