Tyyr wrote:It's actually one of the more plausible interstellar space ships I've seen proposed, right down to the need for a Whipple shield. Being able to manufacture a significant amount of antimatter is obviously a stumbling block but its really more of a question of volume than anything else.
Most of it is relatively plausible. The only part that really makes me want to do the math is the fuel consumed, matter/anti-matter reactions are great but 70% of that energy is lost to neutrinos and would be relatively useless for propulsion.
So its not as simple a matter as it might appear on the surface. Still better than just about anything else out there if you can work with it but it's not a perfect conversion. Honestly I'd be looking for a way to get the energy beaming technology in both the Solar system and Pandora's system in order to eliminate the need for the anti-matter engines entirely.
Lighthawk wrote:So only 30% of the actual energy released is worth anything to the ship? How does that compare to other energy sources?
Captain Seafort wrote:Lighthawk wrote:So only 30% of the actual energy released is worth anything to the ship? How does that compare to other energy sources?
That's still several Mt/kg, more than an order of magnitude more than U-235.
Lighthawk wrote:Right I know it's still a big chunk o power, but I ment how is that in terms of efficency?
Captain Seafort wrote:Lighthawk wrote:Right I know it's still a big chunk o power, but I ment how is that in terms of efficency?
I've no idea about modern weapons, but in Little Boy, less than one per cent of the uranium fissioned.
Size Length = 1,502.4 meters; Width = 302.25 meters; Height = 218.3 meters.
Maximum Acceleration 1.5 g.
Cargo Capacity 350 metric tons Pandora to Earth
Mission Profile: 0.46 year initial acceleration @ 1.5 g to reach 0.7 c; 5.83 years cruise @ 0.7 c; 0.46 year deceleration; 1 year loiter in orbit around Pandora; 0.46 year acceleration @ 1.5 g to 0.7 c for return trip; 5.83 years cruise; 0.46 year final deceleration @ 1.5 g to go into orbit around Earth.
Mission Duration: 6.75 + 1.0 + 6.75 = 14.5 Earth years. However, relativistic effects shorten the time onboard ship to slightly less than 6 years each way.
...In fact, the unobtanium itself enabled the creation of this class of ISV's. It is used in the superconducting magnet arrays which contain and direct the energy of the matter-antimatter annihilation which propels the ship. Without unobtanium, interstellar commerce on this scale would not be possible. Unobtanium is not only the key to Earth's energy needs in the 22nd century, but it is the enabler of interstellar travel and the establishment of a truly spacefaring civilization.
The Venture Star is the ninth ship of its class brought into service, and has made one round trip to the Alpha Centauri System. It is currently outbound on its second voyage, due to arrive there in 2154.
Power Source: Hybrid deuterium fusion / matter-antimatter annihilation.
Propulsion: Two hybrid fusion/matter-antimatter engines. One photon sail. One fusion PME (Planetary Maneuvering Engine.) Beamed photon power from Earth for outward acceleration phase; ship's hybrid fusion / matter-antimatter power for deceleration phase on approach to Pandora. Sequence reversed for return to Earth.
Engines: Two, arranged symmetrically in a tractor configuration.
They are angled outward a few degrees off the ship's longitudinal axis so their exhaust plumes bypass the ship's structure. This results in a slight cosine loss to thrust efficiency, and the body of the ship must be shielded from the plume's thermal radiation, but the mass-savings advantage of a tensile structure outweigh these disadvantages.
Since a very long truss is needed to separate the habitable section of the ship from the engines which produce large amounts of radiation, such a structure would be prohibitively massive if it were a conventional space-frame truss designed for compressive loading. But the carbon-nanotube composite tensile-truss creates the necessary stand-off distance at one tenth the mass. Essentially it is a tow cable with enough torsional rigidity to allow the ship to maneuver, including the pitch-over maneuver which must be performed to turn 180 degrees for the deceleration burn when inbound to Pandora.
A matter-antimatter reaction causes the total conversion of matter into energy, as per Einstein's famous formula of E = mc2.
The antimatter (in this case anti-hydrogen) is contained by a magnetic field in a near-perfect vacuum in which it circulates as a high density cloud of atoms cooled to near-absolute-zero temperature.
