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Astronomical engineering: a strategy for modifying planetary orbits

How’s this for an idea for a science-fiction story?

The sun has unexpectedly started to swell into a red giant – which would engulf and destroy the Earth. So, “to save humanity, the world’s governments have banded together and constructed thousands of rocket engines across the Earth’s surface. Once installed, they propel the planet out of its solar system and onto a 2,500 year journey to resettle in Alpha Centauri.” (Grant Watson.)

The Wandering Earth (Chinese: 流浪地球) is a 2019 Chinese science fiction film directed by Frant Gwo, loosely based on the novella of the same name by author Liu Cixin. Here’s an image of one of the many “Earth Engines.”

The Wandering Earth Movie (Engine)

Our question – Could this be done in real life?

What science in the film did they get wrong?

Helium flash

Thrusting the Earth out of orbit with rockets: consider, how much reaction mass would we need to do this?

Even if you could build engines large enough, mining the Earth (as these engines do in the film) causes a problem. There would barely be any Earth left by the point you mined enough dirt to thrust the planet to Proxima Centauri, 4.2 light-years away. “It would take about 95 percent of the mass of Earth to do this,” Elliott estimates.

Stopping the rotation of the Earth?

Gravitational slingshot around Jupiter

Surviving the radiation around Jupiter

Could ‘The Wandering Earth’ Actually Happen? Here’s What a NASA Engineer Says

Wandering Earth: Rocket scientist explains how we could move our planet. ARS Technia

Other options

We could eventually move human civilization to Mars, which become habitable.


What science could actually work to change Earth’s orbit?

Astronomical engineering: a strategy for modifying planetary orbits
D. G. Korycansky, Gregory Laughlin, Fred C. Adams (7 Feb 2001)

The Sun’s gradual brightening will seriously compromise the Earth’s biosphere within ~ 1E9 years. If Earth’s orbit migrates outward, however, the biosphere could remain intact over the entire main-sequence lifetime of the Sun.

In this paper, we explore the feasibility of engineering such a migration over a long time period. The basic mechanism uses gravitational assists to (in effect) transfer orbital energy from Jupiter to the Earth, and thereby enlarges the orbital radius of Earth.

This transfer is accomplished by a suitable intermediate body, either a Kuiper Belt object or a main belt asteroid. The object first encounters Earth during an inward pass on its initial highly elliptical orbit of large (~ 300 AU) semimajor axis.

The encounter transfers energy from the object to the Earth in standard gravity-assist fashion by passing close to the leading limb of the planet. The resulting outbound trajectory of the object must cross the orbit of Jupiter; with proper timing, the outbound object encounters Jupiter and picks up the energy it lost to Earth.

With small corrections to the trajectory, or additional planetary encounters (e.g., with Saturn), the object can repeat this process over many encounters. To maintain its present flux of solar energy, the Earth must experience roughly one encounter every 6000 years (for an object mass of 1E22 g). We develop the details of this scheme and discuss its ramifications.


As for the Moon, reasoning by analogy with cases of stellar binaries and third-body encounters suggests that the Moon will tend to become unbound by encounters in which O passes inside the Moon’s orbit. (As well, there is the non-zero probability of collisions between O and the Moon, which must be avoided.) Again, detailed quantitative work needs to be done, but it seems that the Moon will be lost from Earth orbit during this process. On the other hand, a subset of encounters could be targeted to “herd” the Moon along with the Earth should that prove necessary.

It has been suggested (cf. Ward and Brownlee, 2000) that the presence of the Moon maintains the Earth’s obliquity in a relatively narrow band about its present value and is thus necessary to preserve the Earth’s habitability. Given that the Moon’s mass is 1/81 that of the Earth, a similarly small increment of the number of encounters should be sufficient to keep it in the Earth’s environment.

