Interplanetary Transport Network
Encyclopedia
Gravitation
Gravitation, or gravity, is a natural phenomenon by which physical bodies attract with a force proportional to their mass. Gravitation is most familiar as the agent that gives weight to objects with mass and causes them to fall to the ground when dropped...
ally determined pathways through the solar system
Solar System
The Solar System consists of the Sun and the astronomical objects gravitationally bound in orbit around it, all of which formed from the collapse of a giant molecular cloud approximately 4.6 billion years ago. The vast majority of the system's mass is in the Sun...
that require very little energy
Energy
In physics, energy is an indirectly observed quantity. It is often understood as the ability a physical system has to do work on other physical systems...
for an object to follow. The ITN makes particular use of Lagrange points as locations where trajectories through space
Outer space
Outer space is the void that exists between celestial bodies, including the Earth. It is not completely empty, but consists of a hard vacuum containing a low density of particles: predominantly a plasma of hydrogen and helium, as well as electromagnetic radiation, magnetic fields, and neutrinos....
are redirected using little or no energy. These points have the peculiar property of allowing objects to orbit
Orbit
In physics, an orbit is the gravitationally curved path of an object around a point in space, for example the orbit of a planet around the center of a star system, such as the Solar System...
around them, despite the absence of any material object therein. Although they use little energy, the transport can take a very long time.
History
The key to the Interplanetary Transport Network was investigating the exact nature of these winding paths near the Lagrange points. They were first investigated by Jules-Henri Poincaré in the 1890s. He noticed that the paths leading to and from any of these points would almost always settle, for a time, on the orbit around it. There are in fact an infiniteInfinity
Infinity is a concept in many fields, most predominantly mathematics and physics, that refers to a quantity without bound or end. People have developed various ideas throughout history about the nature of infinity...
number of paths taking one to the point and back away from it, and all of them require no energy to reach. When plotted, they form a tube with the orbit around the point at one end, a view which traces back to mathematicians Charles C. Conley and Richard P. McGehee in the 1960s. Theoretical work by Edward Belbruno
Edward Belbruno
Edward Belbruno is a mathematician whose interests are in celestial mechanics, dynamical systems, dynamical astronomy, and aerospace engineering....
in 1994 provided the first insight into the nature of the ITN between the Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...
and the Moon
Moon
The Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...
that was used by Hiten
Hiten
The Hiten Spacecraft , given the English name Celestial Maiden and known before launch as MUSES-A , part of the MUSES Program, was built by the Institute of Space and Astronautical Science of Japan and launched on January 24, 1990...
, Japan's first lunar probe. Beginning in 1997 Martin Lo
Martin Lo
Martin Lo is a spacecraft trajectory expert currently working for JPL.- Introduction :Martin has been a research scientist in the Navigation and Mission Design Section at the JPL since 1986...
, Shane D. Ross, and others wrote a series of papers identifying the mathematical basis and applying the technique to the Genesis solar wind sample return
Genesis (spacecraft)
The Genesis spacecraft was a NASA sample return probe which collected a sample of solar wind and returned it to Earth for analysis. It was the first NASA sample return mission to return material since the Apollo Program, and the first to return material from beyond the orbit of the Moon...
, along with Lunar and Jovian missions. They referred to an Interplanetary Superhighway (IPS)
As it turns out, it is very easy to transit from a path leading to the point to one leading back out. This makes sense, since the orbit is unstable, which implies one will eventually end up on one of the outbound paths after spending no energy at all. However, with careful calculation, one can pick which outbound path one wants. This turned out to be exciting, because many of these paths lead right by some interesting points in space, like the Earth's Moon or the Galilean moons
Galilean moons
The Galilean moons are the four moons of Jupiter discovered by Galileo Galilei in January 1610. They are the largest of the many moons of Jupiter and derive their names from the lovers of Zeus: Io, Europa, Ganymede and Callisto. Ganymede, Europa and Io participate in a 1:2:4 orbital resonance...
of Jupiter
Jupiter
Jupiter is the fifth planet from the Sun and the largest planet within the Solar System. It is a gas giant with mass one-thousandth that of the Sun but is two and a half times the mass of all the other planets in our Solar System combined. Jupiter is classified as a gas giant along with Saturn,...
. That means that for the cost of getting to the Earth–Sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
point, which is rather low, one can travel to a huge number of very interesting points for a low additional fuel
Fuel
Fuel is any material that stores energy that can later be extracted to perform mechanical work in a controlled manner. Most fuels used by humans undergo combustion, a redox reaction in which a combustible substance releases energy after it ignites and reacts with the oxygen in the air...
cost or even for free.
