Aerospace Historical Engineering Analysis: Project Thor — When the U.S. tried to turn Telephone Poles into Weapons of Mass Destruction.

Straight out of a Science Fiction Plot, Project Thor was seriously considered by the United States as an alternative to Nuclear weapons in the early 2000s. Also known as “Rods from God”, the concept involved Kinetic Bombardment of targets by dropping metal rods the size of Telephone Poles from space at initial orbital speeds of Mach 20+, resulting in an explosion on the same level of nuclear weapons, but without the fallout.

Could this project really have worked?

The answer may surprise you.

Bottom Line Up Front:

In this edition of The Engineer’s Perspective, I look at and analyze the historical Aerospace program called “Project Thor”. Also known as “Rods from God”.

“Rods from God” was a defense program studied in the early 2000s by the U.S. Department of Defense. It proposed immense, dense metal rods be released from orbit above earth at potential targets. Utilizing orbital speeds, the rod would then impact a target with the strength of a low-grade nuclear weapon.

So how true were all the claims? Could a concept like this really have been that powerful?

Being a former rocket scientist that worked in missile defense, a project like this is totally fascinating to me, so I will perform a low-level, open-source analysis to confirm if these claims were true.

We’ll look into:

1. The History of the Project.
2. Some of the open source claims of the project.
3. The Engineering Behind the Project. A technical analysis of the actual system:
4. What was the actual weight of a rod? Do the claims on the web actually match what a real tungsten rod would weigh?
5. What would the actual destructive force of the Tungsten rod be when it impacts a target? Is it actually the equivalent force of a Nuclear Weapon?
6. How much of a challenge would transporting the rods to space be? Is that even possible?
7. How long it would take for a “Rod from God” projectile to strike a target on earth with only gravity to pull it down?
8. The Conclusion and Feasibility: Going from Science Fiction to Science Fat: I look into whether or not in my opinion, something like this project would feasible and what architectures could make this system Feasible.

1. History:

“Rods From God” was originally called “Project Thor”, an Aerospace defense program that proposed creating a projectile at a fraction of the cost of an ICBM but potentially just as destructive through creative use of physics and technology.

Known Colloquially as “Rods from God”, Project Thor was a defense program initially developed in the 1950s by former Boeing Engineer turned Sci-Fi Writer Jerry Pournelle.

The New York Times quoted the history of the weapon as a creation from the mind of Jerry Pournelle, a science fiction writer who conceived it while working for Boeing in the late 1950s; he called the weapon Thor, and as he explained in an interview, “People periodically rediscover it.”

Pournelle’s idea proposed that telephone-pole-size rod bundles made of tungsten metal be released from orbit-keeping satellites towards targets at speeds around Mach 10. It was an alternative to the Nuclear Weapons Programs that characterized the age, and was noted for not having the same radiation risks (SPF 1 million anyone?).

2. The Claims:

Some of the interesting claims that have been put out regarding Project Thor include:

1. Business Insider saying that a 20 foot tungsten rod 1 food in diameter would weigh around 24,000 lbs.
2. Popular Science stating the weapon had the destructive force of a nuclear warhead
3. A YouTube video stating the destructive force of the Rods equaled 11.5 tons of TNT:

3. The Engineering:

Now, is any of what was said above true? Should we just take the internet’s word and assume everything stated is right?

I like a challenge, so I’ll do the math and find out.

Materials and Mass:

We will then verify if some of the most popular claims of Project Thor are true:

Claim 1: According to Business Insider, a [tungsten] rod of this size would weigh approximately 24,000 lbs.

Pournelle originally envisioned that these rods would be made of Tungsten Metal and be within the dimensions of 20 feet long by 1 foot in diameter.

