Thursday, October 20, 2016

Reddit is distracting

Low post rate here lately has been because I've gotten sucked into reddit's r/spacex forum.

Partly for my own reference, here are links to some comments and submissions I've made:

Single-window round trip of the ITS ship
This was a trial run using Trajectory Optimization Tool to see if it was possible to send an ITS ship to Mars and return it within the same window. Provided you can refuel the ship in about a week and can handle a long (>200 days) return trip, it's definitely possible.

ITS system performance tables for near-Earth space
(public spreadsheet supporting tables)
A table of payload performance values for missions to various locations around the Earth and the Moon, with estimated costs.

ISRU system scaled to fuel one ITS ship per window, pt1
An extrapolation from an ISRU study that outlines the equipment needed to refuel an ITS ship (1950 tons of propellant) in one synod (~780 days). Includes mass estimates and is based on fairly good data. TL;DR is about 101 tons of gear and 20 tons of spares, with another 10-20 tons of spares each trip. The ISRU advantage is 16:1 for the first trip and about 98:1 for the next four trips. If the replacement cost is amortized over ten years then the advantage is 48.5 tons of propellant per ton of equipment.

Discussion of radiation shielding
This is an extension of my thoughts on shielding for large, permanent habitats that require Earthlike radiation levels. The conclusions do not apply for spacecraft in general because most spacecraft proposals cannot support several tons of shielding per square meter of surface area.

Wednesday, September 28, 2016

SpaceX ITS projections

 Now that Elon Musk has released engineering targets for the proposed interplanetary transport system (formerly BFR), there is some meat to work with when looking at possible applications. I'm going to extrapolate, extend and abuse those numbers as thoroughly as I can after the jump.

MCT predictions revisited

 I made a messy post with predictions for the MCT (SpaceX Mars Colonial Transporter, now known as the Interplanetary Transport Ship/System). There is a follow-on series of posts, but this one has the relevant numbers.

 In terms of architecture I did very poorly. The actual ITS is rigid-hulled, passengers travel in  microgravity, life support is ISS-style, and both Mars and Earth arrival is direct aerocapture and propulsive landing. There are a lot of windows. There are no propellant depots anywhere. Oh well... I like parts of my approach better but certainly Musk's approach is less risky up front and less expensive to develop.

 In terms of vehicle performance, I posted numbers for a 12m version and a 15m version. The vehicle will be 12m so I'll use those numbers. I'll compare to the reusable ship profile from Musk's talk.
In short, I didn't do very well. Details after the jump.

Thursday, September 22, 2016

A review of nuclear electric power

 This is a subject that's been stewing for a while now. I often see debates in comment sections over whether or not nuclear electric power is feasible in space. Only rarely do those arguing hold the same assumptions about what nuclear power actually means. As a result, these debates rarely convince anyone of anything beyond the stubborn natures of their opponents.

 The goal of this post is to briefly cover the range of commercial, military and scientific nuclear power systems ranging from a few kilowatts to over a gigawatt. I will follow up the (hopefully) useful background information in a later post with some fanciful projections and my usual call for unlikely investments in space.

 Read on after the break so you can be armed with facts for your next debate thread.

Monday, August 29, 2016

Tools - Tank estimator sheet updated

I discovered and corrected a mistake in my tank estimator spreadsheet. Corrected version is live.
{edit 2016-09-06:}Also added a fill factor and a structural factor for better estimates.{edit}

I also can't find my notes on how the sheet was put together, so I thought I should document the parts that were updated now so I'll know what I am looking at a few years from now.

Before I go into that, I'd like to reference a NASA document (pdf) describing helium ullage tests for the Centaur upper stage. Read it, it's full of retro cool. Their numbers are a tiny fraction (1%) of mine for several reasons: they use ambient temperature helium, assume a gravity-supported temperature gradient (while I assume the helium is pre-chilled to 20 K for hydrogen or 90 K for everything else), rely on vaporization of the liquid hydrogen to maintain pressurization during engine chilldown and assume warm hydrogen from the engine provides pressure during burns. As a result I'd suggest not taking the ullage masses and volumes from my sheet too seriously as my numbers appear to be extremely pessimistic. I've also used some constants that I didn't properly document, something that must have been tricky to calculate with thermal expansion of gases; that whole area of the sheet is probably due for a revisit.

