LOVE. a modular architecture of altitude control balloon for Venus exploration missions (siac)

LOVE: a modular architecture of altitude-control balloon for Venus exploration missions
T.Pougeta*, N.Menetrier–Hacquemanda, F.Florya
a

Federation Open Space Makers, France
* Corresponding Author: thibaut.pouget@outlook.com

Abstract
In terms of scientific exploration, Venus is considered as a high priority by the planetary science community. In
particular, the specificity of its atmosphere is a domain of high interest but suffers a lack of in-situ missions. Indeed,
several missions are currently under development for future exploration using atmospheric probes. For this kind of
mission, the use of a sustentation platform presents a relative simplicity and a great value in terms of recoverable
scientific data which makes it a particularly welladapted method. The purpose of this article is to present a probe
architecture that can evolve in the habitable layer (between 40 to 60km altitudes) of the Venusian atmosphere. This
probe is designed as a sub-part of a main mission or multi-cubesats mission that provides interplanetary cruise and
atmospheric insertion. The proposed system’s architecture is divided into 3 cubesat-format sub-systems: scientific
payload, service module, and altitude control module. Payload module will be provided by a scientific institution.
The service module will be in charge of communications, power supply, and thermal control. Sustentation platform,
using different phase-changed fluids, allows altitude control to meet payload’s requirements. Compliance with the
cubesat standard allows integration as a co-passenger on a main mission. The project is based on a balloon
deployment system without fluid under pressure greater than that authorized by the cubsat standard. To explore
different altitudes, the lift control is done with fluids that change phase depending on the altitude. This generates
oscillations around a phase change altitude. Several fluids are studied to adapt the median attitude to the scientific
need. The amplitude of the oscillation is controlled thanks to the design of the heat exchanger. This presentation
focuses on the theoretical study of the sustaining platform of the project. To be operational, it should be completed
by a prototyping phase and tests in the terrestrial atmosphere. In parallel, the service module should be developed.
Once this development is complete, it would be possible to quickly adapt the design and produce the elements to suit
the scientific need.
Keywords: Venus, atmosphere, Smallsat, altitude-control
Nomenclature
Constant in this project
gv: gravitational acceleration on Venus (8.87m/s²)
Mco2: molar mass of CO2 (0.044 kg/mol)
Mh2: molar mass of dihydrogen (0.002kg/mol)
Mme: molar mass of methanol (0.032kg/mol)
Mn2: molar mass of dinitrogen (0.028kg/mol)
P60: pressure at 60km altitude on Venus (23,900Pa)
R: universal gas constant (8.314 J/(mol.K))
SF: safety factor (3 dimensionless quantity)
T60: temperature at 60km altitude on Venus (263K)
TR200: coefficient of thermal resistance at 200°c (0.8
dimensionless quantity)
YSppd: yield stress PPD-T (3GPa)
Design
LRc: lift ration provided by control altitude fluid
(dimensionless quantity)
LRm: lift ration provided by the main lift gases
(dimensionless quantity)
Lt: tube length(m)
mf: dry flight mass (kg) mass of platform in flight
without lifting gases
mtot: total mass of the platform in flight (kg)
nh2: quantity of dihydrogen (mol)

nme: quantity of methanol (mol)
nn2: quantity of dinitrogen (mol)
rt: tube radius (m)
tppd: tube PPD-T thickness (m)
Vmax: maximum balloon volume (m3)
Design calculation
Fa: Archimedes force (N)
mco2: mass of CO2 (kg) implying displaced air mass
mlg: mass of lifting gases (kg)
: mechanical stress (Pa)
Δp: pressure difference (Pa)
Calculated simulation parameters
ΔLPg: difference in liquid proportion of methanol due to
the liquid portion (dimensionless quantity)
ΔLPl: difference in liquid proportion of methanol due to
the liquid portion (dimensionless quantity)
Δt: time increment (s)
g: heat flux absorbed by the gas portion (W)
l: heat flux absorbed by the liquid portion (W)
Eg: energy of the gas portion (J)
El: energy of the liquid portion (J)

Page 1 of 15

LP: liquid phase methanol portion (dimensionless
quantity)
ma: apparent mass (kg)
Mlg: average molar mass of lifting gases (kg/mol)
nlg: quatity of lifting gases (mol)
rg: lifting gas radius (m)
Sg: enthalpy of the gaseous portion at the end of
vaporization (J)
sg: thermal exchange surface of lifting gases (m²)
Sl: enthalpy of the gaseous portion at the start of
vaporization (J)
Tg: temperature of gas portion (K)
Tl: temperature of liquid portion (K)
Vg: lifting gaz volume (m3)
vz: vertical speef (m/s)
Z: altitude (m)
Simulation parameter depending external parameter
(altitude, geometry, speed)
ρco2: density of CO2 (kg/m3) implying external air
ρh2: density of dihydrogen (kg/m3)
ρlg: overall density of lifting gases (kg/m3)
ρme: density of methanol (kg/m3)
ρn2: density of dinitrogen (kg/m3)
Cph2: Heat capacity of dihydrogen (J/(mol.k))
Cpme: Heat capacity of methanol (J/(mol.k))
Cpn2: Heat capacity of dinitrogen (J/(mol.k))
Cz : baloon drag coefficient (dimensionless quantity)
Pext : external pressure (Pa)
rtg: surface thermal resistance of the gas portion
(W/(m².K))
rtl: surface thermal resistance of the liquid portion
(W/(m².K))
S0g: molar enthalpy of gas methane at vaporization
temperature (J/mol)
S0h2: molar enthalpy of gas dihydrogen at vaporization
temperature (J/mol)
S0l: molar enthalpy of liquid methanol at vaporization
temperature (J/mol)
S0n2: molar enthalpy of gas dinitrogen at vaporization
temperature (J/mol)
Tb: Boiling temperature of methanol (K)
Text: external temperature (K)
Acronyms/Abbreviations
CNSA: China National Space Administration
DAVINCI+: Deep Atmosphere Venus Investigation of
Noble gases, Chemistry, and Imaging
ESA: European Space Agency
ISRO: Indian Space Research Organisation
ISRU: In situ resource utilization
LOVE: LOw-cost Venus Exploration
MarCO: Mars Cube One
MIT: Massachusetts Institute of Technology
NASA: National Aeronautics and Space Administration
(USA)

