The structural system is the main backbone of the Lightcraft. All of the various components play an integral role in providing sound structural support and safety to the crewmembers and payload.
MAIN SKELETAL STRUCTURE
The Lightcraft is an inflated vehicle capable of attaining supersonic speeds while in an atmosphere as well as high-velocity space flight. The primary framework of the lightcraft is constructed around a toroidal pressure vessel at the lightcraft's rim. The main hull section, shaped like a shallow dome, is supported from this structure. The toroidal pressure vessel and main framework of the vehicle are fabricated from an interlocking series of silicon carbide films and frames of varying shapes and sizes.
The toroid itself is pressurized to 25 atmospheres in order to maintain the lenticular lightcraft geometry against the propulsion system loads. The material used in the construction of the toroidal pressure vessel and hull is silicon carbide. Another key component in the framework of the lightcraft are the two high-power, parabolic rectennas that dominate nearly half the vehicle. The central parabolic rectenna is supported by ultra-light "I-beam" truses that are the only spacecraft members to take compressive loads. This basic mechanical framework provides physical integrity to the vehicle during all phases of operation. Active anti-vibrational attenuators are connected at key points in the structure. These attenuators can detect vibrational occurrences and react appropriately, causing counter vibrations, negating detrimental effects in structural members because of oscillatory fluctuations. Numerous system components are built into the hull structure, including the microwave rectennas and photovoltaic power array.
Suspended from the primary pressurized spaceframe through tension curtains is a secondary structure forming an axisymmetric envelope. The envelope is divided into 12 gores, each of which is capable of being individually sealed and pressurized. These gores are used as cabin space for the crew members and as storage space for payload or mission equipment.
HULL LAYERS AND PRESSURIZATION
The exterior shell of the Lightcraft is a double hull comprised of silicon carbide films 0.25 mm thick. Silicon carbide threads run between the outer and inner layers, maintaining a constant thickness of 10 mm between the two strata. This open-cell layered construction allows for the forced circulation of the helium gas coolant between the hull layers, ensuring that the external skin temperature remains within its thermo-structural limits during the brief transatmospheric boost. The external hull skin is also designed to prevent the passage of micrometeoric particles through the second layer of the hull by smashing them into small dust particles.
The outer hull is compartmentalized into 48 individual cells running radially outward, with individual cells being separated by a silicon carbide curtain 0.25 mm thick. This system of separate cells ensures proper circulation over the entire hull area, facilitates repairs and maintenance, and allows for continued operation with punctures occurring in 1 or more cells. A constant pressure of 2 atmospheres of a heliox mixture fills all the main compartments during normal operations. The main torodial tube is maintained at a pressure of 25 atmospheres at all times, except during emergencies. Each of the 6 innermost compartments of the Lightcraft, along with the 12 sub-compartment crew quarters, can be sealed off and pressurized independently from the rest of the interior. The system of multiple airlocks provides added protection for the lightcraft crew at all times. around the center section of the lightcraft, maintain pressure for the hull and crew compartments.
INTELLIGENT SENSOR ARRAYS
Multiple sensor systems are integrated directly into the structural framework of the Lightcraft. Using input from these systems, the computer network can assess both the status of lightcraft's structure and the external conditions around the lightcraft. By analyzing the information gathered through the various sensor systems the computer network can determine the lightcraft's mission worthiness and relay this information to the crew. Types of sensors which the lightcraft incorporates include: temperature, radiation, pressure, structure defect (by use of a fiberoptic network), strain, acoustic and vibration, and static electric and magnetic field level. The mechanical integrity of the spaceframe on the is augmented by the structural integrity system (SIS). The system provides an extensive network of piezoelectric actuators that compensate for propulsive and other structural loads that could compromise the configuration of the spaceframe. The rectenna arrays are especially at risk; their contour must be maintained to an accuracy of 0.5 mm.
The rectenna array is the main power supplier to the lightcraft. Two arrays on the lightcraft's center and rim provide the lightcraft with the power required to operate the propulsion and support systems by capturing beamed laser and microwave energy. The rectennas are able to adjust their focal length during flight to keep the desired shape under a high-acceleration load. This is accomplished by a complex system of cables and piezoelectric metals.
WATER STORAGE SYSTEM
A water storage system is incorporated into the structure of the lightcraft. A tube with a 22-cm diameter runs beneath the toroidal pressure vessel. This area is where the purified water that is used for the cooling system and temperature regulation systems is stored. This water is also used for drinking and food preparation.
An array of superconducting magnets provide the lightcraft with a power-storage system and support for the Maglev belt and Maglev systems. A total of 9 superconducting magnet coils run circumferentially around the lightcraft's outer and inner rims. Two primary magnets follow along the top and bottom of the toroidal pressure vessel. These are the largest magnets found on the lightcraft and provide the majority of the superconducting magnetic engergy storage unit's energy.
The side of the lightcraft opposite of the rectenna contains the photovoltaic arrays. Twelve panels made of Galium Arsenide cover the entire surface. These panels provide the lightcraft with a source of power when the lightcraft is on the ground or is acquiring water. The Photovoltaic placement ensures that the array receives the maximum amount of incoming light while being sufficiently protected from micrometeoric particles by the hull skin.
OUTER HULL MAINTENANCE
To prevent dangerous electrical discharges from outer hull surface irregularities, the entire surface of the Lightcraft must be kept mirror smooth and free of foreign debris at all times during flight. To maintain the craft's structural integrity, it is also imperative that all 12 hull sections remain fully inflated. Because of these requirements, certain methods must be employed to maintain the cleanliness of the outer hull of the Lightcraft. One method involves cycling the SMES units to clean the surface. Electrical current can be pulsed through the magnets at a sub-audible frequency of approximately 20 Hz or lower. The rapidly oscillating magnetic field shakes off any dirt particles clinging to the hull. The second method that is used involves using the liquid helium coolant that normally flows through the main toroid magnets. This helium can be sprayed into the gaseous heliox coolant system, thereby rapidly cooling the outer skin. The large temperature differential between the craft's hull and the ambient atmosphere supersaturates the air closest to the ship, resulting in a cloud of water vapor that condenses at the surface and washes off, taking dirt and debris with it.