Handwavium, Bullshit, Possibility?

[Lighthawk]

Recently came across the stats for the interstellar ship used in Avatar, which resembles typical scifi ships about as much as a seahorse does a horse. Reading through it, a lot of it seemed interesting, yet I wonder about how realistic some of it actually is. On that regard, I was wondering if someone with a better grasp of science and/or engineering know how could give it a look over and an opinion. Obvious a few things are handwaved aside in regards to the details, but is anything clear BS or outright wrong about it?


ISV Venture Star

Function Interstellar vehicle (ISV) designed to transport personnel, supplies, and equipment between Earth and Pandora, and to return personnel and refined unobtanium from Pandora to Earth.

Official Name Interstellar Vehicle ISV Venture Star.

Hull Number 601-09.

Manufacturer Consortium of aerospace contractors under control of RDA.

Design History When the first voyage to the Alpha Centauri system was envisioned, engineers knew that a conventional rocket was hopelessly inadequate. Even the fusion powered rockets used within Earth's solar system could not generate the thrust needed to achieve "relativistic" speeds (some large fraction of the speed of light). Since any starship capable of supporting interstellar commerce on reasonable time scales needed to travel at relativistic speeds, its rocket exhaust velocity, too, had to be near lightspeed to create sufficient thrust. This eliminated chemically powered rocket engines, nuclear thermal engines, plasma engines and fusion engines (despite their long history of successful missions amongst the planets of our solar system in the 21st and early 22nd centuries).

Mission The ISV Venture Star can carry a large payload of cargo and passengers to establish commercial and scientific outposts on alien worlds. The ship's current mission is the exploitation of indigenous resources on Pandora, and is one of twelve ISVs that travel between Earth and Pandora on a continuing basis.

Size Length = 1,502.4 meters; Width = 302.25 meters; Height = 218.3 meters.

Range 4.4 light-years. This range is set by onboard fuel supply and its containment system, and the life-support consumables, and the infrastructure needed to contain them. Because each gram of mass must be accelerated and decelerated (as well as the onboard fuel to accomplish this), every possible weight-saving measure has been taken. The ship carries only enough fuel for the planned mission profile, and a minimal amount of additional maneuvering. There are only enough supplies for the minimum crew needed to remain out of cryosleep. Air, water, and food must be replenished at Pandora, and the ship refueled there with locally-manufactured anti-matter and hydrogen and deuterium harvested from Polyphemus.

Cruising Speed 210,000 kilometers per second (70% of lightspeed, or 0.7 c).

Maximum Acceleration 1.5 g.

Cargo Capacity 350 metric tons Pandora to Earth

Overview

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.

The ISV Venture Star is one of a twelve vehicle fleet which provides commercial space transportation between Earth and Alpha Centauri. As with the other ships of the "Capital Star" class, it was designed to carry a large payload of cargo and passengers to the worlds of the Alpha Centauri star system, especially the rich world of Pandora. The ships of this class are not exploration ships, they are commercial freighters. The ship's mission is to be part of an endlessly looping supply chain which enables the exploitation of the indigenous resources of Pandora. The ISV Venture Star, and the other ships of its class, represent the highest technological achievement in human history. Only the great need for unobtanium and the energy which it allows human civilization to produce could justify the cost of creating these vessels. 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.

Talk of "wormholes" and "warp drives" captured the imagination of twentieth-century sci-fi fans, but no such methods have come to fruition. For now, engineers must rely upon techniques that exploit our current understanding of physics. Visionaries set their sights on the potential for matter-antimatter reactions. The enormous energy released in the annihilation of matter and antimatter is the only known means of creating the kind of propulsion needed for interstellar travel. The first interstellar ship was over four kilometers long, because of the massive refrigeration system required to maintain the conventional low-temperature superconducting magnets that produced the containment field for the matter-antimatter reaction. It was not until the discovery of the high-temperature superconductor unobtanium on Pandora that interstellar travel and commerce became commercially viable. The Capital Star Class ISV was developed using this technology and is one-quarter the size of that first ship, and many times more efficient. 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.

