Why is it a rocket🚀 is used to go straight up into outer space and not just use an airplane ✈️ ? I’m sure there is a good reason but it seems that the gradual assent would be preferred over the straight up approach.
In: Engineering
There are three reasons. In each case I will use the SR-71, one of the fastest aircraft ever built, as the example.
1) The airplane requires air to fly. All aircraft have a service ceiling where the air pressure becomes too low for them to climb further. The SR-71 had a maximum altitude of about 27 km. Below about 120 km air resistance is too great to maintain orbit.
2) The airplane requires air to feed the engines. When you fill an airplane, you are only adding fuel and the air is gathered through the intakes while it flies. No air, no engine. The Falcon 9 uses almost the same fuel as the SR-71 but, since it needs to operate in a vacuum it also needs to carry 2.5 kg of liquid oxygen for each 1 kg of fuel.
3) The airplane can’t carry nearly enough propellant to make orbit. Even with the advantage of being able to harvest more than 2/3 of the propellant in situ, the SR-71 cannot even reach its own full speed or maximum altitude without midair refueling. By comparison, the Falcon 9 is about 90% fuel and the payload takes up a good chunk of the rest.
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