Introduction 

Objects and planets in space are much bigger than daily objects we encounter on Earth and, therefore, they experience much larger gravitational forces that cause them to orbit around, collapse on, or escape from another object. The motion of extraterrestrial objects has always intrigued me, especially the NASA DART project, which is a mission to protect the Earth from potential asteroids impacting its surface. I find the collision of objects in space very interesting because the trajectory of the objects after colliding has to take in so many factors like the mass of the objects, their velocities, and any surrounding objects. 

Before I can explain more about the NASA DART project, however, I need to introduce the basics of gravitation and space physics. I will explain the different parts of space physics, like Newton’s universal law of gravitation, the acceleration of objects due to gravitational forces of the Earth and other objects, and escape speed, the speed it takes for an object to escape an object’s orbit. I will also go into the concept of gravitational potential energy, the energy an object has while in orbit, the energy required to place an object in orbit, and the nature of objects orbiting Earth, also known as Earth satellites. Additionally, I will explain Johannes Kepler’s famous 3 laws of planetary motion for a better understanding of how planets move in space. 

Finally, I will introduce the NASA DART (Double Asteroid Redirection Test), a mission where NASA tries to develop technology to protect the Earth in the unlikely event that an asteroid is headed for Earth. Their goal is to make an object, like a satellite, hit the asteroid, thus changing the trajectory of the asteroid and making it miss the Earth. 

This report is also complemented by Python code that simulates planetary motion. It is available for download on my GitHub here: https://github.com/alyang21/solarsystem 

2. Gravitation 

2.1 Universal Law of Gravitation

On Earth, the acceleration at which an object falls toward the Earth is a constant 9.8 m/s². However, this rate is different on other extraterrestrial objects. This is because the force of gravity exerted on an object depends on its mass as well as the mass of the objects around it. Knowing this, famed physicist Sir Issac Newton derived the Universal Law of Gravitation in 1687 [8]. His equation is

where G is the universal gravitational constant, at 6.67 x 10^-11. Furthermore, this equation suggests that the force depends on both objects’ masses and how far apart they are separated.  In vector form, the equation can be written as 

Furthermore, the sum of the forces on an object by the surrounding objects is just the vector sum of all the forces. 

Figure 1.1 The sum of two vectors is found by placing the two vectors tail to tip, and the resulting vector is from the tail of the first vector to the tip of the second. [1]

2.2 Acceleration Due to Gravity of the Earth

The Earth can be visualized as a number of spherical shells centered at the same point. Since the mass of all the shells combined is the mass of the Earth, and the force of gravity by the Earth comes from the center of the Earth. By taking into account the Earth’s density using its volume and mass, we can derive that the force of gravity by the Earth on an object is F_g = (GM_Em)/R_E² [8]. Since F_g = mg where g is the acceleration by the Earth according to Newton’s second Law, 

2.3 Gravitational Potential Energy

The gravitational potential energy of an object on Earth depends on its distance from the center of the Earth. We also know that work equals force multiplied by displacement, so the work done by the Earth to bring a body of mass m from the height h2 to the height h1 is given by:

In other words, the work done on an object is the difference of potential energy from the initial to final positions of the object. If we say that the potential energy W(h) at a height h above the surface of the Earth so that W(h) = mgh + W₀ where W₀ is a constant, then W₁₂ = W(h₂) – W(h₁) [8]. It is also important to note that h = 0 means points on the surface of the Earth.

If we lift the particle along a vertical path where r₁ is the distance from the center of the Earth at its first point and r₂ is the distance from the center at its second point, then we get

And as a result, 

2.4 Escape Speed

Using the law of conservation of energy, we can find the escape speed for an object out of a planet, or the speed it needs to break through the pull of the planet [8]. If we can find the distance where the object has no more potential energy and only kinetic energy, we can set the energies of the object at those two points equal to each other, thus allowing us to find the initial velocity that the object has to leave the planet with. 

As long as the final velocity is greater than or equal to 0, the object can reach infinity. So,

The initial velocity is the minimum velocity for the object to escape the atmosphere, so

If the object is thrown from the surface of the Earth, h = 0, and 

Thus, we come to the equation 

where R_E is the radius of the Earth. This means that the escape speed is independent of the object’s own mass. Additionally, with the knowledge of the Earth’s radius, we can find that the escape speed is 11.2 km/s.

2.5 Earth Satellites

Earth satellites are objects which revolve around the Earth, usually in the shape of an ellipse. The Moon is the only natural satellite of the Earth, and it has a near-circular orbit. Other satellites have been sent up by humans for telecommunication, geophysics, and meteorology. To find the period that these satellites orbit around the Earth once, we can use the equation for centripetal force, where m is the mass of the satellite and V is its speed [8].

This centripetal force is provided by the gravitational force, similar to equation (1.1) but after substituting the variables for the mass and radius of the Earth, we get 

Setting the two equations together, we find that 

A satellite travels a distance 2πR_E with speed V if the satellite is so close to the Earth’s surface that h can be neglected. The time period the satellite takes to orbit the Earth therefore is

and using the relation g = GM/R_E², we arrive at the equation

Substituting the numerical values, we get

Which is about 85 minutes.

2.6 Energy of an Orbiting Satellite

Notice how K is positive and U_g is negative. When added up, the total energy of the satellite is 

It makes sense that the satellite’s total energy is negative because if the total energy is positive, it would leave the orbit and escape to infinity. 

2.7 Energy Required to Orbit a Satellite

The energy required to put a satellite into Earth’s orbit is the difference between the satellite’s total energy in orbit and its energy at Earth’s surface. For example, if we want to lift the 9000-kg Soyuz vehicle from the Earth’s surface up to the ISS, which is 400 km above the Earth’s surface, we would have to find its energy at the Earth’s surface, as well as its total energy in orbit at the ISS. Using Eq 1.19, we get that the total energy of the Soyuz in the same orbit as the ISS is   where m is 9000 kg and h is 0. Plugging the numbers in, we get that E_orbit is -2.65 x 10¹¹ J. The total energy at the surface is just -GmM_e/R_e because E_surface = K_surface + U_surface and K_surface is 0. Plugging the numbers in, we get E_surface = -5.63 x 10¹¹ J. As explained earlier, the energy required is the change in energy, so the energy required is   = -2.65 x 10¹¹ – (-5.63 x 10¹¹) = 2.98 x 10¹¹ J [8].

2.8 Kepler’s Laws of Planetary Motion

After German astronomer Johannes Kepler obtained the data collected by Tycho Brahe, he was able to analyze the positions of all the known planets and our moon. He realized that the orbits of the planets around the sun were elliptical, and was able to come up with three basic laws of planetary motion [8].

Kepler’s first law states that all planets orbit along an ellipse, where the Sun is one of the foci of the ellipse. An ellipse is the set of all points where the sum of the distance from each point to the two foci is a constant. 

In an elliptical orbit, the point where the planet is the closest to the Sun is called the perihelion, which is represented by point A in Figure 1.4. The figure also shows point B, the farthest point from the Sun. This point is called the aphelion. 

The ellipse is a specific example of a conic section, given by the equation

The variables r and θ from Eq. 1.20 are shown in Figure 1.5. The other two variables,   and e, are constants determined by the total energy and angular momentum of the satellite at a point on the ellipse. The constant e is the eccentricity, which determines how close to being a circle the ellipse is. The closer to 0, the more circular the ellipse is, and the closer to 1, the flatter it is.

Kepler’s second law states that over equal periods of time, a planet will sweep out equal areas. In other words, the area it sweeps divided by the time, also known as the areal velocity, is a constant.

This makes sense when you consider that when the planet is closer to the Sun, it is moving faster. Since the energy of the planet-sun system is conserved, when the planet gets closer to the sun, its gravitational potential energy decreases, so its kinetic energy and velocity must increase.