3. Cargo containers, arranged in four ranks of four modules each. The 16 modules are in turn composed of 6 cargo pods. Depending on the cargo bay configuration of the shuttle, it can hold the contents of two pods and 100 passengers in jump seats, or up to the contents of six pods and no passengers. A mobile transporter running on tracks can position a large robotic arm for transfer of the cargo modules to and from the trans-atmospheric shuttles.

4. Two Valkyrie TAV's (trans-atmospheric vehicles) docked to access tunnels. The tunnels connect to a pressurized tunnel that runs through the truss, and connects to the habitation section.

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. Although intense magnetic fields are used to deflect stray gas molecules, the occasional dust grain requires a physical barrier. The shield is in multiple layers, spaced one hundred meters apart. Impact of a debris grain (traveling at a relative speed of 0.7C) with the first layer of the shield causes vaporization into a plasma. The spray of plasma particles strikes the second layer, and the impacts cause spalling from the back of the second layer. These particles are stopped by the third layer. A fourth layer acts as a backup in the unlikely event that something gets past the third layer. Once cruise speed is reached, this shield is detached and moved by small thrusters thousands of miles in front of the ship, to improve survivability if a larger particle of debris is encountered.

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.

Navigation:

1. Three-axis triangulation from reference stars during cruse phase.

2. Radar ranging when in proximity to planets and satellites.

3. Synthetic-aperture side-looking radar for surface mapping purposes.

Lightspeed Communications:

1. Modulation of beamed power by ±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

3. Standard VHF/UHF radio for short-range communication between orbit and ground.

Superluminal Communications:

Very low bit-rate up- and downlink using McKinney quantum entanglement encoding.

Life Support: All consumables are recycled to the maximum extent possible. Oxygen is reclaimed from carbon dioxide by fractional distillation of the ship's atmosphere, which also removes all gaseous contaminants. Additionally, this process removes water vapor and purifies it for drinking. Steam distillation is used to reclaim more drinking water from urine and solid body waste. The dehydrated and sterilized remains are used as fertilizer in the hydroponic gardens where fresh fruits and vegetable are grown to supplement the crew's diet of freeze-dried and irradiated food.

An auxiliary atmospheric system provides a much larger amount of oxygen, and carbon dioxide removal, for the short periods when the vessel is in orbit around Earth or Pandora, and the passengers and full crew are not in cryosleep. 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.

Crew: 25

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.

Passengers: 200

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.

Cargo, outbound:

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.

5. Developing avatars in amnio tanks.

6. Drugs and other medications that cannot be produced locally.

Cargo, inbound:

1. Refined unobtanium. This is the ISV's raison d'être. It takes precedence over all other items, including returning employees if there is no available mass capacity.

2. Data modules as described above. Typical exported data includes the molecular structure of Pandoran organic compounds that may have medical or other applications on Earth. The data will be used to synthesize them for testing and eventual sale.

3. Small Na'vi artifacts to be sold as collectables to wealthy individuals for extremely high prices.

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.

[Tyyr]

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]

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.

I'd call that the handwavium part of it, where they just say "Well the technology for it exists now."

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 only 30% of the actual energy released is worth anything to the ship? How does that compare to other energy sources?

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.

Which I imagine would be the long term plan of such a system, once they had enough resources and manpower on Pandora.

[Captain Seafort]

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]

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.

Right I know it's still a big chunk o power, but I ment how is that in terms of efficency?

[Captain Seafort]

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.

[Lighthawk]

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.

...damn.

[Tyyr]

Yeah, even with only 30% of the energy being usable it's still phenomenally greater than anything else in existence.

[Tyyr]

The more I thought about this ship the more I like it so I went point by point giving it my best appraisal. TLDR version, very little actual handwavium, mostly good hard science and on the horizon techs.

Size Length = 1,502.4 meters; Width = 302.25 meters; Height = 218.3 meters.

Not a bad size actually. You'd need a large ship for this kind of undertaking. A lot of fuel, a lot of supplies, etc. I'm glad they didn't try to pass off something the size of a 737 as an interstellar space craft.

Maximum Acceleration 1.5 g.

