Maven for company

Print edition : October 17, 2014

The image shows the planet from an altitude of 36,500 km in three ultraviolet wavelength bands. Blue shows the ultraviolet light from the sun scattered from atomic hydrogen gas in an extended cloud that goes to thousands of kilometres above the planet’s surface. Green shows a different wavelength of ultraviolet light that is primarily sunlight reflected off atomic oxygen, showing the smaller oxygen cloud. Red shows ultraviolet sunlight reflected from the planet’s surface; the bright spot in the lower right is light reflected either from polar ice or from clouds. Photo: NASA/University of Colarado, Boulder

LAUNCHED on November 18, 2013, about two weeks after ISRO’s Mars Orbiter Mission (MOM), the National Aeronautics and Space Administration’s (NASA) spacecraft MAVEN (Mars Atmosphere and Volatile EvolutioN) made its successful tryst with the red planet two days ahead of MOM, just as smoothly as MOM did.

MAVEN is designed to have a Martian orbit with a periapsis (nearest distance from Mars) of 150 kilometres and an apoapsis (farthest distance) of about 6,300 km, and an inclination (with respect to the Mars equator) of 75 with a 4.5-hour orbit period as against MOM’s already attained orbit of 428 km × 76,993 km × 150 with an orbit period of about 73 hours.

MAVEN was inserted into a 380 km × 44,600 km × 75 orbit with a 35-hour period from where it will be lowered into the target orbit in the coming three weeks with one main motor burn, which was done soon after Mars Orbit Insertion (MOI) on September 23, and a sequence of small thruster burns to bring down its periapsis close to 150 km and the period close to the targeted 4.5 hours.

One might ask how MAVEN made it to MARS two days ahead after being launched two weeks later. In fact, MAVEN had to take a slightly longer route of 711 million km as against MOM’s 666 million km. Unlike MOM, it did not take a straight trajectory because of its much lower targeted periapsis.

The difference in the journey time essentially comes from the much more powerful rocket that NASA had used to launch MAVEN as compared to ISRO’s PSLV-XL. The rocket launched the upper stage and MAVEN straightaway into the Mars Transfer Trajectory (MTT). In contrast, because of PSLV’s much lower thrust capability, MOM had to make six earth-bound manoeuvres to raise the spacecraft’s apogee and then a main satellite engine firing on December 1, 2013, to put the satellite into the appropriate MTT.

Following this orbit insertion, MAVEN’s long commissioning phase over a six-week period involves manoeuvring it into its designated orbit and testing its eight on-board instruments, after which it will start its year-long primary mission. The payload includes three instrument suites: a Particles and Fields Package (PFP) comprising six instruments, a Remote Sensing Package (RSP), and a Neutral Gas and Ion Mass Spectrometer (NGIS). The spacecraft also carries a communication package, Electra, to relay data from the rovers or lander missions on the Mars surface sent on other Mars missions of NASA.

MAVEN is the first spacecraft to explore the tenuous Martian atmosphere and the mission includes five “deep-dip” campaigns during which the altitude of the spacecraft will be lowered to about 125 km. These measurements will provide information down to the top of the well-mixed lower atmosphere to get a full profile of the top of the atmosphere.

Just as MOM, MAVEN has returned its first images of the extended Martian atmosphere with its Imaging Ultraviolet Spectrograph in three Ultraviolet bands taken from an altitude of 36,500. Since the period also coincided with the predicted period for solar Coronal Mass Ejection (CME) event during September 21-26, MAVEN’s instruments had also been planned to pick up data on how CMEs affect the Martian atmosphere.

Though modest in the payload it carries and its science objectives, MOM, given its much greater apoapsis and larger ellipticity, has also been conceptualised to study the Martian atmosphere as it traverses to larger altitudes up to about 77,000 km altitude. Its Lyman Alpha Spectrometer (LAS) is designed to study the rate of escape of hydrogen (by studying the ratio of hydrogen to deuterium) into space—an indication of the rate at which water has evaporated from Mars. MOM also carries a unique Methane Sensor for Mars (MSM) and it may end up returning some evidence for it—an indication of some life form at some time in Martian history—just as Chandrayaan-1 did for water on the moon.

So there is a natural complementarity in the two missions and the two agencies have been talking of the possibility of working together. There was a discussion meeting between the two in April. “We need to see what conjunctive science can be done. So we decided that we will form a Working Group (WG) and will announce it during the visit of the Prime Minister [Narendra Modi]. It is a good ongoing relationship and it is a good opportunity to look at joint possibilities through this WG. Additional information is always useful for good science,” said K. Radhakrishnan, Chairman, ISRO.

James Green, Director, Planetary Science Division, NASA, expressed a similar view. “With multiple data sets being collected, NASA and ISRO scientists will have a wealth of information to help solve mysteries regarding the Mars atmosphere,” he told the House of Representatives Subcommittee on Space, Committee on Science, Space and Technology. This WG will be set up under the auspices of the U.S.-India Civil Space Joint Working Group. Green visited ISRO on September 17, to carry this forward. This Group, which will include scientists from NASA and ISRO, will have Green and Koteswara Rao, Scientific Secretary, ISRO, as the nodal persons.

One of the first objectives of this collaborative effort will be to look at the Comet Siding Spring, which is predicted to pass by Mars on October 19. Earlier projections had put its closest approach at about 50,000 km, which would have posed some danger to the spacecraft, particularly to MOM, given its larger apoapsis. Now this is estimated to be about 0.15 million km, which may not be such a serious threat. Though safety can still be an issue because these are gross calculations, the comet presents more of an opportunity for both ISRO and NASA to study it from close quarters.

R. Ramachandran