European Space Operations Centre

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European Space Operations Centre
Rosetta.Quick Mission re-Design of Europes
comet chaser
ATA, Barcelona, July, 2004

J. Rodriguez-Canabal, ESA, OPS-GA
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Contents

• Rosetta, Comets, and Space Missions
• Rosetta Original Mission. Spacecraft and Payload
• Re-design of New Mission
• Launch with Ariane 5
• Gravity Assists. Optimization and models.
• Trajectory description. Navigation.
• Fly-by of Lutetia and Steins.
• Approaching 67P/Churyumov-Gerasimenko
• Landing of Philae

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Rosetta ESA-Cornerstone

• In November 1993, ESAs approved Rosetta as a
  cornerstone mission in ESAs Horizon 2000 Science
  Programme.
• Rosetta will be the first mission
• To orbit a comet nucleus.
• To fly alongside a comet as it heads closer to
  the Sun.
• To observe from very close proximity how the
  frozen comet nucleus is transformed by the heat
  of the Sun.
• To send a Lander for controlled touchdown on the
  comet nucleus surface.
• To obtain images from a comets surface and to
  perform in-situ analysis
• To fly near Jupiters orbit using solar cells as
  power source.
• To close encounter two asteroids of the asteroid
  belt

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In situ measurements
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Why the name Rosetta?

• The Rosetta stone (1799) was the key to
  deciphering the old hieroglyphics writing of
  ancient Egypt.
• Decree to honour Ptolemy V (210-180 BC)
• Obelisk from Island of Philae (1815)

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Why to go to a comet?

• Comets have always attracted the attention of
  mankind. The apparitions are recorded in
  documents going back millennia.
• Comets appear suddenly and have been interpreted
  as good signs or as bad omens announcing great
  disgraces.Battle of Hastings (1066 AD)

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Why to go to a comet? (2)

• Are comet dangerous for us?. What happens if a
  comet hit the Earth?. Dinosaurs extinction event
  Chicxulub impact crater in Yucatan (discovered
  1991). We cannot do too much about it !

Meteor Crater
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Why to go to a comet? (3)

• A comet is a celestial body originating very far
  away from the Sun
• Oort cloud, far beyond Pluto (50000 AU)
• Kuiper Belt, beyond Neptune ( 30-100 AU)

• nucleus composed of ice, dust, of a size between
  a few hundred m up to a few km. Carbon
  compounds.Near the Sun it develops a coma (?
  100000 km), and tails (dust, ion) several Mkm

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Why to go to a comet? (4)

• Scientist wants to study comets because these are
  what is left of the primitive cloud. They are
  time capsules preserving the physical and
  chemical conditions that existed when the planets
  were formed 4.5 billions of years ago.
• Comets could have provided water and organic
  material to the Earth.
• Comets can help to understandconditions of
  formation of the solar system

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Space Missions to Comets

• To Halley
• Giotto, 1986, 600 km, 68 km/s and comet
  Grigg-Skjellerup, 1992, 200 km. (ESA)
• VEGA-1 VEGA-2, 9000 km, 78 km/s1986. (RUS)
• Sakigake Suisei, 7 Mkm, 150000 km,1986. (JAP)

Giotto
VEGA
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Space Missions to Comets (2)

• Halley nucleus was full of surprises (size,
  albedo 0.03, jet activity)

Giotto
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Space Missions to Comets (3)

• ISEE-C/ICE to comet Giacobini-Zinner, 1985, NASA,
  8000 km
• Deep Space, 2001, comet Borrelli
• Star Dust comet Wild-2, 2004, 240 km, 2.6 AU

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RosettaReady for Launch Jan 2003

• Launch Jan. 2003 with Ariane 5 G using EPS delay
  ignition.
• Use of 3 Gravity Assists (Mars-Earth-Earth).
  Fly-by of 2 asteroids Siwa and Otawara.
• Large distance from Sun, 5.3 AU, and from Earth
  for long periods.
• Arrival at Wirtanen on Dec. 2011. Orbiting around
  the comet nucleus for 1.5 years (up to
  perihelion)
• Fully optimised for the mission to Wirtanen
  fixed
• Max. min. distances to Sun. (0.9 AU 5.3 AU)
• Propellant (660 kg of MMH. 1030 kg of NTO)
• Lander (landing impact velocity lt 1 m/s)

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Spacecraft

• Wet launch mass 3064 kg
• Solar power (300 W-8 kW)
• 24 x 10 N bipropellant thrusters
• 2 Navigation cameras, 2 Star trackers, 4 Sun
  sensors, 9 Laser gyroscopes, 9 accelerometers
• HGA of 2.2 m, MGA, LGA, S-X band
• Data storage 20Gbits.

