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NASA - IBEX Q and A
July 25, 2008
IBEXArtist's impression of IBEX exploring the edge of our solar system. Credit: NASA GSFC.
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> Watch video about IBEX

What is IBEX?

IBEX is a small explorer NASA mission to map the boundary of the solar system. The acronym IBEX stands for Interstellar Boundary EXplorer.

The IBEX spacecraft is a small satellite the size of a bus tire. IBEX will observe the solar system Boundary while in orbit around Earth. It has "telescopes" on the spacecraft that will look out towards the edge of the solar system. However, these telescopes are different than most telescopes. They collect particles instead of light. These particles are called energetic neutral atoms (ENAs). The ENAs will provide information about the solar system's boundary by traveling toward Earth from beyond the orbit of Pluto. The particles travel for as little as a month to up to 11 years to complete the journey. By collecting these particles, scientists can make the first map of the boundary of our solar system. This boundary is created by the interaction between the solar wind and the interstellar medium. The solar wind streams out into space and carves out a protective bubble around the solar system called the heliosphere.

How Does IBEX study the boundary of the solar system?

Solar system boundariesArtist's impression of our solar system's boundaries. Credit: NASA GSFC.
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> Watch video about the solar system's boundaries

Unlike many satellites in space that collect light, IBEX collects particles. These particles come from the boundary of the solar system and beyond - from the interstellar medium. IBEX has two sensors that collect particles as the satellite orbits the Earth. The satellite spins as it orbits so that over the course of six months, each sensor has the opportunity to collect particles from every part of the sky. As they collect the particles, the sensors and spacecraft keep track of the area the particles came from, the time they entered the sensor, the mass of the particles, and the amount of energy each particle has. This allows the science team to build a map of how many particles of each energy came from each direction in the sky.

By analyzing the map, the team of scientists can determine what the interaction of the solar wind and interstellar medium is like in all of the areas of the protective bubble around the solar system. For example, scientists are trying to find out if there are some areas where the interstellar medium stops the solar wind from flowing outward more quickly (like slamming on the brakes) than other places (where a slow gradual stop may occur.) Also, scientists are trying to determine the overall shape of the bubble which may be affected by differences in density, and magnetic fields in the interstellar medium.

How will IBEX get into space?
Rocket launch

Building the PegasusIn Building 1555 at Vandenberg Air Force Base, workers help guide the fillet on top of the Pegasus XL launch vehicle. Photo credit: NASA
> About IBEX's launch

The L-1011 aircraft is seen from the distance above the clouds. In a close-up on the aircraft, the Pegasus rocket is mated to the underbelly of the plane. The Pegasus rocket separates from the airplane, dropping away from the craft through the atmosphere. After several seconds the rocket fires propelling the rocket into a high altitude orbit. A smoky tail is left trailing behind the rocket's path.

IBEX will begin its ride to space in 2008, when it launches from Kwajalein Island, Marshall Islands. An airplane called an L-1011 will take a Pegasus rocket to high altitude. Then, the Pegasus rocket will fire its own rockets to propel it, and the IBEX spacecraft, into space. The IBEX satellite will climb into an orbit that goes 5/6 of the way to the Moon. This orbit is very high, which allows the satellite to spend much of the time out of the Earth's magnetosphere, which can interfere with its observations. Even though this orbit is high, it is still very far from the solar system boundary that it is measuring.

How will IBEX communicate data?

IBEX will complete one orbit every five to eight days, depending upon conditions at launch. Each orbit, there is a period of time when the spacecraft is inside Earth's magnetosphere. This is an ideal time to communicate with Earth because, being close to the Earth, it does not take a lot of power to send signals back and forth. It uses antennae that are attached to the outside of the spacecraft to send radio signals to receivers on Earth. Due to the rotation of the Earth each day, the IBEX team needs a global network of receivers so that no matter how the satellite and Earth are lined up, there is a receiver available to accept the signal. IBEX has partnered with the Universal Space Network, which is designed to arrange receiving communications from many other missions and satellites. IBEX is never further away from Earth than the Moon, so it takes a second or less for signals to travel between the spacecraft and Earth.

However, IBEX data transfer rates are slow compared with other telescopes due to the nature of the data it collects. IBEX does not need a "high speed" connection, since it only has the opportunity to collect up to a few particles per minute. Communication from the satellite to the ground is 20 times slower than a typical home cable modem (320,000 bits per second,) and from the ground to the satellite only 2,000 bits per second, which is 250 times slower! Once the signal is collected by the receivers on Earth it is carried over the internet to Mission Control Center in Dulles, VA and to the IBEX Science Operation Center in San Antonio, TX.
 

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