PPD-T: poly-p-phenylene terephthalamide, Kevlar®
PTFE: Polytetrafluoroethylene, Teflon®
U: cubsat unit
VERITAS: Venus Emissivity, Radio Science, InSAR,
Topography, and Spectroscopy
VEXAG: Venus Exploration Analysis Group
VLF: Venus Life Finder
VOICE: Venus Volcano Imaging and Climate Explorer

1. Introduction
Note 1: the terms of the lexical fields of life as
viability or habitability are used from the point of view
of life as we know it on Earth.
Note 2: the term “geology” is etymologically linked
to the Earth. But to simplify, this term will be used here
to designate the scientific study of Venus and its
physical properties, its reliefs, its composition, its
history and all the phenomena that have affected it or
still affect it.
Venus is very close to Earth in terms of distance,
size, and composition [1]. With the conditions so close,
Venus should have evolved like Earth and have a very
similar environment with liquid water [2] on the
surface. But currently the reality is very different with a
CO2 atmosphere, a surface temperature of 460°C, a
pressure of 90bar and clouds of sulfuric acid. It is
therefore necessary to understand when and why the
evolution of Earth and Venus diverged. This
understanding could help anticipate the future evolution
of the Earth but to apply this new model to the
exoplanet to be able to distinguish a viable Exoterre and
an infernal Exovenus[3].
In addition to its past, many current details are
unknown to us. We do not know the internal power of
the planet and its impact on tectonic/volcanic activity.
Its atmosphere, unique in the solar system, also presents
many unknowns about its dynamics, chemical
processes, and the presence of aerosol. This is an
element that would allow us to learn more about the
habitability of telluric planets. Indeed, despite the
hellish conditions on the ground, at an altitude of 55km
there are some of the most hospitable conditions in the
solar system. There is a pressure of 0.56bar, 30°C, a
gravity of 0.9g and the thick atmosphere protects
against meteorites and cosmic radiation. These
conditions are so close to the Earth that we could, in the
long term, consider a human presence in the cloud layer
of Venus [4][5].
Exploration of Venus was central to early
spaceflight with dozens of Soviet and American
missions. But instead of the expected twin Earth, it
unveiled the hostile world described above. In addition,
this exploration is difficult because of 3 barriers. First,

Page 2 of 15

the sulfuric acid cloud layer masks the surface from
ultraviolet, visible, and infrared instruments. Second,
the surface conditions heat up the landers, limiting the
lifespan to 2 hours. Finally, a global geological event,
called resurfacing, to renew the entire surface of the
planet about 700 million years ago erases most of the
previous geological traces. Because of this, since the
early 1990s, only two orbital missions have been sent
(Venus Express and Akasuki) and have focused on
studying the atmosphere.
However, we are currently experiencing a renewed
interest in this planet to answer the scientific question
described above. ESA's Envision and NASA's
VERITAS missions aim to study the surface using
radars that pierce the cloud layer. ISRO's Shukrayaan-1,
NASA's Davinci and MIT/Rocket lab's VLF are to
study the atmosphere either from orbit or in-situ.
Finally, the perimeters of the CNSA’s VOICE and
Venera-D of roscosmos are not yet fully defined or
public.
Most of these missions only involve orbiters or
probes that only make the crossing of atmospheric.
However, the atmosphere of Venus is sufficiently dense
to allow the use of an atmospheric platform capable of
maintaining altitude over long periods. This has already
been done in the past with the two Vega balloons which
in the 80s operated for two days each, the lifetime of
their batteries. In addition, a balloon changing altitude
would have the ability to perform, over time,
measurements on a multitude of cloud layers and would
allow us to better understand them. Finally, if it’s able
to descend under the clouds, it could study the lower
haze layer which is relatively unknown and image the
surface in visible and infrared. This visualization,
impossible from orbit, would provide more clues about
the composition and morphology of the rocks to better
understand their past.
In addition, the miniaturization of technologies in
recent years makes it possible to envisage an
atmospheric mission that is both more efficient and
lighter than what has been done in the past. The cloud
layer of Venus, having conditions close to those known
on Earth, lends itself particularly well to the use of
instruments and equipment used on Earth [6].
Under these conditions, the idea of this study is to
propose an architecture for an atmospheric platform of
small size and low cost offering a complement to the
major mission mentioned above. in order not to need to
organize a complete mission with launch, cruise stage
and communication network only for a small platform,
the objective is to make it a co-passenger of a main
mission or participated in a mission carrying a multitude
of small mission. To facilitate interfacing and guarantee
the safety of the associated missions, there are cubsat
standards [7] which the atmospheric platform must
meet.

