The European Venus Explorer (EVE) proposal 2010 current status
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2
C.F. Wilson , E.C. Chassefière , and the EVE Steering committee
2
( Oxford University, Oxford, U.K., Université Paris-Sud, Orsay, France)
1
Summary
Science Goals
The European Venus Explorer (EVE) is a
proposed in situ mission to Venus based on a
balloon platform. It will be proposed to ESA in
December 2010, for consideration under ESA’s
Cosmic Vision programme for launch in 20202023.
ESA's Venus Express orbiter and the Japanese
Venus Climate Orbiter provide a global survey of
Venus, but there are many questions which
cannot be addressed by remote sensing
measurements alone, in particular those related
to the isotopic ratios of noble gases and cloud
chemistry cycles, issues which are the keys to
understanding current climate and evolution of
Venus and other terrestrial planets. The scientific
goals of EVE will therefore be:
In 2007, the EVE team proposed to ESA a large
Venus mission including an orbiter, a cloudlevel balloon, and a lander [Chassefiere et al.,
2008a, 2008b]. This would have been a
complex mission, with significant Russian
contributions: the launcher, EDLS and lander,
as well as much of the science payload, was to
have been provided by Russia.
In 2010, the EVE team plan to propose a
smaller, more focussed mission which could be
achieved by ESA alone. The envisaged mission
will thus consist of a single cloud-level balloon,
with neither an orbiter nor a lander.
The details of the mission proposal are still
under development, but we take this opportunity
to reiterate the science rationale for a cloudlevel in-situ mission, and to summarise the
baseline mission proposal as is currently
envisaged (at time of writing, late July 2010).
1) To derive a unified model of the formation and
evolution of terrestrial planets, by studying the
record preserved in the atmospheric elemental
and isotopic composition, considered together
with data on escape processes.
2) To study the complex chemical and radiative
processes in the cloud-level atmosphere by insitu measurements of gas and aerosol
composition and radiative fluxes.
3) To study the atmospheric dynamics by
measuring the vertical and horizontal movements
of the balloon as it completes a full
circumnavigation of the planet.
The central theme of the mission is to
understand the evolution of Venus and its
climate, with relevance to terrestrial planets
everywhere.
While not, strictly speaking, a science goal, a
wider and no less important aim is to engage
the public in themes of climate evolution and
stability, by emphasising the parallels between
these terrestrial planets.
Mission profile
The detailed mission scenario is currently under
study by CNES with the aid of industrial
contractors, so only the mission outline is given
here.
A Soyuz-2 rocket, launched from Kourou, will
inject the EVE spacecraft into GTO. The EVE
spacecraft, consisting of a carrier module of
approximately 300 kg dry mass and a descent
module of approximately 620 kg mass, will be in
cruise for roughly 6 months. The carrier
spacecraft will act as a telecommunications
relay during the first day of balloon operations.
Subsequent communications from the balloon
will be direct to earth. The balloon will be
equipped with a high gain antenna sized to
provide a data rate of 100 bits per second when
the balloon is visible from the Earth.
CNES 9-metre Venus balloon (developed for
Vega project).
Science payload
The baseline mass allocation of the scientific
payload is 15 kg; however, an increase of this
payload mass to 25 kg is also under
consideration.
The balloon
The balloon will be a Helium superpressure
balloon, designed to maintain a float altitude of
55 km. The environment at this altitude is
perhaps the most benign found outside the
Earth, with temperatures near 20°C, and
pressures near 0.5 bar.
This level of the atmosphere is in the middle of
the main convective region of the atmosphere,
which extends typically from 51 – 60 km in
altitude [Tellman et al., 2009]. The Vega
balloons found vertical winds of order ±1 m/s,
reaching as high as 3 m/s at times. These
updrafts and downdrafts will bring air parcels
from different atmospheric levels to the balloon
where they can be analysed by the scientific
instruments.
The nominal lifetime of the balloon will be 10
Earth days, which is sufficient to complete one
circumnavigation of the planet at this altitude.
The strawman payload, used for sizing of the
balloon and resource requirements, is shown in
the table below.
Isotopic ratios and abundances of noble gases
will be measured using a dedicated isotope &
noble gas mass spectrometer. This instrument
would include getters and/or cryogenic traps to
remove the CO2 and N2 which constitute some
99.9% of the atmosphere, allowing sensitive
measurement of trace species abundances.
The main instrument for characterisation of the
cloud-level chemistry is a GC/MS instrument. A
dedicated aerosol sampling inlet is proposed, in
order to ensure discrimination between gas
phase
composition
and
cloud
droplet
composition. This would build on heritage (and
lessons learned) from the Huygens ACP.
proposed in order in an attempt to replicate
detection from Venera and Vega XRF
instruments of unexpected abundances of Cl, P,
and Fe in the cloud particles [Andreichikov et al.,
1986].
Instrument
Measurent
GC/MS with
dedicated aerosol
collection / pyrolysis
inlet
Chemical composition of
cloud & gas composition.
