How are cargo and crew launched to the ISS?
There is only one way to send cargo and people to the ISS, and its by using the space vehicle per excellence: the rocket. Only the rocket can reach enough velocity to put an object in orbit. We need the object to reach 28000 kilometers per hour so it can stay in orbit. If its velocity is lower, then it won’t achieve orbit and will fall to the surface.
But… How does a rocket work? We only see “fire coming out of a cylinder”, but what it is really happening it’s a mystery that you will discover today, in this page of our website.
To make it easy for you, we will show you a simple diagram of a liquid-fueled rocket engine.
A rocket has two tanks: one which contains fuel (propellant), and another which contains the oxidizer. Fuel and oxidizer mix together at the combustion chamber, where an igniter causes the combustion of that mix. To allow a constant flow of both fuel and oxidizer, turbopumps are installed. As their name says, they pump propellant (fuel) and oxidizer to the engines.
When combustion occurs, gas is obtained as a final product at high temperature and pressure. The gas only has a single escape route, and that is the throat (narrow area in the image). As it has to pass through the throat to go outside, its temperature, pressure and speed increases, expelling the gas at very high speeds. To understand why this happens, let's see it with a brief example:
Imagine that you have a balloon full of water, and you make a hole in the side. The water will begin to flow out of that hole, as it is its only escape route, but the jet will not go very far. If you press on the bag, the water will try to come out faster, coming out with greater speed and pressure, therefore going further.
This is what happens in the combustion chamber: the gas tries to get out as quickly as possible and comes out through the throat, its only possible escape route.
What happens next?
Let’s remember: As the throat is narrow, the temperature, pressure and speed of the gas increases, and it is expelled through the nozzle at supersonic speeds.
The nozzle will determine the way the gas comes out. We won’t get into details, but that determines if the engine is more efficient at sea level or more efficient in the vacuum of space.
What happens once the gas comes out of the nozzle? - The answer is given by Newton's 3rd Law, which says that every action has a reaction. The gas pushes the molecules from the environment and the molecules push the entire vehicle. To understand this, let's look at another example:
Imagine that you are on roller skates, and you push a wall. You will force on the wall, but you will go backwards. I mean, the wall will push you. This is based on the same action-reaction principle. Action: you push the wall. Reaction: The wall pushes you. The same goes for the rocket.
To reach orbit, a huge amount of fuel is needed. That’s why rockets have more than one stage. This means that a rocket is inside of a rocket, called stage, and when a stage’s fuel runs out, it gets discarded, making the stage of the rocket where the payload is located lighter, allowing it to accelerate easier. That’s why space vehicles are so big. You can compare space vehicles with structures of Alcaraz in the Size Comparison Tool, which is just below this text, to really know how big space vehicles are.
Size Comparison Tool
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SCT v1.0
The Size Comparison Tool works thanks to a comparison made between a distance measure of one of Alcaraz’s structures (for example its height or width) and a distance measure of a space vehicle. Aerial images are automatically gotten from Google Earth. We’re working hard to bring more space vehicles to this tool. Now, we’re going to show you the current vehicles used to launch people and cargo into the ISS.
Dragon V2 (Crew/Cargo)
Dragon V2 is the newest vehicle to join the fleet of vehicles that transport crew and cargo to the ISS. Debuting both the Crew Dragon (crewed) and the Cargo Dragon in 2020, it is the first spaceship manufactured by a private company to launch people to space. It is manufactured by the American company SpaceX.
We can distinguish two principal parts in it:
The capsule itself: It’s the upper part. It is pressurized and it is where the crew stays.
The trunk: It’s the lower part, where the solar panels are located and also the cargo which doesn’t need to be in a pressurized environment.
It is a fully reusable spacecraft. Once it splashdowns, it can be refurbished and rehabilitated to be launched again. It’s launched aboard a Falcon 9 rocket, which is also reusable. When it deploys the second stage into its correct altitude, it separates and makes a maneuver in which it falls back to the Earth and lands in the mainland or in an autonomous droneship.
This spacecraft is able to dock automatically into the space station. Its flight deck isn’t like any we have seen before, it just consists of three touchscreens and a few buttons. Also, it can carry up to 7 crew members inside of it. During 2021, this spacecraft will also the first one to launch the first all-civilian space mission into space.
Crew Dragon Tour
Here is a tour of Crew Dragon Endeavour spacecraft recorded by Bob and Doug. They show us its inside and how is the Earth seen from there. We can see how they do a sideflip too! It’s a very spacious ship, innovative in every single detail. In the spacecraft screens, they can do whatever thing they want, like watching Netflix. They also use normal iPads, like the ones we use, to do some tasks.
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Video length: 8min
Language: English
Uploaded by: NASA
Soyuz MS
Soyuz MS is an evolution of the original Soyuz spacecraft, which has been operating since 1966. It allows transporting up to 3 crew members. It also docks automatically to the space station by using the Kurs system. Some of the upgrades on the MS variant are: upgrades of the solar panels, the Kurs system, the flight computer; the ability send telemetry to data-relay satellites, and it also features GNSS systems, to make it easier to locate the spacecraft when it touches down. This spacecraft has lots of history behind: it has docked with the Solyut space stations, with the Mir space station, with the ISS and with an Apollo spacecraft (ASTP).
Soyuz Tour
Mike shows a Soyuz spacecraft to us: how it works, its features and his experience when flying in it.
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Video length: 11min
Language: English
Uploaded by: NASA Johnson
Progress
Progress is almost identical to Soyuz, but it only allows cargo to be sent to the ISS. It’s atmospheric reentry is destructive, so its filled of trash and things that are not needed anymore so they are destroyed during reentry.
Boeing Starliner CST-100
Starliner CST-100 is a crewed spacecraft designed by Boeing for the Commercial Crew program (just as Dragon V2). Physically, its similar to the Orion spacecraft that will carry humans to the moon soon. It has an interesting feature that none of the spacecraft above has: the ability to be launched aboard different launch vehicles.
Currently, its being developed, and hopefully in 2021, its very first crewed mission will be launched. The first crewed spacecraft has been named “Calypso” by the crew.
In this video, you can see its insides and its window during its first test flight.
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Video length: 3min
Language: English (only text)
Uploaded by: Boeing
Inside Starliner
Cygnus
Cygnus is a spacecraft manufactured and launched by Northrop Grumman, for the Commercial Ressuply Services (CRS) program. The V1 Dragon from SpaceX also takes part on this program, but it is already retired. Cygnus’ atmospheric reentry is also destructive, just like the Progress spacecraft, so it is filled of trash and not needed things so they destroy when the spacecraft reenters the atmosphere. It debuted back in 2013.