When antimatter and matter (normal hydrogen) are brought together, they mutually annihilate and produce an enormous amount of energy, which must be directed by an ultra-powerful magnetic field to form the exhaust plume. These photons of energy, although massless, possess momentum, and their ejection provides the thrust to accelerate the ship. Additional thrust is obtained by injecting hydrogen atoms into the plasma before it leaves the engines. The exhaust flare is an incandescent plasma a million times brighter than a welding arc, and over thirty kilometers long. The plume is considered to be one of the most spectacular man-made sights in history.
Structure: The ship's primary structure (which could only exist in zero gravity) consists of the two side-by-side engines attached to a tensile-truss of carbon-nanotube composite. This connects the propulsion section to the payload section, which includes habitation modules for crew, the cryovaults for passengers, amnio tanks for the avatars, and the cargo section. Starting from the forward end:
1. Engines, propellant tanks, and radiators. The propellant tanks are spheres insulated for zero boil-off of the cryogenic hydrogen propellant. The radiators dissipate the heat of the engine section. After a deccel or accel burn phase, the radiators will glow red hot for 2 weeks.
2. The tensile-truss that transfers the thrust of the two engines to the rest of the ship. Although thin, it is rigid enough to prevent the payload section from fishtailing caused by buildup of resonant frequency vibrations during acceleration and deceleration. The section of the truss adjacent to the antimatter engine nozzles is protected by a thermal shield of nearly perfect reflecting materials, to guard against the intense heat radiated from the exhaust plumes.
5. The habitation section consists of three large modules containing the cryovaults and amnio tanks. Inside each module is an open frame structure of advanced composites, with non-load bearing walls made of foam composite. There is almost no metal used in the structure. This is to prevent galactic cosmic radiation from striking metal and producing secondary radiation particles. There are a number of airlocks for the crew, and portals for repair bots that look like high-tech mechanical crabs.
6. Immediately behind these three modules are the two on-duty crew modules, located at the opposite ends of a transverse truss. A pressurized tunnel runs through the truss, connecting the two units. During cruise mode, these modules can be rotated to create an artificial gravity for the on-duty crew. During accel and deccel phases, the modules fold along the longitudinal axis of the ship. In this configuration, the gravity is created by the acceleration of the ship (so all floors and walls are still correctly oriented to the gravity vector). The modules also provide centrifugal artificial gravity during the ISV's one year loiter on orbit at Pandora.
7. At the far end of the structure is the mirror shield, which protects the ship from the intense light of the beamed-power laser from Earth. This mirror is only a few molecules thick, but reflects light efficiently enough to prevent incineration of the habitable section of the starship.
When acceleration is completed, the ship is rotated 180 degrees so that the mirror shield faces forward. Now the shield performs another role, acting as a multi-layer interstellar debris shield.
The largest component of the ship is not located on the primary structure. It is the "sail" which receives the beam of photons and extracts the momentum to accelerate or decelerate the ship. It is a shallow bowl 16 kilometers in diameter and stabilized by rotation. The material of the sail is incredibly thin, being only a few dozen molecules thick in most places. Its basic structure is a fabric woven from carbon nanotube thread, and coated with a refractory ceramic that fills in the interstices. The working side of the sail is further coated with a vacuum-deposited multi-layer diachronic reflector, which is 99.99999% efficient. What little heating of the sail that occurs is dissipated by radiation from its back side. Carbon nanotube cables connect it to the main body of the ship, and these cables also have a diachronic coating which reflects 99.99999% of the beam energy that strikes them, and prevents the cables from instantly vaporizing. When not in use, the sail is folded along molecular hinge lines, and occupies a surprisingly small volume. It is stored in the cargo area when not in use, along with the spools of connecting cables. Rigging and removal of the sail is done autonomously by the service bots, but can be done manually in an emergency by awakening the other two crew teams.
1. Modulation of beamed power by Â±0.1% for high bit-rate uplink during acceleration and deceleration phases.
2. Pulse-width modulated dedicated lasers for downlink and uplink when not using beamed power - bit rate dependent on distance
Very low bit-rate up- and downlink using McKinney quantum entanglement encoding.
Life Support: All consumables are recycled to the maximum extent possible...
Since it is not practical to maintain this condition for the duration of the voyage, in the event of a failure of the cryosleep system the passengers would be euthanized before awakening, so that the crew can continue the mission and deliver the cargo. (The extra crew teams' cryosleep system is separate, and triply-redundant.)
