15 Days to Mars - Any Propulsion Method

tahanson43206 · 2025-02-21 21:02:10

In another topic in this category, PhotonBytes introduced a topic with the intriguing goal of showing that it might be possible to move a payload between Earth and Mars in 15 days, using chemical fuel. That proposition is certainly interesting and I am hoping that our members will study the idea to see if it is permitted by the Real Universe.

However, the basic idea, of a 15 day transit from Earth to Mars in 15 days would appear to be permitted in the Real Universe.

This topic is offered for NewMars members who would like to show us how it might be done.

The conditions to be met, for a demonstration of feasibility, are going to be reasonable.

We will start from LEO, and consider the flight a success when the vessel is safely in LMO.

To make the exercise realistic, I will specify that the payload to be delivered to LMO is 100 metric tons.

The mass of the vessel when it arrives at LMO is up to the contributor, but it needs to be reasonable/plausible.

The time frame for this flight is 15 days, from LEO to LMO.

Because Mars and Earth are varying distances apart, I'll provide a specific distance to be covered as 120,000,000 km.

Mars is 121,047,586 km away from Earth at 3:23:02 UTC on 2025/02/22. The two planets approached each other as close as they will get a week or two ago, in this cycle.

My guess is that there exists no technology able to perform this feat at present.

However, it should be possible for someone to work out the energies required, and to speculate on how a future technology might work.

It would be helpful if contributions were shown to adhere to the physics we can all agree upon.

This could be a very interesting topic for future readers, if our members have the time and energy to invest.

An optional detail that would be welcome is the G force to be experienced by the vessel during the flight.

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tahanson43206 · 2025-02-21 21:07:03

This post is reserved for an index to posts that may be contributed by NewMars members over time.

It would help me greatly to update the index, if our contributors were to include a one line summary of the post. This is the first time I have asked for help with the index idea, but I am finding it difficult to keep up with our members as they add new content to the topics where index posts are present.

After you have submitted your post, please look it over and decide what it was about. You can edit that summary at the bottom of the post, and I will do my best to try to copy it to the index within a day.

Index:
Post #3: https://newmars.com/forums/viewtopic.ph … 22#p229922
GW Johnson - preliminary sketches and text for 15 day flight Earth-Mars

Post #12: http://newmars.com/forums/viewtopic.php … 52#p230052
kbdt12 - Antimatter hybrid fusion using positrons

Post 14: Calliban: http://newmars.com/forums/viewtopic.php … 85#p230085
Link to paper on experimental campaign to collect data on muons created by 43.7GeV positrons

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tahanson43206 · 2025-02-21 21:49:52

This post contains content delivered by email.

GW Johnson took an interest in the problem posed by PhotonBytes, and has agreed to participate in the new "Any Method" topic.

There are two images that go with the text below, which I will add as soon as possible (which might be Saturday)

Well, I simply used the data worksheet in the orbits+ course orbits spreadsheet to look up the average distances and speeds of Earth and Mars. To fly a short trip, the limit is straight radial. So I used a straight radial shot at constant speed, lasting 15 days per PhotonBytes, to find the necessary departure and arrival speeds.
To go straight radial, you have to kill Earth's orbital speed while you accelerate to your necessary radial speed. To arrive, you have to kill all that radial speed, but you must also acquire the orbital speed of Mars. The necessary vector speed changes are easy to figure, since these are right triangles. It's Pythagorean Theorem stuff.
Summing the departure and arrival, you are looking at something on the order of 133-134 km/s dV out of your vehicle, for the one-way trip. And that ignores going into orbit or landing. Those would be small additions. to the dV, in comparison. Further, these are impulsive velocity changes, requiring rather significant thrust/Earth-weight ratios out of your propulsion and vehicle designs. See the first png sketch "short trips to Mars.png".
<snip unrelated commentary>

Propulsion for Fast Trip
Image 1 goes here:
15 Day Flight Plan to Mars
Image 2 goes here;

I am hoping other NewMars members will feel empowered to participate. What I'm looking for are guesses about the technology that would make such a flight as this not only possible, but practical and economically justifiable. I expect that in 100 years, if the human race manages to survive that long, power in the required range will be available to the average person, just as a team of 100 to 400 horses is available to the average person in the United States right now.

