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.