The fate of Mars in this scenario remains unresolved. By the time this migration question becomes urgent, Mars (and perhaps other bodies in the solar system) may have been altered for habitability, or at least become valuable as natural resources. Certainly, the dynamical consequences of significantly re-arranging the Solar System must be evaluated. For example, recent work by Innanen et al. (1998) has shown that if the Earth were removed from the Solar System, then Venus and Mercury would be destabilized within a relatively short time. In addition, the Earth will traverse various secular and mean-motion resonances with the other planets as it moves gradually outward. A larger flux of encounters might be needed to escort the Earth rapidly

Journal reference: Astrophys.Space Sci.275:349-366, 2001. Astronomical Engineering: A Strategy For Modifying Planetary Orbits, Springer Link
Cite as: arXiv:astro-ph/0102126 (or arXiv:astro-ph/0102126v1 for this version)


Moving our sun and entire solar system

Caplan thruster

from Scientist figures out how to move our sun to avoid space collisions, BigThink

Stellar engines: Design considerations for maximizing acceleration, Acta Astronautica, 12/2019

Caplan envisions two stellar engine designs, with one of them based on the idea of encapsulating the sun in a megastructure that would take advantage of its energy. Another engine would make use of a giant sail to move the solar system by about 50 light years during the course of a million years….

One big reason would be to move the solar system if we’re anticipating running into a mega-explosion from a supernova or some such cataclysmic scenario. Of course, we’d need to be way more ahead technologically for any such endeavor.

If you were to be moving the solar system, the convenient thing is that theoretically everything inside it would move along at the same time. Being pulled by the sun’s gravity would keep the contents of the system in consistent orbit.

One of the stellar engine designs involves a thin mirror-like solar sail, like the “Shkladov thruster”. The reflective material would be thinner than a red blood cell. The sail would be positioned over the poles of the sun and would not be orbiting. It would be important to install it in such a way that it won’t interfere with the Earth’s temperature. This would also affect the direction in which we’d be steering the solar system.

Thrust for the sail design would be created by solar radiation reflecting onto the mega-mirror. This is definitely not the fastest way to travel, with the sun being pushed along at the rate of 100 light-year in 230 million years. That’s actually not fast enough to get out of the way of a supernova explosion, admits Caplan.

What would work better is a speedier “active” thruster, called the “Caplan thruster” by Kurzgesagt, which initially approached Caplan to design such engines. It would be propelled by thermonuclear blasts of photon particles. This thruster is a modified version of the “Bussard ramjet,” conceptualized in the 1960s, which works on fusion energy. The engine would need millions of tons of fuel per second to function, creating fusion from matter it collects in the solar wind by utilizing a giant electromagnetic field. More energy would also be gathered by a Dyson sphere megastructure, built around the sun.

Caplan imagines the engine having two jets, with one using hydrogen pointed at the sun, to prevent colliding with it, and another, employing helium, directed away from the star. This would cause net momentum, like from a tug boat, and move the thruster forward.

The astrophysicist calculates this type of thruster would be fast enough to escape a supernova. It could also redirect the galactic orbit of our solar system in as little as 10 million years.

Related articles

Gregory Benford and Larry Niven solved the problems with Shkavdov thrusters for a propulsion system for moving stars

On the Possibility of Detecting Class A Stellar Engines Using Exoplanet Transit Curves,”  Journal of the British Interplanetary Society

See this video

Learning Standards

2016 Massachusetts Science and Technology/Engineering Curriculum Framework

8.MS-ESS1-2. Explain the role of gravity in ocean tides, the orbital motions of planets, their moons, and asteroids in the solar system.

HS-PS2-4. Use mathematical representations of Newton’s law of gravitation and Coulomb’s law to both qualitatively and quantitatively describe and predict the effects of gravitational and electrostatic forces between objects.

Next Generation Science Standards

HS-PS2.B.1 ( High School Physical Sciences ): Newton’s law of universal gravitation and Coulomb’s law provide the mathematical models to describe and predict the effects of gravitational and electrostatic forces between distant objects.

Next Generation Science Standards Appendix F: Science and Engineering Practices

Ask questions that arise from careful observation of phenomena, or unexpected results, to clarify and/or seek additional information.
Ask questions that arise from examining models or a theory, to clarify and/or seek additional information and relationships.
Ask and/or evaluate questions that challenge the premise(s) of an argument, the interpretation of a data set, or the suitability of a design.

A Framework for K-12 Science Education: Practices, Crosscutting Concepts, and Core Ideas (2012)

PS2.B: TYPES OF INTERACTIONS: Gravitational, electric, and magnetic forces between a pair of objects do not require that they be in contact. These forces are explained by force fields that contain energy and can transfer energy through space. These fields can be mapped by their effect on a test object (mass, charge, or magnet, respectively). Objects with mass are sources of gravitational fields and are affected by the gravitational fields of all other objects with mass. Gravitational forces are always attractive. For two human-scale objects, these forces are too small to observe without sensitive instrumentation. Gravitational interactions are non-negligible, however, when very massive objects are involved. Thus the gravitational force due to Earth, acting on an object near Earth’s surface, pulls that object toward the planet’s center. Newton’s law of universal gravitation provides the mathematical model to describe and predict the effects of gravitational forces between distant objects.


