You are not logged in.
There has been a question that has been bugging me for quite a while. I've been working quite a bit this semester with ALS NSCORT on advanced regenerative life support and I'm beginning to get the impression that it is a bit of a Rube Goldberg. The goal, is obviously to minimize equivalent system mass (ESM) but all the systems I am aware of call for the central use of plants for gas exchange and regeneration as well as food. This looks good on the surface but assuming the NASA BVAD values of 30 square meters of plant growth per person for a crew of six that require almost 20 megawatts of power just for artificial lighting! Assuming that the current generation of LED lighting systems proves effective that number could be reduced by an order of magnitude but we are still talking about the lion’s share of energy produced from a ships reactor(s). What I have been wondering is would it be more efficient from an ESM standpoint to use the availability of power in space for advanced propulsion option to cut down on trip time thus decreasing the consumables requirement on the outbound and inbound leg. Once on the surface having fully closed loop life support is not so much an issue since you can extract carbon, oxygen, nitrogen, argon, and to a certain degree water. Also a variety of volatiles given proper planning could be extracted from the surface including water.
That being said I know that ALS will be need for longer missions and eventually for permanent installations and bases on mars, it’s just I’m not sure it makes sense on the inbound and outbound flight, and I think the focus should not be focused on achieving full systems closure, but rather a significant fraction of closure while taking advantage or the resources at hand. It seems overly complicated to me to land on the Martian surface, swimming in a veritable sea of Carbon Dioxide and being terribly concerned about carbon and oxygen recycling within the craft.
So what do you think is ALS or Advance Nuclear Electric propulsion the best use of nuclear power in space?
Does anyone have any idea what the size of the crew rated Prometheus reactor will be? I have been told they are aiming at 200-500 kilowatts am advised that is a very preliminary number.
Offline
The advantage of NEP (to Mars) is not that it would save time, but rather that it would require less propellant. In fact, NEP Mars mission ideas generally take longer than chemical missions.
I agree that growing plants with artificial lighting is a very expensive proposition. It would probably be a lot easier to just bring lots of freeze-dried rations rather than trying to grow food in space.
Most studies that I have seen of manned missions to Mars using NEP assume a reactor in the 5-20 MW range. I don't know much about Prometheus, but 200-500 kw seems low for a manned interplanetary mission.
Offline
There are "long term" concept plans for a Megawatt-scale reactor based on the current SAFE arcitecture (which BTW they are about ready to test a 30kWt reactor), but that is a ways down the road, and would be pretty big & heavy.
The only other prospect for producing that kind of energy is to switch to a rather esoteric reactor concept, the Vapor Core Nuclear Reactor; in the VCR the uranium fuel itself mixed with Fluorine, Potassium, and maybe Sodium are actually vaporized and placed under pressure. The reactor is simply a chaimber lined with a neutron reflector, where a large volume of the fuel/coolant vapor will collect and go critical, producing large amounts of heat. The mixture is hot enough and charged enough to pass off this energy through a MHD "generator" rather than a turbine, permitting very high coolant temperatures and corrispondingly high efficencies with low radiator mass.
I expect this will be the only way short of fusion power to run a VASIMR engine efficently.
As for using plants for a completly closed life support system, I don't see the need for that in the near term if we can harvest 75-85% of the wastes to cut down on supplies needed. Save plant growth for plants or cis-Earth space colonies to grow food or close the loop entirely... For initial bases though, partial regeneration should be plenty.
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
[i]The glass is at 50% of capacity[/i]
Offline
Dumb question time. While travelling from Earth to Mars, why can't you collect sunlight and filter through UV filters before exposing the plants.
Also, my amateur opinion is that 100% systems closure is a "Holy Grail" that may well be beyond our technology and is unnecessary.
On Mars, I want surplus, whereby Marsian C, H, O & N are converted to organic molecules. Micro-terraforming, as it were.
Offline
I have just finished reading Zubrin's "Mars on Earth," a book about the Mars Analog Research Stations in Utah and Devon Island. I would have to agree with his conclusions about food production and life support.
From the experience of over 1000 person days in the research stations this is the overwhelming conclusion -- Keep it simple.
