Interstellar Boundary Explorer

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"IBEX" redirects here. For other uses, see Ibex (disambiguation).
Interstellar Boundary Explorer
IBEX spacecraft.jpg
Names Explorer 91
Mission type Astronomy
Operator NASA
COSPAR ID 2008-051A
SATCAT № 33401
Mission duration Planned: 2 years
Elapsed: 7 years, 9 months and 5 days
Spacecraft properties
Bus MicroStar-1
Manufacturer Orbital Sciences
Launch mass 107 kg (236 lb)[1]
Dry mass 80 kg (176 lb)[1]
Payload mass 26 kg (57 lb)[1]
Dimensions 95 × 58 cm (37 × 23 in)[1]
Power 66 W (116 W max)[1]
Start of mission
Launch date October 19, 2008, 17:47:23 (2008-10-19UTC17:47:23Z) UTC
Rocket Pegasus XL
Launch site Stargazer, Bucholz
Contractor Orbital Sciences
Entered service January 2009[1]
Orbital parameters
Reference system Geocentric
Regime High Earth
Semi-major axis 182,794 km (113,583 mi)
Eccentricity 0.62629
Perigee 61,941.1 km (38,488.4 mi)
Apogee 290,906.2 km (180,760.7 mi)
Inclination 16.8631°
Period 12,963.0 min
RAAN 95.1780°
Argument of perigee 77.2187°
Mean anomaly 357.889°
Mean motion 0.11108 rev/day
Epoch August 15, 2015, 08:48:38 UTC[2]
Revolution number 289

Explorers program
← 90: AIM 92: WISE

Interstellar Boundary Explorer (IBEX) is a NASA satellite that is making a map of the boundary between the Solar System and interstellar space. The mission is part of NASA's Small Explorer program and launched with a Pegasus-XL rocket on October 19, 2008.[3]

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 nominal mission baseline duration was two years to observe the entire Solar System boundary. This was completed by 2011 and its mission was extended to 2013 to continue observations.[4]

IBEX is in a Sun-oriented spin-stabilized orbit around the Earth.[5] In June 2011, IBEX was shifted to a new more efficient orbit.[6] It does not come as close to the Moon in the new orbit, and expends less fuel to maintain its position.[6]


IBEX Lo sensor

The heliospheric boundary of the Solar System is being 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 is recording 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 reads and records data from the particle detectors of each sensor.

Mission parameters[edit]

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.

IBEX is in a highly-eccentric elliptical terrestrial orbit, which ranges from a perigee of about 60,000 km (37,000 mi) to an apogee of about 290,000 km (180,000 mi);[2] that is, about 80% of the distance to the Moon. Its original orbit was about 7,000 by 320,000 km (4,300 by 198,800 mi),[5] which has changed primarily due to an intentional adjustment to prolong the spacecraft's useful life (see Orbit adjusted below).

This very high orbit allows the IBEX satellite to move out of the Earth's magnetosphere when making scientific observations. This extreme altitude is critical due to the amount of charged-particle interference that would occur while taking measurements within the magnetosphere. When within the magnetosphere of the Earth (70,000 km or 43,000 mi), the satellite also performs other functions, including telemetry downlinks.[citation needed]


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 Stargazer airplane that took off from Kwajalein Atoll in the Central Pacific Ocean. The air-drop occurred at 17:47:23 UTC.[3] By launching from this site close to the Equator, the Pegasus rocket lifted as much as 16 kg (35 lb) more mass to orbit than it would have with a launch from the Kennedy Space Center in Florida.[7]

The IBEX was mated to its Pegasus XL rocket at Vandenberg Air Force Base, California, and the combined vehicle was then suspended below the Stargazer mother airplane, and flown to Kwajalein, a several-hours-long flight.[8] The L-1011 arrived at Kwajalein Atoll on Sunday, October 12, 2008.[9]

Orbit adjusted[edit]

In June 2011 IBEX shifted to a new orbit that raised its perigee to more than 30,000 kilometres (19,000 mi). The new orbit avoids taking the spacecraft too close to the Moon, whose gravity can negatively affect IBEX's orbit. Now the spacecraft uses less fuel to maintain a stable orbit, increasing its useful lifespan to more than 40 years.[6]

Data collection[edit]

The ribbon of ENA emissions seen in the IBEX map

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.[10]

On the average IBEX-Hi detects about 500 particles per day, and IBEX-Lo, less than 100.[11] By 2012, over 100 scientific papers related to IBEX were published, described by the PI as "an incredible scientific harvest".[11]

Astronomical results[edit]

Animation illustrating IBEX's collection of data on neutral atoms at the boundary of the Solar System.