Figure 1.7 The area ∂  swept out during time   as the planet moves through angle  . The angle between the radial direction of r and   is  . [4]

Kepler’s third law states that the square of the period is proportional to the cube of the semi-major axis of the orbit. For this law, we have the equation

In this equation, a is the semi-major axis of the ellipse and T is the period. Interestingly, this law can also be derived from Newtonian principles and the principle of conservation of energy [8]. Additionally, his equation applies to any satellite orbiting any large mass, not just our Sun. If we use this equation for a circular orbit of r about the Earth, we get

3. DART Project NASA

It is widely believed that millions of years ago, the dinosaurs were put into extinction when a meteoroid hit the surface of the Earth. Although no meteor has gotten close enough to Earth since then to cause humans to panic, the scientific community agrees that another meteor will eventually cross paths with the Earth. To combat this, NASA started the Double Asteroid Redirection Test, or DART, to see if it is possible to alter the course of an asteroid by sending an object to impact it. 

I first learned about DART when I visited the Kennedy Space Center in Florida and watched a video about its mission. I was immediately intrigued by DART because I had an interest in object collisions from playing pool and baseball. The DART mission added an interesting element that wasn’t involved when playing on a flat billiards table: the gravitational force of other extraterrestrial objects. This mission pushed me to learn about gravitation, planetary motion, and overall space physics in order to understand the DART mission from a scientific perspective.

DART’s target is the binary asteroid system Didymos. Since Didymos is not on a path that would impact the Earth, it is the ideal candidate for the first planetary defense experiment. The impact would be safe, even if something were to go wrong. The asteroid system consists of two asteroids: the larger asteroid named Didymos, and its moonlet, Dimorphos. DART’s plan was to collide with the moonlet Dimorphos, and then we would examine the changes in Dimorphos’ orbit as a result of the impact. 

The journey to Dimorphos was complicated and required many different state-of-the-art technologies. One was the Small-body Maneuvering Autonomous Real Time Navigation (SMART Nav), developed for guidance, navigation, and control (GNC). The system had to be autonomous because NASA cannot control a satellite when it is 11 million kilometers away from Earth. The system was able to distinguish between Didymos and Dimorphos, and accurately navigate to the moonlet, eventually colliding with the smaller asteroid. DART was also equipped with an ion propulsion system that is solar-powered and incredibly fuel-efficient. Speaking of solar-powered, DART had a Roll-Out Solar Array (ROSA), extending 8.5 meters in length on each side. These solar arrays were used before on the ISS, but DART was the first to use them on a planetary spacecraft. Finally, the LICIACube allowed the DART team back on Earth to see images of the impact and the ejecta cloud, helping them assess the impact and its effects on Dimorphos. These technologies, paired with great antennas to send and receive data from the satellite allowed the DART mission to be incredibly successful.

Figure 1.8 The three images above show the various technologies the DART satellite used throughout its mission. SMART Nav (left) helped the satellite accurately impact Dimorphos. ROSA (center) gave the satellite its power for its ion propulsion system (right). [5]

Figure 1.9 DART would impact Dimorphos from the direction Dimorphos is moving towards, slowing it down. This would cause Dimorphos’ new orbit to be closer to Didymos since its orbiting velocity decreased. At the same time, the LICIA Cube, which DART would eject 15 days before impact, would be able to capture images of the impact and send them back to Earth for NASA to examine. [6]

Overall, the DART project was a massive success, lifting off in November 2021 and colliding with Dimorphos in September 2022. However, the mission is not complete. The DART team is still examining the data from the impact in order to explore all the effects of the impact on Dimorphos. You can watch videos about the mission at this link: https://dart.jhuapl.edu/Gallery/ [7]

References 

[1] https://tikz.net/vector_sum/

[2] https://openstax.org/books/university-physics-volume-1/pages/13-3-gravitational-potential-energy-and-total-energy

[3] https://openstax.org/books/university-physics-volume-1/pages/13-4-satellite-orbits-and-Energy

[4] https://openstax.org/books/university-physics-volume-1/pages/13-5-keplers-laws-of-Planetary-motion

[5] https://dart.jhuapl.edu/Mission/Impactor-Spacecraft.php

[6] https://dart.jhuapl.edu/Mission/index.php

[7] https://dart.jhuapl.edu/Gallery/

[8] This work is partially based on the content of this book: NCERT Books for Class 11 Physics, https://www.ncertbooks.guru/ncert-books-class-11-physics/amp/

Appendix

The following code computes the planetary motion of the Earth, Mars, and a fictional comet orbiting around the sun according to gravitational physics. The trajectories of these planets are calculated using Newton’s Universal Law of Gravitation, with given initial conditions for the position and velocities of each object. These trajectories are computed over a 5-year period and are visualized using an animation. The code is written in the Python language and is taken from this blog post: https://towardsdatascience.com/simulate-a-tiny-solar-system-with-python-fbbb68d8207b

Available on my Github page here: https://github.com/alyang21/solarsystem

# Ensure the right backend for Spyder

import matplotlib

matplotlib.use(“Qt5Agg”)

import matplotlib.pyplot as plt

from matplotlib import animation

# Constants and initial setup with constants and the objects’ masses, velocities, and gravitational constants.

G = 6.67e-11                  # constant G

Ms = 2.0e30                   # sun

Me = 5.972e24                 # earth        

Mm = 6.39e23                  # mars

Mc = 6.39e20                  # comet

AU = 1.5e11                   # earth sun distance

daysec = 24.0*60*60           # seconds of a day

e_ap_v = 29290                # earth velocity at aphelion

m_ap_v = 21970                # mars velocity at aphelion

commet_v = 7000               # comet velocity

gravconst_e = G*Me*Ms

gravconst_m = G*Mm*Ms

gravconst_c = G*Mc*Ms

# Starting positions

# earth

xe, ye, ze = 1.0167*AU, 0, 0

xve, yve, zve = 0, e_ap_v, 0

# mars

xm, ym, zm = 1.666*AU, 0, 0

xvm, yvm, zvm = 0, m_ap_v, 0

#comet

xc, yc, zc = 2*AU, 0, 0

xvc, yvc, zvc = 0, commet_v, 0

# sun

xs, ys, zs = 0, 0, 0

xvs, yvs, zvs = 0, 0, 0

t = 0.0

dt = 1*daysec

# these lists store the points that the objects are at

xelist, yelist, zelist = [], [], []

xmlist, ymlist, zmlist = [], [], []

xclist, yclist, zclist = [], [], []

xslist, yslist, zslist = [], [], []

# save the initial position in their respective lists

#earth

xelist.append(xe)

yelist.append(ye)

zelist.append(ze)

#mars

xmlist.append(xm)

ymlist.append(ym)

zmlist.append(zm)

#comet

xclist.append(xc)

yclist.append(yc)

zclist.append(zc)

# Simulation

# The new radii, forces, velocities, and positions are calculated at each second for 5 years. The new position is then added to the object’s list. 

while t < 5*365*daysec:

    ################ earth #############

    # compute G force on earth

    rx,ry,rz = xe – xs, ye – ys, ze – zs

    modr3_e = (rx**2+ry**2+rz**2)**1.5

    fx_e = -gravconst_e*rx/modr3_e     

    fy_e = -gravconst_e*ry/modr3_e

    fz_e = -gravconst_e*rz/modr3_e

    # update quantities how is this calculated?  F = ma -> a = F/m

    xve += fx_e*dt/Me

    yve += fy_e*dt/Me

    zve += fz_e*dt/Me

    # update position

    xe += xve*dt

    ye += yve*dt 

    ze += zve*dt

    # save the position in list

    xelist.append(xe)

    yelist.append(ye)

    zelist.append(ze)

    ################ mars #############

    # compute G force on mars

    rx_m,ry_m,rz_m = xm – xs, ym – ys, zm – zs

    modr3_m = (rx_m**2+ry_m**2+rz_m**2)**1.5

    fx_m = -gravconst_m*rx_m/modr3_m

    fy_m = -gravconst_m*ry_m/modr3_m

    fz_m = -gravconst_m*rz_m/modr3_m

    xvm += fx_m*dt/Mm

    yvm += fy_m*dt/Mm

    zvm += fz_m*dt/Mm

    # update position

    xm += xvm*dt

    ym += yvm*dt 

    zm += zvm*dt

    # save the position in list

    xmlist.append(xm)

    ymlist.append(ym)

    zmlist.append(zm)

