In the film Avatar (which has smashed box office records worldwide), the ISV Venture Star can complete a trip of several light years.
Despite having served on the NASA Advisory Council for 3 years, James Cameron does not claim that the Avatar he has created is scientifically irreproachable. The Canadian director was actually aiming to create plausible fiction which the general public could support without having to continually say: “this thing could never work”… And yet, the most extraordinary element of his film, the spaceship Venture Star capable of leaving the solar system, is very well thought out and even includes some noteworthy notions of astronavigation!
Alpha Centauri: near and yet so far
The astonishing appearance of the ISV (InterStellar Vehicle) Venture Star, seen at the beginning of Avatar, basically seems dictated by its futuristic design and the intention to impress the spectator. But it was, in fact, inspired by the works of the (sometimes controversial) scientist Charles Pellegrino who was also a consultant for this Hollywood blockbuster. According to Mr Pellegrino, it is possible to design a spacecraft capable of reaching slightly distant star systems. And it is worthy of note that the action in Avatar takes place on Pandora, a moon of a giant gaseous planet which is orbiting Alpha Centauri, one of the nearest stars to the Earth. The promotional video for Avatar, below, takes the form of a short scientific documentary in its presentation of Pandora.
Alpha Centauri is only near in an astronomical sense as we are talking here about a distance of 4.4 light years, which basically means that light, at a speed of 300,000 kilometres a second, takes almost four and a half years to get there! James Cameron could therefore have chosen the easy way out and turned to hyperspace as in the Star Trek and Star Wars sagas, imagining spacecraft capable of travelling faster than the speed of light into another dimension using physics which do not yet exist. But this was not the case with Venture Star, a spaceship which approaches the speed of light (70 to 90%) without ever exceeding it and which therefore remains within the rules established by Albert Einstein. As we have already mentioned, this interstellar vehicle adopts the principles of one of Charles Pellegrino’s studies, the Valkyrie concept to be exact.
A plausible sci-fi spaceship
Keen to present a spaceship that “stands up to scrutiny”, the designers of Avatar’s ISV Venture Star did not just make do with stacking modules to obtain an aesthetic look, instead they followed the general design of the Valkyrie concept relatively closely. The spaceship is striking with an overall length of 1.5 km (James Cameron’s original script, nevertheless, counted on half a mile, which is 800 m) and its propulsion unit is apparently placed at the front.
The main components of the Venture Star; a design inspired by studies on the reality of interstellar travel.
A: photon sail attachment (here folded, as used during the departure from Earth). B: radiators for cooling. C: spherical “fuel” (hydrogen and anti-hydrogen) containers. D: matter-antimatter engine nozzles. E: main tensile truss. F: cargo compartments and docking ports for the two shuttles. G: transportation chambers for the cryosleeping passengers and crew living quarters. H: mirror-shield.
Credit: Fox/Lightstorm – Enjoy Space
The impressive spheres contain the “fuel”, namely hydrogen and antihydrogen, the latter being confined in magnetic fields. Without this precaution, the antihydrogen would destroy itself with the material of the tank walls giving off an enormous amount of energy. This is what we do voluntarily, however, by mixing it with hydrogen, only this time it is in thrusters provided expressly for the purpose (see the above diagram) and which are set at a slight angle in relation to the axis of the spaceship. An angle which directs the exhaust plume away from the cargo and passenger compartments and without which there would be an excessive amount of heat and radiation. The same reasoning explains why these compartments are situated at the end of a truss made of a latticework of carbon nanotube (a light and extremely resistant material, several grams of which are made in a laboratory) struts, but we will come back to this. If the passengers were too close to the propulsion section, they would not survive the radiation, and the shield required to protect them would represent a voluminous inert mass. We would also point out the impressive glowing red rectangles: these are the radiators tasked with dissipating the intense heat generated by the matter-antimatter reaction into space. What’s more, they continue to glow for several weeks after the shutdown of the main propulsion unit!
To find out more, we are going to imagine a journey aboard the Venture Star. The passengers transported are plunged into a cryosleep, their bodies kept in suspended animation due to very low temperatures. Use of this method is obvious: it avoids having to carry the food and living quarters essential to 200 passengers for several years, which would result in a mass far too great! The total mass of the systems dedicated to cryosleep being in this hypothesis vastly inferior. However, some astronauts remain awake throughout the journey in order to monitor events and possibly intervene where necessary. This crew live in modules placed at the end of 2 arms which rotate so as to provide them with artificial gravity.
- The passengers of the Venture Star are placed in cryosleep whilst travelling so as to avoid the huge mass associated with the living quarters and food supplies required for 200 people on a journey that lasts 6 years.Credit: Fox/Lightstorm
On leaving the Earth, the Venture Star deploys a sail on its central mast. Extremely thin, with a diameter of 16 km, it is “bombarded” by several laser stations (on Earth and in orbit). The large “mirror” at the rear of the Venture Star protects it from laser beams. At this stage, the matter-antimatter engines are not working and the compartments for the working crew are not rotating at the end of their arms. Said arms are folded down along the axis of the Venture Star, artificial gravity being provided by the constant acceleration of the spaceship (about 1.5 g) which will eventually reach 70% of the speed of light. It is worthy of note that the main truss, a type of “backbone”, is designed to only resist tension force in order, once again, to make substantial savings as regards inert mass. This sail-towed departure therefore observes this principle.
