By R Anil Kumar
NASA plans for the Dragon Spacecraft to dock with the Harmony module of the International Space Station during the Axiom-4 mission at 7am EDT (4.30pm IST) on June 26. Here follows an explainer on why it takes so long to cover a distance of 400 kilometers:
Florida / Bengaluru. The Axiom-4 mission which took-off a few hours ago from launch complex 39A at NASA’s Kennedy Space Center in Florida being piloted by Group Captain Shubhanshu Shukla will be docked with the Harmony module of International Space Station (ISS) at 7 am EDT (4.30pm) on 26 June.
The Axiom-4 mission necessitates an approximate travel duration of 28-29 hours to traverse a distance of 400kms from earth to the International Space Station.
This time frame is not solely attributable to linear distance but rather to the intricate orbital mechanics that govern the process of rendezvousing with ISS.
The following factors elucidate the complexities involved:
Orbital mechanics and trajectory adjustments: The SpaceX Dragon Spacecraft which is deployed aboard a Falcon 9 rocket is initially positioned in the lower orbit than that of ISS. To facilitate docking with the ISS the Spacecraft must undertake a series of trajectory adjustments and altitude modifications to synchronize its orbit with that of ISS.
The process entails multiple orbital manoeuvres including incremental elevation of its orbit and precise alignment of its flight path to intersect with the ISS, which travels at an approximate velocity of 28,000Km/h. Such adjustments demand meticulous timing and propulsion burns to ensure a safe rendezvous, extending the overall travel time.
Phasing and Orbital Synchronization: The ISS revolves around the earth at a high velocity completing an Orbital Cycle approximately every 90 minutes. Subsequently the Dragon Spacecraft must synchronize its Orbital trajectory with the current position of the ISS, which may not be situated directly above the launch site at the time of departure.
This Synchronization process known as phasing, necessitates that the Spacecraft orbit the earth atleast twice while modifying its speed and trajectory to effectively ‘catch up’ with ISS. This methodical sequencing is critical for ensuring precise and secure docking with the International Space Station.
