Robot Probes
Robot probes are useful tools in space exploration. You
Earthlings should appreciate this since most of your space
exploration is currently undertaken by robots! Now, suppose we
want a probe to explore a planet - what design would we
choose? Often it's not just the surface of a planet we want to
explore, but the subsurface. On a harsh planet like Mars, it may
well be that beneath the soil is a layer of ice and beneath that
there might just be seas of liquid water. To explore such a world
we might choose a robot capable of burrowing. Worms make
good efficient burrowers, so let's make our probe worm-like.
However, that might make it slow on the surface, so let's give it legs, but let's keep the legs short so that
they don't get in the way when the probe is burrowing. With short legs we may need a lot of them to
generate stable thrust, so now our probe looks a bit like a millipede or a velvet worm. We could even make
theses leg-like appendages flattened and paddle-like, so that our probe can swim well in and under liquids,
rather like a rag-worm. We can equip the leg-like podia and perhaps the under-surface of the probe with
fields of microscopic recurved hooks to provide traction to enable the probe to crawl over smooth surfaces,
or even up and over vertical barriers. For very smooth surfaces, which prevent the hooks gripping, hollow
hair-like structures can exude a glue-like substance to assist traction. The hairs can be so designed such
that they will only detach easily if moved forwards, but grip if dragged backwards (rather like the foot-pads
of certain frogs).

We need some sensors, not only so the probe can get about, but so that it can collect valuable data about
its surroundings. Let's give it a pair of eyes that can see visible light, ultraviolet and infrared. We can use
these sensors to record daily fluctuations in light levels and to search for life-forms that may radiate heat. It
could have polarised ultraviolet vision to locate the parent star or stars, even when the weather is cloudy.
In the second model I have added a unit to the top of the head,
which consists of six petal-like valves that open out. Through this
an excavator tool can be protruded - perhaps a drill or crushing
jaws to remove hard rocks. In soft sediments our probe could
probably dig without this, by simply wriggling through the soil and
using its many appendages to push the soil behind it as it
burrows. The excavator could contain an aperture to ingest
ground soil particles into the probe for analysis, perhaps after
grinding them to a fine powder. Note the two conical
protuberances at the front of the head - these are probes which
can take in soil and water for analysis.
Chemical analysers can identify a huge repertoire of inorganic and organic chemicals. For more precise
analysis, some of the particles may pass into a miniaturised scanning electron microscope (SEM) inside
the probe. This microscope will scan for microscopic life-forms and can also perform an X-ray analysis of
selected areas of the sample surface to determine the elemental composition of the material. It is also
equipped with an ion-beam to etch away the surface of the sample and probe deeper. A miniaturised mass
spectrometer is also attached for additional analysis of the molecular structure of the sample.
Additional modules can be attached to our probe, such as this
bio-reaction chamber in which soil or liquid samples can be
incubated under various conditions of temperature, light and
nutrient provision. It is not necessary to carry these modules all
the top and so they are detachable. Another useful module is the
atmospheric analysis module. The probe has a mobile tail with
petal-like valves that open to reveal a series of manipulators
which allows the probe to manipulate items, attaching or
detaching these additional modules and operating them.
Our probe can transport a module and detach it and place it at a suitable location, e.g. it could carry the
atmospheric module down into a valley and place it in a sheltered crevice to monitor due formation. Note
that these modules must be removed prior to any burrowing operation. The eyes can also be withdrawn
into the head and closed by heavy shutters to protect these sensors during digging operations. Digging
through ice is particularly difficult since ice is a very resilient material, so perhaps the excavator unit shoul
be able to generate heat, perhaps with the help of a laser beam.
Our probe needs to be able to return the data that it collects
segment. These would need to be retractable, so they can be
withdrawn for their protection during excavations. When deep
beneath the surface the probe will most unlikely be unable to
return data by direct transmission, so it will have to store the
data in its memory banks, but what if it gets trapped? It could
lose valuable data. Well, from the rear end it can release a tiny
worm-like crawler from inside itself.
This crawler has none of the sophisticated instruments of the probe, but it can store data in a memory chip
and tunnel itself back to the surface by retracing the route the probe took. Having so simple a task it can
be much miniaturised, making it far less likely to get trapped by collapse of the burrow. The probe could
also shore up the burrow, perhaps by lining it with mucus-like or silk-like material as it goes. More often
than not though, it would be easier to send it down and wait until it manages to dig itself back to the
surface, by whatever route it can find! It can use its infra-sound emitter and vibration sensor to probe the
substrate in front of it for harder materials and avoid these. The probe will have to be able to act
intelligently by itself, since it may be cut off from base for quite some time. It has a powerful computer
brain, of course. It would also need to be very robust. It's components are impact resistant, so it won't fail
should it miss a couple of steps like ASIMO did. It also has sophisticated systems to locate internal faults
and carry out limited repairs. Powering such a probe would be an immense problem for Earthling
technology. The SEM alone requires a few thousand volts of electricity. We could have a power cell in
each segment and then connect them in series, or we could go for something a bit more sophisticated, like
a nuclear reactor or an anti-matter annihilator.
We shall need a means of safely delivering our probe to the
planet's surface. The capsule opposite relies initially on
parachutes to slow its descent through the atmosphere and
then the chutes detach and when it impacts the surface at a
much reduced speed, it bounces on its twelve shock-absorbers,
which are made of the latest elastic materials, adjusted with the
correct spring stiffness for the local gravity of the planet. On
high gravity worlds, air bags could also be deployed. The
capsule is an icosahedron with 20 faces. Each face can be
opened and our intelligent probe, coiled up in a central
chamber attached to the edges and vertices of the icosahedral
shell can use its gravity sensors to determine which way up it
has landed and select whichever of the 20 exits is most
convenient and crawl out from the capsule.
It will then have to unpack any additional science modules. The capsule can also contain a microwave
driven micro-satellite capable of returning small soil samples to planetary orbit for later collection. The
microwave beam is fired from the ground and propels the micro-satellite upwards at tremendous
accelerations to escape the planet's gravity. The capsule can also contain a more powerful data
transmitter should the data need to be transmitted across interplanetary or interstellar space. If a receiver
is located in orbit, then the antennae on the probe itself should prove sufficient, but should these fail then
the probe can upload its data to the capsule for storage or  transmittance.
Now all we need is a planet to explore. How about Zeta-Drelix 3,
we have received unconfirmed reports of relics of an ancient
and seemingly extinct civilisation on this world...
What kind of robot probe would you
use to explore such a world?
geological probe
Above: a Geodroid prospecting the surface of a planet for important minerals. The feet have built-in
geosensors that map the underlying substrates using thermal conductivity and spectrum analysers.
Retractable arms can collect samples for analysis by internal instruments, including scanning electron / ion
beam microscopy and UV elemental analysis. A telescopic drill can drill to a depth of 40 metres for initial
strata sampling.
Viking Space Probes

