What does Elon Musk mean by when he says, “… Destination is Mars orbit. Will be in deep space for a billion years or so….”?
In early December, Elon Musk, the founder of SpaceX, CEO of Tesla, and countless other companies, tweeted that he will be launching his Roadster into Mars orbit using the Falcon Heavy rocket. In the same tweet, he says, “Will be in deep space for a billion years or so…” which may be confusing to some. I make this assumption because people may not be familiar with the phenomena of orbital decay. Orbital decay is, as the name implies, the decay of an orbiting satellite, both natural and artificial, such as a planet, a moon or the Hubble Space Telescope. The cause for this decay varies for there are four main causes of orbital decay.
The first massive cause is atmospheric drag. Atmospheric drag is the main cause when we are talking about satellites in a low-altitude orbit around Earth, around 160 to ~1000 kilometres off of the Earth’s surface. So, what in the atmosphere causes this drag? There is one simple answer, the interactions between the satellite and the atmospheric particles……..aka friction. One famous case of atmospheric drag is with the Hubble Space Telescope. Launched in 1990, the Hubble Space Telescope took thousands of breath-taking pictures of the universe from the Pillars of Creation to the Crab Nebula. However, the Hubble Space Telescope won’t be taking pictures forever. It is predicted by Ken Sembach, Director of the Space Telescope Science Institute, along with many other NASA engineers and scientists, that the Hubble Space Telescope will last until the late 2030’s if nothing is done to keep the telescope in orbit. And even before the telescope re-enters the Earth’s atmosphere, NASA would most likely push the telescope over the Pacific to avoid danger to the populations or push it into a more stable orbit (space.com and ipfs.io).
What also happened in the 1990s was an atmospheric drag experiment/test conducted by the Australian Government Bureau of Meteorology. In the experiment, they made a hypothetical satellite, 100 kilograms in weight and 1 square metre in size, at an initial height of 300 kilometres. As the days go on, one can see that the satellite slowly but surly decreases in height due to atmospheric drag, from initial height, 300 kilometres, to 289.9 kilometres in the matters of ten and a half days (sws.bom.gov.au).
One other, rather surprising, cause of orbital decay is thermal energy. If the satellite is facing one radiation source, such as the Sun, then one side of the satellite will be hotter than the other. Because the distribution of heat is asymmetrical, it loses momentum. It loses momentum because the hotter side is re-emitting more photons than the much cooler side. As the time goes on, this loss of momentum takes a toll on the satellite’s orbit. For spinning satellites, there are two types of asymmetric thermal energy distribution: along the spin axis of the satellite (called summer-winter effects) and along its equator (called day-night effects). One example of this in action is with the LAGEOS, laser geodynamic satellite. LAGEOS’s orbit is diminishing because of the summer-winter effect which has not been noted (this effect, by the way, does not require a satellite to spin). What is really cool about this satellite is that it contains a Carl Sagan designed plaque with the continents arranged in Pangaea (268 million years ago), the present formation and the formation in 8.4 million years (shows the predicted arrangement). (nasa.gov and scielbo.br)
The next one effects natural satellites that will, in the end, destroy entire planets or moons. Tidal effects is when one more massive object, (we will call this primary body), bulges a smaller, less massive object, (this will be called secondary body), under the primary body’s strong gravitational pull. This attraction slowly degrades the orbit of the satellite. However, the secondary body must be in a retrograde orbit, an orbit going opposite of the primary body’s spin, or in a synchronous orbit, orbiting with the primary body’s spin and same average spin period. This can be seen in the system of 51 Pegasi, located in the Pegasus constellation. In this system, there is a “Jupiter-like planet” that has an extremely fast orbital period of 4.2 days. The planet would spiral into the star if there were more time. The reason it will not is because the star’s life will end before the orbit is completely diminished (ipfs.io and absabs.harvard.edu)
And finally, the last cause of orbital decay is gravitational radiation. Gravitational radiation happens on a massive scale with astronomical bodies that of neutron stars and black holes. When these gigantic objects orbit each other, they make ripples in spacetime, gravitational waves, which, in turn, degrades their orbits. When bodies like black holes merge, they create gravitational waves so powerful, that it can be detected over billions of light years away such as the first gravitational wave discovered in February of 2016. Not only black holes, but neutron stars, as mentioned earlier, can also create extremely powerful gravitational waves such as the waves detected in late 2017. Gravitational radiation produces incomprehensibly energetic events, so much energy in fact, that these gravitational waves are more powerful than all the light in the observable universe combined…….times TEN (actforlibraries.org and ligo.org)!!!!
In the end, the event of orbital decay is why in “a billion years or so…” that Tesla Roadster, Elon’s personal Tesla Roadster, will crash into the Red Planet.
: My name is Jason Pusic and I am a 15 year old science enthusiast. My interests primarily lay in physics, astronomy and astrophysics, but I am a fan of all sciences such as neuroscience, chemistry, evolutionary biology, etc. I hope everyone is loving what not only I post, but what all authors post on this magnificent website!