    ################ comet ##############

    # compute G force on comet

    rx_c,ry_c,rz_c = xc – xs, yc – ys, zc – zs

    modr3_c = (rx_c**2+ry_c**2+rz_c**2)**1.5

    fx_c = -gravconst_c*rx_c/modr3_c

    fy_c = -gravconst_c*ry_c/modr3_c

    fz_c = -gravconst_c*rz_c/modr3_c

    xvc += fx_c*dt/Mc

    yvc += fy_c*dt/Mc

    zvc += fz_c*dt/Mc

    # update position

    xc += xvc*dt

    yc += yvc*dt 

    zc += zvc*dt

    # add to list

    xclist.append(xc)

    yclist.append(yc)

    zclist.append(zc)

    ################ the sun ###########

    # update quantities how is this calculated?  F = ma -> a = F/m

    xvs += -(fx_e+fx_m)*dt/Ms

    yvs += -(fy_e+fy_m)*dt/Ms

    zvs += -(fz_e+fz_m)*dt/Ms

    # # update position

    xs += xvs*dt

    ys += yvs*dt 

    zs += zvs*dt

    xslist.append(xs)

    yslist.append(ys)

    zslist.append(zs)

    # update dt

    t +=dt

print(‘data ready’)

# Animation setup

# grid size

fig, ax = plt.subplots(figsize=(6,6))

ax.set_aspect(‘equal’)

ax.grid()

# earth is blue. The text “Earth” follows point_e as it moves

line_e, = ax.plot([], [], lw=1, c=’blue’)

point_e, = ax.plot([AU], [0], marker=”o”, markersize=4, markeredgecolor=”blue”, markerfacecolor=”blue”)

text_e = ax.text(AU, 0, ‘Earth’)

# mars is red. The text “Mars” follows point_m as it moves

line_m, = ax.plot([], [], lw=1, c=’red’)

point_m, = ax.plot([1.666*AU], [0], marker=”o”, markersize=3, markeredgecolor=”red”, markerfacecolor=”red”)

text_m = ax.text(1.666*AU, 0, ‘Mars’)

# comet is black. The text “Comet” follows point_c as it moves

line_c, = ax.plot([],[], lw=1, c=’black’)

point_c, = ax.plot([2*AU], [0], marker=”o”, markersize=2, markeredgecolor=”black”, markerfacecolor=”black”)

text_c = ax.text(2*AU,0,’Comet’)

# the sun is yellow

point_s, = ax.plot([0], [0], marker=”o”, markersize=7, markeredgecolor=”yellow”, markerfacecolor=”yellow”)

text_s = ax.text(0, 0, ‘Sun’)

ax.axis(‘equal’)

ax.set_xlim(-3*AU, 3*AU)

ax.set_ylim(-3*AU, 3*AU)

exdata, eydata = [], []

mxdata, mydata = [], []

cxdata, cydata = [], []

# The points for each object are put into their respective data sets to be plotted on grid

def update(i):

    exdata.append(xelist[i])

    eydata.append(yelist[i])

    mxdata.append(xmlist[i])

    mydata.append(ymlist[i])

    cxdata.append(xclist[i])

    cydata.append(yclist[i])

    line_e.set_data(exdata,eydata)

    point_e.set_data(xelist[i],yelist[i])

    text_e.set_position((xelist[i],yelist[i]))

    line_m.set_data(mxdata,mydata)

    point_m.set_data(xmlist[i],ymlist[i])

    text_m.set_position((xmlist[i],ymlist[i]))

    line_c.set_data(cxdata,cydata)

    point_c.set_data(xclist[i],yclist[i])

    text_c.set_position((xclist[i],yclist[i]))

    point_s.set_data(xslist[i],yslist[i])

    text_s.set_position((xslist[i],yslist[i]))

    ax.axis(‘equal’)

    ax.set_xlim(-3*AU,3*AU)

    ax.set_ylim(-3*AU,3*AU)

    #print(i)

    return line_e,line_m,line_c,point_s,point_e,point_m,point_c,text_e,text_s,text_m,text_c

anim = animation.FuncAnimation(fig, func=update, frames=len(xelist), interval=1, blit=False)

plt.show(block=True)

About the author

Alexander Yang

Alex is currently a 12th grader at the Livingston High School. He is a dedicated singer-student-athlete with a passion for Math and Physics who is fascinated with data analysis and calculations related to aerospace. He founded his high school’s Rocketry Club, competing in the American Rocketry Challenge and also holding educational community launches to spark interest in rocketry and aerospace. Alex has been a part of his school’s Math Team for all four years of high school, and rising to the Math Honor Society’s Vice President in his Junior year. He was also a camp counselor at the Delaware Aerospace Academy, teaching young students about aviation, space, and rockets. He taught the students to construct and launch model rockets, maglev trains, and solar robots.

In addition to these activities, Alex also plays varsity baseball for his school, being the starting second baseman and starting shortstop in his sophomore and junior years respectively. He has also been an active singer, singing in his school chorus, select chorus, and an outside volunteer chorus. He has auditioned into the NJ All-State Chorus both of the last two years, and he is currently ranked 6th in the state in the Tenor 1 voice part. He is deeply interested in math, data science, physics, and computer science and would like to apply his math and physics knowledge to improve technology. Alex looks to further his knowledge and interest in STEM by studying data science related topics in higher education.

The post Space Physics: The motion of extraterrestrial objects appeared first on Exploratio Journal.

Introduction

Deep space missions have become the interest of space agencies over the past 50 years after humans successfully reached space and our moon. The technology required to explore the solar system and the universe outside our solar system has grown from simple rockets and capsules designed to bring people to the moon to impressive orbiters and satellites equipped with the latest in research technology to expand humanity’s understanding of our solar system and the universe that surrounds us.

This report will present the stories, physics, and science missions of four historic NASA deep space missions: Voyager, Pioneer (10 and 11), Galileo, and Cassini. These missions are of particular interest to me due to their role in boosting human understanding of various planets and the outer edges of the solar system. Voyager used gravity assist and a rare alignment of planets to research Jupiter, Saturn, Uranus, and Neptune. The Pioneer missions both flew by Jupiter and Pioneer 11 also conducted a detailed exploration of Saturn. Galileo sent a probe into Jupiter’s atmosphere and a spacecraft entered the Jovian orbit. Cassini used a probe and spacecraft to learn about Saturn, its rings, and its satellites as well. Combined these missions altered humanity’s concepts of space by confirming existing theories and presenting information that lead to new questions. This paper will analyze the science objectives of each mission, their orbits and launch vehicles, and other particularly interesting information. To conclude, the facts of previous missions will be used to propose ideas for new missions and offer commentary on established plans for future missions as well.

Outline of Missions

Voyager

The Voyager missions were launched in the 1970s to explore deep space beyond what humans had conceived before. Intended to flyby various bodies within the solar system and then continue gathering data outside of our solar system, the Voyager missions have been instrumental in learning about planets within our solar system and about the energy and space outside the solar system as well [1].

Science of the Mission

The Cosmic Ray Subsystem (CRS) looks for energetic particles in plasma and has high sensitivity. Such particles can be found in intense ration fields like the area around Jupiter, or from other stars. The CRS aimed to gather data to provide information on the content of energy and dynamics of cosmic rays across the galaxy in an attempt to better understand ray sources from across the galaxy, even beyond our star [2]. Highly energetic particles can be detected from fields around large planets such as Jupiter. Stars also emit high energy particles which the CRS system tracks. Since Voyager is now beyond our solar system in deep space, these readings provide scientists with important information about the universe that surrounds us.

