Editing Pioneer 1 (section)

== Mission ==
{{refimprove section|date=April 2024}}
[[File:Pioneer I, Reconstructed Replica.jpg|thumb|Reconstructed replica of Pioneer 1]]
Two days after the failure of Pioneer 0 on 17 August 1958, Thor 129, the backup vehicle, was erected on LC-17B in preparation for a September attempt. The postflight investigation of Pioneer 0 pointed to a [[turbopump]] failure, which had also caused the loss of Thor-Able 116 in April.{{fact|date=April 2024}} This was followed by the failure of an Atlas launch on 18 September, so the Air Force moved to replace the turbopumps in their inventory of Thor and Atlas missiles.{{fact|date=April 2024}} Thor 129 was pulled from the pad for modifications and replaced with Thor 130.

On 11 October 1958, Pioneer 1 lifted off smoothly, but the guidance system steered the Thor slightly too high and fast, causing the second stage to be lofted 3° higher than intended. As a result, it shut off 10 seconds earlier than planned, and also bumped the third stage during separation. The third stage was left pitched up about 15° and suffering a velocity shortfall of about 500 feet per second. The [[vernier thruster|vernier engines]] on the third stage were fired to make up for the thrust deficit, but added only 150 feet per second of velocity, insufficient to escape Earth orbit. As a last resort, ground controllers decided that if they could not get Pioneer 1 to the Moon, they would place it in a high Earth orbit by firing the attached solid rocket motor. The inaccurate launch trajectory, however, had placed the probe on an orbital track that resulted in thermal heating and cooling beyond what the primitive temperature control system could handle. The probe's internals fell to near-freezing temperatures, rendering the solid motor igniter inoperable. Pioneer 1 reached a total distance of {{convert|113800|km|0|abbr=on}} before beginning its descent back to Earth.<ref name="ppg581013"/>

The spacecraft was launched from [[Cape Canaveral Air Force Station Space Launch Complex 17|LC-17A]] at Cape Canaveral at 08:42:00 GMT but it did not reach the Moon as planned due to a programming error in the upper stage causing a slight error in burnout velocity and angle (3.5°). This resulted in a ballistic trajectory with a peak altitude of {{convert|113800|km|0|abbr=on}} around 13:00 local time. The real-time transmission was obtained for about 75% of the flight, but the percentage of data recorded for each experiment was variable. Except for the first hour of flight, the signal-to-noise ratio was good. The spacecraft ended transmission when it reentered the Earth's atmosphere after 43 hours of flight on 13 October 1958 at 03:46 GMT over the South [[Pacific Ocean]]. A small quantity of useful scientific information was returned, showing the radiation surrounding Earth was in the form of bands and measuring the extent of the bands, mapping the total ionizing flux, making the first observations of hydromagnetic oscillations of the [[magnetic field]], and taking the first measurements of the density of micrometeorites and the [[Interplanetary Magnetic Field|interplanetary magnetic field]].{{fact|date=April 2024}}