Exploration-Probe to Jupiter Moon Europa

Home , Exploration of Saturn, Vikas (rocket engine)

Aswath Suresh1, Sri Harsha2, Kolluri Surya3, Debrup Laha1, Dhruv Gaba1, Siddhant Bhambri4, Suvaansh Bhambri5 and Karthik Rangarajan1

1New York University, Brooklyn, New York, USA 2San Francisco State University, Holloway Ave, San Francisco, CA 3Institute of Aeronautical Engineering, Hyderabad, Telangana, India 4Department of Electronics and Communication Engineering, Bharati Vidyapeeth’s College of Engineering, India 5Indian Institute of Technology, Roorkee - Haridwar Highway, Roorkee, Uttarakhand 247667

( aswathashh10, sriharsha.yerrabelli, surya.aryan.9,[email protected], gabadhruv1, siddhantbhambri,suvaansh2008bhambri )@gmail.com

Abstract: The human civilization has reached a point in its progression, where inhabiting planets other than Earth is fast becoming a necessity. Jupiter’s moon Europa appears to be an ideal target for colonizing due to the research indicating favorable conditions for human survival and habitation. Europa, or JII, is the smallest of the Galilean satellites. It is slightly smaller than the Moon. It has a surface made of ice (H2O) that is three miles thick. The temperature of the ice on the surface is 90(+ 10) K. Scientists believe that this icy surface was created by gases escaping from the center of the satellite to outside the surface. It is also believed that, in its earlier stages, Europa's surface was 75 km thick. However, the interior's high temperatures have melted away some of the surface from the inside. It has also been speculated that underneath the surface, there are oceans of liquid water and that conditions may be favorable for the Europa to support life. This paper describes in detail an innovative, cost efficient and safe exploration mission to Europa. The design of the launch vehicle rocket will be based on that of GSLV MK III which was designed by ISRO. The GSLV MK III offers a dual advantage of being cost effective while having a high success rate. One of the important challenges of the mission is developing a trajectory to safely land the spacecraft/explorer to its target. The spacecraft will continue in a Hohmann type trajectory which has enough velocity to reach orbital velocity around Europa. After an estimate of 688 days after departure from earth’s low orbit, the spacecraft will arrive at Jupiter. It is important to note that Jupiter’s gravitational field can create a problem for sending probes to one of the satellites. The spacecraft will be designed to withstand the atmosphere of both Jupiter and Europa. If we can make a shield to withstand Jupiter’s harmful atmosphere, we can use the dense atmosphere of Jupiter as aero brakes for the spacecraft. Once optimum speeds are reached, we can proceed to enter Europa’s atmosphere. It is important to note that this whole procedure might take up more energy than required for just a brake system, in which case, the process of using Jupiter’s atmosphere for aero brake assist can be skipped. We propose two alternate designs for the spacecraft. The first one is to use a heavy, yet compact drilling enabled spacecraft that can drill a hole and dive into the sub-surface ocean entirely. If we use this design, an additional satellite dish needs to be added, which will revolve around Europa and communicate with Earth and the explorer simultaneously. Another option is to use a mini-station design, which will completely enter Europa’s surface, yet only parts of it will dive into the sub-surface ocean. The rest will stay on the ground and communicate with Earth. Composite material based heat shield which can withstand nearly 2500 degree Celsius and a parachute landing system will be used to safely land the explorer on the Surface of Europa. The spacecraft explorer will be designed with an intelligent drilling system, which will help it to drill into the moon’s surface, after which the required parts of the spacecraft can enter the water. The scientific instruments on the spacecraft will conduct deep sea exploration for signs of life and conditions for human habitation. The “Copyright © 2017 by ASWATH. Published by The Mars Society with permission.” implementation of a mission based on this idea will most definitely begin a new chapter in the history of space exploration and pave new ways for the survival of the human civilization. 1 Introduction Europa is one of the Galilean moons of Jupiter as shown in Figure 1, along with Io, Ganymede and Callisto. Astronomer Galileo Galilei gets the credit for discovering these moons, among the largest in the solar system. Europa is the smallest of the four but it is one of the more intriguing satellites. The surface of Europa is frozen, covered with a layer of ice, but scientists think there is an ocean beneath the surface. The icy surface also makes the moon one of the most reflective in the solar system. Water plumes were spotted jetting from the moon in 2013, although those observations have not been repeated. Several spacecraft have done flybys of Europa (including Pioneers 10 and 11 and Voyagers 1 and 2 in the 1970s). The Galileo spacecraft did a long-term mission at Jupiter and its moons between 1995 and 2003. Both NASA and the European Space Agency plan missions to Europa and other moons in the 2030s. [1]