Voyager also had a three-part Infrared Interferometer Spectrometer (IRIS) which acted as a thermometer, detecting temperature emissions from space bodies, a sensor for different elements and compounds near atmospheres of space bodies, and a radiometer to measure sunlight reflected at ultraviolet, visible, and infrared frequencies. The use of IRIS as a thermometer in space enables more accurate atmospheric dynamic models [3]. This aids the future of space missions, particularly initiatives to find habitable environments for alien life. Although IRIS shut down in 1988, it transmitted important information about Neptune and Uranus which led to our understanding that the two planets have roughly the same temperature. Since Neptune is substantially further away from the Sun, scientists concluded that the similarity in temperature was due to higher methane content trapping more heat on Neptune.

Voyager 1 has the Golden Record: a message from humanity to intelligent alien species including greetings in 55 human languages, pictures of people and places on Earth, and various samples of music. The two sets of Golden Records spin at 16.67 RPM and play a variety of famous songs from classical Mozart to popular American 1970s songs along with various sounds of nature, humans speaking, and other naturally occurring sounds from the planet. The Golden Record also shows a pulsar map to guide any viewers toward Earth [4]. Pulsars are the remains of dying stars whose rapid spinning and magnetic field emit a beam of light, which is why pulsar diagrams show planets around their star connected with beams of light. Figure 1 depicts the Golden Record as presented on the NASA website.

The spacecraft also had an Optical Calibration Target, a flat rectangle with constant color and light properties for cameras and infrared instruments on the spacecraft to calibrate themselves [5]. The Optical Calibration Target served as a visual target with known properties to compare measurements from space, particularly since different cameras and sensors aboard the Voyager satellites had their own characteristics and exhibited different pictures/visual patterns.

Launch Vehicle and Orbit

Voyager’s launch and path is something of a beauty itself, designed to take advantage of an arrangement of planets which only occurs every 175 years. Voyager swung from planet to planet in a process called gravity assist, because the gravitational pull of each planet (Jupiter, Saturn, Uranus and Neptune) bends the flight path and increases its speed enough to swing it to the next destination. This process minimized the propellant and need for engines and cut the flight time to Neptune from 30 years to 12 years.

Gravity assist lies on satellites orbiting about space bodies in an hyperbolic shape, thus conducting their flybys of planets at periapsis. The hyperbolic orbit is determined by the magnitude of the force of gravity acting on the satellite from the planet or moon it orbits. Since energy is conserved in an orbiting system, and periapsis means that the satellite is the closest to the planet as it will ever be, satellites fly very quickly past their planets [6]. The science equipment and data gathering features onboard then have very little time to actually image and collect data about the planets they fly by.

Launching a deep space vehicle like Voyager requires a period of powered flight which carries the vehicle from Earth’s atmosphere to free flight in space. This requires a launch vehicle to thrust the satellite into orbit which eventually falls off at burnout when the satellite is in free flight. In flight, Voyager 1 focused on flybys of Jupiter, Saturn and Titan, Saturn’s largest moon. Voyager 2 continued from Saturn and Jupiter to Uranus and Neptune as well. Both Satellites are now in deep space beyond the solar system, and it is anticipated that they will continue sending information back to Earth for 20-30 years. They are the longest flying and farthest venturing spacecraft in history and provide scientists with valuable information about the nature of energy and radiation in space [7].

Deep Space Networks

Sharing data from deep space satellites like Voyager back to Earth requires precise time synchronization. This is accomplished by the use of Deep Space Networks (DSNs) in California, Australia and Spain which provide coverage for all space missions [6]. Communication with DSN technology requires precise time information because while in orbit, there are times when a satellite cannot directly communicate with Earth. Whether the sun is between Earth and the satellite, or the body that the satellite is orbiting interferes in the signal, DSN systems can only transmit signals at allocated time intervals. To do so, NASA had used a manual system initially but has now adopted a digital, Sequence of Events (SOE) driven automation system. The SOE for Voyager contains information about the state of the spacecraft, any deviance/changes to the flight path, notification for the beginning and end time of orbits, information about the bit size and format of data being transmitted, and changes in the frequency of information being transmitted [8].

Pioneer

Pioneer 10, launched in March 1972, was built to study Jupiter’s atmosphere, the magnetosphere and moons around Jupiter like Io in particular. Pioneer 10 was the first satellite to fly beyond the asteroid belt, and also collected data on the solar wind patterns and dust distribution around Jupiter. Pioneer 10 completed its flyby of Jupiter in 1973 and became the first spacecraft to ever cross the solar system into interstellar space. Due to a failure of the power source, Pioneer 10 stopped transmitting information to Earth in 2003 but its 30 year flight far exceeded the 21 month mission it was assigned for. It is flying with a trajectory to reach the star Aldebaran in roughly two million years [9]. Pioneer 11 was the twin spacecraft of Pioneer 10, launched in April 1973 to primarily study Saturn although it passed Jupiter in gravity assist. Although Pioneer 11 experienced a number of malfunctions like the temporary failure of the Radioisotope Thermographic Generator, the heat and power source, the mission was a success and significantly enhanced human understanding of Saturn [10].

Science of the Mission

Pioneer 10 and 11 carried a tool called a helium vector magnetometer (HVM) which measured magnetic fields around Jupiter. The NVM protruded ~6.5 meters out from the rest of the satellite to reduce the effects of the spacecraft magnetic field and balance the spin of the spacecraft. Scientists had previously been able to observe the interplanetary magnetic partners from orbits around Mars, and they remained curious about the impact of the Sun’s magnetic field controlling the flow of plasma and magnetic energy to the rest of the solar system. With the Pioneer missions, the HVM collected data on the structure of the interplanetary field up to Jupiter, mapped a specific magnetic field of Jupiter itself and evaluated solar wind interactions about Jupiter [11].

Pursuant to the mission to better understand the Sun’s impact deep in our solar system, Pioneer carried a Cosmic Ray Telescope (CRT) to monitor solar rays and track high energy particles from the Sun. The device also measured particles in Jupiter’s orbit. It was composed of three telescopes, one for high energy particles, another for medium energy, and a last for low energy particles [12]. Coupled with data from future missions including Voyager, this data has led to a more precise understanding of Jupiter’s energy and how the Sun’s energy fades at further points in the solar system.

Pioneer was also the first satellite to take detailed pictures of the Great Red Spot, a massive storm on Jupiter larger than Earth. Pioneer 10 made observations of Jupiter’s poles and enabled a much more detailed perception of Jupiter to Earth’s population.

Launch Vehicle and Orbit

Pioneer 10 was the first spacecraft to use gravity assist to reach escape velocity to leave the solar system. By slingshotting from Jupiter to Saturn, Uranus and Neptune, Pioneer 10 escaped on its trajectory into interstellar space and was the furthest human built device from Earth, until it was surpassed by Voyager in the late 1990s.

When Pioneer was launched from Earth, it entered a heliocentric orbit which was tweaked with small thrust maneuvers from the Pioneer Navigation Team until the gravitational field strength of Jupiter exceeded that of the Sun. After the flyby of Jupiter, Pioneer returned to a heliocentric orbit until it reached Saturn [8]. A paper from researchers at the Jet Propulsion Laboratory about the anomalies detected in Pioneer’s orbit also includes an informative image of the paths taken by both Pioneer missions (see Figure 2).

Pioneer 10 and Pioneer 11 Distinctions

Both Pioneer spacecraft were created almost identical and were simply launched with different intended orbits to research different bodies. Pioneer 11 last transmitted data in 1995 and Pioneer 10 last transmitted data in 2003. Both spacecraft served long after they were anticipated to fail and data from the outer brinks of the solar system lead to an understanding of a discrepancy between the anticipated speed of travel and the real speed dubbed the Pioneer Anomaly. The primary science difference between the two mission lies in their trajectory: Pioneer 10 explored Jupiter, its magnetic field and its satellites in great detail, then flew deeper into the solar system while Pioneer 11 hyperbolically sped past Jupiter, still capturing data and images, primarily aiming for Saturn and research on Saturn’s rings, magnetic fields and properties [10]. Pioneer 11 is now hurtling towards the center of the Milky Way although humanity lost contact with it decades ago. The Golden Record is still prominently shown on both spacecraft for any curious intelligent life in the future.

