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Interstellar Boundary Explorer
Organisation NASA
Mission type Orbiter
Satellite of Earth
Orbital insertion date 2008-10-19, 18:21:00 UTC
Launch date 2008-10-19, 17:47:23 UTC
Carrier rocket L-1011 TriStar / Pegasus XL
Launch site Air-launch, near Kwajalein Atoll
Mission duration ~2 years
elapsed: 1 year, 2 months, and 27 days
COSPAR ID 2008-051A
Home page
Orbital elements
Eccentricity 0.0
Inclination 10.989999771118164°
Orbital period 6,604.0 minutes
Apoapsis 220,886.0 km
Periapsis 7,000.0 km
Orbits per day < 1

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. The IBEX satellite was launched with a Pegasus-XL rocket on October 19, 2008, at 17:47:23 UTC.[1] The nominal mission baseline duration will be two years to observe the entire solar system boundary.

The design and operation of the mission is being led by the Southwest Research Institute, with the Los Alamos National Laboratory and the Lockheed Martin Advanced Technology Center serving as co-investigator institutions responsible for the IBEX-Hi and IBEX-Lo sensors respectively. The Orbital Sciences Corporation manufactured the spacecraft bus and was the location for spacecraft environmental testing.

The IBEX satellite is a sun-oriented spin-stabilized spacecraft in orbit around the Earth.



IBEX Lo sensor

The heliospheric boundary of the Solar System will be imaged by measuring the location and magnitude of charge-exchange collisions occurring in all directions. This 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 their fields-of-view, a conversion surface to convert neutral hydrogen and oxygen into ions, an electrostatic analyzer (ESA) to suppress ultraviolet light and to select ions of a specific energy range, and a detector to count particles and identify the type of each ion. The IBEX-Hi instrument will record particle counts in a higher energy band than the IBEX-Lo does. The scientific payload also includes a Combined Electronics Unit (CEU) that controls the voltages on the collimator and the ESA, and it will read and record data from the particle detectors of each sensor.

Mission parameters

The IBEX satellite, initially launched into a highly-elliptical transfer orbit with a low perigee, used a solid fuel rocket motor as its final boost stage at apogee, in order to raise its perigee greatly and to achieve its desired high-altitude elliptical orbit.

The IBEX is in a highly-eccentric elliptical terrestrial orbit, which ranges from a perigee of about 8,000 kilometres (5,000 mi) to an apogee of about 300,000 kilometres (190,000 mi), that is, about three-quarters of the distance to the Moon. (These orbital numbers vary somewhat due to accumulated atmospheric drag around perigees, and because of gravitational perturbations from the Moon and other astronomical bodies.) This very high orbit allows the IBEX satellite to move out of the Earth's magnetosphere (the Van Allen Belts) when making sciencific observations. This extreme altitude is critical due to the amount of charged-particle interference that would occur while taking images while within the radiation belts. When within the magnetosphere of the Earth (70,000 kilometres/43,000 miles), the satellite will perform other functions, including telemetry downlinks.


IBEX logo, which features a profile of an ibex

The IBEX satellite was carried into outer space October 19, 2008, by a Pegasus XL rocket. The Pegasus rocket was released from a Lockheed L-1011 airplane that took off from Kwajalein Atoll in the Central Pacific Ocean. The air-drop occurred at 17:47:23 GMT[1] By launching from this site close to the Equator, the Pegasus rocket lifted as much as 35 pounds (16 kg) more mass to orbit than it would have with a launch from the Kennedy Space Center in Florida.[2]

The IBEX was mated to its Pegasus XL rocket at Vandenberg Air Force Base, California, and the combined vehicle was then suspended below the L-1011 mother airplane, and flown to Kwajalein, a several-hours-long flight.[3] The L-1011 arrived at Kwajalein Atoll on Sunday, Oct. 12.[4]

Data collection

IBEX is collecting Energetic neutral atom (ENA) emissions that are traveling through the solar system to Earth that cannot be measured by conventional telescopes. These ENAs are created on the boundary of our Solar System by the interactions between solar wind particles and interstellar medium particles.[5]

Initial astronomical results

The bright ribbon of ENA emission as seen in the IBEX map.

Initial data revealed a previously unpredicted "very narrow ribbon that is two to three times brighter than anything else in the sky."[6] Initial interpretations suggest that "the interstellar environment has far more influence on structuring the heliosphere than anyone previously believed"[5] "No one knows what is creating the ENA (energetic neutral atoms) ribbon, but everyone agrees that it means the textbook picture of the heliosphere—in which the solar system's enveloping pocket filled with the solar wind's charged particles is plowing through the onrushing "galactic wind" of the interstellar medium in the shape of a comet—is wrong."[7]


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