Show #29
Title: Carrying the 1's Along Gravitational Highways
Written By: Aaron 
Voices: Pamela & Travis 
Castdate: 051004

// DRAFT SCRIPT - MAY NOT BE FINAL RECORDING SCRIPT //

Pamela: Welcome to another episode of Slacker Astronomy. Each week we bring you a recent news event in the world of astronomy. And when there is nothing to report, we'll continue our protest against the indiscriminent use of dihydrogen monoxide in our swimming pools.
	(overly dramatic - shatner style)
Travis: Think of the children!!
Pamela:	My God! How long will we allow this to go on?!?
Travis:	(charlton heston style) And we call ourselves civilized...
Pamela: (cheerful bunny type) But, we do have something to talk about this week so we can forget about the horrible effects of dihydrogen monoxide, for about 5 minutes at least. 
Travis: Let's talk about gravity - the scale industry's best friend and a woman's worst enemy.
Pamela:	Gravity is usually considered by the lay person to be a pretty weak force.
Travis:	Not only weak, it is boring. It pulls you down. So what? Big whoop. That's nothing compared to the forces of nature, forces of change, the air force, task forces, the light and dark side of the force...
Pamela: Let's stick with the physical forces.
Travis: Okay, gravity may be boring, but it gets points for being consistent. Everything in the Universe has a gravitational pull on everything else. For most things, this pull is so small as to not be measureable. But in our solar system, gravity is the most influential force when it comes to travelling in space.
Pamela:	Since everything in our solar system has a gravitational influence on everything else, calculating a flight plan gets very complicated. For example, when going to the Moon one must take into account the gravity of the Earth, Moon and the Sun. And if you plan to stay in orbit for a very long time, then the gravitational pull of Jupiter also has to be considered.
Travis: As one travels further and longer, the gravitational calculations needed in order to steer the spacecraft get more and more advanced. Eventually they reach a point of chaos when the direction of the spacecraft can no longer be predicted.
Pamela: So mathematicians, physicists and astronomers have been teaming up for a while to conquer this problem, or at least mitigate its effects by being able to predict further and further out. Recently, chemists also joined the fray and together a remarkable discovery was made.
Travis: On large scales, it seems like the tangle of gravitational fields in the solar system resembles what happens when atoms move from one molecule to the next, referred to as a transition state. In fact, the discovers say the parallel is, quote, near perfect, unquote. What they mean is that equations used to understand the gravitational fields in the solar system are the same as the ones that apply to atoms going through a transition state.
Pamela: This is quite a shock. Why would the mathematical description of a complex gravitational system be identical to the mathematical description of atoms changing from one molecule to the next? There is no obvious connection. Yet there it is, in the math.
Travis:	Assuming they remembered the carry the one.
Pamela: Well this is published in the October, 2005 issue of the Notices of the American Mathematical Society. So at least some referees must have looked at this. And the discovery is also built upon some solid and tested understandings of both gravity and chemistry.
Travis: I'm just saying... a one missing here and a two missing there, pretty soon the equation falls apart. Who really understands this enough to check?
Pamela: At some point there is a level of faith required. 
Travis: Like my religious belief in the flying spaghetti monster.
Pamela: Well, more like faith that is earned. In journals like this their reputation is built on the success of their articles.  This is a well respected journal that guards its quality. Sure, things sometimes go wrong. But more often than not, time proves the articles correct. So we have faith in the odds, that this article will be correct as well. 
Travis: And if not, you can bet a hungry pack of competing scientists will let the world know soon enough.
Pamela: Market forces take care of themselves in research as well as economics.
Travis: Too bad they don't work in gasoline prices.
Pamela: This seems to be a neat, clean cut discovery by a team that was really looking at a problem with wide open eyes and thinking outside of their own areas of expertise.
Travis: Let's give a real world example of where this unity takes shape. 
Pamela: Okay, take Jupiter. There are a group of neat comets that orbit the Sun near Jupiter. One of them is called Oterma, discovered in 1942 by a Finnish astronomer. Oterma's orbit around the Sun shifts back and forth over time across the orbit of Jupiter.
Travis: So sometimes Oterma is inside Jupiter's orbit and sometimes it is outside Jupiter's orbit. Shoemaker-Levy 9 also had a similar orbit and, yes, Oterma is expected to eventually slam into Jupiter as well.
Pamela: When Oterma is on the inside of Jupiter, it's orbit resonates with Jupter at 3 to 2. That means it orbits the Sun 3 times for every 2 orbits of Jupiter. When it moves back beyond Jupiter, this resonance flips and Jupiter orbits the sun 3 times for every 2 orbits of Oterma.