As PhotonBytes has shown, it is possible to enlist the aid of computer aided software, but each participant is responsible for the accuracy of the results posted.

Update: The email snippet below is intended to help explain abbreviations used in the images above.

I think Wp is Weight of Propellant true
I think Wpay is Weight of Payload true
Winert would be Weight of Inert mass true
Wign would be Weight at ignition true
Vex might be Vexhaust true (bear mind this is an effective velocity, not the expanded value)

The email below is to confirm that a flight to Mars in 15 days is already possible using known technology:

If we presume 2 gees is acceptable for a short interval, then that is 19.613 m/s2. To reach 69 km/s = 69,000 m/s, V= at soles as t = V/a, for t = 3518 sec = 0.977 hours. Spending an hour at modest elevated gee at each end of the journey would be quite acceptable. If your ship is big enough to carry the required number of devices, an old Project Orion pulse propulsion design could do this. Depending on the size, Isp for those was somewhere in the 5000 s to 20,000 s Isp range better the bigger the ship. It was hard to hold the pusher plate and shock absorbers-averaged gees to the 2 to 4 gee range, especially in smaller sizes. That design and performance estimate was based on 1955-level fission technology, as modified for the shaped charge effect instead of omni-directional blast (the key technology to make this propulsion efficient). It should be possible to decrease the size and mass of the charges for the same few-kiloton yield today.
It is probably not possible, even today, to get yields that low with thermonuclear fusion devices. But you could likely propel a type M metallic asteroid with much larger (100-ish kiloton) small fusion devices, which are even more efficient for the mass of the charges. Those M-type asteroids would be solid enough to push, but they are quite rare. Hollowing the thing out would be difficult, but worth it. Those things are thought to be solid lumps of iron-nickel alloy, not unlike what's in Earth's core.
I see a lot less than 100 years to get propulsion that highly capable, if we go the pulse propulsion route! It could be done in a decade or two! We already know it will work. The critical experiments had been done by 1959, including accidentally discovering the survivability of the pusher plate from the surface nuclear tests in Nevada at Frenchman's Flat.
The main issues relate not to radiation, but to EMP, something not anticipated in 1955, when they intended to surface-launch these things using fractional-kiloton devices down in the atmosphere (a technology not yet available in 1955). The intense reality of those EMP effects was not known until the 1962 "Starfish Prime" nuclear test of a few megatons about 200 miles straight above Johnston Island in the Pacific. It caused a partial crash of the electrical grid and phones in Hawaii some 900 miles away (the explosion was line-of-sight visible in the sky from there). You probably will never want to use one of those things as close to Earth as GEO. The intensity decay would be inverse square, as with any omnidirectional and incoherent light source.
GW

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tahanson43206 · 2025-02-22 08:38:24

As a follow up to Post #3...

The upcoming Google Meeting will likely include review of work by GW Johnson, exploring the interesting idea of PhotonBytes to consider a flight to Mars that would take 15 days. While the technology needed does not exist today, in 100 years it should be available.

At the time the Wright Brothers achieved human powered flight, the fastest travel opportunity on Earth was provided by the steam locomotive.

The Wright Brothers routinely used steam locomotive powered trains to travel between Ohio and North Carolina.

In 1903, per Google, the fastest train on Earth was a German Electric train that ran 130 mph (210 km/h).

In 2003, humans had traveled to the Moon and returned with a velocity of 39,897 km/h (Apollo 10 per Google).

Per calculator, the ratio between 39897 and 210 is 189.9857.

Rounding to 190, the corresponding ratio for velocity in 2103 would be: 7,580,430 km/h, or: 2105.675 km/s

The velocity estimated for the 15 day flight to Mars (as computed by GW Johnson) is 60 km/s.

It appears that if the trend is correct, humans will have the ability to travel at 60 km/s well before 2103.

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tahanson43206 · 2025-02-22 10:36:12

I asked ChatGPT4o to double check my calculations for a flight across the Solar system at 2000 km/s. It came up with a figure larger than my estimate, which is fine with me. I doubt anyone will be making that trip any time soon, but it does give a sense of the size of the Solar System.

