Mariner-H (Mariner Mars '71), also commonly known as Mariner 8, was (along with Mariner 9) part of the Mariner Mars '71 project. It was intended to go into Mars orbit and return images and data, but a launch vehicle failure prevented Mariner 8 from achieving Earth orbit and the spacecraft reentered into the Atlantic Ocean shortly after launch. Mission Mariner 8 was launched on an Atlas-Centaur SLV-3C booster (AC-24). The main Centaur engine was ignited 265 seconds after launch, but the upper stage began to oscillate in pitch and tumbled out of control. The Centaur stage shut down 365 seconds after launch due to starvation caused by the tumbling. The Centaur and spacecraft payload separated and re-entered the Earth's atmosphere approximately downrange and fell into the Atlantic Ocean about north of Puerto Rico. A guidance system failure was suspected as the culprit, but JPL navigation chief Bill O'Neil dismissed the idea that the entire guidance system had failed. He argued that an autopilot malfunction had occurred since the event had occurred at the exact moment when the system was supposed to activate. Investigation proceeded quickly and the problem was soon discovered to be the result of a malfunction in the pitch rate gyro amplifier. A diode intended to protect the system from transient voltages was thought to have been damaged during repairs/installation of the pitch amplifier's printed circuit board, something that would not have been detected through bench tests. , Mariner 8 is the most recent US planetary probe to be lost in a launch vehicle malfunction. Mariner Mars 71 Project The Mariner Mars 71 project consisted of two spacecraft (Mariners H and I), each of which would be inserted into a Martian orbit, and each of which would perform a separate but complementary mission. Either spacecraft could perform either of the two missions. The two spacecraft would have orbited the planet Mars a minimum of 90 days, during which time data would be gathered on the composition, density, pressure, and temperature of the atmosphere, and the composition, temperature, and topography of the surface. Approximately 70 percent of the planetary surface was to be covered, and temporal as well as spatial variations would be observed. Some of the objectives of the Mariner-H mission were successfully added to the Mariner-I (Mariner 9) mission profile. Total research, development, launch, and support costs for the Mariner series of spacecraft (Mariners 1 through 10)