Rosetta

New contact opportunities after Mid November 2015

6.11.2015 After Rosetta's return from an excursion into the bowshock region of the comet to a distance up to 1500 km the possibilities for the establishment of radio links with Philae increase again. With increasing solar distance the comet's surface temperatures go down again minimizing the possible effect of multi-path interference due to reflections on surrounding walls with dielectric properties sufficient to reflect the 2 GHz radio waves. Besides technical reasons for the link problems these interferences earlier seen on the Cassini/Huygens mission might have decreased the probability for a safe radio connection during the past months.

31.7.2015 An article in the Science magazine by Biele et.al. summarizes details about the descent and landing of Philae based on a number of instrument measurements and their interpretations: Jens Biele et.al.,The landing(s) of Philae and inferences about comet surface mechanical properties, Science 31 July 2015, Vol.349 no 6247, DOI: 10.1126/science.aaa9816

 

21.7.2015 No additional data packets from Philae were received after July 9, but the analysis of the last data indicate that Philae is still operating and interprets received commands. Currently recognized problems based on analysis of these data: The second transmitter does not work. As the Philae control system changes automatically from transmitter 1 to 2 if it does not receive a direct response and stays there for 30 minutes before changing back, most radio link opportunities so far were lost.

Analysis of the solar panel charge currents show that the illumination changed more than could be explained from the changed solar incident angle between June and now. This could indicate a movement of the body, but other explanations like a different shadow direction from an obstacle close to the Lander are possible.

Current actions: Commands are being sent through a Philae emergency configuration to disable the transmitter 2 and to start measurement sequences already on board since last November including Ptolomey, COSAC, ROMAP and SESAME as well as taking  images with the CIVA panorama camera. If successful the data should be received by Saturday.

 

10.7.2015 A radio link between Philae and Rosetta was established again on 9 July at 20:45 Finnish Summertime for 22 minutes. This was the first contact since June 24. During this link time the CONSERT instrument was switched on and a few instrument packets received to establish an independent radio link path between Lander and orbiter. Though there were several short link breaks the uninterrupted link time off 12 minutes was the longest so far observed since first contact was established in June.

23.6.2015 The ESA SPC decided to extend the operations support period for the Rosetta mission from earlier end of 2015 until 30 September 2016

 

19.6.2015 16:20-16:39 a 3rd radio link was established between Philae and Rosetta, resulting in a transfer of 180 packets, originally recorded during the active time June 13-14. Theoretical radiolink possibilities are increasing now to daily more than twice 2 hours. Philae's location is now known with a precision of 21 m x 34 m, according to a new CONSERT paper Kofman et al., based on the original triangulation results, now improved using the analysis of the comet tomography measurements with radio signals going through the comet.

17.6.2015 During a second short radio contact early Monday morning 00:22 4 direct packets were received showing a snapshot of the current Lander situation: The central computer is now operating for about 2 hours 35 minutes per comet day. A recorded start-counter indicates that since the beginning of the year it had started 97 times, most likely after the beginning of May, but also earlier starts cannot be excluded. The temperature has increased to -5 C, the temperature of the secondary battery is that close to 0 C that the system seems to have autonomously started with charging the battery. With only 1 measurement point the charging characteristic cannot be established yet, so no information about the health and availability of the rechargeable battery is possible at this moment.

The antennas at the top of the Lander reached already a temperature of +35 C with also the absorbers producing some heat for the interior of the electronics. Rosetta did make some flight path modifications on the 17. to improve the radio link possibilities with Philae. It is currently at an altitude of 180 Km opposed to 200 km on Saturday. A second maneuver is planned to optimize the radio link possibility. It is assumed that science operations will not be possible for at least another week to get all recorded data to ground, analysed and new command sequences updated.

 

 

 

15.6.2015 First analysis of the about 300 received data packets indicate that they came from the Mass Memory and were probably related to recordings from the beginning of May. At that time 4 out of the 6 solar panels wereproducing electrical energy including the one on top of Philae, generating about 24 W for a duration of currently more than an hour per comet rotation. The system information showed that more than 8000 data packets are still waiting in the second FMI-built mass memory to be transmitted to ground during the next radio contact possibilities. While the timing information is uncertain due to the many restarts of the system without clock synchronization opportunity this indicates that Philae might have been operational for the past month without a possibility of sending the data out. Tonight the command sequences for the first planned science operations were uplinked to Rosetta waiting for transmission to Philae during the next days. The very first measurement will be performed with the PP instrument, a permittivity probe for measuring water ice contents of the comet surface material, built by and under responsibility of FMI.

13.6.2015 23:28 Shortly before midnight Philae made for the first time since November 14 radio contact with the orbiter. For 85 seconds Philae's command system was sending housekeeping data indicating that the electronics temperature was -35 C and the maximum available power from the solar panel 24 W.

After analysis of the orientation-related parameters it is planned to start science operations as soon as possible. The details were defined over the past month.

28.5.2015 Due to increased dust activity of the comet and resulting disturbances of Rosetta's star tracker system, the distance to the comet was again increased to now between 150 km and 300 km compared to earlier planned 120 to 180 km. As a consequence of the trajectory change the next theoretical contact opportunity with Philae will be on June 9 for a few hours. Nevertheless the already commanded transponder activation for May 30 remains active. A longer theoretical contact window will open only around Mid June.

 

 

20.5.2015 30.3.2015 15:00 During its 15 km distance close fly-by on Saturday afternoon around 17:00 Finnish time Rosetta experienced severe star tracker issues most likely by misinterpretation of dust particles as unmapped stars. After a series of autonomous recovery and reconfiguration attempts the spacecraft placed itself into safe mode. During Sunday afternoon and Monday the control team at ESOC in Darmstadt got the system step by step back under control. Once the status analysis is completed and possibly needed corrective actions are in place the science activities will be resumed as planned.

Between 12. and 20. March Starting 12 March 2015 Rosetta is trying to make radio contact with the Lander Philae on the comet surface. 11 time windows were calculated where simultaneously the Lander location would be visible for the radio antenna and the Philae solar panel illuminated by the Sun to provide sufficient operational power. The first two contact attempts in the early morning hours and late afternoon of 12 March were not successful.

The attempts will continue until 20 March 2015, then repeated later in April.

So far the autonomous control system of Philae mainly tried to use any available energy from the solar panels for heating the electronics compartment to prevent damage to the components. During any 12.4 hours comet rotation solar energy was available for about 1.5 hours. As the exact location and orientation of Philae is not known, this is only a rough estimate. Only after the internal temperature is above -45 C the computer starts operating and diverts some of the energy to warm the battery compartment.  Once this insulated volume reaches 0 C the battery charging can start. Currently the available energy has about doubled compared to November and is expected to increase by end of July up to 6 fold with the approach to the Sun.

 

Older Rosetta news and more details can be found here.

MP4-animation about the Philae landing and its originally planned operation on the comet (64 MB)

The animation was generated by ESA.