When India’s first human spaceflight, the Gaganyaan-4, comes to an end somewhere far beyond the Earth, a decisive moment is expected to unfold. The capsule carrying Indian astronauts will have to let go of the companion craft that has kept it alive for the entire journey.
Every step of that farewell has now been rehearsed on the ground, and the Indian Space Research Organisation (ISRO) says the results give it fresh confidence ahead of Gaganyaan-1, the initial uncrewed test flight planned for later this year.
Picture the Gaganyaan spacecraft as two parts travelling together. One is the Crew module, the cone-shaped capsule where the astronauts will sit. The other is the Service Module, which sits behind it and acts like a power plant and supply room rolled into one. It provides the electricity, fluids and other support for the crew module.
The two are joined before launch and fly as a single body into space and the on-orbit phase, when the spacecraft carries out its task while circling the Earth.
The umbilical connections, named after the cord that joins a baby to its mother, link the modules together. These special cables and pipes carry power and fluids from the Service Module into the Crew Module. For as long as the mission continues in orbit, those lines are a lifeline.
But when the time comes to re-enter the atmosphere, the Crew Module must travel alone. The Service Module has completed its mission and will be discarded. Engineers call this jettisoning, which simply means releasing a part that is no longer needed. The separation follows a fixed order of carefully planned steps. Small explosive charges known as pyrotechnic devices sever the connections, and jettisoning systems then push the two modules apart safely.
“A moment like this cannot be left to hope. If a cable fails to cut, or if the force of separation damages something inside the capsule, the astronauts' return could be endangered. That is why ISRO built a dedicated test facility at the Vikram Sarabhai Space Centre (VSSC) in Thiruvananthapuram. It is designed to reproduce the conditions of the complete Crew Module and Service Module assembly, with advanced measuring instruments recording every detail of how the system behaves,” explained space analyst Girish Linganna.
At the VSSC, engineers staged the separation, including cutting several of the umbilical lines that tie the two modules together. The verdict was reassuring on two counts. The overall separation system proved properly designed and capable of performing as planned, and the capsule's vital internal systems showed they could absorb the sudden shocks and vibrations of separation without harm.
“Each of these systems guards the crew in its own way. The avionics are the electronic brains of the spacecraft, controlling it and keeping watch over it. The Inertial Navigation Systems are its sense of direction, telling the capsule where it is, which way it faces and how fast it is moving. The Thermal Protection System is its armour. Fitted to the rear and cone-shaped heat shields, it keeps the searing heat of re-entry away from the astronauts. The Crew Module Deployable Umbilical Shield is a protective cover that closes over the spot where the cables and pipes once connected,” Linganna added.
According to the expert, two further systems also depend on pyrotechnic devices. The Crew Module Uprighting System turns the capsule the right way up after it splashes down in the sea, so the crew is not left tilted in the water. The Thermal and Humidity Control System keeps the air inside the cabin at a comfortable temperature and moisture level. All of these components remained intact through the test.
Experts highlighted that this test is the latest tick on a long checklist. Earlier in 2026, ISRO qualified the uprighting system, the umbilical connect-and-disconnect mechanisms, and the loads on the apex cover that sits atop the capsule. In April, the G1 crew module was dropped from an aircraft to prove its parachute descent. The module has since been fully integrated, with its propulsion and control systems installed for flight, re-entry and recovery.
ISRO Chairman V. Narayanan had said in June that the launch was expected in the last quarter of 2026, and repeated in September that it would fly within the year. No date has been announced, though some reports point to a window between mid-October and early November. The flight will carry Vyommitra, a half-humanoid robot, in place of astronauts. The first crewed mission is targeted for 2027.
The road has indeed been long. The uncrewed Gaganyaan-1 mission was first planned for December 2020, and as recently as last October it was expected to fly in December 2025. Each slip has been in the name of safety. With this rehearsal behind them, the teams in Thiruvananthapuram can look to Gaganyaan-1 with steadier hands and a surer heart.