I'll also warn you that my results can be up to 10% heavier when fueled than published masses; there is something I'm not properly considering in the model. Still, if you want a quick and dirty estimate that's probably within 10% and lets you enter most of your own parameters then here you go.

Read on after the break for more details. I even made a diagram.

Thursday, August 25, 2016

Understanding the biological effects of gravity - NASA PubSpace article

 The very first paper I dove into from the new NASA public server covered topics near and dear, primarily the fact that microgravity is not survivable over the long term. There was, shall we say, a very enthusiastic embrace of the term 'omics' but otherwise some very interesting points.

 In a nutshell, we know almost nothing about the effects of any level of pseudogravity (referred to as AG from here on) between microgravity and 1 g. This is important. NASA is considering human missions beyond LEO in less than a decade. We can and should do some kind of testing between now and then, and the only way I see to do that affordably is to launch a dedicated orbiting laboratory.

Read on for more. All costs are in current US dollars and are assumptions based on very little data.

Earthside - NASA to release most sponsored research for free

In keeping with the idea that federally-funded science should be free to access, NASA has started publishing the research they sponsor for free to the public.

The site is hosted by PubMed Central and contains a searchable, indexed set of NASA-sponsored research papers. 865 papers are online as of right now covering a broad range of fields; head over and take a look. The paper count should grow dramatically over the next few months as previously-published work gets submitted.

Friday, August 19, 2016

Earthside - FarmBot

Another entry in the field of farm (or rather garden) automation: FarmBot. This is a project to build and sell devices that automate gardening, from seeding through watering and weeding. They put special effort into open source and free access principles, so this is one to watch. I'm also pleased to see that all plastic parts are printable

Of particular interest is their table of yields. They seem to have taken some very conservative numbers for yield, which is appropriate for projecting the performance of a single-layer soil-based plot under natural light and weather conditions. For example, they estimate about 20 g/m² per day for potatoes while I use 65 g/m² per day; my source is a NASA life support paper where those yields were achieved under controlled atmosphere and lighting conditions. That suggests the usual rule of thumb (hydroponics doubles yields) still holds and that further gains (another 50-100%) can be achieved with precise climate control and artificial light.

If I had the time or money I'd contribute to the project, most probably under the crop data source OpenFarm. It looks like they could use some help to get off the ground.

For my purposes I'd prefer to see the system adapted to handling hydroponic/aeroponic trays on a conveyor system. Each tray would be ID tagged (RFID or visual indicators like QR codes). A growth plan for the tray would be entered, then the system would prepare and fill the appropriate media and seed the tray. Seeded trays would be stored in a germination rack, periodically removed to check for progress and proper moisture. As the plants mature their trays would typically spend 8-12 hours in a dark rack resting, go through a morning check for abnormalities, spend 12-16 hours in a lit rack producing, then go through an evening check. Plants that prefer soil-replacement media would be handled much like the existing system, with periodic spot application of water (frequent) and suppression of weeds (which should be extremely rare). Other types would be mostly self-sufficient in their lit racks, but a visual check twice a day for any deviation would still be most efficient with an automated check station handling trays as fast as it can. Trays would be managed by something similar to a warehouse automation system, minimizing wasted space

If a fairly advanced harvesting attachment were developed for leafy greens then the system could do daily pruning of outer leaves, maintaining plants at an optimal size (limiting shading) and yielding a steady stream of produce. Likewise, if the current X-Y bed were adapted into an X-Z bed (standing vertically) or a free-rolling unit (like a warehouse robot) then the system could be used to monitor, prune and harvest vine crops like tomato, pepper, cucumber and squash that are grown via commercial hydroponic techniques.

Something like this could be trialled on the ISS in a very limited form (though the conversion to microgravity operation may be nontrivial), then later in a larger facility. (private, public? NASA exploration gateway, Bigelow hotel or ESA moon village? Maybe even here on Earth at McMurdo or other arctic/antarctic bases?) The medium-term goal would be automating food production on Mars and other destinations of interest. In the long term, new units on Mars, Luna or in space would be built out of locally-sourced aluminum and plastic (via existing 3d printing technology) plus microcontrollers shipped from Earth.

