Login 
Borrowing techniques from the nuclear and oil and gas industries, Mike Guest addresses sample integrity at its highest level.
Introduction
You’ve collected your environmental samples in the field and taken every care to avoid cross contamination, only to fall at the final hurdle – the laboratory.
To ensure sample integrity, it is vital to reduce foreign contamination in the testing environment as it could taint the samples. Conversely, for certain samples, it is of equal importance that they can be contained in such a way so as to avoid contamination of the testing or wider environment. Examples include samples taken from near nuclear facilities that may have absorbed radiation, or, as outlined in this article, samples from Mars.
Whether you are dealing with the land remediation of London’s Olympic Park site, analysing wastewater treatment effluents (as in AWE International September 2012 and January 2013 respectively), or processing Lunar and Martian samples, the correct procedures and standards must be followed for the handling of all samples.
Contrary to what might be expected, the space industry is no stranger to handling and studying environmental samples and maintaining their integrity in the process. While it’s true that most of the engineering processes used focus on launching and operating vehicles in space that rarely, if ever, come back, some of the most challenging and high profile space missions have involved attempting to bring samples back from other planetary bodies to study here on Earth. Indeed, probably the most high profile mission in history, the Apollo 11 moon landing, had a strong focus on returning lunar samples for study on Earth. Between them, the Apollo landings returned more than 300 kg of samples that are still curated at NASA, Houston.
These samples, and any others that have been or are planned to be returned, are of extremely high scientific value. They can also be considered to have extremely high financial value as well, given the sums of money necessary to obtain them.
All efforts must therefore be made to maintain them in as pristine a condition as possible and to prevent degradation from terrestrial contamination. This must happen continuously, from the moment they are collected, through the return to Earth, and during their processing, handling and curation.
Ambitious missions are currently in the planning stages to return samples from places in the solar system other than the Moon such as from Mars and asteroids, to help us learn about both the history of the Solar System and the characteristics of other bodies that may lead to habitation and resource exploitation.
As with any other samples collected from the environment and returned to laboratories for testing, extraterrestrial samples require high integrity transport, storage and environmental control. The space industry is increasingly turning to other fields that have experience in sample handling and protection, such as the pharmaceutical, nuclear and oil and gas industries, to share knowledge and experience.
Organisations from the above industries have been working with the European Space Agency (ESA) to research and specify the technology necessary to return, handle and protect samples from the Moon, Mars and asteroids, and have worked in close cooperation with companies and institutions not traditionally associated with the space industry.
Designing a facility for Martian samples
One of the primary reasons for returning a sample from the surface of Mars is to investigate it for organic and possibly biological content. It is therefore unknown whether or not these samples might present a hazard to terrestrial biology. As such they must be considered hazardous until proven otherwise.
After the engineering challenge of returning a sample to Earth contained in specially designed hardware, the samples must be placed in a secure facility to have their safety assessed before they can be released to the international scientific community. This facility needs to marry the features of a high containment facility, e.g. a biosafety level 4 facility used for handling the most dangerous pathogens1, with an ultraclean research facility operating at low levels of biological, organic and particulate contamination, such as those used in the pharmaceutical and semi-conductor industries.
These requirements are derived from international law, codified in the Outer Space Treaty of 19572. Space missions must be ratified by the Committee on Space Research (COSPAR) before being allowed to launch. This effort to protect biological cross contamination between planets and preserve the value of our scientific investigation is referred to as planetary protection (PP)3.
Beyond the physical containment barriers such as walls, containment laboratories use a negative pressure environment to ensure the substance under study remains within the designated laboratory. On the other hand, clean rooms use a positive pressure environment to prevent the ingress of external contaminants. Reconciling these two philosophies is one of the main challenges faced when designing a facility specifically for the handling and testing of potentially hazardous environmental samples.
Several studies have been carried out by space agencies4 to investigate the design and technologies required for a facility to handle samples from Mars, including a recent European Space Agency funded study.
Maintaining sample integrity
The investigations to be performed on returned Martian samples will cover almost every aspect of biological, mineralogical and environmental science currently performed on Earth, all executed on the same sample set. The types of contamination to be excluded are therefore wide ranging, as seen in Figure 1.
As well as containment, the need for extreme contamination control drives processes that keep people away from the samples themselves as much as possible, especially during operations on the untouched samples when they are first accessed and analysed. To do this requires operations to be carried out in isolators, such as those used in the nuclear industry.
A distinction is made between isolators and glove boxes, such as those often used in microbiology. Isolators maintain a pressure differential via a low airflow or static air state, rather than the high airflow more common in environments with a maintained pressure differential. This low airflow characteristic also helps to prevent dusty samples from being lost to filtration systems.
Handling the samples
With humans removed from the process, new methods of handling the samples are needed. In traditional containment laboratories, or in high cleanliness environments, handling is often performed via glove ports in isolators, or in the case of laboratories handling nuclear material, with mechanical, through-the-wall manipulators.
In a Mars sample receiving facility, even without the requirement to keep human contact as removed as possible, the use of specially designed isolators may preclude the penetrations in the physical containment barrier necessary for normal handling methods.
Samples must therefore be handled using remote manipulation equipment, such as robotic systems controlled from outside the containment area, via an electrical or optical feed-through. The only interaction with the sample containment will be during maintenance. The systems themselves must also be clean to operate and must avoid shedding contaminants onto the samples during processing. This is especially important given the tight contamination requirements seen in Figure 1.
Sample sizes to the order of tens of grams down to micro-gram dust particles will need to be handled, and the systems will also need to be able to pass samples to instrumentation and take sub-samples of areas of interest for further analysis. As a result, dedicated handling systems are likely to be required depending on the task.