They have used a greenhouse to recycle wastewater and human wastes, and they have used a toilet that burns their waste. Although they have worked out many of its problems the greenhouse has been both stinky and a great consumer of time while the incinerator toilet has worked just fine from day one with minimal maintenance.
Biological systems are complex and much harder to maintain than physical/chemical systems.
I vote for using chemical and if available nuclear thermal propulsion to send lots of mass to Mars on minimum energy (6 to 9 month) transfers. Bring along all your food and try to grow some in greenhouses on Mars as a bonus.
Let's use NEP for trips to Europa, not Mars.
Offline
One of the problems of making a interplanetary greenhouse is that the great big windows are a great big target for space debries and would make vehicle design harder due to the large area needed. There isn't any polymeric material I know of yet that would be flexible enough to fold/inflate and resist puncture either.
One of the biggie issues of a life-based fully closed LSS is, what if all the plants die? Say that package of hydroponic fertilizer sent up freezedried from Earth was contaminated? Then you'd be in deeep trouble. All-chemical systems sufficent to keep crews alive are a must, save the living stuff for fresh vegetables/breads/herbs or fish... a real morale booster when you won't have fresh food from Earth for a few years.
Some time down the road on a Lunar or Martian base, where you can deal with hydroponic leaks and such with gravity, then the extra efficency of living organisms may help lessen the need for chemical systems while providing food, but that should be left for the early colonists and not first visits.
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
[i]The glass is at 50% of capacity[/i]
Offline
One of the problems of making a interplanetary greenhouse is that the great big windows are a great big target for space debries and would make vehicle design harder due to the large area needed. There isn't any polymeric material I know of yet that would be flexible enough to fold/inflate and resist puncture either.
One of the biggie issues of a life-based fully closed LSS is, what if all the plants die? Say that package of hydroponic fertilizer sent up freezedried from Earth was contaminated? Then you'd be in deeep trouble. All-chemical systems sufficent to keep crews alive are a must, save the living stuff for fresh vegetables/breads/herbs or fish... a real morale booster when you won't have fresh food from Earth for a few years.
Some time down the road on a Lunar or Martian base, where you can deal with hydroponic leaks and such with gravity, then the extra efficency of living organisms may help lessen the need for chemical systems while providing food, but that should be left for the early colonists and not first visits.
Once again, I find this persuasive. Do you get weary from always correcting us amateurs?
Offline
The only other prospect for producing that kind of energy is to switch to a rather esoteric reactor concept, the Vapor Core Nuclear Reactor; in the VCR the uranium fuel itself mixed with Fluorine, Potassium, and maybe Sodium are actually vaporized and placed under pressure. The reactor is simply a chaimber lined with a neutron reflector, where a large volume of the fuel/coolant vapor will collect and go critical, producing large amounts of heat. The mixture is hot enough and charged enough to pass off this energy through a MHD "generator" rather than a turbine, permitting very high coolant temperatures and corrispondingly high efficencies with low radiator mass.
Fascinating, I didn't know this type of nuclear reactor was considered. It doesn't use roating objects, so it's more reliable I think. About the use of MHD, as fa r as I know this idea is about 40 years old (at least) but never succeeded because of excessive corosion matters of the conducting walls where the electrons from the plasma were gathered/emitted. And when I read the gplasma contains fluorine, how will this work?
It's nice the current is DC, that's more useful for most applications, I think.
How do you regulate the neutron flux in such a thing? By adding/deleting some kind of moderating gas?
Offline
If the GCNR rocket doesn't work out, then a VCR + VASIMR would be our best bet for high-ISP/high-thrust (beyond ~1,000-1,200 Isp) for interplanetary travel. If the MHD coil can be preserved, then the high efficency and light weight of such a reactor would achieve specific energies (electricty per kilo) greater than any source sans Fusion power.