This is actually more than is probably necessary. Hell even a G is some pretty ferocious acceleration to maintain for any length of time. Constant acceleration at even 0.1G would get you to a significant portion of the speed of light quickly (relatively speaking). Just take a look at the mission profile, only 13.6% of the mission profile is under acceleration. Dragging out the acceleration a bit more, with 1G of acceleration or such, would allow you to build a less significant structure. The trade off is needing to increase the crew's food supply a bit. Without access to the exact design rationale and numbers (which don't exist) it'd be hard to make a call on why they'd go with 1.5G's over something a touch more sedate.

Cargo Capacity 350 metric tons Pandora to Earth

Again, nice and realistic. No supertanker in space here. Even if Unobtanium is as low density as water you could contain the ship's entire cargo in a pair of standard shipping containers.

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.

Again, nicely realistic. Even with a 0.7c capable ship space is still BIG. Put into Star Trek terms Pandora is 6.75 years away at Warp 1, 8 months at warp 2, or 2ish months at Warp 3, and at 4.4 lightyears away its a very close target.

...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.

Which again is true. Without some fantastically lucrative item to be harvested from a target world there's no way you'd be able to justify the capital outlay of building ships like this.

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.

Which is sort of interesting. No mention of how many ships are in service but you'd need 15 or 16 to have a ship constantly on station at Pandora. Otherwise you'll have rather long stretches of time, 7-8 months, when no ship is overhead. If they do have a ship constantly on station we know the minimum number of these ships that they can have which is 15.

Power Source: Hybrid deuterium fusion / matter-antimatter annihilation.

Which is about the only possible fuel with the energy density neccessary to make this possible.

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.

This is an interesting set up actually. Beaming the power to the ship from the ground, or space, is incredibly efficent for the space craft. All the fuel and mass for the power generation are left behind, you just get the juice. It also tells us that it is simpler to deal with anti-matter than it is to replicate this technology on Pandora. Not entirely unreasonable since being able to beam that much energy that kind of distance is something we can't concieve of right now. It's also possible that whatever is fueling the beam on Earth's end is powered by anti-matter. The power requirements for such a beam would far eclipse the ship's engines for power output because even with incredibly tight control over the beam you're going to lose a lot of it to just being beamed out into space. It's a touch I rather like about the design.

Engines: Two, arranged symmetrically in a tractor configuration.

This is one of those details that convinces me they had someone with a clue design this ship. A tractor configuration isn't incredibly manuverable but what it is is incredibly stable and structurally sound. Long thin structures like this ship are in more danager of buckling their structure than they are of crushing it. Slight asymetries in thrust could result in this ship twisting into a pretzel. Using a tractor config puts everything into tension allowing you to get the full strength of the material.

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.

More than likely it would. Your options are this, to put up with the loss in thrust by the slight angling of the engines (which at only a few degrees is minor), or build a pusher config and have to over build the piss out of the ship's structure to keep it sound and radically upgrade the attitude control system.

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.

Technically you could probably get away with very little rigidity. You've got almost 6 years to reorient the ship. Taking a day or so to sort out the ship's orientation wouldn't be out of the question. That said a little rigidity doesn't hurt so if your options are a material with non and a material with some you take the some.

Carbon nano-tubes aren't just technobabbling either, they're 100 to 300 times stronger than steel in tension and provide some rigidity in other loadings. The big problem with them is that they are so long and thin that they buckle easily. You'd want to avoid putting too much strain on the main spar during manuvers though that could be at least partially compensated for by the way you layer the tubes.

A matter-antimatter reaction causes the total conversion of matter into energy, as per Einstein's famous formula of E = mc2.

Actually it's turned into a lot of things, 70% of which are neutrinos who's main claim to fame is a phenominal ability to be totally unaffected by anything which makes them kinda useless. Still, even with getting only 30% of your fuel converted to pure energy in a usuable form its still WAY better than your alternatives.

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.

Which is, currently, not the best way to handle the stuff. You'd be better off using the temperature they're capable of producing to render the stuff down to a liquid or even metallic form then through careful manipulation sublimating only a small part to gas and pulling that off as your fuel.

