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
Because airplanes require air, and the higher the altitude is the less air there is. That is why to actually go to space you need a rocket, rockets do not need air for propulsion.
Airplanes can get into space – what we define as being over 100 km in altitude. It first happened in 1963 by the X-15 craft.
However, getting into **orbit** is completely different. That requires speeds above 17,000 mph, which is far faster than any conventional aircraft can achieve. The X-15 maxed out under 5,000 mph.
1. They work by moving air through their engines. The less air, the less effective their engines are.
2. They work by moving air over their wings. The less air, the less lift.
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The combination of the two factors above explains why each model of aircraft has a different ‘ceiling’.
A jet engine requires air to “breather” and generate thrust. Air is pulled in by a turbofan into the combustion chamber at low velocity. Inside the combustion chamber, energy is added by injecting and burning fuel. Part of this energy goes to a compressor which is used to drive the turbo fan, and the rest is ejected at the back of the jet with both a higher velocity, and more mass due to the added fuel. However without air, the jet engine does not work. There is no air in space. A rocket works by combining a fuel and an oxidizer inside the combustion chamber. This is then ejected by the rocket. Breaking it down to the most basic features, a rocket is self sufficient, because it carrier both fuel and oxygen inside it, where as a jet engine only carrier fuel inside it, and pulls air from the atmosphere.
Less fuel is used going straight up. Planes can reach outer space if their engine doesn’t rely on air (i.e. a rocket motor). The X-15 was able to reach space, albeit briefly.
But it’s not just reaching space, it’s also reaching orbit, and for that you need two things, speed and altitude. Going straight up initially then pitching over is the most fuel efficient way of getting large payloads into orbit.
Rockets dont actually fly straight upwards. I remember watching a video of Elon Musk explaining why and how they fly to space and it’s really interesting! He used a penny and a funnel analogy
Several reasons.
The plane is not airtight and pulls in outside air to keep the occupants alive. No air in space, no alive humans on board.
Jet engines require oxygen to burn fuel. Rockets carry their own fuel and oxidizer so they can thrust in an airless atmosphere.
Plane wings require airflow over the wings to generate lift. No air in space, no ability to leave the atmosphere and climb into space.
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.
>Why is it a rocket is used to go straight up into outer space and not just use an airplane ?
Going into orbit isn’t about going UP. It’s about going horizontally really fast. Rockets go up in order to get out of the thick, lower atmosphere into the thin, upper atmosphere where they can avoid drag and go horizontally faster.
Experimental planes are sometimes carried under the wings of bombers. They sometimes can reach the Karman Line designating the boundary between the atmosphere and space. There is a British company attempting to create a plane that can fly to orbit using air breathing engines and carrying a supply of oxygen and fuel to burn when the air gets too thin. They’re called SABRE engines.
wings and turbines depend on a certain atmospheric pressure to function, flight record is like 30km, obviously that being a purpose built aircraft, not a heavy lift.
there have been concepts to use an assist aircraft (or balloon) to get the shuttle up a bit before finishing with liquid fuel rocket propulsion.
Problem is… you might get up to what… 10 or 20km if your lucky, the space station is 340km up… so a long long way to go.
More importantly, you need to get it moving laterally too. The vast majority of launch thrust is to achieve this, not the vertical climb.
So your shaving only a fraction of the energy cost off the journey, but adding a TON of complexity (and limiting your payload based on what the plane can lift).
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