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Scientific Payload

• Remote Sensing
• OSIRIS (Optical, Spectroscopic and Infrared
  Remote Imaging System)Wide and Narrow angle
  camera.
• ALICE (UV spectrometer) Analyses gases in the
  coma and tail. Production rates of water and CO
  and CO2. Comet surface.
• VIRTIS (Visible and IR Thermal Imaging
  Spectrometer). Maps solids and temperature of
  comet surface.
• MIRO (microwave Instrument). Abundance of major
  gases, surface outgassing rate, nucleus
  subsurface temperature.
• Composition Analysis
• ROSINA (RO Spectrometer for Ion and Neutral
  Analysis) Composition of atmosphere and
  ionosphere, velocities of charged particles, and
  reaction between them.
• COSIMA (Cometary Secondary Ion Mass Analyser).
  Dust grains characteristics
• MIDAS (Micro-Imaging Dust Analysis System) Dust
  environment grain morphology

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Scientific Payload (2)

• Nucleus large structure
• CONSERT (Comet Nucleus Sounding Experiment by
  Radiowave Transmission). Nucleus tomography
• Dust flux, mass distribution
• GIADA (Grain Impact Analyser and Dust
  Accumulator). Number, mass, momentum and velocity
  distribution of dust grains.
• Plasma environment
• RPC (Rosetta Plasma Consortium). 5 sensors
  measure the physical properties of the nucleus,
  structure of the inner coma, cometary activity,
  interaction with solar wind.
• Radio science
• RSI (Radio Science Investigation). S-X band,
  measure mass, density of nucleus. Solar corona
  during conjunction events.

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Spacecraft
VIRTIS
COSIMA
OSIRIS
MIDAS
ALICE
CONSERT
MIRO
ROSINA
GIADA
RPC
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Scientific Payload (3)

• Rosetta Lander
• CONSERT
• ROMAP (RO Lander Magnetometer and Plasma
  Monitor). Local magnetic field and comet/solar
  wind interaction.
• MUPUS (Multi-Purpose Sensors for Surface and
  Subsurface Science). Sensors to measure density,
  thermal and mechanical properties of surface.
• SESAME (Surface Electrical, Seismic and Acoustic
  Monitoring Experiment). Electric, seismic and
  acoustic monitoring. Dust impact monitoring.
• APXS (Alpha, Proton, X-ray Spectrometer).
  Elemental composition of surface.
• ÇIVA/ROLIS (visible IR imaging). 6 cameras and
  spectrometer. Composition, texture, albedo of
  samples from the surface.
• COSAC (Cometary Sampling and Composition). Gas
  analyser for complex organic molecules
• Modulus Ptolemy. Gas chromatography isotopic
  ratios of light elements.
• SD2 (Sample and Distribution Device). Drills 20
  cm deep, collect and deliver samples.

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Rosetta Recovery

• Failure of Ariane Flight 157 on 11.12.2002 led to
  intense work to study alternative scenarios in
  case of cancellation of Rosetta launch on Flight
  158.
• Fixed constraints on spacecraft mass,
  propellant, power, thermal, mechanical, Telemetry
• Use of periodically up-dated database of extended
  alternative mission.
• Very good collaboration of ESA, Industry, and
  Scientists
• January,7, 2003, launch of original Rosetta
  cancelled
• Recommendation of first ESA internal review
  27.01.2003
• No Venus swing-by Maintain mission schedule
• Launchers to be considered Ariane 5, Ariane 5
  ECA, Proton

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Rosetta Recovery (2)

• 25-26 Feb. 2003 ESAs Science Programme Committee
• 67P/Churyumov-Gerasimenko launcher Ariane 5
  launch Feb. 2004 with launch backup in 2005
  using Proton.
• 46P/Wirtanen launcher Proton launch Jan. 2004.
• Intense activity on
• Observation of 67P/Ch-G using HST, and ESO
• Lander constraints. Rebound on 46P/Wirtanen,
  crash on 67P/Ch-G
• Spacecraft constraints. Unloading of MMH, but not
  of NTO. Danger of tanks corrosion
• Launcher performances payload, fairing
  dimensions
• 13-14 May, SPC decided 67P/Ch-G with Ariane 5 G
  and backup 2005 using Proton or AR 5 ECA.

