© EADS Astrium Ltd Credit images: European Space Agency Venus Express Dr Jerry Bolter EADS Astrium...

© EADS Astrium Ltd Credit images: European Space Agency

Venus ExpressDr Jerry Bolter

EADS Astrium Ltd


From Mars to Venus

Christmas 2003, Mars Express entered Mars orbit

First European spacecraft to ever orbit a planet

Stunning science results since arrival

More than 2 years before its launch, ESA sought proposals for re-use of platform

– Same units

– Same industrial team

– Ready to launch in 2005 Of 9 proposals, ESA

selected Venus Express


Venus Exploration History

1962: Mariner 2First Fly-by

1967: Venera 4

First atmospheric probe

1970: Venera 7

First landing

1975: Venera 9

First ground pictures

1989: Magellan

Radar mapping

2005: Venus Express

Global survey

of the atmosphere


The ‘Ashen Light’ of Venus

[P. Moore]


Why Venus Express? Venus is the nearest planetary neighbour to Earth

– A solid planet, the same size as Earth and yet ….

– Very high surface temperatures (470degC) and pressures (90bar)

– Highly sulphurous clouds

– Believed to be highly volcanic

– Absorbs less solar energy than the Earth and only slightly more than distant, frozen Mars

– Venus rotation is very slow yet suffers hurricane-force winds and storms with giant vortices over

the poles Strong concerns about the Earth’s climate

– Reduction in ice-fields leading to changes in ocean current circulations and global warming whilst

– Scientists cannot explain even the basic features on the nearest and most Earth-like planet Planetary alignments necessitated a very short-duration programme if the

scientific opportunities were not to be missed ESA mission based on re-use of its Mars Express spacecraft


Venus Express – key objectives (1/2)

Global investigation of Venus atmosphere

– Structure

– Composition

– Dynamics Study of the plasma

environment and interaction with solar wind

Aid understanding of long-term climatic evolution of Earth

Venus Express instruments largely working in infra-red wavelengths

Seven instruments carried in total

100

50

0

Altitude (km)

from Sun

MICROWAVE

NEARINFRARED

ULTRAVIOLETTHERMALINFRARED


Venus Express – key objectives (2/2)

First European mission to Venus

Other firsts:First global monitoring of the composition of the lower atmosphere in near IR range

First coherent study of the atmospheric temperature and dynamics at different levels from the surface to 200 km

First measurement of the global temperature distribution from orbit

First study of the middle and upper atmosphere dynamics from O2, O and NO emissions

First measurements of the non-thermal atmosphere escape

First coherent observations of Venus in the spectral range from UV to Thermal IR

First application of the solar/stellar occultation technique at Venus

First use of 3D ion analyser, high energy resolution electron spectrometer and energetic neutral atom imager


Science mission

Major objectives:– Global survey of atmosphere

composition,– Measurements of temperature

distribution,– Study of atmosphere dynamics,– Study of interaction between

atmosphere and solar wind.

Mission duration:– Nominal mission: 2 Venus days (about

500 days),– Possible extension of 2 Venus days,

pending on spacecraft resources.

Instrument Objective Heritage

ASPERA Analyser of Space Plasmas and Energetic Atoms

Mars Express

MAG Magnetometer Rosetta

PFS High-resolution IR Fourier spectrometer

Mars Express

SPICAV UV and IR Atmospheric Spectrometer

Mars Express

VeRA Radio Science Experiment Rosetta

VIRTIS UV Visible Near IR Mapping Spectrometer

Rosetta

VMC Venus Monitoring Camera

Venus Express Instruments


ASPERA

Analyser of Space Plasmas and Energetic Neutral Atom Imager

Inherited from Mars Express To determine the plasma-induced

atmospheric escape To measure the interaction of the solar

wind with the ionosphere Instrument operates continuously to

gather data on ion, electron and neutral atom distributions around Venus

Both components are the same as Mars Express, but with new thermal radiators

MU moved from top floor to Y sidewall to avoid full solar illumination

IMA = Ion Measurement Assembly MU = Main Unit

IMA

MU


MAG

Magnetometer

Magnetometer instruments and electronics inherited from Rosetta

Two sensors are flown MAGIS (Inboard sensor) on new bracket MAGOS (Outboard sensor) on new

deployable boom To measure magnetic field in the vicinity of

the spacecraft Instruments operate continuously to gather

data on magnetic fields associated with the planet or plasma


PFSPlanetary Fourier Spectrometer

All four modules derived from Mars Express instrument

Small modifications applied Location as on Mars Express, i.e., on

spacecraft ‘cold’ face Instrument is a high resolution Fourier

IR spectrometer optimised for atmospheric studies

To provide 3D temperature fields of the lower atmosphere up to 50 km, minor constituent variations (H2O and CO2) and optical properties of atmospheric aerosols.

