The Indian Space Programme

by Gurbir Singh

  During the 300-day cruise from Earth to Mars, ISRO monitored MOM using its ground stations during the 12 hours a day that it was visible in the sky from India and with assistance from NASA’s DSN at other times.[886] The first picture taken by the Mars Colour Camera was of the Earth two weeks after launch. The other four instruments, too, were switched on for short periods for testing and calibration. To ensure that MOM arrived at the right place at the right time with high precision, four Trajectory Control Manoeuvers (TCM) were scheduled, of which only three were carried out, TCM-1 on 11 December 2013, TCM-2 on 11 June 2014, TCM-3 scheduled for August 2014 was omitted as no correction was deemed required and TCM-4 on 22 September 2014. The TCMs were designed to cater for small course variations resulting from navigation errors and effects of external forces, such as gravity or solar radiation pressure.

  Date

  IST

  Event

  Engine Burn duration (s)

  Apogee (km)

  05/11/13

  14:38

  Launch

  935

  23,550

  07/11/13

  01:17

  1st orbit increase

  416

  28,825

  08/11/13

  02:18

  2 ND orbit increase

  570.6

  40,186

  09/11/13

  02:10

  3rd orbit increase

  707

  71,636

  11/11/13

  02:06

  4th orbit increase

  incomplete

  78,276

  12/11/13

  05:03

  4th orbit increase (supplemental)

  303.8

  118,642

  16/11/13

  01:27

  5th orbit increase

  243.5

  192,874

  01/12/13

  00:49

  Trans Mars Injection

  1328.89

  Table 15‑4 Series of Earth orbits prior to departure for Mars

  The first two TCMs required engine burns for forty seconds and nine seconds, collectively changing MOM’s velocity by 9.33 m/s.[887] The third TCM was skipped in favour of revised TCM-4. Two days before arrival, a joint LAM and eight-thruster burn lasting for four seconds reduced MOM’s velocity by 2.1 m/s. Although a very short burn resulted a tiny change in velocity, this burn was significant as it verified that the LAM operated as expected. For additional assurance, ISRO had been mirroring on the ground the LAM burns using an identical LAM at the VSSC. Had this test on 22 September not gone according to plan, ISRO would have had time to engage plan B for Mars Orbit Insertion. Plan B involved using only the eight small thrusters to perform the breaking manoeuvre to enter Martian orbit. The lower capacity of the smaller thrusters would have required a longer burn of ninety minutes. The mid-point of the burn would have remained the same, but it had to start earlier. That is why a test was conducted on 22 September. Plan B would have resulted in an even more elliptical orbit (an apoapsis of 0.27 million km) and only about 3 kg of propellant would have remained making mission success a “touch and go.”[888]

  Navigation and guidance had brought MOM to within 1,847 km of the surface of Mars on 24 September 2014. Travelling at 6.5 km/s and accelerating by virtue of its approach to Mars, MOM had to slow down by 1099 m/s to enter orbit.[889] Had the braking manoeuvre failed, the mission would have become a flyby and not an orbiter. To decelerate, MOM had to point in the opposite direction of travel and fire its LAM and the eight small thrusters for 24 minutes. Two key events coincided with this breaking manoeuvre. Five minutes after firing the LAM and the eight small thrusters, MOM entered Mars’ shadow and lost sight of the Sun for the first time since leaving Earth. A few minutes later, still during the engine burn, MOM disappeared behind Mars and lost contact with Earth. Both events were expected and planned for. The required commands for reorientation, start engine firing, stop engine firing and re-point to Earth had been uploaded to MOM a few days earlier. Given the 42-minute lag in round trip communication, real-time communication was not practical, and all spacecraft far from Earth are designed to operate autonomously. Following the engine burn, which consumed 250 kg of propellant, MOM decelerated and entered Martian orbit. A few minutes after MOM came out of the eclipse, it reoriented its high gain antenna to point to Earth and then sent signals to Earth that the engine burn and orbit insertion went to plan. About 12.5 minutes after transmission, NASA’s DSN station in Canberra, Australia, received the signals from MOM and forwarded them to ISRO, confirming that MOM had entered orbit around Mars and could finally live up to its name, Mars Orbiter Mission. MOM achieved an orbit of 421 x 76,993 km with a period of 73 hours and had 37 kg of usable propellant left. On 24 September 2014, MOM joined four other Mars orbiters, ESA’s Mars Express and three NASA orbiters, Mars Reconnaissance Orbiter, Mars Odyssey and MAVEN (Mars Atmosphere and Volatile EvolutioN), which had arrived just three days earlier. In addition, NASA was operating two rovers, Opportunity and Curiosity, on the Martian surface.