Once the Venture Star is travelling at its cruising speed (210,000 km/s), the sail folds down and the spacecraft turns 180° so that its mirror is now at the front and can act as a shield against any collisions. This is important because at this speed the smallest grain of dust would cause irreparable damage. The mirror-shield completes a complex set of protective features comprising a magnetic field tasked with deflecting the smallest of particles, another shield projected forwards once the cruising speed is reached and which remains therefore always in the forefront of its momentum, as well as the laser weapons that can target and destroy obstacles that it is impossible to navigate around. And lastly, the crew responsible for monitoring the journey enjoys artificial gravity as the arms, at the end of which are attached their living quarters, now open up and start rotating.
The Venture Star as seen from the passenger compartment side.
A: one of the two matter-antimatter engine nozzles. B: spherical “fuel” (hydrogen and anti-hydrogen) containers. C: cargo compartments. D: one of the two Valkyrie shuttles berthed at its docking port. E: passenger chambers. F: arms at the end of which are placed the crew quarters. G: hinges enabling the arms to be folded down so as to station the crew quarters along the spaceship axis (acceleration and deceleration phases).
Credit: Fox/Lightstorm – Enjoy Space
Destination: Alpha Centauri
Several years later and cruising through the Alpha Centauri system, the Venture Star has to “brake”… But would this deceleration not perhaps destroy the truss mentioned above which only resists tension force? No, because do not forget that the spaceship turned 180° once its cruising speed was reached! Therefore, when the matter-antimatter engines are activated, they are going to pull on the rest of the interstellar cruiser causing an inverse traction which will keep the truss rigid. The arms holding the crew living quarters stop rotating and fold back down along the axis of the spaceship: the deceleration then provides artificial gravity. Minor navigation changes in order to go into orbit around Pandora are carried out by fusion planetary manoeuvring engines.
There is, in fact, one last step before being able to reach the ground in this far-off world. An immense spacecraft such as the Venture Star cannot land and this chore is assigned to two onboard shuttles tasked with completing the necessary trips. We would point out that these transatmospheric vehicles are called Valkyrie in the film… Valkyrie? Yes, like the name of Charles Pellegrino’s interstellar spaceship concept which inspired the Venture Star.
The Venture Star did exist!
It is not just a question of the allusion that James Cameron makes to space projects. The name of the ISV Venture Star is in itself a direct reference to a study carried out by the company Lockheed Martin for NASA! The ambition was to develop a totally self-sufficient space shuttle which could reach orbit without booster rockets. Engineers also hoped to reduce the cost of accessing space by a factor of 10 whilst offering a level of safety equal to that of air transportation. Despite more than 1 billion dollars invested in research and the preparation of a reduced-scale prototype dubbed X-33, the programme came to a technological stalemate and was abandoned in 2001. The Venture Star therefore existed in project form with numerous illustrations from the American Space Agency presenting it as the future of human space flight.
The real Venture Star! A NASA and Lockheed Martin project which was to have succeeded in creating totally self-sufficient shuttles capable of carrying several astronauts and a 20 tonne payload.
Whereas its fictional namesake in Avatar illustrates a rather in-depth study of the issues of interstellar flights as we have just seen. However, Charles Pellegrino’s concept is not the only one and other scientists and engineers have been looking into what needs to be done (and confronted as difficulties) to give our civilisation the ability to travel to planets orbiting the nearest stars.
Astronaut and scientist Franklin Chang-Diaz has been working for several years on a plasma engine prototype by the name of VASIMR (Variable Specific Impulse Magnetoplasma Rocket). With a sufficiently powerful source of electric energy (small nuclear plant for example), this mode of propulsion would make it possible to complete the Earth-Mars journey in just 39 days instead of more than 6 months with current technologies. This type of research bears witness to the actual efforts being made to give mankind a real capacity for interplanetary travel, the first step prior to aiming for other star systems.
Their solutions are not necessarily the same, but they all come up against the same double snag: the mode of propulsion and the energy required. The technologies currently used in rockets are totally inadequate and that is why highly futuristic perspectives such as using matter-antimatter are at the heart of the many studies carried out. Unfortunately, it could all be nothing but pipe dreams that will never reach the drawing or science fiction film stage, meaning that Man will remain a prisoner of his own solar system or even his own world… A hypothesis that some scientists, such as Donald Brownlee in his book Rare Earth, envisage and prove in all seriousness! But after all, would Christopher Columbus ever have imagined that one day his dangerous crossing of the Atlantic would be completed in just a few hours by flying several thousands of metres above the waves? Certainly not. And yet…
Published on 17 February 2010