A Guide to the Cargo Spacecraft of the ISS and Tiangong

What to Expect

Space stations like the International Space Station (ISS) and China’s Tiangong space station are humanity’s outposts in orbit, requiring a constant flow of supplies to sustain crews and scientific endeavors. Cargo spacecraft, the unsung heroes of space exploration, deliver everything from food and water to cutting-edge experiments, ensuring these stations remain operational. This guide dives into the past, present, and future of cargo resupply spacecraft for the ISS and Tiangong, exploring their designs, missions, and the intricate logistics that keep these orbital laboratories humming.

The Vital Role of Cargo Spacecraft

Space stations, floating hundreds of kilometers above Earth, are isolated environments where every necessity—air, water, food, equipment—must be delivered from the ground. Cargo spacecraft are specialized vehicles designed to carry these essentials, often operating autonomously to dock with or be berthed to their respective stations. Unlike crewed spacecraft, which prioritize human transport, cargo vehicles focus on maximizing payload capacity and reliability. They also handle waste removal, orbit maintenance, and, in some cases, the return of scientific results to Earth.

The ISS, a collaborative effort involving NASA, Roscosmos, ESA, JAXA, and other partners, has been continuously occupied since 2000. Tiangong, operated by the China National Space Administration (CNSA), is a newer station, with its core module launched in 2021. Each station’s cargo needs reflect its design, crew size, and mission goals. The ISS relies on a diverse fleet of spacecraft from multiple nations, while Tiangong depends solely on China’s Tianzhou. This guide covers the full spectrum of cargo spacecraft—past, present, and planned—detailing their contributions to these iconic space stations.

Historical Cargo Spacecraft of the ISS

The ISS’s early years saw a variety of cargo spacecraft, some of which have been retired but played pivotal roles in establishing the station’s supply chain. These vehicles laid the groundwork for modern resupply operations.

Progress (Early Variants)

The Progress spacecraft has been a cornerstone of ISS logistics since the station’s inception. Originating in the Soviet era as a derivative of the Soyuz spacecraft, Progress was first used in 1978 to supply the Salyut space stations. By the time the ISS was operational, Progress had evolved through several variants, including the Progress M and M1 models.

The Progress M, introduced in 1989, was the first to service the ISS, starting with the Zarya module in 1998. It carried about 2,300 kilograms of cargo, including food, water, scientific equipment, and propellant. The Progress M1, launched in 2000, prioritized fuel delivery, with a capacity of 1,800 kilograms of propellant but less dry cargo. Both variants were launched from the Baikonur Cosmodrome on Soyuz rockets and docked autonomously using the Kurs system. After unloading, they were filled with waste and burned up on reentry. These early models were reliable but limited by their Soviet-era design, lacking the flexibility of modern spacecraft.

Automated Transfer Vehicle (ATV)

The Automated Transfer Vehicle (ATV), developed by the European Space Agency (ESA), was a significant contributor to ISS resupply from 2008 to 2014. The ATV was a large, sophisticated spacecraft, measuring 10.3 meters long and 4.5 meters wide, with a cargo capacity of up to 7,667 kilograms. It was launched on an Ariane 5 rocket from Kourou, French Guiana.

The ATV carried a mix of pressurized cargo (food, clothes, experiments), unpressurized cargo (external equipment), water, oxygen, and propellant. Its high capacity made it ideal for delivering large payloads, such as water tanks or new batteries. Like Progress, it docked autonomously to the Russian segment of the ISS, using a system compatible with Russia’s docking ports. The ATV also performed orbit-reboost maneuvers, a critical function for maintaining the ISS’s altitude. After unloading, it was filled with up to 6,500 kilograms of waste and destroyed during reentry. Five ATV missions were flown, each named after notable scientists or visionaries, such as Johannes Kepler and Albert Einstein.

The ATV’s design was a leap forward, with advanced navigation and a spacious cargo bay. However, its high cost and ESA’s shift toward other projects, like the Orion spacecraft, led to its retirement. Its legacy lives on in technologies used by other spacecraft, such as the service module for Orion.

Kounotori (H-II Transfer Vehicle)

Japan’s Kounotori, or H-II Transfer Vehicle (HTV), serviced the ISS from 2009 to 2020. Developed by JAXA, Kounotori was a versatile spacecraft with a cargo capacity of 6,000 kilograms, including both pressurized and unpressurized payloads. Launched on the H-IIB rocket from the Tanegashima Space Center, it was berthed to the ISS’s U.S. segment using the station’s robotic arm.

