This timeline is similar to America First in Space, but what if delays plagued the US satellite program Project Vanguard as in our timeline?
1946-1947: British Interplanetary Society manned rocket proposal "Megaroc" intrigued the British Government, causing the government to not deny the proposal outrightly. This is the divergence point from our main timeline.
1947: The British government attempted to propose to the government of the United States for a collaboration of the Megaroc project. Truman, who was the US president at that time, decided to turn the proposal down citing lack of funds, after some ponderings on the project made by him. Though the turn-down effectively kill off the project for good, the idea of the potential implications if taking a lead in space technology would sip into Truman's mind. As in our timeline, USA launched a group of fruit flies into space, making them the first animals in space.
1957: In October, the Soviets launched Sputnik 1 satellite into orbit. This results in a "Sputnik Moment" as in our timeline and confirming some of Truman's convictions.
1958: Partially as a result of the aforementioned Sputnik Shock, DARPA and NASA were created in 1958 to have America to compete against Soviets. For the same reasons and as in our timeline, funding for STEM education in the U.S. is increased. Besides that, 1st American satellite "Explorer 1" is launched and discovered the Van Allen belt.
1959: Soviet Union's Luna 1 become the first spacecraft to enter heliocentric orbit. At the same year, Luna 3 becomes the first spacecraft to photograph the far side of the moon.
1961: In January 1961, monkey Ham becomes the first hominid in space after being launched by American Mercury rocket into a suborbital trajectory. Later in March 24th, Alan Shepard, an American astronaut, becomes the first man in space, albeit being launched in a suborbital trajectory akin to Ham's. Shepard would receive a ticker tape parade for the feat of being the first person in space.
The bigger shock to the American public came in April when the Soviet Union responds by launching cosmonaut Yuri Gagarin into orbit, which prompt US president Kennedy to set a national goal for a manned Moon mission.
1962: NASA's robotic spacecraft Mariner 2 successfully fly by Venus.
1963: US President Kennedy is assassinated. Cosmonaut Valentina Tereshkova is the first woman in space.
1965: First space rendezvous is achieved by the Americans, meanwhile cosmonaut Alexey Leonov made the mankind's first spacewalk.
1966: First space docking is done with an American Gemini spacecraft and an American Agena Target Vehicle. Luna 9, a Soviet Union spacecraft, is the first spacecraft perform a soft landing on the Moon.
1967: Apollo 1 disaster.
1968: Astronauts Frank Borman, James Lovell and Bill Anders, who are travelling in the Apollo 8 mission, becomes the first humans to travel out of Earth's gravitational influence and into the Lunar influence.
1969: On July, astronauts Neil Armstrong landed on the moon with Buzz Aldrin in Apollo 11 mission. Armstrong is the first human to step his foot on moon, saying: "That's one small step for man, one giant leap for mankind".
1970: NASA's Apollo 13 safely returns to Earth after suffering a damage while on its Moon mission.
1971: First space station Salyut 1 is launched by the Soviet Union.
1972: NASA's Pioneer 10 and 11 spacecrafts are launched to the outer planets and into interstellar space.
1973: Launch of Mariner 10, the first NASA robotic spacecraft mission to planet Mercury, and the first American space station Skylab.
1977: NASA's Voyager 1 and 2 is launched to flyby the outer planets and into interstellar space. The former spacecraft would become the first spacecraft to enter interstellar space eventually.
1979: Skylab decays from Earth orbit.
1981: American space shuttle "Columbia" is the first orbital space plane to be launched into space.
1986: Challenger space shuttle disaster. First parts of Soviet Union's MIR space station is launched into space.
1991: Dissolution of the Soviet Union, which brings the decades old Cold War to an end.
1998: First parts of ISS (International Space Station) is launched into orbit.
2001: MIR space station fall backs to Earth.
2003: Space Shuttle Columbia disaster.
2006: First robotic spacecraft mission to planet Pluto, "New Horizons" is launched by NASA.
2007: First robotic spacecraft mission to dwarf planet Ceres, "Dawn" is launched by NASA.
2010: Major completion of ISS.
2015: Both NASA's Dawn and New Horizons spacecrafts arrived Ceres and Pluto respectively. LIGO (Laser Interferometer Gravitational-Wave Observatory), with help and contributions from American scientists and international scientists who come from countries like Australia and Italy, detected the first gravitational wave.
2016: LIGO announced the gravitational wave discovery.
2017: LIGO and other observatories detected both gravitational waves and electromagnetic waves emitted from a collision of two neutron stars in a distant galaxy.
2019: Five of Jupiter's moons with provisional designations S/2003 J5, S/2003 J15, S/2003 J3, S/2017 J4 and S/2018 J1 receive the official names of Eirene, Philophrosyne, Eupheme, Pandia and Ersa respectively.