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Rosetta Recovery (3)

• Missions considered for recovery

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Ariane 5 EPS Delayed Ignition

• The engine of the upper stage, EPS, of Ariane 5
  is ignited after cut-off of the central core
  engine, but it can be re-started or its ignition
  delayed.
• A delayed ignition increases the time from launch
  to injection, but substantially increases the
  performance
• Flight software for delayed re-ignition of the
  EPS qualified on AR 503

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The Big Jump
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AR 5 Delayed EPS ignition

• Only 2 Launcher Flight Programs needed for a
  launch period of 21 days (26.02 17.03.2004)
  with 2 launch attempts per day. Original mission
  had 14 FP.
• Earth escape targets V? 3.545 km/s, ?? 2

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AR 5 Delayed EPS ignition
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Gravity Assists

• Gravity Assists have been used since 1973 Mariner
  10 mission, that flew by Venus in its way to
  Mercury.Later Pioneer 11 to Saturn, Voyager 1
  2 (Jupiter, Saturn, Uranus, Neptune), Galileo to
  Jupiter, Ulysses out of the ecliptic, Vega, ICE
  to comet Giacobini-Zinner, Giotto, etc.
• Gravity Assist or swing-by is a significant
  trajectory perturbation due to a close approach
  to a celestial body. Foundations laid down since
  early 20th century. Applications to missions
  described by 1965.
• Gravity assist is based on the deflection of the
  arrival relative velocity, V?a, to the departure
  relative velocity V?d, with
  V?a V?d .

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Gravity Assists (2)
Va?
Vra?
?V EGA
Swing-by
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Gravity Assists (3)

• The change of velocity is Vd Va (V?d - V?a
  ).
• The deflection angle is given by sin?/2 1 /
  (1r? V?2 /?)The change of velocity is ?v 2
  V? sin?/2 2 V? ?/(? r? V?2 )

r? planet radius, V?a Hohmann transfer
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Gravity Assists (4)

• The ?VEGA (?V-Earth Gravity Assist) is the use of
  a swingby of the Earth after a ?V manoeuvre.
  (Hollenbeck 1975).
• Launch from Earth into a 2 or 3 years
  heliocentric trajectory (V? lt 5 km/s), followed
  by a manoeuvre near aphelion (few hundred meters)
  to target either before or after perihelion
  produces a relative V? 10 km/s.

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Finding the good way there

• Comet of interest perihelion ? 1 AU, Aphelion ?
  5-6 AU
• Departure from Earth or last Earth swing-by with
  relative velocity of 9-11 km/s. Gravity Assists
  is needed
• Delta-V Earth GA high propellant consumption (3
  years round trip, with launch at V? 3.4 km/s,
  900 m/s needed to reach the 9 km/s)
• Mars GA Earth GA - launch at 3.5 km/s, one
  revolution before Mars, or at3.9 km/s, one
  revolution between Mars and Earth return.
• Venus GA thermal problems with the spacecraft
  are confirmed.
• The strategy Launch Earth within one year can
  be used to solve constraints from launcher
  performance (modification of V?)

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COMET RENDEZ-VOUS STRATEGIES
01/2003 Mars GA (A window)
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Finding solutions

• Sequential approach
• Feasible missions
• Optimization using simple models
• Full numerical optimization with all mission
  constraints
• Given a sequence of swing-by, and the number of
  revolutions between swing-by, a discrete search
  provides the swing-by times.
• Techniques to accelerate the search keep tables
  of Lambert solutions, prune trajectories, order
  results.
• Pay attention to - Number of revolutions in
  between swing-by, and cases - singular cases
  multiple swing-by of same body at 180 or 360
• Using a constrained non-linear parameter
  optimisation method, optimise sequence of events,
  launch conditions, and introduce Deep Space
  Manoeuvres to force to zero any manoeuvres at
  swing-by.

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Finding solutions

• Parameter optimisation min F(x), x?En, with qi(x)
  0, gi(x) gt 0.To ensure convergence, it is
  important to make a good selection of the
  variables, the constraints, and the cost
  function.
• The cost function is typically the useful mass,
  or the sum of the modulus of the ?V with
  weighting factors.
• The variables can be position and velocity
  vectors at some points in the trajectory, dates,
  impact vectors, angles, orbital elements, etc.
• The constraints describe the initial/final
  conditions, trajectory matching at selected
  points, minimum swing-by height, technical
  constraints to control behaviour of the solution.

