DESC:TECHNICAL FIELD
[1] The present disclosure generally relates to devices to generate thrust or propulsion. In particular, the present disclosure relates to thrusters for use in micro-, nano- and pico-satellites.

BACKGROUND
[2] Background description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.
[3] Satellite miniaturization for developing low cost, low power solutions for technology demonstration and research and development has led to a need for miniaturized avionics and propulsion systems. Micro-propulsion systems are necessary for de-orbiting, formation flying and attitude control. The size, mass, operational power constraints imposed on the micro-propulsion systems makes its design and integration extremely challenging. For instance, nano satellites are a class of satellites with mass ranging from 1 – 10 kg and the available power on these satellites is between 2.5 – 200 W. The conventional propulsion systems including chemical propulsion, electrical propulsion, owing to the requirements such as pressurized vessels and high voltage power, respectively cannot be easily implemented to obtain thrust in nano satellites. Such constraints have led to a significant research towards developing micro-propulsion systems including MEMS-based technologies that can meet the thrust requirements and be integrated to the nano and pico satellites.
[4] A monopropellant milli-Newton thruster system and a piezo actuated butane microthruster, VACCO is one of the commercially available miniature propulsion system. In this thruster, liquid butane is stored at 5-7 bar pressure, and as per the thrust requirements, it is vaporized in a chamber using a MEMS based heater. VACCO is an example of a resistojet thruster that comprise passing a stored liquid or gas through a heater passage to convert it into vapor and then accelerating the vapor through a nozzle. The power requirement of such a system is very high because of the high heat of vaporization and the sensible heating involved. Another proposed evaporative micro-propulsion system working principle is analogous to a thermal ink jet printer. Water is held to a thin channel by surface tension forces. Once electrical heating is provided, rapid conversion of liquid to vapor occurs. When the vapor pressure is greater than the capillary forces at the liquid meniscus, the vapor escapes through the meniscus and accelerates along a nozzle to produce the required thrust. The design faced the challenge of having non-robust heaters, and low output thrust. Even though the heater was placed at the opening of the water reservoir before the nozzle entry, the high specific heat capacity of water in addition to the thermal dissipation in the silicon-based device resulted in a significant energy loss due to sensible heating. The size of the throat of the nozzle is limited by the coupled need to have high surface tension-induced pinning which is inversely related to the throat dimensions. A similar challenge is faced by the resisto-heaters using water as a working fluid. This results in a high-power requirement for the desired thrust. The existing SmallSat propulsion systems, including resistojets, cold gas, electrospray, solid propellant, face the shortcoming of high mass, high power requirement, and low specific impulse and are insufficient to meet the requirements of the nanosatellites.
[5] Therefore, there is a need to develop simple, light weight propulsion systems that are environmentally friendly and can meet the system requirement for thrust and specific impulse. This invention is based on a thin-film evaporation based micro-thruster that utilizes water as the propellant

OBJECTS OF THE INVENTION
[6] An object of the present invention is to provide a microthruster and a method of fabricating the microthruster.
[7] Another object of the present invention is to provide a microthruster using a non-toxic propellant.
[8] Another object of the present invention is to provide a microthruster that consumes less power.
[9] Another object of the present invention is to provide a microthruster suitable for use with micro-, nano-, and pico-satellites.

