Rosetta Probe Deploys Philae Lander on Comet

Philae separating from Rosetta. Image captured by OSIRIS camera, courtesy of ESA.

by Nur Hussein, staff writer

This is the tale of a space robot making an incredibly daring stunt-landing on a comet after detaching from a space probe and controlled by a crack team of brilliant international scientists and engineers; forget the movies with questionable quasi-science, there’s nothing more exciting than the real deal. Last night, when the Philae lander separated from the ESA Rosetta space probe, there was concern that either the thruster needed to make the landing on the comet, or the thruster’s controls might have sustained some damage. All of the ESA scientists who spoke during the ESA live streaming event said it had been a long, sleepless night.

The image shows comet 67P/CG acquired by the ROLIS instrument on the Philae lander during descent on Nov 12, 2014 14:38:41 UT from a distance of approximately 3 km from the surface. Image courtesy of ESA.

Colin Snodgrass, a research fellow in astronomy and planetary science at Open University U.K., has been working on the Rosetta project, coordinating ground-based observing support; he also worked on the Optical, Spectroscopic and Infrared Remote Imaging System (OSIRIS) while at the Max Planck Institute for Solar System Research. Snodgrass told Krypton Radio, “The thruster is only meant to fire on touchdown, so we won’t know until later, but it seems like it may not work. It is only one of the three ways it tries to fix itself to the comet though!”

Today, Philae landed in working order at 7:35 a.m. Pacific, though its orientation on the “ground” is not yet known. A thruster on the top of the craft was supposed to have fired for 15 seconds to push the lander down onto the surface and to prevent it from bouncing before ice screws in the landing struts secured it firmly onto the comet. The thruster did not actually fire, but the lander made it down intact. It was a particularly harrowing moment for the scientists back at the ESA for they had no control of the lander when it was making its risky maneuver, and it relied entirely on the internal programmed logic to help it descend and land.The lander attempted to anchor itself with harpoons on to the surface of Comet 67P/Churyumov-Gerasimenko in a maneuver worthy of any sci-fi action film, and infinitely more nerve-wracking. ESA has just confirmed, though, that the harpoon anchors did not fire on landing, so the lander is still not considered stable, though the ice screws are confirmed to have deployed correctly. Assuming they’re not damaged, the harpoons can be re-fired in an attempt to get a more solid grasp of the comet. Philae successfully began transmitting telemetry data immediately after touching down.

The entire mission is a culmination of over two decades of planning, 10 years of space voyage for the Rosetta probe that was flung into space via a gravitational slingshot, at a cost of 1.4 billion euros. A high risk gamble that ESA hopes will pay off big time, it is a milestone in the history of human space exploration as this is the first time a space probe has been captured in a comet’s orbit, and also the first that a landing has been attempted on one. The landing site, chosen and designated site “J” last month and now renamed “Agilkea” after an island in the Nile river in southern Egypt, is located on the “head” of the duck-shaped comet.

ESA’s director general, Jean Jacques Dordain, said after the landing, “Philae has landed. This is a big step for human civilization … The biggest problem of success is that it looks easy. And when you know the sum of the expertise, the education, and the teamwork between 20 nations and corporations with international partners, you know that success is not coming from the sky. It comes from hard work and expertise.”

The Philae lander with the location of all the on-board instruments.

The Philae lander carries the following instruments:

  1. APXS (Alpha X-ray Spectrometer) – A detector for alpha particles and X-rays, this will be used to study th elemental composition of the surface
  2. ÇIVA – Six micro-cameras for taking those panoramic shots we love! Also, a spectrometer for analyzing the composition, texture and albedo of surface samples
  3. CONSERT (Comet Nucleus Sounding Experiment by Radiowave Transmission) – This instrument uses radio waves to scan the internals of the comet. It works in tandem with the orbiter which sends the radio waves through the nucleus to be picked up by a transponder on the lander. Robot teamwork gets the science done!
  4. COSAC (Cometary Sampling and Composition experiment) – A gas analyzer for detecting complex organic molecules.
  5. Ptolemy – Another gas analyzer, for measuring isotope ratios of light elements.a is an evolved gas analyser, which obtains accurate measurements of isotopic ratios of light elements. It is about the size of a small shoe box and has a mass of less than 5 kg.
  6. MUPUS (Multi-Purpose Sensors for Surface and Subsurface Science) – Resides on the lander’s anchor, and its sensors collect information on the surface density, thermal and mechanical properties.
  7. ROLIS (Rosetta Lander Imaging System) – A CCD imager that will take hi-res images (get ready for some cool new desktop wallpaper, space fans). It is for obtaining photos of the surface and documenting the sampling areas, before and after the sampling process.
  8. ROMAP (Rosetta Lander Magnetometer and Plasma Monitor) – There are multiple sensors in this instrument, which is for studying magnetic fields, local pressure, and solar winds.
  9. SD2 (Sample and Distribution Device) – A mechanical assembly that drills up to 20 cm into the surface to collect samples, then distributes them to different instrument stations such as ovens or a spectrometer.
  10. SESAME (Surface Electrical Sounding and Acoustic Monitoring Experiments) – A collection of three instruments to study the comet outer layers:
    Three instruments measure properties of the comet’s outer layers:

    • Cometary Acoustic Sounding Surface Experiment (CASSE) – Studies how sound is conducted through the surface.
    • Permittivity Probe (PP) – Studies the electrical properties of the surface
    • Dust Impact Monitor (DIM) – Measures the amount of dust that falls back to the surface.

Philae’s batteries will last up to 64 hours in which time ESA scientists will conduct their investigations using the on-board tools. After the batteries drain, the solar panels can recharge them provided there is enough sunlight (will there be? we might only know post-landing), and Philae will be able to be used for about an hour for every few days of recharging. The lander is expected to work until March of next year, but after that the surface will become too hot as the comet gets nearer to the sun. Comet 67P/Churyumov-Gerasimenko will pass perihelion on August 13th, 2015.

The Rosetta mission hopes to find out more about the origins of the solar system; comets are a snapshot of the composition of the solar system when it first formed. We are basically undertaking space archaeology, with comets being a frozen artifact that provides us with clues of our cosmic past. Rosetta and Philae have Twitter accounts which you can follow to get news of their progress in their mission. You can follow the lander’s mission at @Philae2014 and the Rosetta orbiter’s is at @ESA_Rosetta.

“We are extremely relieved to be safely on the surface of the comet, especially given the extra challenges that we faced with the health of the lander,” said Stephan Ulamec, Philae Lander Manager at the DLR German Aerospace Center. “In the next hours we’ll learn exactly where and how we’ve landed, and we’ll start getting as much science as we can from the surface of this fascinating world.” We’ll keep updating as more news becomes available.

Update: ESA has just announced that it will hold a press briefing tomorrow, November 13, 2014, at 5:00 a.m. Pacific. We’ll be there!

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About Nur Hussein

Nur is a tinkerer of programmable things, an apprentice in an ancient order of technomages. He enjoys fantasy, sci-fi, comic books, and Lego in his spare time. His favourite authors are Asimov and Tolkien. He also loves Celtic and American folk music. You can follow him on twitter: @nurhussein

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