2. Scientific background
2.1 Reminder on the atmosphere of Venus
Venus is a terrestrial planet with a mass and
gravity like that of Earth. However, its atmosphere is
much more massive and is made up of 97% CO2 and
3% nitrogen. With the greenhouse effect, the surface
temperature is 470°C and 90bar pressure. The
temperature and pressure decrease with altitude to leave
a "habitable" zone at 0.5 bar and 30°C at 55km altitude.
It is around this altitude, between 60km and 40km that
the layers of sulfuric acid clouds are found which
completely hide the surface of the planet [8].
For dynamic behaviour, the atmosphere has an
independent rotation of the planet. This phenomenon
called super rotation causes a regular wind of 100m/s in
the habitable zone and a rotation of the planet in
100h[9][10]. The rotation of the planet being extremely
slow (sidereal days of 224 Earth days) this revolution of
the atmosphere of 100h is approximately the duration of
a day-night cycle of a platform in levitation at an
altitude of 50km. Each hemisphere is also characterized
by Hadley cells in each hemisphere with weak currents
of about ten meters per second from the poles to the
equator below 60 km and from the equator to the pole
above [11].
2.2. Scientific objectives
The definition of scientific investigations that
can be performed with an atmospheric platform is based
on the study of NASA's Venus Exploration Analysis
Group, VEXAG. This group regularly publishes a study
of the goals, great point to understand on the planet,
investigation, the questions to be answered to
understand the goal and the investigation, the elements
analysed to answer the goal [12]. In addition, they
analyse which type of platform can respond to which
investigation [13]. Atmospheric platforms are among
the best vectors and are divided into 3 categories.
The fixed altitude platforms study only one
altitude located around 55km. Thanks to the super
rotation, it would go around the planet in a hundred
hours allowing it to fly over a large region. It can
measure the magnetism trapped in the crust [14] to
better understand the global magnetic activity that is
now extinct. It can also, by acoustic instruments, detect
seismic activities [15] which will inform us about the
current geological activity. However, it is especially
efficient in the study of the atmosphere. It can measure
the concentration of isotopes of certain elements, which
would inform us about the basic constituents of the
planet and the possible dispersion of certain elements. It
would also make it possible to study the dynamics and
heat transfer in the atmosphere on a large and small
scale. Finally, it can study the chemical composition,
their interaction, and the presence of aerosol in the

Page 3 of 15

atmosphere to better understand the functioning of the
cloud layer, see if there is still volcanic outgassing and
potentially identify the absorber of ultraviolet rays
present in the atmosphere.
The second type of atmospheric platform has a
variable altitude between 50 and 60km, i.e., in the cloud
layer. Such a platform would make it possible to carry
out the same investigations as a platform at a fixed
altitude, but instead of being limited to an altitude, it
would cover the entire cloud layer. It would therefore
offer us a global view of the dynamics, chemistry, and
heat exchanges of this unique zone in the solar system.
The conclusions would allow us to know more about the
evolution of telluric planets for application to the
exoplanet.
The last type of atmospheric platform has a
variable altitude between 40 and 60km above sea level.
In addition to the investigations of the previous model,
this downward extension of the domain makes it
possible to explore the lower haze layer. This layer is
quite unknown because hidden from orbit by the clouds
above and probably has their origin. Descending to
40km allows you to pass under the clouds and therefore
observe the surface with ultraviolet, visible, or infrared
instruments where orbiters can only use radar and some
infrared windows. The study of rocks under different
wavelengths to have more information on their
composition. This progress would allow us to learn
more about surface-atmosphere interactions and to
detect potential rock of hydrated origin, allowing us to
better understand the past of the planet. This direct
observation would improve our knowledge of the
morphology of certain regions, making it possible to
date formations by stratigraphy, or to look for traces of
erosion.

communication costs. The client is therefore not
necessarily a large space agency but perhaps a more
modest space agency, a university, a private company
laboratory, a research institute, or an association.

3. Mission philosophy
The name LOVE is for LOw-cost Venus
Exploration. His idea is to propose mission models in
the atmosphere of Venus for a budget that could be
assumed by more moderate actors than space agencies.
This is done by applying the cubesat economic model to
interplanetary exploration and more particularly the
Venusian atmosphere. The need starts from a customer
with a scientific questioning requiring investigations in
the Venusian atmosphere but not retained within the
framework of a major mission. It provides the scientific
instrumentation in the cubsat format necessary for the
investigation, the financing of the service part presented
in this study as well as the requirements on the flight
envelope of the platform. Then there remains the
negotiation and financing of a co-passenger seat on a
mission to Venus as well as the bandwidth for
communications. The costs are more modest due to the
small size of the mission, the standardization of
equipment and the sharing of launch, transit, and

4. Technical Solution
4.1 Lift solution
The first point is to design a means of
generating lift in the habitable zone of Venus.
Technologies requiring a constant supply of energy to
maintain altitude such as aerodynes or hot air balloons
are excluded. Indeed, either it should evolve at more
than 100m/s to stay on the lighted side by countering the
super rotation or spent several dozen hours in the dark.
This would require an aircraft that is too fast or with too
much battery to be compatible with our objective of
simplicity and lightness. The chosen solution is
therefore a carrying gas aerostat. Solutions using the
wind guardian with altitude such as a double kite system
or gradient flight can also be used but this promising
technique does not have the level of maturity sufficient
for this project.

The platform is divided into 3 parts:
Instrumentation: The payload including the
scientific instrumentation provided by the customer
according to the desired investigations.
Service module: the role of the service module
is to provide everything necessary for the operation of
the instrument. This includes energy, computer control,
communications, and thermal management. It also
includes management of altitude control
Sustentation assembly: the base of the platform
is the system allowing everything to be maintained at
altitude and to control this altitude.
This platform is not designed to support
atmospheric entry. It must therefore be released into the
atmosphere after being protected by a heat shield. It can
integrate the entry capsule of an atmospheric probe like
DAVINCI+ or a lander like Venera-D. If the platform
finds a place on a purely orbital mission, it will be
necessary to add a minimalist capsule to protect it.
Finally, in the case of a mission carrying a multitude of
small missions, it is possible for a capsule to lag several
atmospheric platforms and probes.
The goal of the LOVE project is to present a
service module architecture and suspension assembly
allowing a customer to develop the mission. The use of
the cubsat format simplifies things by developing a
service module and the standard suspension assembly to
which the payload can be quickly adapted.
This study focuses on solutions for lift and
altitude control.

