Adding an Earth-sized magnetic field to Mars

Mars has only the ancient remnants of a magnetic field. What little chunks of field it does have (imprinted into magnetic rocks) are regional in scale and do nothing at all for radiation shielding (I once calculated this). Additionally, over a long enough timescale (tens of millions of years), the solar wind will erode the atmosphere of a terraformed Mars. So, let’s just get on with replacing the lost magnetic field.

To do this, we aren’t going to do something silly like restart the core. We’re going to rely on a tried and true existing technology: cryogenic superconductors. Just put a superconducting ring around the equator of Mars. Turns out, this wouldn’t even cost that much to build. I will be using Magnesium Diboride (MgB2) because it’s cheap, has pretty good performance (critical temperature of 39K, critical current of like 105 A/cm2 at 5K), and both Boron and Magnesium are known to exist fairly commonly on Mars. (Magnesium is super common, and Boron has been found in clays at >150ppm concentrations–according to this paper–and probably exists in far higher concentrations somewhere since Mars once had a quite active water cycle. I’ll assume that by the time the residents of Mars want to do this sort of thing, the costs of extracting these minerals will be similar to that of Earth (maybe a poor assumption, but why would you do this unless there are like millions of people on Mars, at a minimum?). We’ll also assume that because of the ridiculous scale being operated at, and because MgB2 is a pretty easy superconductor to make (just need to heat the mixture of Magnesium and Boron powders), the cost of actually building the ring will be some single-digit multiple of the raw costs of the material.

Okay. So just how big is the Earth’s magnetic field? We’ll use its total energy (when approximated as current on a sphere) to estimate what we’ll need as far as current in the ring. According to this, the Earth’s magnetic field stores about 1026 erg, or 1019J (roughly half the energy the world uses in a year). The energy stored in an inductor is just:
(according to Wikipedia)
Where L is inductance and I is the current in the ring.

To calculate the inductance L of a ring of radius R with wire radius a and number of turns N, we use the approximation:
L \approx N^2 R \mu_0 \mu_r \left ( \textup{ln}\left ( \frac{8 R}{a} \right ) - 2\right )

(from here)

Since N=1 and we’ll conservatively (very conservatively) say the relative permeability  \mu_r = 1, and since the current I is related to the critical current density Jc such that: I=J_c \pi a^2, we can write the equation as:

E\,=\,\frac{1}{2}\,R \mu_0 \left ( \textup{ln}\left ( \frac{8 R}{a} \right ) - 2\right )\cdot\left (J_c \pi a^2\right )^{2}
If we let a=.42m, R=rMars, and Jc = 105 A/cm2:*r_Mars*(mu_0)*(ln(8*r_Mars/(.42m))-2)*(10^5A/cm^2*pi*(.42m)^2)^2 = 1.047*10^19 Joules, when we only needed 10^19 J to equal the same energy as Earth’s magnetic field.

Given the density of MgB2 is 2.57g/cc (source), the mass of the superconductor is:*pi*r_Mars*pi*(42cm)^2*2.57g/cc or about 3*1010kg, 30 million tons, almost have of which is boron. The Earth mines about 4 million tons of Boron a year, so the Earth produces enough boron to build that thing in about 4 years (we’ll mine this on Mars, of course). Pretty reasonable, considering we’re doing some pretty hardcore terraforming, here.

Given a price of about 10USD/kg for Boron (just spitballing here, since Ferroboron is half boron by molarity and 15-20% boron by mass and is 1-2USD/kg… of course, boron ore is much cheaper) and like 2USD/kg for magnesium metal (just look up the spot prices for Mg and Ferroboron), so about USD6/kg of bulk MgB2.

This whole thing would cost about 180B USD in raw materials but would store about 3 trillion kWh for a ridiculously low price per kWh of storage (like 6 cents/kWh! For storage that can be reused!). Of course, there is also insulation and cooling, plus some method to inject power into the ring.


NOTE: Some Japanese researchers recently (last 2-3 years I think?) published a paper about the thing I am proposing here. I can’t find the paper now, but I assume they did I better job than I did. Also, I don’t really buy into Jim Greene’s L1 magnetosphere, since the solar wind does actually shoot straight out from the sun but actually follows the spirals of the Interplanetary Magnetic Field, so I’m pretty sure solar wind would hit Mars because the shadow of a big magnetosphere at L1 would miss Mars.

