After four failed launches, the program once again succeeded with SLV-4, renamed Vanguard II. After two more failures, the program ended with the launch of Vanguard III in 1959. Despite being overshadowed by Sputnik, and having to overcome the widespread humiliation of its unsuccessful early attempts, the Vanguard Project eventually met its scientific objectives, providing a wealth of information on the size and shape of the Earth, air density, temperature ranges, and micrometeorite impact. The Vanguard 1 radio continued to transmit until 1964, and tracking data obtained with this satellite revealed that Earth is not quite a perfect sphere: it is slightly pear-shaped, elevated at the North Pole and flattened at the South Pole. It corrected ideas about the atmosphere's density at high altitudes and improved the accuracy of world maps. The Vanguard program was transferred to NASA when that agency was created in mid-1958. The Vanguard "Satellite Launch Vehicle", a term invented for the operational SLV rockets as opposed to the Test Vehicle TV versions, was a much smaller and lighter launcher than the Redstone-based Jupiter-C/Juno 1 rocket which launched the Explorer satellites, or the immense R-7 that the Soviets used to launch the early Sputniks. The Vanguard 1 program introduced much of the technology that has since been applied in later U.S. satellite programs, from rocket launching to satellite tracking. For example, it validated in flight that solar cells could be used for several years to power radio transmitters. Vanguard's solar cells operated for about seven years, while conventional batteries used to power another on-board transmitter lasted only 20 days. Although Vanguard's solar-powered "voice" became silent in 1964, it continues to serve the scientific community. Ground-based optical tracking of the now-inert Vanguards continues to provide information about the effects of the Sun, Moon, and atmosphere on satellite orbits. Vanguard I marked its 50th year in space on March 17, 2008. In the years following its launch, the small satellite has made more than 196,990 revolutions of the Earth and traveled 5.7 billion nautical miles, the distance from Earth to beyond the dwarf planet Pluto and halfway back. Original estimates had the orbit lasting for 2000 years, but it was discovered that solar radiation pressure and atmospheric drag during high levels of solar activity produced significant perturbations in the perigee height of the satellite, which caused a significant decrease in its expected lifetime to about 240 years. The first Vanguard flight, a successful suborbital test of the Vanguard TV0 single-stage vehicle, was launched on December 8, 1956.