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.