Page 4 of 15

C: lithium hydride, water, and CO2:
Like solution B, the platform transports lithium
hydride and water, but in lesser amounts. Once in the
atmosphere, in addition to water, external CO2 is also
introduced into the reactor. This CO2 reacts with LiOH,
the waste product of the first reaction, producing
Li2CO3 and water. This water thus produced replaces
part of the water imported from the Earth.
Fig. 1. Selection chart for lifting solution
The lifting gas and its mode of transport should
be defined. Safety standards and the mass of tanks
prohibiting the use of high-pressure storage. Cryogenic
transport entails a risk for the main mission in the event
of degassing and is therefore excluded. Solutions based
on electrolysis of imported water or atmospheric CO2
are excluded because they are too slow and too energy
consuming to be used during the descent into the
atmosphere. There remains the storage of liquid or solid
precursor allowing chemical production of the carrier
gas. Several solutions of increasing performance and
complexity are discussed below.
A: direct water vaporizing:
The lifting gas is water. It is stored in a liquid state
during the Earth-Venus transit. It heats up during the
fall in the atmosphere and ends up vaporizing below
40km altitude. To remain in the gaseous state and
generate lift, the balloon must regularly pass below an
altitude of 40km and expose the platform to more than
100°C.

Fig. 2. block diagram of the solution direct water
vaporizing
B: lithium hydride and water:
During transit, the platform contains water in a
liquid state and lithium hydride stored in a solid state.
During the fall in the atmosphere, the water is injected
into the lithium hydride. The spontaneous chemical
reaction produces hydrogen which is the lifting gas and
lithium hydroxide. The hydrogen is injected into the
balloon and the reactor which contained the lithium
hydride, now full of lithium hydroxide, is dropped once
the chemical reaction is finished.

Fig. 3. block diagram of the solution lithium hydride
and water

Fig. 4. block diagram of the solution lithium hydride,
water, and CO2
D: hydrazine
The platform transport hydrazine. During
descent into the atmosphere, hydrazine is brought into
contact with a catalyst and spontaneously decomposes
into hydrogen and nitrogen, which are both carrier gases
in the atmosphere of Venus. The injection of hydrazine
on the catalyst must be done in a controlled way
because it is exothermic. During the descent, hydrazine
is injected continuously to keep the balloon inflated but
without applying excessive pressure and temperature.

Fig. 5. block diagram of the solution hydrazine
To be able to evaluate the effectiveness of each
solution, we calculate different parameters for a lift of 1
kg in the atmosphere of Venus. These different
parameters are:
The number of moles of lifting gases: You can
use the ideal gas law to determine the density of the
gases in the regions to be studied. In ideal gas, all other
things being equal, the volume of a gas is proportional
to its number of moles. So, comparing the number of
moles of lifting gas makes it possible to compare the
size of the balloon necessary without having fixed the
external parameters (pressure, temperature).
Mass transported: it is the mass of precursor
necessary to produce the lifting gases in their
conditioning of interplanetary transport. It does not
include the mass of the tanks (see below).
Volume transported: this is the volume of
precursor necessary to produce the lifting gases in their
interplanetary transport conditioning. This parameter
makes it possible to compare the mass of the tank
necessary for transport.
Vaporization temperature at 1 bar: the pressure
inside the tanks being limited to 1bar for safety reasons,

Page 5 of 15

this is the pressure for which the tanks are sized. The
temperature of the fluid must therefore not exceed the
vaporization temperature at this pressure during the
interplanetary transit at the risk of causing the tank to
explode.
Table 1. Comparative table of lift generation methods
solution
A
B
C
D
gas 1
H2O
H2
H2
H2
Nb moles
38.5
23.8
23.8
20
N/A
N/A

N/A
N/A

N/A
N/A

N2
10

Nb moles
total

28.5

23.8

23.8

30

Precursor1
Nb moles
Mass(kg)
Volume
(L)
Tv 1bar
(°C)

H2O
38.5
0.692
0.692

H2O
23.8
0.429
0.429

H2O
11.9
0.214
0.214

H4N2
10
0.32
0.312

100

100

100

114

Precursor2
Nb moles
Mass(kg)
Volume
(L)
Tv 1bar
(°C)

N/A
N/A
N/A
N/A

LiH
23.8
0.19
0.244

LiH
23.8
0.19
0.244

N/A
N/A
N/A
N/A

N/A

688

688

N/A

Total
Mass
Total
volume
(L)
Tv min
(°C)

0.692

0.619

0.405

0.32

Fig. 6. Selection chart for lift control solution

0.692

0,673

0.458

0.319

100

100

100

114

Recover
Nb moles
Mass (kg)

N/A
N/A
N/A

N/A
N/A
N/A

CO2
11.9
0.524

N/A
N/A
N/A

Waste

Dropped
Nb moles
Mass (kg)

N/A

LiOH
23.8
0.571

LiCO3
11.9
0.798

N/A
N/A
N/A

The idea is to use a liquid fluid at high altitude
and gaseous at low altitude. It is therefore necessary that
the main carrying gas generates a lift slightly lower than
the weight of the platform. If the altitude control fluid is
in the liquid phase, the lack of lift causes the descend of
platform. At low altitude, the fluid vaporizes generating
additional lift which raises the platform. Each fluid has
a transition altitude which corresponds to the
temperature and vaporization pressure of the fluid. This
means that the balloon will oscillate around this altitude.
The amplitude of these oscillations is determined by the
heat exchange surface. The larger this surface, the
weaker the oscillations will be because the platform
rises shortly before enough fluid has liquefied and vice
versa. The geometry of the balloon being dictated by the
lift, a tube is added to increase the exchange surface.
Depending on the needs, we can predetermine the
trajectory of the platform, select the altitude thanks to
the chosen fluid and determine the amplitude according
to the length of the tube.