Sample environment control
As well as controlling terrestrial contamination, the environment in which the samples are kept must be carefully controlled in order to prevent damage that may compromise the sample for future scientific research. While it may seem logical that Martian samples should be kept in similar conditions to those on Mars, six mbar of pressure and an average temperature of -50° C, the preservation of these conditions cannot be assured throughout the six month long return from Mars. Re-inserting the samples into such an environment could have detrimental effects.
As seen in Table 1, a preliminary environment specification was reached. It must be stressed, however, that these parameters should not be taken as definitive and final, as they are based on the expertise and knowledge available at the time, so as to allow a complete design iteration to be made. These environmental factors must be constantly monitored and maintained in order to prevent unintended damage to the sample.
In addition, the environment must also be controlled for shock, vibration and strong electromagnetic fields to prevent physical damage to the sample. This is true throughout the lifetime of the samples, from collection to curation in perpetuity. Physical protection of the samples
The design of the isolators for handling and storing the samples has requirements exceeding those currently provided by conventional designs and technology.
These include reconciling the leak tightness integrity and contamination requirements that could only be achieved through a double wall design, where the interstitial space contains the same atmosphere as inside the isolator, but at a slightly higher pressure, so that any leaks that did occur would be into the isolator or surrounding laboratory from an inert space.
To construct isolators with complete double walls, in a Russian doll style, presents considerable difficulties for both interfaces and access during the extensive commissioning foreseen for the internal equipment. Integrity of the solid metal body of the isolator is not expected to be an issue. Several organisations have recently embarked on an ESA funded study to investigate the design of these isolators for the facility and to investigate smarter solutions than a full double walled design.
Transport of samples
As with many environmental samples, the first concern is to return them to the laboratory for analysis, keeping the samples in as close to the same state as they were collected as possible. For a space mission, the majority of transport from the collection location to the laboratory is in a ‘low risk’ environment of space for the sample integrity, where the only contamination source is the spacecraft.
The highest risk comes on return to Earth. As seen in Figure 3 the space specific engineering challenge comes in ensuring that the sample lands on Earth in one piece. The basic principles of sample protection cannot be ignored, however, as even a perfect landing followed by sample contamination en route from the landing site to the laboratory is still a high risk. Sample containers must therefore be robust and well sealed.
For a sample container carrying Martian samples, the additional risk of uncontrolled release of the sample is addressed by a triple sealing philosophy. This is analogous to the World Health Organization’s (WHO) requirements for transporting dangerous pathogens – only at a somewhat higher integrity. The container must have a 1×10-6 probability of releasing a virus sized particle, currently held to be 20nm in diameter, into the terrestrial biosphere.
A study to design a container for Mars samples focused on bringing sealing technology from the oil and gas industry into the design of a sample container, and demonstrated that it can remain sealed and monitored in flight and on the ground until it is returned to the sample receiving facility.
Round trip contamination
Spacecraft to Mars have taken precautions to ensure biological cleanliness since the first landers in the 1970s. The NASA Viking landers sterilised the entire landed hardware by Dry Heat Microbial Reduction (DHMR), literally baking the spacecraft in an oven to reduce the bioload6. This procedure has acted as the yardstick for future missions and served to lay down the requirements they must meet, although as we have come to learn more about Mars and its habitability these techniques have been refined over the years.
For a sample return mission, the spacecraft itself needs to minimise contamination of the sample with material carried from Earth during all the sample collection and storage operations necessary to return it. To this end, Mars spacecraft are assembled in cleanroom facilities that are better controlled than those for missions with no PP constraints.
A typical clean environment for a Mars spacecraft, whether it intends to return or not, is an ISO 7 clean room7 with additional controls, comparable to the European Union Guide to Good Manufacturing Practice (EU GGMP) Pharmaceutical Grade D controls for microbiological contamination. These include tighter controls on cleanroom occupancy, personnel dress and ingress and egress than is normal for an ISO 7 environment.
The tighter controls mean that Mars-bound spacecraft often need dedicated facilities for assembly and tests with higher grade infrastructure, such as filtration systems and change areas. As an example, a dedicated facility is used for building the ExoMars spacecraft at Thales Alenia Space in Turin, and the Open University built a very high grade (ISO 5) facility for assembling the Beagle 2 Mars lander.
For equipment in proximity to the sample, such as that which will collect and store it, as well as any preliminary analysis instrumentation aboard, microbial, organic and particulate inorganic contamination must be minimised during manufacture and assembly of the spacecraft.
Precision cleaning techniques are required during manufacture, assembly and testing of the hardware to remove contamination. Ultrasonic baths, solvent wiping and accelerated CO2 snow cleaning have all been used or are being considered for use, but all share a requirement to be gentle on the hardware. Instrumentation must then be assembled and tested in much more highly controlled environments than the spacecraft itself, ideally in laminar flow cabinets or glove boxes held at a positive pressure to prevent transport of contamination.
Working towards a Mars sample return mission
Although a Mars sample return mission is some way off, the technology developments required to contain and study the sample on return will need to be developed early on, as no mission will be allowed to progress to flight without first demonstrating that the facility is in place and ready to receive the samples.
The technology will also be useful in developing facilities used to curate other samples to be returned from planetary bodies without such stringent PP requirements, such as the Moon or asteroids. The development of handling technologies will be especially beneficial to these applications. An ESA funded early study has recently begun into double walled isolators and ESA is also looking to investigate remote manipulation technologies in the near future.
Conclusion
Whether you are testing environmental samples contaminated by the nuclear and oil and gas industries, or something a little less Earth bound, the same fundamental techniques must be applied. While the containment of extraterrestrial samples requires more extreme measures than are necessary for many of us, we can all look to these high standards to maintain paramount integrity of our samples from the field to the laboratory. After all – if a job is worth doing, it’s worth doing well.
Published: 27th Nov 2013 in AWE International