Kounotori’s design featured a pressurized logistics carrier for crew-accessible cargo and an unpressurized section with an exposed pallet for external payloads, such as batteries or satellites. This pallet could be retrieved by the ISS’s robotic arm, allowing astronauts to install equipment during spacewalks. Kounotori’s large capacity and flexibility made it a key player in ISS upgrades, particularly during the replacement of the station’s solar array batteries. Like the ATV, it was filled with waste and burned up on reentry. Nine missions were flown, with the final one in 2020 marking the end of its service.

Kounotori’s contributions extended beyond cargo delivery. It tested technologies like wireless power transfer and deployed small satellites from its unpressurized section. Its retirement paved the way for JAXA’s next-generation vehicle, the HTV-X, which is discussed later.

Current Cargo Spacecraft of the ISS

Today, the ISS relies on three active cargo spacecraft: Russia’s Progress, Northrop Grumman’s Cygnus, and SpaceX’s Dragon. Each brings unique capabilities, reflecting the diversity of the ISS partnership.

Progress (Modern Variants)

The modern Progress spacecraft, including the Progress MS series, is an evolution of its earlier counterparts. Introduced in 2015, the Progress MS features upgraded avionics, improved solar panels, and enhanced redundancy. It carries approximately 2,625 kilograms of cargo, including 950 kilograms of propellant, 420 kilograms of water, and 50 kilograms of compressed gases, alongside dry goods like food and experiments.

Launched from Baikonur on Soyuz 2.1a rockets, Progress MS docks autonomously to the Russian segment, typically the Zvezda or Poisk modules. Its Kurs-NA docking system is more precise than earlier versions, ensuring smooth connections. The spacecraft’s three modules—pressurized cargo, refueling, and service—allow it to deliver a balanced mix of supplies. After unloading, it’s packed with up to 1,800 kilograms of waste and deorbited over the Pacific Ocean.

Progress remains a workhorse, with multiple launches each year. Its simplicity and reliability make it indispensable, though its single-use design limits cost efficiency compared to newer vehicles. Recent missions, like Progress MS-31 in July 2025, highlight its ongoing role in ISS operations.

Cygnus

The Cygnus spacecraft, built by Northrop Grumman, is a key component of NASA’s commercial resupply program. First flown in 2013, the enhanced Cygnus can carry up to 3,750 kilograms of cargo. Its cylindrical cargo module, built by Thales Alenia Space, is pressurized for crew access, while external fixtures allow for unpressurized payloads like CubeSats. Cygnus launches on Antares rockets from Wallops Flight Facility or, occasionally, Atlas V rockets from Cape Canaveral.

Unlike Progress, Cygnus is berthed to the ISS’s U.S. segment (Unity or Harmony modules) using the Canadarm2 robotic arm. Its solar arrays, mounted on the service module, provide power during its weeks-long stay. After unloading, Cygnus is filled with up to 3,500 kilograms of waste and burns up on reentry. Recent missions have included deploying small satellites and testing fire-resistant materials, showcasing its versatility.

Cygnus’s commercial origins reflect NASA’s shift toward outsourcing logistics. Its high capacity and flexibility make it a vital part of the ISS supply chain, with missions scheduled through at least 2026.

Dragon and Dragon 2

SpaceX’s Dragon spacecraft and its successor, Dragon 2, are the only reusable cargo vehicles servicing the ISS. The original Dragon, first flown in 2012, carries up to 3,000 kilograms to the station and returns 2,500 kilograms to Earth. Dragon 2, introduced in 2020, adds autonomous docking capabilities, reducing reliance on the robotic arm. Both launch on Falcon 9 rockets from Kennedy Space Center or Cape Canaveral.

Dragon’s design includes a pressurized capsule for crew-accessible cargo and an unpressurized trunk for external payloads. The capsule’s heat shield enables a soft landing in the Pacific Ocean via parachutes, allowing SpaceX to recover and refurbish it. This reusability sets Dragon apart, as it can return valuable experiments or equipment for analysis. The trunk, which carries solar panels, is jettisoned before reentry.

Dragon’s versatility supports a wide range of missions, from delivering food to installing new solar arrays. Its ability to return cargo makes it critical for scientific research, with missions continuing to support the ISS through the 2020s.

Future Cargo Spacecraft for the ISS

The ISS’s cargo resupply is evolving as new vehicles emerge and existing ones are phased out. NASA’s commercial focus and international partnerships are driving the development of next-generation spacecraft.

HTV-X

JAXA’s HTV-X, the successor to Kounotori, is slated to begin ISS resupply missions in 2026. Designed to be more cost-effective and versatile, HTV-X will carry up to 5,800 kilograms of cargo, slightly less than Kounotori but with improved efficiency. It will launch on Japan’s H3 rocket from Tanegashima.

