The scientific objectives of ESA’s Comet Orbiter ROSETTA and Lander PHILAE

ISSI Meeting, Berne, Switzerland 20-24 January, 2014 page 1

The scientific objectives

of ESA’s Comet Orbiter ROSETTA and Lander PHILAE

Susan McKenna-Lawlor

Space Technology Ireland, Maynooth, Co. Kildare, Ireland


Cometary material is believed to constitute a unique repository of information concerning the sources that contributed to making up the composition of the proto-solar nebula, Also, regarding the processes that resulted in the appearance of the planetesimals which later formed the planetary bodies.

The Early Solar System


Direct knowledge concerning the volatiles in a comet nucleus is particularly difficult to obtain as remote observations, even during fly-by missions, only cover species in the coma which have been altered by physio-chemical processes (such as sublimation and interactions with solar radiation and the solar wind). Today, ESA’s Rosetta Mission is taking up the challenge to study the mysterious environment of a distant comet throughcombining remote observations from an Orbiter with ground truth from a Lander deployed on the comet’s surface.

The Early Solar System


The prime scientific objectives of ROSETTA are (a) to investigate the origin of our Solar System through monitoring various characteristics of comet 67P/Churyumov-Gerasimenko (67 P-G) as it follows a trajectory initially towards, then away from the Sun and (b) to analyze complementary data obtained from an active lander.

ROSETTA is a Planetary Cornerstone

Mission in the long term program

Horizon 2000 of the

European Space Agency.


LaunchRosetta was launched on 2 March 2004. It is scheduled to deploy its lander (Philae) onto the nucleus of comet 67P/C-G in November 2014.


Size: main structure 2.8 x 2.1 x 2.0 m3

diameter of solar arrays 32 metres

Launch mass - total: 3000 kg (approx.) - propellant 1670 kg (approx.) - science payload 165 kg - Lander 100 kg

Solar array output 850 W at 3.4 AU, 395 W at 5.25 AU

Propulsion subsystem 24 bi-propellant 10N thrusters

Operational mission 12 years

The Spacecraft vital statistics


Solar panel array

at ESA-ESTEC

en route (CIVA-P image)


The Philae Lander

A 100 kg Lander (Philae) is carried aboard the Orbiter. When the Orbiter is aligned correctly at the target comet the Lander will be commanded to eject from the s/c and unfold its three legs, ready for a gentle touchdown at the end of a ballistic descent. On landing, the legs will damp out most of the kinetic energy to reduce the chance of bouncing. Also, they can lift or tilt Philae to provide an upright position for the Lander.


Space Technology Ireland (STIL) designed, tested and constructed the

Electrical Support System (ESS) processor unit for Rosetta which is

dedicated to communicating with Philae.

Electrical Support System ESS


During the Cruise Phase the command and data streams passing through the umbilical connector of the Lander to Rosetta’s onboard computer are handled by the ESS.




Functional block diagram of the ESS unit



The Flight Model of the ESS unit


Orbiter Payload

Orbiter Science

The Cruise Phase • Earth/Mars flybys• Asteroid Flybys

The Target Comet/Comet Rendezvous

Lander Payload and Observations

Lander Science

Conclusion

Presentation Outline


ALICE Ultraviolet Imaging Spectrometer CONSERT Comet Nucleus Sounding COSIMA Cometary Secondary Ion Mass Analyser GIADA Grain Impact Analyser and Dust Accumulator MIDAS Micro-Imaging Analysis System MIRO Microwave Instrument for the Rosetta Orbiter OSIRIS Rosetta Orbiter Imaging System ROSINA Rosetta Orbiter Spectrometer for Ion and Neutral Analysis RPC Rosetta Plasma Consortium RSI Radio Science Investigation SREM Standard Radiation Monitor VIRTIS Visible and Infrared Mapping Spectrometer

ROSETTA Orbiter Payload


Orbiter Instruments Location


Orbiter Instruments

The ultraviolet imaging spectrograph ALICE will determine the production rates of numerous atoms and gas molecules, study small dust grains and ions in the coma, and characterize the surface of the nucleus at UV wavelengths.

ALICE

CONSERT The deep interior of the comet nucleus is investigated by radio sounding using CONSERT which will transmit long wavelength radio waves through the nucleus.

The secondary ion mass spectrometer COSIMA will perform in situ compositional analysis of the coma dust (including chemical characterization of its main organic components, identification of homologous and functional groups, and determination of the mineralogical and petrographical classifications of its inorganic phases).