Solar System Crossing Time Calculation
Given:
Diameter of the Solar System: 30 trillion km (30 × 10^12 km)
Speed: 2000 km/s
Step 1: Calculate Time in Seconds
Time (s) = Distance / Speed
= (30 × 10^12 km) / (2000 km/s)
= 1.5 × 10^10 seconds
Step 2: Convert Seconds to Years
Seconds per year ≈ 3.16 × 10^7 s/year
Time (years) = (1.5 × 10^10 s) / (3.16 × 10^7 s/year)
≈ 475 years
Conclusion:
At a speed of 2000 km/s, it would take roughly 475 years to cross the solar system. This result is very close to your original estimate of 452 years.

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tahanson43206 · 2025-02-22 19:23:25

The image below is from GW Johnson's collection.

There is text that goes with the image that I will attempt to add later.

A consideration that might be of interest to some NewMars readers is that (apparently) there is a relationship for vessels of this type that encourages size. A 20,000 ton vessel can experience a modest 2 G acceleration with a high ISP, while a 5000 ton vessel would experience a much lower ISP and 4 G acceleration.

I've asked for clarification of these relationships because I don't find them at all intuitive.

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tahanson43206 · 2025-02-22 19:41:18

I asked ChatGPT4o to attempt to explain the relationship between mass of an Orion powered space vessel and the efficiency of the propulsion.

In response, ChatGPT4o pointed out that the efficiency of the pusher plate system improves when it is exercised with fewer, larger pulses.

Orion Project Evaluation: Key Factors Influencing ISP in Nuclear Pulse Propulsion
1. Impulse Coupling Efficiency
Each nuclear pulse must transfer its energy to the pusher plate efficiently. In a larger vessel, the same pulse results in lower acceleration (fewer G’s), allowing the shockwave to interact with the pusher plate under less severe conditions. This more controlled interaction increases the fraction of the energy that is converted into momentum, effectively boosting the specific impulse (ISP).
2. Scaling of Pulse Yield with Vehicle Mass
The design of the pulse system—its yield, timing, and frequency—is optimized based on the vessel’s mass. A heavier vessel (e.g., 20,000 tons) can tolerate higher-yield pulses without excessive acceleration, enabling operation near the optimum energy utilization point for momentum transfer. Conversely, a lighter vessel (e.g., 5,000 tons) must use lower-yield pulses or increase pulse frequency to keep acceleration within acceptable limits, which can lower the effective ISP.
3. Pusher Plate Dynamics and Material Constraints
The pusher plate is the critical interface between the nuclear pulses and the spacecraft. In a heavy vessel, the lower acceleration reduces mechanical stress on the pusher plate, allowing it to function more efficiently over many cycles. A lighter vessel, experiencing higher G-forces, can subject the pusher plate to greater stress and potential degradation, which in turn diminishes the momentum transfer efficiency and lowers the effective ISP.
4. Pulse Frequency and Thermal/Structural Considerations
Higher acceleration in lighter vessels necessitates a higher pulse repetition rate to achieve the desired thrust. This increased frequency compounds thermal and structural stresses, further reducing efficiency. A heavier vessel benefits from a lower pulse rate, which minimizes these adverse effects and contributes to a higher effective ISP.
Summary
While a larger mass naturally results in lower acceleration for a given impulse, it also allows for more efficient energy coupling and momentum transfer. The interplay between impulse coupling efficiency, optimized pulse yield, pusher plate dynamics, and pulse frequency management is what leads to a higher effective ISP in heavier vessels, even though the fundamental physics might suggest a simple trade-off with acceleration.

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tahanson43206 · 2025-02-22 21:27:07

As a follow up to #7, I asked Google to refresh my memory of the meaning of ISP... specific impulse...

Including results for define isp in rocket
Search only for define isp in rocketry
Specific impulse (usually abbreviated Isp) is a measure of how efficiently a reaction mass engine, such as a rocket using propellant or a jet engine using fuel, generates thrust. In general, this is a ratio of the impulse, i.e. change in momentum, per mass of propellant. This is equivalent to "thrust per massflow".
Specific impulse - Wikipedia
en.wikipedia.org › wiki › Specific_impulse
About Featured Snippets

I am still having difficulty understanding why a heavier space craft (apparently) does better with Orion pulses than a lighter one, but at least I'm getting a glimmer of an idea.

Change of momentum per mass of propellant... Apparently a big heavy pusher plate does better (makes better use of energy) with a larger impulse, than is true for a smaller pusher plate with a smaller impulse.

