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ESA fires surface penetrators at ice target in search of planetary burrowers


August 22, 2013

The penetrator hitting the ice target as part of efforts to develop a way to deliver instruments beneath a planet's surface (Image: Astrium)

The penetrator hitting the ice target as part of efforts to develop a way to deliver instruments beneath a planet's surface (Image: Astrium)

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Normally, a spacecraft slamming into a planet’s surface at the speed of sound is considered a bad thing, but the European Space Agency (ESA) plans to do just that. As part of its Core Technology Programme for Cosmic Vision, the agency fired a pair of experimental surface penetrators from a rocket sled at a test facility at the UK Military of Defence Pendine site in Wales last July. The goal is to find ways of delivering instruments beneath the ground or ice of alien worlds without drilling.

Landers have come a long way since the days when all they could do is passively take pictures and temperature readings. Now, they can rove about and the NASA Curiosity rover has conducted the first robotic drilling operation on another planet. It works, but such drilling is complicated, slow and limited in how deep it can go or how great an area it can cover. It would be much simpler to just drop instrument packages from orbit over a wide area and let them burrow under the sand or ice using their own momentum. The trick is having them dig in instead of smashing to bits on impact.

Building a penetrator for the job is actually very simple and the technology has been around since Barnes Wallis worked on the problem during World War II as a way of taking out German bunkers. The Americans had a similar problem during the 1991 Gulf War and in less than a month came up with penetrator bombs made out of surplus 8-inch (203 mm) artillery gun barrels that could plow through reinforced concrete. Something like these would be perfect for dropping on Mars or the moons of Jupiter, but no launch vehicle or probe known could carry a 2-ton penetrator such a distance, so a compromise needs to be made between strength and weight.

The problem is, a penetrator is the opposite of how space engineers think. It can’t be made out of the usual light alloys used in spacecraft as it needs to be made of relatively thick steel. Also, the instrument package needs to withstand massive g-forces on impact instead of the usual five g’s and below, so they need to be designed along the lines of an anti-aircraft shell’s electronic proximity fuse.

The ESA penetrator program is being conducted by a consortium of agencies and companies led by Astrium UK. The current experimental design is intended to test the feasibility of using a penetrator to deliver an instrument package beneath the surface of a planet or icy moon to a depth of 3 m (10 ft).

Weighing 20 kg (44 lb) and measuring 400 mm (15.7 in) long and 200 mm (7.8 in) in diameter, it consists of a steel shell with spring-mounted aluminum instrument bays on the inside. Between the two is a vacuum to insulate the instruments against heat. The rear is an additional hollow section to provide aerodynamic stability. The payload is accelerometers to record the g-forces and a dummy sampling mechanism. If this were operational, it would be able to collect a few grams of samples 10 to 20 cm (3.9 to 7.8 in) from the shell.

For the tests, 12 solid rockets shot the penetrator down a 300 m (984 ft) rocket sled track. As it left the track 1.5 seconds after ignition, it was going at 341 m/s (762 mph, 1,227 km/h) and struck its target with the force of 24,000 g’s.

There were two impact tests, both of which used targets housed in a steel and concrete bunker. The first on July 11 was fired into about ten tonnes of ice to simulate the surface of moons like Europa. The second on July 16 used sand as a stand in for Martian soil.

When the the penetrator hit, the ice shattered into small crystals and the shell was dented when it struck a steel roof beam. On hitting the sand, the penetrator burrowed to a depth of one meter (3.2 ft) in and one meter up. Unlike the ice test, it wasn't dented, but the surface was sand blasted. One unfortunate result was that the penetrator struck at an angle of 22° instead of 8°, though this was attributed to aerodynamic lift during horizontal flight, which wouldn't occur when dropped from space.

The next step of the program will be to study the effect of the impact on the penetrator and to work on developing a battery and communication system robust enough to survive a very unpleasant landing.

The video below by study participant QinetiQ shows the impact tests.

Source: ESA

About the Author
David Szondy David Szondy is a freelance writer based in Monroe, Washington. An award-winning playwright, he has contributed to Charged and iQ magazine and is the author of the website Tales of Future Past. All articles by David Szondy

this is a ridiculous idea -

we will seem like such a violent primitive race to any "aliens" we might discover by blowing a hole into their home

come on now


Lifting 2 tonnes to LEO is not a problem. Refuel the rocket in orbit by scavenging unused fuel from other rockets and away it goes.


Pretty cool idea.. Why not have two payloads.. One deploys out in front of the sensors payload.. So the sensors are separated from the 24,000g force..

So basically just before impact the sensor payload fires in the opposite direction of the driller.. With just enough force to create equilibrium force on impact..

That's pretty cool.. Huh?


This is an interesting problem which depends on the target. I remember years ago about a demonstration that I saw. A five gallon plastic bucket was filled with sand. A 30/30 high powered rifle was fired at the bucket and only penetrated a few inches into the sand. Next, a broadhead hunting arrow was fired from a 60lb. bow and it amazingly went through the bucket and out the other side. Had the target been a series of sheets of 1/4 inch plywood, the arrow would barely penetrate but the bullet would easily pass through many layers. Another interesting demonstration performed years ago was done with a more powerful 30-06 being fired at a series of boards. When fired at point blank range, the bullet only penetrated about eight inches of wood but when fired from 100 yards away it penetrated about 48 inches of wood. This difference was attributed to the bullet wobbling as it left the barrel but at 100 yards it had stabilized and even though traveling at a somewhat slower velocity, it drilled through many more boards. Anyway, the point is that there are many variables to be considered when designing a planet penetrating projectile. When you don't know the exact composition of the target, it becomes even more difficult.



Are you thinking about apply 2399.5G in the opposite direction on the sensor?

Etienne Couritas

JPLAZ1912, a much simpler idea would be to have the main sensor package detach from the penetrator high in the atmosphere, but remain attached by a long lead as it parachutes down. When the penetrator makes impact, it reels in the sensor package so that they both end up in the same place.

Joel Detrow
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