Planetary protection for ExoMars: An interview with Gerhard Kminek
Credit: ESA - Anneke Le Floc'h
The first mission of ESA's ExoMars programme, which is scheduled to arrive at Mars in October 2016, consists of the Trace Gas Orbiter (TGO) plus an entry, descent and landing demonstrator module (EDM), also known as Schiaparelli.
ESA's planetary protection officer is Gerhard Kminek. We asked Gerhard to tell us more about the complexities of planetary protection during preparations for the launch of ESA's first mission to land a spacecraft on Mars.
What is planetary protection?
Any spacecraft that we send from Earth to another world carries organic material and microbes. These can contaminate a place that was previously pristine. Special care must be taken in sending spacecraft to Mars, or any other world with a potential for past or present life. These missions have to meet strict limits for both microbiological contamination and impact probabilities - these limits are described in the respective planetary protection requirements.
Why is planetary protection important?
Half a century ago planetary protection constraints were introduced to ensure that scientific investigations designed to detect alien life forms would not be compromised by the presence of terrestrial life. This would definitely not be a good return on the investment! If contamination is caused by particles or organic material, the amount remains more or less constant, but microbes multiply rapidly over time, so it is important – and more difficult – to reduce and control all traces of microorganisms before the spacecraft is launched.
How is ExoMars 2016 implementing planetary protection?
Since Mars is a planet with potential for past or present life, ExoMars 2016 has stringent planetary protection requirements with respect to microbiological contamination on Schiaparelli, and the probability of impact on Mars of the TGO and the Proton rocket's upper stage.
What facilities have you been using for Schiaparelli?
|Taking microbiological samples from Schiaparelli, inside the portable cleanroom tent, at Baikonur. Credit: ESA|
Schiaparelli has been assembled on the premises of Thales Alenia Space in Turin, Italy, in a new Biological Contamination Controlled Clean Room (BCCCR) that was provided by the ExoMars programme. We also assembled a portable cleanroom tent for temporary use at Thales Alenia Space in Cannes (France) and later at the Baikonur launch site.
The microbiological contamination in the air and on the surfaces of the BCCCR is 10 000 times less than in a normal cleanroom used for spacecraft assembly and testing. This is achieved by using filters to remove dust and microbes and by minimising contamination by staff working inside the room. People need to wear full body garments, sterilised gloves, face masks etc. These are then discarded and washed by a specialist company before reuse.
The BCCCR undergoes a dedicated cleaning programme every day. Chemical agents that kill microbes are used on the floor and on the walls to a height of two metres. We also perform daily microbiological tests to monitor changes in contamination.
Can you tell us more about the precautions in the cleanroom?
There are usually four or five people in the cleanroom, though the number can vary. They work in the cleanroom for up to four hours at a time.
Before they enter the BCCCR they have to undress to their underwear in a changing room and put on a dedicated pyjama-type undergarment. They then move to another changing room where they don a sterile bunny suit, gloves etc. so that only their eyes are remain uncovered.
To enter the cleanroom they need to walk through an air shower. The air shower blows jets of air for about 30 seconds to remove and filter any remaining contaminants. The door to the cleanroom remains locked until the air shower has been completed. However, when you leave at the end of the work shift, you can go straight through.
If someone gets an infection, such as a cold or flu, or a skin disease that results in shedding of a lot of particles, they are not allowed to work on the spacecraft.
No one is allowed inside the cleanroom without having completed two or three training sessions about the planetary protection procedures, depending on their specific role. This includes all contractors as well as people working on the payloads.
What about the microbiology lab?
|Assembling Schiaparelli in the microbiological laboratory in Turin, Italy. Credit: ESA|
In order to check the microbiological contamination of the cleanroom and the flight hardware the ExoMars programme has built a microbiological laboratory at the Thales Alenia Space site in Turin, Italy. Three specialists work there. They take samples of the air, use sterilised cloths to sample large surfaces and nylon swabs for small areas. In the lab they extract the biological samples, and count the microbiological contamination. The number of spores is then counted every 24, 48 and 72 hours and these figures are plotted to reveal quite quickly any contamination problems that might arise.