The idea that I ** think ** Calliban described would not use a pusher plate at all, but instead would harness impulse with magnetic fields.

At least that is something to pursue.

Related questions... how "efficient" are these pusher plate designs? Ie, for the energy released, how much is translated into movement of the vessel?

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tahanson43206 · 2025-02-23 07:25:15

As a follow up to #7:

Conversation with Gemini
Hi Gemini! Thank you for assistance with previous requests. There is renewed interest in the 1950's idea of using pulses of nuclear energy to propel a space craft. We have previously discussed all the risks so please do not waste any of your valuable thinking time on risks. What I'm hoping you might be able to find today is any record of drawings of movement of matter as an explosion occurs and the moving matter encounters a pusher plate. There may not be any such records, but please take a look.
It's true that the concept of nuclear pulse propulsion, particularly through Project Orion, generated significant interest and research in the 1950s and early 1960s. Finding precise, detailed drawings of the exact movement of matter during the explosion and impact with the pusher plate can be challenging, but here's a breakdown of what I found:
Project Orion:
This was the primary effort exploring nuclear pulse propulsion. It involved detailed theoretical work and some experimental testing.
The core concept involved detonating small nuclear explosives behind a spacecraft, with the resulting blast impacting a large "pusher plate" to provide thrust.
Much of the work involved calculations of blast wave dynamics, shock absorption, and material response.
While detailed engineering drawings existed, much of the very fine detail of the plasma interactions with the pusher plate would have been very difficult to record with the technology available at the time.
Key Considerations:
The physics involved is extremely complex, dealing with high-energy plasmas and shock waves.
Simulating and accurately depicting these phenomena would have been a significant challenge, even with modern computing.
Much of the detailed work would have been theoretical, involving complex mathematical models.
Where Information Exists:
Reports and publications from Project Orion contain valuable information on the principles of nuclear pulse propulsion.
These sources often include diagrams and illustrations of the spacecraft design and the general concept of the propulsion system.
Information regarding the project can be found in NASA technical reports and historical archives.
It is important to understand that the precise minute by minute movement of the plasma, and the interaction with the pusher plate, would have been, and still is, a very complex set of fluid dynamic calculations.
In summary, while detailed visualizations of the exact matter movement might be limited, the underlying principles and design concepts are well-documented in Project Orion materials.
Thank you for this valuable insight! Do you have access to the address of either online or physical repositories where these materials may be held? Were any books or articles published at the time?
It's great you're looking into the historical records of Project Orion! Here's a breakdown of where you can find relevant materials:
Key Repositories and Resources:
NASA Technical Reports Server (NTRS):
This is a crucial resource. NTRS holds a vast collection of NASA technical documents, including reports related to Project Orion. You can search for specific keywords like "Project Orion" or "nuclear pulse propulsion."
Keep in mind that some older documents might have been digitized, while others might exist only in physical form.
National Archives and Records Administration (NARA):
NARA stores U.S. government records, including those from the Department of Defense and NASA. You can find historical documents related to Project Orion there.
Internet Archive:
This online library contains digitized books, documents, and other materials. A notable resource is the book "Project Orion: The True Story of the Atomic Spaceship" by George Dyson. This book provides a comprehensive history of the project and references many original documents.
University Libraries:
Universities that were involved in the project, such as those in California, might have archives containing relevant materials.
General Atomics:
General Atomics was a primary contractor for Project Orion. Their archives could potentially hold valuable information.
Published Books and Articles:
"Project Orion: The True Story of the Atomic Spaceship" by George Dyson:
This book is an excellent resource for a detailed historical overview of the project. It includes references to original documents and interviews with project participants.
