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European Space Operations Centre


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Title: European Space Operations Centre

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

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

Rosetta ESA-Cornerstone
  • In November 1993, ESAs approved Rosetta as a
    cornerstone mission in ESAs Horizon 2000 Science
  • 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

In situ measurements
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)

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)

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
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

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

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)

Space Missions to Comets (2)
  • Halley nucleus was full of surprises (size,
    albedo 0.03, jet activity)

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

RosettaReady for Launch Jan 2003
  • Launch Jan. 2003 with Ariane 5 G using EPS delay
  • 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
  • Fully optimised for the mission to Wirtanen
  • 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)

  • 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.

Scientific Payload
  • Remote Sensing
  • OSIRIS (Optical, Spectroscopic and Infrared
    Remote Imaging System)Wide and Narrow angle
  • 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

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.

Scientific Payload (3)
  • Rosetta Lander
  • 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.

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
  • 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
  • January,7, 2003, launch of original Rosetta
  • Recommendation of first ESA internal review
  • No Venus swing-by Maintain mission schedule
  • Launchers to be considered Ariane 5, Ariane 5
    ECA, Proton

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
  • 13-14 May, SPC decided 67P/Ch-G with Ariane 5 G
    and backup 2005 using Proton or AR 5 ECA.

Rosetta Recovery (3)
  • Missions considered for recovery

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
  • A delayed ignition increases the time from launch
    to injection, but substantially increases the
  • Flight software for delayed re-ignition of the
    EPS qualified on AR 503

The Big Jump
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

AR 5 Delayed EPS ignition
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 .

Gravity Assists (2)
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
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.

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?)

01/2003 Mars GA (A window)
Finding solutions
  • Sequential approach
  • Feasible missions
  • Optimization using simple models
  • Full numerical optimization with all mission
  • 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
  • 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

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
  • 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.

  • 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,
  • 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

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
    ?Ea1 ?Ma ?Ed2
    ?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
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

AR 5 Delayed EPS ignitionEstimated performances
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.

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

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

Distances to Earth Sun
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.

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
Planet swing-by (2)
  • Earth -2

Earth -3
  • Orbit Determination and Trajectory Correction
  • 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
  • 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

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,
  • 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, ..)

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)

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

Interplanetary Navigation
  • COVARIANCE ANALYSIS Knowledge and Dispersion
  • 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
Interplanetary Navigation
  • Mars swing-by is critical. Minimum altitude
    selected at 250 km.Very good experience with
    Mars Express

Interplanetary Navigation (2)
  • Last Earth swing-by should be as low as possible,
    baseline 530 km, but not critical

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

  • 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

  • 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.

  • Comet models 2 km radius, 12 hr rotational period

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
  • 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

Approaching 67P (2)
  • Near comet operation phases up to Lander delivery
    do not depend on the comet characteristics.

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

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.

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

Philae Landing (4)
  • Delivery Trajectory and Landing errors (3-?).
    Vimpact lt 120 cm/s

Philae Landing (5)
  • 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.