China's astronauts, or taikonauts, in the space station are expecting a load of cargo brought by China's space courier Tianzhou-6 cargo ship, which launched from the Wenchang Spacecraft Launch Site on Wednesday night.

The Tianzhou-6 cargo ship contains a 22.5-cubic-meter cargo compartment with 50 lockers to place daily necessities for the taikonauts and equipment needed for in-orbit experiments.

About 70 kilograms of fresh fruit are aboard the spacecraft for delivery to China Space Station, roughly twice the weight of that carried by Tianzhou-5.

Fruit that's convenient to eat, rich in nutrition with long storage life is always the preferred choice. In previous missions, apples, bananas and grapes were sent.

"We plan to send a large refrigerator to the space station to ensure that the supply for the taikonauts contains not only fruits but also some frozen food," Wang Ran, lead designer of cargo spacecraft systems at China Academy of Space Technology (CAST), told China Media Group (CMG). "For example, in the future, if they wish to eat grilled steak, we will freeze the beef on the ground and deliver it to the space station."

"We will bolster our ability gradually to ensure a better life for the taikonauts," said Wang.

Besides food, the cargo ship will also deliver other daily necessities such as clothes, holiday and sanitation supplies, as well as experimental equipment for the taikonauts.

Jia Dongyong, chief mechanical designer for the Tianzhou cargo spacecraft system at CAST, told CMG that the Tianzhou-6 cargo ship is the most capable space cargo ship currently in service.

With a maximum launch mass of 14 tonnes, the Tianzhou-6 spacecraft now has a payload ratio of 0.53, said Jia.

The payload ratio refers to the proportion of cargo weight to the total weight of the whole spacecraft. The higher the ratio, the stronger the cargo capacity of the spacecraft.

Upgraded payload capacity

Another important mission for Tianzhou-6 is to replenish propellants for the space station.

The Tianzhou-6 cargo craft will be the first of a new batch of China's cargo ships – from Tianzhou-6 to Tianzhou-11 – to boost their loading capacity from the previous 6.9 tonnes to 7.4 tonnes.

The cargo spacecraft is 10.6 meters long and consists of two parts – a smaller lower part as its propellant module and a larger upper part as the cargo module.

Since it has entered the application and development stage, China's space station no longer requires large amounts of propellant for altitude adjustment.

Therefore, the Tianzhou-6 cargo ship has reduced the number of its propellant tanks from eight to four compared with its predecessors, leaving room for more payload.

"The volume of the airtight cabin (cargo cabin) has been increased by 20 percent, meaning an increase in the loading capacity by 1.2 tonnes, from 5.5 tonnes previously to 6.7 tonnes currently," said Jia. "That's why we will mainly launch such improved cargo spacecraft in the future."

Tianzhou-6's launch is of great significance for the technical verification of the new batch of improved cargo spacecraft and the mass production of subsequent spacecraft, Jia added.

The Tianzhou-6 cargo craft is the first spacecraft to visit the Shenzhou-15 crew in orbit. It was launched atop a Long March-7 carrier rocket, the country's new-generation medium liquid-propellant carrier rocket with high reliability and safety.

With a total length of 53.1 meters and a diameter of 3.35 meters, the rocket is bundled with four boosters and has a takeoff weight of nearly 600 tonnes and a payload capacity of about 14 tonnes to low-Earth orbit.

The Tianzhou-6 mission is the 7th launch for the Long March-7 rocket.

In addition to undertaking cargo launch missions to the space station, the Long March-7 rocket will also launch low- and medium-orbit satellites in the future. 

Read more: Long March-7 rocket to send Tianzhou-6 cargo ship to China Space Station