Image of Project Thor entering the atmosphere at Hypersonic Speeds courtesy of Veritasium

Let’s estimate the mass of the rod based on Tungsten’s density, and the estimation of a cylinder’s mass:

Density of Tunsten is 19.25 g per cubic Centimeter:

Screenshot of Properties of Tungsten courtesty of periodic-table.org

The Mass of a cylinder is given by:

and obtain a total mass of ~32,657 Kg;

This is converts to approximately ~72,000 lbs:

Verdict: Very Wrong. At 72,000lbs, The Business Insider article claims VASTLY understate the true mass of a rod of this material and dimensions! A more realistic weight of a Rod of God is literally three times heavier!

The force of a Nuclear Weapon?

Claim 2 and Claim 3 make the argument that:

1. Claim 2: The weapon could carry the destructive force of a nuclear warhead
2. Claim 3: The amount of destructive force was equal to 11.5 tons of TNT.

We can actually estimate the amount of energy in Joules that a Rod from God could produce, and compare it to a nuclear weapon utilizing the Velocity and Mass portions of the Kinetic Energy equation:

Force Equation Illustrated

By increasing the velocity by a small fraction you can significantly increase the Force output, hence why faster objects hit much harder.

Think of a bullet vs. a pebble. Both can be similar in size, but one will hurt more than the other due to the speed it is traveling.

Let’s fill in the blanks and come up with the numbers:

• Mass = ~32657 Kg
• Velocity needs to be around Mach 10.
• Convert Mach 1 (741 mph at sea level) to Mach 10 → 741mph*10 = 7,410 mph
• Take the result (7,410 mph) and convert this to kilometers, (km/h),→ 7410 *1.62 = ~12,000kph
• Then convert 12,000km/h to km/s = 12,000/3600 = 3.33km/s
• Finally, convert km/s = m/s = 3330m/s
• Finally, to get the energy of an impact from the weapon, we fill in the number for Ek equation:
• 0.5*32657(3330(sq)) = 181065103650 Joules, or ~181 billion Joules
• The energy in Kilotons is a little less than half a kiloton:

• This amounts to 48 tons (American) of TNT!:

The explosion from the impact would impart 4.4 times more kinetic energy than the largest weapon in the U.S. Inventory — The GBU-43, Massive Ordinance Air Blast, or MOAB (Colloquially known as Mother Of All Bombs):

Massive Ordinance Air Blast

Specifications from the MOAB Wikipedia Page

The energy from the impact of a Rod from God would be just over twice as powerful as one of the smallest Nuclear Warheads, the Davy Crockett, with a blast yield of 20 tons of TNT:

Davy Crockett Nuclear Weapon (Courtesy of Wikipedia)

Verdicts:

1. Claim 2 is TRUE. A Project Thor projectile would actually have been more powerful than the W54 nuclear warhead.
2. Claim 3 is FALSE: The Project Thor Projectile would have been 4.4 times more powerful than the claim in the Youtube video.

Bring ’em up

According to Jerry Pournelle, Project Thor’s Concept of Operations would be to host the Rods within a satellite in orbit over earth and release the Rods from orbit to be pulled in by gravity.

From Purnelle’s time until the early 2000s when this was looked at by the U.S. force as “Hypersonic Rod Bundles”, it was not possible to bring rods of this mass into orbit:

Image of “Zeus”, a fictional version of Project Thor from the 2013 movie “G.I. Joe: Retaliation”

This being the 2020s, over 50 years after Jerry Pournelle conceived of this idea, would this task be any easier?

Just. Barely.

Previous calculations from last edition estimated a projectile to weigh 72,000 lbs, or 36 U.S. Tons. How does today’s space industry fair with carrying this cargo: SpaceX’s Starship, and NASA’s Space Launch System (SLS).

Starship:

SpaceX’s Starship’s page estimates a 100+ U.S. Tons capacity, meaning we will be limited to re-supplying Project Thor with 2 rods at around 72 U.S. tons per launch:

NASA’s SLS:

NASA’s Space Launch System is between 70–130 metric tons (77–143 U.S. tons), and creates a limit of between 2–4 rods (72–144 U.S. tons) being hoisted into orbit at a time:

72/36 = ~2 rods

144/36 = ~3.99 Rods

A heavy lift:

With SLS and SpaceX, it’s possible to bring Project Thor’s “Rods from God” into space. The caveat is the weight of the rods strains the current ability of the Space Cargo industry, capping NASA’s SLS efforts to re-supply project Thor with 2–4 rods at a time, while SpaceX’s Starship limit is 2.