  Science from Martian Orbit

  The MOM was designed with six objectives, three technology and three scientific.[890]

  Design and develop a Mars orbiter with the capability to perform earth bound manoeuvres, Martian Transfer and Mars Orbit Insertion after nearly 300 days of travel.

  Incorporation of autonomous features in spacecraft.

  Design, plan and operate deep space communication with the orbiter (ca 400 million km).

  Exploration of Mars surface features, morphology, topography, mineralogy.

  Study of constituents of Martian atmosphere and dynamics of the upper atmosphere.

  Detect emanations of gaseous constituents from the surface/subsurface looking for clues for geological and biological activities.

  Instrument

  Origin

  Purpose

  Lyman Alpha Photometer (LAP)

  Laboratory for Electro Optics Systems, Bangalore

  Help understand the processes responsible for the current Martian atmosphere

  Methane Sensor for Mars (MSM)

  SAC, Ahmedabad

  Detect, measure and understand the presence of methane on Mars

  Mars Colour Camera

  SAC, Ahmedabad

  Image Martian surface and atmospheric features as they change during the day and seasons

  Thermal Imaging Spectrometer (TIS)

  SAC, Ahmedabad

  Image Mars using infrared wavelength. It can operate during the day or at night

  Mars Exospheric Neutral Composition Analyser (MENCA)

  VSSC, Thiruvananthapuram

  Measure and analyse the constituents of the Martian exosphere

  Table 15‑5 Overview of Mars Orbiter Mission’s Science Payload

  Unlike Chandrayaan-1, the haste at which the Mars mission was developed did not allow time to engage international partners. MOM is carrying a package of five scientific instruments selected from a shortlist of twelve, all of which were designed and built in-house by ISRO. Two instruments are designed to look at the Martian atmosphere, two at the surface and one sampling Mars’ upper atmosphere. Between them, the instruments measure the vertical composition of the Martian atmosphere; investigate the rate at which the atmosphere has been dissipating into space; image the Martian surface, thermally during day and night and visually during day time; and attempt to detect and measure emissions of methane.

  Lyman Alpha Photometer

  Mars today has no permanent deposits of surface liquid water on its surface and only a very thin atmosphere, typically around 1% that of the Earth. Astronomers estimate that in the past Mars had a much denser atmosphere and enough water to cover the Martian surface in a 500 m deep ocean. Lyman Alpha Photometer (LAP) is an instrument designed to collect data that will eventually lead scientists to understand what happened to the original Martian water and atmosphere. It was built by ISRO’s Laboratory for Electro-Optics Systems in Bangalore. LAP has th
ree objectives:

  Generate spatial (whole of Mars) and temporal (through all seasons) profiles of hydrogen and deuterium Lyman alpha intensities

  Characterise deuterium-enrichment in the upper atmosphere as the light hydrogen atoms escape, and

  Determine with the help of (i) and (ii) the rate at which Mars is losing water as hydrogen/deuterium atoms have their origins in water molecules.

  Hydrogen exists in two stable forms known as isotopes. Hydrogen (H) with a single proton in the nucleus and Deuterium (D) with a proton and a neutron in the nucleus. LAP measures the relative abundances of these two types of hydrogen. LAP is an optical instrument that looks at the Martian atmosphere and, using an absorption cell technique, measures first the incoming hydrogen and then the deuterium Lyman alpha radiation. On Earth, 99.98% of all hydrogen is H. A series of measurements can be used to generate an intensity ratio for D/H isotopes.

  Mars is about half the size of the Earth but only about 10% of its mass. This low mass, and thus weaker gravity, allows the very light hydrogen molecules to escape easily from Mars. The absence of a Martian magnetic field allows the UV radiation from the Sun to interact directly with the upper atmosphere. The Ozone layer that acts as a barrier on Earth is not present on Mars. This UV radiation breaks the water molecules in the Martian atmosphere into O and H2. Mars has been experiencing this slow evaporation of its atmosphere for millions of years. As the rates of evaporation of the heavier deuterium and lighter hydrogen, forms are different, over time more H escapes than D increasing the D/H ratio.