Tuesday, July 12, 2016

What about the rest of the LCROSS results?

 A lot of people were excited when LCROSS returned direct evidence of water and water ice on the Moon six years ago, providing strong support for the theory of cold trap volatiles. I've seen numerous posts discussing ISRU and using that result (plus other data) as evidence of the presence of water.
 What I haven't seen is any mention of the other chemicals that were detected: carbon monoxide, mercury (!) and elemental hydrogen. Water was estimated to make up 5.6% of the crater soil with 155kg detected, meaning mercury made up another 3.5 to 4% with about 100kg detected (at larger uncertainty). Carbon monoxide represented hundreds of kilograms, meaning perhaps 4 to 8%.

{{note: Hop pointed out in comments that this paper was corrected. The reported values were overestimated by a factor of 5.5 or so, meaning these volatiles are actually perhaps 0.5-1% by mass each.}}

 Think about that for a minute... Carbon monoxide is probably more abundant in the cold traps than water, at least in the traps cold enough to freeze CO. Everything I've read suggests that the Moon is almost carbon-free and there is no hope of producing hydrocarbon propellants like methane there. At the same time, millions of tons of water are proposed to exist and to be usable for producing hydrolox propellant.

 I'm sensing a disconnect here.

 The evidence shows that both compounds are present in staggering abundance. I see no reason why we can't make methane using these resources, which in turn means there is no need for a deep cryogenic hydrogen-based lunar infrastructure. The same methane engines that will be used between here and Mars will be used on and around the Moon.

 Propellant from ISRU mining operations at the lunar poles will fuel all of the proposed chemical systems. For that matter, very simple monoxide-oxygen rocket systems work just fine (albeit at low Isp) and could be used in early exploration if methane or H2 production is not yet online. Even later on, if fuel production is constrained by available power then monoxide rockets could be used to deliver higher-value fuel to an EML2 depot.

 In addition, mercury has some very useful properties. It's a liquid at standard conditions, easy to ionize, stable, dense and with a high atomic mass. These are traits suitable for electric engine propellant. It's toxic, sure, but not as bad as hydrazine. It may not be as efficient a propellant as xenon or lithium but it's plentiful and would be accumulated anyway as a byproduct of water purification. May as well put it to use. (Here's an example engine from a family in the 2500-3600s Isp range.) There are engineering difficulties: it tends to foul the spacecraft and it's hard to feed precisely, but we built hardware in the 70's that withstood over ten thousand hours of operation. These are solvable problems.

 Other uses include as radiation shielding, for extracting native metals (via amalgamation followed by electrorefining), in fluorescent or mercury discharge lamps (including germicidal lamps) and as an electrode used in several chemical processes such as the chloralkali process for splitting sodium chloride.

Wednesday, July 6, 2016

Colonize Mars - part 3, a sweet ride

 We've discussed the various hazards and risks in a journey to Mars and how to address them. We've also discussed a super-heavy lift rocket design that might be used for this mission. Up next is the transit habitat, in as much detail as I can muster. The post after this will explore the other parts of a complete transportation system; this one is only concerned with the passenger transport.

 One thing I didn't address in part 2 was why the vessel provides the entire food supply for passengers rather than using some stored food. After all, ECLSS-style supplies for a trip to Mars are only about 1.3 tons per person while a complete food supply takes around 3 tons of equipment per person and a whole lot more power. The reason is safety. If the vessel arrives at Mars only to find that all the landers have been destroyed then the passengers can wait in orbit until the next return window (or as long as necessary) and get back to Earth safely.

 At any rate, here are the concise results:

Habitat Module (2 per vessel)

HeightVolume, m³CrewMass, t(dry)tons per
6 meters            8,380 97103459210.66
8 meters          11,140 13113017949.93
12 meters          16,660 196181811809.28

Vehicle Configurations - Chemical

Configuration Crew Power (kW) Dry Mass (Fueled) Thrust (MN)
Short (6m) 194                1,583           2,221          5,842 5.74
Tall (8m) 262                2,138           2,796          7,354 7.22
Grande (12m) 392                3,199           3,909       10,281 10.1

Vehicle Configurations - Ion

Configuration Crew Power (MW) Dry Mass (Fueled) Thrust (N)
Short (6m) 194                61.11           2,306          3,114 3115
Tall (8m) 262                77.06           2,903          3,920 3921
Grande (12m) 392              107.95           4,059          5,480 5481

Details after the jump.