Isotopic / Noble Gas
Mass Spectrometer
Measurement of trace gas
abundances
Tunable Diode Laser
Measurement of chemically
active species; measurement
of oxygen isotopic ratio
Nephelometer
Refractive index / particle
distribution of cloud particles
Attenuated Total
Reflection
spectrometer
Optical spectroscopy of
cloud particle composition
X-ray fluorescence
analysis of cloud
particles
Measure elemental
abundances in cloud
particles (incl. S, Cl, P, Fe).
Atmospheric package
(p, T, acc, vertical
wind)
Local meteorological
parameters
Optical package Radiometer
Upward and downward
fluxes in 6 channels (UV,
Vis, near-IR, thermal IR)
VLBI beacon / USO
Enables VLBI localisation of
balloon probe
Electrical / EM
package
Characterisation of E-M
activity; Search for lightning.
Camera
Public relations; search for
contrasts in cloud images.
Instruments under consideration
balloon’s science payload.
for
the
Gaseous composition measurement wil be
further improved by inclusion of a Tunable
Diode Laser. This focus would be on
chemically active species which could not be
measured using a GC or MS. The TDL would
also enable the measurement of oxygen
isotopic ratios,
To improve the characterisation of cloud
particles, three further instruments are being
considered. A polarising nephelometer, which
measures the intensity and polarisation of light
scattered from cloud particles, would help
characterise the refractive index and size
distribution of particles, returning much needed
data for interpretation of remote sensing data
and calculations of radiative balance. An
attenuated total reflection spectrometer
would obtain absorption spectra of liquid
aerosol deposited on the sample prisms.
Finally, X-ray fluorescence analysis is
The baseline payload also includes basic
meteorological
sensors
pressure,
temperature, vertical wind, and accelerometers –
in order to provide context for the chemistry
measurements. Also, a basic set of simple
radiometers measuring upward and downward
fluxes will provide context for the science
measurements, by providing information about
spatial variation in overlying UV absorber layers
and lower cloud optical depth.
An
electrical
&
EM
characterisation
instrument will investigate Venus lightning; it will
include optical, acoustic and magnetic signatures
for lightning; but will also address the mechanism
of lightning production by measuring electrical
conductivity and electric fields at the cloud level,
as well as characterising the background
electromagnetic activity.
Finally, at least one camera will be included in
the payload. The camera would probably be a
wide angle camera showing the gondola upper
deck as well as the balloon. Although its main
purpose would be for public relations, camera
images might reveal inhomogeneities in the local
cloud field and can be used to investigate the
angular distribution of light intensity at the cloud
level.
International participation
The 2010 EVE proposal is for a small, tightly
focussed mission provided by ESA alone. There
will not be any major mission elements provided
by international partners.
However, there will be opportunities for
international partners to contribute instruments to
the science payload, and to participate in
instrument science teams.
The possibility of a Venus orbiter, launched
independently from EVE but able to provide data
relay for an EVE balloon, is being investigated.
Key technology developments
References
EVE is a low risk mission. It benefits from a
precursor mission, the Vega balloons of 1984
[Sagdeev et al., 1986], which demonstrated the
viability of deploying and operating helium
superpressure balloons in the clouds of Venus.
B.M. Andreichikov et al. (1986), ‘Elemental
abundances in Venus aerosols by X-ray
radiometry: preliminary results’, Sov. Astron.
Letters 12(1).
As part of the Vega balloons development work,
the French Space Agency (CNES) prepared
and tested two balloon prototypes: a 3.5 m
diameter balloon (which was flown on Venus)
and a 9 m diameter balloon. The 5.8 m balloon
being proposed for EVE is thus within the range
of balloons previously qualified at CNES.
The main technology developments which will
be required for this mission are :






Entry Shell (TPS) development within
ESA.
Parachute system
Balloon deployment & inflation system
Power : batteries & solar cells
Steerable High Gain Antenna
Science payload
E. Chassefière et al.(2009a), ‘European Venus
Explorer (EVE): An in-situ mission to Venus’,
Experimental Astronomy, Volume 23, Issue 3,
pp.741-760, 2009. doi:10.1007/s10686-0089093-x.
E. Chassefière et al.(2009b), ‘European Venus
Explorer (EVE): An in-situ mission to Venus
using a balloon platform’, Advances in Space
Research, 2009, doi:10.1016/j.asr.2008.11.025.
R.Z. Sagdeev et al. (1986), ‘Overview of VEGA
Venus
balloon
in
situ
meteorological
measurements’, Science vol. 231, p. 1411-1414.
doi: 10.1126/science.231.4744.1411.
S. Tellmann et al. (2006),’ Structure of the Venus
neutral atmosphere as observed by the Radio
Science experiment VeRa on Venus Express’,
Journal of Geophysical Research, Vol. 114,
E00B36, doi:10.1029/2008JE003204.
For further information and updates, please see the EVE website:
http://www.univie.ac.at/EVE/