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A craft approaching a Halo from the exterior face of the ring would have to “fall in step” with its seven kilometers per second rotation rate, while also taking into account the curved exterior surface. At that speed, and at that distance from the Halo’s central spin axis, the craft would undergo a constant outward force of approximately one Earth gravity. At the same time, if there was a pilot error, or the craft lost power for whatever reason, an approach from the exterior might prove to be the safest way to dock with a Halo—the constant centrifugal force means that most conceivable errors would cause the craft to be thrown clear of the ring, instead of crashing into it. Approaching a Halo’s inner surface would, in some respects, be far less complicated than approaching a planet or a moon, but attempting to land on a Halo’s inner surface would be significantly more problematic. Although it is established that the Forerunners had artificial gravity generation technology, it doesn’t seem that this comes into play when landing on a Halo. Not only does a Halo structure have a fairly small mass, even compared to a small moon, but the mass is evenly distributed radially. The craft would therefore feel a gravitational tug, albeit small, from all segments of the ring. Succinctly, since a Halo has a trivial amount of gravity, a spacecraft could approach a Halo and comfortably sit within its circumference as the ring rotated around it.
Approaching the inner ring surface would be the tough part. Although a craft could sit essentially immobile as the ring spun around it, recall that the ring is spinning at seven kilometers per second. That equates to 4.45 miles/second, or roughly 15,660 miles per hour (by comparison, the equator of Earth is moving at rather pedestrian 1,670 kilometers per hour, or 1,037 miles per hour). To minimize the relative motion, a craft landing on the interior of the ring would have to similarly move a speed of, or close to, seven kilometers per second—under nearly 1G of acceleration— while slowly moving outwards from the ring’s spin axis. Just as any pilot error/malfunction/power outage on a craft approaching the ring from the exterior would be minimized by the tendency of the centrifugal force to throw the craft away from the ring, the same force on a craft approaching from the inside would tend to throw it against a ring moving at twenty-one times the speed of sound. Of course, for there to be sound, there has to be at atmosphere. Larry Niven describes how this is possible on a Ringworld: “We wouldn’t even have to roof it over. Put walls a thousand miles high at each rim, aimed at the sun, and very little air will leak over the edges.” It turns out that walls a fraction of that size (though higher than they appear in the game) would hold in enough of an atmosphere to make a Halo habitable, but that same atmosphere might represent a danger to craft attempting to land. If the craft is in a spiral trajectory—revolving around the Halo spin axis at the same rate the ring spins—lowering itself slowly onto the ring, there is little problem. Friction with the atmosphere would be minimal and, in fact, in this instance there would be less re-entry heating than a craft would experience approaching a planet like Earth. If the spacecraft/ring relative velocity were not nullified, a craft on approach to a Halo would suddenly find itself subject to air friction—resulting in both intense heat and shear—of a supersonic airflow. While there would certainly be shear in a Halo atmosphere due to the ring’s rotation, and the upper layers of air would not be moving at near the speed as that near the surface, without the proper approach, a ship attempting to land on the inner surface of a Halo could still be met with near-instantaneous incineration—not a particularly welcoming introduction. Only the Beginning? A physics professor once said to me, “Any topic, studied in sufficient detail, becomes infinitely complex.” Here we’ve merely skimmed the cream of the richness of science, explicit and implied, of the Halo universe. As suggested earlier, an entire book could, and perhaps should, be written about the subject. We’ve discussed weaponry very little, and haven’t even covered issues like the wind and weather on a Halo. My post-planetarium show dinner companions might, in fact, be both appalled and delighted that such entertaining intellectual musings could find their genesis in a video game where lots of things explode. |
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