Light weight nuclear reactor, updating Mars Direct

RobertDyck · 2014-02-06 16:06:25

The Mars Direct ERV included an SP-100 nuclear reactor. This produced power for the ISPP unit. Development for SP-100 started during Ronald Regan's SDI, and was current when Mars Direct was first written in 1989. In fact development for SP-100 was completed in 1992. However, in 2007 a new one was developed. This chart shows nuclear reactors for space. SP-100 is designed for 100 kWe (kiloWatt electric), converted from 2000 watts thermal. Reactor mass is 5422 kg. The power reactor on the Mars Direct ERV was listed as 80 kWe and mass 3.5 metric tonnes (3500 kg). However, the SAFE-400 reactor developed in 2007 will produce 100 kWe from only 400 kW thermal. That reactor masses only 512 kg. So new technology allows us to save 3 metric tonnes!

Mars Direct ERV was to mount the reactor in a rover, with a power cable trailing back to the ERV. The rover would drive off to a crater, then park in the bottom. For radiation protection. Mars Exploration Rovers (Spirit & Opportunity) massed 185 kg (not including lander, etc), but Curiosity rover masses 899 kg. Can anyone tell me what the mass is for Curiosity's instruments, communications, arm, RTG? Everything other than mobility stuff? If a SAFE-400 reactor plus power cable replaced all that, would it fit? Mars Direct ERV budgetted 0.5t for a light truck, would using Curiosity mobility stuff actually mass less?

The next is the ERV cabin. Let's replace the cabin with Dragon. Budget was 3.0t for structure + 1.0t life support + 1.0t solar power + 0.5t reaction control system + 0.1t communications and information management + 0.5t furniture and interior = 6.1t total. That doesn't include consumables, EVA suits, or spares. Dragon is listed as 4.2t dry weight plus 1,290kg propellant = 5.49t launch weight. That's the unmanned cargo version to supply ISS, so add life support. I don't have figures for DragonRider. Dragon solar panels provide 4 kWe peak power, so that's Earth orbit. The ERV has 5 kWe. Mars has 47% as much sunlight, so to provide 5 kW of power when leaving Mars, the Dragon solar panels would have to be 2.5 times as large. Assuming the spacecraft needs that much power.

So far looks like mass is under budget.

Last edited by RobertDyck (2014-02-07 20:10:59)

RobertDyck · 2014-02-06 17:36:18

Life Support. Let's start by looking at equipment installed on ISS. This is sized for 3 crew; the other 3 are supported by the Russian side. This is what I provided for the Mars Homestead Project - Phase One: Hillside Settlement. But that was sized for 12 crew, this is adjusted for 4 crew.

Waste Collector Subsystem: (space toilet)
This is designed for zero-G, we may use a simpler toilet in the gravity of Mars, but it is a starting point. Their description:
"The Waste Collector Subsystem (WCS) is the main item in the Hygiene compartment. The WCS provides for the collection of human waste, both liquid and solid, including vomitus and all hygiene related materials including, but not limited to, fecal wipes and sanitary napkins. The WCS has the ability to support missions of unlimited length through safe and convenient maintenance. Air entrainment is utilized to pull liquid and solid waste away from the user. The WCS removes bacteria, vomitus, trash, fecal odors, hair, skin particles and other body particles from the entrainment air before the air returns to the cabin. Urine is collected by a separate air stream, where it is separated and pumped to a Urine Processor Assembly (UPA)."
Performance/Features:
- Urine separator and fan motors are 120 volt DC with a urine pumping capacity of 40 to 41 ml/sec @ 3,900 RPM
- Commode fan motor is 115 VAC, 400 Hz, 3 phase for Shuttle Unit (ISS is TBD)
- Fecal canister sized to fit 20 compactions with .25 lbs fecal matter with 500 square inches paper waste
- Compactor motor is 28 VDC with a compaction force of 100 pounds Operating media: air Power, Urine & Feces Collection: 340 - 375 Watts Feces Compaction/Processing: 250 watts
Pressure: ambient
Size: 27" x 27" x 46"
Weight: 246 lbs.