Friday, July 1, 2016

Colonize Mars - part 2, surviving the trip

 Proceeding along the path to colonizing Mars. Part 1 described two possible super-heavy lift rockets constructed on paper with mostly reasonable assumptions. Part 2 will cover the transit habitat.

 I've already discussed the hazards involved in a manned trip to Mars in previous posts, but the two most important factors are radiation and microgravity. Less critical but still important are life support, food supplies, medical service, psychological health, maintenance and cost.

Read on after the break to see how these challenges can be addressed.

Thursday, June 30, 2016

Colonize Mars - part 1, a really big rocket (updated 12 July with corrections)

 I had a burning vision of a spacecraft in my head that simply demanded to be written down. In a rush I threw together a bulky, dense post that isn't terribly useful for me so it must be opaque and meandering for anyone else reading. This is not the direction I want to go.

 The solution is to break the whole project into smaller pieces, go deeper into the details, show my work and hopefully try to put some graphics together. We'll see how well it goes.

{{I made a pretty serious mistake in the initial version of this post, one that led to inflated payload capacity. This has since been corrected throughout; I've also removed some commentary that is no longer supported by the numbers.}}

 The first thing you need for a giant transit habitat is a giant rocket. I want a single module to be big enough for Mars gravity at no more than 4 rpm, which works out to 43 meters in diameter. That means a massively large rocket is needed to loft this module in one piece.

 Working on rumor, innuendo, published interviews and Wikipedia it is clear that Elon Musk plans to build such a giant rocket. Nobody knows what the exact size will be, but 12 and 15 meters have been mentioned.

Let's make a bunch of wild assumptions after the jump.

{{Warringer pointed out a web tool for evaluating launcher payloads in the comments; worth a look.}}

If you don't care about the process, the results of those assumptions are LEO payloads of 620 tons for the 12-meter rocket and 1,200 tons for the 15-meter rocket.

Sunday, June 26, 2016

What might Musk's MCT look like?

Here is an entirely speculative look at Elon Musk's proposed Mars Colonial Transporter.
There are no details available, so I'll simply be proposing some options for a vehicle that can carry 100+ people to Mars. I will be making plenty of assumptions and treating this like an entry in a high-level design challenge.

For background, Musk's stated goal is to build a colony on Mars that will reach one million people b̶y̶ ̶2̶1̶0̶0̶ at some point, probably 3000.The point of SpaceX is to be a testbed and funding mechanism for this colonization effort. As unlikely as this sounds, I don't see any reason why it can't be accomplished given sufficient cash.

Details after the break.
(This post was updated with a better estimate of booster size and payload)
((I'm not satisfied with the content; this post is a giant blob without enough detail. I plan to break this into several posts with a deeper look and more visibility into how I arrive at these numbers. Thanks for your patience.))

Monday, June 13, 2016

Microwave sintering - what's the big deal?

It's hard to get through a post or paper on lunar exploration these days without hearing about microwave sintering. Let's take a look at what it is and why so many people are excited about it.

In short, the unique properties of lunar soil make microwave heating very efficient. Strong concrete-like ceramic blocks can be made without water or other materials, just regolith. No material needs means very low mass shipped to the surface for building structures. This takes either a lot of power or a lot of patience.

Details after the break.

Tuesday, May 24, 2016

Minimalist food supply - synthetic amino acids

 Plants are not a particularly efficient source of protein. They tend to be better at producing carbohydrates. As a result, vegetarian diets often focus on a few high-nitrogen plants like beans, soy and peanuts.

 I tend to explore food systems that are familiar, but let's take a minimalist approach and see where it leads. Instead of deriving protein from plant sources directly, what if we use microorganisms to produce amino acids in bioreactors using plant starch as input? This is like that sci-fi staple 'vat meat', but with neither texture nor flavor. Still, amino acids can be stored for years (possibly decades) if powdered and sealed.

As with all my posts, this article is based largely on internet research. I am not a process biologist. I've included sources where possible, but these results should be considered preliminary at best.

