All posts by Kent Nebergall

Kent Nebergall became involved with the Mars Society in 2004, when he won the Mars Society’s Kepler Prize to design the Mars Direct Earth Return Vehicle. He has given several convention track talks each year ever since, focusing on new inventions for space settlement, along with gaining a systematic and historical understanding of the human need and ability to do so. Kent is a business analyst in the Chicago suburbs, where he’s worked in over a dozen industries. Kent served as astronomer for Mars Desert Research Station (MDRS) Crew 32, commander of Crew 124, and has helped design and build the new MDRS science dome. He is on the Mars Society Steering Committee.

Low-Thrust Breakthrough Propulsion Round-Up

Next Big Future has produced a number of articles recently on breakthrough propulsion.  Here is a summary of the current state of the art on these speculative systems.

Low-Thrust Propulsion systems are too weak to be used to launch from the surface of a planet, but have extreme efficiency and high exhaust velocities.  Basically, a space probe like Dawn had the propulsive force equivalent two sheets of paper held on your hand.  Yet it could thrust for years with this system.  Over the course of eight years, it thrust over 2000 days, with a change in velocity of 24,000 mph/ 38,000 kph.  That's more than it took to launch it into interplanetary space to begin with, and while using less than 937 pounds/425 kg of propellant on board.  Ion drive takes a slowly-released gas, gives it an electrostatic charge, and then accelerates it in a magnetic field and neutralizes the charge as it exits the engine.  Newer systems, such as the speculative EM-Drive, promise to work with no on-board propellant. 

While creating full-antimatter is very, very difficult and energy-intensive, making simple positrons (antimatter electrons) is fairly simple.  A group is working on a system that can fit on a cubesat for a demonstrator.  Rather than make full anti-matter atoms and trying to store them and use them later in an engine, a positon system is basically an ion drive system like Dawn uses, but using positrons made on the ship itself instead of ionized gas.  Positrons are naturally produced by radioactive materials.  So a sample of a radioisotope is placed on board, and the positrons it emits are cooled enough to allow them to be directed and accelerated in a magnetic field like in a conventional ion drive.  The resulting particles exit the vehicle at ten percent the speed of light.  If idealized, these systems could get to Mars in weeks, Pluto in months, and Alpha Centauri in 40 years.   The developer, Positron Dynamics, plans to launch a cubesat demonstrator somewhere between the middle of this year and next year.  The near term application of these motors would be as a more-efficient substitute for ion drive in positioning communications satellites.  In the longer term, they would be very useful for asteroid mining.  

To make a complex system a bit easier to understand, a small fuel pellet is compressed by a magnetic field and bombarded with particles.  It undergoes nuclear fission and the plasma is further compressed by the magnetic field.  The combination of compression and the heat, self-generated plasma magnetic field, and particle mix of the tiny fission explosion can trigger a fusion explosion, similar to the way an atomic bomb can trigger a thermonuclear (fusion) bomb.   As with the Positron example, this could theoretically get a vessel to Mars in a month.  It would generate exhaust ISP(the efficiency of a rocket)  of 30,000 seconds.   By contrast, a typical chemical rocket has an ISP under 450 seconds. 

This is similar to  EM drive, in that it depends on A) very tiny effects that can barely be observed and B) processes that defy conventional physics, but appear to be explained by some aspects of science.  When I say barely observable, we are talking 2 to 12 micronewtons.  A tiny bottle-rocket has 3 newtons of average thrust, or a million times as much as these experimental engines.  That said, they hope to get up to 10-20 millinewtons in a decade or two.  That said, a microthrust, propellantless system has no theoretical output limit, because there is no propellant to be used up.  This is why those who propose systems like this often speak of starships. 


The positron system seems quite logical, and can be demonstrated soon.  It has limits, though, because it relies on radioactive decay of highly radioactive materials.  This can be scaled down into tiny systems.   The PuFF system will require a lot of expensive research to get worked out, over a fairly long time period.  That said, it has a lot of similarities to Project Daedalus, and could be used for a simple starship probe eventually.  Such a system is at least a decade away, and would be quite large.  Mach Effect is a lot like EM Drive, but while the effects are more explainable, they seem to be even less powerful.   To power a vehicle with any velocity, it also has to be scaled up quite a bit.  
With new systems that can provide fission and possibly fusion electrical power coming online very shortly, systems that require lots of electricity (advanced ion drive, these propellantless systems, and so on) may be arriving sooner rather than later.  Expect to see something interesting in this range within five to ten years.  

