What’s happening in Rosetta mission control today

Yesterday’s orbit correction manoeuvre (OCM) – dubbed CATP for ‘Close Approach Trajectory – pre-Insertion’ – went off without problems, delivering the desired 3.2 m/s of speed decrease.

We now have just one final burn of around 1 m/s that will slow Rosetta and kick it onto the first of the comet orbit arcs (see video below). This will take place on Wednesday, which will also be celebrated as the official ‘arrival day’ at ESOC with a formal programme and media briefing (you can follow via webcast).

The Rosetta Flight Control Team (FCT) are very busy, as today marks the first day in a new weekly work cycle that will see thruster burns taking place on Wed/Sun well into 2015.

Rosetta will, follow, at least for now, a three-legged triangular orbit that requires a small thruster burn at each apex. The legs are about 100 km long and it will take Rosetta between three and four days to complete each one.

Under the new cycle, for the Wednesday burn, Mondays will be the planning day (for Sunday burns, it will be Thursday). Planning day means an intense round of activity not only for the FCT, but also for the flight dynamics teams.

Late in the day, by 20:00CEST, flight dynamics will deliver all their products required for the coming cycle (based on their analysis of the resulting orbit and the preceding burns) to the FCT, who will merge this with other products (including instrument activities coming from the Rosetta Science Operations Centre at ESAC – see comment at end), make sure all activities are conflict free and generate the stack of commands that must be uploaded to carry it all out.

The FCT are also busy generating plans and data related to the ground stations and other systems used to control Rosetta. This involves a great deal of checking, cross-checking and time-line updating, as well as resolving any conflicts that are found.

To get an idea of how tight the schedule is, note that the set of commands on board Rosetta now expire at 12:00 CEST Tuesday, 5 August. In other words, if nothing else is done, Rosetta would run out of instructions tomorrow at lunch time!

So, the next set of commands, including the Wednesday burn commands, must be readied and then uploaded tonight overnight.

This next set will cover the timeframe 12:00 CEST Tuesday to 12:00 CEST Friday. The cycle then repeats for the Sunday burn.

And this very brief description relates only to the FCT activities; in parallel, the Rosetta Science Operations Centre at ESAC must also generate a complex set of instructions for the instruments, which also must be planned and uploaded on a very tight schedule.



  • Hannes says:

    Go, Go, Go!

  • Arthur says:

    Thank you, emily, Daniel and all the others letting us foillow this exciting journey through the space to Chury !

    May the sience be with you !


  • Pete Williams says:

    I have to say something different…keep that coffee pot boiling ESA. Your teams are going to be busy for the next few days. Congratulations, a superb job. All that way and now…finally pulling into the bus station.!

  • John Edmondson says:

    Awesome results so far – Jeremiah (Horrox) and Isaac (Newton) would be proud of you!

  • Simon says:

    Why is Rosetta flying a “three-legged triangular orbit” to get closer to 67P, as the burns at each apex require a lot of fuel?
    I’m curious to find out what the benefits of such an approach are…

    • Howard Haigh says:

      I suspect that you have to know pretty precisely both the mass and centre of gravity of any body that you hope to go into a circular orbit around and those values are not yet known with sufficient precision to make it possible. The initial orbits and the monitoring of Rosetta’s position with respect to 67P will probably allow later orbits to be more circular and maintained with lower expenditure of thruster fuel.

      • Yes, not knowing the exact center is probably a main reason for a triangular path.

        I suspect that the other main reason is that the comet doesn’t have enough gravity to force Rosetta into an orbit. So, for a circular or oval orbit you will need continuous burns in order to create the necessary speed vector. In turn this will exaust the fuels very quickly and shorten the available time. On the other hand, you can fly in a straight path exactly by shutting all burners off. So, a path composed from straight parts requires only limited burns for the turning points.

        I love inverse engineering!!

    • Pete Williams says:

      I suppose the triangular orbits are going to be used to suss out in the shortest possible time the best place to ‘drop’ the lander.
      The coming months are going to be vey, very busy and ‘stuff’ done now will count as time well spent as the comet approaches the sun. Is that odd, double shape going to cause any problems for a stable orbit and indeed in finding a safe place to land?