In this lesson students view scenes from the Tremors series of movies. Students take notes on the animal’s biology: external anatomy, internal anatomy, lifecycle and behavior. We use our notes to speculate on the evolution and anatomy of these creatures, called Graboids.


Based on the scenes, have the students explain the graboid lifecycle.

Graboid lifecycle

Graboids and sounds

How do graboids navigate underground and detect food sources?

Sonar is the use of sound to navigate, communicate with, or detect objects – on or under the surface of the water – such as another vessel.

Active sonar uses a sound transmitter and a receiver. Active sonar creates a pulse of sound, often called a “ping”, and then listens for reflections (echo) of the pulse. Here we see an animation from the US Navy made in the 1940’s, showing how sonar works.

Old Navy Sub sonar GIF

Some animals have natural sonar, such as bats and whales.

The Tremors movies imply that graboids have a similar way of detecting prey.

Graboid sonar

Internal anatomy

As this is a science fiction movie these creatures aren’t real. But the film makers made it clear that these animals would have realistic internal as well as external anatomy.  In this section we ask students to speculate what kind of organs a creature like this would or wouldn’t have, based on the available information.

Students work in groups to come up with answers – and they have to justify their conclusions. For instance, they might claim that the animal has no skeleton: If so, explain why they conclude this. Or they might claim it does have a skeleton: if so, explain why they conclude this.

graboid anatomy Christopher Stoll dbaubpv

from deviantart.com/christopher-stoll


Evolution of graboids

Based on the observed characteristics, what animals are graboids most closely related to?

What animals in the past might they have evolved from?

Could students make a speculative family tree/cladogram, showing the possible evolution of graboids?

clades & phylogenies

clades rotate = equivalent phylogenies

Gradualism vs. Punctuated Equilibrium

Introductory material

This packet is given to students at the beginning of the class. TBA


Teacher reference material


You may choose to make some of this material available to students during or after viewing the scenes. However, withhold the majority of this material until after the students finish the section in which they speculate and justify their conclusions.


1.0 Introduction

2.0 External Anatomy
2.1 – Graboids
2.2 – Shriekers
2.3 – AssBlasters

3.0 Internal Anatomy

4.0 Ecology

5.0 Evolutionary Overview
5.1 – Evolutionary History
5.2 – Issues of Reproduction
5.3 – Development of Shrieker Legs
5.4 – AssBlasters’ Reproductive Role
5.5 – AssBlaster Biochemistry

6.0 Hypothetical Taxonomy

7.0 Historical and Mythological References

8.0 Threat Assessment

Monster Guide




External anatomy


Internal anatomy




Evolutionary history


The following is from www.scifi.com/tremors/monsters/analysis/06_taxonomy.html

Graboid SyFy

The proper taxonomical classification of Graboids, Shriekers and AssBlasters was a curious challenge because the Graboid species does not clearly belong to any previously known Family grouping. To complete its zoological nomenclature, we were forced to look much deeper into the evolutionary tree than we had expected.

Graboids have been described by some witnesses as being “reptilian,” but this is probably no more accurate than describing the AssBlaster as a bird because it flies or the Shrieker as a frog because it undergoes a metamorphosis. The Graboid does not appear to possess any of the features of true reptiles, though the Shrieker and AssBlaster, curiously, each possess some, such as clawed toes. However, they share just as many similarities with birds and mammals, so a reptilian classification was not indicated.

In fact, Graboids, Shriekers and AssBlasters do not appear to belong to any existing class of vertebrates. They clearly are not fish, and it takes only a slightly more professional observer to see that they they are also neither amphibians nor reptiles, neither birds nor mammals.

It is doubtful that they are even vertebrates, although they do seem to possess endoskeletonlike structures. Vertebrates, it should be stressed, derive from a family of creatures called notochords, which gave rise to fish. Also descended from notochords are amphibians, reptiles, birds and mammals. All these different forms share a heritage of organs and anatomy, ranging from bilateral symmetry to a similarity of organ/tissue types and functions.