Old Space Station, NewSpace Station

There has been much said of the recent budget proposal, that zeros out funding for the International Space Station in the year 2025.  What never seems to be mentioned is that the ISS was due to be retired in 2024.  This is already a four year extension over the original retirement date of 2020.  The station costs a sizable portion of NASA's budget to operate, and may not be sustainable from a structural standpoint after the year 2028.  The ISS has a pressurized volume of 388 cubic meters, and cost $100 billion to construct. 

Bigelow Areospace originally planned to have two of its BA330 modules ready to launch by 2017.  These modules have 330 cubic meters of habitable volume - almost equal to the entire ISS.  Note that the power input from the BA330 solar panels is much lower, so such a new station would not have the same capacity to run experiments.  The ISS has solar arrays the size of an American football field, and generate 84-120 kilowatts. The BA330 power levels are not yet published, but the solar arrays are far smaller.

Bigelow already has a small prototype, called BEAM, attached to the ISS.  This is giving NASA experience with the technology and allows the crews on ISS to experiment with this new inflatable habitat system.  Bigelow is now proposing a new module, a full BA330, to be attached to ISS.  This module is called XBASE.  This could be ready by 2021, although it may be delayed due to the requirement to launch on the as-yet-undeveloped ULA Vulcan launch vehicle.  


ISS was built with parts that are no longer in production.  Much like the Space Shuttle before it, the cost of maintaining a system with limited spare parts becomes prohibitive with time.  Also, without the Space Shuttle, large modules cannot be returned to earth to be rebuilt and relaunched. Similarly, the spacesuits on the US side needed to maintain ISS are in many cases leftover from the Shuttle era.  They are far beyond their designed lifespan and are having age-related and design flaw-related issues.  Extending the life of the ISS beyond 2024 becomes more of a risk with each passing year, and the costs will increase as parts become harder to come by.  A key strength of the ISS, the vast solar power system, must run on batteries 45 percent of the time as the station goes into the shadow of the earth on each orbit.  Those batteries also have a finite lifespan. 

We are in a race to build a new system before the old system is retired.  We failed to do this with the Space Shuttle, as several proposed replacements were cancelled prior to retirement of the shuttle.  We also need new spacesuits sooner rather than later.  The XBASE proposal could be launched as an adjunct to the old space station.  This would give the new station access to power and more extensive facilities, while still being a brand new facility.  Not everything on board the ISS is completely worn out.  Some facilities are a decade newer than others.  It may be possible to move some systems over to the Bigelow module to extend their operational lives.  It may also be possible to use the XBASE as a primary facility while maintaining some experiments on the old ISS indefinitely.  ISS already does this to some degree - the original Russian module was the habitat, propulsion, and power system for the ISS in the early stages of construction.  Now, it is primarily just a hallway connecting newer Russian modules on one side with newer US/EU/Japan modules on the other.  

A system with ISS and XBASE combined, with the later addition of one or two more Bigelow habitats, would give a graceful exit to the ISS facility and offer a new platform for life support, habitation, and more modern experiments.  As systems on ISS wore out or were no longer maintainable, they could be shut down and bypassed.  When the overall cost to benefit ratio of the system exceeds practicality, we can simply separate the facilities and send ISS to the bottom of the Pacific as originally intended.  

Having BA330 dependent on Vulcan appears to be a mistake.  Perhaps they can launch something on the Falcon Heavy on a shorter time frame if Vulcan is delayed.  Since all new rocket projects are delayed, that seems a solid bet.  The default Falcon fairing is far too small for BA330, but the payload capacity in terms of mass is far better than Vulcan.  It should be possible to equip a Falcon Heavy with an oversized fairing for the mission, provided the aerodynamics and weight/balance issues can be settled. 

Site Updates – Patreon, Spacesuits, and Plans

Lots of small updates. I've added a Patreon account so that people interested in this site can help sponsor it directly.  By showing support for this work, you help offset the costs of site improvements and make it easier to focus on new content. You also get a vote in what new content will be shown in this site.  In the sections on invention and entrepreneurship, I'll be adding a detailed analysis as to why I chose Patreon and what impact that has on being a start-up like MacroInvent. 