Tell us about the cleanroom tent
We had to base some activities, such as thermal vacuum tests and vibration tests, in Cannes. The lander was mostly closed, so that was not a problem. But sometimes we had to open it, so we had to have a similar environment to the one in Turin.
We decided to buy a 150 square metre modular tent with a laminar floor that we could use on a temporary basis. It is made of transparent plastic and has a metal frame.
The portable cleanroom tent at Thales Alenia Space at Cannes.
Credit: ESA – B. Bethge
The TAS-I planetary protection team, inside the cleanroom tent at Baikonur.
Credit: Thales Alenia Space
The same safety procedures were used as in Turin. One side of the tent was open, but there was a continuous, filtered airflow from one side to the other to remove contaminants. This also allowed movement of hardware in and out.
When we no longer needed it in Cannes, we packed the clean tent with the flight hardware and shipped it to the launch site in Baikonur so that we could use it for the final preparation of the lander.
ExoMars 2016 spacecraft in the Proton fairing connected to the air conditioning unit of the transport rail-car at Baikonur.
Credit: ESA – B. Bethge
We set up a microbiology lab in Baikonur, with the same team and facilities as in Turin. When it arrived in Baikonur, Schiaparelli was placed inside the tent and microbiological samples were taken regularly until the closure of the Schiaparelli capsule. After closure, the Schiaparelli capsule was put on top of the TGO.
The entire spacecraft is placed in the Proton rocket's fairing, then the fully assembled Proton is moved to the launch tower on a dedicated rail car. During the transport to the pad and on the launch tower, dedicated air conditioning systems with high efficiency filters provide air to the rocket fairing. Both air conditioning systems have already been tested several times to ensure that they meet our biological contamination requirements.
How did you transport Schiaparelli to Baikonur?
During transport we closed the Schiaparelli capsule to avoid re-contamination. There is a double lip seal around the perimeter of the capsule and a venting system in the capsule back shield fitted with a filter allowing air to go in and out during the launch and atmospheric entry on Mars.
The transport container has an inner shell and an outer shell - a container inside a container. After closing, both shells are flushed with pure nitrogen. An air conditioning system with high efficiency filters is used to provide air and temperature control to the container while it is closed. It was taken from France to Italy by road and then transported to Baikonur by air.
Will the procedures be the same for ExoMars 2020?
The ExoMars 2020 mission is based on a broad cooperation between ESA and Roscosmos with contributions from NASA. The flight system consists of a cruise stage, a lander capsule and a rover system.
Most of the procedures will be the same as for Schiaparelli. Everything being built in Russia, such as the lander capsule, will be handled in a new cleanroom similar to the one at Thales Alenia Space Italy in Turin. A new microbiological contamination controlled cleanroom – with a different design - has just been finished at the Airbus Defence and Space premises in Stevenage, UK, to house the rover during its assembly and testing.
|Glove boxes in the bioburden controlled cleanroom at Thales Alenia Space Italy for the aseptic and ultra-clean assembly of the hardware for processing and analysing the Mars samples. Credit: ESA/Thales Alenia Space|
However, the ExoMars rover will carry instruments developed in Germany, France and the United States to search for life, so we will have to be extra careful about planetary protection – even more than for Schiaparelli. Whereas Schiaparelli alone has to be clean enough not to contaminate Mars, the flight hardware on the ExoMars rover that is processing and analysing the samples will also have to be organically clean and sterile.
To achieve and maintain the strict cleanliness levels, the ExoMars programme has purchased four new custom-made glove boxes – stainless steel cabinets with gloves inside. These are installed in the Thales Alenia Space cleanroom in Turin that was used for the assembly of Schiaparelli. The precision-cleaned and sterile parts of the sample handling system and part of the rover payload will be introduced into these glove boxes for further assembly and test activities.
While still in the glove box, the entire sample handling and analysis assembly is put in a metal enclosure, filled with argon and sealed under positive internal pressure to avoid any re-contamination. This mini lab will be placed inside the rover, where it will remain sealed until it is used after landing on Mars.