Two roads to Mars

Print edition : November 15, 2013

ISRO's Mars orbiter. Photo: ISRO

NASA's MAVEN spacecraft. Photo: NASA's Goddard Space Flight Centre

Although the American MAVEN’s planned study of atmosphere is more comprehensive than MOM’s, combined information from the two missions should tell us a lot about the Martian atmosphere.

THE month of November will see two interplanetary missions of two space-faring nations but with incomparable capacities—in terms of availability of resources, infrastructure, past experience and expertise, widely different numbers of scientists and institutions engaged in space science, and hugely disparate financial capacities to absorb failures—head for Mars.

Interestingly, both missions have planned for their respective insertions into the Martian orbit on the same date of September 21, 2014. This is because the earth-Mars configuration is such that this is when the two spacecraft will reach the closest approach to Mars (periapsis) and will enable easy capture by the planet into its orbit.

For the Indian Space Research Organisation (ISRO), its Mars Orbiter Mission (MOM), which is slated for launch on November 5, will be a maiden journey to the red planet. For the National Aeronautics and Space Administration (NASA) of the United States, whose missions to Mars date back to 1964, the Mars Atmosphere and Volatile Evolution Mission (MAVEN), which is scheduled for launch on November 18, it will be its 22nd mission. Indeed, MAVEN is the second mission in the now-discontinued Mars Scout Programme, launched in 2006 as a series of small, low-cost (each costing less than $485 million) robotic missions to Mars after the Phoenix Lander mission of 2007.

Naturally, the mission objectives, too, widely differ in their scope. MOM’s objectives are somewhat more modest and general compared with MAVEN’s, which are designed to answer specific questions, given NASA’s findings on the planet over the past five decades. Also, the on-orbit mission life of MOM is only 6 months compared with MAVEN’s one year. Although both MOM and MAVEN have three instrument packages, MOM only has five instruments, while MAVEN has eight. Correspondingly, the dry masses of the two spacecraft differ: 500 kg and 903 kg respectively.

“One of the main objectives of the first Indian mission to Mars,” as the brief information brochure on the mission, the only document released by ISRO so far, says, “is to develop the technologies required for design, planning, management and operations of an interplanetary mission.”

Clearly, these are the kind of goals one would set on the learning curve and, rightly, the mission has been billed as a “technology demonstrator”.

Specifically, MOM’s technological objectives are stated to be:

• Designing and realisation of a Mars orbiter with the capability to survive and perform earth-bound manoeuvres, cruise phase 300 days of travel, Mars orbit insertion/capture and on-orbit phase around mars;

• Deep space communication, navigation, mission planning and management; and

• Incorporation of autonomous features to handle contingency situations.

Its scientific objectives include the exploration of Mars’ surface features, morphology, mineralogy and atmosphere by indigenous scientific instruments.

NASA would have clearly acquired enormous experience in terms of the technological capabilities that ISRO aims to acquire in its maiden Mars mission. Although the scientific objectives that MOM has set out to achieve seem general, ISRO scientists have claimed that the mission will perform science that has so far not been done. “The mission,” J. Goswami, director of ISRO’s Physical Research Laboratory (PRL) in Ahmedabad, said in January, “has a very specific scientific objective as we want to study the atmosphere of Mars and the mission will explore things that have not been done by other countries.” Among the instruments that the payload will carry is the methane sensor, which has not been carried by other nations in the past.

The payload of a limited mass of 15 kg comprises three instrument packages:

1. Atmospheric studies package: Besides the instrument Methane Sensor for Mars (MSM), this package includes the Lyman Alpha Spectrometer (LAP) designed to understand the process of water loss from the planet by measuring the relative abundances of deuterium and hydrogen in the Martian atmosphere.

2. The particle environment studies package is a single instrument package consisting of the Mars Exospheric Neutral Component Analyser (MENCA). This instrument is of the heritage of Chandrayaan-1’s Altitudinal Composition Explorer (CHACE), which had indicated the first signs of water on the moon even before the M3 instrument of NASA aboard Chandrayaan-1 did.

3. The third package meant for Surface Imaging Studies consists of the Mars Colour Camera (MCC) and the Thermal Infrared Imaging Spectrometer (TIS), the latter being important for the study of the geology, soil characteristics and mineralogy of the planet.

MAVEN also has exploration of the planet’s upper atmosphere as one of its key objectives. In fact, it has been billed as the first spacecraft mission dedicated to exploring the upper atmosphere of Mars. But this is moot because both spacecraft will enter the Martian orbit on the same date.

Specifically, the mission has the following four primary objectives:

• Determine how the rate of loss of volatiles—such as CO, NO and water—from the Mars atmosphere to space has played through time and how it has affected the history of Mars’ atmosphere and climate;

• Determine the current state of the upper atmosphere, ionosphere, and interactions with the sun and solar wind;

• Determine the current rates of escape of neutral gases and ions to space and the processes controlling them; and

• Determine the ratios of stable isotopes that will tell Mars’ history of loss through time.

Clearly, there is considerable overlap between the two missions as far as upper atmospheric studies are concerned, and the two missions together should throw considerable light on the issue. But what is to be noted is that NASA has not included looking for methane as one of its aims, which MOM specifically aims to do. Given the present doubts about finding methane in the atmosphere, MOM’s findings will be unique and of interest. Ultimately, of course, the outcomes will depend on the capabilities of the respective instruments and their manoeuvres in orbit. For instance, as against the MAVEN’s Mars orbit of 150 km × 6,200 km with 75° inclination, MOM’s orbit is 363.6 km × 80,000 km with 150° inclination, which is not only much more elliptical and more inclined but farther from the Mars surface as well.

More significantly, the spacecraft has the capability of carrying out what has been termed “deep-dip” campaigns for specific observations when the spacecraft orbit will be lowered five times during the mission to an altitude of 125 km. These measurements are aimed to study the atmosphere down to the top of the well-mixed lower atmosphere, enabling a full profile of the atmosphere. The MAVEN fact sheet states that “the spacecraft will make measurements in all regions of ‘near-Mars’ space. These measurements will allow scientists to characterise the current state of the upper atmosphere and the ionosphere, determine the rates of loss of gas to space today, and extrapolate backward in time in order to determine the total loss to space through time.”

MAVEN’s three instrument suites comprise

1. Particles and Field (P&F) package, which consists of six instruments: i. Solar Wind Electron Analyser (SWEA) to measure solar wind and ionospheric electrons; ii. Solar Wind Ion Analyser (SWIA) to measure solar wind and ion density and velocity; iii. Supra Thermal and Thermal Ion composition (STATIC) to measure thermal ions to moderate-energy escaping ions; iv. Solar Energetic Particle to determine the impact of SEPs on the upper atmosphere; v. Langmuir Probe and Waves (LPW) to determine ionospheric properties and wave heating of escaping ions and solar extreme ultraviolet (EUV) input to atmosphere; and vi. Magnetometer (MAG) to measure interplanetary solar wind and the ionospheric magnetic field.

2. Remote-sensing package consisting of a single Imaging Ultraviolet Spectrometer (IUVS) to measure global characteristics of the upper atmosphere and ionosphere.

3. The Neutral Gas and Ion Mass Spectrometer (NGIMS) package to measure the composition and isotopes of neutral gases and ions.

Although MAVEN’s planned study of atmosphere is more comprehensive than MOM’s, the latter’s carefully conceptualised experiments should complement the former’s findings, and the combined information from the two missions should tell us a lot about the Martian atmosphere in 2015 just as Chandrayaan-1 and NASA’s Lunar Reconnaissance Orbiter (LRO) findings about water on the moon have complemented each other.

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