These are big reactors, none of that dinky kilowatt stuff from Prometheous, the smallest one they computed numbers for on p.29 of the second link is a 19MT system. This includes everything though, raditors and all, since the coolant runs at such a high temperature. It makes 21 Megawatts of electricty though. The bigger the better too, and its likly that such a powerplant will run future spaceships when we're ready to colonize in earnest... They computed figures for a 210 MWe reactor, and it could theoretically weigh only 67MT.
http://www.inspi.ufl.edu/index.html]htt … index.html
http://www.spacetransportation.com/ast/ … _knigh.pdf
Some people in Florida working of UofF working on such advanced nuclear concepts expressly for spaceflight. The arch enemies of Bruce Gagnon & Co. I imagine... other neat things include modular, easy to make core design for solid-core NTR rockets of various size and ultra-high temperature ceramics (4,000 degree tollerance is not implausable).
The easiest way to throttle the reactor would probably be to increase or decrease the coverage of the neutron reflector around the reactor, permitting more neutrons to escape which will not induce further reaction.
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
[i]The glass is at 50% of capacity[/i]
Offline
What do you think of this:
http://www.spaceref.com/news/viewsr.htm … ?pid=12645
http://www.spaceref.com/news/viewsr.htm … ?pid=12645
Description
NASA/MSFC has a requirement for research focused on the design, fabrication, testing, and evaluation of reactor systems and components associated with both passive and pumped liquid metal systems which will be (non-nuclear) tested in the EFF-TF facilities at MSFC.
This activity shall include: 1) a theoretical analysis for determination of how to accomplish less than 5 ppm impurities in alkaline metal during purification processing and for heat pipe module fill, 2) Generate engineering fabrication drawings for liquid metal purification loop capable of producing Sodium (Na), and Sodium/Potassium (NaK) mixture with less than 5 ppm oxygen content in the liquid metals. This loop must also be designed to be used as a component tester for various rector components associated with pumped liquid metal systems, and 3) Fabrication and fill of both stock quantities and known volume cylinders of less than 5 ppm of Na and NaK using loop identified in item #2 (above). NASA/MSFC intends to purchase the items from New Mexico Institute of Mining and Technology, 901 University Blvd SE, Albuquerque, NM 87106-4339.
This recommendation is made pursuant to FAR 6.302-1, which implements the authority for 10 U.S.C. 2304©(1) for acquisition of supplies or services from only one source and no other supplies or services will satisfy agency requirements.
Competition is impractical for the following reasons: In order to properly address the aspects necessary to build, test, and flight qualify nuclear systems, components, and support equipment using non-nuclear testing, experience is necessary in both (prototypic) non-nuclear testing and nuclear testing of US space flight systems. Additionally, the experience related to the flight systems must be related to the reactor system itself, including intimate experience with the pumped liquid metal loop. To date, the United States has only flown 1 system in 1965 (SNAP 10A), making the "pool" of personnel who have flight reactor experience (related to pumped liquid metal) very limited.
Because the work on-going at MSFC is geared towards flight systems, it is a necessity that the components/systems tested in MSFC's facilities take into account and use the experience that was gained from flight programs in order to decrease time and effort needed for current development (and avoid mistakes based on "lessons learned") of these systems in a timely manner.
To date, there have only been 2 facilities that have performed prototypic non-nuclear testing of space fission reactor systems.
New Mexico institute and MSFC. The facilities at the New Mexico Institute are the only facilities in the United States that has actually tested a space flight reactor unit (topaz reactors). The same personnel who performed the flight qualification testing of the SNAP 10A reactor are also the same personnel who were responsible for testing the flight topaz reactors at New Mexico Institute. Other than at New Mexico Institute, the necessary experience to perform the scope of work for this task is non-existent. The Government intends to acquire a commercial item using FAR Part 12. Interested organizations may submit their capabilities and qualifications to perform the effort in writing to the identified point of contact not later than 4:30 p.m. local time on May 7, 2004. Such capabilities/qualifications will be evaluated solely for the purpose of determining whether or not to conduct this procurement on a competitive basis.
Offline
The Prometheous-class reactors' primary coolant is either liquid sodium or sodium/potassium alloy, which is a great coolant with its high heat capacity and low vapor pressure, but may present realibility issues over long-term use because of corrosion caused by impurities. This MSFC project looks to overcome such problems by building a system that can clean the material before loading into the reactor.
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
[i]The glass is at 50% of capacity[/i]
Offline