Rosetta – Philae and the Comet

Rosetta_NAVCAM_comet_67P_20140919_mosaic_625A news that caught my attention recently was about the spacecraft Rosetta, and that it had landed a module, Philae, on a comet.

I thought it was special because-
As compared to planets which seem stable and calm, a comet in my mind is a racing ball of fire.
Also a planet is this large thing, and a comet is small.

So am I implying that landing a vessel on a planet is common, but its special if on a comet ?

Of course there is no basis for my idle perceptions.
Landing sites on the Moon and Mars are pin-pointed in advance, and well achieived too. A planet is this huge hurtling, spininng massive sphere – subject to great forces, and creator of its own.
Exploratory vessels have their trajectories defined for years in advance. Satellites have their orbits planned, monitored and corrected. Its all very amazing and hi-tech.

Am I implying now that a comet landing is also no great deal ? :)

I guess I still find the idea of a comet landing very fascinating, almost unreal.
Here a some more stunning facts:

  • The Rosetta spacecraft was launched in 2004 – 10 years ago.
  • The comet, 67P/Churyumov-Gerasimenko, is a big rock, about 4 kms in it longest dimension.
  • On its way to comet 67P, Rosetta passed through the main asteroid belt, and made the first European close encounter with several of these primitive objects.
  • Rosetta was the first spacecraft to fly close to Jupiter’s orbit using solar cells as its main power source.

Rosetta is the first spacecraft to orbit a comet nucleus,and is the first spacecraft to fly alongside a comet as it heads towards the inner Solar System. It is planned to be the first spacecraft to examine at close proximity how a frozen comet is transformed by the warmth of the Sun. Shortly after its arrival at 67P, the Rosetta orbiter dispatched the Philae lander for the first controlled touchdown on a comet nucleus. The robotic lander’s instruments obtained the first images from a comet’s surface and made the first in-situ analysis of its composition.
Comets are thought to have delivered a vast quantity of water to Earth, and they may have also seeded Earth with organic molecules. Rosetta and Philae will also search for organic molecules, nucleic acids (the building blocks of DNA and RNA) and amino acids (the building blocks of proteins) by sampling and analysing the comet’s nucleus and coma cloud of gas and dust, helping assess the contribution comets made to the beginnings of life on Earth.
Got me thinking about what a comet is ?
Since this doesnt seem to be the (stereo)typical comet with the long tail, racing towards the sun and then away from it.

Looks like 2 main things differentiate a planet from a comet:
Size – It should be fairly large.
Stability of orbit – it should have a consistently circular orbit.

Pertinent Physical details for Rosetta and Philae


Orbiter Launch mass: 2,900 kg (6,400 lb)
Orbiter Dry mass: 1,230 kg (2,710 lb)
Lander: 100 kg (220 lb)
Orbiter Payload mass: 165 kg (364 lb)
Lander Payload mass: 27 kg (60 lb)


2.8 × 2.1 × 2 m (9.2 × 6.9 × 6.6 ft)


850 watts at 3.4 AU

Electrical power for the spacecraft comes from two solar arrays totalling 64 square metres (690 sq ft).[36] Each solar array is subdivided into five solar panels, with each panel being 2.25 × 2.736 m (7.38 × 8.98 ft). The individual solar cells are made of silicon, 200 µm thick, and 61.95 × 37.75 mm (2.44 × 1.49 in).[37] The solar arrays generate a maximum of approximately 1,500 watts at perihelion,[37] a minimum of 400 watts in hibernation mode at 5.2 AU, and 850 watts when comet operations begin at 3.4 AU.[35] Spacecraft power is controlled by a redundant Terma power module and is stored in four 10-A·h NiCd batteries supplying 28 volts to the bus.


S band (low gain antenna)
X band (high gain antenna)

7.8 bit/s (S band) up to 91 kbit/s (X band)


2.2 m (7.2 ft) steerable high-gain parabolic dish antenna, a 0.8 m (2.6 ft) fixed-position medium-gain antenna, and two omnidirectional low-gain antennas.


24 paired bipropellant 10 N thrusters, with four pairs of thrusters being used for delta-v burns. The spacecraft carried 1,719.1 kg of propellant at launch: 659.6 kg of monomethylhydrazine fuel and 1,059.5 kg of dinitrogen tetroxide oxidiser, contained in two 1,108-litre grade 5 titanium alloy tanks and providing delta-v of at least 2,300 metres per second (7,500 ft/s) over the course of the mission. Propellant pressurisation is provided by two 68-litre high-pressure helium tanks.


(Each equipment of the payload was developed in different parts of Europe.)

For Nucleus

The investigation of the nucleus is done by three spectroscopes(ultraviolet, optical and infra-red), one microwave radio antenna (to determine the quantity and temperature of substances like water, ammonia and CO2) and one radar (to explore the deep interior of the comet).

For Gas and particles

  • A double-focus magnetic mass spectrometer DFMS and a reflectron type time of flight mass spectrometer RTOF. The DFMS has a high resolution (can resolve N2 from CO) for molecules up to 300 amu. The RTOF is highly sensitive for neutral molecules and for ions.
  • A high-resolution atomic force microscope will investigate several physical aspects of the dust particles.
  • A secondary ion mass spectrometry, using indium ions to analyse the composition of dust particles . It can detect ions up to a mass of 6500 amu.
  • A dust grain analyser

References / Further Information

ESA site

Wikipedia pages on Rosetta and 67P/Churyumov-Gerasimenko

Newpaper reports

3 thoughts on “Rosetta – Philae and the Comet

  1. Pingback: Landing on 67P/Churyumov-Gerasimenko | Ghoomi Ghoomi Blog

  2. Pingback: Technological wizardry | The World Matters

  3. Pingback: Better than Sci-fi | Suraj and the Light

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