SUMMARY
[10] In a first aspect, the present disclosure provides a microthruster. The microthruster includes a base structure including a plurality of microstructures fluidically coupled to a reservoir, and configured to extract a liquid from the reservoir. At least a part of the extracted liquid is converted to a vapor. The base structure further includes a vapor gap disposed proximal to the plurality of microstructures, fluidically coupled to the plurality of microstructures and configured to receive the converted vapor. The base structure further includes a nozzle fluidically coupled to the vapor gap. The converted vapor from the vapor gap is accelerated through the nozzle. When the accelerated vapor exits the nozzle, the microthruster generates a thrust.
[11] In some embodiments, the base structure further includes a patterned bottom wafer, and a patterned top wafer bonded to the patterned bottom wafer, such that at least one of the reservoir, the vapor gap, the plurality of microstructures, and the nozzle is formed between the patterned bottom wafer and the patterned top wafer.
[12] In some embodiments, the microthruster further includes a heating unit thermally coupled to the plurality of microstructures. The heating unit is configured to generate heat. The heat generated by the heating unit converts the at least part of the extracted liquid to the vapor.
[13] In some embodiments, the heating unit includes a thin-film heater.
[14] In some embodiments, the plurality of microstructures includes a plurality of micro-pillars, forming a plurality of capillaries. The plurality of capillaries extracts the liquid from the reservoir through capillary action.
[15] In some embodiments, the microthruster further includes a second heating unit thermally coupled to the nozzle. The second heating unit is configured to generate heat. The heat generated by the second heating unit superheats the vapor accelerating through the nozzle.
[16] In some embodiments, surfaces downstream of the plurality of microstructures includes a coating. The coating is configured to restrict passage of the liquid to the surfaces downstream of the plurality of microstructures.
[17] In some embodiments, the liquid is selected from a group comprising water, and a mixture of water and anti-freeze.
[18] In some embodiments, the microthruster is configured for use with any of micro-satellites, nano-satellites, and pico-satellites.
[19] In a second aspect, the present disclosure provides a method of fabricating a microthruster. The method includes providing a base structure. The method further includes forming, in the base structure, a plurality of microstructures fluidically coupled to a reservoir, and configured to extract the liquid from the reservoir. The method further includes forming, in the base structure, a vapor gap disposed proximal to the plurality of microstructures, and fluidically coupled to the plurality of microstructures. The method further includes forming, in the base structure, a nozzle fluidically coupled to the vapor chamber.
[20] In some embodiments, providing the base structure further includes patterning a bottom wafer; patterning a top wafer; and bonding the patterned top wafer to the patterned bottom wafer, such that at least one of the reservoir, the vapor gap, the plurality of microstructures, and the nozzle is formed between the patterned bottom wafer and the patterned top wafer.
[21] In some embodiments, the method further includes providing a heating unit thermally coupled to the plurality of microstructures. The heating unit is configured to generate heat. The heat generated by the heating unit converts the at least part of the received liquid to vapor.
[22] In some embodiments, the method further includes providing a second heating unit thermally coupled to the nozzle. The second heating unit is configured to generate heat. The heat generated by the second heating unit superheats the vapor accelerating through the nozzle.
[23] In some embodiments, the method further includes providing, on surfaces downstream of the plurality of microstructures, a coating. The coating is configured to restrict passage of the liquid to the surfaces downstream of the plurality of microstructures.
[24] In some embodiments, forming, in the base structure, the plurality of microstructures further includes forming a plurality of micro-pillars, forming a plurality of capillaries. The plurality of capillaries extracts the liquid through capillary action.
[25] Various objects, features, aspects, and advantages of the inventive subject matter will become more apparent from the following detailed description of preferred embodiments, along with the accompanying drawing figures in which like numerals represent like components.

BRIEF DESCRIPTION OF THE DRAWINGS
[26] The accompanying drawings are included to provide a further understanding of the present disclosure and are incorporated in and constitute a part of this specification. The drawings illustrate exemplary embodiments of the present disclosure and, together with the description, serve to explain the principles of the present disclosure.
[27] FIGs. 1A and1B illustrate schematic top and sectional views, respectively, of a microthruster, according to an embodiment of the present disclosure;
[28] FIG. 2 illustrates a flow diagram for a method of fabricating the microthruster, according to an embodiment of the present disclosure;
[29] FIG. 3A illustrates an exemplary schematic representation of a processes for fabricating the microthruster; and
[30] FIG. 3B illustrates another exemplary schematic representation of a processes for fabricating the microthruster.

