Earths scientists have anticipated the arrival of Apophis since 2002. Apophis, an asteroid of some size with a wide ranging eliptical orbit, will pass inside the orbits of our communication satellites (our geosynchronous zone) during 2029, and closer still in 2036. Apophis, the “serpent that dwells in darkness” is of unknown density, is 270 meters in diameter, and 460 feet long, weighing in, according to speculation, at about 46 million tons. Since the asteroid is traveling at a speed of 13,129 miles per hour, and in view of the fact that we know neither its mass, nor its direction of spin, it is impossible to predict with any certainty the probability of impact with our Earth.
Such an impact could wipe out half a continent. The asteroid that destroyed all life on Earth, and ended the Cretaceous period of Earth’s history, killing all the dinosaurs some 65 million years ago, was 6.2 miles across, and struck with the force of a billion times the atomic bombs that ended world war ll. Apophis, though somewhat smaller, if it were to make contact with our planet would do considerable damage.
Scientists know that Apophis like most objects in space has a spin, but are unsure of the direction of that spin. In scientific terms, retrograde motion is spin in the direction opposite to the movement of something else, in this case, the planet Earth, and is the contrary of direct or prograde motion. While we are told the likelihood of Earth impact is between 1 in 45,000 and 1 in several million, scientists quietly admit that they just can’t be sure yet. Spin and mass are required to make plausible conjecture. They are forced by circumstances to concede the possibility of a calamitous impact. Furthermore, in the event that the asteroid collides with one of our satellites, the outcome is still more unpredictable.
Scientists in Germany, and separately, in Japan, are developing ways to deal with Apophis, and any future asteroids they may threaten life on earth. In Germany, the European Space Agency is planning a mission using fuel driven rocketry to explode the asteroid into smaller particles, most of which will burn up in our atmosphere, with the remainder doing only minimal damage, should they reach the surface of our planet. A test mission is called Don Quijote; the mission name refers to (as we spell it) “Don Quixote”, the novel by Spanish author Miguel de Cervantes, about a knight-errant who tilted with windmills. In mission Don Quijote, An impact craft called Hidalgo will collide with an asteroid selected for the test, at a rate of 6 miles per second. The collision will be monitored by an orbiter called Sancho, and the outcome analyzed.
The Japanese, in the person of Shengping Gong and his team of scientists at the Tsinghua University in Beijing, are working in collaboration with the German team, and are utilizing new and still-in-development solar sail technology to change Apophis’ trajectory, and thus to avoid impaction. Solar sail space travel is inexpensive, and allows speeds of 9/10 the speed of light. In pursuit of Apophis, a small (10 kilogram) spacecraft driven by solar sail will orbit the Earth retrograde, building up speed for a collision course with Apophis. Collision velocity will be at 201,324 mph. The Japanese scientists say this impact in space will obliterate the asteroid into nothing.
400 years ago, Johannes Kepler proposed the idea of exploring the galaxy using sails to catch a theoretical “solar breeze.” Space vehicles would move among the stars, as sailing ships sail the ocean. Kepler’s solar breeze has been disproven, but NASA today, as is Japan, is experimenting with giant solar sails to push craft through the cosmos by light. A solar powered spacecraft doesn’t rely on soon-expended propellant, and so can voyage for decades, propelled by sunlight; the sun is its engine. NASA reminds us of the familiar tale of The Tortoise and the Hare. Conventional rocketry jumps to a quick start, like a hare or a rabbit. Light propelled vehicles, here compared to slow moving tortoises, take time to reach their high end speeds, but eventually will move five times faster than fuel driven rockets, and will be able to take man to the stars. NASA scientists write: “A solar sail would begin its journey at a slow but steady pace, gradually picking up speed as the sun continues to exert force upon it. Sooner or later, no matter how fast it goes, the rocket ship will run out of power. In contrast, the solar sail craft has an endless supply of power from the sun. Additionally, the solar sail could potentially return to Earth, whereas the rocket powered vehicle would not have any propellant to bring it back.” Once propelled into space by a traditional launch rocket, the sails are deployed using an inflatable boom system triggered by a built-in deployment mechanism, The small, compact parcel opens to a sizable sail to harness the power of the sun.
Some interesting notes of solar sailing: Arthur C. Clark popularized the phrase in May of 1964 in his short story, “Sunjammer”.
Japan, and the Japan Aerospace Exploration Agency, launched IKAROS (Interplanetary Kite-craft Accelerated by Radiation Of the Sun) in May of 2010, successfully demonstrating solar-sail technology in interplanetary space. “IKAROS” derives from “Icarus”, the tale of Daedalus, a young craftsman who attempted to escape from Crete on waxen sails, only to be foiled by the heat of the sun. The waxen wings unfortunately melted.
Images from NASA, and en.wikipedia.org