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A human tribe is a Von Neumann probe

After thinking a while about why self-replicating robots do not exist (thanks, Casey: ), we’re reminded that living things do this regularly. I’m tempted to write “a human is a von Neumann probe,” but that wouldn’t be accurate. A single human cannot reproduce, and even a pair would quickly run into survival problems unless they got lucky (and there’s some amount of genetic variety needed, with the minimum number of individuals being somewhere between 50 and 5,000 to ensure enough genetic diversity). The human is by default in society, usually a band or tribe in the past and now in cities. Our survival depends on it. This has enabled us to span from pole to pole with a vast array of lifestyles.

Even a band (10-50 people) enables specialization and folklore. A full tribe (made of several bands, enough for genetic diversity) is a self-contained unit of humanity. Enough to replicate and perpetuate neolithic technology, which includes domesticated animals, plants, spoken language, and perhaps even written language. An individual or family would have difficulty maintaining this, but a tribe should be capable of it. And with the tools of written technology, could maintain knowledge and learn between generations.

What’s interesting about neolithic technology versus later developments is that this is before humanity became dependent on vast trade routes and city-state social structures (although those did develop in that time). Still small enough to be self-contained within a tribe and replicated most places on Earth (with adaption). Other than biological materials (seeds, animals… which are reproducible and not a fundamentally limited geological resource), it is still really easy to bootstrap neolithic technology and could be done by a small group of people. The Bronze Age requires tin and bronze, which are very limited in geologic availability (requiring vast trade networks) and require more sophisticated processing.

My favorite exploration of Neolithic technology is the Primitive Technology Youtube channel. He bootstraps from nothing (no knives, etc, just himself in shorts) and has gotten extremely far in technology development.

No doubt his efforts rely on a lot of free time enabled by modern food distribution systems, but they all could be replicated by a tribe. He has made some interesting advances, such as a sort of centrifugal blower and the beginnings of a bootstrapping of iron technology using iron bacteria (found all over) instead of geographically limited iron ore. He also makes use of domesticated yams.

Now I’ve been thinking a lot about potatoes. They’re remarkably easy to grow and extremely efficient in area, store reasonably well, easy to propagate, etc. It really is a good choice if you had to pick one staple to survive on Mars with (hello, Matt Damon). But they were not introduced into the New World until the 1500s. Same with corn (maize), and a bunch of other things. Corn is a particularly efficient way of growing calories. A similar thing is true of other domesticated crops. …and animals, such as donkeys, horse, oxen, etc. Any neolithic tribe could’ve utilized these resources, but these resources weren’t all available until the modern era (i.e. starting in the 1500s). There’s some evidence that domestication of, say, potatoes, helped speed the industrial revolution due to their efficiency. You could say that it was these domestic plants and animals that enabled the industrial revolution as much as any other particular scientific, economic, etc advance.

Any of these could’ve been introduced to neolithic tribes 10,000 years ago or even earlier. Maybe 100,000 years ago. One could have taught them writing. A single tribe had enough resources to bootstrap these “technologies,” and their productivity would’ve been vastly improved. Unlike our heavy industry today, they do not require a vast, globe-spanning economy to replicate. They can be planted and replicated by a single, neolithic tribe to their great benefit. Self-contained, self-replicating… (or requiring just some assistance from people to replicate).

Domestic plants and animals are remarkable technologies. Seeds in particular… little, unassuming von Neumann machines. Iron bacteria could’ve bootstrapped the Iron Age 100,000 years earlier. Give a tractor to a neolithic tribe, and it would stop as soon as it ran out of gas. A steam tractor maybe could’ve lasted longer and maybe animal grease could serve as oil, but the industrial toolchain in order to maintain any such engine would be beyond a single tribe’s ability. But oxen or other beasts of burden? Easy to maintain and replicate in comparison. Even with some amount of semi-autonomous intelligence. There are your self-replicating robots!

This is the potential of biology in simplifying the technology bootstrap process. It’s unfortunate that biological processes tend to be so inefficient. Their relevance to bootstrapping a Mars civilization may be difficult to gauge relative to the more energy-efficient heavy machinery approach… Also, not only is it inefficient, it’s also only viable in a relatively narrow temperature and pressure range which mostly makes it irrelevant to space settlement…

…but perhaps this is worth another look. I think the fact that biology can play a part in bootstrapping is one of the most important arguments for (at least partial) terrraforming… if you can make Mars Earth-like enough for at least SOMETHING to grow, maybe we can use biology to help bootstrap human civilization there. If Mars is terraformed, then the basic human unit, the tribe, would be sufficient to replicate civilization given a continuity of knowledge of written language.