DETAILED DESCRIPTION
[31] The following is a detailed description of embodiments of the disclosure depicted in the accompanying drawings. The embodiments are in such details as to clearly communicate the disclosure. However, the amount of detail offered is not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present disclosure as defined by the appended claims.
[32] In an aspect, the present disclosure provides a microthruster. The microthruster includes a base structure including a plurality of microstructures fluidically coupled to a reservoir, and configured to extract a liquid from the reservoir. At least a part of the extracted liquid is converted to a vapor. The base structure further includes a vapor gap disposed proximal to the plurality of microstructures, fluidically coupled to the plurality of microstructures and configured to receive the converted vapor. The base structure further includes a nozzle fluidically coupled to the vapor gap. The converted vapor from the vapor gap is accelerated through the nozzle. When the accelerated vapor exits the nozzle, the microthruster generates a thrust.
[33] In another aspect, the present disclosure provides a method of fabricating a microthruster. The method includes providing a base structure. The method further includes forming, in the base structure, a plurality of microstructures fluidically coupled to a reservoir, and configured to extract the liquid from the reservoir. The method further includes forming, in the base structure, a vapor gap disposed proximal to the plurality of microstructures, and fluidically coupled to the plurality of microstructures. The method further includes forming, in the base structure, a nozzle fluidically coupled to the vapor chamber.
[34] FIGs. 1A and1B illustrate schematic top and sectional views, respectively, of a microthruster 100, according to an embodiment of the present disclosure. Referring FIGs. 1A and 1B, the microthruster 100 includes a base structure 102. The base structure 102 includes a plurality of microstructures 108 fluidically coupled to a reservoir 106 and configured to extract a liquid from the reservoir 106. In some embodiments, the reservoir 106 may be formed fully or partially within the base structure 102. In some other embodiments, the reservoir 106 may be external to the base structure 102. In the illustrated embodiment of FIGs. 1A and 1B, the reservoir 106 is formed within the base structure 102.
[35] In some embodiments, the plurality of microstructures 108 includes a plurality of micro-pillars 110 placed, forming a plurality of capillaries 112. The plurality of capillaries 112 extracts the liquid from the reservoir 106 through capillary action. Thus, the transport, or feeding, of the liquid from the reservoir 106 occurs passively, without need for any external driving mechanisms, such as a pump or other flow control mechanisms.
[36] In some embodiments, the microthruster 100 includes a heating unit 130 thermally coupled to the plurality of microstructures 108. The heating unit 130 is configured to generate heat. The heat generated by the heating unit 130 converts the at least part of the received liquid to vapor. In some embodiments, the heating unit 130 includes a thin-film heater.
[37] The base structure 102 further includes a vapor gap 104 disposed proximal to the plurality of microstructures 108, fluidically coupled to the plurality of microstructures 108. In the illustrated embodiment of FIGs. 1A and 1B, the vapor gap 104 is disposed above the plurality of microstructures 108 within the base structure 102. The vapor gap 104 is configured to receive the converted vapor.
[38] The base structure 102 further includes a nozzle 114 fluidically coupled with the vapor gap 104. The converted vapor from the vapor gap 104 is accelerated through the nozzle 114. When the accelerated vapor exits the nozzle 114, the microthruster 100 generates a thrust.
[39] In some embodiments, the liquid is water. Water is an inexpensive, nontoxic green propellant and is easy to handle. However, the concept of capillary fed heating of thin film of liquid can also be utilized with other fluids. The relevant criteria are the surface tension, which leads to capillary force-led imbibition of liquid to the plurality of microstructures 108 and retention of liquid, and low vapor pressure such that the evaporation of the liquid at power-off condition is low. Other liquids such as a mixture of water and antifreeze may be utilized avoid freezing of the mixture at the nozzle exit. The surface tension of water changes from ~76 dynes/cm to 69 dynes/cm (that is by 0.91 time) as the temperature changes from 0 °C to 45 °C. This change in surface tension is not expected to cause a significant difference in operation of the device in terms of wicking and retention of liquid in the plurality of microstructures 108. Since the capillary pressure is directly proportional to the surface tension, it changes by ~0.91 times over a temperature change of ~ 50 °C and does not affect the feeding mechanism in the microthruster 100. The liquid may have sufficiently high surface tensions, such that the liquid is retained in the plurality of microstructures 108, and the volatility of the liquid should be such that a part of the liquid may be vaporized using the heating. In some embodiments, the liquid may include a mixture of water and anti-freeze. In some other embodiments, the liquid may include any other volatile liquids with moderate surface tensions similar to that of water.
[40] In some embodiments, the microthruster 100 further includes a second heating unit 132 thermally coupled to the nozzle 114. The second heating unit 132 is configured to generate heat. The heat generated by the second heating unit 132 superheats the vapor accelerating through the nozzle 114. As the enthalpy of the vapor increases through superheating, the kinetic energy of the vapor exiting the nozzle increases, which may allow the vapor to generate a greater thrust. Further, superheating of the vapor prevents condensation of the vapor on the surfaces of the nozzle 114.
[41] In some embodiments, surfaces downstream of the plurality of microstructures 108 include a coating 136. The coating 136 is configured to restrict passage of the liquid to the surfaces downstream of the plurality of microstructures 108. For example, when the liquid is water, the coating 136 may be a hydrophobic coating. Further, the surfaces transporting the liquid from the reservoir 106 up to the plurality of microstructures 108 may include a coating that promotes wettability of the liquid on the surface. This wettability difference may act as a passive valve that restricts the flow of the liquid beyond the plurality of microstructures 108 and allows flow of vapor only.
[42] In some embodiments, the base structure 102 includes a patterned bottom wafer 150, and a patterned top wafer 152 bonded to the patterned bottom wafer 150, such that at least one of the reservoir 106, the vapor gap 104, the plurality of microstructures 108, and the nozzle 114 is formed between the patterned bottom wafer 150 and the patterned top wafer 152. In some embodiments, the vapor gap 104 may be formed by etching or machining the top wafer 152. In some embodiments, the bottom wafer 150 is a silicon wafer. In some embodiments, the top wafer 152 is a glass wafer or a polycarbonate wafer.
[43] The liquid is fed into the plurality of microstructures 108 from the reservoir 106 through capillary action of the plurality of microstructures 108. The liquid extracted from the reservoir 106 may form a liquid film in the plurality of microstructures 108. The thickness of the liquid film may be controlled by varying the configuration of the plurality of microstructures 108. In an example, the thickness of the liquid film may be maintained at about 100 µm. As liquid is evaporated, the liquid film is replenished by liquid from the reservoir 106.
[44] The capillary pressure Pc for the plurality of microstructures 108 is given by,