Pioneer Anomaly

Years into both Pioneer flights, it was noticed that the spacecraft were not moving with the acceleration that was predicted. On the outer edges of the solar system, both Pioneer spacecraft slowed down (5000 km per year). This deviation in behavior initially caused concern in the physics community, because without a reasonable explanation, the Newtonian models of physics would have to be questioned. Eventually, Doppler data (information about lightwaves of different wavelengths) were transmitted from Pioneer back to Earth which set the record straight. The reason for the slow down was simply the anisotropic dispersion of the internal heat generated from the science tools onboard each spacecraft. A paper from JPL describes the issue, saying that “Pioneer spacecraft were powered by SNAP-19 (Space Nuclear Ancillary Power) RTGs mounted on long extended booms designed to protect the on-board electronics from heat and radiation impact”. When these SNAPs got hot, the thermal radiation produced could disrupt the balance of forces on Pioneer, but NASA had placed them on specially balanced rods far away from the body of the spacecraft in order to balance each other out. The failure of this system is currently being researched and remains a topic of interest to amend for future missions. Since the balancing mechanism did not work, SNAP emitted thermal photons in an uneven way, which in return caused a recoil force in the opposite direction of the photos. After all, momentum is still conserved within the photon-spacecraft body. This uneven distribution of force is the current accepted explanation for the discrepancy between anticipated and real speed [13].

Galileo

NASA’s Galileo mission was a historic first for human exploration in space and led to an immense growth in understanding Jupiter. Galileo was the first satellite to ever orbit an outer planet, and it spent eight years orbiting Jupiter gathering information on the planet itself and its various moons. Data gathered from Galileo is the basis for future missions to Europa to explore the potential of subsurface water, among other future space missions as well.

Science of the Mission

Galileo used plasma and particle detectors like the Voyager and Pioneer missions, but employed a much more sophisticated set of cameras and sensors for near-Jupiter orbit.

The Solid State Imaging Camera (SSI) was intended to study Jupiter and its satellites using a modified spare of the narrow angle telescope used on Voyager. The camera operated in eight filtered band passes and provided higher resolution, better filters and more effective bandwidth. Although the SSI did not come with an ultraviolet band, the images were clearer and more useful than prior missions. The amended design from the Voyager mission also improved performance in baffling, a process which eliminates visual noise from scattered light. The primary science missions of this advanced camera was to investigate Jupiter’s atmosphere and clouds, measure and determine the properties of Jovian satellites, map the distribution of minerals on the surface of Jupiter’s moons and search for any other behavior or atmospheric emissions, particularly from the night side of Jupiter [14].

Galileo also carried the Heavy Ion Counter (HIC), an engineering experiment to monitor heavy ion activity in order to find information on radiation near Jupiter and determine the parameters for designing future radiation safe electric material for deep space exploration. The experiment included two Low Energy Telescopes (LETs) used to sample a wide range of energies. The information gathered from Galileo, when combined with data from Pioneer and Voyager, has offered important guidance to scientists about the future of electricity and radiation in space.

Since the Galileo mission was orbiting around Juptier and could not escape further into deep space, it was instructed to hurtle towards Jupiter’s atmosphere in 2003 where it was destroyed. The mission was over because it had collected enough relevant data for NASA to use. Galileo also took a number of detailed pictures of Jovian satellites, including the moon Io (see Figure 3).

Launch Vehicle and Orbit

Galileo was the first mission to ever orbit an outer planet. To do so, the spacecraft had to use gravity assist from Venus and Earth to pass the asteroid belt and reach Jupiter. Galileo did one flyby of Venus and one of Earth, gathering enough momentum from the hyperbolic path it traced around both to thrust itself towards Jupiter. Along the way, Galileo even took pictures and gathered data of a few large bodies in the asteroid belt. Galileo was composed of a spacecraft and a probe. The spacecraft was the source of thrust around other bodies while the probe was intended to be a short-lived tool descending in the atmosphere to measure temperature and other atmospheric factors. Six years after leaving Earth, Galileo reached Jupiter and the probe separated from the spacecraft, entering Jupiter’s atmosphere. The probe descended for just under an hour with parachutes and transmitted data on the strong winds, intense heat and unexpected dryness of the Jovian atmosphere before it was vaporized by the head [15].

While the spacecraft relayed this information from the probe back to Earth, mission scientists at NASA had to determine the right moment to activate the engine on the spacecraft to enter Jupiter’s orbit. Too little thrust, and Galileo would sail past Jupiter into deep space, and too much thrust would force the spacecraft to the same short lived life as the probe: melted in the atmosphere. The decisions made were successful and Galileo entered orbit, where it remained for two years. Galileo maintained a long elliptical orbit around Jupiter because the different distances away from the planet enabled the devices onboard to gather data on the planet, the rings around it and conduct flybys of important moons [16].

The Galileo spacecraft and probe were launched by an Inertial Upper Stage (IUS) launch vehicle. IUS is an unpiloted booster used from the 1980s to the early 2000s. After launching from the ground, the IUS employed a second stage launch boosting its payload into higher orbit, or in Galileo’s case, to another planet of the solar system. The IUS was designed by Boeing and the two rocket burns happened one hour, then six and a half hours into flight [17].

Cassini

Cassini was a joint mission between NASA, European Space Agency and the Italian Space Agency to explore Saturn, its moons and its rings. Much like Galileo, Cassini employed a probe called Huygens to explore Titan, Saturn’s largest moon, while a spacecraft orbited Saturn gathering other data.

Science of the Mission

The science devices onboard the Cassini orbiter fall into three categories: Optical Sensing, Fields/Particles and Microwave Sensing.

With regards to Optical Sensing operations, Cassini carried a Visible and Infrared Mapping Spectrometer (VIMS) which collected light that is visible to humans, and infrared light of longer wavelengths. VIMS separated light by the wavelengths it detected which allowed scientists to break down the composition of Saturn’s atmosphere, its rings and its satellites as well. This proved important during orbit because NASA determined that Titan has an ice volcano, and Titan also had clear polarity similar to Earth with cold poles and a warmer center. While VIMS was used to disassemble specific views on Saturn, Cassini also carried an Imaging Science Subsystem (ISS) which functioned as the main eyes for the spacecraft. While VIMS focused on the visible spectrum and infrared light, ISS also caught ultraviolet light [18]. The ISS made Cassini famous both due to its role in navigation and because most of the iconic pictures from Cassini came from ISS. Popular images of Saturn and its rings came from the ISS, along with important data about the surface of Titan. This information came from blocking all but certain wavelengths to see below the atmospheric smog.

To better conceptualize the plasma, electric/magnetic fields and energy systems around Saturn, Cassini also carried a Magnetometer (MAG) and the Cassini Plasma Spectrometer (CAPS). MAG was a simple device similar to tools used in other missions. While the Cassini spacecraft orbited Saturn, it recorded the direction and strength of magnetic fields around the spacecraft to develop a 3-D model of the magnetosphere and understand how it impacts the moons, the rings and gasses around Saturn. Thanks to Cassini’s elliptical path around Saturn, it orbited in and out of the magnetosphere which allowed a more sophisticated model to be built based on observations from inside and outside the zone of interest. Going deep into Saturn’s dense helium core would yield more information as well, but remains a figment of imagination right now because any human built spacecraft would vaporize well before getting to the center of Saturn. Much like the Voyager spacecraft, having a magnetic detector right next to a metal body would significantly skew results, so MAG was actually installed on an 11 meter metal arm as far away from the spacecraft as possible [19]. This arm was folded at takeoff and simply opened two years after it left Earth. CAPS had three sensors: an electron sensor, ion mass spectrometer and ion beam sensor. Each of them measured particle kinetic energy and direction, but the ion mass spectrometer collected data on particle mass as well [20]. Yet again thanks to an elliptical orbit which enabled the spacecraft to interact with Saturn’s atmosphere at different radii from the surface of the planet, CAPS was able to collect information about the composition of the atmosphere and magnetosphere

To collect information on microwave activity, Cassini also carried the Radio Science Subsystem (RSS) which sent its own radio signals towards Saturn and learned about the objects it interacted with by the radio waves which bounced back towards Cassini. This was used to learn about gravity fields, the structure of the rings of Saturn and some of the surface properties as well [21]. Coupled with the visual data from the cameras and the atmosphere information from the probe, this led to a much more complete model of Saturn and deeper understanding of the rings and satellites around it.