What instruments would you place on a robot space probe?

The Viking space probes (Viking 1 and Viking 2) were two NASA missions to explore Mars in the 1970s. Both missions deployed a pair of robot probes: one lander and one orbiter. These probes were very advanced at the time and are still technological marvels today: they are fine examples of human ingenuity. The diagram above shows a Viking lander (landing probe) and a labeled version is given below.

Viking Lander Technical Specifications

Length: 3m; Height: 2m
Mass (fully fitted): 576 kg

The body platform of each lander is hexagonal and constructed from aluminium and titanium alloys. Three alternate sides are shorter, such that in plan view the body resembles a triangle with blunted corners with a landing leg on each short side. The body is covered in spun fiberglass and Dacron cloth to protect equipment and conserve heat. the lander and external assemblies are painted light grey (with a rubber-based silicone)to protect it against abrasion and reflect solar heat.


Deployment of the Landing Probes

Viking 1 landed on Mars in the Chryse Planitia (Plane of Gold, 22.697 oN) in July 1976.
Viking 2 landed on Mars in the colder Utopia Planitia (Plane of Paradise, 48.269 oN) in September 1976.

The lander (landing probe) and aeroshell separate from the orbiter (orbiting probe), placed in orbit around Mars, and descend. The aeroshell acts as a heat shield and carried out some measurements on the upper atmosphere (composition and ionization). It also possessed 12 hydrazine mono-propellent thrusters to maneuver the lander and direct it to the chosen landing site. The lander and aeroshell were encased in two bioshield valves, which enclosed them like an egg. These ensured that the lander remained sterile during launch and were jettisoned on leaving Earth orbit. Prior to launch, the entire assembly inside the bioshield was sterilised by heating to high temperatures to prevent accidental contamination of Mars by microorganisms from Earth.

the lander was initially connected to the orbiter by an umbiliocal cord during the cruise phase to Mars, which allowed power and data transmission. An additional base cover over the top of the lander (between the lander and the bioshield cap) protected the lander during initial entry. The parachute system and the mortar to fire the chute were situated on top of the lander beneath the base cover.