Size calculation for Mars:
This uses air instead of water to flush urine. Using the figure of 1.50kg urine per person per day, and assuming the same density as water (1 gram per ml) that works out to 1500ml per person, or 37.5 seconds per day of toilet operation. Feces compaction cycle time is not listed, but for the sake of estimation let's say 30 seconds and one use per person per day. Ignoring the commode fan, toilet operation per person per day will be 375 watts * 37.5 seconds + 250 watts * 30 seconds = 21562.5 watt seconds per person per day, or for a 4 person crew 0.023958 kWh per day.

Water Processor Assembly
"The Water Processor Assembly (WPA) provides the capability to produce potable quality water from humidity condensate, reclaimed urine distillate, and waste shower, handwash and oral hygiene waters. Primary treatment is provided by particulate filtration, ion exchange, and carbon sorption. In addition, a high-temperature catalytic oxidation process removes residual organics and kills microorganisms to meet final potable water quality specifications."
Performance/Features:
- Receives and stores waste water
- Removes free gas (gas separators), particulates (particulate filter), ionic and high molecular weight organic species (multifiltration beds); oxidizes residual organics and destroys micro-organisms (catalyst bed); and removes oxidation products and doses processed water with iodine (ion exchange bed).
- Delivers processed water at 15 to 30 psig at up to 500 lbs./hr
- Capacity to hold 112 lbs. of product water
Operating Media: Water
Flow rate: 500 lbs./hr (Delivery)
Power: 915 watts
Size: 75 ft3
Weight: 1,450 lbs.

Size calculation for Mars:
Effluents per person per day are Respiration & Perspiration water 5.02lb + Food preparation latent water 0.08lb + Urine 3.31lb + Feces water 0.20lb + Hygiene water 27.68lb + Clothes wash water, liquid 26.17lb + latent 1.33lb = 63.79lb total. A 4 person crew will generate 255.16lb which will require 0.51032 hours of operation per day, or 0.467 kWh per day.

Oxygen Generation Assembly
"The SPE ® Oxygen Generation Assembly (OGA) uses Proton Exchange Membrane (PEM) based electrolysis to convert water from the Water Processor Assembly into oxygen and hydrogen. Oxygen is used for crew respiration and animal respiration, while the hydrogen is vented to space vacuum. It is anticipated that the hydrogen will eventually be used in a carbon dioxide (CO2) reduction process to recover the oxygen that is contained in the CO2."
Performance/Features:
- Oxygen generation rate for the electrolysis cell stack is selectable for flow rates between 4.0 and 20.4 lbs./day
- Electrolysis cell stack maximum oxygen pressure is 45 psia
- Electrolysis cell stack maximum hydrogen pressure is 80 psia Operating Media: Water, oxygen, hydrogen

Size calculation for Mars:
Unfortunately power figures are not given for oxygen generation, but the following web site does give power figures for oxygen generation using electrolysis vs. reverse fuel cell (proton exchange membrane). The ideal figures are the same, but as they point out efficiency in the real world is not ideal.
Reference: http://hyperphysics.phy-astr.gsu.edu/hb … ctrol.html
The key figures from this site are:
1 mole (18.01528 grams) of water converts into 1 mole (2.01588 grams) of hydrogen and 1/2 mole (15.9994 grams) of oxygen. Power consumed: 237.1 kJ = 0.06586 kWh. So generating 0.84kg * 4 people = 3.36 kg oxygen per day will take 13.83 kWh or 0.57625 kW of continuous power 24 hours per day.

Sabatier reactor
Half of the oxygen astronauts breathe ends up as water, the other half is incorporated in CO2. Half of the oxygen in CO2 comes from inhaled oxygen, the other half comes from oxygen atoms in food. So an oxygen generation system that only breaks-up water has an oxygen recycling efficiency of at best 50%. A Sabatier takes all of the hydrogen from oxygen generation together with half of the CO2 from the sorbet to form methane and water. That water is enough to supply the oxygen generator so it closes the loop. Methane and the other half of the CO2 would be dumped to space. On Mars we will also need a closed loop system. A Sabatier reactor is exothermic, so the primary concern is getting rid of waste heat.

