Archive for ESA

Rosetta and Philae: So Much More Than Science

Posted in The Universe and Stuff with tags , , , , on November 15, 2014 by telescoper

Time to break radio silence, so to speak, with a short post about the main event that’s happened in the astronomical world while I’ve been indisposed, namely the separation of the probe Philae from its parent spacecraft Rosetta and subsequent successful landing  on  Comet 67P/Churyumov-Gerasimenko. There’s been  a huge amount of media coverage and in-depth specialist analysis of this going on over the past few days, and it isn’t reallly in my own area of specialism, so there isn’t much point in trying to do my own version of events here. If you’re looking for a science briefing then you could do a lot worse than the official European Space Agency web pages here. I’ll confine myself to a few general reflections.

First, as has been widely reported, the final stages of Philae’s  approach were clearly a bit hairy (appropriately enough, since the word “comet” is derived from the Greek word for “hair”).  Although it homed in on its intended landing site pretty accurately, when it got close the thrusters intended to help it settle onto the surface didn’t fire and the “harpoons” supposed to fasten it to the surface also failed. As a consequence of all this, Philae bounced off the surface, floated in space for about two hrs, during which it travelled about 1km across the surface of the comet; that’s an average speed of about 0.14 m/s relative to the surface of the comet. It then encountered the surface again, bounced again for about 7 min, and then come to rest on 2 legs, with one pointing into space, against a cliff on the edge of a crater, with only one solar panel in operation because of the shade from the cliff.

It’s worth noting that the escape velocity from the surface of Comet 67P/Churyumov-Gerasimenko is only about 0.5 m/s and the probe met the surface of the comet at about twice that speed. Without significant intervention to stick it down, Philae could quite easily have bounced off and into space forever. The loss of the thruster and the failure of the harpoons made that a very likely outcome, but the mission’s luck held out. Fortune favours the brave.

Here’s just one of the remarkably vivid pictures taken of the surface of the Comet taken by Philae from its precarious resting place. I don’t know about you but to me it looks very eerie but at the same time it almost makes me feel like I am there in person, as if I could reach out and touch it…

comet_surface

It then became clear that the rate at which Philae was using power from its batteries was exceeding the rate at which it could recharge using its solar panel. For a time it was by no means obvious that it could perform all its science tasks in the short time (~60 hours) remaining before it would run out of juice, but in the end, according to the experts, it did accomplish about 80% of its science goals before going into hibernation.

I’ve heard some folk – including a few astronomers – claiming that Philae’s difficulties have cast a big shadow over the Rosetta mission. That’s clearly nonsense. In fact, the odds that Philae would ever  attach itself to its target were only about 50-50. And even if it did succed there was a chance some of its on board instruments may well have failed. After all, they had spent 10 years in the hostile environment of space waiting to be called into action. As it turned out, Philae’s achievements are at the upper end of the range of expectations. But even if the probe had failed entirely then there would still have been the huge amount of science being done by Rosetta itself. Overall, I think the mission so far has been a stunning success and there’s a lot more to come.

From a non-scientific point of view the perilous landing of Philae was even a bonus, as it made a public that is in danger of becoming blasé about spaceflight realise (a) that it is incredibly difficult and (b) there are people clever enough to make it work. The tension that mounted as events unfolded had people gripped largely because people could see in their mind’s eye this little thing, like a washing machine on legs, bouncing about in slow motion across an alien landscape. It was a drama largely acted out in our own imagination, and all the more absorbing for that.

Yesterday I was chatting with a friend who was trying to understand what Philae was doing as it bounced. It is quite difficult, if you think about it, to apply physical intuition to this situation. On the Earth we think of the “up” and “down” directions as being unambiguously defined, but “up” actually means two different things: (i) perpendicular to the Earth’s surface; and (ii) in the opposite direction to which gravity makes things fall (“down”) . On a spherical object such as a planet, gravity acts towards the centre, hence “what goes up  (i)  must come down  (ii)” .

Comet 67P/Churyumov-Gerasimenko, however, is far from spherical (even by the standards of a theoretical physicist):

Comet_close

This means that bouncing up off the surface does not necessarily result in coming straight back down again – gravity may well pull in a quite different direction. Add to that the spinning of the comet and its uneven surface, and you can understand how difficult it was to figure out where Philae ended up and precisely how it had got there!

Another comment I’ve heard concerns the cost. At €1.4 Billion it does sound expensive, but divide that among the population of the European Union (currently over 500 million) and it doesn’t sound so much, about the cost of a cup of coffee, and remember that the mission has lasted over years.  Philae has succeeded in generating a  huge amount of scientific data and I have no doubt that important conclusions will soon be drawn from the measurements it has made, but it’s not just the science that justifies the (modest) pricetag. Rosetta is an achievement that all humanity can celebrate. It is a demonstration of what we can achieve collectively if we have ambition, imagination and determination. Setting ourselves targets and reaching them. Asking ourselves questions and answering them. This is what makes us humans what we are. Venturing into space changes our perspective on our own world, something we need to do urgently if humanity is to survive on Earth.