The three known forms of genus Caederus lack many of the features inherent to members of the vertebrate line. Most obviously, they lack eyes. Their multistage life cycle is similarly dissociated from known vertebrate reproductive models. In fact, research has not yet yielded any proof that the Graboid species is connected to the vertebrate line.

Regardless, the Graboid, the Shrieker and the AssBlaster are all highly sophisticated lifeforms, which implies that they represent the culmination of a long evolutionary history. Only three other non-vertebrate lines of animal life on Earth have reached a similar level of sophistication: arthropods, annelids and mollusks.

Arthropods (including insects, arachnids, crustaceans and other forms) typically have hard, segmented or jointed exoskeletons, and generally remain small in size when compared with vertebrates. Most arthropods evolved with multiple external limbs and some form of eyes. All these traits are inconsistent with the speculated evolution of C. americana.

Available evidence suggests the Graboid also is not a member of the subphylum Annelida. Annelids — earthworms — share some traits with the Graboid, such as an underground habitat, stiff hairs in the skin to assist in locomotion and an ability to extract nutrients directly from the soil. No annelid, however, has ever possessed anything resembling an endoskeleton or semirigid support system, which C. americana is believed to possess. In addition, C. americana and C. mexicana possess other features not found in annelids: segmented jaws; prehensile mouth tentacles; a multiphase life cycle; and thermal sensors. The Graboid is also larger and more sophisticated than any known annelid, making it highly unlikely that genus Caederus belongs in this subphylum.

Genus Caederus might be unique, in a class of its own. It might even be extraterrestrial. More likely, though, it is a form of mollusk.

The subphylum Mollusca is one of the oldest, most diversified and successful on Earth. It includes clams, mussels, snails, slugs, cuttlefish, nautili, squids and octopi. The most advanced form of mollusks are the cephalopods (octopi and squids), which share many important features with the Graboid.

Cephalopods have multiple tentacles, ranging from eight to dozens, all surrounding a mouth or gullet — an arrangement that resembles the Graboid’s tentacled mouth structure. Furthermore, some cephalopods (such as the prehistoric ammonites or the modern nautilus) have external shells or carapaces, as does the Graboid.

At least one cephalopod, the cuttlefish, has a Graboid-like external carapace, or bony structure. In addition, octopi have enough control over the muscles of their skin to change their texture from craggy to smooth, suggesting a skin musculature similar to that of the Graboid, although of different degree.

The “wing structure” of the AssBlaster bears at least a passing resemblance to the rippling “fins” of the cuttlefish. Although no known aquatic cephalopod ejects combustible compounds, it is a compelling similarity that several eject prodigious clouds of ink as a defensive mechanism, and some have a hydrojet-like propulsive organ that resembles the AssBlaster’s dramatically fiery self-launching ability.

Cephalopods are water-breathers, but other mollusks, including snails and slugs, exist on dry land. Many cephalopods, as well as certain bivalve mollusks, are able to survive for short durations out of the water.

Cephalopods are the most intelligent non-vertebrate animals known to exist. Studies have indicated that they might possess a capacity for memory, learning and problem-solving, and witnesses have reported signs of social behavior among groups of squid and octopi. Cephalopods might well be as intelligent as some species of birds or mammals; certainly, they seem to show a level of “smart” behavior similar to that of genus Caederus.

Finally, cephalopods have managed to achieve significant size and mass in aquatic habitats. The giant squid, for instance, is a deep-ocean-dweller that might rival the Graboid in size. The largest known giant squid have weighed several tons and stretched up to 55 feet from their flukes to the extremity of their longest tentacle.

Although the Graboid and its related forms possess features previously undocumented among cephalopods (such as jointed limbs, endoskeletons and a multiphase life cycle), these differences do not disqualify their categorization as mollusks. For example, bivalve mollusks (clams and mussels) possess hinged shells; it is not unreasonable to assume that the Graboid family of mollusks may have developed hinged internal shells and eventually evolved more complex internal skeletons.

However, no mollusk has evolved anything resembling the thermal sensors of the Shrieker and AssBlaster; likewise, the incendiary metabolism of the AssBlaster is unique to the Graboid species. Furthermore, no cephalopod or other mollusk possesses a life cycle nearly as complex as that of genus Caederus.