Figure 1: The puzzling, fascinating surface of Jupiter's icy moon Europa looms large in images taken by NASA's Galileo spacecraft. Credit: NASA/JPL-Caltech/SETI Institute

A. Facts about Europa Age: Europa is estimated to be about 4.5 billion years old, about the same age of Jupiter. Distance from the sun: On average, Europa's distance from the sun is about 485 million miles (or 780 million kilometers). “Copyright © 2017 by ASWATH. Published by The Mars Society with permission.”

Distance from Jupiter: Europa is Jupiter's sixth satellite. Its orbital distance from Jupiter is 414,000 miles (670,900 km). It takes Europa three and a half Earth-days to orbit Jupiter. Europa is tidally locked, so the same side faces Jupiter at all times. Size: Europa is 1,900 miles (3,100 km) in diameter, making it smaller than Earth's moon, but larger than Pluto. It is the smallest of the Galilean moons. Temperature: Europa's surface temperature at the equator never rises above minus 260 degrees Fahrenheit (minus 160 degrees Celsius). At the poles of the moon, the temperature never rises above minus 370 F (minus 220 C). B. Discovery Galileo Galilei discovered Europa on Jan. 8, 1610. It is possible that German astronomer Simon Marius (1573-1624) also discovered the moon at the same time. However, he did not publish his observations, so it is Galileo who is most often credited with the discovery. For this reason, Europa and Jupiter's other three largest moons are often called the Galilean moons. Galileo, however, called the moons the Medicean planets in honour of the Medici family. It is possible Galileo actually observed Europa a day earlier, on Jan. 7, 1610. However, because he was using a low- powered telescope, he couldn't differentiate Europa from Io, another of Jupiter's moons. It wasn't until later that Galileo realized they were two separate bodies. The discovery not only had astronomical, but also religious implications. At the time, the Catholic Church supported the idea that everything orbited the Earth, an idea supported in ancient times by Aristotle and Ptolemy. Galileo's observations of Jupiter's moons — as well as noticing that Venus went through "phases" similar to our own moon — gave compelling evidence that not everything revolved around the Earth. As telescopic observations improved, however, a new view of the universe emerged. The moons and the planets were not unchanging and perfect; for example, mountains seen on the moon showed that geological processes happened elsewhere. Also, all planets revolved around the sun. Over time, moons around other planets were discovered — and additional moons found around Jupiter. Marius, the other "discoverer," first proposed that the four moons be given their current names, from Greek mythology. But it wasn't until the 19th century that the moons were officially given the so-called Galilean names we know them by today. All of Jupiter's moons are named for the god's lovers (or victims, depending on your point of view). In Greek mythology, Europa was abducted by Zeus (the counterpart of the Roman god Jupiter), who had taken the form of a spotless white bull to seduce her. She decorated the “bull” with flowers and rode on its back to Crete. Once in Crete, Zeus then transformed back to his original form and seduced her. Europa was the queen of Crete and bore Zeus many children. C. Characteristics of Europa A prominent feature of Europa is its high degree of reflectivity. Europa's icy crust gives it an albedo — light reflectivity — of 0.64, one of the highest of all of the moons in the entire solar system. Scientists estimate that Europa’s surface is about 20 million to 180 million years old, which makes it fairly young. Pictures and data from the Galileo spacecraft suggest Europa is made of silicate “Copyright © 2017 by ASWATH. Published by The Mars Society with permission.” rock, and has an iron core and rocky mantle, much like Earth does. Unlike the interior of Earth, however, the rocky interior of Europa is surrounded by a layer of water and/or ice that is between 50 and 105 miles (80 and 170 km) thick, according to NASA. From fluctuations in Europa's magnetic field that suggests a conductor of some sort, scientists also think there is an ocean deep beneath the surface of the moon. This ocean could contain some form of life. This possibility of extra-terrestrial life is one of the reasons interest in Europa remains high. In fact, recent studies have given new life to the theory that Europa can support life. The surface of Europa is covered with cracks. Many believe these cracks are the result of tidal forces on the ocean beneath the surface. It's possible that, when Europa's orbit takes it close to Jupiter, the tide of the sea beneath the ice rises higher than normal. If this is so, the constant raising and lowering of the sea caused many of the cracks observed on the surface of the moon. Obtaining samples of the ocean may not require drilling through the icy crust. In 2013, the Hubble Space Telescope identified geysers of water vapour spewing from the moon's south pole. The plumes subsequently disappeared, leading scientists to wonder if the features were a cyclical event. In 2014, scientists found that Europa