Initial data revealed a previously unpredicted "very narrow ribbon that is two to three times brighter than anything else in the sky".[12] Initial interpretations suggest that "the interstellar environment has far more influence on structuring the heliosphere than anyone previously believed".[10] It is unknown what is creating the ENA (energetic neutral atoms) ribbon.[13] The Sun is currently traveling through the Local Interstellar Cloud, and the heliosphere's size and shape are key factors in determining its shielding power from cosmic rays. Should IBEX detect changes in the shape of the ribbon, that could show how the heliosphere is interacting with the Local Fluff.[14] It has also observed ENAs from the Earth's magnetosphere.[4]

In October 2010, significant changes were detected in the ribbon after six months, based on the second set of IBEX observations.[15]

It went on to detect neutral atoms from outside the Solar System, which were found to differ in composition from the Sun.[16] IBEX discovered the Sun has no bow shock.[16] The speed of the heliosphere in relation to the local cloud is thought to be 23 kilometres per second (52,000 mph), instead of previous estimate of 26 km/s (59,000 mph).[16] Those speeds equate to 25% less pressure on the Sun's heliosphere than previously thought.[16] The velocity of the LISM (Local Interstellar Medium) relative to the Sun's was previously measured to be 26.3 km/s (59,000 mph) by Ulysses, whereas IBEX measured it at 23.2 km/s (52,000 mph).[17]

In July 2013, IBEX results revealed a 4-lobed tail on the Solar System's heliosphere.[18] The spacecraft has also imaged stellar-wind bubbles, called "astrospheres," around other stars, as well as the tails from these astrospheres.[19]

Data transfer rate[edit]

Compared to other space observatories, IBEX has a low data transfer rate due to the limited requirements of the mission.[20]

"... 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."

— NASA's IBEX Q and A[20]


  1. ^ a b c d e f "IBEX (Interstellar Boundary Explorer)". eoPortal. European Space Agency. Retrieved August 13, 2015. 
  2. ^ a b "IBEX Satellite details 2008-051A NORAD 33401". August 13, 2015. Retrieved August 13, 2015. 
  3. ^ a b Ray, Justin (October 19, 2008). "Mission Status Center: Pegasus/IBEX". Spaceflight Now. Retrieved November 27, 2009. 
  4. ^ a b IBEX - Update Archive
  5. ^ a b "Fact Sheet: IBEX" (PDF). FS001_06_3695. Retrieved April 27, 2015. 
  6. ^ a b c McComas, Dave (November 14, 2011). "IBEX Orbit-Raising Maneuver". Retrieved March 1, 2012. 
  7. ^ McComas, Dave (November 15, 2006). "IBEX November 2006". Southwest Research Institute. Retrieved November 19, 2009. 
  8. ^ "Expendable Launch Vehicle Status Report". NASA KSC. October 3, 2008. 
  9. ^ "Interstellar Boundary Explorer Mission". NASA. October 14, 2008. 
  10. ^ a b Dave McComas (October 15, 2009). "IBEX: Interstellar Boundary Explorer:". NASA Southwest Research Institute. Retrieved September 5, 2010. 
  11. ^ a b IBEX Update October 15, 2012
  12. ^ Southwest Research Institute (October 16, 2009). "First IBEX Maps Reveal Fascinating Interactions Occurring At The Edge Of The Solar System". ScienceDaily. Retrieved November 27, 2009. 
  13. ^ Richard A. Kerr (October 16, 2009). "Tying Up the Solar System With a Ribbon of Charged Particles". Science 326 (5951). pp. 350–351. Retrieved November 27, 2009. 
  14. ^ Tony Phillips (January 25, 2010). "Mysterious band of particles holds clues to Solar System's future". Science@NASA. Retrieved September 5, 2010. 
  15. ^ NASA news release (October 2, 2010). "The Ever-Changing Edge of the Solar System". Astrobiology Magazine. Retrieved November 8, 2010. 
  16. ^ a b c d NASA - IBEX Reveals a Missing Boundary At the Edge Of the Solar System
  17. ^ No Shocks for This Bow: IBEX Says We’re Wrong
  18. ^ Fox, Karen C. (July 10, 2013). "NASA’s IBEX Provides First View Of the Solar System’s Tail". NASA. Retrieved August 13, 2015. 
  19. ^ "July 2013: IBEX Observes the Solar System's Heliotail". Southwest Research Institute. July 10, 2013. Retrieved August 13, 2015. 
  20. ^ a b "IBEX Q and A". NASA. July 25, 2008. Retrieved May 14, 2015. 

Further reading[edit]

  • McComas, D.; Allegrini, F.; Bartolone, L.; Bochsler, P.; Bzowski, M.; et al. (September 2005). The Interstellar Boundary Explorer (IBEX) Mission. Solar Wind 11 / SOHO 16 - Connecting Sun and Heliosphere. June 12-17, 2005. Whistler, British Columbia, Canada. Bibcode:2005ESASP.592..689M. 

External links[edit]