Scientific instruments of Rosetta's Philae lander
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Scientific instruments of Rosetta's Philae
lander
23 September 2014, by Tim Reyes, Universe Today
functioned as constraints on the instrument
selection that could be packed and carried along on
the journey. There was a maximum weight,
maximum volume, and power. The final mass of
Philae is 100 kg (220 lbs). Its volume is 1 × 1 × 0.8
meters (3.3 × 3.3 × 2.6 ft) about the size of a four
burner oven-range. However, Philae must function
on a small amount of stored energy upon arrival:
1000 Watt-Hours (equivalent of a 100 watt bulb
running for 10 hours). Once that power is drained, it
will produce a maximum of 8 watts of electricity
from Solar panels to be stored in a 130 Watt-Hour
battery.
Without any assurance that they would land
fortuitously and produce more power, the Philae
Rosetta’s Philae lander includes a carefully selected set designers provided a high capacity battery that is
of instruments and is being prepared for a November charged, one time only, by the primary spacecraft
11th dispatch to analyze a comet’s surface. Credit:
solar arrays (64 sq meters) before the descent to
ESA, Composite – T.Reyes
the comet. With an initial science command
When traveling to far off lands, one packs carefully. sequence on-board Philae and the battery power
What you carry must be comprehensive but not so stored from Rosetta, Philae will not waste any time
much that it is a burden. And once you arrive, you to begin analysis—not unlike a forensic analysis—to
must be prepared to do something extraordinary to do a "dissection" of a comet. Thereafter, they utilize
make the long journey worthwhile. the smaller battery which will take at least 16 hours
to recharge but will permit Philae to study
What will the lander do once it arrives and gets 67P/Churyumov-Gerasimenko for potentially
settled in its new surroundings? As Henry David months.
Thoreau said, "It is not worthwhile to go around the
world to count the cats in Zanzibar." So it is with There are 10 science instrument packages on the
the Rosetta lander Philae. With the stage set – a Philae lander. The instruments use absorbed,
landing site chosen and landing date of November scattered, and emitted light, electrical conductivity,
11th, the Philae lander is equipped with a carefully magnetism, heat, and even acoustics to assay the
thought-out set of scientific instruments. properties of the comet. Those properties include
Comprehensive and compact, Philae is a like a the surface structure (the morphology and chemical
Swiss Army knife of tools to undertake the first on- makeup of surface material), interior structure of
site (in-situ) examination of a comet. P67, and the magnetic field and plasmas (ionized
gases) above the surface. Additionally, Philae has
Now, consider the scientific instruments on Philae an arm for one instrument and the Philae main
which were selected about 15 years ago. Just like body can be rotated 360 degrees around its Z-axis.
any good traveler, budgets had to be set which The post which supports Philae and includes a
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impact dampener. and make Philae possible and, together with
Rosetta, fit within payload limits of the launch
CIVA and ROLIS imaging systems. CIVA vehicle, power limitations of the solar cells and
represents three cameras which share some batteries, limitations of the command and data
hardware with ROLIS. CIVA-P (Panoramic) is system and radio transmitters.
seven identical cameras, distributed around the
Philae body but with two functioning in tandem for APXS. This is a Alpha Proton X-ray Spectrometer.
stereo imaging. Each has a 60 degree field of view This is a near must-have instrument of the space
and uses as 1024×1024 CCD detector. As most scientist's Swiss Army Knife. APXS spectrometers
people can recall, digital cameras have advanced have become a common fixture on all Mars Rover
quickly in the last 15 years. Philae's imagers were missions and Philae's is an upgraded version of
designed in the late 1990s, near state-of-the-art, Mars Pathfinder's. The legacy of the APXS design
but today they are surpassed, at least in number of is the early experiments by Ernest Rutherford and
pixels, by most smartphones. However, besides others that led to discovering the structure of the
hardware, image processing in software has atom and the quantum nature of light and matter.
advanced as well and the images may be
enhanced to double their resolution. This instrument has a small source of Alpha particle
emission (Curium 244) essential to its operation.