may host a form of plate tectonics. Previously, Earth was the only known body in the solar system with a dynamic crust, which is considered helpful in the evolution of life on the planet. D. Europa: Where life may evolve? The presence of water beneath the moon's frozen crust makes scientists rank it as one of the best spots in the solar system with the potential for life to evolve. The icy depths of the moons are thought to contain vents to the mantle much as oceans on Earth do. These vents could provide the necessary thermal environment to help life evolve. If life exists on the moon, it may have gotten a kick from deposits from comets. Early in the life of the solar system, the icy bodies may have delivered organic material to the moon. In 2016, a study suggested that Europa produces 10 times more oxygen than hydrogen, which is similar to Earth. This could make its probable ocean friendlier for life — and the moon may not need to rely on tidal heating to generate enough energy. Instead, chemical reactions would be enough to drive the cycle. 2 Mission Plan This Mission Plan describes in detail an innovative, cost efficient and safe exploration mission to Europa. The Europa Mission can be envisaged as a rendezvous problem. The rendezvous mission consists of following steps I) The design of the launch vehicle rocket will be based on that of GSLV MK III which was designed by ISRO. The GSLV MK III offers a dual advantage of being cost effective while having a high success rate. II) One of the important challenges of the mission is developing a trajectory to safely land the spacecraft/explorer to its target. III) The spacecraft will continue in a Hohmann type trajectory which has enough velocity to reach orbital velocity around Europa. After an estimate of 688 days after departure from earth’s low orbit, the spacecraft will arrive at Jupiter at a velocity of 9.342 km/s, relative to the Sun and 7.61 “Copyright © 2017 by ASWATH. Published by The Mars Society with permission.” km/s relative to Jupiter. However, this velocity will increase dramatically as it approaches the planet. IV) Upon arrival to the Jovian atmosphere the spacecraft will be flying at 60.09 km/s at 71,370 km from the center of the planet. It is important to note that at this distance the escape velocity is 59.609 km/s. Therefore, the probe will only require a decrease of 1.089 km/s to acquire the necessary velocity which will place it in the elliptical orbit which will take it to Europa and deliver the spacecraft to this transfer trajectory. V) It is important to note that Jupiter’s gravitational field can create a problem for sending probes to one of the satellites. The spacecraft will be designed to withstand the atmosphere of both Jupiter and Europa. If we can make a shield to withstand Jupiter’s harmful atmosphere, we can use the dense atmosphere of Jupiter as aero brakes for the spacecraft. VI) The velocity of the spacecraft at most will be 15.758 km/s relative to Jupiter and 1.378 km/s relative to Europa, which orbits Jupiter at 14.38 km/s. The spacecraft's orbital velocity around Europa will place it in a circular orbit, at an altitude of 185.2 km. Once optimum speeds are reached, we can proceed to enter Europa’s atmosphere. VII) It is important to note that this whole procedure might take up more energy than required for just a brake system, in which case, the process of using Jupiter’s atmosphere for aero brake assist can be skipped. VIII) We propose two alternate designs for the spacecraft. The first one is to use a heavy, yet compact drilling enabled spacecraft that can drill a hole and dive into the sub-surface ocean entirely. If we use this design, an additional satellite dish needs to be added, which will revolve around Europa and communicate with Earth and the explorer simultaneously. IX) Another option is to use a mini-station design, which will completely enter Europa’s surface, yet only parts of it will dive into the sub-surface ocean. The rest will stay on the ground and communicate with Earth. X) Composite material based heat shield which can withstand nearly 2500 degree Celsius and a parachute landing system will be used to safely land the explorer on the Surface of Europa. The spacecraft explorer will be designed with an intelligent drilling system, which will help it to drill into the moon’s surface, after which the required parts of the spacecraft can enter the water. XI) The scientific instruments on the spacecraft will conduct deep sea exploration for signs of life and conditions for human habitation. The implementation of a mission based on this idea will most definitely begin a new chapter in the history of space exploration and pave new ways for the survival of the human civilization. 3 Launch Vehicle

GSLV Mk III is a three-stage cost effective heavy lift launch vehicle developed by ISRO as shown figure 2. GSLV Mk III launch vehicle, which includes AUV and cryobot. It has three stage propulsion mechanism: one liquid and two solid fuels. The rocket with its three stage “Copyright © 2017 by ASWATH. Published by The Mars Society with permission.” propulsion system will carry the spacecraft with AUV and Cryobot and put it into the Earth’s elliptical orbit.