where, a is the surface area of each of the micro-pillars, h is the height of each of the micro-pillars, is the contact angle of liquid on silicon, and is the surface tension of liquid.
[45] The height of the micro-pillars affects not only the capillary pressure, but also the thickness of the imbibed liquid. The dynamics of propagation of the liquid by the plurality of microstructures 108 is given by the competition between capillary force and the viscous dissipation. The viscous pressure-drop when the liquid imbibes through the plurality of microstructures 108 by a length L is given by,

Where, is the liquid viscosity, is the speed of liquid imbibition, and is the in-plane permittivity. The length scale of the flow path can also introduce viscous dissipation of the vapor during flow though the plurality of microstructures 108, and the nozzle 114, which needs to be minimized.
[46] The imbibition time is calculated by equating viscous pressure drop over a length, L to the capillary pressure as,

[47] In some examples, the micropillars 110 are square shaped and have a size a of about 20 µm and a height h of about 50 µm, with an interpillar spacing of about ~ 20 µm. For the above size and height of the plurality of micro-pillars 110, Pc is about 104 Pa, which ensures that the liquid film is retained even while operating under vacuum conditions, such as when implemented in satellites.
[48] The heating unit 130 is further located such that the heat generated by the heating unit 130 is directed to vaporising the liquid film specifically, and not in heating the bulk liquid.
[49] The thrust generated by the microthruster 100 depends on rate of vaporization, exit velocity and pressure. The thrust F, generated due to the accelerating vapor through the nozzle exit is given as,

