India’s second Moon mission, Chandrayaan 2, is almost upon us. It will be carrying 13 different payloads distributed across three modules including the Orbiter, Vikram Lander and Pragyan Rover. All the payloads will be sent to the Moon aboard ISRO’s Geosynchronous Satellite Launch Vehicle-MkIII (GSLV Mk-III) rocket engine which is its launch platform. The take-off has been scheduled on 22 July 2019 and it will be launching from ISRO’s Satish Dhawan Space Centre in Sriharikota at 2.51 am IST. In this article, we’ll be taking an in-depth look at the Vikram Lander and its payloads along with its primary objectives.
ISRO staff working on the Vikram Lander from the Chandrayaan 2 mission at the ISRO Satellite Integration and test establishment (ISITE), in Bengaluru. Image: PTI.
What is the Vikram Lander?
The Vikram Lander is a module that will enable the delivery of the Pragyan Rover to the lunar surface while conducting a few experiments of its own. The rover will roll out once the lander has successfully landed at the desired spot. It also consists of several instruments or payloads that will be constantly carrying out experiments throughout its mission time.
It’s named ‘Vikram’ to honour the late Dr Vikram Sarabhai, who was the former chairman of ISRO and is widely regarded as the ‘Father of the Indian Space Programme’. It has been developed to operate for 14 days or one Lunar day. During this time period, the Vikram Lander will be constantly communicating with the Indian Deep Space Network (IDSN) in Byalalu near Bengaluru. The same network will be used by the Orbiter and Rover for communications. The lander weighs 1,471 kg including the Pragyan Rover (27 kg) inside and it’s capable of generating about 650 W of electricity.
Initially, Russia’s Federal Space Agency known as Roscosmos was commissioned with developing the lander in collaboration with ISRO back in 2007. However, the delivery was postponed as Russia wasn’t able to build the lander within the deadline. After Roscosmos failed in its Fobos-Grunt mission to Mars, Russia pushed back the delivery and wasn’t able to provide the lander even by 2015. At the end, ISRO had no choice and decided to take up its development on its own.
Landing on the surface of the Moon
The Vikram Lander will be making a soft landing on the lunar surface. A soft landing is actually a technical term to indicate a landing technique that prevents any kind of damage to sensitive instruments onboard. On the contrary, hard landings are those that don’t need to worry about delicate instruments, for example, aeroplanes and space shuttle landings. With the onboard central-mounted propulsion system, the lander will make a vertical descent to the predetermined landing site near the South Polar region of the moon.
#Chandrayaan2: After much ado, here it is at last: the Vikram lander, the first spacecraft from India that could potentially touch the Moon's surface in September this year! @isro #Chandrayaan2TheMoon pic.twitter.com/w6ALvIp4wc
— Tech2 (@tech2eets) June 12, 2019
ISRO’s Space Applications Centre (SAC) is developing several sensors to ensure that the lander can navigate and touch down safely. It includes an Orbiter High-Resolution Camera (OHRC), Ka-band Altimeter, Lander Position Detection Camera (LPDC) and Lander Hazard Detection and Avoidance Camera (LHDAC).
Before it begins its Entry-Descent-Landing manoeuvre, the stacked Orbiter and Vikram Lander will enter the lunar orbit. The OHRC is attached to the orbiter that will image and scan the landing site to find the exact descent point. Once determined, the lander will detach from the orbiter. After detaching, the lander will carry out complex manoeuvres using the other sensors and it will make use of rough braking and fine braking to stabilise the landing at the descent point. This entire complex operation will go on for a nail-biting 15 minutes. The landing sequence is scheduled on 6 September 2019.
What are the payloads onboard the Vikram Lander?
Just like the other modules, the Vikram lander will contain several payloads to carry out science experiments during its mission. Three payloads will be making their way to the lunar surface onboard the lander consisting of a Langmuir probe, thermal probe and a seismometer.
Radio Anatomy of Moon Bound Hypersensitive ionosphere and Atmosphere
The first payload is a Langmuir probe, an instrument that can measure the electron temperature, electron density and electric potential of a plasma. It’s said that the lunar atmosphere, especially in the ionosphere layer, has a highly dynamic plasma environment. Because of the absence of a global magnetic field and a thick atmosphere, the environment is drastically different when it comes to the interaction between solar winds and the Moon. This makes it an ideal playground to conduct various experiments to understand the plasma environment around celestial bodies not governed by a magnetic field.
On the Vikram lander, a Langmuir probe named 'Radio Anatomy of Moon Bound Hypersensitive ionosphere and Atmosphere' or RAMBHA for short, is installed. It has two primary objectives that will study and measure the lunar surface plasma environment. The ambient electron density and electron temperature will be measured near the lunar surface. Also, the temporal evolution of lunar plasma density will be measured that will observe how the plasma density changes over time under different solar conditions.
Chandra’s Surface Thermo-physical Experiment
The Vikram lander will be measuring the vertical temperature gradient and thermal conductivity of the lunar surface. Named as 'Chandra’s Surface Thermo-physical Experiment' or ChaSTE, it’s essentially a thermal probe that includes a sensor and a heater. In order to measure the vertical temperature gradient, the probe will be inserted into the lunar regolith or the loose layer of the lunar surface up to a depth of around 10 cm. It will operate in a passive and active mode. When in its passive mode, it will continuously measure the temperature at different depths of the lunar surface. In the active mode, ChaSTE will measure the temperature variations over a set period of time and the thermal conductivity of the lunar regolith.
Instrument for Lunar Seismic Activity
Finally, the third payload is a simple seismometer named 'Instrument for Lunar Seismic Activity' or ILSA for short. It’s a triple-axis, MEMs-based seismometer capable of detecting the tiniest ground displacement, velocity or acceleration that occurs whenever there’s a lunar quake. Yes, just like the Earth, there are quakes on the Moon. The seismometer is accurate enough to detect acceleration as low as 100 ng per square root Hertz with a dynamic range of +/- 0.5 g and a bandwidth of 40 Hz. To maintain the dynamic range, ILSA uses a coarse-range sensor and a fine-range sensor in combination.
Additionally, the Vikram Lander will also have a NASA experiment onboard called the 'Laser Retro-reflector Array' for Lunar Landers. This instrument has mirrors installed on it that will be used to reflect laser signals from the Orbiter to locate the position of the Vikram lander on the Moon. It will also be able to measure the distance between the Earth and the Moon accurately.
Configuration of the Chandrayaan-2 mission rover, lander and orbiter (labelled). Image: ISRO
This is going to be the first time India is going to land on the surface of the Moon, including its first lander and rover mission. The overall objective of the Chandrayaan 2 mission, according to ISRO, is to conduct a “detailed study of topography, seismography, mineral identification and distribution, surface chemical composition, thermo-physical characteristics of the top soil and composition of the tenuous lunar atmosphere, leading to a new understanding of the origin and evolution of the Moon.” Both the lander and rover will conduct its set of experiments for 14 days or one lunar day while the Orbiter will continue its mission for a year.
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