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.

This is one of the handwaved parts. M/AM annihilation gets you a lot of energy, but just using the products of that reaction alone is not a very efficent way to produce thrust as things like gamma rays and other products of the reaction can't currently be harnessed to generate thrust on their own. They can be used to heat up another material, like the hydrogen injection, but without a reflector that's only a small portion of the gamma rays being created.

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:

Again, I have to comment on the structure. This is just about the perfect configuration to use in this situation.

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.

The radiators are something I question, if they're redhot then what is being used as the thermal sink? I can't see a ship like this, where every gram of material is horded, carrying along water or something purely to store thermal energy. Waste heat is a big problem for a space ship.

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.

You'd need to coat most of the ship in this thermal sheild. This is one of the handwaved areas that allows this ship to work.

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.

You've got another handwaved area here. Right now we don't know how to freeze someone then thaw them again without causing so much cellular damage that it kills them. Never mind the whole them waking up part. Still, as far as hand waved stuff goes this is way less out there than something like non-centrifugal artifical gravity.

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.

Providing artificual gravity for the crew is a nice touch. It actually makes it just a matter of taking a shuttle to the surface for them to get back to life on Earth.

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.

Which it would need to do very well. A lot of energy is going to be beamed towards this ship. The size of the sail itself will help this as it allows a diffuse beam to be sent during innitial acceleration and final deceleration. A very good radiator would also help.

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.

This is actually hard science. It's called a Whipple shield and it's the best way to "armor" a ship against interstellar debris. The biggest issue with this is that this mirror is keeping your ship from being melted. Any damage to it during the return leg of the trip could be very very bad. I'd expect some repair material to be kept on board for repairs to the shield. In fact I'd probably remove the reflective portion and stow it on the ship and just move forward the other layers.

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.

This is an interesting idea and also a bit of real world science. Beamed propulsion is a concept that's gotten some real interest from some designers. In ground bound applications a very concentrated laser is focused on the bottom of a space craft which focuses the beam even further and superheats the air directly below the craft, causing massive nearly instaneous expansion (ie an explosion) pushing the ship up. In space the pressure exerted by the beam can be used to impart acceleration on a ship.

The biggest problem with this method of propulsion is keeping the beam coherent enough to do work at great distances. A laser beam will diffuse eventually. You can see it with a laser pointer. At something an inch away it's an intense dot. A something twenty feet away its a bigger dot. The beam is diffusing. The problem with this in regards to space ship travel is you want the intensity of the beam, power/area, as high as possible and the area term is just getting bigger the farther away you go consequently causing the intensity to drop tremendously. So you either have to get the beam more coherent, or start upping the power on it to make up for the diffusion. At the start of the journey it's not too bad, but after a month of 1.5G acceleration this ship is long gone, after .46 years its well outside the solar system in interstellar space. You've not only got distance but the dust along the way robbing power. The power output of this laser system must be phenomenal.

There's also another thing we can glean from this description of operation, the beaming system is either parked at the L2, L4, or L5 points around the Earth or put somewhere else beyond the orbit of the earth. L4 and L5 contain quite a bit of interstellar dust, not a big deal for a piece of kit like this but why put up with it? L2 is likely to be crowded with observatories who will most likely NOT like you firing off the solar systems biggest spot light right next to them. My money would be on it being positioned well above or below the orbital disk. Keeps it away from heavily trafficed lanes, interference from planetary bodies, and allow you to bring the ships in well away from anything you might not like them hitting.

Finally, there's the sail. Specifically what it's made from. In this propulsion design the entire ship will be hanging from it essentially and carbon nano-tubes work best in tension.

Lightspeed Communications:

1. Modulation of beamed power by ±0.1% for high bit-rate uplink during acceleration and deceleration phases.

Why not, the thing's a big laser anyways.

2. Pulse-width modulated dedicated lasers for downlink and uplink when not using beamed power - bit rate dependent on distance

If this is viable beyond beaming distance then it speaks to some phenomenal ability to focus a laser beam.

