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The upcoming Axiom-4 mission to the International Space Station (ISS) marks a pivotal moment for India, as Shubhanshu Shukla is set to become only the second Indian to venture into space. The mission, initially slated for Wednesday from NASA’s Kennedy Space Center, has been temporarily delayed due to a technical issue. This important flight will carry a crew of four astronauts: Peggy Whitson (United States), Shubhanshu Shukla (India), Slawosz Uznanski-Wisniewski (Poland), and Tibor Kapu (Hungary), aboard SpaceX’s Crew Dragon spacecraft, propelled by a Falcon 9 rocket. As reported by The Indian Express, this delay is due to a “technical snag” with the SpaceX rocket.
Before any space launch, scientists meticulously determine a “launch window” – a precise timeframe during which the rocket must lift off to efficiently and safely reach its destination, whether the ISS, the Moon, or Mars. This careful planning is crucial because all celestial bodies, including Earth, the Moon, and the ISS, are in constant motion. Rockets cannot simply launch at any moment; scientists must calculate the exact timing for the spacecraft to follow a precise trajectory and intercept its target, a process known as “celestial alignment.”
Consider it like catching a moving train: arriving too early or too late means you miss it. Similarly, rockets must launch at the perfect instant to “catch” the ISS as both orbit Earth.
A spacecraft doesn’t fly directly to the ISS. Instead, it first enters orbit around Earth, circling the planet multiple times. This gradual approach allows it to progressively match the ISS’s orbit, conserving substantial fuel – a critical factor for mission success and cost-effectiveness.
Attempting a direct, straight-line flight to the ISS would necessitate constant acceleration against gravity, consuming an immense amount of fuel. Imagine cycling straight up a steep hill – it’s arduous and energy-intensive. A winding path with gentler turns, however, allows for easier ascent with less energy expended. Similarly, spacecraft follow a curved trajectory after reaching a certain height and speed, smoothly transitioning into orbit and conserving energy far more efficiently than a straight ascent.
The Falcon 9 rocket, a creation of Elon Musk’s SpaceX, is a partially reusable launch vehicle. Its components can be recovered and reused for subsequent missions, making space travel more sustainable. Falcon 9 is employed to deploy satellites, deliver supplies, and transport the Dragon spacecraft into space, primarily for missions to low Earth orbit (up to 2,000 kilometers above Earth), but capable of reaching farther distances when required.
The rocket comprises two main sections, or stages:
The International Space Station orbits Earth at an approximate altitude of 400 kilometers and a remarkable speed of around 28,000 kilometers per hour. Due to this high velocity, the Dragon spacecraft cannot simply travel directly to it. Instead, after reaching space, Dragon systematically raises its altitude and adjusts its trajectory to synchronize with that of the ISS.
To achieve this, the spacecraft executes a series of “phasing maneuvers.” These are minor, calculated changes in its orbit that help it align with the ISS. Dragon accomplishes this using 16 small engines called Draco thrusters, each generating approximately 0.4 kilonewtons of force, providing precise pushes to guide the spacecraft.
The Dragon spacecraft typically takes around 28 hours to reach the ISS from launch. In contrast, Russia’s Soyuz spacecraft can complete the same journey in a mere eight hours. This difference stems from their distinct flight plans, which are dictated by their design and capabilities.
Dragon is a relatively newer spacecraft, having first launched in 2012, while Soyuz has been operational since the 1960s. As a newer vehicle, Dragon necessitates more testing and fine-tuning. SpaceX is continuously working to optimize its launch timing and orbital paths through complex mathematical models, with the aim of reducing the journey duration in the future.
Given that Dragon is still undergoing refinement, astronauts on board spend additional time verifying its systems. They also gather crucial in-flight data, which is transmitted back to Earth for engineers to analyze.These essential safety and performance checks are part of the detailed preparations that The Indian Express highlighted regarding the mission’s comprehensive approach. These checks contribute to the longer travel time compared to older spacecraft like Soyuz, which no longer require such detailed scrutiny.
As the Dragon capsule nears the ISS, it first establishes communication with the space station. It then performs a final positioning maneuver and enters an invisible “keep-out sphere” around the ISS, approximately 200 meters wide. Within this safety zone, the spacecraft meticulously aligns itself with the docking port.
At this stage, Dragon activates its autonomous docking system. Utilizing GPS, cameras, and imaging sensors like Lidar (which employs lasers to measure distance), the spacecraft feeds data to its onboard computer. The computer processes this information to precisely calculate how and when to fire the Draco thrusters, enabling the capsule to move slowly and accurately towards the ISS.
Despite both Dragon and the ISS moving at extremely high speeds, their relative speed to each other is nearly zero, making docking feasible. While most docking is performed automatically, astronauts onboard Dragon can assume manual control if necessary.
Types of Thrusters Used:
Once the Dragon capsule docks with the ISS, immediate entry for the crew is not possible. The spacecraft remains connected for one to two hours to allow for stabilization and safety checks. Engineers ensure that pressure levels are equalized and that there are no leaks between the two vehicles. Only after these comprehensive checks are completed do the astronauts open the transfer gates and move into the International Space Station to commence their mission.
(Girish Linganna is an award-winning science communicator and a Defence, Aerospace & Geopolitical Analyst. He is the Managing Director of ADD Engineering Components India Pvt. Ltd., a subsidiary of ADD Engineering GmbH, Germany. Contact: girishlinganna@gmail.com)
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