Tonight is a big night for the planet occupied entirely by robots: the Mars Orbiter Mission is the second spacecraft in two days to slip into orbit around the red planet, and the first interplanetary mission from India. Don't take this accomplishment lightly: the failure rate for Mars missions is still painfully high.

The Mars Orbiter Mission is also known as MOM to those feeling downright familiar with bringing a space probe into the family. For those somewhere in between on the intimacy scale, Mangalyaan is the unofficial name for the probe. It translates into Mars craft, a functional if unexciting name for a proof-of-concept technology demonstration to help the Indian space agency build capability for interplanetary missions.

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Top image: Artist's concept of Mangalyaan's orbital insertion around Mars. Image credit: ISRO

Indian Space Research Organization (ISRO) mission engineers after Mangalyaan's successful launch on a Polar Satellite Launch Vehicle rocket. Approximately 20% of ISRO employees, and 10% of their engineers, are women. Image credit: AP/Aijaz Rahi

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The history of Mars exploration is fraught, making every arrival a well-earned victory. As the Prime Minister pointed out in his post-arrival remarks, of 51 attempts to reach Mars by countries around the world, only 21 have succeeded. Mangalyaan is the first attempt by the Indian space program to reach Mars, or any other interplanetary body. Now it is the seventh operational Mars explorer.

Mangalyaan undergoing electromagnetic interference (EMI) and compatibility (EMC) testing. Image credit: ISRO

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The mission is entirely homegrown, with the craft launching on a Polar Satellite Launch Vehicle back on November 5th, 2013. A successful launch is one of the critical junctures for a mission, getting the probe out of Earth's gravity well without exploding or dropping the probe on a bad orbit. Mangalyaan looped around Earth at the start of its journey, raising its orbit and building up speed before flinging off into space. Despite launching a few days earlier than Maven, the probe arrived at Mars a few days later.

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A PSLV boosts Mangalyaan out of the Earth's gravity well in November 2013. Image credit: ISRO

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The Mangalyaan mission consists of three phases: 1. A geocentric phase of looping around Earth using an energy-efficient Hohmann Transfer Orbit; 2. A heliocentric phase tangentially departing Earth orbit and tangentially entering Mars orbit through a half-ellipse around the sun; and 3. a Martian phase of looping around the planet in a hyperbolic orbit.

Orbital diagram of the Mangalyaan mission to Mars. Image credit: ISRO

Like Maven, not every planned trajectory correction manoeuvre was necessary for Mangalyaan. After adjustments in December, the craft was so closely following its designed trajectory that it skipped its April correction. It did have a 16-second burn in June to keep it on target, but the August burn was postponed until September 22nd.

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Orbital insertion diagram. Image credit: ISRO

The real trick for this mission was successfully leaving its heliocentric ellipse and slipping into orbit around Mars.

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Due to the orbital dynamics of the arrival, the robot was doing this trickiest part of the dance while hiding behind Mars, a communications blackout to amplify the 12.5 minute communications delay.

Scientists celebrate the confirmation that Mangalyaan successfully completed an orbital insertion around Mars. Image credit: Doordarshan News

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When it emerged from behind the planet and let scientists back on Earth know it was now safely locked in a gravitational dance around Mars, the celebration was instantaneous. The spacecraft's measured velocity is just 0.3 m/s lower than anticipated, coasting along at a healthy 1,098.7 m/s.

This mission to Mars is the cheapest ever accomplished. Getting to Mars is expensive: NASA's newly-arrived MAVEN cost in the neighbourhood of $671 million, the 2003 ESA Mars Express Orbiter carried a pricetag of $386 million, and even the failed Phobus-Grunt mission with Russia's rocket and China's satellite cost $117 million. India managed a successful mission with only $74 million, a delightfully low pricetag that came with a few hard constraints. (The total mission cost is debatable; check out this thread for qualifications.)

One of those constraints is a hard practical constraint on payload weight, which ties directly into the probe's unusually elliptical orbit. The original rocket intended to propel Mangalyaan on its journey kept blowing up, so the space agency switched to the more-reliable Polar Satellite Launch Vehicle (PSLV). Because the launch vehicle couldn't carry more weight, so the craft has less fuel than would be ideal, so the probe doesn't have spare juice to burn to circularize and tighten up the orbit. The final placement of the probe isn't awesome for science, but considering the main objective of the mission is, "Get to Mars without blowing up on launch, freezing in transition, or overshooting and flying out into deep space," the circularity of the orbit is a minor detail.

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Along with proving that India can reach Mars, the mission is a technology demonstration of India's deep space communication, navigation, planning, and management capacity.

The spacecraft being lowered into a space simulation chamber for thermovacuum tests. Image credit: ISRO

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The time-delay between here and Mars also means that Mangalyaan needed to incorporate autonomous features handling contingency situations to do things like adjust its burn time for a successful orbital insertion. It took over 13 hours to upload and verify all the commands and contingencies for the orbital insertion just ten days before arrival. Adding to the complexity of the situation, the manoeuvres took place on the dark side of Mars, forcing the probe to rely on battery power instead of its solar panels.

The spacecraft can reorient by tweaking rotation speed of these attached wheels. Image credit: ISRO

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As a bonus to completing the technological objectives, Mangalyaan has a five-instrument payload to investigate Mars. The equipment is a mix of cameras and detectors that overlaps with similar equipment carried by other spacecraft orbiting around the red planet.

Schematic of Mangalyaan's instrument payload. Image credit: ISRO

Three instruments are directed towards atmospheric observations like Maven: the Methane Sensor for Mars (MSM), the Mars Enospheric Neutral Composition Analyser (MENCA), and the Lyman Alpha Photometer (LAP). The MSM will track atmospheric methane, mapping spacial and temporal variation. The instrument measures reflected solar radiation, so it will only be functional in daylight. MENCA is a mass spectrometer intended to determine the electrically-neutral components of the upper atmosphere. LAP detects lyman-alpha emission, a process that will allow the probe to detect deuterium and hydrogen gas loss processes in the upper atmosphere.

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Test photograph in Earth orbit by the Mars Color Camera on November 19, 2013. Image credit: IRSO

The other two instruments are a pair of cameras for optical and infrared light: the Mars Colour Camera (MCC) and the Thermal Infrared Imaging Spectrometer (TIS). MCC is a tri-colour optical camera. The space agency hopes to use it not just to track Martian surface features and weather, but also to give a scientific side-eye to the Martian moons Phobos and Deimos. TIS detects infrared light, and is thus capable of monitoring temperature and thermal emission day and night. It will be able to map surface composition and mineralogy with distinctive thermal spectra.

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Mangalyaan packs a lot of hope into a relatively small package. Image credit: ISRO

Mangalyaan's arrival marks India as just the fourth space agency to successfully send a probe orbiting Mars, joining NASA, the European Space Agency, and the now-restructured Soviet space program. In the glow of their success, the Indian space agency is already talking about a Mars lander within the decade.

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Of course, it's not a real Mars mission without a social media presence, so the Indian space agency happily obliged with its very first Tweet from Mangalyaan:

And of course, the internet responded in kind:

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Indian Prime Minister Narendra Modi offers context for this outstanding achievement: "If our cricket team wins a tournament, the nation celebrates. Our scientists' achievement is greater." Congratulations to the team, and welcome to Mars!

Follow along with the Mangalyaan mission on the mission page, on Facebook, or on Twitter.