  LAP was first switched on and tested on 6 February 2014 16 million km from Earth when still end route to Mars. The basic health checks to verify the instrument’s operation were conducted over twenty minutes. It now collects data from orbit for about 30 minutes on either side of a close approach of each orbit when MOM is closer than about 3,000 km to Mars. The data LAP has collected is currently being processed but not yet published, and it continues to function as planned.[891]

  Methane Sensor for Mars

  Produced by the SAC in Ahmedabad, MSM weighs 2.54 kg and is attracting the most attention. On Earth, methane is associated with life. When it was detected on Mars in 2003, there was speculation that this was the long sought after evidence of life on Mars. Since then, methane on Mars has been detected by telescopes on Earth, from Martian orbit and by rovers on the surface of Mars.[892] Although the methane detections have been repeated and confirmed, the instances of detection have been sporadic, and the concentrations detected extremely tenuous. Adding to the mystery is the sudden disappearance of the detected methane. Once produced, Methane vanishes in several decades so the detected Methane is not ancient but new. Why and how Methane is produced is a puzzle. Methane can have multiple sources other than undiscovered Martian life form, geochemical, geological and perhaps local processes acting on organic chemicals brought to the surface of Mars by meteorites.

  MSM is designed to detect methane with a sensitivity of 38–60 parts per billion (ppb) during a single ten-second observation. The typical background level of methane on Mars is 0.7 ppb. The 2003 measurement detected 250 ppb, but all other observations have been in the range of 10–100 ppb. NASA’s rover Curiosity, also known as Mars Science Laboratory, has been on the surface of Mars with a sophisticated collection of scientific instruments since August 2012. It sampled the Martian atmosphere six times between October 2012 and June 2013 and found no methane. However, a few months later it detected significant levels of methane in short bursts. The levels were tiny, but still an order of magnitude above the background levels. Subsequent measurements confirmed that normal background levels had returned. Detection of methane is potentially the first step in the discovery of evidence of ancient or existing life on Mars but what has been observed on Mars to date does not offer a coherent picture.[893]

  It is designed to measure a total column of methane in the Martian atmosphere from orbit. During its orbit, about twice each week, MOM can observe specific areas of Mars from around 400 km and the full disc from 77,000 km. It uses a Fabry-Perot Etalon sensor, the first time one has been used in space. It detects and measures methane variations over place and time. As the instrument uses reflected light, only the day side of the atmosphere can be sampled. MSM was tested observing the Earth before it arrived at Mars.[894] MSM was first activated after launch, while MOM was in Earth orbit and observed the Sahara Desert. It was reactivated seven times in total before arriving at Mars. The observations of the Earth and the darkness of space were used for initial calibration. MSM’s initial observations of Mars were recorded from near apogee. At a distance of nearly 77,000 km where the relative motion between MOM and Mars is less than 100 m/s, the whole disc of Mars can be seen but only at low resolution. MSM has not yet recorded close-up observations when MOM is at perigee. This will be a challenge because, although the images will be of a higher resolution, at perigee, MOM will have a relative motion of 4,000 m/s. Over time, these observations could help identify the geographical site associated with methane detections on Mars.

  MOM is expected to make repeated measurements over many years from which seasonal patterns may emerge. Collectively, these data will help determine the dynamic nature of the methane cycle on Mars. In March 2015, ISRO published MSM’s observations of Mars for the first-time reporting that it had not recorded any significant observations of methane until then, but the observations were sufficient to indicate that the MSM instrument was functioning as expected.[895]

