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power 0.18 W. A despin mechanism consisted of two 7 gram
weights which spooled out to the end of two 150 cm wires when
triggered by a hydraulic timer 10 hours after launch. The weights
were designed to slow the spacecraft spin from 400 rpm to 6 rpm
and then weights and wires were released. 

After a successful launch Pioneer 4 achieved its primary objective
(an Earth-Moon trajectory), returned radiation data and provided a
valuable tracking exercise. The probe passed within 60,000 km
of the Moon's surface (7.2 E, 5.7 S) on 4 March 1959 at 22:25
UT (5:25 p.m. EST) at a speed of 7,230 km/hr. The distance
was not close enough to trigger the photoelectric sensor. The
probe was tracked for 82 hours to a distance of 655,000 km and
reached perihelion on 18 March 1959 at 01:00 UT. The cylindrical
fourth stage casing (173 cm long, 15 cm diameter, 4.65 kg) went
into orbit with the probe. 

Launch Information:
Launch Date/Time: 1959-03-03 at 17:11:00 UTC
Launch Site/Country: Cape Canaveral, United States
Vehicle: Juno 2 (Juno II)
On-orbit dry mass: 6.1 kg

Orbital Information:
Orbit: Orbiter
Central Body: Sun
Epoch start date/time:1959.062:17:11:00 (03 Mar)
Periapisis: .98 AU
Apoapsis: 1.13 AU
Orbital Period: 398 d
Inclination: 29.9 degree
Eccentricity: .07109
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