The transfers are so low-energy that they make travel to almost any point in the solar system possible. On the downside, these transfers are very slow, and only useful for automated probes. Nevertheless, they have already been used to transfer spacecraft out to the Earth-Sun point, a useful point for studying the Sun that was used in a number of recent missions, including the Genesis mission
Genesis (spacecraft)
The Genesis spacecraft was a NASA sample return probe which collected a sample of solar wind and returned it to Earth for analysis. It was the first NASA sample return mission to return material since the Apollo Program, and the first to return material from beyond the orbit of the Moon...
. The Solar and Heliospheric Observatory
Solar and Heliospheric Observatory
The Solar and Heliospheric Observatory is a spacecraft built by a European industrial consortium led by Matra Marconi Space that was launched on a Lockheed Martin Atlas IIAS launch vehicle on December 2, 1995 to study the Sun, and has discovered over 2100 comets. It began normal operations in May...
began operations at L1 in 1996. The network is also relevant to understanding solar system dynamics; Comet
Comet
A comet is an icy small Solar System body that, when close enough to the Sun, displays a visible coma and sometimes also a tail. These phenomena are both due to the effects of solar radiation and the solar wind upon the nucleus of the comet...
Shoemaker-Levy 9
Comet Shoemaker-Levy 9
Comet Shoemaker–Levy 9 was a comet that broke apart and collided with Jupiter in July 1994, providing the first direct observation of an extraterrestrial collision of solar system objects. This generated a large amount of coverage in the popular media, and the comet was closely observed by...
followed such a trajectory to collide with Jupiter.
Further explanation
In addition to orbits around Lagrange points, the rich dynamics that arise from the gravitational pull of more than one mass yield interesting trajectories, also known as low energy transfersLow energy transfers
A low energy transfer, or low energy trajectory, is a route in space which allows spacecraft to change orbits using very little fuel. These routes work in the Earth-Moon system and also in other systems, such as traveling between the satellites of Jupiter...
. For example, the gravity environment of the Sun-Earth-Moon system allows spacecraft to travel great distances on very little fuel, albeit on an often circuitous route. Launched in 1978, the ISEE-3 spacecraft was sent on a mission to orbit around one of the Lagrange points. The spacecraft was able to maneuver around the Earth's neighborhood using little fuel by taking advantage of the unique gravity environment. After the primary mission was completed, ISEE-3 went on to accomplish other goals, including a flight through the geomagnetic tail and a comet flyby. The mission was subsequently renamed the International Cometary Explorer
International Cometary Explorer
The International Cometary Explorer spacecraft was originally known as International Sun/Earth Explorer 3 satellite, launched August 12, 1978. It was part of the ISEE international cooperative program between NASA and ESRO/ESA to study the interaction between the Earth's magnetic field and the...
(ICE).
The first low energy transfer utilizing this network was the rescue of Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
's Hiten
Hiten
The Hiten Spacecraft , given the English name Celestial Maiden and known before launch as MUSES-A , part of the MUSES Program, was built by the Institute of Space and Astronautical Science of Japan and launched on January 24, 1990...
lunar mission in 1991. Another example of the use of the ITN was NASA
NASA
The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...
's recent Genesis mission, which orbited the Sun-Earth point for over two years collecting material, before being redirected to the Lagrange point, and finally redirected from there back to Earth. Most recently, SMART-1
SMART-1
SMART-1 was a Swedish-designed European Space Agency satellite that orbited around the Moon. It was launched on September 27, 2003 at 23:14 UTC from the Guiana Space Centre in Kourou, French Guiana. "SMART" stands for Small Missions for Advanced Research in Technology...
of the European Space Agency
European Space Agency
The European Space Agency , established in 1975, is an intergovernmental organisation dedicated to the exploration of space, currently with 18 member states...
used another low energy transfer from the ITN.
The ITN is based around a series of orbital paths predicted by chaos theory
Chaos theory
Chaos theory is a field of study in mathematics, with applications in several disciplines including physics, economics, biology, and philosophy. Chaos theory studies the behavior of dynamical systems that are highly sensitive to initial conditions, an effect which is popularly referred to as the...
and the restricted three-body problem leading to and from the unstable orbits around the Lagrange points – points in space where the gravity between various bodies balances with the centrifugal force of an object there. For any two bodies in which one body orbits around the other, such as a star/planet or planet/moon system, there are three such points, denoted through . For instance, the Earth-Moon point lies on a line between the two, where gravitational forces between them exactly balance with the centrifugal force of an object placed in orbit there. For two bodies whose ratio of masses exceeds 24.96, there are two additional stable points denoted as and . These five points have particularly low delta-v
Delta-v
In astrodynamics a Δv or delta-v is a scalar which takes units of speed. It is a measure of the amount of "effort" that is needed to change from one trajectory to another by making an orbital maneuver....
requirements, and appear to be the lowest-energy transfers possible, even lower than the common Hohmann transfer orbit
Hohmann transfer orbit
In orbital mechanics, the Hohmann transfer orbit is an elliptical orbit used to transfer between two circular orbits, typically both in the same plane....
that has dominated orbital navigation in the past.
