National Aeronautics and Space Administration Logo
Follow this link to skip to the main content NASA Banner
Solar System Exploration
Explorer 33
Missions to the Moon
 By Target   By Name   By Decade 
Beyond Our Solar System Our Solar System Sun Mercury Venus Moon Earth Mars Dwarf Planets Dwarf Planets Dwarf Planets Asteroids Comets Jupiter Saturn Uranus Neptune Kuiper Belt
Explorer 33
Explorer 33 Mission to Earth's Moon

Mission Type: Orbiter
Launch Vehicle: Thor-Delta E-1 (no. 39 / Thor no. 467 / DSV-3E)
Launch Site: Eastern Test Range / launch complex 17A, Cape Canaveral, USA
NASA Center: Goddard Space Flight Center
Spacecraft Mass: 93.4 kg
Spacecraft Instruments: 1) fluxgate magnetometers; 2) thermal ion probe; 3) ion chamber; 4) tubes plus p-on-n junction; and 5) Faraday-cup probe
Spacecraft Dimensions: Octagonal body 71 cm in diameter, 20 cm high
Spacecraft Power: 4 arrays of solar cells
Project Manager: Paul G. Marcotte, Goddard Space Flight Center
Principal Scientists: Dr. Norman F. Ness, Goddard Space Flight Center
Deep Space Chronicle: A Chronology of Deep Space and Planetary Probes 1958-2000, Monographs in Aerospace History No. 24, by Asif A. Siddiqi

National Space Science Data Center,

Solar System Log by Andrew Wilson, published 1987 by Jane's Publishing Co. Ltd.

Explorer 33 was designed to become the first U.S. spacecraft to enter lunar orbit (planned parameters were 1,300 x 6,440 kilometers at 175° inclination), but the Thor Delta E-1 second stage accelerated too rapidly for compensation by the probe's retrorocket to achieve lunar orbit.

Instead, the spacecraft (56.7 kg by this time) went into an eccentric Earth orbit of 15,897 x 435,330 kilometers. The main solid-propellant retrorocket engine later stabilized the orbit to a less eccentric 30,550 x 449,174-kilometer orbit at 28.9° inclination. In its new orbit, the probe returned key data on Earth's magnetic tail, the interplanetary magnetic field, and radiation.

Key Dates
1 Jul 1966:  Launch (16:02:25 UT)
21 Sep 1971:  Contact Lost
Status: Partial Success
Fast Facts
Explorer 33 Facts This was intended to be the United State's first lunar orbiter, but it was travelling too fast to be caputred by the Moon's gravity.

NASA's Lunar Orbiter 1 achieved that goal later in 1966, snapping hte first picture of Earth from the Moon (right).

Even though Explorer 33 missed its primary target, it still returned useful information on interplanetary space.
Awards and Recognition   Solar System Exploration Roadmap   Contact Us   Site Map   Print This Page
NASA Official: Kristen Erickson
Advisory: Dr. James Green, Director of Planetary Science
Outreach Manager: Alice Wessen
Curator/Editor: Phil Davis
Science Writers: Courtney O'Connor and Bill Dunford
Producer: Greg Baerg
Webmaster: David Martin
> NASA Science Mission Directorate
> Budgets, Strategic Plans and Accountability Reports
> Equal Employment Opportunity Data
   Posted Pursuant to the No Fear Act
> Information-Dissemination Policies and Inventories
> Freedom of Information Act
> Privacy Policy & Important Notices
> Inspector General Hotline
> Office of the Inspector General
> NASA Communications Policy
> NASA Advisory Council
> Open Government at NASA
Last Updated: 29 Nov 2010