Demonstrating the Philae lander on the Space Station

Watch ESA astronaut Alexander Gerst demonstrate how Philae will land on the surface of comet 67P/Churyumov–Gerasimenko.

Alexander narrates the story of the Rosetta mission and performs a demonstration that visualises the difficulties of landing on an object that has little gravitational pull. Using the weightless environment of the International Space Station, Alexander attempts to land ‘Philae’ (an ear plug) onto the selected landing site of the ‘comet’ (an inactive SPHERES robot) with increasing levels of difficulty: a rotating comet that is not moving to one that is both rotating and moving.

As the video shows this is a challenging task for Alexander on the Space Station, and he wishes the Rosetta mission all the best with their landing attempt next week.

This video is one of the six experiments and demonstrations in the Flying Classroom programme, where Alexander uses small items to demonstrate several principles of physics in microgravity to students aged 10–17 years.




  • THOMAS says:

    At around 3:10: “ …to represent the comet, which in reality is a dirty snowball of approximately 4 kms across…”.

    Slight mistake here: he should have said: “…to represent the comet, which in theory is supposed to be a dirty snowball of approximately 4 kms across, but which in reality, as the images we have now acquired clearly show, is actually a highly misshapen lump of stratified rock…”.

    I increasingly sense that die-hard believers in the standard theory will become ever more impervious to the value of mere observational evidence as the mission progresses.

    • Mark McCaughrean says:

      With all respect, Thomas, the direct observational evidence of a density of 0.4g/cm3 would appear to contradict your view on this. It cannot be rock. Appearances can be very, very deceptive.

      • THOMAS says:

        With all due respect, Mark, the obviously totally rocky nature of the comet (and not just its “appearance”), with tens of thousands of stratified boulders lying at the feet of hundreds of stratified cliff-faces, would appear to contradict the figure of 0.4g/cm3. This figure of 0.4g/cm3 has nothing whatever to do with “direct observational evidence”. It is a CALCULATION, made on the basis of a gravity-only THEORY which steadfastly refuses to take any account whatever of the obvious electromagnetic forces being exerted on the comet nucleus (as witness those dead-straight jets of dust being machined off the neck region in particular and off the rest of the comet surface in general). Those electromagnetic forces give a totally wrong reading for the alleged density, just as they can also severely perturb readings for physical properties down here on Earth.

        Correct scientific method puts observation before theory, as you fully know.

        And theories can be very, very wrong… Are you still honestly clinging to the “dirty snowball” model in the face of all the REAL observational evidence? How do YOU explain all those boulders piled up at the base of hundred-metre high cliff-faces? Was that observation expected in a “dirty snowball” model?

        • Cometstalker says:

          If electrostatic forces are applied between comet and orbiter then how to determinate its direction? Push or pull? The gravity is always pulling. This could mean that the density is 0.4 g/cm^3 plus-minus a factor. Also the orbiter at its close, about 7-8 km above the surface trajectory would have noticed the huge multi kilovolt per meter field strenght if present. Ever walked under a 400 kVDC power-line? I have a low power DC generator that deliveres 100kV and to stand safely away from it at about 2 meters it is not possible to notice any pull or push with this huge field strenght.

          • THOMAS says:


            Not “electrostatic” but “electromagnetic” forces. It’s a question of polarity. Try it with two bar magnets: one way round, they pull, the other way round, they push.

            67P is PUSHING. If it were pulling, then the density would have been calculated to be at least 4 g/cm^3 and Rosetta would have had to quickly use up all its precious energy resources to prevent it from being pulled straight down and crashing directly onto the surface of the comet.

            67P is pushing like with every other body in the universe, because nature has miraculously provided it with an electric shield (or natural insulation, if you prefer) which electric engineers call a “double layer”, acting to separate areas of positive and negative charge. This is also, at a totally different scale, what maintains the integrity of the cells which every living organism is composed of, in the shape of what we call “cell-walls”. It’s one of the basic mechanisms of life… Nature is lazy, it uses the same +/- force from the infinitely small up to the infinitely large. It is thereby also allowing us to communicate on this blog and enjoy the comforts of modern life via the binary 01 principle every time we use our brain, a computer, a Smartphone, a washing-machine or everything else which is electrically powered.

            As for the “400 kVDC power-line” or your personal “low power DC generator”, what’s the issue? Ever since the most brilliant electrical engineer of all time, Thomas Edison invented the majority of the major electrical applications which we now take for granted around a century ago, we have fortunately learnt enough about the way electricity works down here on Earth to be able to protect ourselves most of the time from its more unpleasant properties, via suitable man-made insulation, contact-breaker and other safety systems.

