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Halo Science 101
August 4, 2020
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August 4, 2020
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# Halo Science 101

May 2, 2007 Page 5 of 6

One Spinning Ring to Rule them All

After our brief wandering through a Halo’s space, let’s make a closer examination. What is life like, and what are some implications of life on a planet-sized spinning metal ring? Altough it is established in the Halo universe that the Forerunners, Covenant, and even humans have some degree of artificial gravity generation technology, gravity on a Halo is largely simulated by centrifugal force. Since modern-day science knows no way to generate gravity artificially, a very common technique used in both literary (e.g. Ringworld, Rendezvous with Rama) and cinematic (e.g. Mission to Mars, 2001: A Space Odyssey) science fiction is to use the centrifugal force of a spinning ring or cylindrical structure to simulate gravity. More germane to this topic, Larry Niven describes how gravity would be simulated on a ringworld:

”There are other advantages. We can spin it for gravity. A rotation on its axis of 770 miles/second would give the Ringworld one gravity outward.”

The apparent gravity on Installations 04 and 05 is close to that of Earth. For a Halo with a radius of 5,000 kilometers to simulate one Earth gravity, it would have to spin with a tangential speed of slightly over seven kilometers per second. That implies that the Halo would rotate once every hour and fifteen minutes, or 19 ¼ times a day.

The concepts of day and night would, therefore, take on entirely different meanings on a Halo than they do on Earth. For that matter, they would even be entirely different than that for Niven’s Ringworld. In Niven’s novels, the ringworld has “shadow squares,” almost a mini ringworld, encircling the central star at a smaller radius:

”Set up an inner ring of shadow squares—light orbiting structures to block out part of the sunlight—and we can have day-and-night cycles in whatever period we like.”

The view from the surface of a Halo

The shadow squares are connected with thin but extremely strong filament. By alternately passing and obscuring light, the shadow squares simulate day and night—the size of both the shadow squares and their interstices dictating the duration of each. The orientation in space of a Halo would determine what percentage of each rotation would receive both sunlight and shadow; however, if Halos orbit their gas giant in the equatorial plane, as it appears they do in the game, then a Halo goes into eclipse periodically as well. While there exist tilted, or inclined, orbits that never go into eclipse, by virtue of the fact that we can see that Installation 04 orbits between Threshold and Basis, it is not in one of these orbits. Given the stated size of Threshold, and the apparent distance to Basis, it is likely that Installation 04 would be plunged into complete darkness at least once every Earth day.

An object—a soldier, an Elite, a Scorpion MBT, a Warthog recon vehicle, anything—in direct contact with the surface of the ring would perceive the centrifugal force to be the equivalent of gravity. Anything not in direct contact would tend to follow basic laws of dynamics, but laws that might seem counter-intuitive at first. On the second level of Halo: Combat Evolved (a level called “Halo,” in fact), Master Chief can see a waterfall shortly after making ring-fall.

Figure 2 shows the results of computer simulations of the trajectory of one drop of water over the waterfall if it were subject to Earth’s gravity, and the trajectory of one drop of water on a Halo—assuming that the waterfall is 305 meters (1,000 feet) high and oriented along the Halo’s spin direction. We see that a drop would fall two meters farther on a Halo than on Earth. That’s not a great difference, but if the water flow were oriented perpendicular to the spin direction, it would deflect two meters to the side, which would look odd for somebody used to viewing terrestrial waterfalls.

The ring’s spin would have an even more pronounced effect on objects with a longer time of flight. While most of the combat in Halo takes place at close range, let’s assume we want to use our M808B Scorpion Main Battle Tank, which fires hypervelocity rounds, as a piece of artillery and fire projectiles at a much greater distance. Entry-level physics students learn about trajectories—that the trajectory of a projectile fired from a cannon takes the shape of a parabola (actually, an ellipse, since the trajectory represents a partial orbit). In the absence of wind, a round fired straight up will return straight down, and completely ruin the day of whosoever fired it. Long range trajectories on a Halo would be quite different.

Figure 3 shows the results of computer simulations of long-range trajectories of rounds fired from the inside surface of a 5,000-kilometer ring spinning at nineteen times per day. The assumed muzzle velocity was 1,000 meters per second. Figure 3 shows the trajectories for initial barrel elevations of thirty, forty-five, sixty, and ninety degrees above local “horizontal,” both in the direction of the ring rotation (+X) and in the direction counter to the ring rotation (-X). We can see that a round fired straight up does not, in fact, return to where it was fired, but rather eighteen kilometers downrange due to the seven kilometers per second speed that the round had before it was even fired. Note a marked asymmetry between projectiles fired in the spin direction as opposed to the anti-spin direction. Rounds fired in the spin direction have a greater initial horizontal velocity, and impact the ring sooner than those fired in the direction opposite to the ring’s spin. A rocket fired from a launcher, or a projectile from a fuel rod gun, would suffer similar deflections if it had to travel long range.

Targeting distant objects for living combatants would be counter-intuitive on a ring where centrifugal force substitutes for gravity. Automated fire control systems would have to determine, then take into account for targeting calculations, the orientation of the weapon with respect to the Halo. There is actually a hint of this in the game. In the first Halo game, the assault rifle has a “compass” that always points to the planet Threshold. If the ring’s orientation is known (and this might be a simple calibration), then it would be fairly easy for a microprocessor to take into account the ring’s spin when targeting.

So, long-range targeting for projectile weapons would be counter-intuitive. Some of the weapons available to Master Chief in the Halo universe are, however, Covenant particle beam weapons: plasma pistols and plasma rifles. Particle beams travel at large fraction of the speed of light. A beam of light would transverse the entire diameter of a Halo in thirty-three milliseconds, and a particle beam would take only slightly longer. So a particle beam simply does not have time to undergo the deflection of a projectile—where the weapon is pointed is where the damage will occur.

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