Wednesday, 12 October 2016

The ESA Rosetta Mission to a Comet - Part 1

The ESA Rosetta Mission to a Comet – A Talk at University of Alberta by Matt Taylor (Part 1)
On Tuesday Oct 4, 2016, Dr. Matt Taylor, the Project Scientist of ESA’s Rosetta Comet probe did a talk at the University of Alberta.  This, of course, is the fascinating mission to comet 67-P/Churyumov-Gerasimenko, which was launched in 2004 and rendezvoused with 67-P in 2014.  It has just recently (late Sept 2016) been decommissioned, via flying it into the comet. For simplicity, I will generally refer to it as 67-P or “the comet”, much as Matt Taylor did during the lecture.

The talk was enormously well attended and well received.  Here are some of my notes from the presentation, in point form.
I have broken the blog into two parts, since there is a lot of information.  This is Part 1, which describes  an overview of the mission and the trip to the comet.  Part 2 will focus on the mission once the craft had caught up with the comet, and will be published next week.

The Speaker

  • Dr. Matt Taylor has a PhD in space physics from the Imperial College of London.  His undergrad was in physics, from the University of Liverpool.
  • He has been with the ESA (European Space Agency) since 2005, working on the Cluster project and the ESA-China Double Star mission.
  • The Cluster mission is based on a set of 4 satellites flying in formation around the Earth, measuring the solar wind and its effect on the Earth.
  • He became involved with the Rosetta mission in 2013 and has been with it since then.  As he noted on several occasions, he was just one part of a large team of professionals of all sorts, that were jointly responsible for the success of the mission.
  • As he noted, the Rosetta mission has been quite different from the Cluster mission.  For one thing, it is easier to explain to his mother (and most of the public) – after all, flying a spacecraft around a comet, then landing a probe on it, is more intuitive for the average person than mapping the solar wind and its interactions with the Earth.
  • He is an excellent speaker, and livened up the talk with some comments about:
  •        o The various conspiracy theories generated by the mission.
  •    o   Rock band Queen’s member Brian May’s (who is also an astrophysics PhD) following of the mission.
  •    o   The metal band Napalm Death has also given shout-outs to the Rosetta mission.
  •    o   He also made many amusing allusions to SF pop culture’s intersection with Rosetta, particularly the Star Wars saga (but others, such as Star Trek, Battlestar Gallactica and Blade Runner got some mentions too) .

An Overview of the Rosetta Mission’s Purpose

  • The purpose, of course, was to visit a comet and gain close-in scientific data on its composition and other features of interest.
  • Comets are assumed to contain relatively pristine material, from around the time that the solar nebula first formed the sun and planets.  So, examining a comet gives us information about how the solar system, our home, came about.
  • Comets are thought to be short term visitors to the inner solar system, for the most part.  They have spent most of their existence in the far, outer solar system, before their orbits are perturbed enough to send them into our part of the solar system.  Thus, their material should be mostly unchanged, since the solar system’s formation, billions of years ago.
  • There have been theories that most of the water in the Earth’s oceans came from comets and asteroids during the early stages of the solar system.  So, one of Rosetta’s purposes was to get some close-in data, to support or refute that.
  •  Likewise with the elements needed for life – the so-called “organic” elements, primarily carbon (as Earth life is carbon-based).  Were these brought to the Earth by asteroids and comets, in the early days of the solar system?
  • Of course, comets have just flat-out fascinated humanity for as long as we have records.  Some cave art might depict comets .
  • Certainly there are many famous depictions of comets in historical art, such as the Bayeux Tapestry, which depicts Halley’s comet.

  • Thus, a comet mission is a natural.  In fact, the precursor of Rosetta was to be a sample return mission, though that never happened.  Instead, the lab (the Philae lander) was brought to the comet.
  • Note that there have been flyby missions to comets in the past (the NASA Deep Impact mission for example), but Rosetta was the first tourist to visit, orbit and ultimately settle down, so to speak.
  • The comet chosen for the Rosetta mission is known as 67-P/Churyumov-Gerasimenko.   For simplicity, I will generally refer to it as 67-P or “the comet”, much as Matt Taylor did during the lecture.
  • Note that the designation 67-P stands for the 67th periodic comet discovered.  Halley’s comet was the first, so it is officially called 1P/Halley.
  • Before the mission, 67-P was thought to be a 4 km potato shaped object (from the best Earth-based photos).  Now, we know that is actually 4100 meters long and shaped like a rubber duck.  That’s progress.
  • This photo reminds me more of the head of a Tyrannosaur, though.  Jurassic Park, Jupiter Division. 