Superluminal Communications:

Very low bit-rate up- and downlink using McKinney quantum entanglement encoding.

This concept actually makes me giggle like a schoolgirl as its a potentially viable method of superlumial communication. I'm curious as to what would constitute "low bit-rate" that far in the future. Given that the lower bound for the reaction to occur is 10,000 times the speed of light a message could be transmitted from Pandora to Earth in a maximum of 3.85 hours. Right now we have no idea what the upper limit is, just that it has to occur at atleast 10,000c. So theoretically you could transmit a message at the start of a duty shift and get a reply by the end of it. Improving your bit rate would be as simple a matter as building a transmitter with more entangled pairs. One down side to this method of communication is that transmitter and receiever are an inseperable pair. You cannot just tune them into another frequency.

Life Support: All consumables are recycled to the maximum extent possible...

All pretty much bog standard long duration mission stuff. Nothing too far out there.

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.)

Here's one of those passages that makes me love this thing and want to buy the guy who wrote it a beer. In a way its a very macabe statement, if the passengers start to wake up too early we'll just kill'em before they can suck up our oxygen. It's very much at odds with the way we expect our space program to run things right now but it's the kind of pragmatism a vessel of this type requires.

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.

Interesting idea, no idea how it would really work but they do have the core problem down. What we call freezer burn is really the formation of large ice crystals in the subject due to slow freezing. These crystals puncture cell walls and destroy structural integrity. In a frozen steak it just results in a mushy final product. In a human it results in death. For food we rapidly deep freeze things. This keeps the crystals small, cell integrity mostly intact, and the food acceptable afterwards. For something you want to live afterwards you need no crystals at all. Even small ones can destroy the machinery of a cell. Based off the number of passengers it looks like they would pretty much expect at least one dead body per run.

Crew: 25

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.

This is interesting. The crew requirements are small, which isn't surprising. Most of the ship's transit is largely just coasting along. Most sophisticated systems require suprisingly few personel monitoring them once they get up to speed. I do find the number rather curious. A crew of five would create an odd social dynamic. Simply put, you've got two pairs and an odd man/woman out. Given 20 months of close confinement with only each other to deal with its going to be rather natural for the group to start pairing off. With an even number of crewmen, evenly divided between the sexes (or not, depending on how the crew swings), and carefully screened prior to the trip everyone has a "bunk buddy". An odd number would put a lot of pressure on the crew that you probably don't want. These people are going to be stuffed into a volume of space not much larger than a small passenger jet with only each other for over a year and a half. Actually, since they rotate each crew would be working with one another for almost five years between chances to deal with other people. The only chance you'd get to shuffle around would be at Pandora or at Earth. In between you're stuck with the assholes you're with. That's kind of a weakness in this scheme actually. At least one of the crews will have to perform two shifts of work during the transit. Unless there's something funky about cryosleep it'll largely be like 40 months of straight work with the same crew. I'd have looked into dragging the shifts out to 27 months so each crew works for two years then gets a year long break at Pandora and then another two years of work and home to Earth. Of course you can just make the crew unisex and unisexual orientiation (away from their fellow crewmembers) but if I recall that won't work out very well either. Simply put the men will be ready to kill one another after over two years with no women and the women will be in pretty much in the same place. Both genders need the ability to let off some steam and reproductive fluids from time to time.

As shitty a movie as Mission to Mars was I think it did get something sort of right. The command crew was a married couple. Now they didn't do the obvious and make the entire crew up of married couples, which likely would have led to a lot of tension on the ship, but they did at least get it partly right. That would be my go to arrangement for this kind of ship, a crew of 3 married couples working 27 month shifts.

Of course if you've got some open minded astronauts five can work though more in a certain kind of movie.

Passengers: 200

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.

Yet another of those very grim passages that actually moves a bit from necessity and more too... well the corporation being some cold cold bastards. Too injured to do your job but still under contract? Sorry, no dead weight around here. *BLAM* It would seem to be a non-issue to simply cryo-sleep someone on sight, load them on the ship overhead and send them home. If you're bound and determined to make them serve out their contract make them work it off on Earth or something.