Transit

gas 2
Nb moles

ISRU

flight

4.2 Altitude control solution
There is a great scientific interest in being able
to modify the altitude to explore several layers of the
atmosphere and/or past under the cloud layer. Three
criteria are decisive in the choice of the altitude control
solution. This solution must have a limited energy
consumption to prevent the batteries needed to cross the
unlit side from affecting the payload. Then, it must be
possible to guarantee that the platform can easily ascend
to a safe altitude if it risks overheating at low altitude.
Finally, it is necessary to limit the excess pressure
applied to the balloon to avoid oversizing the resistance
of the envelope. Air heating or water electrolysis
solutions require too much energy to be acceptable and
do not allow you to ascend without energy. An air
ballast balloon allows rapid ascent without energy input
but requires over-pressurizing the entire balloon and
requires energy to be piloted. Mechanical compression
balloons are overpressure and require folding that is not
easily compatible with the cubsat format. The gas
pumping solution also allows rapid safety when
degassing but requires energy to compress the gases in
tanks that take on volume. The solution adopted is the
use of a phase change fluid.

N/A
N/A

Page 6 of 15

Table 2. Comparative table of lift control fluids useable
between 40 and 60km altitude
Fluid

2-Methyl
pentane
n-hexane
Methanol
n-heptane
Water
Toluene

Chemical
formula

Transition
altitude
(km)
57.1

Tv
(°C)

Pv
(bar)

C6H14

Molar
mass
(kg/mol)
86.2

12.6

0.178

C6H14
CH4O
C7H16
H2O
C7H8

86.2
32
100.2
18
92.1

55
54.4
47.9
47.1
43.8

29
34.8
91.7
97.3
120

0.236
0.271
0.756
0.841
1.29

Fig. 7. Simulation of natural oscillation for different
fluids (Green=methanol, blue= water, red= toluene) and
tube lengths (continuous=2m, dotted=10m). continuous
green (methanol with 2m tube) corresponds to the
reference design of §5.
The volume of the balloon must be sized with a
volume greater than what the lift gases will occupy at
the maximum altitude of the oscillations. This prevents
the gases from exerting pressure on the envelope other
than the pressure due to Archimedes' force. This makes
it possible to limit the tension on the envelope and
therefore to reduce its mass. In addition, its dual fluid
system provides redundancy. Indeed, in this study,
97.5% of the lift is provided by the main lift gases
which do not change state. 5% of lift is generated by the
altitude control fluid so that during the oscillation the
lift can vary from 97.5% in descent to 102.5% in climb.
This therefore provides a 2.5% margin for leakage
through the envelope. The platform will continue to
maintain its altitude if the lift is greater than 100%, but
this will have the effect of reducing the amplitude of the
oscillations.
In addition to the control pre-established by the
design, the piloting can be done by a system of trapping
the fluid in the tube thanks to a valve between the latter
and the balloon. The idea is, by closing the valve, to
maintain part of the altitude control fluid in a liquid
state at temperatures higher than what is allowed. The
increase in pressure that this implies is the dimensioning
factor of the tube according to the minimum altitude
desired. From an energy consumption point of view, this
solution is economical because it only includes closing
the valve. For safety measures, it is necessary to provide
a mechanical opening of the valve under a pressure

corresponding to the minimum altitude, to release the
fluid and raise the platform if it goes too low.
Control is done in 3 ways:
Increase the amplitude: To increase the
amplitude of the oscillations, the valve must be closed
when descending. This means maintaining lift less than
the weight of the platform and maintaining descent if
the valves are closed. It is then necessary to open the
valve at the low point of the new oscillation.
Decrease the amplitude: To decrease the
amplitude of the oscillations, the valve must be closed at
the start of the ascent to trap part of the altitude change
fluid. With a lower amount of fluid, the oscillations are
smaller.
Hovering: it is impossible to maintain flight at
a fixed altitude for a long period of time. The altitude of
the hover must be lower than the low point of the
previous oscillations. As for a descent, the valves are
closed to maintain a lift lower than the weight of the
platform. As the target altitude is approached, the valve
is gradually opened to reduce the rate of descent. The
goal is to find the balance point of the lift to cancel the
vertical speed. It is impossible to find your point of
balance perfectly and once you have gone up, it is
impossible to stop it. So, the hovering time is limited
but determined by the piloting precision. As a reminder,
in the idea of the mission, this type of hover is
especially interesting to pass under the clouds, therefore
at a high temperature that the platform cannot withstand
over a long period.

Fig. 8. Simulation of different piloting cases. Start of
piloting at 7.5h. Natural oscillation in green. Damped
oscillation in blue (46% trapped methanol). Oscillation
amplifies in red (descent at 35km). Stationary in orange
(10h at 35km). These are the cases of control of the
reference design of §5.

Page 7 of 15

5. Reference design
The section below is a preliminary design study of
the suspension system based on possible scientific
requirements and for a minimum size.
5.1. Requirements
We dimension the mission of minimum size; we
therefore consider that the scientific payload fits into 1
cubsat unit (cube of 10cm side and 1.3kg). This
approach by standard unit allows to have a direct
proportionality between the payload and the rest of the
components. The design of this instrument being
defined by the desired scientific investigation, it will not
be detailed in this study.
The service module allowing the operation of the
payload is also considered how entering a cubesat unit.
Its design depends on certain external elements such as
the electrical consumption of the payload as well as the
amount of data to be transmitted to Earth directly or not.
It will not be detailed in this study.
Both elements are designed for normal continuous
operation between -10 and 70°C. Their thermal
insulation is sized to withstand 10 hours at 185°C before
returning to its normal operating range.
The natural oscillation of the platform, determined
by the design, must vary from 50 to 60km of altitude.
This corresponds to the normal range of variation of a
variable altitude balloon defined by VEXAG (see §2.2).
This altitude makes it possible to carry out
investigations on the functioning of the atmosphere
while remaining within a temperature range (-10°C to
77°C) acceptable for conventional equipment. We add a
piloting capacity to lower the oscillations and / or
maintain hover up to 35km altitude. This fully covers
the improved range of variation defined by VEXAG. It
allows a better exploration of the lower haze layer but
also to carry out investigations on the surface by
observing it directly under the clouds. However, this
exposes the platform to temperatures of 182°C. It will
be checked in this study that the materials of the
suspension assembly are suitable for these temperatures
and the mechanical calculations will be made for the
resistance of the materials at this temperature.
5.2. Main lift
The main lift has the role of ensuring 97.5% of the
lift of the platform. The most effective solution present
in §4.1 is selected, i.e. transport in the form of
hydrazine. In flight, it forms hydrogen (59.5mol) and
nitrogen (29.7mol) which remains in a gaseous state
over the entire altitude range of the platform. It is
transported in the form of hydrazine (29.7 mol) in a tank
sized to contain a pressure of 1 bar with a safety factor
of 4. At this pressure, the vaporization temperature
(exceeding it would cause the tank to burst) of 114° C
which is above the standard operating range of a cubsat.

