stage to perform unintended pitch maneuvers. The guidance system was modified to have greater redundancy, and efforts were made to improve quality control. On 17 March 1958, Vanguard TV-4 finally succeeded in orbiting the Vanguard 1 satellite. By that time, however, the Army's Juno (Jupiter-C) had already launched the United States' first satellite, Explorer 1. The Vanguard TV-4 rocket had put the satellite Vanguard 1, to a relatively high orbit of (). Vanguard 1 and its third stage remain in orbit as the oldest man-made artifacts in space. The following four flights, TV-5 and SLV (Satellite Launch Vehicle) Vanguard SLV-1, Vanguard SLV-2 and Vanguard SLV-3 all failed, but on 17 February 1959, Vanguard SLV-4 launched Vanguard 2, weighing , into orbit. The SLVs were the "production" Vanguard rockets. Vanguard SLV-5 and Vanguard SLV-6 also failed, but the final flight on 18 September 1959, successfully orbited the Vanguard 3 satellite. That last mission was designated Vanguard TV-4BU, because it used a remaining test vehicle, which had been upgraded with a new third stage, the Allegany Ballistics Laboratory X-248A2 Altair. This more powerful motor enabled the launch of the heavier payload. The combination of the AJ10 liquid engine and X-248 solid motor was also used, under the name Able, as an upper stage combination for Thor and Atlas space launch vehicles. Launches Vanguard launched 3 satellites out of 11 launch attempts: Vanguard TV3 - December 6, 1957 - Failed to orbit satellite Vanguard TV3 Backup - February 5, 1958 - Failed to orbit satellite Vanguard 1 (Vanguard TV4) - March 17, 1958 - Orbited satellite Vanguard TV5 - April 28, 1958 - Failed to orbit satellite Vanguard SLV-1 - May 27, 1958 - Failed to orbit 10.0 kg satellite Vanguard SLV-2 - June 26, 1958 - Failed to orbit 10.0 kg satellite Vanguard SLV-3 - September 26, 1958 - Failed to orbit 10.0 kg satellite Vanguard 2 (Vanguard SLV-4) - February 17, 1959 - Orbited satellite Vanguard SLV-5 - April 13, 1959 - Failed to orbit Vanguard SLV-6 - June 22, 1959 - Failed to orbit 10.3 kg satellite Vanguard 3 (Vanguard TV4-BU, also Vanguard SLV-7) - September 18, 1959 - Orbited satellite Specifications Stage Number: 1 - Vanguard Mass: Empty Mass: Thrust (vac): Isp (sea level): Burn time: 145 s Diameter: Length: Propellants: LOX/Kerosene Engines: General Electric X-405 Stage Number: 2 - Delta A Mass: Empty Mass: Thrust (vac): Isp: Burn