The document discusses water-based film-evaporation microthrusters. 1. They utilize the film evaporation principle to expel water propellant through micro-nozzles using efficient thermal valving, allowing for precise maneuvering of small satellites with low power. 2. Testing showed maximum thrust occurs at nozzle throats less than 1.5 μm wide, but widths below 1 μm are needed to prevent leaking and ice generation issues. 3. An improved design was proposed with an array of 1 μm wide nozzles that is expected to resolve prior reliability problems.

1. Water-Based Microthrusters
or
Film-Evaporation Microthruster
Film-evaporation micro thrusters are a type of
propulsion system used in small satellites for precise
maneuvering in space. They utilize the film evaporation
principle to expel a propellant through a micro-nozzle,
allowing for efficient and controlled movement.
The use of water as a propellant offers environmental
and safety advantages, making it an attractive solution
for a wide range of emerging technologies.
by ROHAN SHARMA
[ Aeronautical ]

2. What are CubeSats?
CubeSats are a class of nanosatellites that use a
standard size and form factor. The standard CubeSat
size uses a “one unit” or “1U” measuring 10x10x10
cms and is extendable to larger sizes; 1.5, 2, 3, 6,
and even 12U.
The smallest CubeSat measures 0.25U, which is only a few
hundred grams.
Small satellite propulsion systems are defined as
propulsion systems that require less than or equal to
200 W of power during nominal thruster operations.

3. Overview of Micropropulsion
Compared with conventional propulsion systems, micro propulsion systems
have the following two characteristics in general.
1. They are capable of generating a relatively small thrust (100 mN
magnitude or less) and impulse (μNsmNs).
2. Volume and weight are relatively small. Generally, weight is in
kilograms or lower orders of magnitude. A propulsion system only
with characteristic (1) above is usually called a micropropulsion
system.

4. Need of Propulsion System
• Orbital satellites and spacecraft.
• Interplanetary spacecraft and probes.
• Control of re-entry vehicles.
• Automated resupply missions to the International Space Station.
• Ascent roll control and stabilisation of light to heavy launch vehicles .
• Launch vehicle upper stage attitude, orbital and roll control.

5. Type of Satellite Propulsion Systems:-
The propulsion system is actually a mechanical system
which turns different forms of energy into kinetic energy.
According to the kind of energy utilized, they are roughly
divided into four categories.
1. Gas thruster system :- Using the potential energy of high-
pressure gas stored in a high-pressure vessel (nitrogen,
helium, hydrogen, etc.), accelerating the propellant gas, so
that it is ejected at high speed from the nozzle, to produce
thrust.
2. Chemical propulsion system :- catalytic reaction and
combustion utilizing the propellant that release inherent
chemical energy, are used to accelerate the reaction product
(usually gas). The reaction product is sprayed through the
nozzle at high speed, to produce thrust.
3. Electric propulsion system :- using the means of electric
heating, electromagnetic, or electrostatic to accelerate the
propellant, and emerge with a high-velocity jet-flow.
4. Nuclear propulsion system :- Energy produced by nuclear
fission (or fusion) making the propellant working fluid
(typically an inert reaction substance such as hydrogen or
helium) heated to a high temperature, then the reaction is
ejected from the high-speed spray nozzle, producing thrust

6. Gas Thruster :-
The gas thruster is currently the widely used and the most mature one for micro/nano satellite.
It mainly consists of a propellant tank, solenoid valve, pipeline, a nozzle.
There are many propellants available for gas thruster, such as liquidnitrogen, liquid
ammonia, freon, helium, or butane, which produce thrust by the pressure of the medium
itself in the propellant tank. It produces thrust of 10-100 mN magnitude, and it is
successfully used in many small satellites.
The University of Surrey SNAP-1 gas thrusters which were used successfully on a
satellite launched in 2000.

7. Pulsed Plasma Thruster (PPT)
The PPT is one of the earliest researched electric thrusters. In1964 in the Soviet Zond-2
satellite, it was used in flight tests for the first Time. Because it relies on an electromagnetic
field to accelerate the plasma to produce thrust, it is an electromagnetic electric thruster.
PPT system comprises of a solid propellant rod, propellant feed supply spring, propellant thrust
ring, spark generator, and the yin and yang electrodes.