COSIMA


GIADA

MIDAS

MIDAS is an innovative scanning probe microscope able to image small structures in 3D at nano-meter scale resolution. It will determine the dimensions and microstructure of individual dust grains.

MIRO

The surface and near-surface temperatures as well as the temperature gradient in the nucleus will be determined by the MIRO instrument at microwavelengths. MIRO will also measure outgassing rates and isotopic ratios of certain major volatile species by measuring their molecular transitions.

GIADA will measure the number, mass, momentum and velocity distribution of dust grains in the near-comet environment. Giada will analyse both grains that travel directly from the nucleus to the spacecraft and those that arrive from other directions having had their ejection momentum altered by solar radiation pressure.

Orbiter Instruments contd.


OSIRIS This remote sensing suite of instruments will characterize the nucleus surface over a wide wavelength range from the far-UV (70 nm) to millimetres (1.3 mm) at high spatial resolution. In addition to determining the size, shape, rotational state, and detailed surface topography of the nucleus OSIRIS will characterize sublimation and erosion processes on the nucleus surface.

ROSINA will determine the composition of the comet’satmosphere and ionosphere, measure the temperature and bulk velocity of the gas and ions and investigate reactions in which they take part. ROSINA’s pressure sensor can measure both total and RAM pressure and will be used to determine the gas density and rate of radial gas flow.

ROSINA



RPC The comet plasma environment and its interaction with the solar wind is monitored in situ by five sensors, which have been combined into one instrument suite sharing common subsystems and run by the Rosetta Plasma Consortium (RPC).



VIRTIS The infrared imaging spectrometer VIRTIS will focus on the detection and characterization of specific signatures such as typical spectral bands of minerals and molecules so as to identify and quantify the different constituents of cometary material, Also VIRTIS will study the thermal evolution of the comet nucleus as a function of the solar radiation input.

RSI The Radio Science Investigation (RSI) exploits the communication link to the ground stations on Earth to address fundamental aspects of cometary physics (including determining: the mass and bulk density of the nucleus; the gravity field; non-gravitational forces; size and shape of the nucleus; its internal structure; the composition and roughness of its surface; the abundance of large dust grains; the plasma content of the coma. The combined dust and gas mass flux at the orbiter etc.)

SREM The radiation environment will be measured by a standard radiation monitor, SREM.



Orbiter Science

The evolution of the comet along the orbit around the Sun is investigated by monitoring the nucleus and the near-nucleus environment from a pre-perihelion distance of about 3.4 AU (orbit insertion) through perihelion passage at 1.24 AU and back out to about 2 AU post-perihelion.

Rosetta studies how a comet nucleus develops its activity at large heliocentric distance and how such a process functions at high solar radiation levels close to the Sun.

The chemical, mineralogical and isotopic composition of both the comet nucleus (near the surface) and the inner coma is determined allowing identification and quantification of the chemical reaction chains by which the observed coma gas species are produced from the original icy material on the nucleus.

Study of the chemical (isotopic) composition of the ices and dust grains at the comet will provide information on the processes through which these constituents were produced.


1. 2004 /03/02 Launch (Kourou)

2. 2005/03/04 Earth (flyby 1950km)

3. 2007/02/25 Mars (flyby 250km)

4. 2007/11/13 Earth (flyby 5300km)

5. 2008/09/05 Steins (flyby 802km)

6. 2009/11/13 Earth (flyby 2481km)

7. 2010/07/10 Lutetia (flyby 3162km)

8. 2014/05/22 Close approach to 67P

9. 2014/11/10 Landing on 67P

--- done --- future

Cruise Phase


Cruise Phase / First Earth Swingby

23

Rosetta Navigation Camera A25 July 2004

NavCAM, March 2005

NavCAM, March 2005

04 March 2005 at 1900 km altitude

In-flight Validation of Asteroid Flyby Mode


Autonomous Operations of the Lander via Battery

Closest Approach: 250.6 kmCIVA takes spectacular

images ROMAP detects bow shock, the

pileup region and signatures of surface magnetic anomalies.

Cruise Phase / Mars Swingby February 25, 2007.


Date: 5 September 2008, Closest approach: 802 km, Velocity: 8.6 km/s

Cruise Phase / Steins flyby


Steins was seen to be an oblate body resembling a diamond with dimensions 6.67 x 5.81 x 4.47 km3.

Its surface is mostly covered with shallow craters with some of the larger craters pitted with smaller ones.

A deficit of craters with D < 0.5 km is attributed to surface reshaping due to the Yarkovsky-O’Keefe-Radzievskii-Paddack (YORP) effect which would have caused landslides which filled in the smaller craters*.

