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European Space Operations Centre. Rosetta. Quick Mission re-Design of Europe’s comet chaser. ATA, Barcelona, July, 2004. J. Rodriguez-Canabal, ESA, OPS-GA. Contents. Rosetta, Comets, and Space Missions Rosetta Original Mission. Spacecraft and Payload Re-design of New Mission

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    1. European Space Operations Centre Rosetta.Quick Mission re-Design of Europe’s comet chaser ATA, Barcelona, July, 2004 J. Rodriguez-Canabal, ESA, OPS-GA

    2. 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

    3. Rosetta ESA-Cornerstone • In November 1993, ESA’s approved Rosetta as a cornerstone mission in ESA’s 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 comet’s surface and to perform in-situ analysis • To fly near Jupiter’s orbit using solar cells as power source. • To close encounter two asteroids of the asteroid belt

    4. In situ measurements

    5. 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)

    6. 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)

    7. 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

    8. 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

    9. 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

    10. 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

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

    12. 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

    13. 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 < 1 m/s)

    14. 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.

    15. 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

    16. 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.


    18. 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.

    19. 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

    20. Rosetta Recovery (2) • 25-26 Feb. 2003 ESA’s 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.

    21. Rosetta Recovery (3) • Missions considered for recovery

    22. 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

    23. The Big Jump

    24. 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°

    25. AR 5 Delayed EPS ignition

    26. 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 |.

    27. VPlanet Vrd  Vd VPlanet VPlanet Vd VPlanet Va Gravity Assists (2) Va Vra Swing-by V EGA

    28. Gravity Assists (3) • The change of velocity is Vd = Va + (Vd - Va ). • The deflection angle is given by: sin/2 = 1 / (1+r V2 /)The change of velocity is: v = 2 Vsin/2 = 2 V /(+ r V2 ) r = planet radius, Va = Hohmann transfer

    29. 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< 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.

    30. 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)

    31. COMET RENDEZ-VOUSSTRATEGIES 01/2003: Mars GA (A window)

    32. 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.

    33. Finding solutions • Parameter optimisation min F(x), xEn, with qi(x) = 0, gi(x) > 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.

    34. Optimization • Problem is defined as:min F(x), xEn, gk(x)=0, k=1,…q, gk(x)>0, k=q+1,…,m • Sequential Quadratic Programming is a generalized Newton’s 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= 2F+2/r  gi 2 gi

    35. 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 CometTL TDSM1 TE1TDSM2TMTE2TDSM3TE3TDSM4TcEa1 Ma Ed2 Ed3Ea1 Ma Ed2 Ed3RDSM4 < 4.4 AU (Solar Power)RpE1 , RpE2 , RpE3 > RminE , RpM > RminM; Vswing-by =0.TC > TC min, ( RC < RC min )VL < Vmax, (Ariane 5 performances) Variables 18 Constraints 7

    36. 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

    37. AR 5 Delayed EPS ignitionEstimated performances  

    38. 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.

    39. 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

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

    41. Events

    42. Distances to Earth & Sun

    43. 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.

    44. 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

    45. Planet swing-by (2) Earth -2 Earth -3

    46. 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

    47. 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 ( < 1 m ) • Signal propagation (troposphere, ionosphere, spacecraft transponder) • Modelling of forces (planets, solar radiation pressure, out-gassing, open thrusters, ..)

    48. 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 A+C1) –1 • Consider covariance: Pc = P + S Py ST , S = -P AT W B , Py = E (Y YT)

    49. 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

    50. Interplanetary Navigation • Deterministic Manoeuvres - Implementation Errors - No re-optimisation - Degradation of Knowledge • Mid-Course Corrections - Improve dispersion errors at target - Implementation errors -Degradation of knowledge • COVARIANCE ANALYSIS – Knowledge and Dispersion Matrixes Dispersion and Knowledge mapped at pericentre of 1st Earth swing-by