On July 22nd, India launched an ambitious mission to simultaneously deliver an orbiter, lander, and rover to the Moon. Launched from the Satish Dhawan Space Centre on a domestically-built GSLV Mk III rocket, Chandrayaan-2 is expected to enter lunar orbit on August 20th. If everything goes well, the mission’s lander module will touch down on September 7th.
Attempting a multifaceted mission of this nature is a bold move, but the Indian Space Research Organisation (ISRO) does have the benefit of experience. The Chandrayaan-1 mission, launched in 2008, spent nearly a year operating in lunar orbit. That mission also included the so-called Moon Impact Probe (MIP), which deliberately crashed into the surface near the Shackleton crater. The MIP wasn’t designed to survive the impact, but it still secured India a position on the short list of countries that have placed an object on the lunar surface.
If the lander component of Chandrayaan-2, named Vikram after Indian space pioneer Vikram Sarabhai, can safely touch down on the lunar surface it will be a historic accomplishment for the ISRO. To date, the only countries to perform a controlled landing on the Moon are the Soviet Union, the United States, and China. Earlier in the year, it seemed Israel would secure its position as the fourth country to perform the feat with their Beresheet spacecraft, but a last second fault caused the craft to crash into the surface. The loss of Beresheet, while unfortunate, has given India an unexpected chance to take the coveted fourth position despite Israel’s head start.
We have a few months before the big event, but so far, everything has gone according to plan for Chandrayaan-2. As we await word that the spacecraft has successfully entered orbit around the Moon, let’s take a closer look at how this ambitious mission is supposed to work.
Robots Don’t Need to Rush
Apollo Trans-Lunar Injection
Considering that Apollo 11’s 50th anniversary has gotten everyone talking about the Moon again, you’re probably aware that Neil Armstrong, Michael Collins, and Buzz Aldrin didn’t spend months crammed into the relatively tiny Command Module. They made the round-trip, including their excursion to the lunar surface, in just eight days. So if it only took a few days to reach the Moon in 1969, why will it take Chandrayaan-2 months to make the same trip in 2019?
Put simply, the accelerated transit to the Moon and back was necessitated by the humans onboard. For every day they were in the capsule, the crew needed air to breathe, food to eat, and water to drink. Because of this human element, the Apollo missions took the shortest route possible: a direct transfer from Earth orbit to the Moon’s gravitational sphere of influence. To perform the maneuver, known as Trans-Lunar Injection (TLI), they needed an incredibly powerful rocket that could accelerate the spacecraft to the necessary velocity. Enter the towering Saturn V, which still holds the record for the most powerful rocket ever put into operation.
Chandrayaan-2 projected orbit
Now to be fair, with a mass of approximately 8.5% of the Apollo spacecraft, Chandrayaan-2 certainly wouldn’t need a rocket as powerful as the Saturn V to perform a similar TLI. But it would need one with a bit more kick than the GSLV Mk III, which was designed for lifting geosynchronous communication satellites. Putting a spacecraft into a geostationary transfer orbit accelerates it to a velocity that’s almost, but not quite, enough to get to the Moon. Because of this, Chandrayaan-2 will need to make up the difference with a series of burns designed to gradually raise its orbit over the next few weeks.
This method of reaching the Moon would be completely impractical for a human mission. But with Chandrayaan-2’s only passengers being the Vikram lander and Pragyan rover, there’s nobody to complain about the fact they’re flying Economy. It’s worth noting that a commercial launch provider could certainly have put the mission on a more direct route to the Moon, but there’s a certain aspect of national pride involved in Chandrayaan-2 being entirely “homegrown”.
Assuming a successful lunar capture on or around August 20th, Chandrayaan-2 will then proceed to make several more engine burns to gradually lower its orbit around the Moon, with the ultimate goal being a circular orbit at an altitude of 100 kilometers. The orbiter module of the spacecraft will remain in this orbit for a year or more, operating a suite of instruments designed to study the Moon’s surface, including high resolution cameras and synthetic aperture radar.
Vikram lander with Pragyan rover visible
While the orbiter remains above, the Vikram lander will detach and begin preparations for descent. It will first adjust its orbit to take it over the Moon’s southern region at an altitude of 30 kilometers, where it will scan the surface for an appropriate landing site. Once the vehicle has performed a series of self-checks, it will perform a landing burn that will bring it to rest in the vicinity of the South Pole–Aitken Basin on September 7th. This area was selected due to its relatively flat topology and interesting mineral deposits.
The timing of the landing is important, as the goal is to put Vikram on the surface at the beginning of the lunar day, which lasts for 14 Earth days. As the craft is not expected to survive the subsequent lunar night, any delay in landing will result in a reduced amount of time to conduct science on the surface. Landing too late in the lunar day cut short China’s Chang’e 4 mission, a fate which the ISRO will surely want to avoid with Chandrayaan-2.
On the surface, Vikram has a number of instruments at its disposal, including a seismometer and temperature probes. It’s also carrying a laser retroreflector array built by NASA’s Goddard Space Flight Center which will allow orbiting satellites to take precise distance measurements when they pass overhead. But the real highlight of the mission will come when the ramp is lowered for the Pragyan rover.
Resembling the Sojourner rover NASA deployed on Mars, Pragyan will navigate on the lunar surface with 3D stereoscopic cameras and perform observations with its laser and x-ray spectroscopes. The rover will travel approximately 500 meters away from Vikram, using the lander as a communications relay between it and Ground Control on Earth.
Success by Degrees
Space travel is already exceptionally difficult, but making a controlled landing on another world and surviving long enough to conduct useful science is even more challenging. There’s a reason so few countries have been able to pull off the feat. It took the Soviet Union nine attempts before they were able to give humanity the first up-close view of the lunar surface in 1966, and the United States crashed several Ranger-class probes before they even attempted to land Surveyor 1. Given historic precedent, “ambitious” might be something of an understatement when talking about deploying an orbiter, lander, and rover all in the same mission.
But the important thing to remember is that, no matter what happens, the Indian Space Research Organisation will be able to collect important data and gain invaluable real-world experience. If Vikram comes down too hard, or Pragyan’s ramp jams, it will surely be a disappointment. But it won’t be a waste.