HTV-X features a modular design, with a pressurized cargo module and an optional unpressurized section. It will berth to the ISS’s U.S. segment, continuing Kounotori’s legacy of supporting external payloads. Enhancements include better autonomy and the ability to deploy satellites independently, reducing reliance on the ISS’s robotic arm. JAXA plans to use HTV-X for commercial missions, potentially serving private space stations post-ISS. Its first mission will test these capabilities, paving the way for Japan’s continued role in orbital logistics.

Dream Chaser

Sierra Space’s Dream Chaser, a reusable spaceplane, is a promising addition to NASA’s commercial resupply program. Scheduled for its first ISS mission in 2026, Dream Chaser can carry up to 5,500 kilograms of cargo and return 1,750 kilograms to Earth. It launches atop a Vulcan Centaur rocket from Cape Canaveral and lands on a runway, like the Space Shuttle.

Dream Chaser’s lifting-body design allows for gentle reentries, ideal for delicate scientific payloads. Its Shooting Star cargo module is disposable, burning up on reentry with waste, while the spaceplane itself is reusable. It will berth to the ISS’s U.S. segment, delivering a mix of pressurized and unpressurized cargo. NASA has contracted Sierra Space for at least seven missions, signaling confidence in Dream Chaser’s role through the ISS’s planned end in 2030.

Potential Commercial Ventures

NASA is exploring additional commercial resupply options as the ISS approaches its retirement. Companies like Blue Origin and Boeing are developing cargo vehicles for future stations, which could serve the ISS in its final years. These vehicles, still in early stages, aim to leverage reusable technologies and modular designs. While details are scarce, NASA’s push for commercialization suggests a diverse cargo fleet by the late 2020s, potentially including uncrewed versions of crewed spacecraft like Boeing’s Starliner.

Historical Cargo Spacecraft of Tiangong

Tiangong’s cargo resupply history is tied to its predecessor stations, Tiangong-1 and Tiangong-2, which served as testbeds for China’s space station technology.

Tianzhou (Early Missions)

The Tianzhou spacecraft debuted in 2017 with Tianzhou-1, servicing the Tiangong-2 testbed. A derivative of the Tiangong-1 module, Tianzhou-1 carried 6,000 kilograms of cargo, including propellant, food, and experiments. Launched on a Long March 7 rocket from Wenchang Spacecraft Launch Site, it tested automated docking and propellant transfer, critical for the operational Tiangong station.

Tianzhou-1 docked with Tiangong-2 three times during its mission, demonstrating China’s mastery of rendezvous technology. It also conducted experiments in orbital refueling, a step toward sustaining long-term stations. After five months, it was deorbited over the Pacific. These early missions validated Tianzhou’s design, setting the stage for its role in the current Tiangong program.

Current Cargo Spacecraft of Tiangong

Tiangong relies exclusively on the Tianzhou spacecraft, which has evolved into a robust, automated vehicle tailored to the station’s needs.

Tianzhou (Modern Variants)

The modern Tianzhou, used since the Tianhe core module’s launch in 2021, is a 9-meter-long, 3.35-meter-wide spacecraft with a cargo capacity of 6,500 kilograms. It features a pressurized cargo module for crew-accessible supplies and a service module with solar arrays and propulsion. Tianzhou docks autonomously to Tiangong’s Tianhe module using a Chinese docking mechanism based on Russia’s APAS-89 system, with a 800-mm transfer passage.

Tianzhou carries a mix of dry goods (food, clothes, experiments), propellant, and external payloads. Its refueling system, using a metal bellows tank and pressurized-gas recycling, allows it to transfer propellant to Tiangong, maintaining the station’s 400-kilometer orbit. Recent missions, like Tianzhou-8 in 2025, delivered supplies for two crew rotations, while Tianzhou-9, launched in July 2025, carried upgraded spacesuits and exercise equipment.

Tianzhou’s logistics are streamlined, with QR-coded items and a Wi-Fi network enabling crew to manage cargo via tablets. It supports Tiangong’s 120 food varieties, including dishes like kung pao chicken, stored in coolers. After unloading, Tianzhou is filled with waste and burns up on reentry, as it’s not designed for cargo return.

Future Cargo Spacecraft for Tiangong

China’s plans for Tiangong include expanding the station and enhancing its resupply capabilities. Tianzhou will remain the backbone, with potential upgrades and new vehicles on the horizon.

Tianzhou Upgrades

The CNSA is refining Tianzhou to support Tiangong’s expansion into a four- or six-module configuration. Future variants may increase cargo capacity to 7,000 kilograms and incorporate partial reusability, inspired by SpaceX’s Dragon. Enhanced propulsion systems could allow Tianzhou to service co-orbiting assets like the Xuntian space telescope, which will dock with Tiangong for refueling and maintenance by 2026.