The descent capsule (consisting of lander, aeroshell and base cover) separated from the orbiter and first traversed the interplanetary medium permeated by the solar wind. The following details the descent of Viking 1. The capsule entered the upper atmosphere of Mars at 250 km altitude at about 1600 km/h, with the aeroshell heat shield directed forwards. Friction between the atmosphere and aeroshell slowed descent and caused temperatures to reach something like 1500 C. The heat shield had a sacrificial outer surface layer which burnt away, as intended, carrying away much of the heat with it. The aeroshell provided some aerodynamic lift at about 30 km. At 6.4 km and 1600 km/h the parachute was deployed and seven seconds later the aeroshell was ejected and the lander's three legs extended. After about a minute the chute had slowed the lander to 60 m/s. At 1200 m the lander's three terminal descent engines ignited and the chute and base cover were jettisoned.


Orbiting Probe Specifications

The orbiter (2 325 kg, 3.3 m in height) was equipped with a visual imaging subsystem (VIS), an infrared thermal mapper (IRTM) and the Mars atmospheric water detector (MAWD). The VIS consisted of a pair of identical cameras and telescopes and was used in imaging and selecting suitable landing sites for the landing probes and to map the planet's surface globally. The IRTM mapped temperatures on the planet's surface, which provided data on surface composition and roughness and internal heat sources, e.g. due to underlying magma pockets. The MAWD was an infrared spectrometer used to map the distribution of water vapour over the planet's surface, providing data on weather and seasons. The orbiter was powered by four solar panels (total surface area 15 m2 and a total span of 9.7 m) and equipped with nitrogen gas thrusters. A Sun sensor maintained lock on the Sun for navigation and orientation (the Sun provided a reference for pitch and yaw). The star Canopus, monitored by the Canopus sensor, was also used as a fixed reference point for roll). The brain of the orbiter consisted of two onboard computers with 4096 (computer) words of plated-wire memory. A moveable 1.5 m dish antenna provided remote high-gain S-band communication with Earth (that is by means of a directed radio beam) while an additional low-gain antenna (operating in all directions) provided communications when nearer to Earth. (S-band is a specified range of microwave frequencies).


Landing Probe Specifications

  1. Landing legs (x 3): consist of a main strut and A-frame assembly, each with a 30.5 cm diameter footpad. The main struts contained bonded, crushed aluminium honeycomb to absorb the shock of landing. Vertical descent velocity at touch down was 2.5 m/s.


  2. Descent engines (x 3): functioned after parachute separation: each generated 2600 N of force, situated 120 degrees apart, burned hydrazine mono-propellent. Each had 18 small nozzles to distribute thrust so as to cause minimal disturbance to the landing site. Suuplied by two spherical titanium fuel tanks. A radar altimeter (solid-state pulse radar) with two antennas: one beneath the lander (and one mounted through the aeroshell). Backup systems: alternative sets of radar altimeter electronics could be switched to either radar antenna; the terminal descent landing radar could work with 3 of its 4 beams.


  3. Terminal descent landing radar: measures velocity of the lander during descent (consists of 4 continuous-wave Doppler radar beams accurate to within 1 m/s). This was used to determine the correct time to jettison the chute and ignite the descent engines.
  4. reaction control engines (x 4): burn hydrazine mono-propellent and used to control roll: two pairs, one mounted on each fuel tank.


  5. S-band antenna dish - for direct communication with Earth (a 76 cm parabolic reflector dish). Measurements of radio signals (changes in frequency, amplitude and phase) sent by the probe provided information on the global gravitational field of Mars, the local gravitational fields at the landing sites in addition to the radius of Mars at the landing sites and the rotation of Mars about its axis. Measurement of radio signal travel times provided a measurement of the curvature of space and time by the energy density of the Sun and confirmed predictions of Einstein's General Theory of Relativity to within 0.1% accuracy.


