Mission to Mars by Buzz Aldrin

Author:Buzz Aldrin [Aldrin, Buzz]
Language: eng
Format: epub
ISBN: 978-1-4262-1018-1
Publisher: National Geographic Society
Published: 2013-05-06T22:00:00+00:00

Robotic spacecraft surveys a large asteroid.

(Illustration Credit 5.6)

Private Sentinel telescope eyes asteroid population.

(Illustration Credit 5.7)

Along with the need to come to terms with the dangers of asteroids, there are several other important outcomes of their study. The United States, Europe, and Japan have successfully hurled spacecraft to asteroids, with more robotic probes to key NEOs on the books.

Russian engineers have been promoting the idea of an automated craft emplacing a location transmitter on asteroid 99942 Apophis, to maintain a more accurate track of this potentially hazardous 690-to-1,080-foot-diameter object. By doing that, we would obtain a very accurate orbit of this NEO, along with an early warning of whether it’s on a menacing course with Earth in the years to come.

We already know that the Apophis trajectory places it on an extremely close flyby of Earth in 2029—it is so close, in fact, that it will zip below our geosynchronous satellites. Earth’s gravitational tug on Apophis, some worry, may alter its course in such a way as to run into our planet in 2036. But the chance of that happening, experts say, is very, very slim.

My review of Apophis has been enlightening in several ways, specifically in picturing a rotating Earth orbit around the sun where the sun-Earth line is fixed. What an NEO does, if its semi-major axis is inside Earth: It does a series of loops around the inside of that circle, then comes back within the vicinity of Earth. Those set of loops are essentially the number of years before it comes back close to Earth.

By Apophis whisking past Earth in 2029, that gravity-assist pass is going to change this NEO so its semi-major axis is outside Earth. Until 2036, it will do a series of loops that are outside the circle and traveling in the opposite direction. In other words, Earth’s rotating coordinate frame is moving ahead of Apophis.

Simply, Apophis is going to be doing loop-the-loops, getting ahead of Earth, and then it’s going to buzz by Earth and do loop-the-loops outside of Earth’s orbit. That’s what the gravity swingby of planet Earth is doing to this NEO, and I was really amazed when I found that out.

It is a good lesson learned on what an asteroid and its orbit around the sun, or period, do in terms of its availability for a revisit by a robot or a human crew, which is not a constant. It is analogous to understanding some of the inertial cycler orbits that are necessary to sustain a long-term space program.

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