    • Marco says:

      Rosetta will be in front of the comet about the same distance from the sun, at a distance where comet C-P ‘s gravity is negligible. The triangle is to keep a safe distance as a fail safe rather than a “hover” which would have a collision trajectory in the absence of burns. The apex burns would be a fraction of a meter per second delta-v, not really wasteful

    • Andrea A. says:

      Well, well, you are all getting close to it.
      We fly the 3 legs because we can not set a spacecraft in orbit around an object we do not know yet. We are missing gravity potetnial, position of centre of mass, detaield shape model, and reference points (landmarks) to navigate the spacecraft (we have no other references once there).
      The three legs allow us to observe the object from different angles so get a complete view.
      We do feel the gravity and we are not hovering the comet, we are flying next to it to measure its gravity potential.
      Due to the low gravity the propellant used for these manoeuvres is not that much; during the whole rendezvous from May till today we have used several hunders of kg of propellant, these manoeuvres will use at most a few hundreds grams each. We are in a low gravity environment, it does not cost that much to manoeuvre. Of course our tanks are limited so we have to be careful in what we do.

  • ophiuco says:

    I would like to know this: when the Rosetta’s orbit becomes almost circular at a distance from the center of the comet of 30 Km, what will be the orbital velocity of Rosetta? From my own calculus I have stimated it will be 0.3 Km/h, more or less.

    • Let’ s assume 67P has an effective radius of 2 km and the density of 0.1 gm/cm^3 – then its mass is 3 x 10^12 kg. So, at 30 km, the orbital period would be ~25 days and the orbital velocity 86 m/sec (~ 0.3 km/hr). So, your number is reasonable, although I suspect that the mass will be higher than that estimated from outgassing in 2012, and thus the 30 km orbital velocity will be higher as well.

  • A question about the right … words: Here you talk about “a three-legged triangular orbit” that Rosetta will enter into August 6th – but elsewhere is was pointed out that an actual orbit (i.e. where the s/c is under control of the target body’s gravity field) is only achieved later in the mission at significantly lower altitude. So: do we “enter orbit” Wednesday – or are we rather “stopping the approach” and begin to”follow the comet” along its heliocentric orbit?

  • Mark says:

    Very exciting to follow this mission. Thanks for letting us ride along!

    I’m fascinated by the extremes in “terrain” on the surface — I’m sure there will be long and vigorous debates on where to set the lander down. 😉

    If I guess right, the large, smooth “plain” might be better from an engineering viewpoint (fewer landing hazards), but could be less interesting once you arrive. It could be that the smooth area with visible craters is the result of much less activity over the years, while the brighter, “rougher” areas have seen (and will probably see) much more recent activity. Of course, I might have it all backwards, too. 😉

    Best of luck over the coming months!

  • Iain Melville says:

    Hi Emz! I’m following this with bated breath over here in Sweden. Good luck to Rosetta and all who are sailing her. Looking forward to more stunning images and some great science. Cheers. Iain

  • Jeff says:

    Just way too cool. Lots of work over these 10+ years. Best of luck to you all. We’ll be watching!

  • Jeff says:

    Outstanding. Lots of work in these 10 plus years! Best of luck to you all. We’ll be watching!

  • Rob says:

    Good Luck! All of this incredible work will soon pay off!

  • Birgit Hofmann says:

    I see, that´s very cost-intensive and difficult, well :

    ” May the force be with you ” !!!
    Good luck for the mission-team !!!

  • Birgit Hofmann says:

    Oh, sorry, i mean : time-consuming…..

  • morganism says:

    Congrats teams !
    It is really encouraging to have the ESA and the teams releasing info right away, and blogging up a coma of explanations.
    Know you folks are busy, but thanks for the info !

    Tremendous achievement.

    Is really cool to have these orbits for the science too.
    We get to find out densities of the separate lobes from the telemetry early !

    Awe inspiring visuals, and cool to have the outgassing low on arrival to get the mapping work done, and the lenses clean.

    Am looking forward to the spectra, and the low orbit images too !

  • Luis says:

    Felicitaciones, y gracias por darnos datos tan importantes.

  • peter deblois says:

    There are no words.
    What has transpired will leave it’s mark forever.
    Thanks to the men and women who have dedicated their lives to the pursuit of knowledge which will hopefully benefit mankind not diminish it.
    We are all witness to this event the likes of which we may never fully appreciate.

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