Launch Vehicle and Orbit

Cassini’s orbit is a work of gravity and geometric art. While the path appears to be elliptical, Saturn is actually acting much more like a focus point for the orbit. That is to say, Saturn is relatively close to the end of the major axis of the ellipse. In reality, the orbit of Cassini has been a combination of two hyperbolic traces: a choreography between Saturn and Titan, a massive moon. Cassini begins its journey towards Saturn, crossing between the planet and its rings, when it is the furthest away from Saturn: a point known as apoapse. After that point, Cassini swirls around and away from Titan towards Saturn. Prior to the Cassini mission, Titan was only photographed by Voyager and observed from Earth [22]. These close, hyperbolic orbits not only enabled more detailed photography and research, but the Huygens probe was able to get to the surface of Titan and gather important information.

Cassini was guided to space by the Titan IV-B launch vehicle, which was NASA’s most powerful launch vehicle at the time employing a two stage launch system. The Titan series had been used by the Air Force for various military applications, and were employed extensively by NASA due to their reliability and sheer power [23].

Conclusion and Future Missions

Right now, NASA has dozens of plans to conduct flybys of important asteroids and planets in the coming years. Venus and Mercury seem to be of particular interest, which makes sense given the past focus on Jupiter and Saturn. While the space community believes firmly in the importance of such initiatives, and supports the continued research of planets and space bodies, there is interest in the Europa Clipper mission scheduled for 2024 [24]. Prior images of Europa from NASA show a fascinating fractured surface (see Figure 4) which appears interesting to study. The plan is for NASA to send a spacecraft into Jupiter’s orbit in order to conduct numerous fast flybys of Europa, likely employing the same broadly elliptical shaped orbit around Saturn. Given that Europa is known to have icy surfaces and might harbor water, there is also value in sending a probe to Europa’s atmosphere to better understand its habitability. The same techniques from Galileo can be employed and the information from a probe coupled with a spacecraft would likely yield more direction for future missions than just distant observations from a spacecraft [25].

The exploration of space was unthinkable 100 years ago and has become a reality today. Deploying principles like gravity assist, using hyperbolic flybys of planets and manipulating energy across our solar system has enabled humanity to access and explore worlds previously only dreamt of. As the advent of a period of continued space exploration dawns and humanity prepares to take off on the path to understanding the universe around us better, it is important to recall the physics and engineering concepts discovered and proven in past missions while embracing the future of innovation and change to come.

Bibliography

[1] “Voyager – The Interstellar Mission,” voyager.jpl.nasa.gov. http://voyager.jpl.nasa.gov/mission/interstellar-mission/

[2] J. W. | P. Thursday, October 24, and 2019, “40 years later, these Voyager instruments still talk to NASA,” Astronomy.com, Oct. 29, 2019. https://astronomy.com/magazine/2019/10/after-40-years-voyager-still-talks-to-nasa-with-7 -instruments

[3] “Voyager – Spacecraft – Infrared Interferometer Spectrometer and Radiometer (IRIS),” voyager.jpl.nasa.gov. https://voyager.jpl.nasa.gov/mission/spacecraft/instruments/iris/

[4] J. Lee Oakes, “Voyager Golden Record: Through Struggle to the Stars,” Smithsonian Music, Sep. 24, 2019. https://music.si.edu/story/voyager-golden-record-through-struggle-stars

[5] “Ring-Moon Systems Node – Voyager 1 Narrow Angle Camera Description,” pds-rings.seti.org. https://pds-rings.seti.org/voyager/iss/inst_cat_na1.html (accessed Nov. 20, 2022).

[6] R. Braeunig, “Basics of Space Flight: Orbital Mechanics,” www.braeunig.us. http://www.braeunig.us/space/orbmech.htm#launch (accessed Nov. 20, 2022).

[7] NASA, “Voyager 3D Model,” NASA Solar System Exploration, Jul. 26, 2019. https://solarsystem.nasa.gov/missions/voyager-1/in-depth/

[8] R. Hill, S. A. Chien, C. Smyth, K. Fayyad, and T. Santos, “Planning for Deep Space Network Operations,” undefined, 1995, Accessed: Nov. 20, 2022. [Online]. Available: https://www.semanticscholar.org/paper/Planning-for-Deep-Space-Network-Operations-Hill -Chien/64e8702993baffc32f911272ba1122a91bbd3ba3#citing-papers

[9] “The Outer Planets: Missions: Pioneer 10 & 11,” lasp.colorado.edu.https://lasp.colorado.edu/outerplanets/missions_pioneers.php

[10] “Pioneer 10 and 11, outer solar system explorers,” The Planetary Society. https://www.planetary.org/space-missions/pioneer

[11] “In Depth | Pioneer 10 – NASA Solar System Exploration,” NASA Solar System Exploration, Jul. 24, 2019. https://solarsystem.nasa.gov/missions/pioneer-10/in-depth/

[12] F. McDonald, “Cosmic Ray Telescope Experiment (CRT), Pioneer 10/11 Program,” Technical Report, Maryland Univ. College Park, MD United States Inst. for Physical Science and Technology, Jun. 1999, Accessed: Nov. 20, 2022. [Online]. Available: https://ui.adsabs.harvard.edu/abs/1999STIN…9964263M/abstract

[13] S. G. Turyshev and V. T. Toth, “The Pioneer Anomaly,” Living Reviews in Relativity, vol. 13, no. 1, 2010, doi: 10.12942/lrr-2010-4.

[14] “NASA – NSSDCA – Experiment – Details,” nssdc.gsfc.nasa.gov. https://nssdc.gsfc.nasa.gov/nmc/experiment/display.action?id=1989-084B-10#:~:text=Des cription

[15] “Galileo – In Depth,” NASA Solar System Exploration, Aug. 15, 2018. https://solarsystem.nasa.gov/missions/galileo/in-depth/

[16] “Galileo Project Information,” nssdc.gsfc.nasa.gov. https://nssdc.gsfc.nasa.gov/planetary/galileo.html

[17] “Boeing Inertial Upper Stage Space Payload Booster,” National Museum of the United States Air ForceTM. https://www.nationalmuseum.af.mil/Visit/Museum-Exhibits/Fact-Sheets/Display/Article/6 93053/boeing-inertial-upper-stage-space-payload-booster/#:~:text=The%20Inertial%20Up per%20Stage (accessed Nov. 20, 2022).

[18] “Imaging Science Subsystem (ISS) | Cassini Orbiter – NASA Solar System Exploration,” NASA Solar System Exploration, Sep. 04, 2018. https://solarsystem.nasa.gov/missions/cassini/mission/spacecraft/cassini-orbiter/imaging-science- subsystem/

[19] “Magnetometer (MAG) | Cassini Orbiter,” NASA Solar System Exploration. http://solarsystem.nasa.gov/missions/cassini/mission/spacecraft/cassini-orbiter/magnetome ter/ (accessed Nov. 20, 2022).

[20] “Cassini Plasma Spectrometer (CAPS) | Cassini Orbiter,” NASA Solar System Exploration. http://solarsystem.nasa.gov/missions/cassini/mission/spacecraft/cassini-orbiter/cassini-plas ma-spectrometer/ (accessed Nov. 20, 2022).

