Rocket engineers realized that a vehicle with enough velocity to orbit the Earth had enough kinetic energy to vaporize itself on re-entering the Earth's atmosphere. (A satellite in low Earth orbit, at an altitude of 200 to 2000 km, has a velocity of up to 28,000 km/h (17,000 mph) which means it has a specific kinetic energy of up to 30 MJ/kg).
And yet, they knew that some meteorites reached the ground without being destroyed by friction with the Earth's atmosphere.
In 1951, H. Julian Allen and A. J. Eggers, of the U.S. National Advisory Committee for Aeronautics (NACA), discovered that a blunt, high drag shape, dissipated about 99% of the energy into the air, rather than into the vehicle. This meant that a satellite could be safely returned to the ground without the aid of massive amounts fuel for retro rockets.
Air molecules moving over the wings an aircraft provide the lifting force but also a drag force that is overcome by the engines. Exactly how the air affects an aircraft depends upon the ratio of the speed of the aircraft to the speed of sound through the air. This is known as the Mach number in honour of Ernst Mach, a physicist who studied shockwaves created by supersonic bullets late in the 19th century.
A speed of Mach 1 means that an aircraft is flying at the speed of sound and a spacecraft, re-entering the earth's atmosphere, is travelling very much faster, at a hypersonic speed close to Mach 25. Low earth orbit re-entry speeds are typically near 17,500 mph. Many miles above the earth's surface, the air density is very low but the temperature of the airflow is so high that the chemical bonds of the diatomic molecules of the air are broken. This produces an electrically charged plasma around the re-entry vehicle while its lower surface generates strong shock waves.
U.S. research was abruptly energized on October 4, 1957, when the Soviet Union launched the satellite Sputnik 1 into Earth orbit. Less than a month later, the Soviets launched a satellite carrying a dog named Laika who survived in space for seven days before being anaethetized as the oxygen supply ran out.
The blunt body theory was initially treated as a military secret (as a nuclear weapon in orbit was useless if it was unable to survive re-entry) but it was eventually published in 1958 and was used to design heat shields for the re-entry capsules of the Mercury, Gemini, Apollo, and Soyuz space capsules. An ablative heat shield made of ceramic material slowly burned away in the high temperature plasma flow, behind the bow shock wave. The change of phase of the ceramic shield, from solid to liquid to gas, and the convection of the flow away from the spacecraft protecting the astronauts from the heat of re-entry.
After a few failures, the United States launched an Explorer 1 satellite, on a Jupiter-C rocket, into space in February 1958 and later that year, the National Aeronautics and Space Administration (NASA) was established as a civilian agency with the goal of peaceful exploration of space for the benefit of all people.
On October 7, 1959, the Soviet probe Luna 3 took the first photographs of the, previously unseen, far side of the Moon.
However, Sputnik had proven that the Soviet R-7 rocket was capable of reaching any point in the USA carrying a nuclear weapon. It was potentially the first intercontinental ballistic missile or ICBM.
Governments realized that there was no feasible defence against rocket propelled nuclear weapons, once they were launched. Conventional long range bombers were no longer the only way to deliver nuclear weapons. The Soviet R-7 and American Atlas, and Titan rockets were quickly modified to carry nuclear warheads and the Cold War became more intense.
On April 12, 1961, the Vostok-K rocket launched Yuri Gagarin into the vacuum of space. He was the first man to orbited once around the planet (in 108 minutes) and safely return to the ground in the descent module Vostok I. On May 5, 1961, a Mercury-Redstone 3 launched Alan Shepard into a suborbital flight mission to become the first American and the second person to travel into space.
In 1963, NASA used Atlas rockets to launch John Glenn into Earth orbit and, also in 1963, Canada launched the satellite Alouette I to become the third country with an Earth satellite.
The 1960's saw rapid development of rocket technology both in the Soviet Union, (with Vostok, Soyuz and Proton) and in the United States (with the X-15 and X-20 Dyna-Soar aircraft). Also France, Britain, Japan, Australia and other countries began research programs particularly for communications. In 1967, the X-15 rocket propelled aircraft set the air speed record at 4,534 mph (7,297 km/h) or Mach 6.1. This record was renewed by the X-43 in the 21st century.
NASA used Saturn V rockets to launch missions between 1969 and 1972 including the manned spaceflight programs, Project Mercury, Project Gemini and the Apollo program.