…but maybe something smaller than full terraforming is sufficient? Humans, even with just neolithic technology, are remarkably adaptable (if we can find an energy source). We can live indefinitely in the Arctic by harvesting animals (including fish, etc) using neolithic technology. Some humans live nearly their whole lives on the water using pre-modern tech. Perhaps with some clever new inventions that could be bootstrapped with neolithic-level-tech, there may be some future domesticated plants or animals (or other?) that enable humans to live on a partially terraformed Mars with something as small as a tribe. After all, we used animal intestines to produce the impermeable gas bags of the mighty zeppelins. What new domesticated life form might enable us to live on Mars with a much simpler bootstrap chain?

Can we harden living things for the Martian environment? I’m reminded that the Armstrong Limit of pressure is dictated by the boiling point of water at the human body temperature. Other living things, such as lizards (not to mention hardy plants), can still live and move with body temperatures low enough that Mars’ pressure at Hellas Basin would be high that water would not boil. There’s also the possibility of some sort of toughened skin designed to maintain internal pressure and temperature. Lichen or similar lifeforms may even be able to photosynthesize under Martian conditions:

…so what is the REAL Martian potato? Could some domesticated lichen produce food and important chemicals for a growing Martian civilization? Maybe some sort of domesticated lichen that produces hydrogen peroxide? Could some sort of genetically modified reptile beasts of burden serve as our self-replicating robots? Could we grow tough membranes (with built-in molecular pressure pumps powered by photosynthesis) to make our pressurized cities? How can we simplify the industrial tool-chain so self-sufficiency becomes tractable?

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COVID 19 and Global Warming

It seems to me that we have an accelerated time experiment on the realities and effects of government reactions to a major problem. Governments’ around the world handling of COVID 19 is a microcosm of the handling of Global warming.

Both are considered to be disasters of epic proportions by some and a tempest in a teapot by others. Some consider massive government intervention to be absolutely critical to controlling and solving the problem. While others see no reason for government interference at all.

COVID 19 is an issue that is working on the time scale of days and weeks while global warming is working on the scale of years and decades. My thought is that watching how governments and populations interpret and handle COVID 19 across the next year is a fair indication of how global warming will be handled across the next century.

So I suggest that people of many viewpoints should track the reactions, truths, and lies of the current epidemic with an eye to how global warming will be played out. the relevant timescale is about 100 to 1. Are the leaders of the various countries operating in the best interests of their people, or just using a crisis to gain more power and wealth? Are they creating a crisis for their own manipulative needs. Or are they doing everything right. Let’s all keep an eye on this with the long view.

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Modeling COVID-19: When will the peak occur in the US?

CDC Statement on first possible community transmission case in the US

CDC Statement on first possible community transmission case of COVID-19 in the US

So, given that the CDC recently confirmed the first possible instance of community transmission of COVID-19 (Novel Coronavirus) in the US, I thought I’d guesstimate roughly when the peak of the epidemic would occur in the US with some (extremely) rough modeling.

I’ll be modeling it using the usual logistical model (which I think turns out to be the wrong model for a virus… but let’s just run with it for now) you all learned in your first Differential Equations course. I’ve recently been brushing up on my differential equations (have been getting rusty) in Khan Academy:

The rate of change of the population N (in this case, Coronavirus cases) with respect to time can be given as:

dN/dt = r*N*(1-N/k)

Where r is the exponential constant (related to doubling-time) and k is the “carrying capacity”, i.e. max number of cases (not actually a good definition for a virus… but again, let’s run with it).

This is solved as: 

N(t) = N0*k/((k-N0)*e^(-r*t) + N0)

Where N0 is the population at time = 0.