CIVA-P will have the immediate task, as part of the The principles of Rutherford Back-scattering of
initial autonomous command sequence, of Alpha particles is used to detect the presence of
surveying the complete landing site. It is critical to lighter elements such as Hydrogen or Beryllium
the deployment of other instruments. It will also (those close to an Alpha particle in mass, a Helium
utilize the Z-axis rotation of the Philae body to nucleus). The mass of such lighter elemental
survey. CIVA-M/V is a microscopic 3-color imager particles will absorb a measurable amount of
(7 micron resolution) and CIVA-M/I is a near infra- energy from the Alpha particle during an elastic
red spectrometer (wavelength range of 1 to 4 collision; as happens in Rutherford back-scattering
microns) that will inspect each of the samples that near 180 degrees. However, some Alpha particles
is delivered to the COSAC & PTOLEMY ovens are absorbed rather than reflected by the nuclei of
before the samples are heated. the material. Absorption of an Alpha particle causes
emission of a proton with a measurable kinetic
ROLIS is a single camera, also with a 1024×1024 energy that is also unique to the elemental particle
CCD detector, with the primary role of surveying from which it came (in the cometary material); this
the landing site during the descent phase. The is used to detect heavier elements such as
camera is fixed and downward pointing with an f/5 magnesium or sulfur. Lastly, inner shell electrons in
(f-ratio) focus adjustable lens with a 57 degree field the material of interest can be expelled by Alpha
of view. During descent it is set to infinity and will particles. When electrons from outer shells replace
take images every 5 seconds. Its electronics will these lost electrons, they emit an X-Ray of specific
compress the data to minimize the total data that energy (quantum) that is unique to that elementary
must be stored and transmitted to Rosetta. Focus particle; thus, heavier elements such as Iron or
will adjust just prior to touchdown but thereafter, the Nickel are detectable. APXS is the embodiment of
camera functions in macro mode to early 20th Century Particles Physics.
spectroscopically survey the comet immediately
underneath Philae. Rotation of the Philae body will CONSERT. COmet Nucleus Sounding Experiment
create a "working circle" for ROLIS. by Radio wave Transmission, as the name
suggests, will transmit radio waves into the comet's
The multi-role design of ROLIS clearly shows how nucleus. The Rosetta orbiter transmits 90 MHz
scientists and engineers worked together to overall radio waves and simultaneously Philae stands on
reduce weight, volume, and power consumption, the surface to receive with the comet residing
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between them. Consequently, the time of travel SD2 Sample Drill and Distribution device will
through the comet and the remaining energy of the penetrate the surface and subsurface to a depth of
radio waves is a signature of the material through 20 cm. Each retrieved sample will be a few cubic
which it propagated. Many radio transmissions and millimeters in volume and distributed to 26 ovens
receptions by CONSERT through a multitude of mounted on a carousel. The ovens heat the sample
angles will be required to determine the interior which creates a gas that is delivered to the gas
structure of the comet. It is similar to how one might chromatographs and mass spectrometers that are
sense the shape of a shadowy object standing in COSAC and PTOLEMY. Observations and analysis
front of you by panning one's head left and right to of APXS and ROLIS data will be used to determine
watch how the silhouette changes; altogether your the sampling locations all of which will be on a
brain perceives the shape of the object. With "working circle" from the rotation of Philae's body
CONSERT data, a complex deconvolution process about its Z-axis.
using computers is necessary. The precision to
which the comet's interior is known improves with COSAC Cometary Sampling and Composition
more measurements. experiment. The first gas chromatograph (GC) I
saw was in a college lab and was being used by
MUPUS. Multi-Purpose Sensor for Surface and the lab manager for forensic tests supporting the
Subsurface Science is a suite of detectors for local police department. The intent of Philae is
measuring the energy balance, thermal and nothing less than to perform forensic tests on a
mechanical properties of the comet's surface and comet hundred of million of miles from Earth. Philae
subsurface down to a depth of 30 cm (1 foot). is effectively Sherlock Holmes' spy glass and
There are three major parts to MUPUS. There is Sherlock is all the researchers back on Earth. The
the PEN which is the penetrator tube. PEN is COSAC gas chromatograph includes a mass
attached to a hammering arm that extends up to spectrometer and will measure the quantities of
1.2 meters from the body. It deploys with sufficient elements and molecules, particularly complex
downward force to penetrate and bury PEN below organic molecules, making up comet material.
the surface; multiple hammer strokes are possible. While that first lab GC I saw was closer to the size
At the tip, or anchor, of PEN (the penetrator tube) is of Philae, the two GCs in Philae are about the size
an accelerometer and standard PT100 (Platinum of shoe boxes.
