At the time of launch from the solar system, the 300 kilometer payload lightsail was surrounded by a larger retroreflective ring lightsail, 1000 kilometers in diameter, with a hole in the center where the payload lightsail was attached. The ring lightsail had a mass of 72,000 tons, giving a total launch weight of lightsails and payload of over 82,000 tons.
Interstellar Laser Propulsion System
The laser power needed to push the 82,000 ton interstellar vehicle at an acceleration of one percent of earth gravity was just over 1300 terawatts. This was obtained from an array of 1000 laser generators orbiting around Mercury. Each laser generator used a thirty kilometer diameter lightweight reflector that collected 6.5 terawatts of sunlight. The reflector was designed to pass most of the solar spectrum and only reflect into its solar-pumped laser the 1.5 terawatts of sunlight that was at the right wavelength for the laser to use. The lasers were quite efficient, so each of the 1000 lasers generated 1.3 terawatts, to produce the total of 1300 terawatts needed to send the expedition on its way.
The transmitter lens for the laser propulsion system consisted of rings of thin plastic film stretched over a spiderweb-like circular wire mesh held in tension by slow rotation about the mesh axis. The lens was designed with circular zones of decreasing width that were alternately empty and covered with plastic film whose thickness was chosen to produce a phase delay of one half a wavelength in the laser light. This huge Fresnel zone plate, 100 kilometers in diameter, collimated the laser beam coming from Mercury and sent it off to Barnard with essentially negligible divergence. The relative configuration of the lasers, lens, and lightsails during the launch and deceleration phases can be seen in Figure 1.
The accelerating lasers were left on for eighteen years while the spacecraft continued to gain speed. The lasers were turned off, back in the solar system, in 2044. The last of the light from the lasers traveled for two more years before it finally reached the interstellar spacecraft. Thrust at the spacecraft stopped in 2046, just short of twenty years after launch. The spacecraft was now at two lightyears distance from the Sun and four lightyears from Barnard, and was traveling at twenty percent of the speed of light. The mission now entered the coast phase. For the next 20 years the spacecraft and its drugged crew coasted through interstellar space, covering a lightyear every five years, while back in the solar system, the transmitter lens was increased in diameter from 100 to 300 kilometers. Then, in 2060, the laser array was turned on again at a tripled frequency. The combined beams from the lasers filled the 300 kilometer diameter Fresnel lens and beamed out toward the distant star.
Figure 1—Interstellar laser propulsion system.
[J. Spacecraft, Vol 21, No. 2,pp. 187-195(1984) ]
After two years, the lasers were turned off, and used elsewhere. The two-light-year-long pulse of high energy laser light traveled across the six lightyears to the Barnard system, where it caught up with the spacecraft as it was 0.2 lightyears away from its destination. Before the pulse of laser light reached the interstellar vehicle, the revived crew on the interstellar vehicle had separated the lightsail into two pieces. The inner 300 kilometer lightsail carrying the crew and payload was detached and turned around to face the ring-shaped lightsail. The ring lightsail had computer-controlled actuators to give it the proper optical curvature. When the laser beam arrived, most of the laser beam struck the larger 1000 kilometer ring sail, bounced off the mirrored surface, and was focused back onto the smaller 300 kilometer payload lightsail as shown in the lower portion of Figure 1. The laser light accelerated the massive 72,000 ton ring lightsail at one percent of Earth gravity and during the two year period the ring lightsail increased its velocity slightly. The same laser power focused back on the much lighter payload lightsail, however, decelerated the smaller lightsail at nearly ten percent of Earth gravity. In the two years that the laser beam was on, the payload lightsail and its cargo of humans and exploration vehicles slowed from its interstellar velocity of twenty percent of the speed of light to come to rest in the Barnard system. Meanwhile, the ring lightsail continued on into deep space, its function completed.
