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© EADS Astrium Ltd Credit images: European Space Agency
Venus ExpressDr Jerry Bolter
EADS Astrium Ltd
© EADS Astrium Ltd Credit images: European Space Agency
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
© EADS Astrium Ltd Credit images: European Space Agency
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
© EADS Astrium Ltd Credit images: European Space Agency
© EADS Astrium Ltd Credit images: European Space Agency
The ‘Ashen Light’ of Venus
[P. Moore]
© EADS Astrium Ltd Credit images: European Space Agency
© EADS Astrium Ltd Credit images: European Space Agency
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
© EADS Astrium Ltd Credit images: European Space Agency
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
© EADS Astrium Ltd Credit images: European Space Agency
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
© EADS Astrium Ltd Credit images: European Space Agency
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
© EADS Astrium Ltd Credit images: European Space Agency
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
© EADS Astrium Ltd Credit images: European Space Agency
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
© EADS Astrium Ltd Credit images: European Space Agency
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
© EADS Astrium Ltd Credit images: European Space Agency
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
© EADS Astrium Ltd Credit images: European Space Agency
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
© EADS Astrium Ltd Credit images: European Space Agency
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
© EADS Astrium Ltd Credit images: European Space Agency
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
© EADS Astrium Ltd Credit images: European Space Agency
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
© EADS Astrium Ltd Credit images: European Space Agency
From Mars Express to Venus Express
Mars Express:– 1223 kg at launch.
Venus Express:– 1270 kg at launch.
© EADS Astrium Ltd Credit images: European Space Agency
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
© EADS Astrium Ltd Credit images: European Space Agency
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
© EADS Astrium Ltd Credit images: European Space Agency
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
© EADS Astrium Ltd Credit images: European Space Agency
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.
© EADS Astrium Ltd Credit images: European Space Agency
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
© EADS Astrium Ltd Credit images: European Space Agency
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.
© EADS Astrium Ltd Credit images: European Space Agency
© EADS Astrium Ltd Credit images: European Space Agency
Spacecraft Structure
Status in July 2003
Contraves, Zürich
© EADS Astrium Ltd Credit images: European Space Agency
Chemical Propulsion System
Helium tank
Fuel tanks
Main Engine
Thrusters
Status in March 2004
EADS Astrium
Stevenage
© EADS Astrium Ltd Credit images: European Space Agency
Platform and Payload Integration
Status in August 2004
Spacecraft during assembly at Alenia Spazio, Turin.
© ESA
© ESA
© EADS Astrium Ltd Credit images: European Space Agency
Spacecraft Test
Status in January-April 2005
Intespace, Toulouse
Spacecraft during sine vibration test
© ESA
© ESA
Spacecraft during thermal vacuum test
© EADS Astrium Ltd Credit images: European Space Agency
Launch Campaign @ Baikonur
Status in August to November
2005
Departure for Baikonur
© ESA
© ESA
Departure from Baikonur!
© EADS Astrium Ltd Credit images: European Space Agency
Launch Phase
© EADS Astrium Ltd Credit images: European Space Agency
Cruise Phase
November 9th, 2005
November 9th, 2005April 11th, 2006
April 11th, 2006
© EADS Astrium Ltd Credit images: European Space Agency
Cruise Phase
© EADS Astrium Ltd Credit images: European Space Agency
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
© EADS Astrium Ltd Credit images: European Space Agency
Launch Animation
© EADS Astrium Ltd Credit images: European Space Agency
Venus Express – First Images
Acknowledgements ESA EADS Astrium SAS EADS Astrium Ltd