Resistance Thermometer). Together, the anchor
sensors will determine the hardness profile at the PTOLEMY. An Evolved Gas Analyzer [ref], a
landing site and the thermal diffusivity at the final different type of gas chromatograph. The purpose
depth [ref]. As it penetrates the surfaces, more or of Ptolemy is to measure the quantities of specific
less deceleration indicates harder or softer isotopes to derive the isotopic ratios, for example, 2
material. The PEN includes an array of 16 thermal parts isotope C12 to one part C13. By definition,
detectors along its length to measure subsurface isotopes of an element have the same number of
temperatures and thermal conductivity. The PEN protons but different numbers of neutrons in their
also has a heat source to transmit heat to the nuclei. One example is the 3 isotopes of Carbon,
cometary material and measure its thermal C12, C13 and C14; the numbers being the number
dynamics. With the heat source off, detectors in of neutrons. Some isotopes are stable while others
PEN will monitor the temperature and energy can be unstable – radioactive and decay into stable
balance of the comet as it approaches the Sun and forms of the same element or into other elements.
heats up. The second part is the MUPUS TM, a What is of interest to Ptolemy investigators is the
radiometer atop the PEN which will measure ratio of stable isotopes (natural and not those
thermal dynamics of the surface. TM consists of affected by, or that result from, radioactive decay)
four thermopile sensors with optical filters to cover for the elements H, C, N, O and S, but particularly
a wavelength range from 6-25 µm. Carbon. The ratios will be telltale indicators of
where and how comets are created. Until now,
3/6spectroscopic measurements of comets to compartment showing the location of COSAC, PTOLEMY,
determine isotopic ratios have been from a distance the CONSERT antennas, the SESAME dust sensor and
and the accuracy has been inadequate for drawing ÇIVA cameras. Philae is about the size of a dishwasher
or four burner oven. Credit: “Capabilities of Philae, the
firm conclusions about the origin of comets and
Rosetta Lander, J. Biele, S. Ulamec, September 2007
how comets are linked to the creation of planets
and the evolution of the Solar Nebula, the
Next is the SESAME/PP detector – the Permittivity
birthplace of our planetary system surrounding the
Probe. Permittivity is the measure of the resistance
Sun, our star. An evolved gas analyzer will heat up
a material has to electric fields. SESAME/PP will
a sample (~1000 C) to transform the materials into
deliver an oscillating (sine wave) electric field into
a gaseous state which a spectrometer can very
the comet. Philae's feet carry the receivers –
accurately measure quantities. A similar instrument,
electrodes and AC sine generators to emit the
TEGA (Thermal Evolved Gas Analyzer) was an
electric field. The resistance of the cometary
instrument on Mars Phoenix lander.
material to about a 2 meter depth is thus measured
providing another essential property of the comet –
SESAME Surface Electrical Sounding and
the permittivity.
Acoustic Monitoring Experiment This instrument
involves three unique detectors. The first is the
The third detector is called SESAME/DIM. This is
SESAME/CASSE, the acoustic detector. Each
the comet dust counter. There were several
landing foot of Philae has acoustic emitters and
references used to compile these instrument
receivers. Each of the legs will take turns
descriptions. For this instrument, there is, what I
transmitting acoustic waves (100 Hertz to KiloHertz
would call, a beautiful description which I will simply
range) into the comet which the sensors of the
quote here with reference. "The Dust Impact
other legs will measure. How that wave is
Monitor (DIM) cube on top of the Lander balcony is
attenuated, that is, weakened and transformed, by
a dust sensor with three active orthogonal (50 × 16)
the cometary material it passes through, can be
mm piezo sensors. From the measurement of the
used along with other cometary properties gained
transient peak voltage and half contact duration,
from Philae instruments, to determine daily and
velocities and radii of impacting dust particles can
seasonal variations in the comet's structure to a
be calculated. Particles with radii from about 0.5 µm
depth of about 2 meters. Also, in a passive
to 3 mm and velocities from 0.025–0.25 m/s can be
(listening) mode, CASSE will monitor sound waves
measured. If the background noise is very high, or
from creaks, groans inside the comet caused
the rate and/or the amplitudes of the burst signal
potentially by stresses from Solar heating and
are too high, the system automatically switches to
venting gases.
