Beagle 2: Lessons Learned
The Mars Express spacecraft, carrying the Beagle 2 lander, was launched on 2 June 2003, arriving in the vicinity of Mars in December. The separation of Beagle 2 from Mars Express occurred on 19 December. The satellite continued with its successful insertion into a Mars orbit on 25 December, the day on which Beagle 2 was due to land. The Beagle 2 probe never was heard from again, despite a terrestrial radio telescope and orbital searches. The Beagle 2 team has issued their final report (297 pages), which is excerpted here for lessons learned in executing such a complex mission.
As the Executive Summary introduces, Beagle 2′s loss to the astrobiology community is considerable: "Mars Express represented at its inception a unique opportunity for Europe to explore Mars. The Beagle 2 probe was conceived to search for evidence of past and present life on the surface of the planet." The Mars Express orbiter continues to send back stunning high-resolution images as it maps the red planet for the coming years of its service life.
Beagle 2 [the UK led small lander on ESA's Mars Express] was flown successfully from launch through to ejection from Mars Express by a combined academic and industrial team. …Beagle 2 failed to communicate after its entry, descent and landing of 25th December 2003. It is presumed to have failed during this critical mission phase.
The "lessons learned" apply to any potential reflight of a small lander like Beagle 2 and most if not all lander missions to Mars (and elsewhere in many cases), some however are very specific to a "Beagle 2" type design and relate to detailed design issues and lessons from testing etc. and some will strike the reader as very obvious (some perhaps only in hindsight).
Interview with Colin Pillinger, Beagle 2 Chief Scientist, European Space Agency
Astrobiology Magazine (AM): It has been reported that when Beagle’s airbag system was tested once before launch in Ohio, that it failed the certification but flew anyway without another test. Could you clear up this as true or false?
Colin Pillinger (CP): Not true. it was tested extensively at JSC [NASA Johnson Space Center], Houston.
AM: When considering Beagle 3, what would you change about the Beagle 2 design?
CP: In a reflight landing has to be a priority.
AM: It has been reported that a transponder was hoped for prior to flight, that it would have greatly helped the landing search, but couldn’t be put on Beagle 2 in time. Could you clear up the importance of this kind of tracking beacon if this reporting was true?
CP: We looked at this, but we had no satellites in position around Mars to monitor Beagle 2 during its descent.
This long list does not imply however that the design for Beagle 2 was inadequate but rather highlights the routes and ways to improve and make a small lander most robust and to ease the load on any future lander teams in terms of designers, integration and test teams and operations staff. Beagle 2 was severely constrained by mass, volume and schedule and given adequate margins, time and resources many of these lessons would have been implemented on Beagle 2. We firmly believe that small Mars landers in the 60-130 kg class are possible given innovative design and engineering.
Beagle 2 was required to fit within a tightly constrained mass and volume limit. Consequently only very limited margins within the project were possible, forcing Beagle 2 to adopt innovative solutions to try and ensure a robust as possible probe design.
Beagle 2 was initially capped to a mass budget of 60kg ejected mass with a residual mass of 3kg remaining on Mars Express; when a formal request was made (August 2002) to increase this to 69 kg + 5kg no decision was taken by the project. The Beagle 2 design team were always continually battling throughout the programme to control mass, not knowing whether it would be accepted for launch. The probe mass was eventually only accepted after delivery when it weighed 68.9 kg + 4.9 kg (March 2003). Under the circumstances any other mass requests were impossible. It is worth noting that the on-surface lander mass was very much as originally conceived, nearly all mass growth occurred in the EDLS, primarily due to the airbags/gasbags.
Given development, schedule and funding problems some key tests originally planned by the Beagle 2 team e.g. lander drop test, and pilot chute ejection and aeroshell release pyrotechnic-shock tests had to be deleted. Priority was given to mission critical key developments, (main parachute, airbags/gasbags, electronics, software), and to the completion of the assembly and test programme. Shock tests were carried out on Beagle 2 components however this was part of the formal mechanical qualification (a functional test before and after) and not under operational conditions. The Beagle 2 team fully agree that more testing would have been valuable and would be keen to carry out such a future test programme with appropriate hardware to eliminate uncertainties in developing future lander systems.
|Simulation of Beagle 2 on the martian surface.|
Credit: All Rights Reserved Beagle 2
The extremely high cost of a realistic test (and ultimately schedule limitations) was also a deciding factor. Instead the main parachute was tested at low altitudes using coated fabric to simulate the effects of low pressures on Mars and via extensive mechanical load tests. The pilot chute has Huygens heritage. Some aspects of the Huygens parachute system were tested at high altitude. US suppliers for critical components (in particular for the entry, descent and landing system) were selected by Beagle 2 to provide maximum use of existing world-wide expertise. US International Traffic in Arms Regulations (ITAR) and Intellectual Property Rights (IPR) issues however prevented complete oversight of the probe design by the whole Beagle 2 team, particularly on issues relating to the EDLS, the airbags/gasbags, and their gassing system, the pilot parachute and its deployment device.
The Beagle 2 Airbags/Gasbags ILC Dover, who provided the airbags/gasbags for Beagle 2, produced the airbags for Pathfinder and the MER Missions; all these missions using airbags/gasbags have been successful. The same manufacturing and materials technologies were employed for Beagle 2. The successful US technology was however developed for larger landers. Whilst the construction principles were retained for Beagle 2, the actual design is functionally unique and of mainly of UK origin.
After airbag/gasbag test failures, caused by design specification and development problems, the operational regime for the airbags/gasbags was revised by Astrium. A delay in inflation was introduced to overcome concerns on leak rate and material chemical reaction with the inflation gas. A reduced impact velocity was also defined, allowing a lower inflation pressure to avoid overpressurisation failure. Design detail remained unaffected and the need to introduce new technology or yet more mass growth was avoided. Flight of the original design would have likely led to mission failure. These changes brought the airbag/gasbag operational scenario closer to that of Pathfinder and MER. Further efforts to make the airbags/gasbags more robust required a large incremental change in mass and volume to accommodate an additional protection layer in the airbag/gasbag structure. This was not feasible within the mission constraints.
|Around the table with bits of the mass spectrometer and some of the mass spectrometer team.|
Credit: All Rights Reserved Beagle 2
Beagle 2 acknowledges that the airbag/gasbag test programme was limited by access to and the cost of US test facilities (none were available in Europe). A series of ten tests were carried out with the airbag/gasbag design. As tests were performed in each case the data from earlier tests were fed back into the programme; the final four tests, reflecting the revised operational scenario, were deemed successful. ESA were provided with all the results but declined an opportunity to view film of the tests. More comprehensive testing could have been achieved with an earlier start to the programme.
The Entry, Descent and Landing (EDL) lessons learned are perhaps the most important, and this is the most risky part of the mission, and the time during the Beagle-2 mission that it probably failed.
Related Web Pages
Five Year Retrospective: Mars Pathfinder
Open University: Beagle
Space Research Centre: Leicester
Mars Express PPARC
ESA’s Beagle: Sniffing Out Life on Mars
Call from the Red Phone
Isidis, Martian Impact Basin