The vehicle has two solid strap-ons, a core liquid booster and a cryogenic upper stage. GSLV Mk III is designed to carry 4-ton class of satellites into Geosynchronous Transfer Orbit (GTO) or about 10 tons to Low Earth Orbit (LEO), which is about twice the capability of GSLV Mk II. The two strap-on motors of GSLV Mk III are located on either side of its core liquid booster. Designated as ‘S200’, each carries 205 tons of composite solid propellant and their ignition results in vehicle lift -off. S200s function for 140 seconds. During strap-ons functioning phase, the two clustered Vikas liquid Engines of L110 liquid core booster will ignite 114 secs after lift -off to further augment the thrust of the vehicle. These two engines continue to function after the separation of the strap-ons at about 140 seconds after lift -off. The first experimental flight of LVM3, the LVM3-X/CARE mission lifted off from Sriharikota on December 18, 2014 and successfully tested the atmospheric phase of flight. Crew module Atmospheric Reentry Experiment was also carried out in this flight. The module reentered, deployed its parachutes as planned and splashed down in the Bay of Bengal. [2-3].

Figure 2: GSLV MK III Credit: ISRO

The first developmental flight of GSLV Mk III, the GSLV-Mk III-D1 successfully placed GSAT- 19 satellite to a Geosynchronous Transfer Orbit (GTO) on June 05, 2017 from SDSC SHAR, Sriharikota. “Copyright © 2017 by ASWATH. Published by The Mars Society with permission.”

A. Vehicle Specifications

Table 1: Vehicle Specification Height : 43.43 meters Vehicle Diameter : 4.0 meters

Heat Shield (Payload Fairing) Diameter : 5.0 meters

Number of Stages : 3

Lift Off Mass : 640 tonnes

C25 stage is newly developed, totally indigenous upper stage of GSLV Mk III. This is the terminal stage of the vehicle loaded with 28 tons of propellants (LOX & LH2). The stage has an overall diameter of 4 m and length of 13.5 m. It is integrated on top of the L110 core liquid stage. The ignition of C25 stage takes place 2 seconds after the separation of the L110 stage about 322 seconds after lift-off. The functioning duration of C25 is 643 seconds and this will facilitate the GSAT-19 carried on-board to reach the intended GTO. Vehicle specification is as shown in table 1. B. Technical Specifications I) Payload to LEO: 8000 kg

Figure 3: Cryogenic Stage. Credit: ISRO

The powerful cryogenic stage as shown in figure 3 of GSLV Mk III enables it to place heavy payloads into Low Earth Orbits of 600 km altitude. “Copyright © 2017 by ASWATH. Published by The Mars Society with permission.”

II) Payload to GTO: 4000 kg

Figure 4: Class Satellite GSAT series. Credit: ISRO

GSLV Mk III will be capable of placing the 4 tonne class satellites as shown in figure 4 of the GSAT series into Geosynchronous Transfer Orbits.

III) Cryogenic Upper Stage: C25

Figure 5: C25 Cryogenic Engine. Credit: ISRO

The C25 as shown in figure 5 is powered by CE-20, India’s largest cryogenic engine, designed and developed by the Liquid Propulsion Systems Centre. Its specification as shown in table 2.

Table 2: C25 Specification Cryo Stage Height : 13.5 meters

Cryo Stage Diameter : 4.0 meters

Fuel : 28 tonnes of LOX + LH2

IV) Solid Rocket Boosters: S200

Figure 6: Solid Rocket Boosters. Credit: ISRO

GSLV Mk III uses two S200 solid rocket boosters as shown in figure 6 to provide the huge amount of thrust required for lift off. The S200 was developed at Vikram Sarabhai Space Centre. Booster specification as shown in table 3.