Although the forces balance at these points, the first three points (the ones on the line between a certain large mass (e.g. a star
Star
A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...
) and a smaller, orbiting mass (e.g. a planet
Planet
A planet is a celestial body orbiting a star or stellar remnant that is massive enough to be rounded by its own gravity, is not massive enough to cause thermonuclear fusion, and has cleared its neighbouring region of planetesimals.The term planet is ancient, with ties to history, science,...
)) are not stable equilibrium
Mechanical equilibrium
A standard definition of static equilibrium is:This is a strict definition, and often the term "static equilibrium" is used in a more relaxed manner interchangeably with "mechanical equilibrium", as defined next....
points. If a spacecraft
Spacecraft
A spacecraft or spaceship is a craft or machine designed for spaceflight. Spacecraft are used for a variety of purposes, including communications, earth observation, meteorology, navigation, planetary exploration and transportation of humans and cargo....
placed at the Earth-Moon point is given even a slight nudge towards the Moon, for instance, the Moon's gravity will now be greater and the spacecraft will be pulled away from the point. The entire system is in motion, so the spacecraft will not actually hit the Moon, but will travel in a winding path, off into space. There is, however, a semi-stable orbit around each of these points. The orbits for two of the points, and , are stable, but the orbits for through are stable only on the order of month
Month
A month is a unit of time, used with calendars, which was first used and invented in Mesopotamia, as a natural period related to the motion of the Moon; month and Moon are cognates. The traditional concept arose with the cycle of moon phases; such months are synodic months and last approximately...
s.
See also
- Gravitational slingshotGravitational slingshotIn orbital mechanics and aerospace engineering, a gravitational slingshot, gravity assist maneuver, or swing-by is the use of the relative movement and gravity of a planet or other celestial body to alter the path and speed of a spacecraft, typically in order to save propellant, time, and expense...
- Gravitational keyholeGravitational keyholeA gravitational keyhole, or resonance keyhole, is a small region of space that could alter the course of a passing asteroid due to a planet's gravity in a way that could cause such an asteroid to collide with that planet on its next orbital pass...
- Low energy transfersLow energy transfersA low energy transfer, or low energy trajectory, is a route in space which allows spacecraft to change orbits using very little fuel. These routes work in the Earth-Moon system and also in other systems, such as traveling between the satellites of Jupiter...
- Orbital mechanics
- Interplanetary spaceflight
- Hill sphereHill sphereAn astronomical body's Hill sphere is the region in which it dominates the attraction of satellites. To be retained by a planet, a moon must have an orbit that lies within the planet's Hill sphere. That moon would, in turn, have a Hill sphere of its own...
- Horseshoe orbitHorseshoe orbitA horseshoe orbit is a type of co-orbital motion of a small orbiting body relative to a larger orbiting body . The orbital period of the smaller body is very nearly the same as for the larger body, and its path appears to have a horseshoe shape in a rotating reference frame as viewed from the...
External links
- "The Interplanetary Transport Network" American Scientist, May-June 2006 (Subscription)
- "Ride the celestial subway" New Scientist, 27 March 2006
- "Tube Route" Science, 18 November 2005
- "Navigating Celestial Currents" Science News, 18 April 2005
- "Next Exit 0.5 Million Kilometers" Engineering and Science, 2002
- "Mathematics Unites The Heavens And The Atom" Space Daily, 28 September 2005
- "Asteroids Lost in Space" Physical Review Focus, 14 June 2002
- Interplanetary Transport Network lecture by Shane D. Ross
- "Cylindrical manifolds and tube dynamics in the restricted three-body problem" - PhD dissertation by Shane D. Ross
- Capture Dynamics and Chaotic Motions in Celestial Mechanics: With the Construction of Low Energy Transfers - A mathematical analysis of aspects of the ITN, Edward BelbrunoEdward BelbrunoEdward Belbruno is a mathematician whose interests are in celestial mechanics, dynamical systems, dynamical astronomy, and aerospace engineering....
- The Dynamical Mechanism of Ballistic Lunar Capture Transfers in the Four-Body Problem from the Perspective of Invariant Manifolds and Hill's Regions by Edward BelbrunoEdward BelbrunoEdward Belbruno is a mathematician whose interests are in celestial mechanics, dynamical systems, dynamical astronomy, and aerospace engineering....
- Dynamical Systems, the Three-Body Problem, and Space Mission Design, by Wang Sang Koon, Martin W. Lo, Jerrold E. Marsden, Shane D. Ross (book available as PDF). ISBN 978-0-615-24095-4
- 2007-10-08 audio interview with Ed Belbruno on low-energy transfer