Furthermore the sheer amount of Tungsten needed for this project could very well exceed what is found on planet earth. The total mass of just 4 rods that accurately fit Jerry Pournelle’s requirements for Material and Mass would exceed 288,000 lbs, straining the capabilities of the current 2020s commercial space industry.

The Challenge of Orbits:

A popular Youtube video made claims that it could take several hours for Geosynchronous (GEO) orbit to an hour and half for Low Earth Orbit (LEO):

But is this true? How long it would take for a “Rod from God” projectile to strike a target on earth with only gravity to pull it down.

I will try to find out.

The different types of orbits:

Most satellites fall into 3 major categories for orbit:

• Geosynchronous or Geostationary Orbit (GEO)
• Medium Earth Orbit (MEO)
• Low Earth Orbit (LEO)

GEO means your one satellite is always (relatively) over target, but you have to be further way from earth due to rotational speed of the planet in relation to gravitational pull. While Geosynchronous and Geostationary orbits are slightly different, I will treat them for this context as the same:

Overview and comparision of distances between LEO, MEO and GEO orbits (Courtesy of Wikipedia)

• MEO and LEO in theory keep you closer to reduce time for the Rod to hit target: But since your satellite is closer to earth, gravity has greater pull, so now your satellite has to travel faster to keep from crashing back into earth. This results in a limited strike window, and thus, you will need multiple satellites to keep Rods on target.

Image showing how objects in LEO orbit cannot stay on top of target due to speed and distance (Courtesy of NASA)

So how long then would a Rod from God actually take to strike a target on earth from each orbit?

Now Comes the Math:

Now one would initially think seems straight forward:

1. Take the distance from GEO/MEO/LEO.
2. Take the orbital speed
3. Finally, divide this Speed into the distance and you have the time it takes for the rod to get to earth.

But this is wrong.

ALL WRONG.

Assuming that the rod is released by the Satellite without any force, and Gravity takes over, We ARE NOT travelling to earth at the GEO (~7000mph), MEO (11,000mph), or LEO (15,600 mph) speeds listed here:

Orbital Speeds listed in Wikipedia

No.

The speeds listed ARE NOT satellites traveling to earth at that speed. They are traveling AROUND EARTH at that speed.

So what speed are we heading to earth at then if we are depending on the pull of Gravity to collide a Rod from God to earth?

As it turns out, it’s a speed so slow that it would take Millenia for the Rod to come back to earth, but to get a grasp on why this is, we need to get an idea of much force (In Newtons) the earth would place on a Rod from God.

To do that, we utilize Isaac Newton’s Universal Gravity Equation:

Image Courtesy of Wikipedia

We have the equation, so now let’s identify the force exerted on a Rod from God at different locations:

• On the surface of earth
• At LEO Orbit
• At GEO Orbit

Furthermore, let’s make the following assumptions before we start the calculations:

• The Satellite holding a Rod simply releases the projectile without assistance
• The only force acting on the rod is Earth’s gravitational field.
• Earth’s gravity will influence the tungsten rod orbit less than a smaller satellite’s orbit due to the rod’s larger density mass.

Now that we know what we are calculating for, and what assumptions we are making, let’s start:

1. We’ll start off by identifying the Force exerted by Gravity on a Rod that is on Earth:

Mass of Earth = 5.97 x 10^24 kg

Mass of Rod   = ~32,000 kg
R = Radius of Earth + GEO Distance:
    Radius of Earth (Re)    = 6,378.1 km
    R^2 = 0
F = ((5.97 x 10^24)*(32,000)) = 1.91*10^29
  = 6.67*10^-11 * 1.116*10^14
F = 1.27*10^19 N

The Gravity is exerting 12,700,000,000,000,000,000 Newtons of force on the rod when it is on earth’s surface. As expected, it’s a lot.