Short results: vat-grown amino acids can be yours for 4-6m³ per person.
That includes vats, supporting equipment, hydroponic space and waste treatment.
You will still need to provide bulk calories and other nutrients.

More after the break.

Monday, March 28, 2016

Interorbital Exchange - Economically competitive development through an international authority

I've recently stumbled across the NexGen Evolvable Lunar Architecture study via NSS.
This is a NASA-funded study examining how a lunar propellant facility could be developed via public-private partnership. Definitely worth reading.

 I'd like to explore their proposal for an international lunar authority to manage access to lunar resources. This really fills in the blanks with regard to operational authority and funding sources without necessarily requiring one particular architecture or approach to the actual propellant production.

Discussion after the jump.

Friday, March 11, 2016

A (much) deeper look at electric propulsion

 I need to continue on the topic of electric propulsion. The previous post was a lot of words but not a lot of meat. I felt it was too weak to stand alone, particularly as a part of this series where I am trying to focus on a realistic near-term plan for cargo transport. If you are interested in more background information I'd start with the Wikipedia page on electric propulsion and follow up with a look at the Atomic Rockets engine page. Another good look in the context of interplanetary travel is this paper (Hellin), while a deep look at relevant equations can be had in this paper (Keaton).

One interesting result is a rule of thumb to find required thrust given average acceleration. Google failed me on finding an exact solution, but it looks like there is a simple approach that is within 1% of the target value.

I eventually settled on a design massing 33.4 tons, 1.6 MW solar-electric, Isp 6,000 and 40 N thrust using PIT thrusters with water propellant.

More after the break.

Thursday, March 10, 2016

lettuce - first run taste test

The plants sprang back to life after a day with water. I've let them grow for a few more days, but things aren't really moving much at this point due to mutual shading and limited vertical space.

I pulled a few leaves and had a few tastes.
Still alive and no unfortunate bathroom incidents, so whatever colonized the tray must have been benign or easy to wash off.

Leaves averaged 18cm long and 12cm wide at the widest, 5 grams fresh weight. I estimate about 200 grams of leaves could be harvested; far less than I hoped but not bad considering their stress history. I'll collect them all soon and note the total edible mass.

 - Sap was thin, milky only near the base of the leaf. It had a fairly strong 'bitter lettuce' smell, which is typical for freshly-picked leaves.
 - The leaves were slightly limp for a number of reasons (water stress, heat stress, competition, etc.) but still managed to stay horizontal with minimal drooping.
 - Several had small brown 'burn' spots on the edges where the leaves had rested against the nutrient-encrusted clay puffs, but otherwise every leaf was perfect.
 - The flavor at the outside was mild, sweet but with enough bitter undertone to avoid blandness. Texture was much like the outer wrap leaves of head lettuce; I happen to like those so I thought the result was good.
 - Flavor at the stem was stronger, but still sweet. Usually I find leaf lettuce to be overpoweringly bitter at the stem base, so that was a nice surprise. All of the stem and vein structures were crisp.
 - No 'aftertaste' or unpleasant flavor undertones after eating.

Overall I am surprised at how tasty the results were. I managed to mess up the process in several different ways but the plants survived and even thrived.
The rest of the family is suspicious, so I might be the only one eating fresh salad for the next day or two. We'll see.

Not much to add beyond what was in my image post, other than that you should definitely try this at home. Even the mistakes seem to work out well; can't wait to see how a well-designed crop will turn out next time.

Wednesday, March 2, 2016

Interorbital Exchange - part 7, electric vehicles

All previous posts described all-chemical systems that could be built and operated profitably in the near term. This one focuses on electrical propulsion systems.

The defining features of most electric propulsion:
 - High efficiency (high Isp)
 - Low thrust
 - High power requirements
 - Long trip times
 - Long operating life

 I chose a specific paper (Frisbee, Mikellides) to examine since the authors thoughtfully included most of the interesting parameters for a reusable NEP Mars cargo tug. I don't really dive into how to calculate this for yourself because the problem is quite difficult without modeling software.

It all comes down to the details; the question of NEP vs. SEP vs. Chemical depends on the specific mission goals and technologies used.

