The Beagle had landed: Andy Pye speaks to Professor Steve Burnage, chief engineer for Beagle 2's Spin-Up Eject Mechanism (SUEM) about the testing processes which ultimately proved that it did, after all, perform its objective of getting the probe to Mars.
Plenty of speculation took place over the years as to the demise of the mission, from it missing the planet completely, burning up on entry, hitting poor weather or striking the ground far too hard, due to using the wrong atmospheric model.
However, we now know that it only missed the nominal target by two miles and that it had partially opened most of its solar array panels. Unfortunately, not activating the last panel in the clam shell resulted in the main antenna not being exposed and thus no communication could take place. In effect, it was one very dormant probe, sitting there for more than 10 years awaiting the command to start working.
And so, the 2015 Royal Aeronautical Society Team Silver Medal Award was given to the entire Beagle 2 Engineering Team, comprising more than 230 professional engineers across many companies, led from Astrium at Stevenage (now Airbus Defence and Space). Presenting the award, the Royal Aeronautical Society described the achievement of whole Beagle 2 team as "a triumph of engineering and ingenuity, which underpinned a successful descent and landing of the Beagle 2 on Mars... a significant success for the UK at the very first attempt."
In fact, this was the team's second award: earlier in 2015, the Beagle 2 project team, scientists and engineers, were awarded the Sir Arthur Clarke Award for project/team achievement by the British Interplanetary Society at the UK Space Conference.
A team at Lockheed Martin, Ampthill, provided a key piece of equipment which supported the Beagle 2 probe on the ESA Mars Express Orbiter during its launch and transfer to the red planet. Professor Steve Burnage, the chief engineer for the Spin-Up Eject Mechanism (SUEM), and past president of the Society of Environmental Engineers, was one of the design team invited to the event at the Royal Society.
"Meeting up with the rest of the UK team, experience a mixture of elation and closure that the mission was far more of a success than we had grown to live with, yet frustrating that for the failure of a couple of panels we would have had a successful mission," he says
"However, it was really satisfying to find out that the original calculations were spot on after all. It's a great honour to be part of the team that has won this award and to be recognised for our hard work after all this time.'
Following its seven month, 250 million mile journey to Mars, to certify the SUEM for space flight and subsequent ejection of the Beagle2 probe, it was subjected to a rigorous series of environmental trials to demonstrate adequate reliability and mission performance.
A series of low-temperature thermal tests were undertaken to check that distortion of the system did not impact the performance of the ejection mechanism, both in terms of resulting eject velocity and spin rates. The challenge was how to simulate Spin Up and Ejection under zero gravity. Initial tests were undertaken using a simple cable and counterweight system to counter the ejected mass of the probe. This was found to be problematic, due to losses incurred within the steel cable as it bent over two pulleys. In addition, the twist in the cable also affected the rotation rate of the ejected probe.
A solution was found using bungee rope and a cable tensioning device. By freely suspending the ejected probe mass and bungee suspension system (in effect the moving parts) at the same height as the SUEM ejection face, the cable reaction force was recorded.
The dummy probe was then positioned over and locked, installed and the SUEM locked and primed for ejection. The bungee suspension system was then tensioned to the same cable reaction force as when measured when freely suspended. When the SUEM functioned under test, it was effectively (over the first few centimetres) ejecting under zero gravitational influence.
This test was repeated 32 times to gauge the wear on the SUEM mechanisms as well as to derive the statistical variation in performance and reliability growth figures.
This was borne out when Beagle 2 was ejected six days out from Mars to allow Mars Express to make course corrections to enable it to manoeuvre into orbit. During these course corrections, it was calculated that the reaction forces imparted into Mars Express were within 2 per cent of nominal SUEM performance.
Beagle 2 separated from Mars Express at an eject velocity of 0.285m/s and a spin rate of 11.72rpm, while both were travelling at 20,000 kph.
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|Title Annotation:||Space travel|
|Date:||Feb 1, 2016|
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