At the beginning, the number of cases rises exponentially. Early research says the doubling-time of COVID-19 was 7.4 days in the early days of the outbreak in China, according to: Early Transmission Dynamics in Wuhan, China, of Novel Coronavirus–Infected Pneumonia

This is related to the exponential constant by:
r = ln(2)/(7.4 days) = 0.09366853791 (1/days)

According to Wikipedia, 28% of the US population became infected with the Spanish Flu (carrying capacity?):

And US population is currently about 327 million people, so we’ll use 91.56 million as our “carrying capacity”:

k= 9.156*10^7 or 9.156e7 (in more compact notation)

And since community transmission just started, we can set N0 = 1. Therefore our equation becomes:
N(t) = 9.156e7/((9.156e7-1)*e^(-0.09366853791 (1/days)*t) + 1)

If we plot t in days: 

modeled infected population vs time

modeled infected population vs time*e%5E%28-0.09366853791*t%29+%2B+1%29+for+1%3Ct%3C365

So sometime before 200 days from now, COVID-19 should have peaked in the US. Taking the derivative with respect to time, we see there will be a period of about two months when the number of new infections per day will be super high:

US infected per day vs time

US infected per day vs time (simple COVID-19 model) link

This compares fairly well with the peak of deaths for Spanish Flu in the US:

(Thanks again Wikipedia:

We can try overlaying these, and we see that the width of the peak of infections is fairly similar to the width of the peak of deaths from Spanish Flu in the US.

About two months of chaos, potentially. And we have about 5-6 months until this peak.

My model is pretty terrible. A virus doesn’t really have a carrying capacity in the same way… But it does seem to have pretty similar characteristics. I know almost nothing about virus modeling, this is COMPLETELY an amateur, toy model. A guess. There are professionals (like the CDC and the WHO) who do this for a living and you should listen to them, not me. Also, obligatory relevant XKCD webcomic:

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SpaceX is great. But Mars needs more than SpaceX.

With the death of Mars One, there are no high-profile companies looking to settle Mars besides SpaceX.

Mars settlement future is currently single-string. Reliant on a single company. What can we do to change that?

Am I missing someone?

On a second note, I’m really missing XCOR. They had something special. SpaceX is doing very well. Has the right architecture for launch (reusability) and wants humans space settlement. And they have a drive to get it done quickly and execute. Blue Origin has only the first two (right architecture and wanting settlement), although hopefully the others will follow… someday?
XCOR had that (although their execution was well beyond concept phase, it did end up lacking a bit). They unfortunately did not have the financial backing of the other two. But they had something more, that’s kind of special: a sort of egalitarian sensibility. They were often fairly right-libertarian in spoken philosophy (as was common among early New Space companies), but they weren’t founded by charismatic billionaires or near-billionaires and so were more worker-focused. They offered free space rides (as part of the shakedown process for Lynx, as I understand it) to all their employees who wished it. That is something special.

So even beyond Mars, we basically have just two companies with the right mix of backing, vision, execution, and technology, and only one is really executing right now (Virgin Galactic seems too small right now… and with the split, seems less likely to be pursuing orbital anytime soon). It’d really be nice if we had a third or a fourth, particularly if they had an XCOR-like egalitarian esprit de corps. Perhaps Musk could eventually be persuaded to transition SpaceX in that direction? Or Bezos/Blue? (I wouldn’t hold my breath for either, but it is a possibility… You can’t have Musk’s democracy on Mars without, you know, democracy… but power is seductive.)

Additionally, I have some ideas for space commerce that require the ability to launch one or two people to Earth orbit (with recovery) for less than a million dollars (ideally <$100k). But on a dedicated launch. XCOR had that, see here:



…but neither SpaceX nor Blue appear to be offering anything close to that now or in the future.

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2019 Goff Family Pictures

My friends and neighbors the Buies helped us take some family pictures last Saturday at an old abandoned barn over by Waneka Lake. It’s been a while since I’ve posted family pictures, so here are a few of my favorites:

2019 Family Picture #1
Family Picture #2
The Pip
Jonny Man
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Capstone Project

I am considering sponsoring a capstone project at Florida Polytechnic this year. I believe I have a compensating nozzle that could be checked out within the two semesters the project would last. I had an intern from the school this last summer to work on remote control and robotics for small construction equipment. If I can get them to move on hardware, we should have cold flow tested before Christmas.

If Verification of compensation with cold flow is done, does anyone have a connection with hot fire testing capability that could be done at little or no cost? If so, what sizes and what propellants would be allowable?

I have lost touch with the people that I would have asked a decade ago. And several of the companies they were associated with are gone.