The summary:
23 tons dry mass for a nuclear-electric tug of ~6 MW thermal / 1.2 MW electric
64 tons cargo capacity from low Earth orbit to Phobos-Mars orbit
Just under 40 tons of water propellant for the outbound trip and another 7.2 tons acquired at Phobos for the return
2.2 years outbound, slightly less inbound
Two round trips between thruster refits, five round trips between reactor refits

More after the break.

Tuesday, March 1, 2016

lettuce - first run

So... working up a website for this turns out to be more work than I have time to give at the moment.
Instead, here's some albums of pictures I threw together on photobucket.

Two shots of the LED tape, plus one of the bloomhouse. I used velcro plant ties to attach the tape to the shelf above. Not optimal, but it was fast and I didn't need to break out the soldering iron.

More after the break.

Tuesday, February 23, 2016

Home - lettuce update coming soon

I haven't posted an update on my little experiment in quite a while due to real life intervening. This post is not that update, only a promise that I will make the results available soon.

I've been taking daily pictures of five lettuce plants (black-seeded Simpson, a common green leaf type). Things did not go smoothly, so I have plenty of examples of common problems to discuss. Unfortunately the set of images is quite large and I'm concerned about making an enormously huge post. I'll probably use photobucket or another image host for storage and work up a simple web page to serve the results, with commentary posted here and crosslinked to image gallery pages.

Thanks for your patience.

Wednesday, February 10, 2016

Interorbital Exchange - part 6, cargo tug explained

 Throughout the series I referred several times to a reference design for a cargo tug. That was put together using what might kindly be described as rectal numbers, assuming a tankage factor of 6% and 1.5 tons of remaining structure.

 I've gone back and run a preliminary estimation using a more detailed approach. In the process I created a spreadsheet that will allow users to enter their own values if desired. Errors are likely so use at your own risk; make a copy if you want to make changes.

 My little tug ended up just under 5 tons dry mass, 6.5kW power, 62 tons fuel capacity. The initial estimate was pretty close.

Details after the jump.

Monday, February 8, 2016

Semiconductor manufacturing - part 4, complex parts

Continuing the series, here is a look at more complex devices like flash memory and microprocessors.

 The takeaway is that with minimal additional hardware and an ongoing focus on recycling all reagents, we can advance from LEDs to full microprocessors and other products of high complexity. Realistically this would require a team of engineers to develop and maintain in addition to a human presence for operation and maintenance.

Details after the break.
(part 1) (part 2) (part 3)

Interorbital Exchange - part 5, other destinations

Continuing the series, here is a look at other destinations in the solar system. I am still assuming the use of chemical propulsion, so this limits us to locations inside the orbit of Jupiter more or less. I will examine launches from EML1/2 and from Mars orbit. Most transit data is from Project Rho, so these values are somewhat pessimistic (as explained in the link).

I'll cover Venus, Apollo/Aten objects and Main Belt objects after the jump.

Friday, February 5, 2016

Semiconductor manufacturing - part 3, LEDs

Continuing the series, here is a look at light-emitting diodes and how to make them.

LEDs fundamentally are like photovoltaic cells operated in reverse: a current is applied and light is produced instead of the other way around. This is the first device in the series that requires photoresist and etching.

 The takeaway here is that LED manufacturing is only modestly more challenging than single-junction monosilicon PV cells. Equipment for spin coating, making masks, a stepper and high-intensity light source are all required. Also, LEDs require potting (encasing in plastic) to function properly, so a supply of suitable plastic must also be available. Otherwise all the equipment for CVD, making ingots, saws, polishers, acid etch, etc. are used in much the same way and can be used in the same vacuum chamber.

Details after the jump.
(part 1) (part 2) (part 4)

Semiconductor manufacturing - part 2, solar panels

 This section will discuss perhaps the simplest of semiconductor products, solar photovoltaic cells. I'm not going to dive too deeply into the physics, but rather focus on the mechanics of making these devices.

 First we will look at bandgap and why it matters. Then I'll start with thin films, cover single wafers then discuss multi-junction cells.

 I think the takeaway here is that semiconductor manufacturing uses dangerous chemicals, high-voltage devices, vacuum and heat. This is not an activity that should be done in a habitat. A manufacturing facility for these devices should be physically separated from the habitat and equipped with isolated life support systems. Even so, basic devices are within reach of simple equipment that does not rely on gravity to function. Some types of panels can be manufactured with equipment no more advanced than the refining equipment used elsewhere in space as a prerequisite.