CO2 removal
There is a paper on microwave regeneration of silver oxide sorbent. Ag2O is easy to regenerate, it only takes heat and either vacuum or low partial pressure of CO2. Microwave regeneration takes less power than an electro-resistive oven (electric oven). Solid amine has lower mass than Ag2O, and liquid amine can be used on the surface of Mars since it has gravity. Solid amine coating on Styrofoam beads takes too much volume for a spacesuit, so Ag2O is preferred for a suit. There are several papers on regenerating amines, but for simplicity let's assume Ag2O for all CO2 sorption. Regenerating the sorbent (removing CO2 from it) takes power in the form of heat, but operating the sorbent doesn't take power to remove CO2 from the air. It just sits in a duct with fans blowing across it.
Reference: "Microwave Regenerable Air Purification Device", James E. Atwater, John T. Holtsnider, Richard R. Wheeler Jr., NASA-CR-201945

Size calculation for Mars:
Ag2O has an energy of 1.865 kJ/g CO2. For 1.00kg per person per day that works out to 7460 kJ per day for 4 people, or 2.07 kWh, or 0.086 kW of continuous power 24 hours per day.

Dehumidifier
Hamilton Sundstrand lists a dehumidifier, but has no details. A "good" dehumidifier for a house on Earth has an efficiency factor (EF) of 2.4 litres per kWh when operating at 27°C (80.6°F) and 60% relative humidity. Evaporates per person per day will be Respiration & Perspiration water 2.28kg + Clothes wash water, latent 0.60kg = 2.88kg = 2.88 litres. I don't know how to adjust dehumidifier efficiency for temperature and relative humidity, so I'll just use the 2.4 factor. For a 4 person crew that means 4.8 kWh per day, or 0.2 kW continuous power 24 hours per day.

Cabin fan assembly
The Hamilton Sundstrand fan circulates air in each station module. I suggest we plan for one for the habitat. It is listed as using 120 VDC, pressure rise of 1.35-3.49" H2O, and flow rate 300-500 cfm (cubic feet per minute), but it doesn't give current (amps) or power (watts). A commercial fan (Fantech CVS 400A) can produce 1.5" H2O static pressure and 204 cfm flow rate. It would take two of them to match the flow rate of the ISS fan. But this is for 4 crew in a Dragon, so let's use just one. The CVS fan is rated for 156 watts.

Power Consumption Summary
To summarize power consumption for all equipment of the primary life support system, for 4 people:

toilet: 375 watt peak, 0.023958 kWh per day
water processor: 915 watt peak, 0.467 kWh per day
oxygen generation: 0.57625 kW continuous
CO2 removal: 0.086 kW continuous
dehumidifier: 0.2 kW continuous
circulation fan: 0.156 kW continuous

That adds up to 1.03770833 kW. Ok, so adding one kilowatt power generation for life support is reasonable.

Last edited by RobertDyck (2014-02-06 18:19:34)

louis · 2014-02-06 19:12:24

RobertDyck wrote:

Life Support. Let's start by looking at equipment installed on ISS. This is sized for 3 crew; the other 3 are supported by the Russian side. This is what I provided for the Mars Homestead Project - Phase One: Hillside Settlement. But that was sized for 12 crew, this is adjusted for 4 crew.
Waste Collector Subsystem: (space toilet)
This is designed for zero-G, we may use a simpler toilet in the gravity of Mars, but it is a starting point. Their description:
"The Waste Collector Subsystem (WCS) is the main item in the Hygiene compartment. The WCS provides for the collection of human waste, both liquid and solid, including vomitus and all hygiene related materials including, but not limited to, fecal wipes and sanitary napkins. The WCS has the ability to support missions of unlimited length through safe and convenient maintenance. Air entrainment is utilized to pull liquid and solid waste away from the user. The WCS removes bacteria, vomitus, trash, fecal odors, hair, skin particles and other body particles from the entrainment air before the air returns to the cabin. Urine is collected by a separate air stream, where it is separated and pumped to a Urine Processor Assembly (UPA)."
Performance/Features:
- Urine separator and fan motors are 120 volt DC with a urine pumping capacity of 40 to 41 ml/sec @ 3,900 RPM
- Commode fan motor is 115 VAC, 400 Hz, 3 phase for Shuttle Unit (ISS is TBD)
- Fecal canister sized to fit 20 compactions with .25 lbs fecal matter with 500 square inches paper waste
- Compactor motor is 28 VDC with a compaction force of 100 pounds Operating media: air Power, Urine & Feces Collection: 340 - 375 Watts Feces Compaction/Processing: 250 watts
Pressure: ambient
Size: 27" x 27" x 46"
Weight: 246 lbs.
Size calculation for Mars:
This uses air instead of water to flush urine. Using the figure of 1.50kg urine per person per day, and assuming the same density as water (1 gram per ml) that works out to 1500ml per person, or 37.5 seconds per day of toilet operation. Feces compaction cycle time is not listed, but for the sake of estimation let's say 30 seconds and one use per person per day. Ignoring the commode fan, toilet operation per person per day will be 375 watts * 37.5 seconds + 250 watts * 30 seconds = 21562.5 watt seconds per person per day, or for a 4 person crew 0.023958 kWh per day.
Water Processor Assembly
"The Water Processor Assembly (WPA) provides the capability to produce potable quality water from humidity condensate, reclaimed urine distillate, and waste shower, handwash and oral hygiene waters. Primary treatment is provided by particulate filtration, ion exchange, and carbon sorption. In addition, a high-temperature catalytic oxidation process removes residual organics and kills microorganisms to meet final potable water quality specifications."
Performance/Features:
- Receives and stores waste water
- Removes free gas (gas separators), particulates (particulate filter), ionic and high molecular weight organic species (multifiltration beds); oxidizes residual organics and destroys micro-organisms (catalyst bed); and removes oxidation products and doses processed water with iodine (ion exchange bed).
- Delivers processed water at 15 to 30 psig at up to 500 lbs./hr
- Capacity to hold 112 lbs. of product water
Operating Media: Water
Flow rate: 500 lbs./hr (Delivery)
Power: 915 watts
Size: 75 ft3
Weight: 1,450 lbs.
Size calculation for Mars:
Effluents per person per day are Respiration & Perspiration water 5.02lb + Food preparation latent water 0.08lb + Urine 3.31lb + Feces water 0.20lb + Hygiene water 27.68lb + Clothes wash water, liquid 26.17lb + latent 1.33lb = 63.79lb total. A 4 person crew will generate 255.16lb which will require 0.51032 hours of operation per day, or 0.467 kWh per day.
Oxygen Generation Assembly
"The SPE ® Oxygen Generation Assembly (OGA) uses Proton Exchange Membrane (PEM) based electrolysis to convert water from the Water Processor Assembly into oxygen and hydrogen. Oxygen is used for crew respiration and animal respiration, while the hydrogen is vented to space vacuum. It is anticipated that the hydrogen will eventually be used in a carbon dioxide (CO2) reduction process to recover the oxygen that is contained in the CO2."
Performance/Features:
- Oxygen generation rate for the electrolysis cell stack is selectable for flow rates between 4.0 and 20.4 lbs./day
- Electrolysis cell stack maximum oxygen pressure is 45 psia
- Electrolysis cell stack maximum hydrogen pressure is 80 psia Operating Media: Water, oxygen, hydrogen
Size calculation for Mars:
Unfortunately power figures are not given for oxygen generation, but the following web site does give power figures for oxygen generation using electrolysis vs. reverse fuel cell (proton exchange membrane). The ideal figures are the same, but as they point out efficiency in the real world is not ideal.
Reference: http://hyperphysics.phy-astr.gsu.edu/hb … ctrol.html
The key figures from this site are:
1 mole (18.01528 grams) of water converts into 1 mole (2.01588 grams) of hydrogen and 1/2 mole (15.9994 grams) of oxygen. Power consumed: 237.1 kJ = 0.06586 kWh. So generating 0.84kg * 4 people = 3.36 kg oxygen per day will take 13.83 kWh or 0.57625 kW of continuous power 24 hours per day.
Sabatier reactor
Half of the oxygen astronauts breathe ends up as water, the other half is incorporated in CO2. Half of the oxygen in CO2 comes from inhaled oxygen, the other half comes from oxygen atoms in food. So an oxygen generation system that only breaks-up water has an oxygen recycling efficiency of at best 50%. A Sabatier takes all of the hydrogen from oxygen generation together with half of the CO2 from the sorbet to form methane and water. That water is enough to supply the oxygen generator so it closes the loop. Methane and the other half of the CO2 would be dumped to space. On Mars we will also need a closed loop system. A Sabatier reactor is exothermic, so the primary concern is getting rid of waste heat.
CO2 removal
There is a paper on microwave regeneration of silver oxide sorbent. Ag2O is easy to regenerate, it only takes heat and either vacuum or low partial pressure of CO2. Microwave regeneration takes less power than an electro-resistive oven (electric oven). Solid amine has lower mass than Ag2O, and liquid amine can be used on the surface of Mars since it has gravity. Solid amine coating on Styrofoam beads takes too much volume for a spacesuit, so Ag2O is preferred for a suit. There are several papers on regenerating amines, but for simplicity let's assume Ag2O for all CO2 sorption. Regenerating the sorbent (removing CO2 from it) takes power in the form of heat, but operating the sorbent doesn't take power to remove CO2 from the air. It just sits in a duct with fans blowing across it.
Reference: "Microwave Regenerable Air Purification Device", James E. Atwater, John T. Holtsnider, Richard R. Wheeler Jr., NASA-CR-201945
Size calculation for Mars:
Ag2O has an energy of 1.865 kJ/g CO2. For 1.00kg per person per day that works out to 7460 kJ per day for 4 people, or 2.07 kWh, or 0.086 kW of continuous power 24 hours per day.
Dehumidifier
Hamilton Sundstrand lists a dehumidifier, but has no details. A "good" dehumidifier for a house on Earth has an efficiency factor (EF) of 2.4 litres per kWh when operating at 27°C (80.6°F) and 60% relative humidity. Evaporates per person per day will be Respiration & Perspiration water 2.28kg + Clothes wash water, latent 0.60kg = 2.88kg = 2.88 litres. I don't know how to adjust dehumidifier efficiency for temperature and relative humidity, so I'll just use the 2.4 factor. For a 4 person crew that means 4.8 kWh per day, or 0.2 kW continuous power 24 hours per day.
Cabin fan assembly
The Hamilton Sundstrand fan circulates air in each station module. I suggest we plan for one for the habitat. It is listed as using 120 VDC, pressure rise of 1.35-3.49" H2O, and flow rate 300-500 cfm (cubic feet per minute), but it doesn't give current (amps) or power (watts). A commercial fan (Fantech CVS 400A) can produce 1.5" H2O static pressure and 204 cfm flow rate. It would take two of them to match the flow rate of the ISS fan. But this is for 4 crew in a Dragon, so let's use just one. The CVS fan is rated for 156 watts.
Power Consumption Summary
To summarize power consumption for all equipment of the primary life support system, for 4 people:
toilet: 375 watt peak, 0.023958 kWh per day
water processor: 915 watt peak, 0.467 kWh per day
oxygen generation: 0.57625 kW continuous
CO2 removal: 0.086 kW continuous
dehumidifier: 0.2 kW continuous
circulation fan: 0.156 kW continuous
That adds up to 1.03770833 kW. Ok, so adding one kilowatt power generation for life support is reasonable.