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On Avoiding Some of the Mistakes of Apollo

Today is the 50th anniversary of the Apollo 11 moon landing. With a blog named Selenian Boondocks, I figured it probably made sense for me to say something. Earlier this year, thanks to some good advice from several friends, I took my boys to watch the Apollo 11 movie while it was still available in IMAX theaters. That movie was powerful, and really for the first time in my life helped me really connect with that historic feat. But on reflecting today about the Apollo 11 landings, I can’t help but feel somewhat depressed. NASA may have gone to the Moon 50 years ago, but we haven’t been back in over 46 years–longer than I, or most living Americans have been alive1. While NASA is currently in the planning stages of trying to send people back to the Moon, I’d like to see if we can avoid some of the mistakes we made last time.

The Fruits of Apollo2
While the Apollo Program succeeded brilliantly at its narrow goal of “before this decade is out, landing a man on the moon and returning him safely to the Earth,” the way Apollo was carried out practically guaranteed that we wouldn’t be going back for a long time. There has been a lot of commentary on this topic over the past several years, but I’d like to highlight a few of the reasons why I think the Apollo Program ended up not leading to anything more lasting in lunar development:

  • Probably most fundamental, creating a long-term human presence on the Moon was never a goal of the Apollo program. The goals of the Apollo Program were very narrow, and we shouldn’t be surprised that, as I wrote almost a decade and a half ago, your focus determines your path.
  • The Apollo Program was built around expensive, expendable launch and in-space hardware for which NASA was the only user, and for which there weren’t really many other real applications. With an expendable architecture for which NASA is the only customer, NASA either had to pay to keep the assembly lines open or lose the capability. And because keeping those assembly lines had required such a big surge in NASA funding earlier, that funding surge became increasingly hard to justify in the face of other fiscal pressures.
  • The Apollo Program, as John Marburger put it, did almost nothing to “build a lasting infrastructure to reduce the expense and risk of future operations.”

Additionally, while Apollo dramatically advanced the state of the art in human spaceflight in countless areas, it has also left us saddled with many negative effects we’re still feeling to this day:

  • A key part of politically selling Apollo the first time, was setting up NASA centers throughout the Southern United States. As I understand it, Johnson sold Apollo partially as a way to help bring high-paying, high-tech aerospace jobs to the South, which in many areas was still not very industrialized. That we’re still paying for that Faustian bargain today is obvious given how much NASA human spaceflight policy over the past decade continues driven by parochial interests from legislators in Alabama, Texas, Mississippi, and Florida.
  • One aspect of that has been the Apollo “standing army” of contractors. After Apollo ended, NASA’s shuttle program was partially driven by finding ways to maintain as much of the Apollo workforce as possible, and that has continued on through ISS, Constellation, and now SLS/Orion. I can empathize with the desire to not let good people go when you have them, but this desire to keep the team together in perpetuity is still distorting our human spaceflight program 50yrs later.
  • The processes behind how NASA approaches human spaceflight were developed in an environment of a “waste anything but time” budgets. While those processes might be an appropriate fit for Apollo-level budgets, they pretty much make it impossible for NASA to do anything in human spaceflight for less than $1B.

In some ways, in spite of how amazing the Apollo Program was, and how many advances it made to the state of the art of human spaceflight, I think it is reasonable to wonder if we wouldn’t be further along in our exploration and economic development of the solar system had Kennedy not made the Moon shot goal in 1961.

We can’t change the past, but I’d at least like to suggest a few ideas for how to hopefully avoid repeating the same mistakes this time around.

Suggestions on How To Avoid An Apollo Redux
Here are a short, non-exhaustive list of ideas for things we could do differently this time, to avoid repeating the same mistakes:

  • Leverage Multi-User Systems as Much as Possible: We may be politically stuck with SLS for the foreseeable future, but that doesn’t mean we can’t try to design an architecture that leverages, as much as possible, vehicles that have other customers outside of the lunar program. The obvious example being launch — if NASA can design their architecture to take maximum advantage of commercial launchers used for commercial, DoD, and non-human spaceflight NASA missions, that means that even if NASA had to pause lunar missions for some reason, the launch portion of that transportation system wouldn’t go away. I think people don’t realize how much Von Braun would’ve loved to have today’s commercial launch industry when he was trying to do Apollo3.
  • Avoid Single-Source Solutions as Much as Possible: Like with COTS and Commercial Crew, there are real benefits to having more than one potential provider for systems. Tying cislunar transportation to one launcher, one individual, one launch site, etc. makes things unnecessarily brittle–and I don’t just mean SLS here. I have many friends who verge on a “we should just give Elon all the moneys” attitude, but an open architecture that fosters competition, and provides redundancy is good.
  • Maximize Reusability From Day One: I know a lot of people who think that we should focus on getting a basic capability as soon as possible, and save bells and whistles like reuse for later. But I’m not sure this logic is as wise as it sounds on the surface. An expendable architecture is likely going to be a lot more expensive, and requires a lot of ongoing funding to keep production lines open or the capability goes away. It’s harder to cancel a capability when you’re talking reusable systems that don’t take a huge amount of money to keep alive when you’re not actively using them. Also, reuse fundamentally requires refueling, which creates a natural market for ISRU–it’s a lot easier to sell ISRU when vehicles are designed for refueling, and you just have to make the case that you can better serve existing in-space refueling customers. In the long-term, in-space reuse of transportation elements is critical to lowering the cost of cislunar trade enough to pull the Moon into humanity’s economic sphere, and I think we’d be wise to start incorporating reuse as early as possible in the program.
  • Create Infrastructure to Reduce the Expense and Risk of Future Operations: This one is a little more contentious, and could easily use its own blog series, but I think that creating and maintaining on-orbit space logistics capabilities can be a key part of avoiding the mistakes of Apollo. Having a modest facility4in lunar orbit both makes refueling of reusable elements simpler, but also may make surface operations safer by providing much closer search and rescue options. Avoiding overdoing the infrastructure prematurely is a delicate balance, but if done right, such a facility also provides something that doesn’t instantly go away if funding gets throttled back.
  • Maybe Try Settlement From the Start? If a lasting human presence is important, it might be worth deliberately accelerating that process using something like a Lunar One-Way To Stay (for a while) architecture. Having early lunar explorers/settlers stay for deliberately longer duration than the typically proposed days/weeks long missions can dramatically improve the amount you can do on the surface for a given transportation budget, probably would make it a lot easier to get ISRU debugged and up to scale, and forces you to build lasting surface infrastructure a lot sooner.

There is probably a lot more that I could say on the topic, but I’ll save that for future blog posts.

I’d like to end with some more excerpts from John Marburger’s speech from about a decade ago about how we need to adjust our approach to human spaceflight. His comments have aged pretty well in my opinion:

If we are serious about this, then our objective must be more than a disconnected series of missions, each conducted at huge expense and risk, and none building a lasting infrastructure to reduce the expense and risk of future operations. If we are serious, we will build capability, not just on the ground but in space. And our objective must be to make the use of space for human purposes a routine function.

If the architecture of the exploration phase is not crafted with sustainability in mind, we will look back on a century or more of huge expenditures with nothing more to show for them than a litter of ritual monuments scattered across the planets and their moons.

OSTP Director John Marburger at the Goddard Memorial Symposium, March 7th 2008
Posted in Commercial Space, COTS, Lunar Commerce, Lunar Exploration and Development, Propellant Depots, Space Development, Space Exploration, Space Policy, Space Settlement | 21 Comments

Initial BFR (Starship) is not much more powerful than Falcon Heavy

In 2016 when Elon Musk unveiled ITS, everyone thought it was ridiculous and huge. It dwarfed the Saturn V. People were scratching their heads as to how it could possibly launch from LC-39A as pictured, since the 42 Raptors were to produce 128 MegaNewtons of thrust, almost 4 times the Saturn V. SpaceX had only ever launched the Falcon 9 at that point and just recently had started landing them. But now they’re proposing something 4 times the thrust of Saturn V with 42 engines?? Outrageous! Surely that will put a bunch of buildings in danger, exceed the limits of the pad, and cause major problems on the Space Coast. And who even NEEDS a rocket that big?? And the upper stage is a reusable SSTO! Impossible!

In the time since then, ITS (the Interplanetary Transport System which was, before 2016, known as the MCT, or Mars Colonial Transporter–a name not likely to go over well with those with a recent history of European overlords) became BFR (Big… um, Falcon Rocket) and then finally Starship. It went from 42 Raptor engines of 300 tons of thrust, down to 31 of 170 tons of thrust and now, in a tweet, Musk said first flights of the booster would only have “around 20” Raptors:

Raptor has achieved its 172 ton thrust, and so absent subcooling of the propellant, that’s likely where it will be for the first operational missions (or perhaps slightly less for margin).