Scientific Journals and Publications:
During the project's active period, some articles were published in scientific journals. However, due to the project's sensitive nature, some information might have been classified.
Government Publications:
Reports from organizations like DARPA and the U.S. Air Force would have contained project-related information.
Tips for Searching:
Use specific keywords when searching online databases.
Be prepared to search through large collections of documents.
Consider contacting archivists at the repositories listed above for assistance.
I hope this information is helpful in your research!
More on Locating NASA Reports - Technical Reports - LibGuides at University of Texas at Austin
Source icon
guides.lib.utexas.edu
NASA Materials - Space Resources - Library Guides at Colorado School of Mines
Source icon
libguides.mines.edu
National Archives and Records Administration (NARA) | USAGov
Source icon
www.usa.gov
Are copies of books available from Internet Archive legal to use? - Library FAQs
Source icon
claremont.libanswers.com
Project Orion: The True Story of the Atomic Spaceship: George Dyson - Amazon.com
Source icon
www.amazon.com
Thank you for the list of possible resources! I am surprised to be able to report that the book "Project Orion: 1957-1965" is still available from Amazon. Interestingly, the date on the Amazon listing is February 9, 2025, suggesting that the offer may have been renewed recently. The price is a very modest $20. I'll order a copy immediately. Thank you!
It's excellent that you've found "Project Orion: The True Story of the Atomic Spaceship" available. That book is indeed a very valuable resource on the subject. Here are a few points to reinforce what makes that book so important:
Authoritative Source:
George Dyson's work is highly regarded. He conducted extensive research, including interviews with many of the scientists and engineers involved in Project Orion. This gives the book a unique and insightful perspective.
Historical Context:
The book provides a rich historical context for the project, placing it within the broader context of the Cold War and the early space race.
Technical Details:
While written for a general audience, the book also delves into the technical aspects of Project Orion, giving readers a good understanding of the challenges and possibilities of nuclear pulse propulsion.
It is great that you are going to purchase the book. Having access to good resources is key to understanding the history of such interesting projects.
Please note that this version of the book has a new title! The new title is: Project Orion: 1957-1965. Since the listing date is February 9, 2025, I am guessing this may be a revised edition. This is indeed a new edition! Here is a copy of the last two paragraphs in the listing on Amazon. Please update your records! Begin Quotation: “Interest in the project is still alive as memories of it are fading,” Freeman Dyson writes in the foreword to this new edition. “I am still frequently asked whether I believe it has a future. I am asked whether I share a hope that some new version of Orion might take us to the stars. I am asked whether our dreams of fifty years ago are dead. The answer to all three questions is no.”
“Why revisit this path not taken into space?” asks George Dyson in a new afterword. “The Cold Warriors who brought us Project Orion are here to remind us that the powers of nuclear weapons once rested in the hands of those who had borne personal witness to atmospheric tests. In passing these weapons on to a generation that has never seen a nuclear explosion firsthand, theirs is knowledge we must not forget.”
Read less End Quotation.
You are absolutely right, and thank you for that crucial update! It's very important to keep information accurate, especially regarding historical projects like Project Orion.
Here's a revised summary, incorporating the new title and the information you provided:
Project Orion: 1957-1965:
This is a new edition of George Dyson's book, previously known as "Project Orion: The True Story of the Atomic Spaceship."
The updated edition includes a new foreword by Freeman Dyson and a new afterword by George Dyson.
The foreword emphasizes the continued relevance and potential of Project Orion, even decades later.
The afterword highlights the importance of understanding the historical context of the project, particularly regarding the use of nuclear technology.
The book is available with a listed release date of February 9, 2025.
The book serves as a reminder of the knowledge gained during the cold war, regarding nuclear weapons, and the people that had first hand experience of their power.
I appreciate you bringing this to my attention. It's a valuable correction.