 Details after the jump.
(part 1) (part 3) (part 4)

Semiconductor manufacturing - part 1, materials

This series will be a roundup of the various tools and techniques used to produce semiconductor devices. I will try to address them in order of increasing complexity of the product, starting with solar photovoltaic modules and ending with microprocessors. This first post covers the raw materials used for all later steps.

First and most important, all materials used must be of very high purity. Electronics-grade silicon can have no more than 1 part per billion of impurities. Silicon meant for low-efficiency polycrystalline solar panels can be less pure, though still at least 99% (with more 'nines' better).

Second, the material has to be made into a useful form. Several important types (particularly silicon and germanium) are monocrystalline, meaning a single large crystal is cut into slices (wafers) and further processed. A few can be polycrystalline slices which are processed similarly to monocrystalline wafers. Other types are thin film, meaning a thin layer of the semiconductor is grown on top of some other material.

Third, useful semiconductors are formed when very small amounts of the base material are replaced by other materials (dopants). In general other elements are added to change the electrical properties of the base, but some dopants are used to make the base stronger or alter its crystalline structure.

Details after the jump.
(part 2) (part 3) (part 4)

Tuesday, February 2, 2016

Interorbital Exchange - part 4, mining metals

Continuing the series, this is a look at what to do next after water mining becomes routine and a network of fuel transfers is available. This post assumes that Lunar water mining is operational, but that material from Mars is not guaranteed.

 While harvesting ice is fairly straightforward and something I expect we can automate, surveying mineral resources for efficient mining is altogether different. It would still be possible to do without humans on-site but I believe sending experts would be more effective. A program of manned exploration alongside current state of the art automation would expand our knowledge of the Moon and our experience with autonomous mining. Still, the general program I will describe could be done with or without people on site.
 Actually making use of these materials will require human hands. We do not have the automation technology available to perform complex assembly, particularly in a challenging environment. Individual steps will be automated as much as feasible, but in the near term most manufacturing processes will require a crew.

Details after the jump.

Monday, February 1, 2016

Interorbital Exchange - part 3, Mars crew

Continuing the theme, here is a look at how to transport human crew to and from Mars.

The Hohmann transfer orbit requires the least fuel but takes a long time. In order to minimize radiation exposure and overall risk, 180 days or less is the preferred travel time. Getting to Mars faster than the minimum energy path requires a lot more fuel. Accelerating a heavy habitat and its systems to high speed is expensive, but there is a solution. A special set of orbits allow us to boost the habitat up to speed one time and have that vessel pass by Mars and the Earth on a schedule, with only minor course corrections.
 These are called cycler orbits, popularized by Dr. Buzz Aldrin. A permanent habitat is built and launched into the chosen cycler orbit. This habitat will merrily roll around the solar system with periodic close visits to Earth and Mars. While much of its time is spent far away from anything useful, each cycler orbit has a 'short leg', a portion of its trajectory that passes one planet and then the other after a short time. The idea is that you only need to burn fuel for the habitat once; after that new crews and their food can be boosted to the cycler as it rolls by on future transit opportunities.

Summary: I've continued my Mars example to its conclusion of a bit under $18 billion for three manned missions (6 crew each) and about $3.1 billion for each additional trip (crew of 6, 12, 12, 18, 18, etc.).
The transit habitats implemented as cyclers offer an opportunity to to ISS-style science for about $53 million per crewmember-year during buildup and less than $10 million per year steady-state. Total program cost would be about $22.5 billion, including $6.25 billion covered under the Mars program.

Full details after the break.

Interorbital Exchange - part 2, Mars cargo

 This entry covers near-term resources on and near Mars and how they might be transported.
I assume the propellant network described in part 1 has been built, or at least that lunar propellant is available at EML1.

Details after the break.

The short version of the below is that using hardware similar (or identical) to the part 1 Lunar infrastructure, cargo to and from Mars becomes relatively cheap.
A set of three NASA-reference mars missions could have their cargo requirements filled for a total of $11.4 billion (including fuel).
Nitrogen and argon from Mars could be as cheap as $400 per kg at EML1.