  6. UHF relay - send signals to orbiter (which can then relay them to Earth).


  7. Computer brain - two channels with plated-wire memories, each with 18 000 words of storage capacity; one channel kept in reserve. Instructions were stored for the first 22 days of the mission and the computers could be reprogrammed from Earth.


  8. Radioisotope thermoelectric generators (RTG) x 2 - each generating 35 W and connected in series to double voltage and reduce power loss, each weighed 15.3 kg. These provided continuous heat (from the decay of carried plutonium-236) and hence electricity. The sunlight on Mars is half as strong as it is on Earth and nighttime temperatures can fall to -120oC. Excess heat could be conveyed by thermal switches into the lander's interior when needed. Covers over the generators prevented excess heat loss.


  9. Rechargeable nickel-cadmium batteries (x 4) - these stored excess electrical power produced by the generators until it was needed (i.e. until need exceeded the rate of power generation).


  10. Data acquisition and processing unit - data was either transmitted immediately to Earth or held in data storage memory or on a tape recorder. The memory was a temporary store with 8 200 word capacity. The recorder could store 40 million bits, record at two different speeds and play back at five.


  11. X-ray fluorescence spectrometer measured atmospheric and soil elemental composition. The soil was supplied by the sample collector boom. When bombarded by X-rays, each element gives off characteristic frequencies of X-rays. This instrument could not identify the light elements, including C, O and N, however, so was not used in organic analysis.


  12. Gas chromatograph mass spectrometer (GCMS) - atmospheric gases and soil samples (the latter vaporised first in an oven) could be analysed for its molecular composition, such as the type of organic molecules present. the gas chromatograph (GC) is a column consisting of a coiled tube coated with beads: gases entering the column adsorb to the beads to different extents depending on their chemical nature and so different molecular species take different characteristic times to traverse the column. Molecular species exiting the column are then passed to the mass spectrometer (MS) for further analysis. The MS ionizes the gaseous molecules and measures their charge to mass ratio, from which the nature of the molecule can be inferred. Heating the sample in the oven first to 200 C enables analysis of volatiles, then heating the remaining sample to 500 C releases compounds produced by thermal degradation (pyrolysis).


  13. Two identical facsimile cameras (scanning mirror rotation about the horizontal (azimuth) causes mechanical scanning as the image is generated one pixel at a time): can view the area that the sampler can reach as well as the surrounding terrain. each camera has 12 photosensitive solid-state diodes: 4 for panchromatic hi-res mode (gives a deeper focal field); 3 color sensors (red, green and blue) for color mode; 3 for infrared (IR) imaging (to identify mineral groups); 1 for rapid panchromatic panorama scans (operational mode) and 1 with a red filter and reduced sensitivity for imaging the Sun.


  14. Camera test charts (three grids on top of the lander) - calibrate color and also contain UV sensitive test strips to allow the amount of UV radiation to be measured. One test chart has a pair of magnets to collect magnetic particles from the atmosphere which the camera can image.


  15. Mirrors - allow cameras to view parts of the lander not directly viewable. One of the mirrors is a reflector with x 4 magnification, situated next to one of the camera test grids to allow the camera to view samples collected by the boom up close.


  16. Sample collector boom - can be rotated horizontally and vertically; constructed from two ribbons of stainless steel attached along their edges: when the boom extends the two surfaces separate to form a tube, when retracted they flatten and can be rolled up. A cable running along the center between the two ribbons provides electrical power to the motors at the boom head. The head possesses a scoop with a moveable lid and a temperature sensor and can sieve particles to obtain the size required for teh various tests on the samples. The head has 2 pairs of permanent magnets to collect magnetic particles from the planet surface.


  17. Magnetic sampling instruments - two pairs of permanent magnets on the back of teh head of the sampling boom (each consisting of a ring magnet with a magnetic disc of opposite polarity in the center) were used to sample magnetic particles from the soil. the head is then brought before the magnifying mirror on top of the lander for the cameras to image the particles. A third magnetic pair is located on one of the camera test charts, to collect magnetic atmospheric dust (such as those thrown up by the lander's activities). The latter can be imaged directly by the cameras. the magnets on the collector head can be cleaned by the magnet cleaning brush (which consists of a fork with two twines with wires attached).