Still, the shared traits documented above and elsewhere in this document are significant enough to justify a tentative classification of the Graboid, the Shrieker and the AssBlaster as distant, terrestrial relatives of class Cephalopoda.

Next piece to add






Learning Standards

This unit addresses critical thinking skills in the Next Generation Science Standards, which are based on “A Framework for K-12 Science Education: Practices, Crosscutting Concepts, and Core Ideas”, by the National Research Council of the National Academies. In this document we read

“Through discussion and reflection, students can come to realize that scientific inquiry embodies a set of values. These values include respect for the importance of logical thinking, precision, open-mindedness, objectivity, skepticism, and a requirement for transparent research procedures and honest reporting of findings.”

Next Generation Science Standards: Science & Engineering Practices
● Ask questions that arise from careful observation of phenomena, or unexpected results, to clarify and/or seek additional information.
● Ask questions that arise from examining models or a theory, to clarify and/or seek additional information and relationships.
● Ask questions to determine relationships, including quantitative relationships, between independent and dependent variables.
● Ask questions to clarify and refine a model, an explanation, or an engineering problem.
● Evaluate a question to determine if it is testable and relevant.
● Ask questions that can be investigated within the scope of the school laboratory, research facilities, or field (e.g., outdoor environment) with available resources and, when appropriate, frame a hypothesis based on a model or theory.
● Ask and/or evaluate questions that challenge the premise(s) of an argument, the interpretation of a data set, or the suitability of the design

Science and engineering practices: NSTA National Science Teacher Association

Next Gen Science Standards Appendix F: Science and engineering practices


The Expanse is a series of science fiction novels, novellas and stories by James S. A. Corey – the pen name of authors Daniel Abraham and Ty Franck. The first novel, Leviathan Wakes, was nominated for the Hugo Award for Best Novel in 2012. In 2017 the series as a whole was nominated for the ‘Best Series’ Hugo Award.

These novels are the basis of an American science fiction television series developed by Mark Fergus and Hawk Ostby. The series received positive reviews from critics, who highlighted its visuals, character development, and political narrative. It received a Hugo Award for Best Dramatic Presentation as well as a Saturn Award nomination.

  • Wikipedia

James A Corey The Expanse Leviathan Wakes Caliban's War







Related works

  • “The Butcher of Anderson Station” (The Expanse short story) (2011)
  • Gods of Risk (The Expanse novella) (2012)
  • “Drive” (The Expanse short story) (2012)
  • The Churn (The Expanse novella) (2014)
  • The Vital Abyss (The Expanse novella) (2015)
  • Strange Dogs (The Expanse novella) (2017)

Television series


Possible rocket engines

from ATOMIC ROCKETSHIPS OF THE SPACE PATROL or “So You Wanna Build A Rocket?” by Winchell D. Chung Jr..

Here is your handy-dandy cheat-sheet of rocket engines. Use this as a jumping-off point, there is no way I can keep this up-to-date. Google is your friend!

I’ll point out a few of the more useful items on the sheet:

  • Aluminum-Oxygen is feeble, but is great for a lunar base (the raw materials are in the dirt).

  • VASIMR is the current favorite among ion-drive fans. Use this with orbit-to-orbit ships that never land on a planet. It can “shift gears” like an automobile.

  • Solar Moth might be a good emergency back-up engine.

  • Nuclear Thermal Solid Core is better than feeble chemical rockets, but not as much as you’d expect.

  • Nuclear Thermal Vapor Core is what you design along the way while learning how to make a gas core atomic rocket.

  • Nuclear Thermal Gas Core Open-Cycle is a full-blown honest-to-Heinlein atomic rocket, spraying glowing radioactive death in its exhaust.

  • Nuclear Thermal Gas Core Closed-Cycle is an attempt to have the advantages of both nuclear solid core and gas core, but often has the disadvantages of both. It has about half the exhaust velocity of an open-cycle atomic rocket.

  • Orion Nuclear Pulse is a rocket driven by detonating hundreds of nuclear bombs. If you can get past freaking out about the “bomb” part, it actually has many advantages. Don’t miss the Medusa variant.

  • Magneto Inertial Fusion This is the best fusion-power rocket design to date.

  • Zubrin’s Nuclear Salt Water This is the most over-the-top rocket. Imagine a continuously detonating Orion drive. There are many scientist who question how the rocket can possibly survive turning the drive on.