What now for SpaceX's Mars-bound Telsa Roadster?
If the SpaceX Falcon Heavy is the world's most powerful rocket, then the Tesla Roadster that it shot into interplanetary space holds the record for the fastest car in history. This cosmic convertible will orbit around the Sun once every 1.6 years, but how long will it continue to do so, and what will be its fate? Will it still look as pristine a billion years from now as it did in the videos beamed back to Earth? Probably not.
At the moment, there are five US spacecraft speeding out of our Solar System, never to return. Billions of years from now, when our Sun has turned into a red giant and engulfed the Earth in nuclear fire, the Pioneer, Voyager, and New Horizons probes will still be traveling through our galaxy like a quintet of robotic Odysseus's.
Even back in our system and revolving about our Earth are satellites that will still be around for many millions of years. For example, one Earth-orbiting satellite, LAGEOS-1, is a passive laser reflector satellite that will not only remain circling our planet for 8.4 million years, but will remain functional for most of that time.
With a track record like that, it looks as if the Tesla Roadster that rocketed into space on February 6, 2018 will be cruising happily among the stars as a permanent monument to the early days of commercial deep space travel. It's a nice thought that the Starman mannequin driver and his cherry red ride will still be around long after the pyramids have crumbled to sand.
Except that's not going to happen. In fact, the Starman and the Roadster are in for a very unpleasant time and may not be in very good shape after a few years. And their lifespan, while huge by human standards, may be rather limited.
At the moment, the Falcon Heavy second stage and the Roadster attached to it are in an orbit that Jonathan McDowell of the Harvard-Smithsonian Center for Astrophysics has recalculated from Elon Musk's rather generous rough estimate of a few hours after liftoff. According to McDowell, the second stage is a Hohmann transfer orbit, which is most economical orbit in terms of energy for going from one place to another.
Where Musk estimated that the second stage was circling the Sun at a distance between 91 million mi (150 million km) and 240 million mi (390 million km) with an inclination of 29º to the ecliptic, McDowell calculates that its orbit is between 92 million mi (148 million km) and 158 million mi (255 million km) with an inclination of 1.1º and a period of about 1.6 years. This puts its farthest distance from the sun just beyond the orbit of Mars.
The popular idea is that the Roadster will orbit the Sun for hundreds of millions, if not billions of years, but that isn't the case. The second stage and Roadster are now essentially a near-Earth object (NEO), much like the asteroids that space agencies keep an eye on just in case a large one is going to hit the Earth.
One thing that marks NEOs is that they don't have very long careers. They're interplanetary jaywalkers with all the hazards that implies. Planets and asteroids in circular orbits stay out of each other's way and are relatively stable, but NEOs, and the Roadster, are in eccentric orbits that cross the orbits of the planets. This makes their trajectories very unstable.
The second stage will cross the orbits of Earth and Mars and its trajectory will certainly be perturbed by Jupiter's gravitational field, so there is a small chance that it might strike Earth or Mars many thousands of years from now, though it's so small that it will burn up in the atmosphere. Another possibility is that it might get flung out past Jupiter or inward past Venus. It might even be propelled into the Sun, as happens to many near-Earth asteroids after a few tens of millions of years. The orbital mechanics are very complex, so it's difficult to predict, but the upshot is that the Roadster won't be roaming the Solar System for as long as its neighbors.
Another problem is that with the Roadster so close to the plane of the ecliptic, it's in danger of being struck by cosmic debris. There is a very small chance that it might be hit by a large object like an asteroid, but the greater threat is from micrometeoroids, which over the millennia will hit the car time and again. Each of these will cause small and not-so-small amounts of damage, until it could one day look like it's been shot at by a cannon filled with sand and gravel.
But the much greater problem is that the Roadster isn't a purpose-built spacecraft. It's a production electric car, which means it's as suitable for surviving the environment of space as a chocolate Easter bunny in a convection oven.
We're used to stories of interplanetary spacecraft functioning long past the predicted end of their service life. Mars rovers expected to operate for 90 days are still rolling after many years, and the Voyager probes are still working 40 years after their launch. Even the defunct machines, like the Kepler Space Telescope, can be expected to be around for many millions of years in a relatively intact condition. Why not the roadster, then?