Table 3: Booster Specification Booster Height 25 meters

Booster Diameter 3.2 meters

Fuel 205 tonnes of HTPB (nominal)

Figure 7: L110 Liquid Stage. Credit: ISRO

The L110 liquid stage as shown in figure 7 is powered by two Vikas engines designed and developed at the Liquid Propulsion Systems Centre. L110 specification as shown in table 4.

Table 4: L110 Specification Stage Height 21 meters

Stage diameter 4 meters

Engine 2 * Vikas

Fuel 110 tonnes of UDMH + N2O4

4 Trajectory

Figure 8: Showing the spacecraft interchanging the orbit with orbit velocity + ΔV boost to achieve escape velocity. (ISRO)

Low cost rocket GSLV MK III is used to inject the spacecraft into a parking orbit of the Earth. As the spacecraft goes away towards apogee, its velocity decreases, but as it’s comes back its velocity increases because of the earth gravitational pull. Engine is fired when velocity is high i.e. when the spacecraft is close to the earth. This raises the orbit and increases the velocity with least amount of fuel. With six main engine burns, the spacecraft is gradually maneuvered into a departure hyperbolic trajectory with which it escapes from the Earth`s Sphere of Influence with Earth’s orbital velocity + ΔV boost as shown in the figure 8. [4] The sphere of influence of earth ends at 918347 km from the surface of the earth beyond which the perturbing force on the orbiter is due to the Sun only. Now the sun is much more massive than any other planets and its gravity dominates the solar system. Gravitational influence of a planet, as compared to the sun is only significant near the planet.

• Placed in the Earth’s orbit 27 days prior to the launch date to revolve around Earth’s orbit for 6 times.

• After the completion of 6th revolution, it attains the escape velocity and moves away from Earth’s Gravity but gravitational pull of Sun and Mars and along with simultaneous engine fire brings the probe back to earth’s orbit for the final time.

• At this moment, the escape velocity is high enough to surpass the Earth, Mars and Sun’s Gravitational pull and moves towards Jupiter.

• The total travel time would be taking about 585 days.

Once on the trajectory, the probe is on its way to Jupiter moon Europa on the journey of 6 years as shown in figure 9.

Figure 9: Journey to Jupiter Moon Europa. Credits: NASA

● After six years of travel, the spacecraft will enter into the Javian atmosphere. It will be flying at 160,000 miles per hour.[5-8]

● The mission of this journey is to reduce the Arrival Velocity (AV) when it reaches Europa.

● This is done by a series of techniques: - The main engine is ignited in the opposite direction to slow down the probe and inserted into the Jupiter’s orbit; the closer to Jupiter the better. - Additionally, we will be using the dense atmosphere of Jupiter as aero brakes for the probe to slow down.

Figure 10: Hohmann Transfer

● After attaining the optimum speed, we proceed to enter the Europa’s atmosphere.

● Hohmann transfer is done by 2 burns as shown in figure 10.

● Burn 1 - JOI(Jupiter Orbit Insertion)

● Burn 2 - EOI(Europa Orbit Insertion)

● The spacecraft reaches the Europa’s atmosphere by attaining optimum velocity, the retrograde rockets fitted with the spacecraft is ignited to decelerating the speed.

Figure 11: Europa Lander. Credits: NASA

5 Launch Dates & Landing Dates

The launch dates and landing dates are calculated and shown as follows

Launch from Leaving Earth’s Perihelion Jupiter’s Gravity Europa Landing Earth Gravity

Thursday, 1 Tuesday, 27 Thursday, 10 May Monday, 2 Monday, 9 February 2018 February 2018 2018 September 2019 September 2019

Monday, 4 March Monday, 1 April Wednesday, 12 Sunday, 4 October Sunday, 11 2019 2019 June 2019 2020 October 2020

Tuesday, 31 Tuesday, 28 Thursday, 9 July Monday, 1 Monday, 8 March 2020 April 2020 2020 November 2021 November 2021

Planetary positions of the planets during the missions[9]: - A. Mission [2018 - 02-01 to 2019 - 09-09] B. Mission [2019 - 03-04 to 2020 -10-11] “Copyright © 2017 by ASWATH. Published by The Mars Society with permission.”

C. Mission [2020 - 03-31 to 2021 - 11-08]

A. Mission [2018 - 02-01 to 2019 - 09-09] Planetary position as per date 01:02:2018 AD.

Planetary position as per date 10:05:2018 AD.

