# Pioneer 4

> U.S. space probe which performed a lunar flyby

**Wikidata**: [Q597119](https://www.wikidata.org/wiki/Q597119)  
**Wikipedia**: [English](https://en.wikipedia.org/wiki/Pioneer_4)  
**Source**: https://4ort.xyz/entity/pioneer-4

## Summary
Pioneer 4 was a U.S. space probe launched in 1959 that performed a successful flyby of the Moon. It was the first American spacecraft to escape Earth's gravity and enter a heliocentric orbit, becoming an artificial satellite of the Sun.

## Key Facts
- **Launch Date:** March 3, 1959, at 05:10:56 UTC
- **Mission Type:** Lunar flyby probe and artificial satellite of the Sun
- **Launch Vehicle:** Juno II (booster AM-14)
- **Operator/Manufacturer:** Jet Propulsion Laboratory (JPL)
- **Mass:** 6.1 kilograms (launch weight)
- **Lunar Flyby Distance:** 58,983 kilometers (achieved March 4, 1959)
- **Data Transmission Duration:** 82.5 hours
- **Orbital Period:** 398 days around the Sun
- **Preceded By:** Pioneer 3 (a failed mission)
- **Succeeded By:** Pioneer P-1 (a failed mission)

## FAQs
### Q: What was the primary achievement of Pioneer 4?
A: Pioneer 4 successfully performed a flyby of the Moon on March 4, 1959, passing within 58,983 kilometers of the lunar surface. It subsequently became the first U.S. probe to enter a heliocentric orbit, meaning it orbits the Sun.

### Q: How long did Pioneer 4 transmit data?
A: The spacecraft provided 82.5 hours of data transmission following its launch. The mission officially recorded a "loss of signal" on March 6, 1959.

### Q: What launch vehicle was used for Pioneer 4?
A: Pioneer 4 was launched using a Juno II rocket (specifically configuration AM-14) from Cape Canaveral Launch Complex 5.

## Why It Matters
Pioneer 4 was a landmark mission in the early American space program, representing the first time a U.S. spacecraft successfully reached the vicinity of the Moon and transitioned into a permanent solar orbit. Following the launch failure of its predecessor, Pioneer 3, Pioneer 4 demonstrated the functional capability of the Juno II launch vehicle and the tracking expertise of the Jet Propulsion Laboratory. 

By achieving a heliocentric orbit, it proved that human-made objects could be placed into stable orbits around the Sun, effectively becoming artificial planets. Although it did not pass as close to the Moon as originally planned, the 82.5 hours of data it transmitted provided essential information for the Pioneer program and future deep-space exploration efforts.

## Notable For
- **First U.S. Solar Satellite:** It was the first American probe to achieve a heliocentric orbit (orbiting the Sun).
- **Successful Lunar Flyby:** Reached the Moon on March 4, 1959, passing at a distance of 58,983 km.
- **Juno II Success:** Validated the Juno II booster system for deep-space missions after previous failures in the program.
- **Extended Tracking:** Maintained a communication link for over 82 hours, providing a significant data set for early space flight.

## Body

### Mission Launch and Objectives
Pioneer 4 was part of the Pioneer program, a series of early U.S. space exploration missions. It was manufactured and operated by the Jet Propulsion Laboratory (JPL). The probe was launched on March 3, 1959, from Cape Canaveral Launch Complex 5 using a Juno II rocket. Its primary objective was to fly past the Moon and return radiation data.

### Lunar Flyby and Trajectory
On March 4, 1959, the spacecraft achieved its closest approach to the Moon at a distance of 58,983 kilometers. While this was further than the intended distance, it was sufficient to fulfill flyby objectives. Following the encounter, the probe's velocity was high enough to escape Earth's gravitational influence entirely.

### Heliocentric Orbit Specifications
After passing the Moon, Pioneer 4 entered an orbit around the Sun. Its orbital characteristics include:
*   **Apoapsis:** 1.13 AU
*   **Periapsis:** 0.98 AU
*   **Semi-major axis:** 164,780,000 km
*   **Orbital Inclination:** 1.5°
*   **Orbital Eccentricity:** 0.07109
*   **Orbital Period:** 398 days

### Technical Specifications and IDs
The probe had a launch mass of 6.1 kg. It is identified in various catalogs by the following designations:
*   **COSPAR ID:** 1959-013A
*   **NSSDCA ID:** 1959-013A
*   **SCN:** 00113
*   **Harvard Designation:** 1959 Nu 1

The mission concluded its active phase on March 6, 1959, when the signal was lost after 82.5 hours of operation.

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## References

1. Jonathan's Space Report
2. Freebase Data Dumps. 2013
3. [NSSDCA/COSPAR ID: 1959-013A](https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id=1959-013A)
4. BabelNet