            Up in space, it’s another kettle of fish: we can only wait to see what happens to Rosetta and Philae over the coming days, weeks and months in the totally natural, electrically hostile environment of Comet 67P, where neither can simply throw a switch and wait for the repairman to put things right again.

          • Cometstalker says:

            Ok no electrostatic force present, fine as this anyhow does not last forever and soon decays or changes due to a lot of reasons.
            If electro magnetism is the case there are two essential factors that are to be considered. The polarity is essential as it decides if the force vector is pull or push and this depends of the current direction, i see no way that this would not be random.
            Second and most important is the fact that an electro magnetic or permanent magnetic force decays with its distance a factor ^3 (volumetric, cubically) and gravity as well as electromagnetic radiation like photons are decaying with the distance a factor ^2 ( the square law).
            Edison and other guys knew this as well and you can try this yourself with some magnetic toys and a scale plus ruler
            This is essential and i see no way that the closing in orbit was affected by any electromagnetic force as such an anomaly would be clearly noticed and would make mega headlines all over this planet.
            Alternative if magnetism, permanent or electro induced does behave otherwise on comets than in any school lab where kids are doing their workshop this is very new science that is not well established and you can make great headlines if you can set up some theses and present som experiment. Give it a try and i wish you to be successful.

          • THOMAS says:

            @ Cometstalker, the laboratory is already up there with Rosetta and 67P, we just need to wait for the results.

  • DavidW says:

    Hi Emily,
    Here is the poem I’ve written for the landing, you can pass it on to the team, if you think it’s worth it.
    Regards David

    Philae’s journey to Agilkia

    Slowly, I separate from my companion
    For ten or so long years we’ve journeyed
    Always together, but now:
    I shall fall gently to my craggy old new world
    For seven long hours my legs unfurled, I descend to Agilkia

    Do I descend to dust?
    Black ice?
    That, at my touch will crumble?
    Hold fast?
    Or forever and ever will I tumble?

    Throughout my short long journey
    I will observe.
    Our past my ever nearing future coming closer
    I will gather. Sample. Enquire. Examine.
    Test, sort, and observe again, over and over until?

    My companion will listen and pass on
    Relay knowledge to you, oh so distant
    Whether I end in glorious death or not
    I have lived to the full and succeeded
    Whatever comes
    I will have won

    David Williams

  • Phil Stooke says:

    Images tell you what things look like, not what they actually are. Remember too that ice at -70 C behaves very much like rock so areas of solid ice might indeed look like rock, and the many fractures (or loss of more volatile materials from pore space) can reduce density below that of solid ice.

    I increasingly sense that die-hard believers in non-standard theories will become ever more impervious to the value of mere observational evidence as the mission progresses.

    • THOMAS says:

      Phil, there is not a single tiny ice-cube, let alone ice-cliffs or ice boulders anywhere on the surface of the comet. It’s not I who say it, it’s the Rosetta mission scientists who say it. What we are seeing is rock and rocks.

      So why did we spend 20 years and a billion dollars to get these images if they were immediately to be trashed because “Images tell you what things look like, not what they actually are”. Why did we even bother to fit Rosetta with cameras in that case?

      • THOMAS says:

        And what DO YOU accept as “observational evidence” if it’s not the images obtained?

  • Jacob nielsen says:

    I’d say the most apparent deviation from the ‘dirty snowball’ term and concept would be size rather than chemistry: this comet may be dirty, but snowballs are molded by hands and no hands are this big and there are no giants at play in space.

    EU is not a challenge to physics, EU is a system of belief. The ‘thunderbolts’ site is a place for believers. It offers a cosmology for the common man, with lines connecting to monotheistic religion (one ruling force: electric potential). Want to be a desciple? Go there, donate and enroll as a supporter.

    There has been nothing published about the Rosetta mission that conflicts substantially with established physics, the steady progression of the mission demonstrates this. This mission is about 67p and applied technology, and has been a triumph for established science. Nothing revealed about 67p shakes the foundation.

    • THOMAS says:

      @Jacob nielsen

      Sorry to disagree. The religious , monotheistic belief is on the side of the Genesis story of the standard Big Bang theory and the.”lux fiat” (let there be light) dogma. Paradoxically, the standard theory has subsequently needed to invent all the dark fairy dust of black holes, dark matter and dark energy to sustain itself and the funding machine which goes with it.

