Mission pilot Shubhanshu Shukla (second from left) with three of his crewmates, mission commander Peggy Whitson (U.S.) and mission specialists Sławosz Uznański (Poland) and Tibor Kapu (Hungary) onboard the Dragon crew capsule en route to the ISS, June 25, 2025.
| Photo Credit: X.com/@SpaceX
At 12.01 pm IST on June 25, a crew capsule containing 4 astronauts, together with India’s Group Capt. Shubhanshu Shukla on his first spaceflight, lifted off atop a Falcon 9 rocket from NASA’s spaceport in Florida.
The lift-off marked the begin of the long-awaited Axiom-4 mission.
The launch was clean. By the time the rocket’s two levels had accomplished their work, the crew capsule — referred to as Dragon — was travelling at a number of thousand kilometres per hour.
The capsule’s vacation spot was the International Space Station (ISS), which orbits the earth at roughly 400 km above sea degree. At the time of lift-off, Axiom Space, the firm orchestrating this mission, mentioned Dragon would dock with the ISS in 28 hours.
Why does a spacecraft travelling so quick need 28 hours to reach a spot that’s little greater than the distance between Chennai and Bengaluru away?
It helps to image the capsule and the ISS as two race-cars on separate lanes of the identical observe moderately than as a automotive attempting to drive straight up to a spot 400 km forward. Everything occurs sideways round the earth, and the choreography is dictated by orbital mechanics and strict security guidelines.
To share the ISS’s lane, the capsule wanted to match each its altitude and its velocity vector. This was achieved utilizing uncooked pace in addition to timing.
Going straight up 400 km would go away Dragon with just about zero sideways pace, inflicting it to fall again nearly instantly — like a ball that has been thrown up.
The Falcon 9 rocket vaulted Dragon right into a low, barely elliptical parking orbit about 200 km excessive. Its pace there was round 27,000 km/hr, which the capsule maintained simply to keep away from spiralling again down in direction of the floor.
The ISS can also be larger than this parking orbit, at round 400 km, and subsequently circles the earth a little bit extra slowly to keep away from spiralling down. While the ISS takes round 92 minutes to go round the earth as soon as, Dragon began by taking round 88 minutes. Thus, by being decrease than the ISS, Dragon slowly fell behind in its orbit till it had caught up with the ISS.
After its system check-outs, the Dragon capsule carried out a collection of small thruster burns, a.ok.a. phasing burns, to first elevate its apogee (the level of its elliptical orbit farthest from the earth) after which its entire orbit.
Each of those burns was timed such that after finishing a number of orbits, Dragon ended up being precisely the place the ISS could be. This was considerably like merging right into a freeway at the proper exit moderately than steering straight in direction of one other automotive.
For the Axiom-4 mission, the mission planners designed a pre-docking profile that lasted about 28 hours, or about 18 orbits. At the finish of this profile, the Dragon crew capsule was on the right facet of the ISS, the place a free docking port was positioned, and at a time when the ISS crew was awake.
Once Dragon got here inside 30 km or so of the ISS, it moved itself right into a (*28*) aligned with the ISS. From right here, the guidelines required the capsule to transfer at no various metres per second. Once it was inside 20 m of the ISS, Dragon was to sluggish to just a few centimetres per second.
There are holding factors at 400 m, 220 m, 20 m, and 1 m from the ISS, the place the Dragon crew, together with Group Capt. Shukla — who’s the designated mission pilot — would have had to carry out go/no-go polls and LIDAR checks. Even if there had been one unsuitable sensor studying on this course of, Dragon would have been required to retreat from the ISS alongside a pre-programmed path.
This deliberate pacing alone added a number of hours to the crew capsule’s method in direction of the ISS.
The undeniable fact that Axiom Space and NASA used SpaceX’s Dragon crew capsule for this mission can also be related. It allowed the mission operators to go for a extra conservative, fuel-rich profile that additionally allowed the crew to end check-outs, eat, and sleep earlier than beginning the intense docking train.
Published – June 26, 2025 03:30 pm IST
