Interstellar Boundary Explorer (IBEX) - Mission
The Interstellar Boundary Explorer (IBEX) is a NASA satellite that will make the first map of the boundary between the Solar System and interstellar space. The mission is part of NASA's Small Explorer program. IBEX was launched on a Pegasus-XL rocket on October 19, 2008, at 17:47:23 GMT. The nominal mission baseline duration will be two years to image the entire solar system boundary.
The heliospheric* boundary of the solar system will be imaged by measuring the location and magnitude of charge-exchange collisions occurring in all directions that will ultimately yield a map of the termination shock** of the solar wind. The satellite's payload consists of two energetic neutral atom (ENA) imagers, IBEX-Hi and IBEX-Lo. Each of these sensors consists of a collimator that limits field of view, a conversion surface to convert neutral hydrogen and oxygen into ions, an electrostatic analyzer to suppress ultraviolet light and select ions of a specific energy range, and a detector to identify particle counts and the identity of each ion. IBEX-Hi will record particle counts at a higher energy band than IBEX-Lo. The payload also includes a Combined Electronics Unit (CEU) that controls the voltages on the collimator and ESA and will read and record data from the particle detectors of each sensor.
The satellite is a sun-oriented spinner in a highly-eccentric elliptical Earth orbit, ranging from 5,000 kilometres (3,100 mi) at perigee to 250,000–300,000 kilometres (160,000–190,000 mi) or three-quarters the distance to the moon at apogee and allowing it to move out of the Earth's magnetosphere when performing science operations. This is critical due to the large degree of interference that would occur while imaging within the magnetosphere. When within the magnetosphere of the Earth (70,000 kilometres/43,000 miles), the satellite will perform housekeeping operations such as downlink. The spacecraft used a solid fuel rocket motor as a final boost stage to achieve this elliptical orbit.
* The heliosphere is a bubble in space "blown" into the interstellar medium (the hydrogen and helium gas that permeates the galaxy) by the solar wind. Although electrically neutral atoms from interstellar space can penetrate this bubble, virtually all of the material in the heliosphere emanates from the Sun itself.
** The termination shock is the point in the heliosphere where the solar wind slows down to subsonic speed (with respect to the star) due to interactions with the local interstellar medium. This causes compression, heating, and a change in the magnetic field. In our solar system the termination shock is believed to be 75 to 90 astronomical units from the Sun. In 2007, Voyager II passed through the sun's termination shock.[6] Voyager II actually passed through the termination shock five times because the shock boundary fluctuates in its distance from the sun as a result of fluctuations in solar flare activity; i.e., changes in the ejections of gas and dust from the sun.
The shock arises because solar wind particles are emitted from stars at about 400 km/s, while the speed of sound (in the interstellar medium) is about 100 km/s. (The exact speed depends on the density, which fluctuates considerably.) The interstellar medium, although very low in density, nonetheless has a constant pressure associated with it; the pressure from the solar wind decreases with the square of the distance from the star. As one moves far enough away from the star, the pressure from the interstellar medium becomes sufficient to slow the solar wind down to below its speed of sound; this causes a shock wave.
The heliospheric* boundary of the solar system will be imaged by measuring the location and magnitude of charge-exchange collisions occurring in all directions that will ultimately yield a map of the termination shock** of the solar wind. The satellite's payload consists of two energetic neutral atom (ENA) imagers, IBEX-Hi and IBEX-Lo. Each of these sensors consists of a collimator that limits field of view, a conversion surface to convert neutral hydrogen and oxygen into ions, an electrostatic analyzer to suppress ultraviolet light and select ions of a specific energy range, and a detector to identify particle counts and the identity of each ion. IBEX-Hi will record particle counts at a higher energy band than IBEX-Lo. The payload also includes a Combined Electronics Unit (CEU) that controls the voltages on the collimator and ESA and will read and record data from the particle detectors of each sensor.
The satellite is a sun-oriented spinner in a highly-eccentric elliptical Earth orbit, ranging from 5,000 kilometres (3,100 mi) at perigee to 250,000–300,000 kilometres (160,000–190,000 mi) or three-quarters the distance to the moon at apogee and allowing it to move out of the Earth's magnetosphere when performing science operations. This is critical due to the large degree of interference that would occur while imaging within the magnetosphere. When within the magnetosphere of the Earth (70,000 kilometres/43,000 miles), the satellite will perform housekeeping operations such as downlink. The spacecraft used a solid fuel rocket motor as a final boost stage to achieve this elliptical orbit.
* The heliosphere is a bubble in space "blown" into the interstellar medium (the hydrogen and helium gas that permeates the galaxy) by the solar wind. Although electrically neutral atoms from interstellar space can penetrate this bubble, virtually all of the material in the heliosphere emanates from the Sun itself.
** The termination shock is the point in the heliosphere where the solar wind slows down to subsonic speed (with respect to the star) due to interactions with the local interstellar medium. This causes compression, heating, and a change in the magnetic field. In our solar system the termination shock is believed to be 75 to 90 astronomical units from the Sun. In 2007, Voyager II passed through the sun's termination shock.[6] Voyager II actually passed through the termination shock five times because the shock boundary fluctuates in its distance from the sun as a result of fluctuations in solar flare activity; i.e., changes in the ejections of gas and dust from the sun.
The shock arises because solar wind particles are emitted from stars at about 400 km/s, while the speed of sound (in the interstellar medium) is about 100 km/s. (The exact speed depends on the density, which fluctuates considerably.) The interstellar medium, although very low in density, nonetheless has a constant pressure associated with it; the pressure from the solar wind decreases with the square of the distance from the star. As one moves far enough away from the star, the pressure from the interstellar medium becomes sufficient to slow the solar wind down to below its speed of sound; this causes a shock wave.
