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.