The answer is very simple. Space engineers have spent decades studying how to build spacecraft and especially which materials to build them out of. They know which ones can withstand the extreme heat and cold of space, the hard ultraviolet (UV) radiation, as well as the X-rays, gamma rays, and cosmic rays that are constantly bombarding our technology outside the protection of Earth's atmosphere and Van Allen belts.
The Tesla Roadster, on the other hand, was designed to drive on Earthside roads, not galavant between the Earth and Mars. It was made to be light and fast, and have good road handling. That may be fine on the twisting roads of Italy, but the engineering that went into the Roadster is now a positive detriment in space.
The biggest problem is that the Roadster, and Starman, and made up largely of rubber, plastics, and carbon composites, which consist of long chain organic molecules that include epoxy resins, polypropylene, polystyrene, polyvinyl chloride, nylon, and many others. These make up the carbon composite car body, the fabrics in the interior, the cushions in the seats, electrical insulation, and a myriad of fasteners, fairings, and adhesive compounds. Starman and his suit are made almost entirely out of organic polymers and even the safety glass in the car's windscreen is a plastic laminate.
All of these, at this very moment, are being subjected to dangerously high temperature variations as the sunlit areas heat to 260º F (127º C) and the shaded areas plunging to -280º F (-173º C). Fortunately, the second stage is slowly rotating, so the car is being evenly baked like a rotisserie chicken, but as the vehicle orbits toward and away from the Sun, it will produce strong thermal stresses that will produce all manner of material fatigue. Also, the rotation means that anything that comes loose can fly away.
But the worst is all that radiation hitting those long polymer chain molecules. As the rays strike, they will break down the molecules bit by bit, converting them into free radicals. The same goes for the pigments used to give the Roadster its red color. Eventually, the car will become bleached, then everything made of polymers will disintegrate and crumble into dust.
It's all happened before and it doesn't take very long. If you look at pictures of the old Apollo moon missions of the late 1960s and early 70s, you'll be familiar with the images of spacesuited American astronauts saluting the flag and the Lunar Module wrapped in gold Mylar foil to keep it cool under the harsh lunar sun. If you were to go back to those landing sites, you'd find the flag poles empty and the descent stage of the module largely unclad because half a century of radiation has done its work.
So what will the Tesla Roadster look like in a couple of centuries? The most obvious thing will be that the carbon composite body will be gone as the epoxy resins have all broken down and the carbon fibers fallen apart. The rubber tires on the wheels won't be there either.
Many other bits will have come loose as the adhesives turned brittle and ceased to stick. Even the windscreen will have a yellowy opaque look, provided the laminate hasn't failed completely or a meteoroid hasn't slammed into it. In the cockpit, Starman is now reduced to a few metal joints. The seats are bare metal frames with the fabric covers now powder, and the foam rubber cushions long gone.
Other materials in the car will also suffer over time. Any lubricants will have frozen or boiled away. Those that remain will degrade like the plastics, turning into a brittle mess. If any graphite was used for lubricant, the water molecules that make graphite powder slippery will evaporate and the carbon molecules left behind will now have the property of jeweler's polish.
It's very likely that the 6,831 lithium-ion cells that powered the Roadster will have been removed before leaving Earth. The FAA probably wouldn't have been too happy about 700 lb (317 kg) of fire-prone batteries sitting atop the Falcon Heavy, turning into a very large bomb. However, there was a battery aboard to run the cameras that beamed back video to Earth. That battery may, depending on its design, start to generate gas and may one day explode. Meanwhile, the electronics used to transmit video will very soon be fried by the radiation as the delicate micro circuits are destroyed bit by bit.
Even the metals in the car will be affected. The roadster uses advanced alloys – some of which might start to outgas. Radiation will eventually affect the crystalline structure of the alloys and may give them a patina, such as is sometimes found on metallic objects in very dry deserts. Over millions of years, some may become brittle. Some may develop something similar to tin pest, where tin alters its structure at very low temperatures and appears to rot.
In the end, if some distant future expedition does retrieve the Roadster, it will be in a sorry state – a battered, bare metal frame with a few pockets of organic chemical dust. But maybe that won't be so bad. Maybe it will give it the right air of romance, like the Parthenon or Stonehenge. Or maybe it will be regarded as a challenge by the finders, who may embark on the greatest car restoration project in history.
Let's hope they get the paint job right.