Prometheus
The interstellar lightsail vehicle that took the exploration crew to the Barnard system was named Prometheus, the bringer of light. Its configuration is shown in Figure 2, and consists of a large lightsail supporting a payload containing the crew, their habitat, and their exploration vehicles. Running all the way through the center of Prometheus is a four-meter-diameter, sixty-meter-long shaft with an elevator platform that runs up and down the shaft to supply transportation between decks. A major fraction of the payload volume was taken up by four exploration vehicle units. Each unit consisted of a planetary lander vehicle called the Surface Lander and Ascent Module (SLAM), holding within itself a winged Surface Excursion Module (SEM).
The largest component of Prometheus is the lightsail, 1000 kilometers in diameter at launch, and 300 kilometers in diameter during the deceleration and exploration phases of the mission. The frame of the lightsail consists of a hexagonal mesh trusswork made of wires held in tension by a slow rotation of the lightsail around its axis. Attached to the mesh wires are large ultrathin triangular sheets of perforated reflective aluminum film. The perforations in the film are made smaller than a wavelength of light, so they reduce the weight of the film without significantly affecting the reflective properties.
Capping the top of Prometheus on the side toward the direction of travel is a huge double-decked compartmented area that holds the various consumables for use during the 50-year mission, the workshops for the spaceship's computer motile, and an airlock for access to the lightsail. At the very center of the starside deck is the starside science dome, a three-meter-diameter glass hemisphere that was used by the star-science instruments to investigate the Barnard star system as Prometheus was moving toward it.
At the base of Prometheus are five crew decks. Each deck is a flat cylinder twenty meters in diameter and three meters thick. The control deck at the bottom contains an airlock and the engineering, communication, science, and command consoles to operate the lightcraft and the science instruments. In the center of the control deck is the earthside science dome, a three-meter-diameter hemisphere in the floor, surrounded by a thick circular waist-high wall containing racks of scientific instruments that look out through the dome or directly into the vacuum through holes in the deck. Above the control deck is the living area deck containing the communal dining area, kitchen, exercise room, medical facilities, two small video theaters, and a lounge with a large sofa facing a three-by-four-meter oval view window. The next two decks are the crew quarters decks that are fitted out with individual suites for each of the twenty crew members. Each suite has a private bathroom, sitting area, work area, and a separate bedroom. The wall separating the bedroom from the sitting area is a floor-to-ceiling viewwall that can be seen from either side. There is another view screen in the ceiling above the bed.
Figure 2—Prometheus
Above the two crew quarters decks is the hydroponics deck. This contains the hydroponics gardens and the tissue cultures to supply fresh food to the crew. The water in the hydroponics tanks provides additional radiation shielding for the crew quarters below. In the ceilings of four of the corridors running between the hydroponics tanks are air locks that allow access to the four Surface Lander and Ascent Module (SLAM) spacecraft that are clustered around the central shaft, stacked upside down between the hydroponics deck and the storage deck. Each SLAM is forty-six meters long and six meters in diameter.
Surface Lander and Ascent Module
The Surface Lander and Ascent Module (SLAM) is a brute-force chemical rocket that was designed to get the planetary exploration crew and the Surface Excursion Module (SEM) down to the surface of the various worlds in the Barnard system. The upper portion of the SLAM, the Ascent Propulsion Stage (APS), is designed to take the crew off the world and return them back to Prometheus at the end of the surface exploration mission. As is shown in Figure
3, the basic shape of the SLAM is a tall cylinder with four descent engines and two main tanks.
The Surface Lander and Ascent Module has a great deal of similarity to the Lunar Excursion Module (LEM) used in the Apollo lunar landings, except that instead of being optimized for a specific airless body, the Surface Lander and Ascent Module had to be general purpose enough to land on planetoids that could be larger than the Moon, as well as have significant atmospheres. The three legs of the Surface Lander and Ascent Module are the minimum for stability, while the weight penalties for any more were felt to be prohibitive.
The Surface Lander and Ascent Module (SLAM) carries within itself the Surface Excursion Module (SEM), an aerospace plane that is almost as large as the lander. Embedded in the side of the SLAM is a long, slim crease that just fits the outer contours of the SEM. The seals on the upper portions were designed to have low gas leakage so that the SLAM crew could transfer to the SEM with minor loss of air.