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Optimization

• Problem is defined asmin F(x), x?En, gk(x)0,
  k1,q, gk(x)gt0, kq1,,m
• Sequential Quadratic Programming is a generalized
  Newtons method that, starting in a given point,
  finds a better point by minimizing a quadratic
  model of the problem.Packages OPTIMA, MATLAB,
  NPSOL, NLPQL, SQP
• OPTIMA penalty function P(x,r)F(x) g(x)T
  g(x)/r.Quadratic sub-problem min ½ pT B p
  fTp, with Ap-½ r ? - g where ? (½ r I A
  B-1 AT) (A B-1 f g) f ? F(x), A ?g/?x, B
  ?2F2/r ? gi ?2 gi

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Selection of model

• Rosetta 67P. Patched conics. No asteroids. Free
  Launch date and comet rendezvous date.L DSM1
  E1 DSM2 M E2 DSM3 E3 DSM4
  Comet TL TDSM1 TE1
  TDSM2 TM TE2
  TDSM3 TE3 TDSM4
  Tc
  ?Ea1 ?Ma ?Ed2
  ?Ed3
  ?Ea1 ?Ma
  ?Ed2 ?Ed3RDSM4 lt 4.4
  AU (Solar Power)RpE1 , RpE2 , RpE3 gt RminE ,
  RpM gt RminM ?Vswing-by 0.TC gt TC
  min, (? RC lt RC min )V?L lt V?max,
  (Ariane 5 performances)

Variables 18
Constraints 7
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Selection of model (2)

• Arc M-E2, Lambert ? V?dM , V?aM , V?E2a , V?E2d
• Arc DSM2-M, back propagation ? RDSM2
• Arc E1-DSM2, Lambert ? ?VDSM2 , V?E1d , V?E1a
• Arc DSM1-E1, back propagation ? RDSM1
• Arc L-DSM1, Lambert ? V?L , ?VDSM1
• Arc E2-DSM3, forwards propagation ? RDSM3
• Arc DSM3-E3, Lambert ? ?VDSM3 , V?E3a , V?E3d
• Arc E3-DSM4, forwards propagation ? RDSM4
• Arc DSM4-C, Lambert ? ?VDSM4 , ?VRDV
• V?L ? ML ? ? ?Vi /ISp ? MRDV

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AR 5 Delayed EPS ignitionEstimated performances
?
?
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Selection of model (3)

• Similarly can be solved the Launch Window problem
  where the fixed parameters are TL , TC , V?L ,
  ?L .
• 18 variables, 5 constraints.

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The acrobatics

• Launch-Earth-Mars-Earth-Earth-Comet
• L-E1, 370 d, 170 m/sE1-M, 730 dM-E2, 260
  dE2-E3, 727 dE3-DSM,540 m/sDSM-67P, 1110 d
• Near comet, 445 d
• 7160 M km !!Earth 940 Mkm/year

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Trajectory

• Trajectory Earth-Earth
• Manoeuvre Optimisation
• DSM1.1 Perihelion (6/2004)
• DSM2.1 Aphelion (12/2004)
• Variation with launch day

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Events
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Distances to Earth Sun
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Rosetta got an extra

• The propellant left for Near Comet operations,
  after rendezvous with 67P, varies by 20 kg, (33
  of allocation at comet).After a delay of 5 days,
  Rosetta was launched on March, 2.

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Planet swing-by

• Conditions at the first Earth swing-by depends on
  the day of launch
• Conditions at Mars swing-by or at subsequent
  Earth swing-by are very fixed

Earth -1
Mars
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Planet swing-by (2)

• Earth -2

Earth -3
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Navigation

• Orbit Determination and Trajectory Correction
  Manoeuvres
• Measurements
• Distance measurement (radio tracking range) (2-5
  m error)
• Relative velocity spacecraft Ground Station
  (Doppler) (1 mm/s error)
• Delta-DOR (Differential one-way ranging) ( 20
  cm error)
• Onboard Optical Measurements (Camera, star
  trackers)
• Delta-DOR measurements use spacecraft signal
  simultaneously received by 2 ground stations. It
  is a type of Very Long Baseline Interferometry
  measurement and determines, with very high
  accuracy, the spacecraft position in the
  plane-of-sky

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Navigation (2)

• By using the signal from a nearby quasar, both GS
  cancel the common error sources (atmosphere,
  propagation media, clocks)
• Delta-DOR measurements are very useful in
  critical phases of a mission planet approach,
  prior to a swing-by, orbit insertion, landing,
  etc.
• Other sources of errors are
• Station position ( lt 1 m )
• Signal propagation (troposphere, ionosphere,
  spacecraft transponder)
• Modelling of forces (planets, solar radiation
  pressure, out-gassing, open thrusters, ..)