The transport of hydrazine in cubsats has already been
studied for propulsion needs (monopropellant)[16]. The
tank is placed on a reactor including a catalyst in contact
with which the hydrazine decomposes into hydrogen
and nitrogen during the filling of the balloon. This
reactor allows the gradual and controlled injection of
hydrazine to control the thermal rise.
Design calculation
All the calculations of this study were done
incrementally to obtain the total dry mass in flight, the
mass of the platform, balloon and tube included. Here
we confirm the lift calculations.
The lift is done by the Archimedes force. We are in
ideal gas, and we consider the pressure and the
temperature to be identical inside and outside the
balloon.

Since the Archimedes force must compensate for the
lift, which both depends on the acceleration of gravity,
we can overcome it. In addition, we must calculate the
average molar mass of the lifting gases knowing that the
use of hydrazine creates a proportion of 1 mol of
dinitrogen for 2 mol of dihydrogen.

We therefore have a total of 89.2 mol distributed for
1 third (29.7 mol) of dinitrogen and 2 thirds (59.5 mol)
of dihydrogen. To generate this gas, you need as many
mol of hydrazine as of nitrogen, therefore 29.7 mol.
5.3. lift control
The altitude control system provides 5% of the
variable lift thanks to methanol (12.7 mol). This fluid is
chosen because the transition altitude is 54.5 km,
exposing the platform to an average temperature of
around thirty degrees Celsius. During transport, the
methanol is contained in a tube wrapped around the
hydrazine tank. The tube is sized to resist a pressure of
22.4 bars with a safety factor of 3. standard use of a
cubsat. The transport of methanol in cubsats has already
been studied for propulsion needs (resistojet) [17]. The
walls of the tube consist of two layers. A first layer of
17.1 µm of PPD-T (Kevlar®) has the role of supporting
the pressure exerted by the methanol in the trapping

Page 8 of 15

phase. PPD-T is chosen because it is extremely resistant
and loses little resistance at temperatures of around
200°C. A second layer of 6µm of PTFE (Teflon ®) on
the outside provides sealing and protects against sulfuric
acid clouds [2]. These two materials remain stable at a
temperature of 182°C that the platform will encounter at
an altitude of 35km. The resistance calculations are
made at this temperature which is more binding.
This tube connects the service module on the
one hand and the tank on the other. A bypass allows the
gas leaving the reactor to reach the balloon after having
passed through the tube. This bypass is self-opting to
close once the reactor has been jettisoned with the
hydrazine tank. In flight, the tube acts as a heat
exchanger, the liquid methanol descending into it
increasing its contact surface. It is this role of heat
exchanger which determined its length of 2m. The
simulations give a natural oscillation having a high
point at 59.1 km, a low point at 50.2 km and a period of
5 hours.

pressure of the liquid methanol trapped in the tube
would mechanically open the valve to prevent the
platform from overheating or the tube bursting. The
valve, ring and spring are made of aluminum alloy
while the control wire is made of PPD-T. The valve and
the ring are made of INVAR (nickel-iron alloy), the
spring is made of steel and the control wire is made of
PPD-T. These materials remain stable at a temperature
of 182°C that the platform will encounter at an altitude
of 35km. The assembly is located inside the balloon and
the tube, therefore protected from external attacks. The
actuator that pulls the cable is inside the service module
and therefore protected by its insulation. INVAR and
PPD-T have a low thermal expansion which avoids
blockages or opening in the valve due to a deformation
of the system.

Fig. 8. Valve details
Design calculation
The number of moles of the lift control system
is calculated in the same way as for the main lift
Fig. 8. Natural oscillation of reference platform
The tube also acts as a methanol trap for
piloting the platform. For this a valve is installed at the
junction of the tube with the balloon. If you want to
descend below the minimum altitude of the natural
oscillation, you must close the valve while enough
methanol is in the liquid state in the tube to prevent
having a positive lift. We design the platform for a
minimum altitude of 35km, therefore a temperature of
182°C and a pressure of 5.9 bar. At this temperature, the
vaporization pressure of methanol is 28.3 bars, the tube
must therefore be able to withstand a pressure of 22.4
bars to maintain the methanol trapped in the liquid state.
To simplify the design as much as possible, the
valve is insert on the balloon side and closed by pushing
it on a ring at the end of the tube. This closure is
controlled by a wire inside the tube drawn from the
service module. The valve return spring guarantees a
default opening which, in the event of a failure of the
piloting system, would cause the platform to return to its
natural oscillation (between 50 and 60km altitude). In
addition, the maximum traction that the valve closing
system exerts on the cable is limited to the force exerted
by 22.4 bars on the surface of the valve. Thus, in the
event of a descent below an altitude of 35 km, the

There is therefore 12.7 mol of methanol which
represents a volume of 0.514 L in the liquid state. It is
this volume that the tube must contain. The radius of the
tube and its length are therefore linked, and the
simulation (see §6) gives a length of 2m and a radius of
9.05mm.
We can therefore calculate the thickness of
PPD-T from the stress

If we dimension as accurately as possible, it is
necessary that:

