Preparing Rosetta to listen for lander

At the time of writing, the Rosetta orbiter has received no new signals from the Philae lander on the surface of Comet 67P/C-G since the last, very brief, signal receipt on the evening of 14 June.

This was expected, however, as the spacecraft was performing pre-planned science observations – involving either a spacecraft slew or off-pointing from the comet nucleus – throughout the two possible Philae-Rosetta daily communication slots.

On Monday 15 June, teams at ESA, DLR and CNES agreed to a new orbiter trajectory that will optimise the opportunities for lander-to-orbiter communication. This includes a change to nadir pointing (that is, pointing directly at the comet nucleus) during the daily communication slots, which will come into effect Wednesday morning, in line with the new trajectory change.

Rosetta’s science investigations will also be adjusted to adapt to the new trajectory.

Commands to adjust the trajectory were successfully uploaded Monday evening; further commands will be uplinked on Thursday evening. The spacecraft will perform two manoeuvres, one on Wednesday morning and the second on Saturday morning. The effect of the two ‘dog-leg’ burns will be to bring the orbiter to a distance of 180 km from the comet and to reproduce the orbiter-comet geometry of the first contact.

This orbit lowering had been planned previously with the objective of flying as low as safely possible, since no star tracker problems have been detected while flying in the terminator plane at 200 km altitude. But now it also has the advantage of improving communication possibilities with Philae.

This morning, 16 June, the spacecraft was at about 224 km and moving out to about 235 km from the comet on its pre-planned trajectory. When Philae’s signal was first received on 13 June the spacecraft-comet separation was 200 km; by 14 June this was 206 km and the signal was weaker.

It is only once the orbiter is on the new trajectory, flying closer to the comet with nadir pointing in the latitudes of the lander that the communication possibilities will be improved.

 

Comments

19 Comments

  • Jean-Pierre Urbain says:

    On a fait ça, nous les humains! Soif de connaître, de comprendre, d’expliquer. Magnifique exemple de ce que l’on peut réalisée par la coopération, cette fois à l’échelle européenne.

  • So Rosetta has “received no new signals from the Philae lander […] since the last, very brief, signal receipt on the evening of 14 June” – so the statement (seemingly attributed to S. Ulamec) in http://www.deutschlandfunk.de/kometenlander-philae-ende-des-dornroeschen-schlafs.676.de.html?dram:article_id=322698 that on the 15th Philae was heard from again, “sogar noch länger als am Wochenende, aber mit Unterbrechungen,” is incorrect?

  • Herbert says:

    Strange!
    The BBC mentions there was a second encounter of about 3 times 10 seconds receipt on Sunday.
    And new contact on Monday for about 4 minutes.
    Could you inform what is correct?

    • Margarita says:

      If you watch the question time at the end of press conference replay http://www.esa.int/spaceinvideos/Videos/2015/06/Replay_of_Rosetta_conference
      you will see that the BBC representative asked about this.
      It was confirmed that Philae had not made contact on the 15th (as Daniel has informed us above) and that this had not been expected as (I think I’m quoting correctly, but the full details are in the recording) Rosetta would not have been in the position to receive signals from the lander.

  • sergio says:

    Hello Daniel.

    Thanks a lot for this update.

    After the excitement of the first piece of news, we were all searching for more updated news. Of course I understand that all of you must be very busy and that the discussions must be heavy and the choices/decisions not easy to make.

    Please keep us uddated about those manouvre status.

    Hummm… by the way, don’t repeat it… but… EUROPE IS THE BEST, and you, guys, are on the TOP OF THE LIST !

    😀

  • Roberto Nesci says:

    Let us wait for the new orbit, good luck Rosetta !

  • Harvey says:

    200 to 206km is only 3% on distance, 6% on power, or 0.25dB in signal terms.
    That’s a very small difference; if communication was that marginal on the first contact one might have expected a very high bit error rate.
    The pointing etc is far more critical, depending on the antenna polar diagram, but is it rally *that* sensitive to distance?

    • Guili says:

      0.25dB for 6km sounds a lot to me. What do you know about the antenna installed on Philae to get those figures ?

      • Gerald says:

        That’s just by the inverse square rule, and the definition of dB:
        10 x log ((206 km / 200 km)²) = 0.25,
        with log of basis 10.

        • Harvey says:

          Exactly.
          We are well into the far field of the antenna, so the inverse square law applies.
          There is an implicit assumption that the 200 to 206km move is radially away from Philae; however it could deviate from that significantly without much likely change from the polar diagram, given the small size of Philae’s antenna.

  • bator says:

    Go rosseta go. We hope you can contact with Philae.

  • masanori says:

    Thank you very much Daniel & Blog team & all the people who have been trying to share these recent updates with public as soon as possible!! In such detailed fashion!! Instead of reporting everything one week later!

    I have an impression that the closer Rosetta gets to Philae the shorter time Rosetta can stay over Philae’s horizon for. Does the team think it will be still long enough? Or does the team even plans to use thrusters to stay long enough above Philae if needed??

    Anyway looking forward to what improvement happens after this attempt!! Hope it works, as I imagine Philae is waiting to start science!

  • Anupam Gupta says:

    Hi Philae,
    Buddy please wake up… please…waiting on pins and needles to hear from you….Good Luck……

  • in french too pleaseeeeeeeee

  • Keven Bennett says:

    Wow! Congratulations on some amazing engineering. It’s not often that an initial loss leads to even greater gain down the road.
    As an American who loves space exploration, I now have three great events to watch:
    New Horizons, 26 days from Pluto, Dawn, now settling into orbit around Ceres, and now Rosetta/Philae in dramatic fashion!
    i hope that the recovery of Philae becomes as routine as our two probes, with events playing out in three corners of the Solar System.
    Thanks for fantastic work!

  • Ramcomet says:

    Well said Keven! Awesome times! Come on Philae!!!

  • Robert Dancer says:

    Congratulations on upholding the philosophy of observational & exploratory science in an anti-intellectual public environment that glories in personal ignorance.

    I follow the Rosetta/ Philae/ 68p G-P saga with great interest!

    Good Luck.

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