By the time you are reading this, India’s first mission to Mars, Mangalyaan will have completed over 1400 days, or 46 months, in orbit around Mars. The
One of the first questions we asked was, how long could the mission extend, and what are the science objectives? Sharma replied, “since the satellite is in very good condition and still there is a good amount of fuel left, the mission may extend to many more years. Current and future objectives are basically to analyse the science data of the different instruments.”
The Scientific Payloads
There are five scientific instruments on board the spacecraft. The Methane Sensor for Mars (MSM) uses reflected sunlight to measure methane in the atmosphere with an accuracy of particles per billion. The instrument is also very good at just measuring the reflected sunlight from Mars, a property known as its albedo. The Mars Colour Camera (MCC) captures the images of the Martian surface, can monitor the red planet for dynamic weather events and provides a context for the data gathered by the other sensors on board. The Lyman Alpha Photometer (LAP) is used to measure the amount of deuterium and hydrogen in the upper atmosphere. The mineralogical studies of the surface of the planet are done through the Thermal Infrared Imaging Spectrometer (TIS) instrument. The instrument measures the thermal emissions on the surface, and the types of soil or minerals can be identified based on the thermal characteristics observed. The instruments are all healthy and working as expected. Mars Exospheric Neutral Composition Analyser (MENCA) measures the neutral gases in the atmosphere, such as nitrogen, oxygen and carbon dioxide. The instrument was developed by the Vikram Sarabhai Space Centre (VSSC).
One of the surprising findings by the MENCA instrument was the discovery of superthermal or hot argon in the upper atmosphere or exosphere of Mars. The particles were discovered at unexpected altitudes. The finding could explain the process by which the atmosphere of Mars has been stripped away. The Martian atmosphere is being stripped away constantly, because of solar activity. This is just one of the many aspects of Mars that the instruments on board MoM continue to study. “Science payloads analysis is underway including the possibility of methane, if it exists, how the atmosphere of Mars disappeared, what are the neutral components of the Martian atmosphere, thermals mapping, mineralogy mapping etc,” explains Sharma.
Over twenty scientific papers have been published in peer-reviewed journals, based on the data gathered by the Mangalyaan mission. The data captured by the mission is available through the Indian Space Science Data Center (ISSDC) web site. The archived data is available for free. In the first year that the data was made available to the public, the site saw over 175,000 hits, with over 200 Gb of data being downloaded. Since science was not the primary objective of the mission, we asked Sharma exactly how the data is proving to be useful. “Mangalyaan has given a huge amount of science data. There are many scientific organizations and scientists working in this field who don’t have actual and current data. The data may help them establish some science goal or retune their models.”
An Eccentric Orbit
One of the successes of the scientific study of the mission is that Mangalyaan is not in a circular orbit around the planet. Instead, the spacecraft is in an eccentric or elliptical orbit. The orbit is similar to the way a comet orbits around the Sun. At its closest point to Mars, known as the periareon, Mangalyaan is at a distance of 421 kilometres. At its farthest point, at its apoareon, the spacecraft is at a distance of a distance of 76,993 kilometres. This unique orbit allows the MoM to capture data that is not possible by any of the other contemporary Mars orbiters. We asked Sharma why this orbit was chosen for Mangalyaan, and what are the benefits of having done so, “based on the capabilities of the PSLV-XL and the position of the Sun in the Mars phase of the mission, the orbit of the spacecraft was decided to be elliptical. This orbit is unique and gives us many firsts, like a full disk image of Mars in one snap, and an image of the far side Phobos.” The unique orbit allows the mission to study the moons of Mars from unique angles, including the moons with Mars in the background.
“Mangalyaan has captured many images of Phobos and Deimos. Some of the unique images included a rising Phobos and the far side of Deimos.” A full disk image means a single capture where the entire planet is visible. The November 2016 issue of the National Geographic magazine featured one such global disc image of Mars captured by MoM. Over 900 images have been beamed back by the mission so far. A number of images captured by the mission have been compiled in an “Atlas of Mars” by ISRO (https://dgit.in/momatlas).
Extending the mission life
A key to extending the life of the mission was handling an event known as the Mars Solar Conjunction. About once every 26 months, the Earth, the Sun and Mars align along a single line. This means that the Sun blocks out communication between Earth and Mars. During the communications blackout, ISRO would not be able to send and receive and signals to and from the orbiter, because of charged particles from the Sun introducing an excessive amount of noise to the signals. The spacecraft had to manage itself entirely autonomously during this period. ISRO ran simulations to ensure that the spacecraft would survive this period of communications blackout. We asked Sharma how the situation on the ground was during the communications blackout. “During this period there was no communication possible. Before starting these periods all possible autonomy of the satellite was enabled to take care of any undesired situation. Since during this time, there is no telemetry we have to rely on autonomy. After the Sun moved away, we started receiving data and analysed the satellite’s condition. No undesired things happened during this blackout period and the satellite was in good condition as expected.” We then asked exactly how the autonomy on the spacecraft worked. “Due to two-way communication delay time, which is variable, we were relying on the autonomous features of the spacecraft. For autonomy, we consider all possible failure cases in advance and based on the failure conditions, the solutions are also pre-programmed. To take care of this, the spacecraft has main and redundant systems for almost everything. So, whenever a failure and a non-nominal condition is detected by the spacecraft, the autonomy triggers and brings the satellite back to nominal.”
Another challenge to the longevity of the mission was to ensure that the solar panels received enough light from the Sun to keep the batteries on board powered. If Mars came in between the orbiter and the Sun for more than a period of 8 hours, then the instruments on board would no longer be able to function. In January 2017, ISRO executed an orbital correction
ISRO is planning a