Both of Falcon 9’s stages are powered by RP1 and liquid oxygen, so only one type of engine is required. Both are the same diameter and are constructed from the same aluminum-lithium alloy, reducing the amount of tooling and the number of processes and resulting in what Musk calls “huge cost savings.”

We don’t build nuclear powered rocket because of various technical and political reasons. Technical Reasons: Nuclear rockets are extremely complex in terms of energy. In a nuclear rocket, the energy from the nuclear reactions is used to heat up the propellant which will be expelled by nozzle in order to produce thrust.

Petroleum fuels

Most liquid chemical rockets use two separate propellants: a fuel and an oxidizer. Typical fuels include kerosene, alcohol, hydrazine and its derivatives, and liquid hydrogen. Many others have been tested and used. Oxidizers include nitric acid, nitrogen tetroxide, liquid oxygen, and liquid fluorine.

BrahMos

According to a NASA-published fact sheet, LOX and LH propellant costs the Agency about $1.65 a gallon.

Many rockets are, however, propelled by liquid hydrogen fuel, which produces ‘clean’ water vapour exhaust, although the production of hydrogen itself can cause significant carbon emissions. Rocket engines release trace gases into the upper atmosphere that contribute to ozone depletion, as well as particles of soot.

In reality the mass of the rocket is reduced as fuel is burned. Therefore its acceleration also increases with time. That causes the velocity to increase even more rapidly. It looks so slow when it takes off because it is moving slowly.

The entire rocket launch industry (114 launches in 2018) produces about as much pollution in a year as one busy airport in one day. SpaceX accounts for about 20% of orbital launches annually. The Falcon 9s produce about 500–700 tons each of water and carbon dioxide per launch.

As of July 2013, estimates of more than 170 million debris smaller than 1 cm (0.4 in), about 670,000 debris 1–10 cm, and approximately 29,000 larger pieces of debris are in orbit. As of July 2016, nearly 18,000 artificial objects are orbiting above Earth, including 1,419 operational satellites.

In 1997 falling space debris from the Detla II rocket hit Oklahoman Lottie Williams, so getting struck by space junk may not be as unlikely as you would think. There are over 1,400 satellites orbiting over us, plus thousands of pieces of space junk that might survive entry through the Earth’s atmosphere.

The estimated population of particles between 1 and 10 cm in diameter is approximately 500,000. The number of particles larger than 1 mm exceeds 100 million. As of January 1, 2020, the amount of material orbiting the Earth exceeded 8,000 metric tons.

A huge asteroid, 2020 KN5,will safely fly past the earth over a pace of 28,000 miles per hour on Thursday, June 4, 2020. Due to the Earth-intersecting orbit, it has been classified as an Apollo asteroid.

Contrary to many rumors that have circulated over the last 55 years, there are no bodies of dead cosmonauts (or astronauts) left in space. Apart from the Apollo missions, all humans in space have been in low Earth orbit, and spacecraft in such low orbits will re-enter the atmosphere within a few years.

The earth does fall down. In fact, the earth is constantly falling down. It’s a good thing too, because that is what keeps the earth from flying out of the solar system under its own momentum. The earth and everything on it is constantly falling towards the sun because of the sun’s immense gravity.

Among the stunning variety of worlds in our solar system, only Earth is known to host life. But other moons and planets show signs of potential habitability.

We float in space because there is very little gravitational force acting on them. Gravity is a force that is caused by the attraction of objects with mass. In space, you are very far from Earth’s center of gravity (other planets have gravity as well), so it doesn’t pull very hard, and we basically float around.

All matter in space is constantly falling down. Space is so big that this falling down motion is so slow that on an astronomical scale that we don’t notice it much. But it is definitely there.