This flyby provided the first close-up view of an E-type asteroid which was inferred from the measured data to have a rubble pile structure.

YORP effect: a phenomenon that occurs when solar photons are absorbed by a body and reradiated as infrared emission which carries off momentum as well as heat. This loss of momentum cam cause a change in the rotation rate of a small body such as an asteroid. In the case of Steins, the resulting high spin rate could have caused material to migrate towards the equator. resulting in the observed distinctive shape.

Cruise Phase / Steins flyby


Cruise Phase / Lutetia flyby

Lutetia Closest Approach:

10 July 2010 – 15:45 UTC CA distance: 3160 km Solar distance: 2.72 AU Earth distance: 3.05 AU

The flyby provided images of up to 60 m/pixel resolution covering about 50% of the surface (mostly in the northern hemisphere which was found to be covered by a thick layer of regolith). 462 images were obtained in 21 narrow and broad band filters (from 0.24 - 1 μm). Also observations were made in the VIS-NIR range.


Cruise Phase / Lutetia flyby

The mass of Lutetia was determined using flyby Doppler data to be 1.7 x 1018 kg. Calculations based on the volume of Lutetia determined from OSIRIS images indicated that its bulk density is very high (~3.4 g/cm3 ).

Assuming that Lutetia has a modest internal porosity, its high density suggests that it is enriched in metallic elements such as iron. Also it may constitute coevidence of partial differentiation of the asteroid’s interior early in its history with an unmelted chondritic surface overlying a higher density interior which once was molten. This is consistent with the spectral data which support a composition similar to iron-rich carbonaceous or enstatite chondrites.

It was inferred that Lutetia may be a primordial planetesimal. According to this scenario it is speculated that, having survived numerous impacts, Lutetia may constitute a hitherto “missing link” between smaller asteroids, which are often shattered rubble piles, and the terrestrial planets.


Characteristics:– Diameter ~4000 m– Density 0.2-1.5 gcm-3

– Aphelion 5,75 AU– Perihelion 1,3 AU– Orb.period 6,57 years– Albedo ca. 0,04 ??– Rotation 12,3 h

Target: Comet 67P/Churyumov-Gerasimenko

Discovered by Klim Churyumov in photographs of 32P/Comas Solá taken by Svetlana Gerasimenko on 22 October 1969.


At the present time, only a few key features of comet 67P/C-G are known (e.g. its rotation period 12.3h , surface gravity ~ 10-4 g.) A possible shape has been reconstructed from precise photometric measurements made by Hubble (Lamy et al., 2007)

Target: Comet 67P/Churyumov-Gerasimenko


Comet Rendezvous

The s/c will be inserted into an orbit about the nucleus at a distance from it of about 25 km. Detailed mapping of the surface will then be undertaken from the Orbiter. Finally, several potential landing sites will be selected for close observation. After final site selection the lander will be released from a height of about 3-5 km. Touch down will take place at < 1 m/s. A harpoon will be immediately fired to anchor the lander and prevent it escaping from the comet’s extremely weak gravity.


APXS Alpha-p-X-ray spectrometer CIVA Panoramic and microscopic imaging system CONSERT Radio sounding, nucleus tomography COSAC Evolved gas analyser - elemental and molecular composition MODULUS Ptolemy Evolved gas analyser - isotopic composition MUPUS Measurements of surface and subsurface properties ROLIS Imaging ROMAP Magnetometer and plasma monitor SD2 Drilling and sample retrieval SESAME Surface electrical, acoustic and dust impact monitoring

Lander Scientific Payload

ISSI Meeting, Berne, Switzerland 20-24 January, 2014 page 33 33

Lander Observations

• In-situ materials analysis– element and isotope distribution– organic molecules – minerals and ices

COSAC (MPAe): mass spectrometer PTOLEMY (OU, UK): isotope analysis APX (MPCh): element analysis

Structure and properties of comet core surface topology

physical properties stratigraphy, global internal structure

temporal variation day and night cycle approach to the Sun

CIVA (IAS, F): panorama, stereo and microscope cameras

ROLIS (DLR): downlooking camera MUPUS (U. Münster): penetrator SD-2 drilling/sample retrieval SESAME (DLR): seismic probe CONSERT (CEPHAG, F): microwave

tomography


Lander observations

For the collection of samples and the deployment of instruments the Lander can be rotated around its z (vertical) axis by 360° defining a “working circle” around the Lander body axis. Thus, arbitrary locations can be accessed by the sampling drill (SD2), the down-looking camera (ROLIS) and other Lander instruments. Also the stereo camera pair of ÇIVA will be able to image a full 360° panorama using the Lander’s rotation capability.