5.4. Balloon

Page 9 of 15

The balloon is spherical with a diameter of
2.6m and an inflated volume of 9.32m3. This volume
corresponds to the volume occupied by all the fluids
(hydrogen, nitrogen, methanol) in the gaseous state at an
altitude of 60km. Full inflation is unlikely because
simulations show that the maximum altitude of
controlled or uncontrolled oscillations is 59.2km and it
is unlikely that methanol is entirely gaseous at such an
altitude. The balloon envelope consists of two layers. A
first layer of 6µm of PPD-T has the role of supporting
the loads. A second layer of 6µm of PTFE on the
outside provides sealing, protects against UV rays and
protects against sulfuric acid clouds [2]. These two
materials remain stable at a temperature of 182°C that
the platform will encounter at an altitude of 35km.
The top of the balloon is connected to an
extraction parachute by a cable. The parachute, fixed
outside the cubesat, is deployed when the platform is
ejected from the disperser. Initially, it stabilizes the
platform in the extraction position. Then the top hatch is
ejected allowing the balloon to deploy. The parachute
and its retaining cable are made of PPD-T. Since it's
only useful for the first few seconds of deployment at
high altitude, it doesn't need to be acid resistant, and it
will come loose. The simulations show that the presence
of the parachute has a minor impact of around 0.3% on
the altitudes of the natural oscillations and no impact on
the piloted oscillations.
Design calculation
We calculate the maximum dimension of the balloon as
being the volume of all fluid in the gaseous state under
the conditions present at 60km altitude

5.5. Assembly
For a mission in cubesat format, we must define the
number of units in which necessary. The payload and
the service module are already in 1U each. The volume
and the mass of the elements integrated for the
suspension system are compatible with 2U giving a total
configuration of 4U.

once the balloon is filled. In these units is, from bottom
to top, the reactor, the hydrazine tank, and the folding
balloon. The tube containing the methanol is wound
around the hydrazine tank, the upper end is attached to
the balloon, the lower end is attached to the bottom of
the service module and the bypass is attached to the
reactor. The stabilization/extraction parachute is placed
on the cover above the balloon.

Fig. 8. Platform in transport configuration
5.6. Deployment sequence
The platform plays a passive role during launch,
interplanetary transit, and atmospheric entry. The
deployment sequence begins with the ejection of the
platform once the capsule has slowed down in the dense
layers and the unnecessary heat shield. The parachute
simply placed on the platform stabilizes the -Z axis in
the direction of the velocity vector. Once stable, the
cover is ejected allowing the deployment of the balloon
and the unrolling of the tube. The hydrazine is gradually
injected into the reactor where it decomposes into
hydrogen and nitrogen. This decomposition releases
heat which is partly absorbed by the methanol when the
gases rise in the tube to reach the balloon. During the
inflation of the balloon, the gases are hotter than the
outside air and therefore have more lift. This slows
down the descent, giving it time to cool down and finish
hydrazine catalysis. Once the tank is empty, the left 2Us
are dropped to relieve the platform. Since the balloon is
connected via the tube to the bottom of the service
module, the latter turns around in its final position,
payload down to observe the surface.

See mass budget in annex A
We define an orthonormal reference x, y, z or we
will say +x=in front, -x= behind, +y=right, -y=left,
+z=top, -z= bottom. The service module occupies the
unit at the bottom right and the payload at the top right.
The two units on the left are common to house the lift
and altitude control assembly. They are jettisonable

Fig. 9. Platform in flight configuration

Page 10 of 15

6. Flight mechanics
The section below gives the flight mechanics
equations for the platform used for simulation. The
trajectory is calculated with the altitude, the speed of
evolution and the energies according to the altitude
conditions and the parameters at the previous time
increment.
6.1. energy of the liquid portion
The internal energies are divided in two parts, the
liquid partion composed only of methanol and the
gaseous partion which is to constitute nitrogen,
hydrogen, and the gaseous fraction of methanol. Note
that the heat exchange at the solid-liquid interface is
negligible because of the small contact surface (only the
section of the tube).
With

With the energy, it is possible to calculate the
temperature and the proportion of liquid methanol.
Knowing that:
If the energy is lower than the vaporization start
entropy, the temperature is lower than the vaporization
temperature and the methanol does not vaporize (the
liquid portion does not decrease)
If the energy is between the vaporization start
entropy and the vaporization end entropy, the
temperature is equal to the vaporization temperature and
part of the methanol vaporizes reducing the liquid
portion
If the energy is greater than the entropy at the end of
vaporization, all the methanol vaporizes and the
calculation of the temperature of the liquid portion is no
longer necessary.

6.2. energy of the gaseous portion
The calculation of the energy of the gaseous portion
are similar.
It is considered that, if the balloon is not filled, the
gases adopt a spherical shape at the top of the balloon.
The lower part of the canvas remaining bent, it is not

involved in heat exchange. We must therefore calculate
the volume of gas and the exchange surface.

To calculate the temperature and phase change, it is
necessary to calculate the entropies at the beginning and
at the end of vaporization for the entire gaseous portion.

The cases are the same as for the liquid portion
If the energy is lower than the entropy at the start of
vaporization, all the methanol liquefies, and the gases
remain at a temperature lower than the vaporization
temperature of methanol at this pressure.
If the energy is between the start and end entropy of
vaporization, part of the methanol will liquefy, and the
overall temperature of the gas will be the vaporization
temperature of methanol at this pressure.
If the energy is greater than the entropy at the end of
vaporization, the already gaseous methanol does not
liquefy.

6.3. dynamic behaviour
To know the dynamic behaviour, it is first necessary
to know the portion of methanol in the liquid state at the
next time increment.

Finally, we must calculate the vertical speed of the
balloon by first passing through the apparent mass of
the platform.

