Rosetta enroute to pre-delivery orbit

Rosetta conducted a manoeuvre today – a thruster burn that lasted 82 seconds – and it was completed as planned, Spacecraft Operations Manager Sylvain Lodiot has confirmed.

 

“The burn looks OK from telemetry, and the spacecraft is in good health,” wrote Sylvain in an email.

The burn got underway at 12:59 UTC (13:59 CET), ended at 13:01 UTC (14:01 CET) and, based on an initial analysis of post-burn telemetry, delivered a change in velocity – ‘delta-v’ – of 0.081 meters/sec. This pushed the spacecraft to leave the 10-km-altitude circular orbit (following the terminator line) – the so-called ‘Close Observation Phase’ (COP) orbit – where it’s been since 15 October.

The COP orbit enabled high-resolution images of the landing site in order to best prepare for Philae’s challenging touch-down.

Today’s manoeuvre is important as it means Rosetta has now started the transition from the COP to the pre-lander-delivery orbit.

Specifically, today’s burn has put Rosetta on a very elliptical trajectory rapidly moving the spacecraft away from the 10-km orbit. In three days, on 31 October, the mission control team will perform another manoeuvre to enter onto the pre-delivery orbit proper.

This is a slightly elliptical orbit at approximately 30 km distance from the comet centre (see the animation above).

After another orbital change taking place about two hours before separation, the spacecraft will finally deploy Philae from a distance of 22.5 km from the comet centre, at 08:35 UT on 12 November.

Comments

21 Comments

  • Rob Macpherson says:

    Very interesting to hear about these manoeuvres.

    As Rosetta gets closer to the sun, is there going to be a need to carry out any Passive Thermal Roll thruster firing?

    Many thanks,

    Rob

  • Hansart says:

    Thanks Daniel for your description, all of us we are so excited to see the final outcome of this manoeuvre and the successful deployment and landing of Philae!
    I just have a question related to this manoeuvre: why going that far from the comet before releasing the lander, and not at the current altitude of 10km or even closer, to increase the degree of precision for a safe landing? Is it due to the rotation of the comet and the need for the spacecraft to follow an escape path?

    • calin says:

      hello,

      Normally a lander would have to kill its vertical velocity after separation and drop directly towards the comet. The reason for these complicated maneuver is that the lander Philae has almost no thrusters capability, one small thruster to “push” itself down once landed and that’s about it, so it must be “dropped” onto the comet on a very precise landing trajectory in the hope that it will find a plane surface to land an anchor on.

      calin

  • Lorand Lukacs jr says:

    God luck with this exeptionally difficult task. Philae sideways on the orbiter released from about 20 km above the Comets surfac moving in opposite dirsctions. Will take seven hours beffrom release untill landing on the smaller lobes J Site. The lander has to stabilize itself hook on the surface and then take some pictures before it contacts the Rosetta mother orbiter. At least 30 minutes after the orbiter have received the information from Philae will telemetry reach the Control Center and confirm the landing.

    The expected procedures are as follows:
    >> During the separation and descent of Philae:
    • CIVA will make a ‘Farewell’ image of the orbiter;
    • ROLIS will take images during the descent;
    • COSAC and PTOLEMY will sample the ‘atmosphere’ of the comet as the lander approaches the surface;
    • ROMAP will measure the interaction between the solar wind and the cometary plasma;
    • SESAME/DIM and SESAME/PP will measure the dust and the plasma environment, respectively;
    • CONSERT, along with other experiments on the orbiter and the lander, will measure the rate of descent and, at the same time, will sense the uppermost surface layers of the comet nucleus.
    Immediately upon landing:
    • CIVA will make a panoramic image of the landing site; this will be used together with other information from the lander to determine where and how Philae has landed.
    • MUPUS will measure the deceleration of the harpoons as they are fired to anchor Philae to the surface;
    • SESAME/CASSE will measure the elastic properties of the surface.
    With Philae safely on the surface, another series of measurements will begin, marking the start of the so-called first science sequence (FSS). This phase will last for a maximum of 54 hours, and the main goal of this phase is to secure a set of the most important scientific measurements at the surface of the comet. The FSS is split into several blocks with distinct science goals.