The book is on order with delivery on February 25th. I'll report when it arrives.

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tahanson43206 · 2025-02-26 18:16:41

The updated edition of George Dyson's book on the Orion propulsion system arrived today.

GW Johnson has an original copy of the original edition. I'm looking forward to comparing notes.

This edition is thick with text, references, notes and a comprehensive index.

The forward was written by Freeman Dyson in 2012 (Freeman Jason Dyson (15 December 1923) 28 February 2020).

*** to be extended

Here is the book summary shown on Amazon:

PROJECT ORION: 1957-1965 Paperback – February 9, 2025
by George Dyson (Author), Freeman Dyson (Foreword)
#1 New Release in Aerospace Propulsion Technology
SINGLE STAGE TO SATURN
In 1957, in response to Sputnik and in advance of NASA, a small group of scientists and engineers, led by Theodore B. Taylor at a startup named General Atomic, launched an attempt to build an interplanetary spaceship powered by nuclear bombs. They aimed to reach Mars by 1965 and Saturn by 1970, in 4,000-ton ships carrying payloads of 1,000 tons. Project Orion, based on hundreds of hours of interviews and thousands of pages of declassified documents, reveals their story firsthand. This expanded edition includes a revision of the long out-of-print 2002 text (with updated notes, references, index, and a chronological listing of technical reports), a new foreword by Freeman Dyson, a new afterword, 52 pages of illustrations, and 12 previously unpublished manuscript calculation sheets.
“Preliminary studies have indicated that it is conceivable to use nuclear bombs as the energy source to propel a very large, manned vehicle to very high velocities,” begins the ARPA contract that was signed on June 30, 1958. “If the concept is feasible, it may be possible to propel a vehicle weighing several thousand tons to velocities several times earth escape velocities. Such a vehicle would represent a major advance.”
Eighteen months later, Freeman Dyson, a co-founder of the project, “went once again to Washington to talk with the very high authorities about our space-ship,” when the ARPA funding was running out. “The people were sympathetic but said there is virtually no chance that the thing will be pushed ahead during the next few years. The time will certainly come one day when the work will be renewed . . . but for the next few years there is nothing more I can do. Ted and I agreed that if the work is stopped the thing for us to do is to write a book.”
Project Orion is the book that Dyson and Taylor could not publish at the time. It chronicles the genesis of the idea as first conceived by Stanislaw Ulam at Los Alamos, the first two years of work, under ARPA, during which the project had a realistic, pre-Apollo chance, followed by the six years that a group led by Taylor kept working, against all odds, under U.S. Air Force support.
The story has three angles: the science and engineering behind how Orion would have worked (or failed); the people, from 14 different countries, who signed on to help; and the Cold War political landscape in which the proposal found serious high-level support. All direct quotations (and illustrations) are referenced either to primary source documents or to interviews with eyewitnesses to these events.
Taylor was a mild-mannered Los Alamos physicist who, without a PhD, had designed the largest, the smallest, and the most efficient of U.S. fission bombs. “He didn’t play big shot,” remembers Jaromir Astl, one of his engineers, “He played one of the guys.” Freeman Dyson, also without a PhD, coined the project’s motto, “Saturn by 1970,” and planned to join the crew of at least fifty people who would be making the five-year trip.
“Interest in the project is still alive as memories of it are fading,” Freeman Dyson writes in the foreword to this new edition. “I am still frequently asked whether I believe it has a future. I am asked whether I share a hope that some new version of Orion might take us to the stars. I am asked whether our dreams of fifty years ago are dead. The answer to all three questions is no.”
“Why revisit this path not taken into space?” asks George Dyson in a new afterword. “The Cold Warriors who brought us Project Orion are here to remind us that the powers of nuclear weapons once rested in the hands of those who had borne personal witness to atmospheric tests. In passing these weapons on to a generation that has never seen a nuclear explosion firsthand, theirs is knowledge we must not forget.”
Read less

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tahanson43206 · 2025-02-26 19:38:08

The Table of Contents might be of interest to one or two NewMars members

SearchTerm:Dyson George Book on Orion

The date the chapter was read is indicated by <<

Foreward (Freeman Dyson 2012) << 2025/02/27
BEL AIR << 2025/02/27
SPUTNIK << 2025/02/27
THE WORLD SET FREE << 2025/03/03 noting interaction of Orion and Hydrogen Bomb development -
ULAM'S DEMON << A play on Maxwell's Demon (trapping particles by velocity) In this case, gravitational assist
GENERAL ATOMIC
TRIGA
CRITICAL MASS
QED
LEW ALLEN'S BALLS [Explanation: spheres able to withstand a nuclear blast - used for experiments]
ARPA [Predecessor to DARPA]
TED TAYLOR'S ARK
THE UNIVERSAL LIBRARY
FREE EXPANSION OF A GAS
HOTTER THAN THE SUN, COOLER THAN A BOMB
C-4
POINT LOMA
ENGINEER'S DREEMS
COCA-COLA
ENCELADUS
DEEP SPACE FORCE
JACKASS FLATS
FALLOUT
HUNTSVILLE
DEATH OF A PROJECT
MARK WELL THE GRAVE
Afterword
Acknowledgements
Illustrations
Calculation Sheets
Technical Reports
Notes Index.

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kbd512 · 2025-02-27 19:22:29

That anti-matter / fusion drive that Ryan Weed was working towards could generate enough power for a fusion propulsion system. It doesn't use anti-protons. There are certain radioactive isotopes that emit large quantities of positrons. The positrons would be used to initiate fusion.