      I was myself a lifelong mainstream disciple up till around 15 years ago when I could no longer swallow all the fairy dust and started to trust the observational evidence which the new generation of telescopes were sending back to us.

      I have donated absolutely nothing to EU organizations in any form whatever. They don’t even know of my existence.

      As for your final paragraph, allow me to say that your conclusions are premature and extremely rash. NOTHING we have seen was expected by the standard theory and the worst for standard theory is still to come, as we will see in the coming days.

      But you can believe whatever you want, of course.

  • Harvey says:

    I’m sorry Thomas, but that is simply not a tenable position scientifically.
    ESA has been navigating with great precision in the vicinity of the comet for months now, on the basis of standard gravitational theory. So the experimental evidence is that that theory works exquisitely well. There is no credible electromanetic force over this scale of distances that have an identical behaviour to gravity.
    The comet is an utterly alien environment. You are using earth-bound eyes to see ‘stratified rock’, but your experience of ‘what things look like’ is almost completely irrelevant on 67P. In any case, as a high altitude climber, I’ve seen plenty of stratified structures like that in ice – they just weren’t pitch black!
    There are many, strange, unexpected aspects to 67P. I personally think the ‘contact binary’ model is over-emphasised as compared to the shape arising from differential ablation. Indeed experimental results may fail to resolve that.
    But that ESA have the mass correct, and that the major force at work is simply gravity, I do not doubt for a moment.

    • THOMAS says:

      @Harvey “There is no credible electromanetic force over this scale of distances that have an identical behaviour to gravity” + “But that ESA have the mass correct, and that the major force at work is simply gravity, I do not doubt for a moment.”

      I fully respect your personal beliefs and absence of doubts. For my part, I (among many others) believe that there is an electromagnetic component to what we call “gravity” which is literally incalculable in environments such as those of comets. There have been too many anomalies observed in the calculated trajectories of numerous space probes even in our back yard (including some of Rosetta’s own flybys on its way to Comet 67P) for your certainties to be so absolute.

      It is Rosetta which will finally settle the debate between the apparently conflicting observations of the clearly rocky composition of the comet’s nucleus on the one hand and the density calculation of 0.4g/cm3 on the other.

  • Phil Stooke says:

    “And what DO YOU accept as “observational evidence” if it’s not the images obtained?”

    Let’s see… the volatile measurements… the density… very solid observations. You only have your own highly creative interpretations of images to set against them. The images are fabulous but we have to be careful not to jump to conclusions which defy all the other data. Things are not always what they seem at first glance.

    I reiterate:

    I increasingly sense that die-hard believers in non-standard theories will become ever more impervious to the value of mere observational evidence as the mission progresses.

    • THOMAS says:

      Phil, there’s no point in arguing the toss on this. Considerably more scientific data will soon be released to settle the issue one way or the other.

      In the meantime, you’re perfectly free to carry on refusing to believe what your eyes are telling you.

  • emily says:

    THOMAS, Andrew R Brown,
    May I kindly remind you that posting the same message on multiple posts multiple times is considered as spam, and contravenes our commenting guidelines ( It seems that I also need to remind you to speak to each other on here with some respect, bearing in mind that not everyone has the opinion. You are both very active on this blog, so it would be a shame to have to prevent either of you from posting here.
    Sorry for not reacting to this sooner today, but obviously it is an extremely busy time for us all here!

    • THOMAS says:

      Emily, sorry to labour the point, (I appreciate that you have other things to attend to), but am I to understand that you are allowing Andrew R Brown’s spamlike allegation in his #comment-162476 to stand, while disallowing my legitimate response (#comment-170092)? May I point out that your admonishment (#comment-170481) would become meaningless in this event.

      (I am not asking you to publish this comment but simply to clear up this matter in an even-handed manner, particularly since the whole ridiculous episode is Andrew R Brown’s doing and I have also wasted precious time having to respond to his paranoid allegations. I assume I don’t need to translate this into French to convince you of my good faith…

      • emily says:

        Hi Thomas , I”m approving this post so that I can post a comment pending from Andrew, which rather than approve out of context on a different post, I copy below (Andrew, I hope posting it here is okay by you (thank you for your honesty), and Thomas, I hope that you can accept this response and that we can all get on with enjoying the events of the next few days. I will delete/trash the other comments relating to this conversation (apologies if I have missed some).