Planetary position as per date 09:09:2019 AD.

B. Mission [2019 - 03-04 to 2020 -10-11] Planetary position as per date 04:03:2019 AD.

Planetary position as per date 04:10:2020 AD.

Planetary position as per date 11:10:2020 AD.

C. Mission [2020 - 03-31 to 2021 - 11-08] Planetary position as per date 31:03:2020 AD.

Planetary position as per date 28:04:2020 AD.

Planetary position as per date 09:07:2020 AD.

Planetary position as per date 01:11:2021 AD.

Planetary position as per date 08:11:2021 AD.

6 Europa’s Atmosphere vs. Probe Shield The spacecraft reaches Europa’s atmosphere by attaining optimum velocity when the retrograde rockets fitted with the spacecraft is ignited to decelerating the speed. This is because the density of Europa’s atmosphere is very low which implies that the gravitational pull of Europa is also very low, which almost one-fourth of the Earth’s gravitational pull. During the landing, it is important to make sure that the sensitive instruments of the probe are safe from the deadly radiations coming out of Jupiter and thus there is a need to have a strong shield against such radiations. Two types shields are required mainly to protect the electronics and the engines and the thrusters. For the electronics, the material for the shield could either be Lead or Titanium. However, lead is too soft to withstand the vibrations during the lunch of the spacecraft. Hence Titanium is chosen as it will be able to withstand all the vibrations. As mentioned by Dunbar [10] each titanium wall measures nearly a square meter (nearly 9 square feet) in area, about 1 centimeter (a third of an inch) in thickness, and 18 kilograms (40 pounds) in mass. This titanium box has a size which is almost the size of an SUV's trunk, and it encloses the Probe's command and data handling box (the spacecraft's brain), power and data distribution unit (its heart) and about 20 other electronic assemblies. The whole vault weighs about 200 kilograms (500 pounds). The vault is not designed to completely prevent every Jovian electron, ion or proton from hitting the system, but it aims to dramatically slow down the aging effect radiation has on electronics for the duration of the mission. The spacecraft will be traveling through strong radiation belts on its way to Jupiter, which creates a need for a stronger shield from Electrostatic Discharge (ESD) protection. The EDSs are more harmful than the other radiations coming from Jupiter. For protecting the engines and the thrusters, Miralon yarn are chosen which are pure carbon nanotube (CNT) fibers. Milberg [11] mentions that these act as better shields than the traditionally used Aluminum foils for ESD which are typically bonded on the surface of the composites. Miralon will act as a surface layer on several components of the flight system’s attitude control motor struts and the main engine housing while it travels through intense radiation belts. 7 Drilling Europa’s Ice Surface with Cryobot The surface of Europa is icy and hence there is a need for a Cryobot to drill the surface of Europa. The cross-sectional view of a Cryobot is shown in Figure 12.

Figure 12: Cross-Sectional view of a cryobot [12]

The cryobot is an environment-friendly robot which is capable of penetrating through water ice. It primarily uses heat for melting ice and gravity for sinking downwards. It has been seen the cryobot has penetrated through ice by melting for up to 3600 meters. While our mission aims to penetrate through the icy surface of Europa for about 20 Kilometers, we assume that the cryobot will be able to penetrate that distance. One of the major reasons for choosing a cryobot for the purpose of penetrating through the icy surface of Europa is that it consumes less power as compared to a regular drill. In addition, the cryobot is capable of measuring temperature, stress, ice movement, and seismic, acoustic, and dielectric properties. The prototype of a cryobot is shown in figure 13. The cryobot will consist of three distinct components namely Autonomous Underwater Vehicles (AUVs), robotic fishes, and the micro gliders.

Figure 13: Prototype of a cryobot [13]

The first of the three major components inside the cryobot are the AUVs. Each AUV is a cylindrically tapered structure consisting of three chambers namely the front cap, the pressure enclosure in the middle, and the tail cone. Each of the front cap and the tail cone are provided with a horizontal and a vertical thruster. The horizontal thrusters can rotate in 360 degrees and are used for steering purposes. The vertical thrusters are for the upward and downward motion of the AUV. In addition to these four horizontal and vertical thrusters, the tail cone is provided with a larger thruster that helps the AUV to propagate in the forward direction. The CAD model of the AUV was prepared in PTC Creo and is shown in 14.