[21] “Radio Science Subsystem (RSS) | Cassini Orbiter – NASA Solar System Exploration,” NASA Solar System Exploration, Sep. 04, 2018. https://solarsystem.nasa.gov/missions/cassini/mission/spacecraft/cassini-orbiter/radio-scien ce-subsystem/

[22] “Ring-Grazing Orbits,” NASA Solar System Exploration, Apr. 11, 2017. https://solarsystem.nasa.gov/news/12966/ring-grazing-orbits/ (accessed Nov. 20, 2022).

[23] “Remember the Titans,” Lockheed Martin, Jun. 15, 2022. https://www.lockheedmartin.com/en-us/news/features/history/titan.html

[24] “Upcoming Events,” nssdc.gsfc.nasa.gov. https://nssdc.gsfc.nasa.gov/planetary/upcoming.html

[25] “Europa Clipper,” www.jpl.nasa.gov. https://www.jpl.nasa.gov/missions/europa-clipper [26] NASA, “Voyager – The Golden Record Cover,” Nasa.gov, 2019. https://voyager.jpl.nasa.gov/golden-record/golden-record-cover

[27] “Ridges and Fractures on Europa,” NASA Solar System Exploration, Mar. 28, 1998. https://solarsystem.nasa.gov/resources/105/ridges-and-fractures-on-europa/?category=miss ions_galileo (accessed Nov. 20, 2022).

About the author

Aniket Martins

Aniket is a senior at Fairfield Ludlowe High School in Fairfield, CT. He is passionate about aerospace engineering and is a member of the American Institute of Aeronautics and Astronautics where he led the 2022 Congressional Visits Day lobbying initiatives for Connecticut. He participated in the University of Florida’s Student Science Training Program in 2022 where he interned at the Nanostructured Energy Systems Lab, completing a research project in Applications of Microfluidic Coolant Systems in Atmospheric Reentry Temperature Regulation for which he won Best Presentation.

Aniket is also passionate about civics and is President of his school’s award winning Model UN team and has won numerous awards at various conferences. At his school he is also President of Mu Alpha Theta Math Honor Society, Vice-President of National Honor Society, Vice-President and Director of Tutoring for English Honor Society, President of Rocketry Club, Founder/President of Engineering Club and an editor for Prospect, the school newspaper. Aniket has won numerous awards in the Connecticut Writing Contest and loves soccer, skiing and tennis.

The post Spacecraft Missions and Orbital Mechanics: Past Stories and Future Initiatives appeared first on Exploratio Journal.

Abstract

This report explores and discusses space debris, or space “junk” – its origin, how it affects the Earth and solutions for debris management. Nowadays, space debris, which is made from “dead satellites” and meteoroids, is one of the biggest global issues that we have to solve immediately. Scientists are trying to solve this problem by detecting space debris by using lasers and telescopes. They are working to solve the issue by planning to charge orbital use fees and using disposal orbit so that they could reduce the amount of space debris in the Earth’s orbit. 

What is space junk?

Space junk, also known as space debris, is any piece of machinery left by humans in space. The majority of orbital debris is made up of human-made materials, such as fragments of spacecraft, tiny flecks of paint from a spacecraft, rocket parts, defunct satellites, or pieces formed through explosions of objects in orbit, floating around in space at high speeds.

The majority of space garbage travels at a breakneck speed of 18,000 miles per hour, almost seven times faster than a bullet. Present and future space-based services, explorations, and activities pose a safety risk to people and property in space and on Earth due to the rate and amount of debris in LEO (Low Earth Orbit).[1]

History of space junk

Over 6050 launches in the past 60 years have resulted in approximately 56450 monitored objects in orbit, of which approximately 28160 remain in space and are continuously tracked by the US Space Surveillance Network and stored in their catalog, and these kinds of debris weight more than 9300 tons in total.[2] About 70% of space debris in LEO was created by China, America, and Russia. 

For example, in 2007, China launched a ballistic missile  from the Xichang Space Launch Center that destroyed a satellite called Fengyun-1C (FY-1C). This had produced the largest space debris generating event in the Earth’s orbit on the record. More than 3000 pieces of debris were produced and 97% of them are remaining in orbit. Moreover, scientists have estimated that 32000 smaller pieces haven’t been tracked yet. [3]

Another event was in 2009. There was a big collision between the Russian satellite (Cosmos 2251) and the US satellite (Iridium 33). Figure 1 shows Cosmos 2251 satellite which produced 1357 pieces of debris and Iridium satellite has produced 528 pieces of debris. Scientists have estimated more than half of the Iridium debris will last at least 100 years in space, while most of the Cosmos debris will last at least 20 to 30 years.[4] The picture below is showing how Cosmos 2251 and Iridium 33 have collided.

Figure 2 shows the history of space junk production and its composition. As it can be seen in the figure, most of the space debris originates from dead and leftover satellites. Moreover, like Cosmos and Iridium satellite collisions, about 9% of space debris is produced because of collisions between satellites.

What kind of debris?

Space debris consists of more than 10 thousand artificial space objects and natural materials. Now, what kind of materials are in the space debris? Most of the space debris consists of natural materials such as meteoroids and human-made materials such as space rockets and satellites (shown in Figure 3).

First off, a natural material meteoroid is a solid object that travels through interplanetary space that is larger than atoms but smaller than asteroids. It travels around the sun with velocities ranging from 11 km/s ~ 72 km/s. Since they move by gravity, they sometimes get into the Earth orbit and become a part of space junk [7]

Secondly, debris from space rockets and satellites are types of artificial materials. More than 10 thousand of these debris objects have been placed into space through more than 6000 rocket and satellite launches, out of which only about 3900 are operating.[8] The main reason satellites produce space debris is that they are in either collision or explosion called in-orbit fragmentation. The most common cause of in-orbit explosions is leftover fuel in tanks or fuel lines and other energy sources that remain on board after a rocket stage or satellite has been discarded in Earth orbit. The harsh space environment can wear down the mechanical integrity of external and internal parts over time, resulting in leaks or mixing of fuel materials, which can lead to self-ignition. As can be seen in Figure 3, most of the debris is the pieces of dead satellites. 

Humans just leave those kinds of satellites in space since the cost is very high to bring the “dead” satellites into the Earth. Additionally, due to lots of missions to space, there are many discarded parts of the rockets that end up in local space. This material can range in size from a discarded rocket stage to microscopic paint chips.[9] 

How do scientists count or track space debris 

There are two ways to detect space debris from the ground. One is to use lasers and the other method is to use a telescopic detector and filter. 

Using a laser with a kHz repetition rate was the initial method to detect space debris. The way scientists detect space debris with laser tracking method is first, they detect space debris with an optical telescope and at the same time, they send laser pulses to the debris so that the distance to the object is calculated by the time which laser travels to the debris and comes back. By combining the time measurement and position determination, scientists can determine the approximate position and size of space debris[11]

Laser observations of space debris structures have been carried out since the turn of the century. However, this approach only operated for a few hours at dusk, when the detection station on Earth is dark and the debris is still lit by the Sun. Figure 4 shows how a laser can detect space debris. [12]

Secondly, scientists use telescopes to detect space debris which is placed in GEO (geostationary earth orbit). For example, in European Space Agency, Zeiss 1M telescope is operated in Spain, as shown in Figure 5, which is used for investigating the property and characteristics of debris in space. This telescope can detect debris, whose size is down to 10~15 cm. Moreover, it is capable of determining the color of the debris which is very important since it allows to determine material property and provides an information of the origin of the detected debris.[14]

How space debris can affect Earth 

Space debris can affect Earth in many ways, mostly negatively. Collisions with active spacecraft are the biggest issue. Any piece of debris greater than 1 cm in diameter will cause a catastrophic impact with an average impact speed of 10 km/s. Collisions between debris and operational satellites cause not only financial but also environmental damage. In the event of a collision, a satellite’s ability to correct its orbit will eventually be lost, and it will become another space danger with no way to steer into a more stable orbital direction. This raises the likelihood of a damaged satellite colliding with another orbital target, such as another satellite or debris, and restarting the debris generation cycle. The more debris in space accumulates, the more likely another collision will occur, adding to the issue. [15] 

Moreover, there is a possibility of dead satellites reentry into Earth orbit. As it can be seen in Figure 7 when the dead satellites re-enter the Earth’s orbit, the break-up starts at around 78 km altitude and this is called the reentry interface. Since the satellite is affected by the wind when re-entering to Earth orbit, the pieces which have low mass but large areas such as solar panel sheds first. Then the catastrophic breakup begins when the time passes and finally leads to a major breakup where all the things are divided into small pieces. These pieces move 50 m/s which means when they reach the ground they will have a massive power. 