8. Field Emission Electric Propulsion
(FEEP)
FEEP is an electrostatic electric propulsion, which relys on a high-voltage
electrostatic field accelerating charged ions to produce thrust.
FEEP mainly includes a transmitter (containing a propellant reservoir chamber), an
accelerating electrode, and a neutralizer. The propellant used includes low melting
point metals, such as cesium, indium, etc. Solid propellant is stored in the
transmitter storage chamber until needed, when the reservoir chamber is heated to
liquefy the propellant. Due to capillary action, the liquid metal flows to the emitter
outlet slit.

9. MEMS Thruster
The development of MEMS technology, there is now a microminiaturized propulsion
systembased on MEMS technology, known as the MEMS thruster in the 1990sThere are
mainly two categories of MEMS thruster.
MEMS electric propulsion MEMS Chemical propuls

10. Elaectrothermal MEMS Electrical Propulsion
Electrothermal MEMS Electrical Propulsion
1. It works in two ways, one is using electrical resistanceheaters to heat gas in
the thrust chamber, and then discharging the gasthrough a nozzle to produce
thrust.
2. MEMS electric thruster is a subliming solid micro-thruster or a vaporizing liquid
micro-thruster. Its operating principle is that the propellantphase transition which is
heated by the heating resistor generates gas,then the gas exits through the
specially shaped nozzle with high speed, andthus producing thrust.

11. LIQUID VAPOURIZATION MEMS ELECTRICAL THRUSTER

12. RESEARCH PAPER REVIEW
FILM-EVAPORATION MICROTHRUSTER FOR CUBESATS
MEMS thermal valving system which exploits surface tension as a control
mechanism to produce thrust in the sub-millinewton range at less than 1 Watt power
at 2 to 5 Volts and using pure liquid water as a green propellant.
CONCEPT
Thermal valving concept is based on a minimum energy state
where fluid internal pressure against a vacuum is in balance
against a capillary force caused by surface tension on a
hydrophobic surface.
continuum approximation applies at the liquid/vapor interface, the capillary gap size d is
found with the Young Laplace equation.
—> τ is surface tension
—> Pvap - vapor pressure
—> θ - contact angle
When the temperature of the meniscus is increased the local vapor
pressure exceeds meniscus strength allowing vacuum boiling.
d=
2𝜏 cos 𝜃
𝑝𝑣𝑎𝑝

13. DESIGN
Nichrome was chosen as heater material for its
availability, low cost, and expected low oxidation
properties. Nichrome was later replaced by platinum
as the preferred heater material after high-yield.

14. Characterization of film-evaporating microcapillaries for
water-based micro thrusters
Film-Evaporating MEMS Tunable Array (FEMTA) Thruster

15. FEMTA theory of operation
These equations are used to find laplace pressure specific impulse
𝑃𝑝 = 𝑃𝑙 𝑇𝑖 + 𝑃𝑣 𝑇𝑖
𝑃𝑙 = 𝜎
1
𝑅𝑐,1
+
1
𝑅𝑐,,2
≈
𝜎
𝑅𝑐
𝑅𝑐 =
𝜔
2 sin(𝜃 − 90°)
-------------------------(1) propellant pressure
-------------------------(2) Laplace equation
-------------------------(3)
- 𝑃𝑙 𝑙𝑎𝑝𝑙𝑎𝑐𝑒 𝑝𝑟𝑒𝑠𝑠𝑢𝑟𝑒 𝑖𝑛𝑑𝑢𝑐𝑒𝑑 𝑏𝑦 𝑠𝑢𝑟𝑓𝑎𝑐𝑒 𝑡𝑒𝑛𝑡𝑖𝑜𝑛
- 𝑃𝑝 propellant pressure under stream
- 𝑃𝑣 is the vapor pressure of water
- Principle radii of curvature (𝑅𝑐 )
- Fluid contact angle (𝜃)
- nozzle throat width (𝑤)