where is the mass flow rate of vapor, is the vapor exit velocity, is the pressure difference between the nozzle exit and the ambient, is the exit area of the nozzle.
[50] Since only a formed liquid film is evaporated to generate thrust for the microthruster 100, the power consumption of the microthruster 100 is low compared to existing technologies. For example, to produce a thrust of about 55 µN, the microthruster 100 may consume a heating power of about 1 W.
[51] Further, the heating unit 130 is configured to generate heat to allow evaporation of the liquid film, and not boiling of the liquid. Boiling can introduce additional complexities to the system. The ejection of vapor bubble by rupturing the liquid interface can lead to instabilities in the system. To avoid that, the vapor gap 104 is provided for flow of vapor through the nozzle114.
[52] The microthruster 100 restricts the liquid film away from the exit of the nozzle 114. Therefore, vacuum-led boiling instabilities are eliminated as the liquid is not exposed to vacuum pressure at the exit. The low height of the micropillars 110 ensures that boiling of the liquid does not occur. In addition, the presence of gap above the plurality of microstructures 108 provides a pathway for the vapor to escape to the nozzle 114 without causing flow instabilities.
[53] In some embodiments, the microthruster 100 includes a secondary reservoir 120. The capillary forces pull the liquid from the reservoir 106, which is further coupled to the secondary reservoir 120. As the liquid gets depleted from the secondary reservoir 120 due to the continuous use of liquid, the space above the liquid is replaced with vapor and is at saturation pressure corresponding to the temperature of the liquid in the secondary reservoir 120. For example, at reservoir temperature equal to 20 °C, the saturation pressure of water vapor is Psat = 2340 Pa which is smaller than the capillary pressure (~104 Pa). Therefore, the feeding into the plurality of microstructures 108 will continue by capillary action even when the secondary reservoir 120 is depleted.
[54] FIG. 2 illustrates a flow diagram for a method 200 of fabricating the microthruster 100, according to an embodiment of the present disclosure. Referring now to FIGs. 1A, 1B, and 2, at step 202, the method 200 includes providing the base structure 102. At step 204, the method 200 further includes forming, in the base structure 102, the plurality of microstructures 108 fluidically coupled to the reservoir 106 and configured to extract the liquid from the reservoir 106. At step 206, the method 200 further includes providing, in the base structure 102, the vapor gap 104 disposed proximal to the plurality of microstructures 108, and fluidically coupled to the plurality of microstructures 108. At step 208, the method 200 further includes forming, in the base structure 102, the nozzle 114 fluidically coupled to the vapor gap 104.
[55] In some embodiments, the step of providing the base structure 102 further includes patterning the bottom wafer 150; patterning the top wafer 152; and bonding the top wafer 152 to the patterned bottom wafer 150, such that at least one of the reservoir 106, the vapor gap 104, the plurality of microstructures 108 and the nozzle 114 is formed between the patterned top wafer 150 and the patterned bottom wafer 152.
[56] In some embodiments, the method 200 further includes providing a heating unit 130 thermally coupled to the plurality of microstructures 108, the heating unit 130 configured to generate heat. The heat generated by the heating unit 130 converts the at least part of the received liquid to vapor.
[57] In some embodiments, the method 200 further includes providing a second heating unit 132 thermally coupled to the nozzle 114, the second heating unit 132 configured to generate heat. The heat generated by the second heating unit 132 superheats the vapor accelerating through the nozzle 114.
[58] In some embodiments, the method 200 further includes providing, on surfaces downstream of the plurality of microstructures 108, a coating 136. The coating 136 is configured to restrict passage of the liquid to the surfaces downstream of the plurality of microstructures 108.
