Why did Axiom-4 need 28 hours to reach the ISS?

Context :

• Mission Overview:
  • Axiom-4 is a private crewed space mission to the International Space Station (ISS), organized by Axiom Space in collaboration with NASA and using SpaceX’s Dragon crew capsule.
  • Launched on June 25 from NASA’s Florida spaceport aboard a Falcon 9 rocket.

Relevance : GS 3(Space , Technology)

• Indian Representation:
  • Group Captain Shubhanshu Shukla, an Indian Air Force officer, is part of the crew — marking his first spaceflight and a significant milestone for India’s global space presence.
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Orbit and Pre-Docking Sequence

• Initial Orbit and Speed:
  • After separation from the Falcon 9, Dragon entered a low elliptical parking orbit ~200 km above Earth, traveling at approx. 27,000 km/h.
  • This orbit allowed the capsule to gradually phase and align with the ISS, which orbits ~400 km above Earth.
• Orbital Mechanics:
  • Rather than flying “upward,” Dragon had to match the ISS’s orbit both in altitude and horizontal velocity.
  • Like two cars merging on a curved highway, Dragon needed precise speed and timing adjustments.

Docking Profile and Safety Protocols

• Duration & Orbits:
  • The docking approach followed a 28-hour profile, completing ~18 orbits before docking.
• Step-by-Step Docking Process:
  • Dragon aligned into a designated approach ‘corridor’ when ~30 km from the ISS.
  • Docking involved progressive slowing, with mandatory hold points at:
    • 400 m, 220 m, 20 m, and 1 m.
  • At each point, the crew (including Group Capt. Shukla, the designated mission pilot) performed:
    • Go/no-go checks
    • LIDAR system verifications
• Abort Protocols:
  • A single faulty sensor or system alert would have required Dragon to abort and retreat safely via a pre-set escape path.
• Deliberate Pacing:
  • These safety steps intentionally extended the final approach time, prioritizing crew and ISS safety.

Operational Advantages and Crew Readiness

• Use of SpaceX’s Dragon Capsule:
  • Known for reliability, automated navigation, and reusability.
  • Allowed for a conservative, fuel-rich approach profile, enhancing mission safety and flexibility.
• Crew Well-being:
  • The slower approach gave the crew time for:
    • System check-outs
    • Rest and meals
    • Final mission prep before docking

Broader Significance

• Technical Excellence:
  • Demonstrates advanced international cooperation in human spaceflight.
  • Highlights the growing role of private aerospace firms in low-Earth orbit missions.
• India’s Emerging Role:
  • Group Capt. Shukla’s inclusion reflects India’s deepening engagement with global human spaceflight programs.