Lander observations contd.

Using the SD2 (Sample Drill and Distribution) system, surface and subsurface samples, a few mm3 in volume, will be acquired (from about 20 cm depth) controlled by a volume checker and distributed to 26 dedicated ovens, mounted on a carousel. Ten ovens (“Medium-temperature ovens”, up to +180°C) are equipped with IR-transparent sapphire windows: ÇIVA-M will obtain microscopic three-color images (7 μm spatial sampling) and a complete near-IR (1 to 4 μm) high-resolution spectrum (40 μm spatial sampling, spectral resolution 10 nm at 4 μm ) of the samples, to assess the scale of their heterogeneity, and to determine the mineralogical and molecular composition of all cometary phases (ices, minerals, refractories).



Each sample will be step-wise heated, and the output gas piped to the PTOLEMY and COSAC instruments in order to identify its elemental, molecular and isotopic composition.

PTOLEMY will measure by chemistry and mass analysis, the H, C, N, O and S stable isotopes, while COSAC will identify, by gas chromatography and high resolution time-of-flight (TOF) mass spectrometry, the molecular composition of the material, in particular of its complex organics. COSAC has also the possibility to measure chirality of the gas, with the aim of identifying potential pre-biotic signatures.



Elemental abundances of the surface material will also be measured by the APXS instrument in a small (few cm2) area below the Lander.

Physical properties of the surface and subsurface material will be derived from optical images (CIVA-P and ROLIS) and accurately determined by direct measurements (MUPUS and SESAME).

MUPUS will deploy several sets of sensors to measure the cohesion of the top surface materials, its density and potential layering, the heat flow, the thermal conductivity and the thermal profile at different locations around the lander down to several tens of centimetres.

SESAME will focus on measuring the mechanical and electrical properties of the surface, typically down to two meters depth, and the dust environment along with its diurnal and long-term variations.



The large-scale structure of the nucleus will be studied by the CONSERT experiment, through studying the propagation of electromagnetic waves transmitted between a unit onboard the Lander and one onboard the Orbiter. The large-scale topography and properties of the nucleus will also be studied through analyzing panoramic stereoscopic images of the landing site after touch down (CIVA-P), and through images acquired during descent (ROLIS).

The magnetic and plasma environment of the nucleus will be measured by the magnetic, electron and ion detectors of the ROMAP experiment onboard Philae.

The goals of the scientific investigations onboard Philae are closely Philae are closely coupled to those of the

Orbiter experiments.


Lander science overview

The Philae science objectives will complement those of the Orbiter investigations and include:

Determination of the composition of cometary surface matter; bulk elemental abundances; isotopes; minerals; ices; carbonaceous compounds; organics and volatiles – all with regard to their dependence on time and insolation.

Investigation of the structure, and the physical, chemical and mineralogical properties of the comet’s surface; its topography, texture, roughness and mechanical, electrical, optical and thermal properties.

Investigation of the local depth structure (stratigraphy) and global internal structure of the comets nucleus

Investigation of its plasma environment


The Orbiter will continue to orbit around the comet, observing what happens as the icy nucleus approaches the Sun, then moves away from it. The mission is scheduled to end in 2015. Surface operations are expected to continue for at least one week but can be significantly extended depending on the prevailing surface conditions.


Conclusion

Following close encounters with two primitive objects in the asteroid belt, Rosetta will rendezvous with comet 67P/Churyumov-Gerasimenko while it is located in a cold region of the Solar System and shows no surface activity (~3 AU). After releasing a Lander onto the dormant nucleus the Orbiter will be the first s/c to fly alongside a comet as it travels toward the inner Solar System.

Instruments onboard the Orbiter will monitor the dust and gas particles released over time to surround the comet and also investigate ongoing interactions with the solar wind. In this regard it will be the first s/c to investigate from close proximity how a frozen comet is transformed by the warmth of the Sun.


Conclusion

The Orbiter acts as a carrier for the Lander during the 10 year cruise phase and host of its release and descent phases. Also its electrical support system (ESS) will handle all Lander commands and data transmissions during on- comet operations.

For the first time, a robotic system will land on a cometary nucleus, with the goal of deciphering, by direct in-situ measurements and observations, the presently unknown key properties of a body conceived to have preserved a pristine sample of those materials that drove the evolution of the Solar System.


Documents

The scientific objectives of ESA’s Comet Orbiter ROSETTA and Lander PHILAE