Appendix 2: Explorer Flight Summary

Vehicle (Launch Date)	Objectives	Results
Jupiter C (31 Jan 1958)	To launch into orbit an 18.13-lb “cosmic ray” satellite.	Placed Explorer I (totaling 30.8 lb, including the 18.13-lb satellite) in an orbit expected to last 3-5 years. Initial orbit had apogee of 1,573 mi, perigee of 224 mi, and period of 114 min. Scientific instrumentation confirmed predicted cosmic radiation levels up to 600-mi altitude, measured frequency of impacts and size of micrometeoroids, provided information on earth's bulge and gravity, obtained data on atmospheric density at extreme altitude, and confirmed success of method to control temperature of satellite's interior. Count rates above 600-mi altitude were very irregular, later found to be the result of very intense trapped radiation about the earth.
Jupiter C (5 Mar 1958)	To launch into orbit an 18.5-lb “cosmic ray” satellite similar to Explorer I and known as Explorer II.	Failed to orbit. Last stage did not ignite. Flight time 885 sec.
Jupiter C (26 Mar 1958)	To launch into orbit a payload almost identical to Explorer II.	Placed Explorer III in an orbit that lasted until 28 June 1958. Initial orbit had apogee of 1,740 mi, perigee of 119 mi, and period of 115.8 min. Scientific instrumentation added to data acquired by Explorer I.
Jupiter C (26 July 1958)	To launch into orbit a 25.8-lb payload carrying two Geiger-Mueller counters, two scintillation counters, and internal temperature measurements transmitted by subcarrier center frequency shift.	Placed Explorer IV in orbit. Initial orbit had apogee of 1,373 mi, perigee of 163 mi, and period of 110 min. Measured cosmic rays and trapped radiation over a wide range of levels and energies. Also explored a far greater volume of space as regards latitude and altitude than Explorers I and III. Collected data on trapped electrons resulting from Argus high-altitude nuclear explosions.
Jupiter C (24 Aug 1958)	To launch into orbit a duplicate of Explorer IV to be known as Explorer V.	Failed to orbit. At 1st-stage separation, the booster rammed the instrument compartment. Flight time, 659 sec.
Jupiter C with “apogee kick” 5th stage added (22 Oct 1958)	To launch into orbit a high-visibility balloon (9.26-lb, 12-ft diameter when inflated), to provide high-altitude atmosphericdensity data and to serve as a radar target.	Failed to orbit. Rotational spin vibrations of the cluster caused the payload to drop off at 112 sec.
Juno II (16 July 1959)	To launch into orbit a multiple-experiment satellite and double-truncated cone (91.5 lb).	Failed to orbit. At liftoff the vehicle deviated sharply to the left and was destroyed at 5 ½ sec after liftoff. Failure of the guidance inverter caused open loop drift of the control system.
Juno II (14 Aug 1959)	Same as attempt of 22 Oct 1958.	Failed to orbit.
Juno II (13 Oct 1959)	Same as attempt of 16 July 1959.	Placed Explorer VII in orbit. Initial orbit had apogee of 681 mi, perigee of 345 mi, and period of 101.3 min.