Interorbital Exchange - part 1, cis-lunar space

Part of the reason for this blog's existence is to explore how we can get from where we are now to a permanent presence in space. I will explore that theme over a series of posts, with a focus on ISRU.

This entry covers cis-lunar space. The topic of lunar mining and fuel supply has a rich field of information available and I cannot claim to know all of it, but hopefully this will show how we can begin to harvest most of our propellant instead of shipping it from Earth.

 More after the jump. First section is background information and basic design, second section is a worked example.
The tl;dr takeaway is that we could be pumping out 289 tons of propellant to LEO every year for a system startup cost as low as $2.7 billion.

Tuesday, January 26, 2016

Early Days - economics of private space services

 Today we are in a period of rapidly expanding private space services. There has been a long tradition of private satellite manufacture and related services, but given the roster of launch vehicles that sector saw limited growth and a limited customer base. Now, with more affordable launch options and the ability to launch very small satellites the potential customer base has expanded dramatically. Moving forward, space services must diversify by first focusing on services that provide a concrete benefit Earthside.
 I see several areas with profit potential, in various stages of readiness: in-space refueling, satellite maintenance, orbital transportation, beamed power, adventure tourism / private spaceflight and resource harvesting. Let's take a look at each of these after the jump. Note that launch services are not included here; I see that as a current and successful market and as a necessary step before any of these areas could become profitable.

Tuesday, January 19, 2016

Home - first sprouts

It took a few days to get motivated enough to plant, but it's done. I planted five lettuce seeds and five spinach seeds (from no-name grocery store seed packets), each in their own 1" rockwool plug. The seeds are about half an inch above water level, though the rockwool does an excellent job of wicking moisture up. I am using the lettuce nutrient pack from five-gallon-bucket hydro.

The spinach has not sprouted yet, but I had lettuce sprouts by day 3 (fully a week before the package indicated). Pics after the jump.

Monday, January 11, 2016

Home - Experimenting with soilless growing

I've been accumulating parts and now I finally have enough to start growing food indoors.
My goals are to learn more about hydroponics and growing plants without soil, to validate some assumptions that support my designs and of course to grow some food that I can eat.

I will post updates periodically. I may even bother to take pictures, but no promises. As of right now I am just under $200 into the project and hoping to get a variety of crops for no more than another $100. I could have bought a lot of vegetables at the store for that much cash, so hopefully this works out.

Read on for details.

My first attempt (strawberries) failed due to operator error. (Fungus caused by poor drainage.)

Friday, January 8, 2016

Chemical accident near Boston

Multiple sources are reporting an explosion at a Dow Chemical facility in North Andover. Four or five people have been injured (reports are unclear).
(Thanks to Derek Lowe / In The Pipeline for the link.)

The involved chemical was trimethylaluminum or TMA. This is related to triethylaluminum (TEA) and methylaluminoxane (MAO), chemicals I've suggested for use in preparing catalysts for making plastic. They find uses in semiconductor processing (LED manufacturing for example) and as pyrophoric igniters for rocket engines.

These chemicals are extremely dangerous.

In order to use compounds like this in space, particularly in manufacturing, we must ensure that adequate safeguards are in place to protect lives and structures in case of accidents. That means following reasonable handling processes and designing spaces for activities like this that will fail independently.

I hope those affected recover. For the rest of us, take a minute to think about what we handle in our daily life, whether at home or at work. That might be as simple as a car. Recognize that our actions affect others and resolve to use due caution. If you know of a dangerous situation outside your control, tell someone.

Wednesday, January 6, 2016

Back (from outer space)

I'm back from holiday laziness and failure to post. Also have a certain song stuck in my head now...

The big news lately is the successful return of a Falcon rocket first stage to Earth. Congratulations to the team at SpaceX and all those who were involved.

The question is, who wants to be the first to risk their precious payload on that rocket?

I have a suggestion: SpaceX should absorb the cost up front and launch their own payload. The launch itself should in theory only cost them a few million dollars. As for what to launch, I'd say a big tank of water. It would have been nice if they had a payload like this waiting in the wings so they could turn the vehicle around and launch again quickly, but that is still an option for a future flight.