Communication Strategy of the Beagle 2 "Think Tank"
As part of the Media update on 27th December, Professor Alan Wells (Lander Operations Control Centre, University of Leicester) outlined details of the work being undertaken by the Beagle 2 team to assess the current situation. A specialist team, titled the "Analysis and Recovery Think Tank", has been established to concentrate on understanding the reasons for Beagle 2's apparent failure to make contact with Earth, and to address the steps that may be taken to resolve these problems.
During the media briefing Professor Wells took time to explain the precise nature of the earlier attempts to make contact with the spacecraft, and detailed the remaining opportunities as follows:
A series of 15 scheduled communication sequences were programmed into Beagle
2's software prior to its separation from Mars Express on Friday 19th December. Routine communication with Mars Express before the separation confirmed that these commands had been successfully uploaded to the lander.After touchdown the planned communication sessions should have automatically been triggered, by the onboard 'clock', to correspond with the known passing of the orbiting spacecraft Mars Odyssey (NASA), and later on in the mission, Mars Express (the ESA 'mother ship'). A number of the pre-programmed sessions were also scheduled to correspond with times when the landing site is in 'sight' of the Jodrell Bank Radio Telescope. Any signal picked up by Jodrell, or an alternative telescope, will only serve to confirm the well-being of Beagle
2 -- it does not offer an opportunity for two-way communication; this can only be achieved via Mars Odyssey or Mars Express.If the lander software is running as planned, and according to the initial timing dictated by the onboard clock, a number of the programmed communication sessions have already passed.
Sessions 1 and 3 (between 04:54 and 06:14 on Christmas Day morning and betwe en
17:33 and 18:53 on Boxing Day evening respectively) both occurred during the martian night, and were intended to open communication with Mars Odyssey. In the planned communication sessions with an orbiting spacecraft, Beagle switches into 'listening' mode for 80 minutes. During the pass over the landing site Mars Odyssey will send out a series of 'hails' which, if picked up by Beagle, will enable the lander's receiver to lock onto the signal from the orbiter and activates the lander's transmitter and communications can proceed (any reply from Beagle would be 'headed' up with the call sign composed by Blur).No response was received by Mars Odyssey to indicate that the 'hail' messages had reached Beagle 2 during either of the above sessions.
When a planned communication session is intended for reception by the Jodrell Bank radio telescope, Beagle 2 is configured to send a repeating unmodulated signal, transmitting for 10 seconds then remaining inactive for 50 seconds, for a duration of 80 minutes.
Sessions 2, 4 and 6 (between 22:20 and 23:40 on Christmas Day evening, between
23:00 and 24:20 on Boxing Day night and between 22:56 and 00:16 27th December respectively) coincided with opportunities to view the surface of Mars with the Jodrell Bank radio telescope. Unfortunately no signal was detected by the giant telescope.Session 5 (between 6:17 and 7:37 on the morning of 27th December) occurred during the martian day, and Beagle 2 should have again been in its 'listening' mode at a time when Mars Odyssey was passing over the landing site. Sessions occurring in the martian daytime differ from those occurring during the night as Beagle would automatically send any stored data when sunlight is available to charge the battery. Beagle is programmed to 'concentrate' on receiving data at night time to avoid draining the battery with power intensive data transmission.
However, again the telemetry returned by Mars Odyssey to Earth did not contain any evidence of communication between the orbiter and lander.
The remaining scheduled communications sessions are as follows:
Sessions coinciding with Mars Odyssey pass:
- Session 7 -- 28/12/03 (18:57 - 20:17 GMT)
- Session 8 -- 29/12/03 (07:41 - 09:01 GMT)
- Session 9 -- 30/12/03 (07:24 - 08:44 GMT)
- Session 10 -- 30/12/03 (20:20 - 21:40 GMT)
- Session 11 -- 31/12/03 (09:04 - 10:24 GMT)
Please note that any signal from Beagle 2 (either directly to the Jodrell Bank radio telescope or via an orbiting spacecraft) will take at least 9 minutes to reach earth, owing to the vast distance that it must travel.
One possible explanation that has been raised for the apparent silence is the potential for incompatibility between the systems on board Beagle and those used by Mars Odyssey. The Beagle team has been in constant contact with the Jet Propulsion Lab, in Pasadena, and fellow scientists there are presently checking through data and records in order to ascertain whether there may be any problems with the transmitters and receivers aboard Odyssey. It is important to note that neither of the communication routes attempted so far has ever been tested, therefore it is possible that the best opportunity for successful communication may arise when Mars Express achieves its final orbit and can take part in the search for Beagle.
