Chandrayaan 2 to enter an orbit around the Moon today, two weeks before planned soft landing
Chandrayaan 2's thrusters will fire at precisely the right moment to slow down the composite for lunar capture.
The second moon mission from India, Chandrayaan 2, is expected to enter the moon's orbit today (20 August), one of the few remaining critical milestones in the mission before the spacecraft attempts to soft-land on the moon's surface on 7 September.
Currently, the Chandrayaan 2 composite is completing its lunar transfer phase, which will bring the spacecraft close enough to the moon that it can transition into the moon's orbit using power from its thrusters. This manoeuver will allow it to break away from the Earth's gravitational pull and fall into the moon's gravity.
An illustration of the orbit-raising to lunar transfer transition of the Chandryaan 2 spacecraft. Image: ISRO
When the moon reached its apogee — its farthest point from the Earth — the Chandrayaan 2 spacecraft's onboard thrusters will fire for a pre-determined period, generating just enough thrust to slow itself down for this 'lunar capture' phase. This controlled transfer event — breaking free from the Earth's orbit of influence and into the moon's — will unfold over several hours, estimated to end by 9.30 am IST on 20 August.
The critical step will require the liquid apogee motors (thrusters) to be fired in the opposite direction to the spacecraft's movement, therefore slowing it down in a what's known as "retrofiring". This allow the spacecraft to come under the influence of the moon's orbit.
With the location of the moon relative to the Earth and the Earth relative to the Sun constantly changing, the intersection of Chandrayaan 2's path with the moon's was predicted and planned well ahead of time.
Orbit-raising diagram for the Chandrayaan 2 misson. Image: ISRO
Once the lunar capture, or entry of the spacecraft into lunar orbit, is complete, the two-week (lunar-bound) phase of the mission will begin. This is an important part of the orbiter's mission: surveilling its year-long home for the first time, ensuring that no damage was caused to its instruments on the journey thus far, and a thorough examination of the Vikram lander's landing site at the moon's South Polar region.
Chandrayaan 2 is expected to make its long-awaited powered descent and landing on 7 September in what the ISRO Chief describes as '15 minutes of terror'.
While today's attempt won't be streamed live, you can follow live updates on the mission on our dedicated Chandrayaan 2 domain, ISRO's website, or Twitter page.