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Navigation (3)

• Effect of biases. Measurement equations z A
  x B y ?where z measurements residuals
  (observed computed). x variables to be
  estimated. y variables known to be biases and
  not estimated.
• Estimated xe (AT W A) -1 (AT W) z W-1 E
  (? ? T)
• Computed error covariance P E (xe x, (xe
  x)T (AT W AC1) 1
• Consider covariance Pc P S Py ST , S -P
  AT W B , Py E (Y YT)

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Correcting the Launcher

• Launcher injection errors corrected by manoeuvres
  that re-optimises the full trajectory.Large
  correction manoeuvre may be needed. Difficult
  first acquisition from Kourou

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Interplanetary Navigation

• COVARIANCE ANALYSIS Knowledge and Dispersion
  Matrixes

• Deterministic Manoeuvres
• - Implementation Errors
• - No re-optimisation
• - Degradation of Knowledge
• Mid-Course Corrections
• - Improve dispersion errors at target
• - Implementation errors -Degradation of knowledge

Dispersion and Knowledge mapped at pericentre of
1st Earth swing-by
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Interplanetary Navigation

• Mars swing-by is critical. Minimum altitude
  selected at 250 km.Very good experience with
  Mars Express

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Interplanetary Navigation (2)

• Last Earth swing-by should be as low as possible,
  baseline 530 km, but not critical

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Interplanetary Navigation

• Propellant Assessment
• Ariane 5 Launching Accuracy
• - Position 39 Km, mostly Along-Track
• - Velocity 36 m/s, mostly radial
• LIC - Launcher Injection Correction
• - 4 days after injection
• Mid-Course Corrections
• - About 17 targetting conditions at pericentre of
  planets swing-by

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Asteroids

• The asteroids to be explored were decided after
  launch.The excellent performance of Ariane 5,
  error in ?V??lt 1.8 m/s, and the optimal launch
  day allow to include 2 asteroids fly-by along the
  mission

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67P/Churyumov-Gerasimenko

• Comet discovered in 1969 by K. Churyumov and S.
  Gerasimenko.Up to 1840 the perihelion was 4 AU.
  A Jupiter encounter reduced it to 3 AU. In 1959
  another Jupiter encounter reduced it to its
  current 1.28 AU.
• Orbital period is about 6.6 years.
• Well observed in 1976, 1982, 1989, and 2002.
• Estimated diameter of nucleus 5 x 3 km.
• Relatively active object. Dust production 60
  220 kg/s.Ratio gas / dust 2.

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67P/Churyumov-Gerasimenko

• Comet models 2 km radius, 12 hr rotational period

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Approaching 67P

• Start of comet rendezvous when distance to Sun
  4 AU
• Operations based on using only the NAVCAM for
  comet detection.Earliest start at (3 Mkm)
• As an improvement OSIRIS could be used for comet
  detection.
• Early comet detection can be used to advance the
  Orbit Insertion Point (OIP). Start of comet
  Global Mapping Phase.
• Power will not drive the earliest start of RV
  operations.Power limit is at 4.4 AU.
• Earliest start of phase is driven by available
  propellant.

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Approaching 67P (2)

• Near comet operation phases up to Lander delivery
  do not depend on the comet characteristics.

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Approaching 67P (3)

• The approach from 600000 km to 40 km, and the
  reduction of the relative velocity from 780 m/s
  to 0.3 m/s will be performed in about 3 months.
• During this period Rosetta will
• get comet images to determine nucleus size,
  shape, rotation, relative positionvelocity,
  identification of landmarks
• avoid cometary debris, and eclipses
• Keep Earth communications
• Keep safety

60
Mapping 67P

• Mapping and selection of landing sites -
  Orbit safety - avoid debris, jets - ensure
  no eclipse, no occultation - cover at least
  80 of illuminated surface, good
  illumination conditions, - volume of data to
  be transmitted to Earth - fly over 5
  selected areas at required illumination
  conditions, and resolution.

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Mapping 67P (2)
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Mapping 67P (3)
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Philae Landing
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Philae Landing (2)

• Montecarlo simulations by MPIAe (M. Hilchenbach,
  Cologne 2003)

Montecarlo calculation for target
comets Variation of radii and densities
still assuming landing on inactive comet, about
3 AU away from the sun.
65
Philae Landing (3)

• Lander Delivery, 12 d- arrive at delivery point
  in a safe orbit, with the proper attitude and
  velocity.- Constraints on Ground visibility,
  Eclipse, Solar Aspect- Mechanical Separation
  System constraints ejection ?V.- Active Descent
  System constraints ?V vertical- SSP landing
  constraints V impact, angles, landing errors

66
Philae Landing (4)

• Delivery Trajectory and Landing errors (3-?).
  Vimpact lt 120 cm/s

67
Philae Landing (5)
68
Conclusions

• Thanks to a very intensive collaboration between
  all people and institutions involved in Rosetta a
  new mission to 67P/Churyumov-Gerasimenko has been
  defined in a very short time.
• 
  
• 
  THANKS FOR YOUR ATTENTION