Wednesday, 28 December 2016

Realistic Is the Interstellar Ship

How Realistic Is the Interstellar Ship from 'Passengers'?
By Elizabeth Howell, Space.com Contributor | December 23, 2016

The Starship Avalon, from the movie "Passengers" seems to have been inspired by some real-world science. The movie "Passengers," which opened yesterday (Dec. 21), explores the fascinations and perils of interstellar travel, but could the kind of starship portrayed in the movie ever exist in real life? The film begins on board the Starship Avalon, which is carrying more than 5,000 passengers to a distant, habitable planet known as Homestead. Travelling at half the speed of light, the crew and passengers are expected to hibernate for 120 years before arriving. That is, until somebody accidentally wakes up 90 years early. Is there anything remotely realistic about this spaceship? Space.com posed that question to several space travel experts, as well as Guy Hendrix Dyas, the film's production designer. Dyas looked at the history of movie spaceships (including the vehicles from the "Star Trek" and "Star Wars" universes) in his quest to come up with something unique for the new film.

The Avalon has three long, thin modules that wrap around a common center and spin (sort of like stripes on a barbershop pole). Dyas said he based that design on sycamore seeds. It appears that the spin also provides the ship with artificial gravity, similar to fictional ships in the movies "Interstellar" and "2001: A Space Odyssey." The ship is powered by eight nuclear fusion reactors, Dyas said, and can run autonomously, healing most systems even with the crew asleep (as seen in the film).

The ship's immense structure is about 1 kilometer (0.62 miles) in length, and Dyas said he imagines that it was assembled in space over decades. The film takes place at an indeterminate point in the future, Dyas said, but he assumed that by the time the ship was being built, humans would have the ability to mine some of the materials from nearby asteroids or the moon to save on transportation costs.

"My approach to the [ship] design was that I tried to go about it as though I was a cruise liner ship designer," Dyas told Space.com. "I wanted to put myself in the shoes of somebody who had been designing a craft that had a portion of it dedicated to entertainment, and of course that led to the array of colors and textual changes in the ship."

This approach led Dyas to design the more functional areas (such as the mess hall) in stainless steel, while a classy passenger pub was decorated in rich oranges, golds and reds, for example. Banks of hibernation pods occupy huge halls in the ship. The crew slumbers in separate quarters, inaccessible to the passengers. The pods are clustered into small groups, perhaps (Dyas suggests) so that if one group's cluster fails, at least the other 5,000 passengers are theoretically unaffected.

The hibernation procedure is not really described in the film, but what's clear to moviegoers is what happens afterward: passengers are soothed by a holographic figure explaining where they are. They are escorted to an elevator, then guided to their individual cabin, where they can relax for the last four months of the journey. In between resting in their quarters, passengers can also get to know the rest of the 5,000 people in common areas, such as the mess hall, the grand concourse, the pool or the bar.

Interstellar propulsion
Nuclear fusion is a possible source of propulsion for interstellar ships, but the problem is the size of the reactors that would need to be assembled in space, or launched there, according to some scientists we talked to. So other methods are being considered to get spacecraft going at interstellar speeds.

One idea under consideration by Philip Lubin, a physics professor at the University of California, Santa Barbara, uses lasers. Under another NIAC grant, he is developing a concept known as Directed Energy Propulsion for Interstellar Exploration, which would generate propulsion from laser photons reflected in a mirror. The long-term goal is to create a spacecraft that can, like in "Passengers," move at a significant fraction of the speed of light.

Antimatter engines are another possibility for fueling interstellar ships, said Andreas Tziolas, the co-founder and president of Icarus Interstellar. Antimatter particles are naturally occurring particles that are "opposites" to regular matter particles — so the positron is the antimatter equivalent to the electron; the particles have the same mass but are different in other ways, including electric charge (the electron is negative, the positron is positive). When matter and antimatter collide, they annihilate, and release energy.

Though it's not stated directly it the film, it's possible the "Passengers" ship is being fueled by the interstellar medium — the tenuous collection of hydrogen particles that populate much of the universe. This concept was proposed in a 1960 thought experiment by American physicist Robert Bussard, who argued it would allow a ship to travel without having to haul fuel along for the ride.

But there's a problem with that idea, according to Geoffrey Landis, a science fiction author and NASA physicist. Since 1960, scientists have discovered that the medium is too sparse to allow fusion to happen, Landis said.

"The idea was, if you don't carry your fuel with you, you might be able to avoid having a simply enormous fuel tank," he said. But with that theory debunked, the problem remains about how to get to such an incredible speed while still hauling fuel with you. [Does Humanity's Destiny Lie in Interstellar Space Travel? (Op-Ed)]

From a practical standpoint, Landis also agreed that a ship that size would likely have to be built largely in space, and that will probably require asteroid mining.

While asteroid mining is still in the future, there are a couple of companies that are getting started on prospecting. Both Deep Space Industries and Planetary Resources have plans to scout out nearby asteroids to learn about their composition, and the possibilities for getting spacecraft out there. Asteroid-mining technology is in an early stage, but both companies are generating other products (such as Earth observation) that have received some support from customers.

Building a business case would take some time, but Landis said it would be very possible to create a spacecraft from extraterrestrial resources.

"In the long term, if we're going to build these enormous habitats, we are going to have to build them from material in space," he said. "That's a very feasible idea. There's literally millions of asteroids out there from which we could harvest materials without having to drag it out of the gravity well of the Earth."

Ship design

Landis also seemed to think that the Avalon creates gravity by rotating.

"I'm getting a little tired of artificial gravity in 'Star Trek' and 'Star Wars,'" he said, referring to the ability of the ships in these long-standing franchises to generate gravity by more theoretical means.

Experts interviewed for the story agreed that, in general, the ship also appears to take into account human factors, which means designing an environment so that it can best accommodate how humans operate.

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