Cryosleep System: The individual passenger compartments are equipped to freeze their occupants solid and maintain them at a very low temperature until the end of the voyage, when they are gradually re-warmed and thawed out. The problem of irreparable cell damage caused by the formation of intra-cellular ice crystals that stymied 20th Century life-extension attempts was solved by using low doses of microwave radiation to jostle the water molecules as the temperature drops, and completely prevents the formation of any ice crystals. The failure rate of this process is less than 1%, and passengers and their heirs release the RDA for any liability as a condition of their employment.
The ship's functioning is largely automated, using triply-redundant, radiation-hardened computers, but emergency manual control is provided for all functions. The minimal crew is cross-trained in all specialties. There are three crew teams of five each, who serve for 20-month tours, and are in cryosleep for the balance of the voyage. This seeming waste of mass was necessitated by the experience of mid- 21st Century space missions when crew members proved psychologically unstable after two years in close confinement. There are two main functions of the human crew: monitoring the power and propulsion systems, and supervising the developing avatars. Humans have the ability to notice anomalies too subtle for the automated monitors, in spite of these systems' tremendous sophistication. In addition to the 15 flight crew there are 10 medical crew in cryosleep, who are awakened before the rest of the passengers to assist with their recovery from suspension.
The passengers are placed in cryosleep so that they do not require any air, water, or food for the duration of the journey. Typical outbound passengers are replacements for RDA personnel, troopers, and avatar operators. Inbound passengers are limited to those who have finished their tour of duty. Unfortunately, the cost of shipping back personnel precludes returning individuals still under contract who have medical problems that cannot be treated on Pandora, so they are euthanized there. The only exception to this policy is for high-level RDA executives.
1. Universal object-manufacturing system (In-situ Stereolighography plant). This can produce large, complex objects from data describing their three-dimensional form and material composition. Using raw materials obtained on Pandora, construction and mining equipment far too large and massive to be shipped from Earth can be produced, along with any replacement parts that are needed. Smaller items such as weapons and furniture, are also created, using design data brought from Earth. Locally-designed items are made as well, or modifications of existing designs.
2. Micro-miniaturized components like mirco- and nanoprocessors and other circuitry elements that cannot be manufactured on Pandora.
3. Data modules. Currently, photochromic glass holographic data-storage cubes are used, each one-centimeter cube containing 100 Petabytes of triply-error-corrected data. Typical imported data includes the specifications for equipment to be manufactured on Pandora.
4. Two Valkyrie shuttlecraft for transfer of personnel and cargo between the orbiting ISV and the surface of Pandora. These vessels are left at Pandora, to replace those from previous missions that have exceeded their design life as manned vehicles. The replaced craft are re-purposed to serve as automated gas harvesters, skimming through Polyphemus's upper atmosphere to obtain hydrogen and deuterium for refueling the ISV.
6. Drugs and other medications that cannot be produced locally.
1. Refined unobtanium. This is the ISV's raison d'Ãªtre. It takes precedence over all other items, including returning employees if there is no available mass capacity.
Potential Hazards: The Venture Star is a vast collection of complex interlocking technologies built to travel from one star system to another in the shortest time without killing the crew and damaging the cargo. At the incredible speed it travels, the ship could be destroyed by colliding with debris larger than a grain of sand. Although statistically rare given the emptiness of space, it is believed that a collision over the life of the ship is possible. Another danger is radiation generated by impacts of smaller particles with the debris shield. These gamma rays result from the incredible speed (0.7 c) of the particle with respect to the ship. If the ship should happen to encounter a high concentration of dust grains, the on-duty crew could receive a lethal dose. Since individuals in cryosleep are more resistant to radiation damage, in such an event automated sensors would awaken one of the other crew teams from cryosleep after the radiation level decreased.
Lighthawk wrote:Unfortunately, the cost of shipping back personnel precludes returning individuals still under contract who have medical problems that cannot be treated on Pandora, so they are euthanized there. The only exception to this policy is for high-level RDA executives.
GrahamKennedy wrote:Lighthawk wrote:Unfortunately, the cost of shipping back personnel precludes returning individuals still under contract who have medical problems that cannot be treated on Pandora, so they are euthanized there. The only exception to this policy is for high-level RDA executives.
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