The Saturn V rocket was 363 feet tall, capable of transporting a crew of three, a moon lander module and a re-entry module into space, allowing astronauts Neil Armstrong and Buzz Aldrin to land on the Moon's surface on July 20, 1969, while Michael Collins remained in lunar orbit in the command and service module. All three returned safely to Earth on July 24, 1969.
Five subsequent Apollo missions also landed astronauts on the Moon, the last mission was in December 1972.The Space Transportation System (STS) better known as the Space Shuttle was used for 135 missions between 1981 and 2011. To reach orbit, the Space Shuttle required three Rocketdyne RS-25 main engines (fuelled by liquid hydrogen and liquid oxygen from a jettisonable external tank), each producing 1,859 kN (418,000 lbf) of thrust at liftoff, plus two recoverable solid rocket boosters (SRB's).
Each SRB provided a maximum thrust of 14.7 MN (3,300,000 lbf) by burning atomized aluminum powder (as fuel) mixed with the oxidizer ammonium perchlorate and an iron powder catalyst. The thrust was about double the most powerful single-combustion chamber, liquid-propellant rocket engine ever flown (the Rocketdyne F-1).
Each solid rocket booster consumed all 1,000,000 pound weight (450,000 kg) of its solid fuel in 2 minutes, by which time the shuttle was about 45 km above the Earth's surface and 2 million pounds lighter, demonstrating Newton's law that (propelling) force = mass x acceleration as the shuttle rapidly accelerated. (Solid fuel rockets cannot be shut down after ignition). The boosters were ejected from the shuttle and descended by parachutes, for recovery and reuse.
However, during re-entry, the shuttle was an un-powered glider except for small steering rockets used for manoeuvring early in the re-entry (because the low density of the air at altitudes above 50 miles is insufficient for aerodynamic control). The aluminum skin of the Shuttle was protected by silicon tiles and carbon composite material covered the leading edge of the wings to withstand the heat. The Shuttle flew at a high angle of attack during re-entry to generate drag and reduce speed. It used hypersonic "S-turn" manoeuvres to kill off speed. The wings were only used for lift during the final approach to landing.
This modified re-entry technique had been developed by Maxime Faget, Director of Engineering and Development at the Manned Spacecraft Center. The space shuttle entered the atmosphere at an extremely high angle of attack of 40°. (The angle between the direction of flight and the wing cord). The underside, facing the direction of flight, creating a large shock wave that deflected most of the heat around the vehicle instead of into it. So the final design used a combination of a ballistic entry (blunt body theory) but at an altitude of about 122,000 m (400,000 ft), where the atmosphere was dense enough, the shuttle was rotated for an aerodynamic re-entry phase. Throughout re-entry, the Shuttle rolled to change lift direction while always keeping maximum deceleration well below 2 g's. (a deceleration of twice gravitational acceleration). These manoeuvres allowed the Shuttle to use its lift to steer toward the runway.
Arthur C. Clarke had proposed a satellite communication system using geostationary orbits in 1945 and this became a reality on August 19, 1964 when Syncom 3 was launched on a Delta D launch vehicle from Cape Canaveral. In orbit, the satellite remained permanently above the International Date Line and was used to telecast the 1964 Summer Olympics in Tokyo to the United States. A geostationary orbit is a circular orbit 35,786 kilometres (22,236 miles) in altitude above Earth's equator. A satellite travelling in the direction of Earth's rotation has an orbital period of exactly 24 hours and, as the direction of travel is the same as the Earth's rotation, it appears to be stationary above a particular point on Earth. Satellite antennas on Earth do not have to track them but can be pointed permanently at the position in the sky where a satellite is located. The orbit requires some station-keeping, to maintain its position, and, to avoid collisions, retired satellites are placed in a higher 'graveyard' orbit.
Rockets have propelled spacecraft throughout the solar system so that astronomers now have close-up images of every planet and many moons, comets, asteroids and smaller objects. And, because of incredible guidance systems, rocket engineers were able to accelerated the Voyager 1 spacecraft out of the solar system and into interstellar space on a journey to neighbouring stars.
(Launched in 1977, NASA estimates Voyager 1 left the solar system about August 25th, 2012, after using Saturn's gravitational pull to accelerate, Voyager 1 headed out at a speed of about 37,000 mph).