The cargo spacecraft does not carry people, is it a manned spacecraft?

Cargo spacecraft are the backbone of manned space flight. Without them, no country's space station can be maintained. Interestingly, if we look back in detail at the historical origins of the world's major spacecraft, we will find that the relationship between manned spacecraft, cargo spacecraft and space stations is not just a simple space docking relationship, but has many similarities in technology and thinking.

Global spacecraft lineup: seven passenger and six cargo

Currently, there are three types of spacecraft in the world that are carrying out manned flight missions: the Soyuz MS, Shenzhou, and Crew Dragon. In addition, the Orion of Lockheed Martin, the Starliner of Boeing, and China's new generation of manned spacecraft are under development. Russia's Seahawk spacecraft is said to be under development, but no detailed progress has been announced. In addition, the development of the Angara rocket scheduled to launch the Seahawk has not been smooth, which is likely to affect its launch schedule.

Soyuz spacecraft detaches from the International Space Station

Interstellar spacecraft flight renderings

There are currently seven different types of cargo spacecraft in the world, including Russia's Progress, China's Tianzhou, the United States' Cygnus, Dragon Cargo, and Dream Chaser, Japan's H2 Rocket Transfer Vehicle (HTV), and Europe's Automated Transfer Vehicle (ATV). However, Dream Chaser is still under development, and Dragon Cargo, ATV, and HTV have just stopped production.

Cygnus spacecraft approaches the International Space Station

3 different design ideas

These spacecraft adopt three different design concepts. The first type of cargo spacecraft can be called a pure cargo spacecraft, which is only responsible for delivering materials from the ground to the space station, and then acting as a garbage truck and returning to the atmosphere to burn up. The second type can be called a multi-purpose type. They not only deliver materials to the space station, but also dock with the space station for a long time, acting as a temporary pressurized cabin for astronauts to work, rest and live in, and of course, they can also serve as a warehouse. The third type is a reusable spacecraft.

The first type of spacecraft is represented by the Progress spacecraft of Russia, the second type is represented by the Tianzhou spacecraft of China, the Cygnus spacecraft of the United States, as well as the ATV and HTV. The third type is represented by the Crew Dragon and the Dream Chaser.

Japan's HTV cargo spacecraft arrives at the International Space Station

There is no clear distinction between these types of spacecraft. Manned spacecraft generally have the ability to carry passengers and cargo. The Crew Dragon and Starliner also use a detachable seat model, and usually remove three seats to increase cargo capacity. Some cargo spacecraft are converted from manned spacecraft, the most typical of which is the Progress spacecraft, which was developed based on the Soyuz spacecraft with the orbital module removed.

Some cargo spacecraft are the forerunner models of manned spacecraft, in order to break through the spacecraft structure, return and landing and other related technologies. When these technologies are successful, further breakthroughs will be made in technologies related to manned flight. This is the case with the cargo Dragon spacecraft, that is, the development model of the Dragon spacecraft and the Progress spacecraft is opposite. In a sense, the cargo Dragon spacecraft is a simplified model of a manned spacecraft. This simplified model can form two spacecrafts with different purposes based on the same set of design blueprints, which is of great significance to simplifying the workload. The Dream Chaser spacecraft also tried to take this development route, but it has not yet succeeded. ATV was also considered to be transformed into a manned spacecraft, but the model was discontinued halfway.

Some cargo spacecraft are newly developed independently. From the beginning of their design, they did not consider any manned round-trip functions, including Tianzhou, HTV and Cygnus spacecraft. They do not need to bear the responsibility of astronauts entering and exiting the atmosphere, so they do not have the ablative material layer, parachute system, pneumatic control system, recoil rocket landing system, etc. required for return. They are really "one-way freight trucks." Some designers once considered using this type of spacecraft to transform it into a round-trip model between the earth and the sky, so as to at least bring back some samples of space experiments, but none of them have been realized. Such missions are now achieved through mixed passenger and cargo manned spacecraft.

Large differences in cargo capacity

Manned spacecraft are usually mixed with passengers and cargo, so it is not convenient to compare cargo capacity, so here we only compare the cargo capacity of several cargo spacecraft. The size of cargo spacecraft varies greatly, and the cargo capacity also varies greatly.

We can find an interesting fact: the cargo uplift capacity of the two types of cargo spacecraft is very different. The total cargo uplift capacity of the Progress spacecraft seems to be worse, but this is mainly because its internal volume is relatively small. If measured by unit space gravity, it is actually second only to the "Dragon Cargo". What is the reason for this? Could it be that the ATV and HTV were not fully loaded before they went into space?

You should know that cargo spacecraft do not fly on their own, but rely on rockets. The size of the rocket's carrying capacity actually determines the weight of the cargo spacecraft and the cargo. The Tianzhou-4 spacecraft is launched by the Long March-7 carrier rocket, the ATV is launched by the Ariane 5 rocket, the HTV is launched by the H2 rocket, and the cargo Dragon spacecraft is launched by the Falcon 9 rocket. The different carrying capacities of these rockets and the differences in the launch mass of the spacecraft determine the size of the spacecraft's cargo capacity.

Tianzhou-4 spacecraft in the factory

Different docking methods

Regardless of whether they are passengers or cargo, the above-mentioned spacecraft can be classified into another category, that is, those that can dock autonomously and those that cannot dock autonomously and must rely on the robotic arm to grab the docking port. Among them, Tianzhou, ATV, "Progress" and "Dream Chaser" belong to the first category, and the rest belong to the second category. These two modes have their own advantages and disadvantages. For spacecraft that can rendezvous and dock autonomously, the docking process is relatively free and there is no need to wait for the idle time of the manipulator, but they need to be equipped with radar, optical sensors, and corresponding attitude and orbit control capabilities, which is relatively expensive; the models that cannot rendezvous and dock autonomously are completely the opposite. If future space stations are equipped with a large number of robotic arms, perhaps the latter type of spacecraft will be more popular.

Dream Chaser and the Space Shuttle

They are all manned spacecraft

Whether it is a cargo spacecraft or a manned spacecraft, they are all manned spacecraft. This is because after they dock with the space station, the internal environment must be opened up. Astronauts must wear cabin spacesuits to enter these two types of spacecraft to carry cargo or perform operations. Therefore, even for cargo spacecraft, the interior must provide an environment where humans can survive, at least to ensure airtightness, and cannot become a leaking part on the space station. Because of this, there is technical interoperability between manned spacecraft, cargo spacecraft, and space station modules. With the continued development of manned space activities, perhaps people can find more common ground between these three types of aircraft, so that the maximum degree of generalization of materials, components, design, technology, and processes can be achieved. This is of great significance to reducing costs, shortening cycles, and expanding production capacity.