Another aspect of space junk’s effect on Earth is the weather. The effect on the weather isn’t direct, however, if the density of the debris increase to the point where it interfere with our ability to use weather satellites it distracts tracking weather changes caused by our ground-based pollution.[17] 

Finally, space debris could fall from the sky and threaten our communities. On average, about 200-400 pieces of debris fall from the sky and enter Earth’s atmosphere every year. Fortunately, since human populations live on a small percentage of the total Earth surface, falling debris is likely to fall into the ocean.[18]

Proposed solutions for debris reduction or removal

One proposed solution for the space debris problem suggested in the literature is to charge operators an “orbital use fee” for every satellite in the Earth’s orbit. According to economist Matthew Burgess, a CIRES(Cooperative Institute for Research in Environmental Sciences) Fellow, and co-author of a recent report, orbital usage fees, if implemented, would boost the space industry’s long-term value. An annual fee of around $235,000 per satellite would quadruple the value of the satellite industry by 2040 by reducing potential satellite and debris collision risk.[19] In another study scientists have predicted the effect of charging “orbital use fee”. As Figure 8 shows, the number of satellites launched and satellites placed in the low earth orbit will be reduced, collision probability between satellites will be decreased dramatically and finally the amount of debris will be also decreased. This shows that charging “orbital use fee” will give a positive impact[20]

Another proposed solution is to deorbit space debris into so-called “disposal orbits.” Re-orbiting items into disposal orbits at the end of their usable lifespan is one method of extracting them from the most commonly used high-altitude orbital regions. This keeps the objects in Earth orbit, but it keeps them out of areas where they could collide with working spacecraft. However, when a space object is moved into a disposal orbit, the collision danger in its original orbital region is reduced, but the collision hazard in the current orbital region is increased. Objects transferred to disposal orbits, on the other hand, may still contribute to the debris hazard in their original orbit because debris created by collisions or explosions in disposal orbits can overlap the original orbit. Moreover, the process to deorbit or accelerate the orbital decay of spacecraft or rocket bodies would be expensive. 

Finally, spacecraft designers, on the other hand, should take a system-level approach to avoid unintended spacecraft breakups. The strategy is to first identify all possible sources of stored energy on a spacecraft nearing the end of its operational life; second, provide a method for benignly dissipating the stored energy satellite for each source; and third, enable these means at the end of the spacecraft’s functional lifetime. [22]

In any case, there is no way to prevent all potential spacecraft breakups: despite precautions, a small number of spacecraft breakups would continue to produce debris, but at a lower level.

My solution

One solution I have come up with to solve the space debris problem is to create a giant magnetic spaceship. Most of the space debris consists of satellites that are human-made and most of those satellites consist of some metallic material. This means some of the space debris is magnetic. Thus, if we could use a magnet which could attract all the leftover dead satellites, and remove them from the earth orbit, we could get rid of some of the space debris. 

To be specific, we could create a magnet spaceship where all the surface of the spaceship is covered with a magnet. The spaceship is going to travel around the low earth orbit and attract magnetic space debris on their surface which pilots are controlling on the earth. If the surface of the spaceship is full of debris, pilots are going to remove all the debris from the surface into the spaceship by using a strong massive vacuum cleaner which automatically cleans the surface of the spacecraft and stores it inside it. Then, there will be another machine in the spacecraft which compresses all the absorbed space debris into small square pieces so that there will be more space to store the space debris. When the spacecraft is full of space debris, pillot will send it back to the earth so that we can recycle and reuse it. 

Conclusion

In summary, space debris problems are treated as a serious global issue. More than 34000 pieces of space debris are orbiting around earth and these have extremely negative effects on the Earth: collision between space debris and satellites, re-enter the Earth orbit and disturb tracking weather change. One of the biggest incidents that have produced massive amounts of space debris was a collision between Cosmos 2251 and Iridium 33. In order to get rid of this space debris, scientists first have to detect them. The way they discover space debris is by using laser and telescope. After they recognize the space debris, scientists plan to charge a fee for orbital use so that companies could reduce using satellites. Also, they work to send the space debris to a disposal orbit. This process is significant for reducing the amount of space debris and clearing up the Earth’s orbit. 

Reference 

[1] Space Debris  https://www.nasa.gov/centers/hq/library/find/bibliographies/space_debris

[2] ESA – About space debris  https://www.esa.int/Safety_Security/Space_Debris/About_space_debris

[3] 2007 Chinese Anti-Satellite Test Fact Sheet 

https://swfound.org/media/9550/chinese_asat_fact_sheet_updated_2012.pdf

[4]2009 Iridium-Cosmos Collision Fact Sheet  

https://swfound.org/media/6575/swf_iridium_cosmos_collision_fact_sheet_updated_2012.pdf

[5]View of Iridium 33 and Cosmos 2251 Debris 180 Minutes Post-Collision. | Download Scientific Diagram 

https://www.researchgate.net/figure/View-of-Iridium-33-and-Cosmos-2251-Debris-180-Minutes-Post-Collision_fig4_266017226

[6]ESA – The history of space debris creation  http://www.esa.int/ESA_Multimedia/Images/2021/03/The_history_of_space_debris_creation

[7]Meteor, a space debris particle flying through the atmosphere  https://www.aeronomie.be/en/encyclopedia/meteor-space-debris-particle-flying-through-atmosphere

[8] ESA – FAQ: Frequently asked questions  https://www.esa.int/Safety_Security/Space_Debris/FAQ_Frequently_asked_questions

[9] ESA – About space debris  http://www.esa.int/Safety_Security/Space_Debris/About_space_debris

[10] Space junk: The cluttered frontier  https://news.mit.edu/2017/space-junk-shards-teflon-0619

[11] Daylight space debris laser ranging  https://www.nature.com/articles/s41467-020-17332-z

[12] What is Space Junk? https://kids.earth.org/space/what-is-space-junk/

[13] DLR – Institute of Technical Physics – Laser-based detection and removal of space debris 

https://www.dlr.de/tp/en/desktopdefault.aspx/tabid-10062/17177_read-41487/

[14] DLR – Institute of Technical Physics – Laser-based detection and removal of space debris 

https://www.dlr.de/tp/en/desktopdefault.aspx/tabid-10062/17177_read-41487/

[15] Scanning and observing  http://www.esa.int/Safety_Security/Space_Debris/Scanning_and_observing2

[16] Hazards of Reentering Space Debris https://www.spaceacademy.net.au/watch/debris/reentryhaz.htm

[17] Space debris as environmental threat and the requirement of Indonesia’s prevention regulation 

https://iopscience.iop.org/article/10.1088/1755-1315/456/1/012081/pdf

[18]Does the debris around Earth affect the atmosphere?  https://www.sciencefocus.com/space/does-the-debris-around-earth-affect-the-atmosphere/

[19] Does Space Junk Fall from the Sky? | NOAA National Environmental Satellite, Data, and Information Service (NESDIS)  https://www.nesdis.noaa.gov/content/does-space-junk-fall-sky

[20] Orbital-use fees could more than quadruple the value of the space industry  https://www.pnas.org/content/117/23/12756

[21] Solving the Space Junk Problem | CIRES  https://cires.colorado.edu/news/solving-space-junk-problem

[22] 7 TECHNIQUES TO REDUCE THE FUTURE DEBRIS HAZARD | Orbital Debris: A Technical Assessment 

https://www.nap.edu/read/4765/chapter/10#139

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About the author

Taewoo Kang

Taewoo is a student at the Stamford American International School in Singapore

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