 

 

 

Rendezvous Rosetta!

Posted in The Universe and Stuff with tags , , on August 6, 2014 by telescoper

Just a quick post to remind you (as if you needed it) that, in about 5 minutes’ time at 10am BST, the ESA spacecraft Rosetta will begin its encounter with a comet (actually Comet 67P/Churyumov-Gerasimenko).

As it approached its target, Rosetta took this picture that revealed the comet to be a rather peculiar beast, rather like a rubber duck:

Comet

Here’s a more recent, closer, view:

Comet_close

Rosetta’s journey began on 2 March 2004 when Rosetta was launched on an Ariane 5 from Europe’s Spaceport in Kourou, French Guyana. Since then, the spacecraft has orbited around the Sun five times, picking up speed through three gravitational “slingshots” at Earth and one at Mars, to enter an orbit similar to that of its target, said comet 67P/Churyumov–Gerasimenko, which is in an elliptical 6.5-year solar orbit that takes it from beyond the orbit of Jupiter at its furthest point, and between the orbits of Mars and Earth at its closest to the Sun.

To perform its rendezvous Rosetta has to match the pace of the comet – currently about 55 000 km/h – and travel alongside it to within just 1 m/s between them. This has required a complex and delicate series of manoeuvres:

The spacecraft will then travel alongside the comet as it approaches the Sun. In November 2014 the Philae probe will be deployed and will land on the comet surface. Rosetta will follow the comet to its closest distance to the Sun on 13 August 2015 and as it moves back towards the outer Solar System. The nominal mission end is December 2015.

I bet there’s quite a lot of stress in the ESA control centre in Darmstad, Germany, as the probe’s epic journey nears its end, not least because telemetry is lost while the burn happens. Those ten years in space will count for little if something goes wrong now. Good luck everyone involved!

You can watch a live feed of the encounter here.

UPDATE: after an agonizing wait – it takes 23 minutes for telemetry to reach Earth from Rosetta – the spacecraft has entered orbit correctly. Well done everyone!

UPDATE: click here for an amazing collection of images of the comet.

UPDATE: Relief at ESA HQ as The Clangers finally emerge to greet the Rosetta Spacecraft:

BuW-AFJIEAA6L3k

Top Ten Gaia Facts

Posted in Astrohype, The Universe and Stuff with tags , , , on December 20, 2013 by telescoper
Gaia looks nothing like the Herschel Space Observatory shown here.

Gaia looks nothing like the Herschel Space Observatory shown here.

Since yesterday’s successful launch of the European Space Agency’s Gaia mission I have been inundated with requests for more information about this impressive satellite and the science behind it. As a service to the community, and for the edification of the public at large, I therefore thought I’d share my list of top ten Gaia facts via the medium of this blog:

  1. The correct pronunciation of GAIA is as in “gayer”. Please bear this in mind when reading any press articles about the mission.
  2. The GAIA spacecraft will orbit the Sun at the Second Lagrange Point, the only place in the Solar System where the  effects of cuts in the UK science budget can not be felt.
  3. The data processing challenges posed by GAIA are immense; the billions of astrometric measurements resulting from the mission will be analysed using the world’s biggest Excel Spreadsheet.
  4. To provide secure backup storage of the complete GAIA data set, the European Space Agency has commandeered the world’s entire stock of 3½ inch floppy disks.
  5. As well as measuring billions of star positions and velocities, GAIA is expected to discover thousands of new asteroids and the hiding place of Lord Lucan.
  6. GAIA can measure star positions to an accuracy of a few microarcseconds. That’s the angle subtended by a single pubic hair at a distance of 1000km.
  7. The precursor to GAIA was a satellite called Hipparcos, which is not how you spell Hipparchus.
  8. The BBC will be shortly be broadcasting a new 26-part TV series about GAIA. Entitled WOW! Gaia! That’s Soo Amaazing… it will be presented by Britain’s leading expert on astrometry, Professor Brian Cox.
  9. Er…
  10. That’s it.

Planck (but only in name?)

Posted in Science Politics, The Universe and Stuff with tags , , , , , , on March 3, 2013 by telescoper

First, a serious announcement. It appears that the announcement of results from the Planck Mission will be streamed live from ESA HQ on 21st March from 10.00 to 12.00 CET (whatever that is). The UK will remain on GMT until 31st March so the  ESA web server will probably crash at 9am British time on 21st March.

There’s a short press release making this announcement here. It says:

On Thursday 21 March 2013, the main scientific findings from the European Space Agency’s Planck spacecraft will be announced at a press briefing to be held at ESA’s Headquarter in Paris. Simultaneously with this event, data products and scientific papers based on the “nominal” operations period will be made public through the Planck Legacy Archive.

