<p>Engineering back-up of the Ranger (block one type) lunar orbiter in the Space Hall at the Smithsonian Air and Space Museum in Washington, D.C.
</p><p>Mapping of the Moon began with the Ranger spacecraft.  They were followed up by the Surveyor program, which actually landed spacecraft on the Moon.  The Lunar Orbiter craft did the high-resolution mapping just before the Apollo Moon landings.
</p><p>There were three types (or "blocks") of Ranger spacecraft.  Ranger 1 and 2 were part of "block one," which was designed to test the Ranger technology in Earth orbit.  The basic spacecraft technology we take for granted today -- three-axis attitude stabilization (without spinning the craft), on-board thrusters, two-way communication, closed-loop tracking (in which the spacecraft measures where it is a space and moves without receiving ground signals), on-board computing, control from the ground using commands that tell the on-board computer to run complex sequences -- all had to be developed for the Ranger program.
</p><p>Sadly, the Atlas-Agena rockets that launched Ranger 1 and Ranger 2 left these craft in orbits which were too low.  The spacecraft could not stabilize themselves or collect solar power.  (NASA would later use the designs for Ranger "block one" for the Mariner space probes of Venus.)
</p><p>"Block two" Rangers were improved versions of the "block one" craft.  They carried a TV camera, a radiation detector, and a seismometer.  The seismometer was designed to be ejected from the craft as it crashed into the Moon.  Retrorockets would slow the seismometer capsule, allowing it to land softly on the lunar surface.  The capsule would then transmit seismic data back to Earth.  
</p><p>Sadly, Ranger 3 missed the Moon due to a trajectory miscalculation on Earth months earlier.  Ranger 4's TV camera and radiation detector failed during the flight to the Moon.  Its seismometer also failed to function, but it did soft-land on the lunar surface.  Ranger 5 also missed the Moon due to a trajectory error.  (The Rangers used gold-plated diodes. NASA discovered that this gold cracked and flaked off in the harsh conditions of outer space.  They were immediately replaced.)
</p><p>The "block three" Rangers carried a high-resolution TV camera.  Items as small as a 12 inches could be discrened on the images it received.  The camera on Ranger 6 failed as it approached the Moon.  But Ranger 7, 8, and 9 performed flawlessly!  Ranger 7 photographed Mare Cognitum, proving that impact craters covered the Moon -- even in the supposedly smooth highlands. Ranger 8 photographed the souther part of Oceanus Procellarum and Mare Nubium, and eventually was told by NASA to crash in Mare Tranquillitatis (where Apollo 11 would land four years later). Ranger 9 was told to crash in the crater Alphonsus.
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Although less scientific knowledge was gained than expected, NASA system engineers learned an immense amount about spacecraft and quality control which would later allow NASA to put a man on the Moon -- SAFELY.
<a rel="nofollow" class="external text" href="https://www.flickr.com/people/23165290@N00">Tim Evanson</a> from Cleveland Heights, Ohio, USA
CC BY-SA 2.0
<a rel="nofollow" class="external text" href="https://www.flickr.com/photos/timevanson/7246253882/">Ranger lunar orbiter - Smithsonian Air and Space Museum - 2012-05-15</a>