IBEX launched via Orbital’s Pegasus XL

by Chris Bergin

NASA’s Interstellar Boundary Explorer (IBEX) spacecraft has been launched via an Orbital Sciences Pegasus XL launch vehicle on Sunday, after it was released by its L-1011 carrier aircraft at around 1:44pm EDT.


With all the interest surrounding SpaceX’s Falcon I launch vehicle of late, many forget that Pegasus was the world’s first privately developed space launch vehicle. Its maiden 1990 mission marked the first all-new, unmanned space launch vehicle developed in the US in more than 20 years.

Other landmarks included the Pegasus being the first winged vehicle to accelerate to eight times the speed of sound, and the first air-launched rocket to place satellites into orbit, using its carrier aircraft as an ‘air breathing reusable first stage.’

The three-stage Pegasus is used by commercial, government and international customers to deploy small satellites weighing up to 1,000 pounds into low-Earth orbit.

Pegasus is carried aloft by the ‘Stargazer’ L-1011 aircraft to approximately 40,000 feet over open ocean, where it is released, free-falls in a horizontal position for five seconds, before igniting its first stage rocket motor.

With the aerodynamic lift generated by its unique delta-shaped wing, Pegasus typically delivers satellites into orbit in a little over 10 minutes, which it has done 39 times before – making it the world’s leading small launch vehicle.

At T+78 seconds, the Orion 50S XL first stage motor burns out ahead of a ballistic coast period prior to shedding its wings and expended first stage. The Orion 50 XL second stage will then fire at T+93 seconds for the push to orbit, burning out at T+2 mins, 47 seconds.

Following a short coast phase, the Orion 38 third stage motor ignites at T+5 mins, 14 seconds for 68 seconds to deliver the IBEX spacecraft into a temporary 125-mile circular parking orbit.

IBEX is then “spun up” to 60 rpm at T+7 mins, 47 seconds, ahead of spacecraft separation at T+8 mins, 22 seconds, which will mark the 40th launch for Pegasus.

Orbital’s L-1011 aircraft picked up the integrated Pegasus XL vehicle from Vandenberg Air Force Base in Californian last week, before the duo arrived at the Reagan Test Site at Kwajalein Atoll in the South Pacific. NASA is providing live coverage of the launch – see live coverage link above.

The IBEX spacecraft is designed to image global interactions at the outer reaches of the solar system. The spacecraft has its own additional solid rocket motor and internal propulsion system, utilized to transport the spacecraft to its final high-altitude orbit of around 200,000 miles.

The $169m IBEX mission was developed by Southwest Research Institute with a national and international team of partners. NASA’s Goddard Space Flight Center manages the Explorers Program for the Science Mission Directorate.

IBEX will use a pair of energetic neutral atom cameras to image interactions between the million mile-per-hour solar wind continually blown out by the Sun and the low-density material between the stars, known as the interstellar medium – interactions never before imaged.

The spacecraft begins imaging the edge of the solar system within a couple of weeks after it reaches final orbit. Every six months, the spacecraft will complete an all-sky map of the interstellar boundaries, expected to reveal much about our home in the galaxy.

“The IBEX mission will provide a much deeper understanding of the Sun’s interaction with the galaxy and will also address a serious challenge facing manned exploration by studying the region that shields us from the majority of galactic cosmic ray radiation,” noted IBEX principal investigator David McComas.

Other spacecraft have continued the exploration of the interstellar boundary region. Recently, a pair of NASA sun-focused satellites, the Solar Terrestrial Relations Observatory mission, detected a higher-energy version of the particles IBEX will observe in the heliosphere.

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