…  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