Travis: The transition of the two resonances is described by math way too complex for Slacker Astronomy to understand, much less try to explain. But the equations used, part of the Hamiltonian Restricted 3 Body Problem, are the same ones used to explain atomic phenomenon such as ionization and the transport of electrons across atomic transition states. 
Pamela: Specifically, the equations address what happens in the bottleneck of such systems. In this case, as the comet moves from one orbit to another and is temporarily captured by Jupiter. In the case of atomic physics, it explains how highly excited Rydberg electrons move from the orbit of one atom to the next.
Travis: This has been tested in space. NASA's Genesis spacecraft flew around the Sun collecting samples of the solar wind. It's orbit is very complex and could only be computed using these equations. 
Pamela: The equations illustrate a path through the solar system between different Lagrange points. Lagrangian points, aka L points, are places in the solar system where objects can be stationary in respect to two other bodies.
Travis: So there are tube shaped highways in the solar system between these L points. Putting a spacecraft in these tubes at certain angles can save the spacecraft tremendous energy while travelling through the solar system. Less internally produced energy means less weight, meaning lower cost and/or more science instruments.
Pamela: These equations also help explain the motion of dangerous near Earth asteroids and comets who are being influenced by the Sun, Earth, Moon and Jupiter. 
Travis: Maybe we can use them to explain Boston traffic patterns.
Pamela: Anyone who can do that will win the Nobel Prize.
Travis: For Physics?
Pamela: For Peace!
Travis: So in summary, a team of physicists, astronomers, chemists and mathematicians have found that equations that govern electrons in transition states of atoms are nearly identical to equations that govern certain small bodies in our solar system and can be used to help plan spacecraft trips in the future.
Pamela: NASA is already planning possible follow up missions for Genesis which would use the same technique to design its orbit while the mathematician, physics and chemistry communities continue to improve upon the equations. 
Travis: And Slacker Astronomy will work on the traffic problem using some chalk, our trusty abbacus, and our 20 fingers and toes.
Pamela :While we're talking about gravity, let's explain how gravitational assist works since it is used so much in science fiction. 
Travis: Gravitational assist is also known as the slingshot effect, slingshot maneuver or any number of variations on the theme. It is a technique used by spacecraft mission planners to change the velocity of spacecraft by using the gravitational pull of other planets.
Pamela: When a spacecraft approaches a planet, it speeds up as the planet's gravity pulls it in. Then, as the spacecraft passes the planet, the  same gravity slows it down. In the end the effect cancels itself out.
Travis: However, if a spacecraft passes very closely behind the planet, then it is also pulled along the planet's orbit because the planet and its center   of gravity is also moving. This speeds up the spacecraft and also changes its direction a bit into the direction of the planet's movement.
Pamela: If a spacecraft passes very closely in front of the planet, then it *loses* speed and changes direction *away* from the direction of the planet's movement. 
Travis: Mission planners use the technique to slow down spacecraft going into the inner solar system from Earth and to speed up spacecraft going into the outer solar system.
Pamela: There is also an additional kick the spacecraft can receive from gravitational assist. If the engines are fired when the spacecraft is nearest the planet, and its velocity is at its greatest, then the extra kinematic motion delivered by the engine is increased. 
Travis:Thus careful firing of the engines can save precious fuel. In fact Jupiter's gravitational field  can triple the efficiency of an engine if used correctly.
Pamela: And of course there is a price to pay thanks to the law of conservation of energy. The planet must slow down, but for a miniscule amount. For example, the Earth gave the Galileo spacecraft a speed boost of around 20,000 miles per hour in two passes in 1990 and 1992. To pay for this, the Earth itself slowed down in its orbit by 5 billionths of an inch per year.
Travis: Bet you didn't feel it when it happened!
Pamela: Thanks for listening to another episode of Slacker Astronomy. Show notes about this topic are available at slackerastronomy.org. Send feedback to info@slackerastronomy.org. 
Travis: Also check out our Slacker Astronomy Extra feed. We are in the middle of posting two new shows to the feed. One is our latest chit chat show and the other is a sound seeing tour from a star party with a talk about how amateurs without telescopes can help professional astronomers. Subscribe via iTunes or on our web page.
Pamela: And please tell your friends!
Travis: On behalf of Pamela and our writer Aaron, I'm Travis Searle. Thanks for listening.
Pamela: Clear skies and clear bandwidth, this has been a podcast for fun, for you, for the voices in our heads.