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3 A Brief History of Space Flight
the interstellar medium and its plasmas, which means that the solar wind has reached
interstellar space. Therefore, based on the definition of the physical boundary of the
solar system, it can be determined by the number of charged particles and the change
of the direction of the magnetic field in the environment where the spacecrafts are
located, to evaluate whether they enter the interstellar space or fly out of the solar
system. In other words, the basic criteria for judging the man-made probes flying out
of the solar system are as follows:
(1) Whether does the number of charged particles from the Sun around the probes
drop abruptly?
(2) Whether are the charged particles from galaxies and stars increasing rapidly?
(3) Whether does the direction of magnetic field change suddenly?
3.6.2 Pioneer Probes
3.6.2.1 Pioneer Program
The Pioneer program is one of a series of unmanned exploration programs for the
planets and interstellar space in the solar system implemented by the United States
in the 1950s−1970s. There were 19 probes planed and launched successively in the
Pioneer program, of which only 10 successfully completed the scheduled exploration
missions, mainly exploring the Moon and the Earth-Moon space, as well as the planets
of the solar system, such as Venus, Jupiter and Saturn, and its interstellar space. The
Pioneer program was implemented in the two phases as follows.
In the first phase (1958−1960), the exploration missions, including the EarthMoon space, the space near the Moon and the Earth-Venus space, were carried out,
whose goals are to demonstrate and verify the feasibility of the probes to reach the
escape velocity of the Earth, and to conduct the lunar exploration research. During
the phase, nine series of Pioneer probes, including Pioneer-0, 1, 2, 3, 4, P-1, P-3,
5 and P-30, were launched successively, of which except for the successful launch
of Pioneer-4 and Pioneer-5, the other probes ended in failures because the rocket
engines failed to reach the escape velocity of the Earth. On March 3, 1959, the coneshaped Pioneer-4 probe which is made of glass fiber material, with the cone height of
0.58 m, the bottom diameter of 0.25 m and the total weight of 6.1 kg, was launched by
Juno II rocket. The Pioneer-4 is the American first lunar probe to successfully break
away from the Earth’s gravity. It flew over the Moon and successfully entered into the
heliocentric orbit, with a perihelion altitude of 0.98 AU, an aphelion of 1.13 AU, an
orbital eccentricity of 0.072, an orbital period of 398 days, and an orbital inclination
of 1.5 degrees. On March 11, 1960, the Pioneer-5 probe with the ball-shaped main
structure was launched by the Thor-Ables IV rocket. The diameter of the Pioneer-5
is 0.66 m, the solar sails 1.4 m long and the weight 43 kg. The pioneer-5 entered
into the heliocentric orbit with a perihelion altitude of 0.71 AU, an aphelion altitude
of 0.99 AU, an orbital eccentricity of 0.1689, an orbital period of 312 days and an
orbital inclination of 3.35 degrees. The pioneer-5 had been operated normally in the
3 A Brief History of Space Flight
the interstellar medium and its plasmas, which means that the solar wind has reached
interstellar space. Therefore, based on the definition of the physical boundary of the
solar system, it can be determined by the number of charged particles and the change
of the direction of the magnetic field in the environment where the spacecrafts are
located, to evaluate whether they enter the interstellar space or fly out of the solar
system. In other words, the basic criteria for judging the man-made probes flying out
of the solar system are as follows:
(1) Whether does the number of charged particles from the Sun around the probes
drop abruptly?
(2) Whether are the charged particles from galaxies and stars increasing rapidly?
(3) Whether does the direction of magnetic field change suddenly?
3.6.2 Pioneer Probes
3.6.2.1 Pioneer Program
The Pioneer program is one of a series of unmanned exploration programs for the
planets and interstellar space in the solar system implemented by the United States
in the 1950s−1970s. There were 19 probes planed and launched successively in the
Pioneer program, of which only 10 successfully completed the scheduled exploration
missions, mainly exploring the Moon and the Earth-Moon space, as well as the planets
of the solar system, such as Venus, Jupiter and Saturn, and its interstellar space. The
Pioneer program was implemented in the two phases as follows.
In the first phase (1958−1960), the exploration missions, including the EarthMoon space, the space near the Moon and the Earth-Venus space, were carried out,
whose goals are to demonstrate and verify the feasibility of the probes to reach the
escape velocity of the Earth, and to conduct the lunar exploration research. During
the phase, nine series of Pioneer probes, including Pioneer-0, 1, 2, 3, 4, P-1, P-3,
5 and P-30, were launched successively, of which except for the successful launch
of Pioneer-4 and Pioneer-5, the other probes ended in failures because the rocket
engines failed to reach the escape velocity of the Earth. On March 3, 1959, the coneshaped Pioneer-4 probe which is made of glass fiber material, with the cone height of
0.58 m, the bottom diameter of 0.25 m and the total weight of 6.1 kg, was launched by
Juno II rocket. The Pioneer-4 is the American first lunar probe to successfully break
away from the Earth’s gravity. It flew over the Moon and successfully entered into the
heliocentric orbit, with a perihelion altitude of 0.98 AU, an aphelion of 1.13 AU, an
orbital eccentricity of 0.072, an orbital period of 398 days, and an orbital inclination
of 1.5 degrees. On March 11, 1960, the Pioneer-5 probe with the ball-shaped main
structure was launched by the Thor-Ables IV rocket. The diameter of the Pioneer-5
is 0.66 m, the solar sails 1.4 m long and the weight 43 kg. The pioneer-5 entered
into the heliocentric orbit with a perihelion altitude of 0.71 AU, an aphelion altitude
of 0.99 AU, an orbital eccentricity of 0.1689, an orbital period of 312 days and an
orbital inclination of 3.35 degrees. The pioneer-5 had been operated normally in the