Figure 14: Schematic view of an AUV

The entire AUV is about 108.4 inches long with a material thickness of about 0.2 inches. The dimensions of each of the components of the AUV are shown in 5.

Table 5: Component dimensions of the AUV Component Length (in) Outer Diameter (in) Material Thickness (in) Front Cap 20 21.4 0.2 Pressure Enclosure 50 20 0.2 Tail Cone 38.4 16.51 0.2

9 Robotic Fish The robotic fishes are small structures that are capable of exploring areas which have a small opening. Since those places can’t be explored by the AUVs due to their large structure, the robotic fishes can be released for that purpose. These fishes will acquire the information and communicate with its nearest AUV which in turn will send the information to the spacecraft and eventually to the Earth via telemetry. The schematic view of a robotic fish is shown in 15. “Copyright © 2017 by ASWATH. Published by The Mars Society with permission.”

Figure 15: Schematic view of a robotic fish 10 Material Selection The pressure under the surface of Europa is about 8 bars and so a material is needed that would be capable of withstanding such high pressure. The ideal material for the manufacturing of the outer structure of the AUVs as well as the robotic fishes is believed to be syntactic foams because of its light-weight, naturally buoyant behavior, low moisture application, and high hydrostatic compressive strength. Another material that could have been used was polymer foams which are lightweight, porous materials composed of air filled pores in polymer materials. However, a couple of drawbacks are associated with its lightweight, such as low strength and high water-absorption which makes it a non-ideal material for its application in deep-sea exploration purposes such as for manufacturing an AUV or robotic fishes. Syntactic foams [14] are two-component composite materials that contain hollow particles dispersed in a matrix and are synthesized by hollow glass microspheres (HGMs) as shown in figure 16. Tiny hollow particles are used in syntactic foams to disperse air in a polymer and make it a lightweight foam. The major advantage of using hollow particles is that the pores are not connected to each other. Thus, even if such foams are damaged, they do not absorb any significant amount of liquid since their pores are not interconnected. The hollow particles are usually made of glass and have diameters on the range of 4 ten-thousandths of an inch to 4 thousandths of an inch (0.01 to 0.1 millimeters) — 1 to 10 times the diameter of a human hair. Enclosing the air inside tiny glass shell makes the material lightweight while keeping it strong enough to withstand those high pressures. For usage in AUVs, it is noticed that thermosetting resins are used as matrix material with hollow glass particle fillers; however, some studies show that soda-lime glass hollow particles can degrade in water due to dealkalization and the rate of degradation is governed by the temperature. For long-term durability, there are alkali-free glass particles that can be used in such systems to prevent from degrading. Usually, the true particle density of the particles used in syntactic foams vary from 150 Kg/m3 to 800 Kg/m3 whereas the density of the matrix material ranges between 1000 Kg/m3 to 1200 Kg/m3.

Figure 16: Three-dimensional solid model representation of syntactic foams containing hollow particles [14]

Different processes [15] such as co-extrusion, lateral extrusion, and molding can be used to manufacture the AUVs as well as the robotic fishes. 11 Sensors and instruments payload There will be multiple sensors [16] located inside the spacecraft. Some of the sensors would be used for detecting the compositions on Europa. These include UV Spectrograph for surface & plume/atmosphere composition, Mass Spectrometer for sniffing the atmosphere, Dust Analyzer for surface & plume composition, and IR Spectrometer for surface chemical fingerprints. The IR spectrometer is important as it is used for detecting life in the atmosphere by taking samples from the atmosphere. It also helps in detecting the various gases in the atmosphere by taking spectrograph. Some of the other sensors that would be used for geology and reconnaissance are Thermal Imager for searching for hot spots & preparing for future landing, a Narrow-Angle Camera for surface mapping & preparing for future landing, and a Wide-Angle Camera for alien landscape in 3D & color. While the first two would be used for both geology and reconnaissance, the third one would be used for geology only. The last of the sensors would be used in ice and ocean. These include a Magnetometer for sensing ocean properties, Faraday Cups for sampling the plasma environment, an Ice-Penetrating Radar for plumbing the ice shell, and a Gravity Science for confirming an ocean.

