Comet landing – the most critical moments

...  that you should watch for!

After reading our earlier landing timeline post with the detailed step-by-step activities that the Rosetta orbiter and the Philae lander will conduct on 12 November, we thought it would be helpful to extract a few of the most critical items that you’ll want to watch for.

Remember, unless otherwise noted: many times are approximate and are subject to change, given the dynamic real-time nature of the lander delivery.

Times below are in UTC/CET, citing ground event time. That is to say, the time that an event in space can be known or confirmed on ground. The actual event in space will have happened 28 min:20 secs earlier, as this is the one-way signal time on 12 November (and we must wait at least this amount of time to know about it or confirm it here on Earth).

Rosetta's first signal after exiting hibernation was received by both NASA’s Goldstone and Canberra ground stations at 18:18 GMT/ 19:18 CET on 20 January 2014, during the first window of opportunity the spacecraft had to communicate with Earth. It was immediately confirmed in ESA’s space operations centre in Darmstadt and the successful wake-up announced via the @ESA_Rosetta twitter account, which tweeted: “Hello, World!”

Philae is set for separation from Rosetta at 09:03 UTC / 10:03 CET on 12 November. The first signal from Philae during descent is expected around 11:03 UTC / 12:03 CET Credit: ESA/J. Mai


 

1. FIRST GO/NOGO 19:30 UTC/20:30 CET 11 Nov

Rosetta is on track: Following a full orbit determination before separation, the Flight Dynamics Team at ESOC confirm that Rosetta & Philae are on the correct orbit and that Rosetta can achieve the delivery trajectory, i.e. it can be at the correct point in space at the correct time so as to deliver the lander onto the surface as planned.

Why critical?

This is the last activity required to plan and command the delivery manoeuvre (i.e. a thruster burn) planned for the morning of 12 November, which will shift Rosetta and Philae onto the correct lander delivery trajectory.

How will we learn about it?

This will be covered live by ESATV and will be shown in the webcast. It will also be reported via twitter and the blog.


 

2. SECOND GO/NOGO 00:00 UTC/01:00 CET 12 Nov

Telecommands to control separation and delivery are complete: This GO/NOGO happens in two steps. (A) By this time, the Flight Dynamics Team at ESOC must have prepared the final instructions to be uploaded to Rosetta to command the delivery operations. (B) The Flight Control Team at ESOC will also check and verify the overall health of the spacecraft, and ensure it’s ready to perform.

Why critical?

By this time, the Flight Dynamics Team must have processed the results of the orbit determination and generated a set of telecommands that will control the delivery operations. These must be made available to the Flight Control Team for merging with the rest of the Rosetta and Philae commands and be uploaded. If for any reason they are not available, lander delivery cannot continue. At the same time, Rosetta has to be ready to proceed with the delicate and critical operations coming up.

How will we learn about it?

This will be covered live by ESATV and will be shown in the webcast. It will also be reported via twitter and the blog.


 

3. THIRD GO/NOGO 01:35 UTC/02:35 CET

Confirm status & health of Philae: The Philae Control Team at the Lander Control Centre (DLR/Cologne) will do a final check and verification of the lander’s health. Note that, when in contact, both the Rosetta and Philae control teams will be monitoring their respective spacecraft status constantly throughout the day.

Why critical?

This is the final verification that the Philae lander is ready for one of the most spectacular missions in spaceflight history.

How will we learn about it?

This will be covered live by ESATV and will be shown in the webcast. It will also be reported via twitter and the blog.


 

4. FINAL DELIVERY MANOEUVRE (THRUSTER BURN) 06:03-07:03 UTC / 07:03-08:03 CET

Rosetta performs the final lander pre-delivery manoeuvre: This is expected to last about 6 minutes and is planned to place the pair onto the correct delivery trajectory. This new orbit will take Rosetta and Philae to a point about 22.5 km from the comet’s centre for separation. Since the separation point is fixed in space and time, the exact time, size and direction of this manoeuvre will only be resolved with the last orbit determination (GO/NOGO No. 1) so as to be able to take into account the exact position where Rosetta was in its orbit.

Why critical?

The burn must be done at the correct time and give the right amount of ‘push’ (change in speed and direction) to Rosetta. If the thrusters over or under perform, or if there is a malfunction on the spacecraft that interferes with the burn, Rosetta may not release Philae at the right point in space, and thus it might not land on the comet in the desired location.

How will we learn about it?

This will be covered live by ESATV and will be shown in the webcast. It will also be reported via twitter and the blog.


 

5. FOURTH GO/NOGO 06:35-07:35 UTC/07:35-08:35 CET

ESOC will make final GO/NOGO decision on lander separation. There is no way for Philae to return to Rosetta, so separation is a one-time event.

Why critical?

If the pre-delivery manoeuvre is not within certain accuracy limits, then Philae would not land in the desired area on the comet. This is also the final verification that everything – the two spacecraft, the orbit, the ground stations, the ground systems and the teams – are ready for landing.

How will we learn about it?

This will be covered live by ESATV and will be shown in the webcast. It will also be reported via twitter and the blog.


 

6. SEPARATION CONFIRMATION RECEIVED ON GROUND 09:03 UTC/10:03 CET

Finding out if separation happened as planned: After separation occurs in space at 08:35 UTC, it will take the radio signals from the transmitter on Rosetta 28 minutes and 20 seconds to reach Earth and be transferred to the Rosetta Mission Control Centre at ESOC. Therefore, we must wait until about 09:03 UTC / 10:03 CET for confirmation the separation has happened correctly. If all goes well, there is a 90-second window for receipt of this signal.

