Explorer 2 (EXPLR2) was to be a repeat of the Explorer 1 mission. However, due to a failure in the rocket during launch, the spacecraft did not reach orbit.

Explorer 2 was launched from Cape Canaveral Air Force Station LC-26A in Florida on March 5, 1958 at 18:28 UTC, by a Jupiter-C launch vehicle. The Jupiter-C had its origins in the United States Army's Project Orbiter in 1954. The project was canceled in 1955, when the decision was made to proceed with Project Vanguard.

Following the launch of the Soviet Sputnik 1 on October 4, 1957, the Army Ballistic Missile Agency (ABMA) was directed to proceed with the launching of a satellite using the Jupiter-C, which had already been flight-tested in nose-cone re-entry tests for the Jupiter IRBM (intermediate-range ballistic missile). Working closely together, ABMA and Jet Propulsion Laboratory (JPL) completed the job of modifying the Jupiter-C and building Explorer 1 in 84 days.

Explorer 2 was equipped with a Geiger counter for the purposes of detecting cosmic rays. After Explorer 3, it was decided that the original Geiger counter had been overwhelmed by strong radiation coming from a belt of charged particles trapped in space by the Earth's magnetic field (see: Van Allen radiation belt). Explorer 2 was also equipped with a wire grid array and an acoustic detector for the purpose of micrometeorite detection.

Windows Internet Explorer (formerly Microsoft Internet Explorer, commonly abbreviated IE or MSIE) is a series of graphical web browsers developed by Microsoft and included as part of the Microsoft Windows line of operating systems, starting in 1995. It was first released as part of the add-on package Plus! for Windows 95 that year. Later versions were available as free downloads, or in service packs, and included in the OEM service releases of Windows 95 and later versions of Windows.

Internet Explorer is the second most widely used web browser, behind Google Chrome, which surpassed it in May 2012, attaining a peak of about 95% usage share during 2002 and 2003 with Internet Explorer 5 and Internet Explorer 6.^{[citation needed]} Since its peak of popularity, its usage share has been declining in the face of renewed competition from other web browsers, and is 34.27% as of January 2012^[update]. It had been slightly higher, 43.55% as of February 2011, just prior to the release of the current version. Microsoft spent over US$100 million per year on Internet Explorer in the late 1990s, with over 1000 people working on it by 1999.