  18. Biology instrument - the samp[ling boom can deliver soil samples to the biology instrument, via an inlet funnel, to test for the presence of life. The samples are then apportioned to three separate experimental chambers, such that the experiments can be run in parallel on the same soil scoop, and a control chamber. the first experiment (pyrolytic release experiment) incubates the sample under Martian conditions and with Martian light for a period of time (5 days) in the presence of radioactively labeled carbon dioxide (carbon-14). If organisms in the soil photosynthesise in a similar manner to organisms on Earth, then they should take in the carbon dioxide and 'fix' the carbon by converting it into larger and less volatile organic compounds to use in metabolism. After 5 days the sample is then heated to 625 C to break down any such formed organic molecules and the radioactivity counted. If organisms fixed the (radioactive) carbon supplied then excess radioactivity will be detected in the pyrolysis products. the result was negative: no carbon fixation occurred. In the second experiment (the labeled release experiment) a soil sample was supplied with water and some minimal organic nutrients as a carbon source (formate, lactate, glycine, alanine and glycolic acid) labeled with radioactive carbon-14 and any gases evolved were measured to see if they were radioactive (i.e. contained carbon-14) and the rate of release was measured over time. (Many bacteria ferment and respire organic nutrients and excrete gaseous carbon-containing molecules such as carbon dioxide and methane). The result was positive: a result which has not yet been fully explained but which is not sufficient by itself to prove the existence of life on Mars. Adding further aliquots of nutrient solution did not, however, cause as much subsequent release of carbon-14. Strong oxidising agents in the soil may be responsible. The control analysis was conducted in the light of the positive result. A sample was heated to very high temperatures to sterilise it and the labeled release experiment repeated on the sterile sample. Radioactive carbon was not given off this time, which is compatible with the presence of life in the original sample. the third experiment was the gas exchange experiment. A soil sample was moistened with water and nutrient solution (which was not radioactively labeled) and incubated in darkness for several days and any gases evolved were detected. Initially the sample was above the nutrient solution and so moistened by water vapour only. the result was positive: oxygen and carbon dioxide were given off. More nutrient and water was added, to wet the sample directly, but this did not result in further oxygen evolution. again, this result could be explained if the soil particles were coated with a strong oxidising agent, perhaps produced by the strong UV light on Mars (Mars has no ozone layer).


  19. Meterology sensors - measured atmospheric temperature and pressure, and wind speed and direction. Mounted on a boom which was immovable once deployed. Viking 1 detected a minimum temperature of -85 C just after dawn and a maximum of about -29 C (inferred by extrapolation due to missing data)at 3:30 in the afternoon. Viking 2 was more northern and detected a minimum temperature of -120 C. Wind speeds initially recorded up to 8 m/s and a maximum of 120 km/h (33 m/s); pressure up to 10.8 mbar (Earth: 1013 mbar average pressure at sea level). Three fine-wire thermocouples (sensitive but fragile0 measures atmospheric temperature. A hot film anemometer measures wind speed (contains a thermocouple which measures heat loss due to the flow of fluid (Martian air) over the surface and from this infers fluid speed) by measuring the amount of current supplied to maintain the temperature of the device This device gives an ambiguous measure of wind direction so a quadrant sensor which has a heated core surrounded by four thermocouples at right angles resolved the ambiguity by giving general wind direction (between them these two devices can measure wind direction accurately). The sample collector boom had a temperature sensor in its head which could be moved about by the boom. An aneroid barometer (wind shielded) is located on the bottom of the lander 9modified to function in the low pressures of the Martian atmosphere) measured atmospheric pressure. An aneroid barometer utilises a small box made of flexible alloy. Changes in external pressure change the volume of the box by tiny amounts which are amplified by levers to generate a readable signal. atmospheric pressure varies annually on Mars as carbon dioxide freezes out of the atmosphere to form a polar cap in winter, alternating between the north and south poles of the planet.


  20. Seismology sensor - three orthogonal (at right angles) miniaturised seismometers detect vibrations of the ground transmitted through the feet of the lander. Housed in a cubical container on top of the lander. Vibrations due to lander motors/machinery and winds are subtracted from the signal. the seismometer on Viking 1 failed to function, that on Viking 2 detected very little seismic activity - Mars is currently not very seismically active.


Did you think to include all these things on your robot probe?