Why critical?

Any incorrect performance during separation could affect the lander’s journey to the comet surface. Any problem with Rosetta during separation might affect Philae’s capability to reach the comet or hamper the possibility of following it during its descent and touch-down (Rosetta must serve as a communication relay platform connecting Philae with Earth).

How will we learn about it?

This will be covered live by ESATV and will be shown in the webcast. It will also be reported via twitter and the blog.


 

7. ACQUISITION OF FIRST SIGNAL (AOS) 10:53 UTC / 11:53 CET

First receipt of signals from Philae via Rosetta during its descent: This AOS means that Rosetta and Philae have successfully established a communication link during the descent, and Rosetta can now relay data from Philae to Earth. Philae will start transmitting telemetry – health & status information – as well as science data obtained so far.

Why critical?

Philae cannot send its data to Earth directly, and must establish a link with Rosetta.

How will we learn about it?

Via ESA’s blog and social media channels.


 

8. TOUCHDOWN AND SAFE LANDING 16:02 UTC / 17:02 CET

Receipt of touchdown confirmation: This signal means that Philae has landed on the comet; anchoring operations would then start (harpoon firing, etc.).

Receipt of signals from Philae after touchdown: This signal means that Philae has successfully survived landing on comet 67P/C-G and is transmitting signals from the surface via Rosetta to Earth.

Note: there is a 40-minute window for receipt of these.

Why critical?

This will indicate that Philae has successfully landed.

How will we learn about it?

This will be covered live by ESATV and will be shown in the webcast. It will also be reported via twitter and the blog.


 

Editor’s Note:

Access the webcast via any of
http://www.esa.int
http://new.livestream.com/ESA/cometlanding

Real-time updates will be provided via Twitter and here in the Rosetta blog. Follow: @ESA_Rosetta, @Philae2014, @esaoperations and @esascience

Comments

9 Comments

  • Rob says:

    This article, coupled with the "Rosetta lined up..." video from 3rd November really gives us a good idea of the sequence of events leading up to Philae landing on 67P.; thanks for all your efforts.

    Audacious, challenging, epoch-making: The Rosetta Mission. One for the history books.

  • sergio says:

    Just amazing.
    Just amazing.
    Just spectacular.
    This mission is just a dream that came true.
    Welldone we all count on you guys : make it land safely.
    Serge

  • Cometstalker says:

    So everyone is focused on landing safely. Of course thats the first goal but soon comes the day when it has fulfilled its task. Once this is done is it possible to restart the gyro stabilization, release the harpoons and screws and then make a small jump with its foot to a safe hight, hoping to drift randomly a few hundred meters and settle down again the best it can on a new place doing so over and over again to capture whatever it gets? A 1m altitude jump leaves it floating for several minutes The worries of overheating is really no concern, please present some calculations of how this can be an issue between earth and mars with a 12 hour rotation of the comet. Im not sure how much radiation it will receive but my guess is less then 500 W/m2 on one side and facing fridge temerature on the shaded side also converting about 20% of its incoming light to electricity, additionally it can twist its head to some extent.

    • Cometstalker says:

      It seams to be a 870 W/m2 radiation minus what gets absorbed by the coma, say 10% leaving about 800W/m2 and converting 20% of this into electricity. On earth just outside the atmosphere the solar radiation constant is about 1300W/m2 and our orbiting satellites can handle this very well. If the comet gets hot it is supposed to release a lot of vapors cooling it down, right? Are you expecting that the comet surface reaches a temperature over +120deg.C?

      • Lorand Lukacs jr says:

        The temperature consern is not about the comet surface but the build up of the temperature on the Philae itself. The lander solar panels temperature shoud not exceed a certain value. Therefore the landing site is selected so the lander is partly in shadow and partly in sunshine. But ceep in mind that The comet will reach its closest point to the Sun (perihelion) in August 2015, at 186 million kilometers and will never be closer. I.e. it stays further away than the Earths orbit which is 150 million kilometer. The surface temperature of the comet varies between -40 to -90 degree on the sunny side and will rise, but never in the (+) region, excempt maybe on the rocks. The frozen ammoniac, carbondioxyde ice and other compounds will sublimate and not melt.
        To move or jump with the lander after its mission is completed may be possible, but I think it was never planned. But similar thoughts are calculated on a low gravity body, i.e. for an astronaut to jump onto the comet 67P in sted for the lander.
        Ref. article: 20140804_Could you jump onto a comet?
        http://blogs.esa.int/rosetta/2014/08/04/could-you-jump-onto-a-comet/

  • If they choose no-go at any of these junctures would they get another chance to insert into landing trajectory ? What determines the different window times for receiving the various confirmation signals ? If window passes without confirmation what then?

    • Marco says:

      My understanding is that these junctures have been simulated and rehearsed, but that any no-go would result in partial mission failure. At that point, it is a matter of back up plans specifically designed for whatever eventuality caused the no-go call to be made. Hopefully, every plausible problem has been simulated and rehearsed.

  • Lorand Lukacs jr says:

    The illustrating following this article should be:
    http://blogs.esa.int/rosetta/files/2014/10/rosetta_delivery_orbits.png
    and referred to video showing the delivery trajectory of Philae by Rosetta:
    http://www.youtube.com/watch?feature=player_embedded&v=4a3eY5siRRk
    ENJOY!

  • carl axness says:

    Good luck and hope all goes well. Cant wait to see some pictures! Hope to watch with my son.

Comments are closed.