Axiom-4 Docking: After a successful Falcon-9 launch, the Axiom-4 mission now faces its next big challenge: docking with the International Space Station (ISS). The process, scheduled to begin 12 to 24 hours post-launch, is largely automated but involves dozens of intricate steps, each demanding pinpoint accuracy.
It all starts with the “phasing” burn. Using 16 Draco thrusters, the Dragon capsule raises its orbit to align with the ISS, which cruises around 418 km above Earth. This is followed by a series of burns — boost, close co-elliptic, transfer, and a final co-elliptic adjustment — bringing Dragon to a position just 2.5 km below the station.
An “out-of-plane” burn then corrects any lateral drift, aligning Dragon perfectly with the ISS docking axis. These manoeuvres are executed autonomously, without crew input, and rely on navigation sensors and computer calculations to avoid fast, risky approaches.
The Critical Close Approach
The final approach is just as complex as the journey itself. Once Dragon is 2.5 km below and 7 km behind the ISS, a 90-second engine burn brings it into the close approach zone. It then moves to within 400 meters, followed by incremental stops at 220 meters (Waypoint 1) and 20 meters (Waypoint 2), just shy of the docking port.
Dragon must pass several “hold points” where it demonstrates its ability to maintain position for hours before proceeding. At the Crew Hands-Off Point, 20 meters from the station, the spacecraft is fully aligned. If anything goes awry, Dragon is programmed to back away automatically without human assistance.
Docking completes with a soft capture as the two crafts connect. Once locked in place, a cable links Dragon to the station’s power and data systems. Pressurisation follows, leak checks are run, and only after clearance are the hatches opened and the crew allowed aboard.
What Could Derail the Docking?
Despite the high-tech choreography, several things could go wrong. Even small errors in trajectory or sensor feedback could throw off alignment. If the guidance system malfunctions, Dragon might miss the docking port — or worse, approach it at an unsafe angle.
Other risks include faulty docking mechanisms, loss of attitude control, or even miscalculations in thrust that could push the vehicle off course. In extreme cases, a malfunction could result in a collision with the ISS.
There’s also the threat of pressure leaks if the seal isn’t airtight after docking, which could cause depressurisation. Plume impingement — where thrusters fire too close to sensitive ISS components — poses another hazard, potentially damaging solar panels or external instruments.
Environmental contamination is also a concern. If Dragon carries leaked coolant or any other toxic substance in its atmosphere, it could compromise the air quality inside the ISS once the hatches open.
Contingency Plans and Safety Protocols
To manage these high-stakes risks, NASA and SpaceX have built multiple layers of contingency into the Axiom-4 mission. First, all burns and movements are pre-programmed and monitored in real time by mission control, ensuring rapid response if systems drift from their path.
The docking procedure is designed to allow for both autonomous operation and manual override. Should the automated systems fail, the crew aboard Dragon can take control. Redundant sensors, cameras, and laser-guided systems provide additional failsafes during the alignment process.
Before entering the ISS’s close approach zone, all systems undergo comprehensive health checks by teams at both NASA and SpaceX. The station itself has multiple safety protocols, including the ability to abort docking procedures and move the station if required.
In case of health emergencies, the ISS is equipped with medical kits and telemedicine support, ensuring preparedness for both minor injuries and serious medical events during docking.
The Axiom-4 mission’s docking phase may be routine on paper, but it’s a mission-critical operation that demands perfection. With sophisticated tech, detailed planning, and robust backups, every move toward the ISS is calculated, because in space, even a few centimetres can make all the difference.
