How to determine if your spacecraft has landed on another planet.

[gkec]

By popular demand, well one person, here is a post about how a computer I programmed landed on Titan.

To make it brief I will concentrate on the sensor that determined that the spacecraft had actually landed.

The sensor was part of the Surface Science Package (SSP) which comprised one of the six or so experiment packages that made up the Cassini Huygens probe that landed on Titan Saturn's largest moon.

Here are some technical details of the Surface Science Package.

The Acc E (External accelerometer) sensor consists of a piezo electric sensor device that generates an electrical signal when compressed. This is mounted on a small mast protruding from the bottom of the spacecraft.

More details here -- includes pictures.

The sensor was continuously sampled by the electronics and the data read into a 512 sample FIFO. If a signal is detected that exceeds a predetermined threshold then the sensor is sampled for a further 512 - 64 samples and then the FIFO is frozen. The electronics signal to the SSP computer that the impact event has occurred and the computer reads out the data (as well as putting the whole package into surface mode) and transmits the data to the onboard CDMS (Command data management system). The CGMS then relays the data to the Cassini spacecraft that is "flying by". Cassini records the data for later playback to Earth once the lander mission has finished.

Anyway here is the data -- all 512 samples. All of the Huygens landed data is publicly available.

The first column is the time in seconds, ignore the second and third columns. The fourth column is the sample number and the data appears in columns 5 and 6 with the digital 8 bit reading and then the corresponding voltage.

As expected the impact occurs at sample 64 with a peak at 65. There was then a reduction in pressure before another peak at sample 70.

Here is a full description of what happened when it landed.

So now you know -- however if you do land your spacecraft like that (dropping onto a fairly hard surface at 10m/s) you will probably have problems getting off the planet.