I've added a "dashboard" of key technologies for Space Exploration and Settlement.  Each challenge is color-coded green (for on track), yellow (for drifting off target) or red (may not be ready concurrently with other supporting technologies, and therefore may limit our capacity in space.)  I've skipped ahead to an article on the crisis with Spacesuits, because that's the first red on the list.  

Videos and slides added from my Mars Society talks at Irvine, CA

Video of my talks at UC Irvine for the Mars Society are now available on YouTube.  The slides are in the description and in the comments thread on those YouTube links. 
For a list of all videos available, see the Videos and Other Content page. 

Risk Reduction Missions for Space Settlement

While the early stages of the NewSpace revolution are in place, what projects could be done to expand human activity into deep space as soon as possible, with minimal cost and risk?  This talk examines a few options that could be launched in the next few years. 

PDF of Presentation

Rapid Space Development and the NewSpace Technology Revolution

This presentation examines the nature of technology revolutions, and the nature of the next revolution in space technology.  It goes on to predict the nature of our expansion into the solar system, using principles from past technology revolutions. 

PDF of Presentation

Elon Musk on Reddit AMA

Elon Musk recently did a Reddit Q&A with members (Ask Me Anything).   This mostly focuses on details of the Mars vehicle update.  Here are some highlights.

Mars Settlement

  • The Mars city design from the video was mostly artistic (“I wouldn’t read too much into that illustration”.  There are no specific plans beyond propellant production, power, and life support.  He wants to enable other industries to go to Mars.
  • The landing sites need to be low altitude for maximum aerobraking.  Close to ice for propellant production and free of giant boulders.  Closer to equator is better for solar power.
  • SpaceX is building the ISRU (propellant production system) in house, and it’s pretty far along.
  • They plan to put communications satellites around Mars at some point.

Technical Details of the BFR and Spaceship

  • The vehicle would burn all the fuel in the main tanks getting to Mars (or the moon or Singapore or whatever).  It would then use the secondary tanks for landing.  In the case of Mars, it would turn the nose of the ship toward the sun and vent the outer tanks.  This would basically make the inner tanks super-cold for the trip.  (Editor note – it would also eliminate the possibility of spinning two spacecraft with a tether for artificial gravity).
    • They eventually will add a cryocooler (which would allow it to spin).
  • The newest Raptor engines being tested are actually sub-scale.  The final production version is being designed for reliability, not performance.
  • the small delta wing is to “balance out” the load on reentry, to keep the ship from entering engines-first.  It can also provide some pitch and yaw control during reentry.
  • The RCS system will be methane/oxygen and pressure fed.
  • Early versions of the tanker will be just a fully-loaded propellant tank ship with no payload.  Later versions will look “kinda weird”.
  • Heat shield tanks are mounted directly to the tank walls.
  • The development will start with a full-scale ship doing short hops of a few hundred kilometers up and across.  They don’t need the deep-space Raptor engines for that.
  • VERY INTERESTING – “Worth noting that BFS is capable of reaching orbit by itself with low payload, but having the BF Booster increases payload by more than an order of magnitude. Earth is the wrong planet for single stage to orbit. No problemo on Mars.”
    • Traditionally, methane doesn’t have the specific impulse to do single stage to orbit.
    • A BFS without the booster would be economical for domestic flights, in theory. They could also return themselves from interior destinations like Chicago to coastal launch facilities with the BFR stage.

Anyway, you can read it in detail if you like from the link above.  I simply gleaned what I could from the stream in the notes here.

Creating eBooks in Scrivener

Why an eBook?

Under the category of Entrepreneurship, writing books on whatever topics you can allow a small to medium stream of secondary income.  It can also help establish your reputation in a particular field, and give you a way to communicate your ideas to a larger audience.  

With the recent advent of eBooks such as Kindle and print on demand, it's become relatively trivial to crank something out.  This short article will simply link to YouTube and other web resources to walk you through the process.  