Next we calculate the force of gravity pulling a Rod to Earth from LEO and GEO orbit, and we will make the following assumptions:

1. Now let’s compare our last calculated force with the force on the rod if it is in a Low Earth orbit of 850 km:

Mass of Earth               = 5.97 x 10^24 kg

Mass of Rod                 = ~32,000 kg
R = Radius of Earth + GEO Distance:
    Radius of Earth (Re)    = 6,378.1 km
    Re Convert to Meters:   = 6,378*1000 = 6378000
    LEO Orbit distance (Ge) = ~850km
    Ge convert to Meters:   = 850*1000 = 850000
F = ((5.97 x 10^24)*(32,000))/(6378000 + 850000)sq = 3.67*10^14
  = 6.67*10^-11 * 3.67*10^15
F = 243901 N

There is 52 BILLION less Newtons of force exerted by Gravity on a Rod of God when the rod is at LEO orbit of 850km (510 miles).

To be thorough, let’s calculate how much Gravitational Force is being exterted on the Rod from Earth when the Rod is in Geosynchronous orbit of ~35,000 km:

Mass of Earth               = 5.97 x 10^24 kg

Mass of Rod                 = ~32,000 kg
R = Radius of Earth + GEO Distance:
    Radius of Earth (Re)    = 6,378.1 km
    Re Convert to Meters:   = 6,378*1000 = 6378000
    GEO Orbit distance (Ge) = ~35,000km
    Ge convert to Meters:   = 35,000*1000 = 35000000
F = ((5.97 x 10^24)*(32,000))/(6378000 + 35000000)sq = 1.116*10^14
  = 6.67*10^-11 * 1.116*10^14
F = 7442 N

The result is a force of only 7,442 Newtons exerted on the rod at GEO orbit from Earth.

The the difference in force between a rod on earth vs. space is enormous. Following First Principles, one can start to assume that with this little force being exerted on the dense Tungsten Rods at LEO and GEO orbits, it could take some long time for the Rod to fall to earth if released without any assistance other than gravity.

To make things easier, I found a rough chart to get an idea of how long it would take for an object in LEO Orbit. The LEO altitude I chose was 850km (Highlighted in Red):

A Graph giving approximates of how long an object in a altitude will stay in orbit. (Courtesy of Australian Space Academy)

The number we are looking at using is 5.5 years based on the chart. We then calculate a compensation for a much larger, more dense object like our Rod from God.

Fortunately the calculation is on this page and states:

The actual lifetime in years can be calculated from:

L = L* (m / A)

where (m/A) is the actual mass to area ratio (kg m-2) of the object in question. Thus, if m/A = 100, the scale is multiplied by 100 to give the actual lifetime in years.

To find the Mass-to-Area Ratio of our object:

Mass = ~32,000 kg (From the last editions of The Engineer’s Perspective)

Surface Area = ~12 square meters:

32,000kg/12 meters square = 2,666.7 kg/meter square

Our Mass-to-area ratio is 2,666.7 kg/square meter.

Now going back to the chart, we input 2,666.7 into the compensation equation of

L = L* ( m / A )

L = 5.5*(2666.7) = 14,668.5 Years.

Bottom Line:

Just for a LEO orbit, without any guidance system or propulsion to guide the Rod directly to its target on earth, we would expect impact in 14,669 years.

The result is difficult for me to believe myself, but this infographic from the European Space Agency helped ease my worry about the calculation:

Info-Graphic of Satellite Orbit times courtesy of European Space Agency

The deeper we look into Rods of God based on First Principles and rough calculations, I have been able to surmise that “Project Thor” would have been very difficult to pull off.

While a popular YouTube video stated that it would take between 1.5 to several hours for a rod to strike a target, I found that was very, very, very, wrong. The initial rough calculations of how long it would take a Rod from God to strike earth WITHOUT ASSISTANCE was over 14,669 years!

And that was only for Low Earth Orbit.