        Dear Emily and all at ESA Rosetta / Philae,

        I apologize unreservedly for my outbursts last night. I am a High Functioning Autistic with Depression / Anxiety Attacks and am on 120mg Duloxetine daily to help stabilize my moods.

        Sometimes if there is a bug or have just been plain busy (both lately) the effects of the medication can and do wane and my moods can go overboard for a brief period.

        I will be seeing my doctor shortly for a review and will tell him about this episode.

        I take back all comments unreservedly.

        I will be following Philae’s descent and landing tomorrow, been a long time coming and all is looking good.

        Andrew R Brown.

        • THOMAS says:

          Emily, many thanks for binning the exchange of comments between Andrew R Brown and myself which indeed had no place in the high-level discussions which are characteristic of this blog.

          I have always felt greatly honoured (and pleasantly surprised) to be allowed to express my anti-establishment interpretation of the Rosetta images and data, amongst other things, which you have been publishing for the past few weeks now. My sincerest thanks to you as moderator(s) and to the ESA team more widely for accepting the expression of such divergent opinions. My intention has only ever been to try to widen other posters’ and other more casual readers’ horizons concerning an alternative model (the EU model) which is to date ill-understood, since I fervently believe that that is the way for science to move forward. It is the evidence from Rosetta and from Philae (all good luck for tomorrow’s landing!) which will help to settle the debate one way or the other.

          I of course accept Andrew’s response unreservedly and would like to state here that I could obviously know nothing of his condition and would obviously not have responded to him in what might have appeared as an over-aggressive manner if I had done so.

          Sincerest apologies, Andrew, and all best wishes for the future. I shall be as enthralled a follower of tomorrow’s landing attempt as yourself and all the other visitors to this blog.

          Thanks again, Emily, for clearing up this matter so adroitly.

  • JR says:

    Just like “Doubting Thomas” (seeing as religion was mentioned in an elder post), didn’t believe what he was told, so Thomas above has not commented on what Harvey said in his post. Trouble starts when we don’t listen to others points of view especially eyewitnesses or in this case, experts and only believe that we are right. Just like the conspiracy theorists on the moon landings.Tthey spoil it for everyone else when we hear the truth from the eyewitnesses who were actually there.

    • THOMAS says:

      @ JR “Thomas above has not commented on what Harvey said in his post”

      I have.

      I leave you to assume responsibility for your “conspiracy theorists” fantasies. I certainly don’t share them.

      As for “eyewitnesses”, we are all direct eyewitnesses of 67P and what is happening on its surfaces, by proxy, via the fabulous images being sent back.

      Like doubting Thomas, I have seen, I am satisfied, I believe in what I see (and what we have seen of every other comet nucleus thus far imaged.

  • John Ross says:

    Re: Thomas’s reply to my post of 11/11 at 03:02 he confirmed that he HAD replied to Harvey’s post of 9/11 at 08:19 when although he had, it didn’t happen until after my post and at 21:14 so it appeared that he wasn’t going to reply as Harvey had made a very good and valid point.
    However, Thomas missed the point that I made on the conspiracy theorists. People as such spoil it for us who believe the experts who have been and seen (e.g. To the moon) and witnessed such. My point is that experts have told us that comets are balls of ice, which we would assume are white, but P67 appears black which Thomas believes must be rock. My question now is: what causes the tail on a comet as it passes ever closer to the sun on its inward journey if it’s not the melting of its icy mantle?

  • JR says:

    Thankfully Thomas appears to have gone into sleep mode like Philae.
    Maybe now we can look forward with exitement to the release of the data which will give conclusive evidence as to the make up of comet 67P (apologies or mis-naming it P67 in an earlier post).
    The news that it has been suggested that they allow Rosetta to land on 67P with its buddy is a good idea as eventually they can die “together” as they were in their lives, if a little further apart!!

  • JR says:

    Interestingly a BBC article on 19/11 on its website about the data fed back by Philae before it went into sleep mode, includes the quote from a science professor that “There is no way it is rock” from the overall density of 67P of 0.4g/cubic cm which we knew, it appears that rock can’t be ruled out but is unlikely. For Thomas’s sake therefore, observation is less accurate in the case of a comet than listening to the experts and accepting first hand accounts from the craft that was sent here to do its job. The black / dark appearance of 67P is caused by a layer of dust 10-20 cm deep. It would be interesting to hear Thomas’s take on this evidence thus far and whether he would change his original stand on the subject.

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