  Mars Colour Camera

  The Mars Colour Camera, too, was built by SAC in Ahmedabad. At 1.27 kg, it is the lightest instrument in the science package. It was constructed from components from disparate sources, including in-house, commercial off-the-shelf (COTS) components. For example, the primary lens (105 mm with f4.0) in the camera was a COTS product weighing 620 g. It was customised and qualified for use in space by engineers at SAC. The modified version now in Martian orbit weighs 310 g. The Mars Colour Camera uses a single commercial high-speed snapshot colour CMOS sensor with a RGB Bayer filter as used in domestic cameras and camcorders. From 77,000 km, Mars subtends an angle of 4°, which the camera can easily capture in its field of view of 5.7°. From its highly elliptical orbit, MOM can take images of Mars at 19 m resolution from 370 km or 4 km resolution from 77,000 km.[896] The Mars Colour Camera was developed using the three-model philosophy. A verification model was developed for demonstrating the proof of concept. A flight model-like and an identical flight model were developed and were subjected to qualification and acceptance level tests, respectively. The development of these models ran almost parallel with feedback from one model incorporated into the other and verified quickly to meet the challenging timeline.

  Mars Colour Camera is designed to image the Martian dust storms, polar ice cap and atmospheric phenomena, as well as surface features, such as volcanoes, valleys and mountains. MOM’s highly elliptical orbit will also allow it to image Deimos, one of Mars’ two moons, from a unique view point. The MCM was activated while in Earth orbit and took images of the Earth in three imaging sessions. Two sessions were conducted on 19 September 2013 and one four days later. The very first image shows India, as well as parts of Asia and Africa. These were taken on 19 September from 7,240 km. The camera’s images comply with the internationally recognised Planetary Data System standard (PDS). To verify the characteristics of the images, ISRO arranged to capture equivalent images of the Earth from INSAT 3A at the same time as the Mars Colour Camera to match the illumination. This exercise helped ISRO scientists to calibrate the Mars Colour Camera.

  By August 2016, MCM had returned more than 540 images, and ISRO has made these images available for scientific investigation and publication by academics and researchers in India. Mars has been imaged by several spacecraft (mostly from NASA) from orbit and the surface using higher quality instruments for many years. The camera’s contribution is not expected to reveal anything dramatic. For a mission that was primarily a technology demonstrator, image
s from the Mars Colour Camera are contributing to scientific publications. There is a remote possibility that in time high-resolution images from the camera combined with data from the MSM may identify geographical locations on Mars where the first extra-terrestrial life may reside.

  Thermal Imaging Spectrometer

  ISRO has been working with remote sensing Thermal Infrared Imaging Systems for many years. They are used in EO satellites, including Kalpana and INSAT-3D. They have also been used by NASA for exploring Mars: 1976 Viking1 & 2 Infrared Thermal Mapper, 1997 Mars Global Surveyor – Thermal Emission Spectrometer and 2001 Odyssey – Thermal Emission Imaging System. The TIS in MOM, weighing 3 kg, was produced by SAC in Ahmedabad. Like the Mars Colour Camera, this instrument was constructed from in-house and customised COTS products. TIS is sensitive to the infrared part of the spectrum (7,000 to 13,000 nanometers) rather than the visible spectrum (400 to 700 nanometers) where the Mars Colour Camera operates. TIS is a spectrometer used to analyse the light rather than a camera that uses light to produce an image. It uses a slit and a grating to split the individual components of infrared light to discover the chemical and mineralogical composition of the source. TIS optics consists of f/1.4 lens assembly with a focal length of 75 mm and field of view + or – 3.18° that directs light to a grating where it is dispersed into constituent wavelengths.[897] Another set of optics then refocuses the dispersed spectrum on a 160 by the 120-pixel sensor.

  Like all MOM’s instruments, TIS was operated before it arrived in the Martian orbit. It was first activated while in Earth orbit on 23 November 2013 to conduct basic health checks. Key system operations were conducted by using TIS to first look at “dark space” (a blank area of space) to establish the instrument’s zero signal baseline, then a 10-minute observation of the Sahara Desert region of the Earth followed by another dark space observation. The measurements recorded during these observations were compared to those from a laboratory and used to calibrate TIS. Five additional dark counts were conducted on 6 February, 13 March, 5 May, 26 June and 18 August 2014 during the Earth-Mars cruise. From the unique characteristic spectra of minerals and soil types, TIS can eventually generate a chemical and mineralogical map of the entire Martian surface. The team that developed TIS has also developed a spectral signal library of specific minerals found on Earth, such as olivine and serpentine. If similar signals are present in Martian observations, identification of minerals on Mars will not be a complex process.