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 between
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.
