24th Feb 2020
To test what will happen when our impactors land on Mars, we need to simulate an impact. We will do this with a Gas Gun for impact testing. It will need to be in many different types of material and each material will need several impacts. We are looking to land at 500 kph ( 310 mph). The likely types of soil are:
- sandy material
- clay material
- shale material
- rocky material
- Calcium Cement
The Calcium Cement is a recent addition due to the findings of the very recent InSight Mole experience. The list is not complete, but these re the main ones on the list. It is not just a job of firing the simulated impactor into a target of material for impact testing. We have to build a target device capable of not expanding as the material is hit. We need to cool the material to at least -50 degrees Celsius. That is about -58 degrees Fahrenheit. To do this we will need to freeze the material for around 2 days in Dry Ice (frozen carbon dioxide). The water content in the material is also important There is likely to be some, but we will need to make the first soil damp as we freeze it.
We will use camera’s to produce the results needed. The cameras are high speed and watch the projectile slow in the chamber as it impacts the material. It will give us a solid G force number. In fact it will calculate the G forces through the entire impact and we can see where the greatest G force numbers occur.
The chamber needs to be immediately flushed with an inert gas like helium as the impact will start burning materials from many sources, even material released from the impact itself through heat and mechanical release.
The chamber then takes about 2 days to clean up before another impact can be scheduled. With a maximum of about 2 a week, a group of 50 will take around 25 weeks or half a year to complete. Impact testing is an exacting job. Our probe will be an irregular shape and will be 60 mm wide to fit inside a 70 mm barrel. We will need to have a sabot made to fit the unit and the barrel. What is a sabot:
a device which ensures the correct positioning of a bullet or shell in the barrel of a gun, attached either to the projectile or inside the barrel and falling away as it leaves the muzzle.
It also stops the hot gasses that propel the unit from escaping around the probe since the barrel is bigger.
Our probe is about the same mass expected to hit Mars. That is 6 kg or 13 lbs. The mass may change, but the figures that we will need can be extrapolated from the base results.
We visited a gas gun last year and met Prof Paul Hazell who is a Professor of Impact Dynamics in the School of Engineering and Information Technology (SEIT) at UNSW Canberra. We are hoping to use their gas gun in the testing, but that is work in progress. Mean time here are some pictures from that visit. Below is Prof Hazell in front of the business end of the beast.
Above is the target chamber and I believe that is one of the cameras used to high speed video the impact testing. I believe the other black tube is used to flood the chamber with helium. There are more cameras out of sight of this picture.
Impactor Testing is not cheap. It will effectively cost us nearly A$8,000 per shot when we factor wages and travel between Sydney and Canberra.
Paul is located in The Australian Defence Force Academy (ADFA). Our military contacts are very interested in these tests and we have proposed that ADFA write a joint paper on the results. That proposal is currently in progress at time of publishing.
Although there is plenty of technical information here, it is a very complex field that I expect that will yield amazing results.
A recent suggestion from one NASA section has suggested that an impactor drop on the moon may be a possibility and we are waiting on more details for that opportunity.
It would appear that we can use a 44 Gallon drum (US 55 Gallon) to house the target material. This is ideal to help freeze the material compared to a plastic container which would be an insulator. We intend to use steel straps around the drum to further strengthen it. The drum would have a Mylar film over the top to hold any loose material in the drum when it is tipped on its side. This is a cheap solution that solves so many problems. Even the circular shape helps with strength of the container.