 After realizing his situation after the crash, why did Rolf laugh?
Sisko Rolf's stocky body was a blur of motion as he cut the rocket jets, doused the twin searchlights, and switched over to the audio beams that served so well on the surface when blind flying was in order. "Trapped us neatly," Rolf said through clenched teeth. Rolf swung the lax controls over hard as the bursts of fire revealed a looming barrier of stone dead ahead, and then he felt the tough skin of the flyer crumple inward. Somehow Rolf found the strength to wrap his fingers around the control levers and snap on a quick burst from the landing rockets. Their mad speed checked momentarily, but the nose of the vertically plunging ship dissolved into an inferno of flame. The ship struck; split open like a rotten squash, and Rolf felt himself being flung far outward through thick blackness. There was light in the narrow pit in which he found himself, light and heat from the yet-glowing debris of the rocket flyer. How many hours later it was when the first faint glow of white light reached his eyes Rolf did not know—it had seemed an eternity of endless plodding along that smooth-floored descending tunnel. "They may have found the sunken seas of Mars," thought Rolf as he moved alertly forward, "water that would give the mining domes new life." As the spinner dropped him slowly down into the vast emptiness of the great shining gulf, Rolf could see that a broad band of stone divided the green fertile plains and forests from the desolate desert wastes of the other half. Toward this barrier the spinner bore him, and Rolf was content to let it move in that direction—from the heights of the wall he could scout out the country beyond. The spinner had slowed its speed; it seemed to Rolf that he must be falling free in space for a time, but the feeble gravity of the tiny world tugged at him more strongly as he neared the wall. So slowly was the spinner dropping that the blackened desolation of the other hemisphere came sliding up beneath his boots. Deftly Rolf nested the spinners again in their pack before he set out toward the heaped-up mass of stone blocks that was the wall. "Sorry," said the tall man as Rolf sprang easily from the ground to their side. Rolf realized with a wrench of sudden fear that they actually hung head downward like flies walking across a ceiling. A hundred paces away Rolf made the dark shapes of armed warriors as they filed downward from the Barrier into the blackened desolation of the desert half of Lomihi.
 He was facing certain death
 He was facing certain death  His laughter was caused from the thick air  He was satisfied with their journey.  He was happy to be away from Garmon