Very interesting calculations - thanks for those!

I notice you don't seem to have anything for heating. Is there a reason for that? Even taking account of waste heat from the machinery, if your max energy ouput is 2Kw I am not sure if that would be sufficient.

Of course I am looking at your figures as a minimum. I would like us to be able to experiment with smelting and agriculture, so would want a much bigger energy ouput.

louis · 2014-02-06 19:19:09

Also - what about communication with Earth. Wouldn't that require a significant output?

RobertDyck · 2014-02-06 19:58:33

I assume existing equipment in Dragon. However, this is the ISS Crew ReSupply version of Dragon. Any recommendation?

RobertDyck · 2014-02-06 22:47:15

I imagine all this life support equipment would be housed in the trunk. Remember Dragon has a trunk instead of a service module. The trunk is just a cylinder, an adapter between launch vehicle and capsule. And solar panels. It's hollow. The original Dragon design had a full service module, but that was their bid for CEV, to travel to lunar orbit and back. By the way, contrary to slander I heard from one member of the Orion team, Dragon still today has a heat shield capable of atmospheric entry when returning from the Moon. That's from an interview with Elon Musk himself. The capsule is intended to be reusable, so housing thrusters for orbital work in the capsule means it's all reusable. So, place all this recycling life support equipment in the trunk. That leaves more living space in the capsule. Dragon is large enough for 7 crew members: one row of 4 seats above, and a second row of 3 beneath. For a Mars ERV, the lower level would be the toilet and storage for Mars samples. There should also be enough room for one person to use exercise equipment. They would have to take turns. Remember, the inside of Dragon is the size of a van. A full size van aka cargo van, not a mini-van, but still.

