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.