As Beagle 2 enters the Martian atmosphere a heat shield slows the descent from more than 5.5 km/s, or 12,000 mph, and prevents the overheating and burning up of the probe. A parachute aids this first task before falling away, taking a rear cover with it. The main parachute then opens and the heat shield is dropped. Nearer the surface a radar altimeter detects that the correct altitude has been reached for inflating three gas bags, these are inflated and cushion the spacecraft’s landing. Once contact has been made with the Martian surface the gas bags and parachute fall away and Beagle 2 drops a final metre to the ground.

Figure 2: Beagle 2 unfolded on the surface of Mars

Once on the surface a spring mechanism opens up the two halves of the lander, unfolding the solar panels, the various pieces of science equipment and its robot arm, as in Figure 2.

This science experiment shows the effect the gas bags will have on Beagle 2’s landing.

Equipment required

• ADC-40/42 or DrDAQ data logger
• PC with PicoScope oscilloscope software installed
• Force sensors FSG15N1A (Farnell InOne 721-6671)
• Retort stand and boss

Additional equipment is required to construct the Beagle 2 lander model — full details can be found in the technicians’ notes

Experiment setup

The Mars lander, Beagle 2, is modelled by a small cylinder of cement. On its underside is a force sensor which produces an output voltage related to the force exerted on it. The higher the force, the higher the output voltage. This sensor will be connected to a computer-based oscilloscope to show what happens to the model during its landing.

Once the model has been constructed, as shown in the technicians' notes, place the model’s suspension and connection system into a boss at the top of a tall retort stand and connect the the DrDAQ or ADC-40/42 and associated computer, as shown in Figure 3 below.

Figure 3: Beagle 2 lander model apparatus

Carrying out the experiment

• Set up the Beagle 2 lander model apparatus as shown in Figure 3 above.
• Connect the DrDAQ or ADC-40/42 to the computer and load PicoScope oscilloscope software
• Connect the output voltage from the force sensor to the voltage input of the computer interface and plug in the 9V battery, keeping this equipment as far from the computer as possible to reduce ‘pick–up’ from it.
• Set the Timebase to 10ms/div.
• Set the X-gain to x1.
• Set the Trigger to Single, Volts, Rising and +24 mV. (You may find that you can decrease this value slightly, but it must be set to a value that prevents it from triggering too early. In a ‘noisy’ environment where there is a lot of ‘pick–up’ from computers, you may have to use a value greater than 24mV.)
• Set the Display setting to -10% (right–hand box at the bottom of the screen). This lets you set when the trace is started from, in this case the first 10% of the display is before impact.

Using the ADC-40/42

Set the Y-gain to x5

Using DrDAQ

• For Input A, select Volts and a Y-gain of x5.
• Leave the other inputs of.
• Scroll the output voltage (mV) axis down until 0 mV shows in the bottom left corner.

The X and Y-gains can be adjusted later if the trace does not display as you would like.

• Place a piece of fairly hard carpet immediately beneath the model.
• Using the attached string lift the model by about 30 cm.
• Click the GO button in the bottom left corner of the PicoScope screen and then let the model fall.
• Note the shape of output voltage (froce) against time.
• If required, print and save the trace.
• Repeat the experiment but with a small inflated balloon attached to the bottom of the model (use a small piece of double-sided sticky tape to attach it directly to the force sensor.)
  Note: You will probably need to increase the Y-gain to x10 or x20 to see the effect.

Questions and discussion of the results

Q1. What effect does the ballon have on the shape of the trace of output voltage (force) against time?

Q2. For a very cushioned or ‘soft’ landing would you want the output voltage (force) to be high or low? Explain.

Q3. For a very cushioned or ‘soft’ landing would you want the impact time to be long or short? Explain.

Q4. What would you expect the trace to look like if you had the same balloon beneath the model but the height of fall was less? Explain.

Q5. What would you expect the trace to look like if you had the same balloon beneath the model, it was dropped from the original height, but its mass was less? Explain.

Further study

For further study repeat the experiment with the balloon attached for falls of different heights. The experiment can also be repeated using a Beagle 2 model of a different mass.