The upper portion of the SLAM consists of the crew living quarters plus the Ascent Propulsion Stage. The upper deck is a three-meter-high cylinder eight meters in diameter. On its top is a forest of electromagnetic antennas for everything from laser communication directly to Earth to omni-antennas that broadcast the position of the ship to the orbiting relay satellites.
The upper deck contains the main docking port at the center. Its exit is upward, into the hydroponics deck of Prometheus. Around the upper lock are the control consoles for the landing and docking maneuvers, and the electronics for the surface science that can be carried out at the SLAM landing site.
Figure 3—Surface Lander and Ascent Module (SLAM)
The middle deck contains the galley, lounge, and the personal quarters for the crew with individual zero-gee sleeping racks, a shower that works as well in zero-gee as in gravity, and two zero-gee toilets. After the SEM crew has left the main lander, the partitions between the sleeping cubicles are rearranged to provide room for a sick bay and a more horizontal sleeping position for the four crew members assigned to the SLAM.
The galley and lounge are the relaxation facilities for the crew. The lounge has a video center facing inward where the crew can watch either videochips or six-year-old programs from the Earth, and a long sofa facing a large viewport window that looks out on the alien scenery from a height of about forty meters. The lower deck of the SLAM contains the engineering facilities. Most of the space is given to suit or equipment storage, and a complex air lock. One of the air-lock exits leads to the upper end of the Jacob's ladder. The other leads to the boarding port for the Surface Excursion Module.
Since the primary purpose of the SLAM is to put the Surface Excursion Module on the surface of the double-planet, some characteristics of the lander are not optimized for crew convenience. The best instance is the "Jacob's Ladder," a long, widely spaced set of rungs that start on one landing leg of the SLAM and work their way up the side of the cylindrical structure to the lower exit lock door. The "Jacob's Ladder" was never meant to be used, since the crew expected to be able to use a powered hoist to reach the top of the ship. In the emergency that arose during the first expedition to Rocheworld, however, the Jacob's Ladder proved to be an adequate, although slow, route up into the ship.
One leg of the SLAM is part of the "Jacob's Ladder," while another leg acts as the lowering rail for the Surface Excursion Module. The wings of the Surface Excursion Module are chopped off in mid-span just after the VTOL fans. The remainder of each wing is stacked as interleaved sections on either side of the tail section of the Surface Excursion Module. Once the Surface Excursion Module has its wings attached, it is a completely independent vehicle with its own propulsion and life support system.
Surface Excursion Module
The Surface Excursion Module (SEM) is a specially designed aerospace vehicle capable of flying as a plane in a planetary atmosphere or as a rocket for short hops through empty space. The crew has given the name Dragonfly to the SEM because of its long wings, eyelike scanner ports at the front, and its ability to hover. An exterior view of the SEM is shown in Figure 4.
For flying long distances in any type of planetary atmosphere, including those which do not have oxygen in them, propulsion for the SEM comes from the heating of the atmosphere with a nuclear reactor powering a jet-bypass turbine. For short hops outside the atmosphere, the engine draws upon a tank of monopropellant, which not only provides reaction mass for the nuclear reactor to work on, but also makes its own contribution to the rocket plenum pressure and temperature.
Unfortunately, the SEM IV aerospace plane was damaged and sank under 200 meters (600 feet) of water during the rocket engine burnthrough and subsequent crash of the SLAM IV lander during an attempted landing on Zuni. Fortunately, the entire crew of ten humans and three flouwen buds managed to survive the crash and are still on Zuni, but without the flying ability of the SEM, the exploration range of the humans is limited to a single small island on the large moon.
Figure 4—Exterior View of Surface Excursion Module (SEM)
Christmas Bush
The hands and eyes of the near-human computers that ran the various vehicles on the expedition are embodied in a repair and maintenance motile used by the computer, popularly called the "Christmas Bush" because of the twinkling laser lights on the bushy multibranched structure. The bushlike design for the robot has a parallel in the development of life forms on Earth. The first form of life on Earth was a worm. The stick-like shape was poorly adapted for manipulation or even locomotion. These stick-like animals then grew smaller sticks, called legs, and the animals could walk, although they were still poor at manipulation. Then the smaller sticks grew yet smaller sticks, and hands with manipulating fingers evolved.