A backup has been built into the communication schedule such that if 10 scheduled sessions pass unsuccessfully then Beagle 2 will switch to an emergency mode 'search mode 1'. Planned Jodrell contact sessions are included in the count because Beagle can have no way of knowing whether these 'one-way' sessions have been successful. When the lander switches to search mode 1 it will proceed to attempt a communication with the best daytime and best nighttime orbiter pass each day -- these times are calculated according to an onboard model of the orbits of both Mars Odyssey and Mars Express.
Session 10 is scheduled for the evening of 30th December, and if a regular contact has not been made by this time 'search mode 1' will be activated, increasing the opportunity for communication with a 'passing' orbiter or for detection of Beagle 2 by radio telescope from Earth.
If a further 10 communication sessions are unsuccessful, Beagle will then switch to 'search mode 2'. The second emergency mode involves the production of a signal throughout the martian day (power is still conserved during the night). With two 'search mode 1' sessions taking place each day, the adoption of search mode 2 would, in theory, begin on January 5th -- soon after the date when Mars Express is first available for communication.
A further explanation for the lack of contact between Beagle and the Earth is that the onboard clock may have been corrupted during the entry, descent, and landing stage of the mission. If this is indeed the case, the above scheduled communication sessions may not have corresponded accurately with the passage of Mars Odyssey over the landing site or with the viewing windows afforded to the Jodrell Bank telescope. It is possible that Beagle 2 is signalling correctly but not at a time when Mars Odyssey is passing or when Jodrell Bank can 'see' Mars. Consequently, when Beagle assumes 'search mode 1' and begins signaling more regularly it may be possible for Odyssey or Jodrell to pick up the 'additional' transmissions.
In addition, a further radio telescope at the University of Stanford, California will begin the hunt for a signal from Beagle 2 the evening of 27th December. The telescope at Stanford has a viewing window that is one hour longer than that afforded to Jodrell Bank -- therefore the opportunity for a signal to be picked up, if it is being transmitted at an unexpected time, will also be increased. The Stanford telescope has previously been used to monitor faint sources of radiation in deep space. Consequently it is thought that there may be some potential for it picking up other indicators of activity on Beagle besides the expected transmitter signal. The onboard processors will produce low levels of radiation that may be weakly 'visible' to the telescope -- this might be considered comparable to looking for signs of Beagle's 'heartbeat', rather than listening for its 'bark'! It was, however, noted that these systems on Beagle have been shielded to protect them from sources of external radiation hence any signal from this internal source may be extremely small. Radio telescope scientists have special ways of distinguishing small signals from other background 'noise'.
Members of the Beagle 2 team are also exploring the possibility of 'recruiting' other radio telescopes to hunt for the signal from Mars. A telescope on the other side of the Earth would allow the search to continue at different times. It is understood that staff at the Parkes telescope (Sydney, Australia) are investigating whether they have appropriate detection equipment to look for Beagle 2.
Whilst it may not be possible to establish two way communications with Beagle 2 via a radio telescope it will aid the team to pinpoint the lander's location, and provide a time reference point. If the onboard clock has been corrupted it is likely to affect the absolute timing of the communication windows rather than the relative timing.
In order to address the potential problems associated with an incorrect clock setting on Beagle 2, a 'blind command' was transmitted by Mars Odyssey during the pass over the landing site yesterday morning (27/12/03 - session 5). The hope is that Beagle may be able to receive such signals, but is not currently able to transmit. The effect of this command would be to reset the onboard clock with the aim of resynchronising the process and prompting an opportunity for successful communication.
'Blind commands' can also be used by the 'Lander Operations Control Centre' (LOCC) to control other processes onboard Beagle 2, without the requirement for two-way communication. Commands to control the motors operating the central hinge, or the hinges controlling the solar arrays may be sent via Mars Odyssey or Mars Express to affect some minor repositioning of the lander -- this approach may be used to correct any potential problems that might have occurred with the opening of the arrays, or if the lander is inappropriately positioned, for example, leaning at a restrictive angle against a rock.
Such a strategy is not without considerable risk because any command may impact other processes taking place on the lander. It is also very difficult to command a spacecraft without any information about its current status -- imagine trying to drive a radio-controlled car around a track without being able to see or hear the movement, or even know what the track looks like! The LOCC team will be able to make a risk assessment by testing the implication of any proposed activity on a working replica of the Beagle lander in their control centre at the University of Leicester.
Finally Professor Wells reassured the gathered media that the team were still in good spirits, and dedicated to the challenge ahead -- and promised that, "We'll keep going until every possibility has been exhausted".
*****28 December 2003 01:20 GMT
No signal received by the Stanford University telescope but equipment was not operating to its highest level of performance.