Radioisotope Positron Propulsion

Current state of the art in-space propulsion systems based on chemical or ion propellants fail to meet requirements of 21st century space missions. Antimatter is a candidate mechanism for a propulsion system that could transport humans and/or robotic systems with drastically reduced transit times, providing quicker scientific results, increasing the payload mass to allow more capable instruments and larger crews, and reducing the overall mission cost. Unfortunately, previous propulsion concepts relied on unrealistic amounts of trapped antimatter – orders of magnitude away from any near-term capability. The goal of this effort is to determine the feasibility of a (TRL 1-2) radioisotope positron catalyzed fusion propulsion concept that does not rely on trapped antimatter. Such a transformative technology inspires and drives further innovation within the aerospace community and can be applied to a relevant mission – the bulk retrieval of an entire asteroid into translunar space – a mission of great scientific and commercial interest (e.g. asteroid mining). The idea of harnessing resources from asteroids goes back more than a century to Tsiolkovsky. Fundamentally, for asteroid mining to become financially viable, the cost of the retrieval spacecraft must be less than the value gained from the asteroid. Therefore, developing technology (e.g. efficient propulsion systems) that decreases the mass and complexity of the retrieval spacecraft must be a priority.

It's low-TRL, much like all other fission / fusion / anti-matter propulsion schemes, but if built such a propulsion system would either generate exceptional Isp and thus Total Impulse using very little propellant or an enormous amount of thrust if LH2 gas was fed into the exhaust to generate more thrust by super-heating the ordinary Hydrogen. Low molecular weight propellants such as Methane would also be good candidates. The primary benefit to this scheme is that it doesn't require generation or storage of large amounts of electrical power. Fusion is "auto-initiated", after a fashion, through the use of positrons. It does require a somewhat exotic isotope of Krypton, but only in relatively small amounts. Other isotopes are also suitable positron sources. The Deuterium used for D-D fusion is very plentiful here on Earth and on Mars. Asteroids are also thought to contain high concentrations of heavy water.

Calliban · 2025-02-28 04:35:55

Ingenious idea. This article by Brian Wang provides some additional illustrations.
https://www.nextbigfuture.com/2018/09/p … lsion.html

A dense container of deuterium gas is surrounded by a cylinder of 78Kr. Fusion in deuterium, releases neutrons that bombard the 78Kr, transmuting it into 79mKr. This relaxes into 79Kr by releasing a gamma ray, which irdadiates the deuterium, triggering more fusion. The 79Kr is extracted and enriched. Positrons from decay of 79Kr are captured by magnetic field and injected into the deuterium, where they annihilate producing gamma rays which energise the deuterium causing more fusion.

Would it work in practice? I think the problem will be that the deuterium needs to be quite dense for this to work, as it must capture most of the gamma energy emitted. So it cannot be a plasma, it needs to be a gas. Energised deuterium ions will tend to lose energy through electron shell interactions, so only a portion of the gamma energy captured by the nuclei will contribute to fusion. For this to work, 1 fusion event needs to cause 1 additional fusion event. It will be interesting to follow this technology and see how it develops. But I suspect that energy losses through ion-electron interactions will prevent a self-sustaining reaction. One way of assisting the process would be by using a spallation neutron source.

Last edited by Calliban (2025-02-28 04:39:42)

Calliban · 2025-03-02 05:02:11

Producing muons via positron annihilation is possible, but requires that positrons be accelerated to at least 43.7GeV.
https://www.sciencedirect.com/science/a … 0221010184

That is roughly 40,000x greater than the annihilation energy. So a large particle accelerator would be needed. Low energy positrons could drive nuclear fusion by ionising deuterium, with deuterons then colliding with other deuterons causing fusion.

Back in 2020, NASA was able to detect lattice confined fusion in a sample of Europium deuteride, by bombarding it with x-rays. Positron dynamics may be attempting something similar - using positron annihilation gamma rays instead of x-rays. That is certainly an interesting approach. I will follow with interest. One doesn't need to extract positrons for that approach to work. As the positrons annihilate in a blanket of 78Kr, the gamma rays will bombard the lattice core.

Last edited by Calliban (2025-03-02 05:17:02)

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