    See information published by ESA on 13 sept. 2014.
    Regards.

  • Lorand Lukacs jr says:

    Please remove the last part of my comment marked by >>> as it repeats itself. it shoul have been >>> in front of Immidiately after landing! Sorry

  • Chip Bradley says:

    This is going to seem like a VERY dumb question, but can someone explain to me how it is that Rosetta is able to “fly” in a circular (or elliptical) path after these close encounter orbit burns when there must be SO little gravitational “pull” on the spacecraft from the comet head? Is there a need for many mid-course corrections due to [what think MUST be] only minute gravitational attraction? Thanks.

    • Jacob nielsen says:

      33@Chip Bradley, watch the video: thruster is burned when there is a ‘flash’ and a small circle on Rosettas path. Avoiding all the calculus, it is so that every orbit has a speed, distance and some eccentricity: orbiting a low mass object means low and/ or slow orbits (or high and super slow orbits). Whenever Rosetta must move from one trajectory to another, thrusters are engaged.

    • calin says:

      The comet mass was estimated to about 10 trillion kilograms, Rosetta’s mass is 3 tons including the lander, the comet radius is around 2,5km (not constant). Enter all this in an online gravity force calculator tool like this one http://astro.unl.edu/classaction/animations/renaissance/gravcalc.html and you will get a gravitational pull of around 0,32Newtons, which is around the force of Earth’s gravity on a mass of about 33g, very small indeed but noticeable. I hope the caculations are right, feel free to correct me!

    • frankuitaalst says:

      @ Chip : I think orbiting at such a close (10 km) distance gives perturbing forces to Rosetta , which result in slowly changing ( not circular ) orbits . So orbital corrections using their thrusters are necessary in order to keep the desired orbit . I also think people at Esa very carefully use their thrusters . If I remember correctly there are 24 of them . Due to the tiny gravitational field I guess they hardly use more than one thruster at the time when they perform a burn . I’m not sure how many , but it would interest me how many thrusters they use nowadays .

    • AndreH says:

      chip: I addition to what Jacob Nielsen says and again avoiding the calculus: For elliptical orbits you have the situation that at the closest point to the comet (or whatever body you orbit) the orbital speed is at is maximum. At the point which is farest out the speed for the given orbit is the minimum.
      This means if you have an extremely elliptical orbit, a very small change of the speed at the far out will make a big change in the orbit.
      So if you want to hit the “breaks” to kill the orbital speed for descent, that is the best point if you do not have infiinit resources of fuel and only small thrusters.
      If you bring the orbital speed down to zero at that point you would simply drop down to the surface. That is more or less the plan here.

  • Kamal Lodaya says:

    Chip: I think it has to be “re-captured” by the comet. This seems to happen at a distance of around 30 km.

    • frankuitaalst says:

      For those who are interested to experiment with a simulation of Rosetta’s behaviour and the Philae lander
      in this post there is a link where one can download a simulation .
      http://blogs.esa.int/rosetta/2014/10/08/go-for-10-km/
      In this simulation it was assumed that Philae separates at half the speed of Rosetta .

      • Daniel says:

        Hi Frank, We’re unaware of any such link…?

        • frankuitaalst says:

          Hi Daniel , the link doesn’t come from Esa , but is an attempt to simulate Rosetta’s behaviour in the comets complex gravity field …

  • Mahdi Hashempour says:

    I wonder if amino acids found there. Then their stereochemistry will talk to us.

  • Warden says:

    Thank you for sharing all this breathtaking Information with us. How is Philae going to stay “upright” during descent?

  • michel says:

    please make a blog about the mission in french, to much dictact of english

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