– These allow the study of the global

atmospheric circulation To provide data on the thermal inertia

of the surface Operates only in observation phases


SPICAVUV and IR Atmospheric Spectrometer

(for solar/stellar occultations)

Derived from Mars Express SPICAL Additional IR channel called SOIR Location as on Mars Express To study atmosphere with both nadir

and limb viewing To measure ozone content and

coupling of O3 and H2

To provide vertical profile of CO2, O3 and dust via stellar occultation

To detect chemical species such as water, carbon monoxide, hydrogen sulphide and trace gases

– These are fundamental inputs to the

meteorological and dynamic models of

the atmosphere Operates only in observation phases


VeRA

Venus Radio Science Experiment

Derived from instrument flown on Rosetta

Synthesiser modified To use radio subsystem to sound

neutral and ionised atmosphere at occultation

To determine the dielectric properties of the surface

To observe gravity anomalies Operates in specific radio science

observation phases Needs to be switched on at all

times for stability reasons


VIRTIS

UV-Visible IR Imaging Spectrometer

Derived from Rosetta instrument To provide mineralogical and

molecular composition of the surface of Venus at medium resolution and global coverage

– Uses spectral analysis of re-diffused

solar light and surface thermal

emissions Mounted on cold face of spacecraft IR detectors need to be kept below

-180°C

– Achieved via passive and active

cooling Operates only in observation

phases


VMC

Wide-angle Venus Monitoring Camera

New design for Venus Express To provide images in the UV, visible

and near IR spectra To provide global spatial and

temporal coverage of the Venus disc


Venus Express Program

ESA programme, dedicated to the observation of Venus –Prime contractor: EADS Astrium SAS–UK major contractors: EADS Astrium Ltd - Mechanical Bus

(structure and propulsion)SciSys – Ground station (ESOC)

–Other UK contractors: AEA Battery Systems Ltd - BatteriesMT Satellite Products - Propellant TanksAmpac-ISP (UK) Ltd - Propellant processing

Major steps:–Programme Kick-off November 2002–Launch (Soyuz/Fregat) November 9th, 2005–Venus rendezvous 11th April, 2006–Spacecraft now in cruise to Venus

Three main challenges:–Maximum re-use of Mars Express/Rosetta (platform and instruments)–Delivery in 3 years–Meet stringent science requirements in Venus’ severe environment


From Mars Express to Venus Express

Mars Express:– 1223 kg at launch.

Venus Express:– 1270 kg at launch.


Impacts from Venus environment

Venus closer to Sun than Mars (Venus - 0.72 AU; Mars – 1.53 AU)

– Thermal flux more than four times higher– The ability to withstand this is the major technical challenge– Radiation flux also four times higher

– Mission duration means that dose depth is comparable to Rosetta For Mars, as an outer planet, the angle between the

Sun and Earth vectors is always less than 40°. For Venus, as an inner planet, the angle between the

Sun and Earth vectors varies from 0 to 360°– For Mars Express the HGA can be pointed at Earth without

exposing the cold face to the Sun

– For Venus Express an additional HGA is required Maximum distance from Venus to Earth is less than

that from Mars (Venus - <1.71 AU; Mars - <2.7 AU)– HGA can be smaller

Venus is bigger and heavier than Mars– More propellant required for Venus Orbit insertion than Mars– Higher total propellant requirement for mission– Overall Venus Express heavier than Mars Express

– Without Beagle 2 the centre of gravity is lower than for Mars Express


From Mars Express to Venus Express

Gallium arsenide cells

– Qualified for ±158ºC

– Reduced sensitivity to radiation Arrays reduced to two panels

(from four)