Page 11 of 15

We therefore calculate the vertical speed which is
positive in ascent and negative in descent. It depends on
the apparent mass and the aerodynamics of the balloon

7. Discussion
It is therefore technically possible to create an
atmospheric platform in cubsat format, but it is
necessary to imagine the context allowing its
deployment and operation. In view of the low mass, a
mission entirely devoted to it would be extremely
expensive. In effect, this means that the cost of the
launch, the cruise stage and the heat shield are fully
borne by the customer for only one, as in the reference
design, or a low number of cubsat units of
instrumentation. The platform is rather designed with
the idea of being a co-passage of a major mission. It is
this mission that would have a dedicated launcher and
would manage trajectory corrections during transit as
well as the Venusian orbit. The optimal solution would
be that the mission already has an entry capsule for an
atmosphere probe or a lander like DAVINCI+,
VENERA D, Venus Life Finder and potentially
Shukrayaan-1. It would be necessary to find a volume of
a few litres in the entry capsule to house a disperser
which would eject the platform as soon as the heat
shield was opened and before the parachutes of the main
probe opened. If the mission only includes an orbiter
such as ENVISION or VERITAS, it will be necessary to
add a small entry capsule dedicated to the atmospheric
platform which will be released from orbit or before
orbital insertion.
In each of the two cases, this makes an additional
mass which should be removed from the mass of the
main mission if the latter is dimensioned to the
maximum of the performance of the launcher.
Obviously, this overload will have to be compensated
with the organizer of the main mission, but the cost will
be counted in tenth or even hundredth of the cost of the
main mission. It therefore becomes assumable by an
actor such as a smaller space agency, a university, a
research institute, or an association. In this context, the
use of the cubesat format has a double interest. First,
these standards impose safety rules that do not endanger
the much more expensive main mission. Second, the
standardization of dimensions and delivery systems
simplifies interfacing because the designers of the main
mission do not have to liaise with the designers of the
atmospheric platform but simply integrate a 4U
disperser and consider the mass.

Fig. 10. Illustration of the integration of two 4U
dispersers in the DAVINCI+ entry capsule after
dropping the rear heat shield.
It is also possible to organize a mission dedicated
solely to the delivery of a multitude of payloads in
cubsat format in the Venusian atmosphere. Some
payloads would be dropped into Venusian orbit such as
the cubesat which is used today for Earth observation.
The rest would be integrated into an entry capsule and
would constitute an atmospheric probe that would only
fall into the atmosphere, ephemeral landers or an
atmospheric platform as described in this study. The
mission organizer would therefore buy a launch and
produce a cruise stage and the entry capsules. This cost
would be distributed among the multitude of
laboratories that would integrate their payload into the
mission. The mission organizer could be a space agency
wanting to stimulate these laboratories, an association
selling places at cost price or a private company seeking
to make a profit by selling this transport service.

Fig. 11. Example of a multi-experiment transport
mission in the Venusian environment [18]
The management of communications is also
subject to discussion. Given the small size of the

Page 12 of 15

mission and of the service module, the transmitter of the
platform will be limited. The balloons of the Vega
missions proved that a small transmitter could transmit
data to earth from the atmosphere of Venus, but at the
cost of a low rate. It is therefore necessary to study the
use of relays in orbit like the lander and Martian rover
whose transmission regularly passes through the orbiter.
These relays could be major orbital missions like
AKASUKI, VERITAS, ENVISION or Shukrayaan-1 or
a dedicated orbiter. This orbiter can also be in cubsat
format and be brought in co-passage of a main mission
or a multiple experience transport mission. The MarCO
6U cubesat proved that despite their small size it was
possible to establish communications from Mars. The
passage or not by a relay also has an impact on the
reception network with the possibility of transmitting
while the atmospheric platform is not in visibility of the
earth.
8. Conclusion
It is theoretically possible to produce a lift
system in the Venusian atmosphere in cubsat format. In
transport configuration, this support system would
occupy in volume is a mass equal to the load supported
in the atmosphere. The atmospheric platform follows
two flight regimes, a natural oscillation and control
manoeuvres. Natural oscillations can be controlled by
the chosen control fluid and the design of the heat
exchanger. The piloting makes it possible to dampen the
oscillations, to amplify them or to hover. Its control is
energy efficient and includes a mechanical safety device
for the platform.
However, the lifting system is only part of the mission.
To be operational, the concept must be completed by an
instrumentation, a service module, an atmospheric entry
vector and a communication channel.

Page 13 of 15

Appendix A: mass budget of reference design
Transit
Mass
(kg)

Flight

Volume
(L)

Mass
(kg)

Note

Volume
(L)

Note

Main lift

Payload

1.3

1

1U

Payload

1.3

1

Scientific investigation

Service
module

1.3

1

1U

Service module

1.3

1

Energy, thermal control,
communication, altitude
control.

Structure 2U

0.164

0.16**

Contains main lift, lift control and
balloon

Jettisoned
Hydrogene

0.119

5,440*

59,5 moles, gas

Hydrazine

0.952

0.942

Nitrogen

0.833

2,720*

29.7 moles, gas

0,407

1,160*

gas <54,4km < liquid

Tube

0.0043

0,514***

Valve

0.0025

0.005

0.371

9,320***

Hydrazine
tank
Reactor

0.065

0.024**

Lift control

0.05

0.05

0.407

0.514

Tube

0.0043

0.0026**

Valve

0.0025

0.005

Methanol

Balloon

Balloon

0.371

0.193

Parachute and
rope

0.003

0.003

4.62

3.89

Total

29.7 moles, liquid
Aluminium, 0.5mm

Jettisoned

Contains the hydrazine catalyst
and the injection management
system

Jettisoned

12,7moles liquid
2m length, 18mm in diameter,
27µm thick, serves as a methanol
tank
At the tube-balloon interface
Spherical, 2.6m in diameter, 9µm
thick

Methanol

Balloon
Destroyed

4.34

* Volume in gaseous state and at 60 km altitude
** envelope volume only
*** Content volume deploys

Page 14 of 15

Serves as a heat exchanger
and methanol trap
Opening gauge at 22bars

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