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European Space Operations Centre

J. Rodriguez-Canabal, ESA,

OPS-GA

Rosetta.Quick Mission re-Design of Europe’s comet

chaser

ATA, Barcelona, July, 2004

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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, 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

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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) VEG

A

Giotto

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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 < 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

OSIRIS

ALICE

VIRTIS

MIRO

ROSINA

COSIMAMIDAS

CONSERT

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 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.

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Rosetta Recovery (3)

Missions considered for recovery

Launch RV Perih.

Vinf

km/s

Dec.

deg.

DV

m/s

min/Max

dist.

Aster.

Baseline

Siwa-Wirta.

2003/01

2012/02

2013/07

3.40 0 149

00.93/5.3 Siwa

Chur-Gera.

2004/02

2014/11

2015/08 3.5 -3

1590-1790

0.88/5.3

Lutetia Rhodia

Wirtanen

2004/01

2012/02

2013/07 5.0 10

.

1120-1750

0.9/5.3

Siwa Isis Julia

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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 | =| Vd |.

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Gravity Assists (2)

Vra

VPlan

et

VPla

netVPla

net

Va

Vd

Vrd

Va

VPlan

et

Vd

V EGA

Swing-by

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Gravity Assists (3)

The change of velocity is Vd = Va + (Vd

- Va ).

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

V2 )Planet /2 v (km/s)

Venus 61.6 4.77

Mars 39.9 3.40

Jupiter 85.8 11.25

r = planet radius, Va = 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

< 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), xEn, 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.

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Optimization

Problem is defined as:min F(x), xEn, 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

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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 Ed3

RDSM4 < 4.4 AU (Solar Power)RpE1 , RpE2 , RpE3 > RminE , RpM > RminM; Vswing-by

=0.TC > TC min, ( RC < RC min )VL < Vmax, (Ariane 5 performances)

Varia

bl

es 1

8C

on

strain

ts 7

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Selection of model (2) Arc M-E2, Lambert VdM

, VaM , VE2a

, VE2d

Arc DSM2-M, back propagation RDSM2

Arc E1-DSM2, Lambert VDSM2 , VE1d

, VE1a

Arc DSM1-E1, back propagation RDSM1

Arc L-DSM1, Lambert VL , VDSM1

Arc E2-DSM3, forwards propagation RDSM3

Arc DSM3-E3, Lambert VDSM3 , VE3a

, VE3d

Arc E3-DSM4, forwards propagation RDSM4

Arc DSM4-C, Lambert VDSM4 , VRDV

VL 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 , VL , 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

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

-1.5 -1.0 -0.5 0.0 0.5 1.0 1.5

X (AU)

Y (

AU

) LAUNCH

DSM1.1

DSM1.2

EARTH 1

Trajectory Earth-Earth

Manoeuvre Optimisation DSM1.1 – Perihelion

(6/2004) DSM2.1 – Aphelion

(12/2004) Variation with

launch day

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Events

Event Date V (m/s)

Vrel. (km/s)

Peric. H (km)

Launch 2004/02/26 3.545

Deep Space Manoeuvre 1.1

2004/05/25 173

Earth gravity assist2005/03/

02 3.9 4300

Deep Space Manoeuvre 2 2006/10/21 65

Mars gravity assist 2007/02/27 8.77 200

Earth gravity assist 2007/11/15 9.33 14000

Deep Space Manoeuvre 32009/03/

16 130

Earth gravity assist 2009/11/11

9.98 550

Deep Space manoeuvre 4. @ (4.4 AU)

2011/05/10 533

Rendezvous with 67P. @ (4.0 AU)

2014/05/23 774

Start nucleus operations at 3.25 AU

2014/10/03

Perihelion pass 2015/08/11

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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 ( < 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) zW-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)

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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

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

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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

TC #Mean (m/s)

1-s (m/s)

Min (m/s)

99% (m/s)

Max (m/s)

LIC 1 45.2 30.5 0.7 138.0 218.6

Phase Launch-Earth 1 4 3.2 1.3 0.08 8.9 13.9

Phase Earth1-Mars 4 1.4 0.6 0.04 3.7 5.6

Phase Mars-Earth2 2 3.9 2.0 0.07 10.6 16.6

Phase Earth2-Earth3 5 1.6 0.8 0.04 4.5 7.0

Phase Earth3-Comet 2 1.7 0.8 0.06 4.5 6.9

Total without LIC 17 11.8 2.7 0.3 32.1 50.1

INTERPLANETARY NAVIGATION BUDGET ESTIMATION

ROSETTA Churyumov-Gerasimenko 2004

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Asteroids

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

(km)Period (hr) Type

21 Lutetia

130x104x74 8.17 M, Mo,

MCv

2867 Steins 17.5 – 5.5 ? C?

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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 position+velocity, identification of landmarks;

avoid cometary debris, and eclipses; Keep Earth communications; Keep safety;

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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* no landing

possible

landingpossible

*still assuming landing on inactive comet, about 3 AU away from the sun.

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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

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Philae Landing (4)

Delivery Trajectory and Landing errors (3-s). Vimpact < 120 cm/s

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Philae Landing (5)

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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