Philae lander makes historic touchdown on comet...

What is philae?

Philae is a robotic European Space Agency lander that accompanied the Rosetta spacecraft until its designed landing on comet 67P/Churyumov–Gerasimenko, over ten years after departing Earth.

On 12 November 2014, the lander achieved the first-ever controlled touchdown on a comet nucleus. Its instruments are expected to obtain the first images from a comet's surface and make the first in situ analysis to determine its composition.

The lander is named after Philae Island in the Nile, where an obelisk was found and used, along with the Rosetta Stone, to decipher Egyptian hieroglyphics.

Mission

 

Video report by the German Aerospace Center about Philae '​s landing mission. (10 min, English, in 1080p HD)

Philae '​s mission is to land successfully on the surface of a comet, attach itself, and transmit data from the surface about the comet's composition. Unlike the Deep Impactprobe, which by design struck comet Tempel 1's nucleus on 4 July 2005, Philae is not an impactor. Some of the instruments and the lander were used for the first time as autonomous systems during the Mars flyby on 25 February 2009. ÇIVA, the camera system, returned some images while the Rosetta instruments were powered down; ROMAP took measurements of the Martian magnetosphere. Most of the other instruments need contact with the surface for analysis and stayed offline during the flyby. An optimistic estimate of mission length is "four to five months".

Scientific goals

The scientific goals of the mission focus on "elemental, isotopic, molecular and mineralogical composition of the cometary material, the characterization of physical properties of the surface and subsurface material, the large-scale structure and the magnetic and plasma environment of the nucleus."

Landing

 

Photograph of comet 67P taken byPhilae approximately 10 km from the surface on 9 November 2014. This image represents an area 857x857 meters.

On 12 November 2014, Philae remained attached to the Rosetta spacecraft after rendezvousing with comet 67P/Churyumov–Gerasimenko. On 15 September 2014, ESA announced Site J, named Agilkia in honour of Agilkia Island by an ESA public contest, on the "head" of the comet as the lander's destination.

A series of four Go/NoGo checks were performed 11-12 November 2014. One of the final tests before detachment from Rosetta showed that the lander's cold-gas thruster was not working correctly, but the "Go" was given. Philae detached from Rosettaon 12 November 2014 at 08:35 UTC, landing seven hours later at 15:35. A confirmed landing signal was received at 16:03 UTC.

In an update from the LCC in ESA's live stream at 16:42 UTC, it was announced that analysis of telemetry indicated that the landing was softer than expected, but that the harpoons had not fired upon landing, and that the thruster had not fired. Subsequent readings indicated that the lander possibly drifted from comet after impact and touched down again. Dr. Stephan Ulamec, Rosetta project manager, stated that "Maybe, today, we didn't just land once, we landed twice!"

Design

 

Rosetta and Philae

The lander was designed to deploy from the main spacecraft body and descend from an orbit of 22.5 kilometres (14 mi) along a ballistic trajectory. It would touch down on the comet's surface at a velocity of around 1 metre per second (3.6 km/h; 2.2 mph).The legs were designed to dampen the initial impact to avoid bouncing as the comet's escape velocity is only around 0.5 m/s (1.8 km/h; 1.1 mph), and the impact energy would drive ice screws into the surface. Philae would then fire two harpoons into the surface at 70 m/s (250 km/h; 160 mph) to anchor itself. A thruster on top of Philae would fire to lessen the bounce upon impact and to reduce the recoil from harpoon firing. 

Communications with Earth will use the orbiter spacecraft as a relay station to reduce the electrical power needed. The mission duration on the surface is planned to be at least one week, but an extended mission lasting months is possible.

The main structure of the lander is made from carbon fiber, shaped into a plate maintaining mechanical stability, a platform for the science instruments, and a hexagonal "sandwich" to connect all the parts. The total mass is about 100 kilograms (220 lb). Its "hood" is covered with solar cells for power generation.

 

Philae landing site Agilkia (Site J)

It was originally planned to rendezvous with the comet 46P/Wirtanen. A failure in a previous Ariane 5 launch vehicle closed the launch window to reach the comet. It necessitated a change in target to the comet 67P/Churyumov–Gerasimenko. The larger mass of comet 67P/C-G and the resulting increased impact velocity required that the landing gear of the redesigned lander be strengthened, in order for the spacecraft and its delicate scientific instruments to survive the landing.

Power management

Philae power management has been planned for two phases. In the first phase, the lander will operate solely on battery power. In the second phase, "it will run on backup batteries recharged by solar cells".

Instruments

 

Philae '​s instruments

The science payload of the lander consists of ten instruments massing 26.7 kilograms (59 lb), making up nearly one-third of the mass of the lander.

APXS 

The Alpha Particle X-ray Spectrometer detects alpha particles and X-rays, which provide information on the elemental composition of the comet's surface. The instrument is an improved version of the APXS of the Mars Pathfinder.

COSAC 

The COmetary SAmpling and Composition instrument is a combined gas chromatograph and time-of-flight mass spectrometer to perform analysis of soil samples and determine the content of volatile components.

Ptolemy 

An instrument measuring stable isotope ratios of key volatiles on the comet's nucleus.

ÇIVA 

The Comet Nucleus Infrared and Visible Analyzer is a group of six identical micro-cameras that take panoramic pictures of the surface. Each camera has a 1024×1024 pixel CCD detector. A spectrometer studies the composition, texture and albedo (reflectivity) of samples collected from the surface.

ROLIS 

The Rosetta Lander Imaging System is a CCD camera that will obtain high-resolution images during descent and stereo panoramic images of areas sampled by other instruments.The CCD detector consists of 1024×1024 pixels.

CONSERT 

The COmet Nucleus Sounding Experiment by Radiowave Transmission experiment will use electromagnetic wave propagation to determine the comet's internal structure. Aradar on Rosetta will transmit a signal through the nucleus to be received by a detector on Philae.

MUPUS 

The MUlti-PUrpose Sensors for Surface and Sub-Surface Science instrument will measure the density, thermal and mechanical properties of the comet's surface.^[40]

ROMAP 

The Rosetta Lander Magnetometer and Plasma Monitor is a magnetometer and plasma sensor to study the nucleus' magnetic field and its interactions with the solar wind.

SESAME 

The Surface Electric Sounding and Acoustic Monitoring Experiments will use three instruments to measure properties of the comet's outer layers. The Cometary Acoustic Sounding Surface Experiment (CASSE) measures the way in which sound travels through the surface. The Permittivity Probe (PP) investigates its electrical characteristics, and the Dust Impact Monitor (DIM) measures dust falling back to the surface.

SD2 

The Drill, Sample, and Distribution subsystem obtains soil samples from the comet at depths of 0 to 230 millimetres (0.0 to 9.1 in) and distributes them to the Ptolemy, COSAC, and ÇIVA subsystems for analyses. The system contains four types of subsystems: drill, carousel, ovens, and volume checker. There are a total of 26 platinum ovens to heat samples—10 medium temperature 180 °C (356 °F) and 16 high temperature 800 °C (1,470 °F)—and one oven to clear the drill bit for reuse.

Rosetta mission’s safe landing gives scientists their first chance to ride a comet and study close up what happens as it gets closer to the sun.

Philae space lander sends first image

Rosetta space probe video