[59] In some embodiments, the step of forming, in the base structure 102, the plurality of microstructures 108 further includes forming a plurality of micro-pillars 110, forming a plurality of capillaries 112. The plurality of capillaries 112 transports the liquid through capillary action.
[60] FIG. 3A illustrates an exemplary schematic representation of a processes 300 for fabricating the microthruster 100. Referring now to FIGs. 1A, 1B and 3A, at step 302, the process 300 includes providing a polished silicon wafer. At steps 304, 306 the process 300 includes performing a photolithography for providing the reservoir 106, the vapor gap 104, and the nozzle 114. At step 308, the process 300 includes performing photolithography and deep reactive ion etching to provide the plurality of microstructures 108 including the plurality of micro-pillars 110 and the plurality of capillaries 112. At step 310, the process 300 includes deposition of oxide on the silicon wafer. At step 312, the process 300 includes deposition of the heating unit 130 on the deposited oxide. At step 314, the process 300 includes deposition of electrical contact pads to facilitate connection of the heating unit 130 with a power supply. At step 316, the process 300 includes deposition of the second heating unit 132 on the top glass wafer. Finally, at step 318, the process 300 includes bonding the glass wafer with the silicon wafer to provide the microthruster 100.
[61] FIG. 3B illustrates an exemplary schematic representation of a processes 350 for fabricating the microthruster 100. Referring now to FIGs. 1A, 1B and 3B, at step 352, the process 350 includes providing a polished silicon wafer. At steps 354, 356 the process 350 includes performing a photolithography for providing the reservoir 106, the microstructures 108, and the nozzle 114. At step 358, the process 350 includes performing deep reactive ion etching to provide the plurality of microstructures 108 including the plurality of micro-pillars 110 and the plurality of capillaries 112. At step 360, the process 350 includes deposition of oxide on the silicon wafer. At step 362, the process 350 includes deposition of the heating unit 130 on the deposited oxide. At step 364, the process 350 includes deposition of electrical contact pads to facilitate connection of the heating unit 130 with a power supply. At step 366, the process 350 includes machining the top wafer 152. At step 368, the process 350 includes bonding the top wafer 150 to the silicon wafer to provide the microthruster 100.
[62] It should be apparent to those skilled in the art that many more modifications besides those already described are possible without departing from the inventive concepts herein. The inventive subject matter, therefore, is not to be restricted except in the spirit of the appended claims. Moreover, in interpreting both the specification and the claims, all terms should be interpreted in the broadest possible manner consistent with the context. In particular, the terms “comprises” and “comprising” should be interpreted as referring to elements, components, or steps in a non-exclusive manner, indicating that the referenced elements, components, or steps may be present, or utilized, or combined with other elements, components, or steps that are not expressly referenced. Where the specification claims refer to at least one of something selected from the group consisting of A, B, C ….and N, the text should be interpreted as requiring only one element from the group, not A plus N, or B plus N, etc. The foregoing description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the appended claims.
[63] While the foregoing describes various embodiments of the invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof. The scope of the invention is determined by the claims that follow. The invention is not limited to the described embodiments, versions or examples, which are included to enable a person having ordinary skill in the art to make and use the invention when combined with information and knowledge available to the person having ordinary skill in the art.

