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Why does it take 6 days to reach the surface? |
In order for Beagle 2 to be sent off on the correct path
to the landing site, Mars express was heading straight for
the planet. It was necessary to release Beagle 2 from the
orbiter in good time so that Mars Express was able to make
a course correction to take it away from the collision course
and get ready to manoeuvre into orbit. It could have been
done longer than 6 days before landing but Beagle 2 is now
flying without any power or way of charging its batteries
so 6 days was the best compromise.
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If
it has no propulsion of its own, how does it get there? |
Space is a vacuum and as there is no drag, Beagle 2 still
has the same velocity that it was given after the spin-up
and eject from Mars Express. It is travelling towards Mars
at 20,000 kph (12,500 mph, Mach 33). Beagle 2 will be on
its own for 6 days and it is not possible to communicate
with it or check any data which would reveal its state of
health. The only system running is a timer chip, which will
wake up the electrical systems around 2.5 hours before Beagle
2 reaches the martian atmosphere. At that point the pre-programmed
descent sequence will begin.
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How does Beagle know when to open its parachutes? |
As the probe enters the martian atmosphere, meets resistance
and begins to decelerate, the accelerometers on board will
detect the change in its velocity. During the next two to
three minutes of headlong descent, it will slow to Mach
1.5. The accelerometers will first recognise an increasing
rate of deceleration and then, after about 74 seconds, a
falling rate of deceleration. The probe will pass through
a condition where the atmosphere's resistance no longer
has a decelerating effect. It will begin freefalling. At
this point the computer will signal the firing of the parachute
deployment device to deploy the pilot parachute at about
7.1 km (4.4 miles) above the surface level of the landing
site.
Again the accelerometer will detect the sudden change in
forward motion. The probe will descend for about 48 seconds
on the pilot parachute, reducing the speed from 1174 kph
(720 mph) to 335 kph (210 mph) until the moment that the
frangibolts, which attach the back cover, are fired. The
main parachute will then be deployed.
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How
does Beagle know when to inflate its airbags? |
Once the heatshield has been discarded, a radar altimeter
trigger (RAT) comes to life. The RAT detects the surface
of the planet every 0.1 sec. About 30 to 40 seconds after
the main parachute has been deployed (about 275m above the
surface) the gas-generator will fill the bags, taking just
2 seconds to complete the task.
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At
what speed does Beagle hit the surface of Mars |
Beagle will be travelling at about 58 kph (36 mph), protected
by its airbags, when it hits the surface. It will then bounce
until it finally comes to rest.
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What happens if it lands upside down? |
The hinge which opens the "clam-shell" shaped
lander is capable of turning Beagle 2 the right way up.
This self-righting mechanism (with a mass of 0.98 kg) has
to produce enough torque to lift the lander base (a mass
of 24.3 kg) under the influence of the martian gravitational
field (which luckily is 38% that of Earth's) rather than
just the lighter lid.
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If Mars is only 35 million miles away, why does Beagle have to travel 250 million miles? |
Mars and Earth were 34,646,418 miles apart (55,758,006 km),
between the centre of each planet, on August 27th 2003 (the
closest since September 12th 57617 BC).
Beagle's journey (for the most part aboard Mars Express)
is 250 million miles and takes 205 days (almost 7 months).
During this time Mars Express, like Earth and Mars, was
travelling on an elliptical orbit around the sun. Mars Express
had to "catch up" with Mars, like a runner on
the inside lane of the track (Earth's position) moving to
the outside lane (Mars's position). Because Mars Express
and Beagle were moving on a curved trajectory, aiming for
a moving target, they ended up travelling further than the
quoted distance of 35 million miles.
Course corrections were made to ensure that Mars Express arrived at the right
place at the right time.
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How do you predict where Beagle 2 will land? |
Knowing where Beagle 2 might have landed depends on how
well flight engineers know the course of Mars Express and
the actual angle at which Beagle 2 entered the atmosphere
of Mars. Other information required is the predicted performance
of the heat shield, the pilot and main parachutes, which
in turn depend on atmospheric pressure, temperature and
wind speed. A computer programme in which six parameters
are varied simultaneously is run for a thousand attempts
at landing. The output of the computer model predicts an
ellipse where Beagle 2 can be expected to come to rest.
Computer models run since the ejection of Beagle 2 on December
19th have predicted smaller and smaller ellipses.
An ellipse of 71 miles (114 km) long by 29 miles (46 km)
wide was predicted for Beagle 2 when Mars Express was half
way to Mars. The original predicted landing ellipse before
launch was much larger at 298 miles (480 km) by 186 miles
(300 km).
The diagram shows an example landing ellipse plotted around
the computer modelled data points.
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What went wrong with Beagle 2? |
Until recently the team has been concentrating all efforts on positive
actions to try and communicate with Beagle 2. As well as continuing to
exhaust all such efforts, a lengthy investigation will begin shortly into possible
reasons why the lander may have failed. Results from this enquiry will be made public.
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Is there any chance that NASA's rovers can go and find
Beagle 2? |
Beagle 2 has landed in the Isidis Planitia basin (about
90 degrees East, 10 degrees North). Spirit has landed in
the Gusev Crater (about 175 degrees East, 15 degrees South).
Opportunity is due to land on the Meridiani Planum (about
354 degrees East, 2 degrees South).
In Earth terms this is approximately equivalent to Beagle
2 being in Sri Lanka (in the Indian Ocean), Spirit being
in Fiji (in the Pacific Ocean) and Opportunity being south
of Ghana (in the South Atlantic Ocean). Mars is about half
the diameter of Earth, but even with these figures you can
get an idea of how far apart the landing sites are.
The NASA rovers can travel up to about a kilometre (0.6
miles) at an average rate of about 1 cm/sec (approximately
0.036 kmph or 0.02 mph), so contact with Beagle 2 would
not be remotely possible.
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Why not find Beagle 2 by imaging the landing site? |
Both Mars Global Surveyor and Mars Express are attempting to image the Beagle 2 landing site. MGS has already spotted NASA's Spirit on the surface, but it knew precisely where to look. To search the landing ellipse for Beagle 2 will take time.
The high resolution stereo camera on Mars Express has, in theory, the resolution to see Beagle 2 if it is deployed, or the parachute canopy (2m per pixel at closest approach), but again it will take a long time to image the whole area. An image of any parts of Beagle 2 on the surface will greatly help the team trying to establish at what point the lander may have failed.
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