Tianzhou’s role in cross-module propellant transfer, using Tiangong as a transit node, will be critical for these missions. Upgrades may also include advanced robotic arms for capturing visiting spacecraft or handling external payloads, building on Tiangong’s existing arm technology.

Mengzhou Cargo Variant

The Mengzhou spacecraft, a reusable crew vehicle designed for Tiangong and lunar missions, includes a cargo section capable of returning 700 kilograms to Earth. While primarily for crew, Mengzhou could be adapted for uncrewed cargo missions, offering Tiangong a reusable resupply option by the late 2020s. Its larger design, accommodating up to seven crew, suggests a cargo capacity exceeding Tianzhou’s, though details remain speculative.

Commercial and International Prospects

The CNSA is exploring commercial cargo missions, encouraging private companies to develop resupply vehicles. This aligns with Tiangong’s goal of hosting commercial activities and international astronauts. While no specific commercial spacecraft have been announced, China’s private sector, including companies like i-Space, could contribute vehicles by the 2030s, mirroring NASA’s commercial model.

Evolution of Cargo Resupply Operations

The history of cargo resupply reflects technological leaps and shifting priorities. Early ISS missions relied heavily on Progress and the Space Shuttle, which carried cargo alongside crews until its retirement in 2011. The ATV and Kounotori introduced high-capacity, specialized vehicles, while NASA’s commercial program with Cygnus and Dragon marked a shift toward privatization. Tiangong’s Tianzhou, evolving from Tiangong-1’s test missions, showcases China’s rapid progress in autonomous logistics.

Today, the ISS benefits from a diversified supply chain, with Progress, Cygnus, and Dragon offering redundancy and flexibility. Tiangong’s single-vehicle approach prioritizes efficiency for its smaller crew. Future plans, like HTV-X, Dream Chaser, and Tianzhou upgrades, point to a trend toward reusability, autonomy, and commercial involvement.

Technical and Operational Challenges

Cargo resupply involves navigating a host of challenges, from launch reliability to orbital mechanics. Here’s a deeper look at the hurdles and solutions.

Launch and Rendezvous Precision

Launching a spacecraft to rendezvous with a station moving at 28,000 kilometers per hour requires pinpoint timing. A launch window may last only seconds, as seen with Progress launches from Baikonur. Autonomous docking systems, like Kurs-NA on Progress or Tianzhou’s APAS-based mechanism, must align spacecraft within centimeters. Failures, though rare, can disrupt schedules, as seen in a 2015 Progress anomaly that delayed supplies.

Cargo Packing and Management

Packing a spacecraft is like solving a 3D puzzle. Items must be secured to withstand launch vibrations, with food vacuum-sealed and instruments padded. Tiangong’s QR-code system streamlines inventory, while the ISS uses detailed manifests. Both stations maintain emergency reserves to buffer delays, but optimizing cargo layout remains a logistical art.

Waste and Reentry

Disposable spacecraft like Progress, Cygnus, and Tianzhou are designed to burn up safely over the Pacific’s “spacecraft cemetery.” Dragon and Dream Chaser’s return capability adds complexity, requiring precise reentry trajectories. Mengzhou’s cargo section could face similar challenges if adapted for resupply.

Cost and Sustainability

Spaceflight costs billions, with single-use spacecraft like Cygnus or Tianzhou adding to expenses. Reusable vehicles like Dragon and Dream Chaser reduce costs, but refurbishment is resource-intensive. China’s push for Tianzhou upgrades and commercial vehicles plans to balance cost and reliability.

The Broader Impact of Cargo Resupply

Cargo spacecraft enable more than just survival—they fuel scientific discovery and international cooperation. ISS experiments in microgravity have led to advances in medicine, materials, and physics, with Dragon’s return capability ensuring results reach Earth. Tiangong’s 23 experimental racks and planned Xuntian telescope will drive research in cosmology and exoplanets.

These missions also inspire. The flawless docking of a Tianzhou or the splashdown of a Dragon capsule captures the imagination, showing what humanity can achieve. As commercial players like Sierra Space and China’s private sector enter the fray, cargo resupply will democratize access to space, paving the way for private stations and lunar outposts.

Summary

Cargo spacecraft are the lifeline of the ISS and Tiangong, evolving from early vehicles like Progress M and Tianzhou-1 to modern workhorses like Dragon and Tianzhou-9. The ISS’s diverse fleet—Progress, Cygnus, Dragon, and retired ATV and Kounotori—reflects its global partnership, while Tiangong’s Tianzhou embodies China’s streamlined approach. Future vehicles like HTV-X, Dream Chaser, and upgraded Tianzhou promise greater efficiency and reusability, ensuring space stations remain hubs of innovation. From delivering spacesuits to enabling cosmic research, these spacecraft sustain humanity’s presence in orbit, bridging the past, present, and future of space exploration.