The Christmas Bush is a manifold extension of this concept. The motile has a six-"armed" main body that repeatedly hexfurcates into copies one-third the size of itself, finally ending up with millions of near-microscopic cilia. Each subsegment has a small amount of intelligence, but is mostly motor and communication system. The segments communicate with each other and transmit power down through the structure by means of light-emitting and light-collecting semiconductor diodes. Blue laser beams are used to closely monitor any human beings near the motile, while red and yellow beams are used monitor the rest of the room. The green beams are used to transmit power and information from one portion of the Christmas Bush to another, giving the metallic surface of the multibranched structure a deep green internal glow. It is the colored red, yellow, and blue lasers sparkling from the various branches of the greenly glowing Christmas Bush that give the motile the appearance of a Christmas tree. The central computer in the spacecraft is the primary controller of the motile, communicating with the various portions of the Christmas Bush through color-coded laser beams. It takes a great deal of computational power to operate the many limbs of the Christmas Bush, but built-in "reflexes" at the various levels of segmentation lessen the load on the main computer.
Figure 5—The Christmas Bush
The Christmas Bush shown in Figure 5 is in its "one gee" form. Three of the "trunks" form "legs," one the "head," and two the "arms." The head portions are "bushed" out to give the detector diodes in the subbranches a three-dimensional view of the space around it. One arm ends with six "hands," demonstrating the manipulating capability of the Christmas Bush and its subportions. The other arm is in its maximally collapsed form. The six "limbs," being one-third the diameter of the trunk, can fit into a circle with the same diameter as the trunk, while the thirty-six "branches," being one-ninth the diameter of the trunk, also fit into the same circle. This is true all the way down to the sixty million cilia at the lowest level. The "hands" of the Christmas Bush have capabilities that go way beyond those of the human hand. The Christmas Bush can stick a "hand" inside a delicate piece of equipment, and using its lasers as a light source and its detectors as eyes, rearrange the parts inside for a near instantaneous repair. The Christmas Bush also has the ability to detach portions of itself to m
ake smaller motiles. These can walk up the walls and along the ceilings using their tiny cilia holding onto microscopic cracks in the surface. The smaller twigs on the Christmas Bush are capable of very rapid motion. In free fall, these rapidly beating twigs allow the motile to propel itself through the air. The speed of motion of the smaller cilia is rapid enough that the motiles can generate sound and thus can talk directly with the humans.
Each member of the crew has a small subtree or "imp" that stays constantly with him or her. The imp usually rides on the shoulder of the human where it can "whisper" in the human's ear, some of the women use the brightly colored laser-illuminated imp as a decorative ornament. In addition to the imp's primary purpose of providing a continuous personal communication link between the crew member and the central computer, it also acts as a health monitor and personal servant for the human. The imps go with the humans inside their spacesuit, and more than one human life was saved by an imp detecting and repairing a suit failure or patching a leak. The imps can also exit the spacesuit, if desired, by worming their way out through the air supply valves.
SECTION 2
BARNARD SYSTEM ASTRONOMICAL DATA
Prepared by:
Linda Regan—Astrophysics
Thomas St. Thomas, Captain, GUSAF—Astrodynamics
Barnard Planetary System
As shown in Figure 6, the Barnard planetary system consists of the red dwarf star Barnard, the huge gas giant planet Gargantua and its large retinue of moons, and an unusual co-rotating double planet Rocheworld. Gargantua is in a standard near-circular planetary orbit around Barnard, while Rocheworld is in a highly elliptical orbit that takes it in very close to Barnard once every orbit, and very close to Gargantua once every three orbits. During its close passage, Rocheworld comes within six gigameters of Gargantua, just outside the orbit of Zeus, the outermost moon of Gargantua. It has been suggested that one lobe of Rocheworld was once an outer large moon of Gargantua, while the other lobe was stray planetoid that interacted with the outer Gargantuan moon to form Rocheworld in its present orbit. Further information about Barnard, Rocheworld, and Gargantua and its moons follows:
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