India’s Moon Mission Is Far From Over



India’s Chandrayaan-2 mission to the Moon was, in a word, ambitious. Lifting off from the Satish Dhawan Space Centre on July 22nd, the mission hoped to simultaneously deliver an orbiter, lander, and rover to our nearest celestial neighbor. The launch and flight to the Moon went off without a hitch, and while there were certainly some tense moments, the spacecraft ultimately put itself into a stable lunar orbit and released the free-flying lander so it could set off on its independent mission.

Unfortunately, just seconds before the Vikram lander touched down, an anomaly occurred. At this point the Indian Space Research Organisation (ISRO) still doesn’t know exactly what happened, but based on the live telemetry stream from the lander, some have theorized the craft started tumbling or otherwise became unstable between three and four kilometers above the surface.

Telemetry indicates a suboptimal landing orientation

In fact, for a brief moment the telemetry display actually showed the Vikram lander completely inverted, with engines seemingly accelerating the spacecraft towards the surface of the Moon. It’s unclear whether this was an accurate depiction of the lander’s orientation in the final moments before impact or a glitch in the real-time display, but it’s certainly not what you want to see when your craft is just seconds away from touchdown.

But for Chandrayaan-2, the story doesn’t end here. The bulk of the mission’s scientific goals were always to be accomplished by the orbiter itself. There were of course a number of scientific payloads aboard the Vikram lander, and even the Pragyan rover that it was carrying down to the surface, but they were always secondary objectives at best. The ISRO was well aware of the difficulties involved in making a soft landing on the Moon, and planned their mission objectives accordingly.

Rather than feel sorrow over the presumed destruction of Vikram and Pragyan, let’s take a look at the scientific hardware aboard the Chandrayaan-2 orbiter, and the long mission that still lies ahead of it.

Long Term Goals

The Chandrayaan-2 orbiter is an evolved version of the spacecraft the ISRO launched to the Moon in 2008 during the Chandrayaan-1 mission. The 682 kg (1,504 lb) craft is a bit longer than your average midsize car, and was designed for a nominal mission length of one year. But given the accuracy with which the craft was placed into its 100 km polar orbit around the Moon, mission planners are now hopeful the craft will remain stable for much longer, perhaps as many as six years longer than originally estimated.

Chandrayaan-2 Orbiter

While the orbiter was responsible for bringing the Vikram lander to the Moon, that was never its primary goal. According to ISRO Chairman Kailasavadivoo Sivan, approximately 90-95% of the scientific goals of the mission were always to be accomplished by the orbiter itself. The loss of the lander and rover were certainly unfortunate, but the impact on overall mission success is considered minimal.

Somewhat ironically, the scientific instruments aboard the orbiter have already been put to good use trying to locate the Vikram lander on the surface. One of the most important pieces of equipment on the orbiter is the Orbiter High Resolution Camera (OHRC), which is capable of 30 centimeters per pixel resolution; slightly edging out NASA’s Lunar Reconnaissance Orbiter in terms of its ability to resolve surface details.

The orbiter also has the Terrain Mapping Camera-2 (TMC-2), a 3D imager which will create a detailed height-map of the lunar surface. Combined with data collected by the orbiter’s ground penetrating synthetic-aperture radar and X-ray spectrometer, Chandrayaan-2 will be able to create a map of the Moon that not only pinpoints potential deposits of subsurface water ice, but provides the terrain detail necessary for future missions to plan their landing.

Surface scanning and mapping will be one of the major priorities as Chandrayaan-2 embarks on its extended mission, but it will also be doing science in the Moon’s tenuous and largely unexplored atmosphere. A quadrupole mass analyzer aboard the orbiter will analyze the composition of the exosphere, and there’s also a radio experiment to study the electron density of the ionosphere.

Determining Vikram’s Fate

While no images have been released to the public as of yet, the ISRO has confirmed that the high resolution camera aboard the Chandrayaan-2 orbiter was able to locate the Vikram lander on the surface. With a resolution of 0.3 meter/pixel, the 2.54 meter wide lander would only show up in images as a small blotch, but apparently that’s enough for the agency to determine that the craft appears to be intact and sitting at an angle. In light of this, the ISRO is currently attempting to make contact with Vikram in the hopes that it somehow survived the hard landing.

Plot of Vikram’s trajectory, note deviation below 2 km.

To be sure, it’s exceptionally unlikely that Vikram will respond to their hails. Some estimates have pointed to a potential impact velocity of better than 100 meters per second, and even if the vehicle’s crumpling structure was able to absorb that amount of energy, the damage to the internal instrumentation was likely catastrophic. Beyond damage sustained during impact, the simple fact that the lander isn’t sitting level could be enough to complicate communications. Antenna alignment is a delicate operation, and unexpected changes to a spacecraft’s orientation can easily prevent it from establishing a link to ground control.

In any event, the clock is ticking. The lander’s touchdown on the surface was planned to coincide with the start of the lunar day, the two-week long period where the Sun is high enough above the horizon to provide the craft with warmth and power. Once the light fades and the temperatures plummet, Vikram’s chances of survival are effectively zero. If potentially one of the greatest comeback stories in the history of space exploration is going to happen, it’ll need to happen very soon.

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