172 tons of thrust times 20 Raptors (could be 19, which packs better) is just 34MN, or just shy of Saturn V. And in the meantime, SpaceX has launched 2 Falcon Heavies, the first one a lower thrust pre-block-5 version and the last one a full thrust block 5 variant. Its 27 engines worked fantastically and produce about 23 MN of thrust. SpaceX has also been building and test-firing flight versions of the Raptor engine, even testing integration into a battleship demo vehicle, the Starhopper. The initial BFR (I’m still calling it that) will have less than 50% more thrust than the rockets SpaceX already is launching. And its possible SpaceX may use, say, 18 engines and throttle them down to 80% for reliability reasons. That’s basically the same as Falcon Heavy, has fewer engines, and addresses all those concerns about flame trench size, infrastructure risk, etc. (Although I suspect that SpaceX will operate with higher thrust.)

BFR is now no longer absurdly over-sized at all. That talking point is over. It’s easily within their demonstrated capability. Fewer staging events also helps. And landing the Super Heavy booster may be easier than landing 3 separate cores simultaneously (no one knows right now). They switched from carbon fiber to stainless steel for fabrication, but that’s probably a step in the right direction if you want the vehicle to fly realsoonnow. Hypothetically (with almost balloon tanks), stainless has the same mass fraction as a carbon fiber (which needs design knock-downs for cryogenics and oxygen, particularly with out-of-autoclave processes) and similar to SpaceX’s current aluminum-lithium alloy. In practice, it seems SpaceX is still literally hammering out the manufacturing process. They have a method that seems to work with Starhopper, but the mass fraction is terrible (built literally by a water tower company). It seems almost like Sea Dragon.

But they don’t HAVE to have extremely good mass ratio. The upper stage doesn’t HAVE to have SSTO-like capability, not at first. It just needs enough to get to orbit with significant payload, say 50 tons. Perhaps it just needs 6.5km/s. That’s also about the delta-v needed to go from the Gateway to LLO then to the lunar surface and back (well, that’s about 6.2km/s total… 5.2km/s if you’re aggressive with your burns).

The difference between 6.5 and 9.5km/s when your exhaust velocity is about 3.7km/s is: e^((9.5-6.5)/3.7) = 2.24. So while SpaceX might be able to theoretically do SSTO with extremely good mass fraction, they can knock that down by a factor of about 2.25 (including long-duration equipment) and still accomplish the mission. That means they may be able to use a fairly crude manufacturing and heatshield system and still accomplish the initial goals of Starship. In fact, Elon has also been discussing an expendable upper stage for certain missions. That gives more options for SpaceX to insert Starship into some operational role much earlier than you might think.

It’s no longer pie in the sky (although the capability is also much lower, but perhaps sufficient). Of course, most of the professional spaceflight community hasn’t grokked that yet. We’ll see how long that takes. With Starlink, it took the splendid orbital launch of 60 satellites for anyone to even raise the question about night time visibility of 12,000 LEO satellites, even though the likely operational visibility was perfectly predictable when it was first announced.

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Disabilities as enabling for space travel

So, the other day I listened to a presentation from the FISO (Future In-Space Operations) working group. They have regular online telecons which anyone can listen to and follow along after the fact on their web archive:

It was titled “Preparing to Survive: The Case for Disabled Astronauts and Colonists”

I highly recommend this one as it’s off the beaten path, out of the box, and has some very interesting things I hadn’t considered before.

One of the most fascinating things I learned is:
Some deaf people are complete immune from dizziness from (for example) short-arm centrifuges. That certainly makes artificial gravity easier. Trivial, even.

Another was a more philosophical point. We’re going to bring our humanity with us. We can’t rely on the fighter jock physique. Even if we start that way, injuries can easily happen along the way, so we better be thinking about designing our spaceships and habitats with accessibility in mind. And maybe.. Just maybe… if everyone is blinded from long-duration exposure to microgravity or from smoke or some chemical accident, it might help to have someone on board not reliant on sight. Or at least you should have a spaceship that is still usable without relying on perfect sight. Or if everyone is disoriented on landing on Mars from months in microgravity, having someone immune to dizziness to guide you might also prove useful.

Very thought-provoking talk. I recommend it.

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