I was interested in the appearance of the word “nominal” in quotes in there so I searched for its meaning in the One True Chambers Dictionary, where I found:

nominal, adj relating to or of the nature of a name or noun; of names; by name; only in name; so-called, but not in reality; inconsiderable, small, minor, in comparison with the real value, hardly more than a matter of form…

Interesting. It seems that the “nominal” could mean, on the one hand, that ESA are being unusually modest about the importance of the forthcoming Planck results or, on the other, that there will now be a host of conspiracy theorists suggesting that the Planck results aren’t real….

That reminds me that years and years ago I had an idea for a crime novel with a plot that revolves around the murder of a prominent cosmologist just as some important scientific discovery is about to be announced. Suspicion gathers that the whole thing is an enormous hoax and the discovery bogus. But the experiment is shrouded in secrecy, and so expensive that it can’t easily be repeated, so  who can tell, and how?

It’s very difficult to know for sure whether any scientific discoveries are genuine or not, even if the data and analysis procedures are made public. There’s always the possibility that everything might have been fabricated simulated, but in most cases the experiment can be repeated at a later date and the fraud eventually exposed, such as in the Schön Scandal.  In Big Science, this may not be practicable. However, Big Science requires big teams of people and the chances are someone would blow the whistle, or try to…

Anyway, I know that there are people out there who take everything I write on this blog absurdly literally so I’ll spell it out that I am in no way suggesting that the Planck mission is a fraud. Or predicting that there’ll be a murder just before the announcements on March 21st. Any similarity purely coincidental and all that. And I’ve never had time to write the book anyway – perhaps a publisher might read this and offer me an advance as an incentive?

Moreover, going back to the Chambers Dictionary, I note the final definition omitted above

…according to plan (space flight)

So that’s that. Nothing sinister. I’m not sure how “nominal” acquired that meaning, mind you, but that’s another story…

The case for JUICE

Posted in Science Politics, The Universe and Stuff with tags , , , on May 8, 2012 by telescoper

telescoper:

Here’s a nice blog peace giving the case for JUICE (The Jupiter Icy Moon Explorer recently selected by the European Space Agency for its next L-class mission).

Originally posted on Well-Bred Insolence:

There’s been a lot of chatter in astronomy circles about the negative consequences of ESA’s latest L-class (i.e. large) space mission selection.  JUICE (The JUpiter Icy moon Explorer) was selected over two rival missions – the New Gravitational wave Observatory (NGO), and the Advanced Telescope for High ENergy Astrophysics (ATHENA).  In the current age of global austerity, one group’s win is several groups’ losses, and understandably the X-Ray and gravitational wave communities are upset at the choice.  Indeed, reading the comments section on astro blogs might make planetary scientists go a little pale. Not least the fact that ATHENA supporters have already delivered a 1450 signature petition demanding a rethink.  The fact that the decision making process has been somewhat cloudy doesn’t help matters.

It does indeed suck that this is a zero-sum game (in fact, probably…

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It’s JUICE!

Posted in Science Politics, The Universe and Stuff with tags , , on May 3, 2012 by telescoper

Not unexpectedly, the European Space Agency announced yesterday that it’s next large mission will be the Jupiter Icy Moon Explorer (aka JUICE). There’s a piece in Physics World about the selection – and rejection of the other two contenders, NGO and ATHENA. Andy Lawrence has commented already on his own blog and is also quoted extensively in the Physics World article.

A lot of allegations are flying around about how the selection process was conducted, specifically relating to conflicts of interest. I don’t know any details, so I won’t comment on whether this is justified outrage or simply sour grapes.

Anyway, for what it’s worth, I think I agree with what Andy Lawrence says in the Physics World story in that the final decision was pretty inevitable after NASA’s decisions in the areas of gravitational waves and X-ray astronomy pulled the rug out from under the other contenders. I’ll also add that, although it’s far from my own specialism, I think JUICE looks like a very exciting mission. I wish it every success.

It just remains to be seen how long the recriminations will rumble on.

Controversy brewing at ESA?

Posted in Science Politics with tags , , , , on April 23, 2012 by telescoper

telescoper:

Interesting stuff over at the e-astronomer relating to ESA’s handling of the process of selecting its next L-class mission. The plot thickens.

Originally posted on The e-Astronomer:

So the Athena folk are somewhat miffed at being pipped by Juice. (This metaphor doesn’t seem quite right ? Ed.) But what about Horse Number Three ? Aren’t the NGO folk doing a Grand Petition ? Nope. It seems their tactic is a semi-formal complaint about inadeqacies in the process : an email letter direct to Gimenez. I am not sure how widely it has been circulated, but I understand it is stern stuff, bringing up issues of inappropriate revisions of costings and risk factors, and inadequately resolved conflicts of interest. Feel free to comment if you have clear knowledge, but please (a) do not leak things that are confidential, and (b) keep coments about process and not about individuals.

Its not really clear what competition means when a very small number of items is under consideration, and moreoever each item represents one community-segment, each of which ESA wishes to…

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