LIST OF REFERENCE NUMERALS
100 Microthruster
102 Base Structure
104 Vapor Gap
106 Reservoir
108 Plurality of Microstructures
110 Plurality of Micro-Pillars
112 Plurality of Capillaries
114 Nozzle
130 Heating Unit
132 Second Heating Unit
136 Coating
120 Secondary Reservoir
150 Bottom Wafer
152 Top Wafer
200 Method
202 Step
204 Step
206 Step
208 Step
300 Process
302 Step
304 Step
306 Step
308 Step
310 Step
312 Step
314 Step
316 Step
318 Step
350 Process
352 Step
354 Step
356 Step
358 Step
360 Step
362 Step
364 Step
366 Step
368 Step

ADVANTAGES OF THE INVENTION
[64] The present invention provides a microthruster and a method of fabricating the microthruster.
[65] The present invention provides a microthruster using a non-toxic propellant.
[66] The present invention provides a microthruster that consumes less power.
[67] The present invention provides a microthruster suitable for use with micro-, nano-, and pico-satellites.

,CLAIMS:1. A microthruster (100) comprising:
a base structure (102) comprising:
a plurality of microstructures (108) fluidically coupled to a reservoir (106), and configured to extract a liquid from the reservoir (106), wherein at least a part of the extracted liquid is converted to a vapor;
a vapor gap (104) disposed proximal to the plurality of microstructures (108), fluidically coupled to the plurality of microstructures (108) and configured to receive the converted vapor; and
a nozzle (114) fluidically coupled to the vapor gap (104),
wherein the converted vapor from the vapor gap (104) is accelerated through the nozzle (114), and
wherein, when the accelerated vapor exits the nozzle (114), the microthruster (100) generates a thrust.
2. The microthruster (100) as claimed in claim 1, wherein the base structure (102) comprises a patterned bottom wafer (150), and a patterned top wafer (152) bonded to the patterned bottom wafer (150), such that at least one of the reservoir (106), the vapor gap (104), the plurality of microstructures (108), and the nozzle (114) is formed between the patterned bottom wafer (150) and the patterned top wafer (152).
3. The microthruster (100) as claimed in claim 1, further comprising a heating unit (130) thermally coupled to the plurality of microstructures (108), the heating unit (130) configured to generate heat, wherein the heat generated by the heating unit (130) converts the at least part of the extracted liquid to the vapor.
4. The microthruster (100) as claimed in claim 3, wherein the heating unit (130) comprises a thin-film heater.

5. The microthruster (100) as claimed in claim 1, wherein the plurality of microstructures (108) comprises a plurality of micro-pillars (110), forming a plurality of capillaries (112), and wherein the plurality of capillaries (112) extracts the liquid from the reservoir (106) through capillary action.
6. The microthruster (100) as claimed in claim 1, further comprising a second heating unit (132) thermally coupled to the nozzle (114), the second heating unit (132) configured to generate heat, wherein the heat generated by the second heating unit (132) superheats the vapor accelerating through the nozzle (114).
7. The microthruster (100) as claimed in claim 1, wherein surfaces downstream of the plurality of microstructures (108) comprise a coating (136), and wherein the coating (136) is configured to restrict passage of the liquid to the surfaces downstream of the plurality of microstructures (108).
8. The microthruster (100) as claimed in claim 1, wherein the liquid is selected from a group comprising water, and a mixture of water and anti-freeze.
9. The microthruster (100) as claimed in claim 1, wherein the microthruster (100) is configured for use with any of micro-satellites, nano-satellites, and pico-satellites.
10. A method of fabricating a microthruster (100), comprising:
providing (202) a base structure (102);
forming (204), in the base structure (102), a plurality of microstructures (108) fluidically coupled to a reservoir (106), and configured to extract the liquid from the reservoir (106);
providing (206), in the base structure (102), a vapor gap (104) disposed proximal to the plurality of microstructures (108), and fluidically coupled to the plurality of microstructures (108);
forming (208), in the base structure (102), a nozzle (114) fluidically coupled to the vapor gap (104).
11. The method as claimed in claim 10, wherein providing the base structure (102) further comprises:
patterning a bottom wafer (150);
patterning a top wafer (152); and
bonding the patterned top wafer (152) to the patterned bottom wafer (150), such that at least one of the reservoir (106), the vapor gap (104), the plurality of microstructures (108), and the nozzle (114) is formed between the patterned bottom wafer (150) and the patterned top wafer (152).
12. The method as claimed in claim 10, further comprising providing a heating unit (130) thermally coupled to the plurality of microstructures (108), the heating unit (130) configured to generate heat, wherein the heat generated by the heating unit (130) converts the at least part of the received liquid to vapor.
13. The method as claimed in claim 10, further comprising providing a second heating unit (132) thermally coupled to the nozzle (114), the second heating unit (132) configured to generate heat, wherein the heat generated by the second heating unit (132) superheats the vapor accelerating through the nozzle (114).
14. The method as claimed in claim 10, further comprising providing, on surfaces downstream of the plurality of microstructures (108), a coating (136), wherein the coating (136) is configured to restrict passage of the liquid to the surfaces downstream of the plurality of microstructures (108).
15. The method as claimed in claim 10, wherein forming, in the base structure (102), the plurality of microstructures (108) further comprises forming a plurality of micro-pillars (110), forming a plurality of capillaries (112), and wherein the plurality of capillaries (112) extracts the liquid through capillary action.