the so called Average Continuous mode; i.e., only
the average signal will be obtained, giving a
measure of the dust flux." [ref]
ROMAP Rosetta Lander Magnetometer and
Plasma detector also includes a third detector, a
pressure sensor. Several spacecraft have flown by
comets and an intrinsic magnetic field, one created
by the comet's nucleus (the main body) has never
been detected. If an intrinsic magnetic field exists, it
is likely to be very weak and landing on the surface
would be necessary. Finding one would be
extraordinary and would turn theories regarding
comets on their heads. Low and behold Philae has
a fluxgate magnetometer.
Side view schematics of the inner structure of the lander
4/6The Earth's magnetic field surrounding us is kind of like a white sheet draped over a Halloween
measured in the 10s of thousands of nano-Teslas trick-or-treater but without eye holes.
(SI unit, billionth of a Tesla). Beyond Earth's field,
the planets, asteroids, and comets are all immersed So at P67's surface, Philae's ROMAP/SPM
in the Sun's magnetic field which, near the Earth, is detector, electrostatic analyzers and a Faraday Cup
measured in single digits, 5 to 10 nano-Tesla. sensor will measure free electrons and ions in the
Philae's detector has a range of +/- 2000 not so empty space. A "cold" plasma surrounds the
nanoTesla; a just in case range but one readily comet; SPM will detect ion kinetic energy in the
offered by fluxgates. It has a sensitivity of 1/100th range of 40 to 8000 electron-volts (eV) and
of a nanoTesla. So, ESA and Rosetta came electrons from 0.35 eV to 4200 eV. Last but not
prepared. The magnetometer can detect a very least, ROMAP includes a pressure sensor which
minute field if it's there. Now let's consider the can measure very low pressure – a millionth or a
Plasma detector. billionth or less than the air pressure we enjoy on
Earth. A Penning Vacuum gauge is utilized which
ionizes the primarily neutral gas near the surface
and measures the current that is generated.
Philae will carry 10 instrument suites to the surface
of 67P/Churyumov-Gerasimenko but altogether the
ten represent 15 different types of detectors. Some
are interdependent, that is, in order to derive
certain properties, one needs multiple data sets.
Landing Philae on the comet surface will provide
the means to measure many properties of a comet
for the fist time and others with significantly higher
accuracy. Altogether, scientists will come closer to
understanding the origins of comets and their
contribution to the evolution of the Solar System.
Philae’s APXS – Alpha Proton X-Ray Spectrometer.
Credit: Inst. for Inorganic Chemistry & Analytical
Chemistry, Max-Planck Institute for Chemistry Source: Universe Today
Much of the dynamics of the Universe involves the
interaction of plasma – ionized gases (generally
missing one or more electrons thus carrying a
positive electric charge) with magnetic fields.
Comets also involve such interactions and Philae
carries a plasma detector to measure the energy,
density and direction of electrons and of positively
charged ions. Active comets are releasing
essentially a neutral gas into space plus small solid
(dust) particles. The Sun's ultraviolet radiation
partially ionizes the cometary gas of the comet's
tail, that is, creates a plasma. At some distance
from the comet nucleus depending on how hot and
dense that plasma is, there is a standoff between
the Sun's magnetic field and the plasma of the tail.
The Sun's B field drapes around the comet's tail
5/6APA citation: Scientific instruments of Rosetta's Philae lander (2014, September 23) retrieved 18 May 2015
from http://phys.org/news/2014-09-scientific-instruments-rosetta-philae-lander.html
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