I had to actually find a sanity-check through an infographic from the European Space Agency.

Knowing this, how would a Rod from God have possibly been feasible as a weapon that could provide critical strike capabilities?

From Science Fiction to Science Fact:

What would it take to make “Rods from God” a reality? What would it take to create a high-level WORKING architecture that would make this system feasible?

I do my best to take what was learned in this high-level analysis about “Rod from God”, and try to make some high level architectural decisions that would make a working system. Along the way I will address some other assumptions that have been made about the project from other analyses on the web.

(*Please note everything here is high level architecture and based on open sources.)

The main implementation goals I will look at are:

1. Stationing and Loading Mechanism for Project Thor
2. Defining the Positioning, Deployment and Propulsion Mechanisms for Project Thor
3. Identifying Terminal Guidance and Maneuvering mechanisms for Project Thor

And a final conclusion about my thoughts on the system.

1. Stationing and Launch:

With the development of the International Space Station (ISS), it would not be difficult to develop a space station in LEO, MEO, and GEO orbit to house at least 6 Rods for Project Thor. Unlike Jerry Pournelle’s time when he envisioned the system in the 1950s, this is no longer the realm of science fiction:

Size comparison of an Astronaut, Space Shuttle, and various space stations. (HistoricSpacecraft.com)

The Station:

The host for the rods would be a space station that would look like a 6-sided orbiting cargo bay similar to the Space Shuttle cargo bay:

Conops:

A good example of a the concept:

Example of a Project Thor Station (Youtube)

But while, this station holds 4 rods, it is conceivable that a slightly larger one with 6 rods could be achieved.

The station would be powered similarly to the ISS, utilizing solar panels when the orbit was facing the sun to power the station, and storing any extra energy for use when the sun was unavailable.

Loading Mechanism:

• The loading mechanism to take the rods from a supply shuttle would be a crane akin to the Canadarm2 crane on the ISS:

SpaceX Dragon commercial cargo craft is grappled by Canadarm2 (Wikipedia)

• Conops:
• The Crane would take rods from a cargo vessel by clamping down to sets of handles on multiple sides of the rod and pulling the rod into the station’s cargo bay.
• The bay would utilize clamps to clasp the handles on the rod opposite of the crane to ensure the rod would stay inside the bay.

Positioning, Deployment, and Propulsion:

A set of Calibration, Deployment, Alignment, and Propulsion steps would be necessary for the rod to transition from storage to engagement, as I had previous mentioned in an earlier entry, depending on the immediate pull of gravity would not be reasonable for a time-critical system requirement.

Conops: The System would do the following:

1. Calibrate Location
2. Deploy Rod for Alignment
3. Align the Rod prior to:
4. Utilizing Thrusters and propulsion to move the rod into a decayed orbit to impact target.

1. Calibrate Location: Being placed in orbit, the system would utilize GPS coordinates just like a satellite to calibrate itself and its location prior to release of a Rod.
2. Deployment: The system would turn and angle itself while the aforementioned bay clamps would release. This would enable the rod’s momentum to push the rod out of the bay. A good example seen of this system can be seen in this Youtube video of the concept:

An example Project Thor System utilizing Momentum to facilitate the projectile’s drift out of its bay. (Youtube)

1. Alignment: Reactive Control System (RCS) Thrusters with GPS sensors attached to the rod would move it into position prior to Thruster activation:

1. Thruster Activation: The RCS systems would then send the rod into a decaying orbit at the target:

1. Thruster Detachment: The RC Systems would then detach prior to the Rod entering the atmosphere:

Terminal Guidance:

With the Rod from God entering the atmosphere at hypersonic speeds, a famous youtube video stated an assumption that a charged particle sheet will develop from shock induced thermal heating (plasma) over the surface of the Rod, preventing GPS Signals from reaching the Rod:

Screenshot of a Rod from God not receiving signals due to plasma “Blackout” (Courtesy of Youtube)

This is FALSE.