– Additional thermal control gives

similar mass

– 1400W near Venus Excess power at Venus

– Larger radiators

– More extreme cold cases

Complexity of spacecraft thermal control is vastly increased


The Spacecraft

The Venus Express spacecraft was designed to provide solutions to all of the key issues

Spacecraft facts

Spacecraft bus dimensions

1.5 x 1.8 x 1.4 m

Spacecraft mass 1240 kg (including 93 kg of payload and 570 kg fuel)

Thrust of main engine 400 N

Attitude thrusters Two sets of four, each delivering 10 Newton each

Solar arrays 5.7 square metres; generating 800 Wattsnear Earth and 1100 Watts at Venus

Power storage Three lithium-ion batteries

Antennas Two dishes = 1.3 m diameter, and = 0.3 m in diameter, 2 low-gain antennas


The Spacecraft Structure

– The spacecraft body is termed a ‘bus’, it is a honeycomb aluminium box (1.5 m wide). With its solar arrays extended, it measures ~ 8 m across

– The scientific instruments mounted in the bus are concentrated on three sides.

Thermal Control– The spacecraft coating, called ‘multi-layer insulation’ or MLI, is composed of 23

layers.

– The MLI is gold instead of black, which provides more capability to reflect the radiation. In general, previous spacecraft have been designed to keep warm while Venus Express is modified to stay cool.

Power– At Venus, the Sun appears twice as powerful as on Earth, so solar radiation to

power the spacecraft is plentiful.

– When the spacecraft is in shadow (eclipse) or when its power demand exceeds the capacity of the solar arrays, electrical power is supplied by three lithium-ion batteries that are charged by the solar-generated power.


The Spacecraft Navigation and Attitude Control

– Venus Express is a three-axis stabilised spacecraft. Through three different systems on board, the spacecraft can acquire data about its position in space, attitude (orientation) and change of velocity.

– These on-board systems provide data necessary to re-orient the spacecraft and the solar arrays.

– The actual spacecraft re-orientation manoeuvre or trajectory correction is performed by means of so-called ‘reaction wheels’ or by firing the thrusters.

Data Storage– The Venus Express on-board computer is responsible for supervising and

managing the overall spacecraft functioning, for handling all data acquired by instruments and sensors and for sending commands through the whole spacecraft.

– Part of the computer is the Solid State Mass Memory, which has a capacity of 12 gigabits. All scientific data collected by the instruments are stored here until they can be downloaded to Earth during the appropriate orbital phase


The Spacecraft Propulsion System

– High pressure gas side – gaseous helium stored under high pressure

– Low pressure gas side – pressure regulated to a level suitable for the propellant tanks

– Liquid side – supplying propellant to the main engine and thrusters

– The propellant tanks, one containing nitrogen tetroxide (NTO) and the other mono-methyl hydrazine (MMH)

– These propellants hypergolically combine in the thrust chambers.

– The thrusters are arranged in four pairs, located at the lower corners of the spacecraft.


Spacecraft Structure

Status in July 2003

Contraves, Zürich


Chemical Propulsion System

Helium tank

Fuel tanks

Main Engine

Thrusters

Status in March 2004

EADS Astrium

Stevenage


Platform and Payload Integration

Status in August 2004

Spacecraft during assembly at Alenia Spazio, Turin.

© ESA

© ESA


Spacecraft Test

Status in January-April 2005

Intespace, Toulouse

Spacecraft during sine vibration test

© ESA

© ESA

Spacecraft during thermal vacuum test


Launch Campaign @ Baikonur

Status in August to November

2005

Departure for Baikonur

© ESA

© ESA

Departure from Baikonur!


Launch Phase


Cruise Phase

November 9th, 2005

November 9th, 2005April 11th, 2006

April 11th, 2006


Cruise Phase


Insertion Phase

Capture:- One burn of 49 minutes with Main Engine (400 N).- Burn consumes 400 kg of fuel (70%) – no backup in the event of failure!- Delta-V was 1251 m/s

• 7 transition burns


Launch Animation


Venus Express – First Images

Acknowledgements ESA EADS Astrium SAS EADS Astrium Ltd

© EADS Astrium Ltd Credit images: European Space Agency Venus Express Dr Jerry Bolter EADS Astrium...

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