12 Communication

The primary modes of communication from the earth to the Probe spacecraft as shown in figure 17 are radio waves and radio frequencies. Data or commands will be sent to the spacecraft to tell what to do and in turn it takes data and sends back to the earth as shown in figure 18 which is called telemetry. The micro gliders are the last of the three major components present inside the cryobot. These are small structures and once these are released from the cryobot, these get attached to the bottom surface of the sheets. The micro gliders examine these sections and send the signal back to the spacecraft via acoustic emission because the frequency between the two layers is different due to which radio waves and radio frequencies won’t be functional in this case. Thus, the spacecraft receives signals from the micro gliders and simultaneously from the robotic fishes and the AUVs. Once the spacecraft receives all the signals, it will send the signals back to earth and this entire procedure will take about 1 hour and 15 minutes approximately.

Figure 18: Radio Communication from Probe to Earth

To find out if there is a problem with the spacecraft, the best way would be to monitor our telemetry and the spacecraft would communicate with us through deep space network [17]. The deep space network is used around the world in order to return data to us and to send commands up to the spacecraft. A lot of key points are designed in the spacecraft that tell us the state of charge of the battery and the temperature at which things are located inside the spacecraft, etc. From the earth, we would look at the telemetry and monitor if the spacecraft is working fine and we would set limits in that so that it gives automatic alerts if something is wrong. Thus, we can look at the telemetry from the ground to make sure that everything is okay and also detect problems if they arise. References [1] Europa: Facts About Jupiter's Icy Moon and Its Ocean, By Elizabeth Howell, Space.com Contributor | June 13, 2016. “Copyright © 2017 by ASWATH. Published by The Mars Society with permission.”

[2] Online available at https://www.isro.gov.in/launchers/gslv-mk-iii [3]"First Experimental Flight of India's Next Generation Launch Vehicle GSLV Mk-III Successful". 18 December 2014. Archived [4] Indian Space Research organization “Mars Orbiter Mission” - [Online]. Available: http://isro.gov.in/pslv-c25-mars-orbiter-mission [5] "Juno Mission to Jupiter" (PDF). NASA FACTS. NASA. April 2009. p. 1. Retrieved April 5, 2011. [6] Brown, Dwayne; Cantillo, Laurie; Dyches, Preston (September 15, 2017). "NASA's Cassini Spacecraft Ends Its Historic Exploration of Saturn". NASA. Retrieved September 15, 2017. [7] Online available at https://saturn.jpl.nasa.gov/ - Cassini Legacy 1997-2017 [8] Online available at https://www.nasa.gov/mission_pages/cassini/main/index.html [9] Screenshots as per the Tabulated dates. Credits: Hayling Graphics: [Online available at http://www.theplanetstoday.com/#]. [10] Dunbar, Brian. “Juno Armored Up to Go to Jupiter.” NASA, NASA, 27 Oct. 2010, www.nasa.gov/mission_pages/juno/news/juno20100712.html. [11] Milberg, Evan. “Composites Protect NASA Spacecraft Headed to Jupiter.” Composites Manufacturing Magazine, 1 Feb. 2017, compositesmanufacturingmagazine.com/2016/02/composites-protect-spacecraft- headed-to-jupiter-for-juno-nasa-mission/. [12] Taylor, Michael Ray. “Cryobots Could Drill Into Icy Moons With Remote Fiber-Optic Laser Power.” Wired, Conde Nast, 3 June 2017, www.wired.com/2012/04/bill-stone-laser-powered-europa-rover/. [13] Prigg, Mark. “Nasa Reveals the Underwater Alien Hunting Robot Set to Go to Europa to Look for Life.” Daily Mail Online, Associated Newspapers, 27 June 2015, www.dailymail.co.uk/sciencetech/article-3140959/Nasa-reveals-robot-spot-life-Europa-s-underground- oceans-prowling-LA-aquarium.html. [14] Gupta, N., Zeltmann, S. E., Shunmugasamy, V. C., & Pinisetty, D. (2013). Applications of Polymer Matrix Syntactic Foams. Jom, 66(2), 245-254. doi:10.1007/s11837-013- 0796-8 [15] Choqueuse, D., Davies, P., Perreux, D., Sohier, L., & Cognard, J. Y. (2010). Mechanical Behavior of Syntactic Foams for Deep Sea Thermally Insulated Pipeline. Applied Mechanics and Materials, 24-25, 97-102. doi:10.4028/www.scientific.net/AMM.24-25.97 [16] Pappalardo, Bob. “Europa Mission Science Overview.” OPAG, 24 Aug. 2015. [17] NASAJuno. “Juno's Communications.” YouTube, YouTube, 28 June 2011.