DARPA’s Falcon Hypersonic Test Vehicle, or HTV-2 demonstrated that it is possible to maintain GPS signal and two way communication with the hypersonic vehicle at hypersonic speeds up to Mach 20:

Screenshot of DARPA/NASA’s Hypersonic Technology Demonstrator page (DARPA)

INS system: An INS system similar to what is found in ICBMs would also be implemented in the rod to help provide redundancy with error mitigation:

Example ICBM INS system from the Minuteman III (TheMilitaryStandard.com)

Example ICBM INS system from the Minuteman III (TheMilitaryStandard.com)

Maneuvering Systems:

Two methods of control that have been established to be successful at hypersonic speeds include:

1. Fins:

1. Or Reaction Control Systems (RCS):

1. Utilizing fins would create an increased drag on one end of the rod, forcing the rod to point in one direction. Control surfaces such as fins are already well-proven with Space Shuttles and Missiles minimizing risk in implementation.
2. Reaction Control Systems were shown to be usable in guiding a hypersonic vehicle at speeds up to Mach 20 with the DARPA HTV-2 demonstrator shown here:

Screenshot of the DARA/NASA HTV-2 demonstrator webpage (DARPA)

Another possible workaround for maneuvering the rod could be changing center of Gravity:

But, my personal bet would be Fins or RCS Thrusters, as both have been proven. Furthermore, center of gravity mechanisms would take up space in the rod, reducing overall kinetic energy upon impact.

4. Conclusion:

In this analysis for “Project Thor” (also known as “Rods of God”), we looked into the feasibility of the project based on First Principles and basic calculations, and found that the project had many interesting and cool abilities, but at the same time, at this level of cursory analysis the project would have been very difficult to pull off.

At the same time, many assumptions that had proliferated over the internet about this project that were just wrong:

• Initial estimates of the mass of the rod of 24,000lbs per Business Insider were three times lighter than the actual mass would have been at 72,000 lbs!
• A popular Youtube Video claimed that it would take 1.5 to several hours to strike the earth if the rod was released and came down on its own, when in reality a Rod of God would take over 14,669 years to hit earth using only gravity without assistance!
• The damage inflicted by this warhead was estimated at 11.5 tons based on a youtube video, while the actual calculated estimate was closer to 48 tons, which is a little over twice as large as the Davy Crockett Nuclear Warhead

Despite all this, the question everyone has is this:

“Could Project Thor be feasible as a weapon with today’s technology?”

My answer is “Yes, but…”

Yes in that nothing that I have calculated or estimated is beyond the reach of what is possible with 2020s technology:

• The Rods could be brought into space via NASAs SLS and SpaceX ships.
• The Rods could be housed: We have created facilities large enough to store items (Think the International Space Station). A mechanical crane is attached to the station and can manipulate and carry crew capsules without any issue. It is feasible to have the crace do the same with sets of rods.
• The Rods could be stored: implementations for the ISS Crane allow it to grab a multitude of payloads. Crew Capsules can lock onto and detach from the space station. Similar mechanisms can be re-purposed for rods to be grabbed by a crane and attached to a bay within a station.
• The Rods could be deployed: Opening and releasing a payload is already possible for the ISS and Space Shuttle.
• The rods can be positioned and put into a degraded orbit to hit a target: Retro Thrusters are found on the ISS and keep the station in orbit to keep the station’s orbit from degrading. The opposite can be implemented on a rod and force its orbit to degrade precisely onto a target.
• Terminal Guidance via maneuvering fins and RCS systems are possible to attach to the rod. All the mechanisms are already found in ICBMs and hypersonic technology demonstrators from DARPA. These would only be implemented in a rod.

Now comes the “But…”: While I am not an expert in politics, a system like this would be highly visible and act as a metaphorical lightning rod from other nations, drawing protests at the highest level of government. Finally, no one would like the idea of a kinetic bombardment system capable of deploying WMD level projectiles flying over their country,

Which is why I feel that this system, to paraphrase Ian Malcolm from Jurassic Park, isn’t in the real of “If we could”, the real question is if we “Should”.

Cheers!