Cargo, outbound:

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.

I expect stereolighography to become a staple of near future sci-fi. It's too interesting and useful a concept not to use big time. Being able to create multi-material parts at once would pushing it along way towards being a serious replacement for other manufacturing methods in situations like this. Even single material parts with final assembly afterwards would be worth it.

2. Micro-miniaturized components like mirco- and nanoprocessors and other circuitry elements that cannot be manufactured on Pandora.

I'd strongly look into a highly standardized system for this and move a manufacturing plant to Pandora. Just saying. Instead of custom building each processor everything runs off one of several overpowered but standard designs that are easy to manufacture on site.

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.

It's an interesting concept. Don't know if it's pure handwavium or not. I don't think it is but the specifics aren't coming to me.

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.

Depending on the life cycle of these things that's a lot of potential fuel harvesters. Though you'd want some back up since the gas they collect is the only way the ISV is getting home.

6. Drugs and other medications that cannot be produced locally.

Hope its the good ones considering end of usefulness care supplied by the company.

Cargo, inbound:

1. Refined unobtanium. This is the ISV's raison d'être. It takes precedence over all other items, including returning employees if there is no available mass capacity.

Another beer buying passage. "Sorry, you're going to have to sit here another year, we need our money more than you." It provides a sort of maximum limit on the amount of unobtanium they can mine and refine in a year, about 350ish tons maximum. Probably less unless getting a ride home from Pandora is rare.

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.

And the final, "buy the man a beer" passage. In order to make this kind of passage "safe" like most of the western world defines it today you really do need some technology like only Star Trek has. Shields mostly. At the speeds the ship travels it is entirely possible that a collision with a small object could annihilate the ship. The Whipple shield will protect the ship to a degree but only against objects directly in its line of travel. A piece of rock the size of a golf ball could theoretically be crossing the ship's path and just manage to miss the shield but still hit the ship. If it does, boom. The good news is that much like the gamma ray shower the destruction will be so fast the crew won't even be able to comprehend it. One second they're alive the next they aren't. The designers and operators of the ship have a very pragmatic mindset, instead of trying to make the on duty crew perfectly safe in any eventuality they do their best and if the worst happens... well they've got a back up on board.

[Lighthawk]

Long time getting around to saying this, but thanks for taking the time and effort on this Tyyr.

Question about the acceleration issue you brought up. Well two maybe, I don't know the neccessary math to check it myself but...

1) At least for the outbound flight from earth, could the acceleration be so high due to the fact that they are beaming the power source to the ship? The further away they get from earth, the less energy that will actually reach the ship right? So they accelerate hard in order to get up to cruising speed while still relatively close to earth.

2) Would a slower acceleration perhaps add too much time to the trip? Considering the incredible speeds invovled, not to meantion time dialation effects, perhaps a gentiler acceleration would just add more time than the RDA wants or can afford.

[Tyyr]

1) Possibly, take advantage of the thrust as much as possible when the beam is at it's highest intensity. That would make some sense for the outbound from and inbound to Earth legs for certain.
2) It's not really going to add much time. Just an additional .23 years for each acceleration event. Now the obvious implications of that are that by accelerating harder you can trim almost a full year off the trip. Again, I dunno the economics or the exact engineering of the ship so I can't say one way or another if that's a worth while trade off against the increased structure of the ship to handle 1.5G's instead of 1G. Dilation effects are only going to start to matter as you get close to cruising speed so the choice between 1.5 and 1G will have little effect for the bulk of the trip.

[Graham Kennedy]

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.

Um.... WHAT?

[Tyyr]

Yeah, I'm not 100% sure why that is. I mean they're going to ship them back eventually anyways. Why not just toss them in the freezer until a free spot opens up and then ship them home?

[Aaron]

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.

Um.... WHAT?

Yeah, sorry you got your arm ripped off by a ten foot tall cat man. Now fuck you, we have to put you down!

[Tyyr]

Maybe they only mean terminal diseases or major medical emergencies? Things that would require loading you on the ship and going home RIGHT NOW. So rather than screw up the year's trillion dollar plus gross they just put you down.