The Spacecraft

from Matt Taylor’s comments and the ESA website

  • The Rosetta orbiter was about 32 meters long, about the size of a bus.  Most of that is the array of solar panels, though.  The main structure of the spacecraft was about 3 meters by 2 meters by 2 meters.
  • The total mass was about 3000 kg, and about half of that was propellant.
  • The solar panels put out about 850 watts at 3.4 AU, about 400 watts at 5.25 AU.
  • For comparison, at the Earth’s surface, 4 “largish” standard residential solar panels would probably put out about 850 watts, on a nice summer’s day, at around noon (well, mine do about 250 watts per panel at that time, anyway).  Of course, Rosetta’s solar panels were only very rarely in shadow, so they operated 24/7.
  • The orbiter had 11 scientific instruments, among them, cameras, mass spectrometers, dust analysers, radar, and other imaging instruments.
  • The Philae lander weighed about 100 km, and was about the size of a washing machine (North American variety).  It had various devices, that were intended to make it “stick” to the comet upon landing, such as harpoons that could be fired into the surface.  As we now know, they didn’t work well enough, so the lander bounced about a km.


  • The lander also carried a spectrometer, cameras, radio-wave probes, gas analysers, a magnetometer, even a drill and an oven to examine samples.
  • The name Rosetta refers to the “Rosetta Stone”, the ancient Egyptian artifact that was instrumental in translating ancient Egyptian hieroglyphics, so that modern people could understand their language.  This was meant to reflect the hope that the findings of the Rosetta space mission could help us understand the composition and formation of the early solar system.

The Trip to 67-P/Churyumov-Gerasimenko

From ESA website and Matt Taylor’s talk

  • In March 2004, the spacecraft was launched with an Ariane 5 rocket.
  • Even this powerful rocket couldn’t launch the probe directly to the comet – that  just takes too much energy.


  • So, the spacecraft took advantage of several “slingshot” manoeuvres, whereby the rocket picks up momentum (and thus velocity) from the inner planets (Earth and Mars, which are “inner” relative to the comet’s location), as it passes by them.
  • There’s a really nice animation of the trip on the ESA site.  Here’s a screen capture and a link (at the end of the blog). 


  • There were 4 flyby “kicks”, three from Earth (2005, 2007 and 2009) and one from Mars (2007).
  • It got some nice photos during those approaches.  Matt Taylor showed an especially dramatic shot of Mars, taken during that flyby.  The spacecraft itself is in the foreground, of course.


  • Here’s a nice Feb 24, 2007 shot of Mars, taken as Rosetta approached the planet, from the Planetary Society’s website.


  • There was a short communications blackout after passing Mars, when Earth was eclipsed.  Then it did a couple more Earth flybys to pick up more speed, before heading for the comet, out around Jupiter.
  •  Here’s a shot of Jupiter, taken by Rosetta when it was near Mars.  The photo is nothing special, it’s just the idea of taking a picture of Jupiter from a spacecraft near Mars that’s is pretty cool, when you think about it.


  • On the way, though, it observed some asteroids, from fairly close distances (a few thousand km).
  • Then it went into hibernation for a few years (May 2011 to Jan 2014), switching off most systems.  That helps to minimize power and fuel consumption (and costs) while the craft is in a fairly uninteresting region of space.
  • It came out of hibernation in Jan 2014 and arrived at the comet in August 2014 (after some braking manoeuvres, to match the comet’s speed).

End of Part 1 (Part 2 to come next blog)


·         Notes from Matt Taylor’s talk at the University of Alberta, Oct 4, 2016.


Science Fiction for you to Read

Now that you have read some real science (astronomy and astrophysics), you should read some science fiction.

Kati of Terra

How about trying Kati of Terra, the 3-novel story of a feisty young Earth woman, making her way in that big, bad, beautiful universe out there.

The Witches’ Stones

Or, you might prefer, the trilogy of the Witches’ Stones (they’re psychic aliens, not actual witches), which follows the interactions of a future Earth confederation, an opposing galactic power, and the Witches of Kordea.  It features Sarah Mackenzie, another feisty young Earth woman (they’re the most interesting type – the novelist who wrote the books is pretty feisty, too).

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