Artemis I: NASA's Orion spacecraft has entered the lunar sphere of influence, five days since its launch atop the Space Launch System (SLS) rocket as part of Artemis I. Orion entered into the lunar sphere of influence at 1:09 pm CST on November 20 (12:39 am IST on November 21). Since Orion has entered into the lunar sphere of influence, the Moon, instead of Earth, is the main gravitational force acting on the spacecraft.
Orion conducted the fourth outbound trajectory correction burn overnight, ahead of the outbound powered flyby burn. Trajectory correction manoeuvres are conducted after or before a rocket reaches an important milestone of its mission and are used to correct errors in the trajectory.
What is outbound powered flyby burn?
The outbound powered flyby burn is the first of the two manoeuvres required to enter the distant retrograde orbit (DRO) around the Moon. The DRO provides a highly stable orbit where little fuel is required to stay for an extended trip in deep space to put Orion's systems to the test in an environment far from Earth.
Orion completed its lunar flyby at 7:44 am EST (6:14 pm IST) on November 21.
What is distant retrograde orbit?
In a statement released by NASA, Artemis Mission Manager Mike Sarafin said DRO allows Orion to spend more time in deep space for a rigorous mission to ensure spacecraft systems, like navigation, power, guidance, thermal control and communication are ready to keep astronauts safe on future crewed missions.
The orbit is described as "distant" because it is at a high altitude from the surface of the Moon, and is termed "retrograde" because Orion will travel around the Moon in the opposite direction to the direction in which the Moon travels around Earth.
Since DRO interacts with two points of the planet-moon system where objects tend to stay put, balanced between the gravitational pull of two large masses, it is highly stable. In the case of Orion, the DRO interacts with two points of the Earth-Moon system. This will allow Orion to reduce fuel consumption and remain in position while travelling around the Moon. By the time Orion reaches the Moon, it will have travelled 2,40,000 miles.
Orion's service module, built by the European Space Agency (ESA), will provide the propulsion to get to DRO. In order to enter and exit DRO, a total of four major targeting navigational burns will be completed. Two of these burns must be conducted close to the Moon, and two far away from the Moon.
Some time after the flyby burn, Orion passed about 130 kilometres above the Moon, on November 21.
Flight controllers fired the orbital manoeuvring system engine for two minutes and 30 seconds to accelerate Orion at a rate of more than 933.42 kilometres per hour.
After this, Orion will perform a second propulsive burn to enter DRO and stabilise itself in the orbit.
According to NASA, Orion will spend about six to 19 days in DRO to collect data and allow mission controllers to assess the performance of the spacecraft.