Creating an eBook in Scrivener for Kindle

Under the category of Entrepreneurship, writing books on whatever topics you can allow a small to medium stream of secondary income.  It can also help establish your reputation in a particular field, and give you a way to communicate your ideas to a larger audience.  

With the recent advent of eBooks such as Kindle and print on demand, it's become relatively trivial to crank something out.  This short article will simply link to YouTube and other web resources to walk you through the process.  

It is possible to publish a Kindle book directly from Word, but it's not recommended.  It is also possible to use a program called Vellum for the Macintosh, but that is $100-250 depending on the version.  Scrivener, while not perfect, is recommended.  At $40, it's a fairly trivial price.  There are versions for both Windows and Macintosh, and a limited version for iPad/iPhone.  Version 2 is current, and can create files for Kindle (.mobi) format.   It can also export to Word, PDF, and so on.  The current version has a few formatting limits, but most of these will be repaired in version 3, which should come out for the Macintosh in late 2017 and PC in 2018.

Before getting started, go to the Literature and Latte YouTube channel and get an introduction to Scrivener.  Decide from there if it's the right choice for you.  If you work on a Macintosh and have a higher budget, consider using Vellum instead.  (My Mac is currently not working, so I can't tell you if the reviews of this are accurate or not from experience.)

Scrivener is available for download at   You can install a license on up to five devices for PC with a PC license or five Macintosh systems, but you cannot mix the two.  The Mac version has a few extra features and is updated first in the development process.   Once your book is created, watch this video to see how to format the file for Kindle.  You can then watch this video to see how to upload it to Kindle Direct Publishing.

If you wish to then take your content and make a print book, you are actually better off doing it in Word.  You can export from Scrivener to Word format and then save that for upload as a print-on-demand book.  I have yet to do this but will post an update in a few weeks when I've completed one. 

Microgravity and Nearsightedness

Microgravity has various negative impacts on health.  While bone and muscle loss are the most well known and dangerous, they have recently been resolved a combination of medicine, diet, and exercise.  

One remaining issue is the fluid shift from the spinal column to the eyes and optic nerves over time.  Roughly two out of three astronauts have negative impacts on vision that linger even after returning to Earth.   

What this means for Space Exploration

The impact of this does not seem to be treatable with diet or exercise.  As noted, roughly a third of astronauts do not have this impact.  We may have to be selective with early Mars missions to find astronauts whose anatomy minimizes the effect.  The only way to test for this may be an extended trip to a space station.  Alternatively, it may be possible to use an MRI of the nervous system to determine the capacity of the individual to deal with microgravity effects on the optic nerves.

Another option would be to spin spacecraft for Mars missions to create artificial gravity.  That begs the question then, at what gravity level does the impact go away?  


Work on spinning space stations should be a higher priority in the near future.  I will be announcing some near-term designs to help isolate and qualify solutions for this issue.  These are parts of my talk at the 2017 Mars Society Conference in Irvine, California. 

Mars Soil Toxic?

A recent study, reflected in numerous news articles, indicates that the surface of Mars may be more toxic than originally thought.  

The short version is as follows:
We already knew that perchlorates exist in may locations in the upper layers of the surface of Mars.  We knew that iron oxide was common  We knew that the sun's ultraviolet light was mostly unfiltered when it hit the surface.

What the study showed was that these factors in combination are 10.8 times better at killing ordinary bacteria than ultraviolet light alone. 


This is actually a good thing for human exploration of Mars.  A key issue as we approach the time of humans traveling to the red planet will be planetary protection.  Humans have ten bacterial cells in our bodies for every human cell, and we shed them constantly.  It's going to be very difficult to keep the spacesuits clean and in good condition without human contact.  The only thing that could make planetary protection a non-issue for early missions is a planet with the ability to sterilize itself at the air and surface dust level.  That is exactly what Mars can do, and it does it over ten times better than we expected.

That said, a key factor in settlement is getting under a blanket of radiation protection such as soil or ice.  If we confined mining operations to A) robotic excavators and B) avoided human interaction with subsurface zones that could touch a water table, we wouldn't have the issue of forward contamination (or back contamination, should life exist there).  This can be managed if one keeps habitats on the surface and buries them in the ice-filled equivalent to sand bags.  This provides better cosmic ray protection, easier construction, and avoids the issue in both directions until the issue of life on Mars is resolved.