16. FEMTA nozzle have shown that the flow is sonic at the exit of the throat. As a result, the
isentropic temperature and pressure at the nozzle throat exit are defined by Eqs. (4) and (5)
where 𝐶𝑝 is the specific heat and 𝑅 is the specific gas constant of water vapor.
DESIGN OF THRUSTER
𝑇𝑒=𝑇𝑖 1 −
𝑅
2𝐶𝑝−𝑅
-------------------------(4)
𝑃𝑒 = 𝑃𝑣 1 −
𝑅
2𝐶𝑝 − 𝑅
𝐶𝑝
𝑅
𝑢𝑒 = [2𝐶𝑝(𝑇𝑖 − 𝑇𝑒)]
1
2
𝑚 = 𝐴𝑒𝑢𝑒
𝑃𝑒
𝑅𝑇𝑒
𝐹 = 𝑚𝑢𝑒 + 𝑃𝑒𝐴𝑒
-------------------------(5)
-------------------------(6)
-------------------------(7)
-------------------------(8)

18. Problems: -
Theoretical Laplace pressure is also plotted for each measurement point and is calculated
from Laplace equation and propellant pressure at a contact angle of 136.1◦. Surface tension
was computed from Eq. (10) at the bulk propellant temperature when the leak occurred.
Ice generation was also observed for a subset of the test-bed nozzles during Laplace
pressure testing. The freezing of the water within the nozzles is caused by evaporative
cooling at the fluid interface.
Outlet width at which ice is generated.

19. NEW Generation FEMTA Design

21. the current generation
FEMTA micronozzle
experiences leaking and ice
generation which limits the
reliability and life span of the
device
CONCLUSION
To diagnose the leaking issue, contact angle and maximum Laplace pressure were
measured within the test-bed nozzles. Contact angle was found to be 136.1◦ on
average. The measured maximum Laplace pressure was higher than the value
predicted by the Young–Laplace equation for minimum throat widths less than 1.5 μm
and lower for minimum throat widths greater than 1.5 μm. Nozzle throats which were
converging or straight produced repeatable Laplace pressure measurements.
However, diverging nozzles had highly unstable fluid interfaces. As a consequence,
ambient vibrations were observed to induce leaking on diverging nozzles.
Observations of ice generation within the test-bed nozzles were also recorded during
Laplace pressure testing. The smallest nozzle throat which produced ice had a throat
outlet area of 64.9 μm2. Not all nozzles with outlet areas larger than 64.9 μm2 were
observed to generate ice and devices which generated ice were not always able to
reproduce the behavior.
MAIN CONCLUSION
The behavior. Based on the icing and Laplace pressure data, it was concluded
that reducing the nozzle throat width below 1 μm would likely resolve both the
leaking and icing issues.
The design consists of an array of 15 micronozzles that are
each 1 μm wide, 6 μm long, and 6 μm deep

22. Working Principle of Film-Evaporation
Microthruster
1 Evaporation Layer
A thin layer of water is uniformly distributed across the evaporator surface,
allowing for efficient heat transfer and rapid vaporization.
2 Heat Source
The presence of a controlled heat source initiates the evaporation process,
ensuring that vapor is generated precisely when needed for propulsion.
3 Vapor Channeling
The vapor generated is channeled towards the propulsion system, where it is
directed to produce thrust for the microthruster.

23. Advantages of Film-Evaporating for
Microthrusters
Efficiency
Film-evaporating
technology
significantly
enhances the
efficiency of water-
based
microthrusters,
allowing for
optimal utilization
of the propulsion
system.
Precision
It enables precise and
controlled vapor
generation, ensuring
that the microthruster
delivers accurate and
predictable
performance.
Reliability
By minimizing the
potential for
residue build-up
and ensuring
consistent
evaporation, this
technology
enhances the
overall reliability of
microthrusters.

24. Challenges in Implementing Film-
Evaporating for Microthrusters
Miniaturization
Ensuring the efficient operation of film-evaporating technology within the
confined space of microthrusters presents significant engineering challenges.
Heat Management
Maintaining precise heat control in compact microthruster designs is crucial
for the reliable operation of film-evaporating systems.
Scaling
Scaling film-evaporating technology for microthrusters while preserving its
efficiency and precision is a complex task that demands innovative solutions.

25. Applications of Water-Based
Microthrusters with Film-Evaporating
Technology
Satellite Propulsion
Water-based microthrusters with film-
evaporating technology are used for precisely
controlling the orientation and position of
satellites in space.
Micro-Robotics
They are employed in the field of micro-
robotics for agile and controlled movement in
various applications.