Last edited by RobertDyck (2014-02-06 23:03:37)

louis · 2014-02-07 07:16:00

I favour two landers with 3 crew in each and a pre-landed hab.

RobertDyck · 2014-02-07 09:00:00

For this exercise, I'm assuming Mars Direct with no changes.

Mars Direct designed the ERV to enter Mars orbit before landing. I would use direct entry, just like Mars Phoenix, Spirit, Opportunity, and Curiosity. JPL has proven that. It also used a 23.5 meter diameter heat shield. This was an umbrella-like fabric. I would recommend the same fabric as DurAFRSI, the latest thermal blanket developed by Ames Research Centre. That fabric is Nextel 440, available here.

NASA expressed concern that mass may be greater than Dr. Zubrin's estimates. But using modern equipment, mass is actually lower. Mars Direct included the Ares launch vehicle, (Dr. Zubrin's book said David Baker was the primary engineer for that). Ares was designed with 4-segment SRBs and 5 SSME. SLS will have 5-segment SRBs and 4 SSME. The largest version of SLS will have new advanced SRBs, but my concern is the new ones may never be finished. Could Mars Direct work with 5-segment SRBs and a full-size upper stage?

My point is, this is using off-the-shelf hardware. I'm giving suppliers where to get the parts. Can we go now?

Tom Kalbfus · 2014-02-07 10:24:36

I think we'll need a new political regime in Washington. We'll probably tip toe across the finish line as far as capabilities go, and then it won't make sense not to go to Mars. I think the Chinese and the Russians will be a big help in this as compedators. If we all hold hands in a single joint venture it will probably take longer, because joint ventures are a good way to eliminate compedators."Hey China! I hear your building a big superbooster, You want to join us in our effort to get to Mars? No need to hurry once you join up Take it easy, no one is going to beat us there now"

RobertDyck · 2014-02-07 10:47:59

Business treats everyone as a customer.

GW Johnson · 2014-02-07 13:41:14

Nextel 440 is very similar to the Nextel 300-series I have used. It's an aluminosilicate, with phase change embrittlement and cracking at about 2300 F, and a meltpoint pretty close to 3200 F. It's square-woven of yarns, close weave, but still porous. It's very much like fiberglass boat cloth, when you handle it.

Up to a point, you can handle stagnation heating at Mars, even in the essentially "white" color. But maybe not for direct entry from interplanetary transfer, that's getting to be too fast, the re-radiating surface temperatures are getting very high. Once you heat it and cool it, that's when the embrittlement and shrinkage cracking occur. For one shot use only, you might tolerate stagnation zone material surface temperatures between the 2300 and 3200 F limits.

The properties and usage limitations are very similar to my ceramic composite heat shield. All the alumino-silicate materials have essentially the same characteristics at high temperatures. I have some curves on this posted over at "exrocketman". They should be a good ballpark guide.

As for Dragon's heat shield, it wasn't originally designed for a free return from the moon, it was designed for a free return from Mars. That's much tougher, being around 17 km/s at entry. It's also why they could fly the same capsule back from LEO unrefurbished 4+ times if they want to. And they probably will.

The Orion guys sneer at it to deflect the knowledge that Dragon is more capable in many ways, just smaller, and therefore much easier to launch. 7 crew in Dragon would be about as cramped as Gemini was. 2 weeks was too much for Borman and Lovell on Gemini 7.

GW

RobertDyck · 2014-02-07 14:13:38

Ok. Could Nextel 440 handle aerocapture into Mars orbit, cool down, then entry?

Tom Kalbfus · 2014-02-07 14:33:55

GW Johnson wrote:

Nextel 440 is very similar to the Nextel 300-series I have used. It's an aluminosilicate, with phase change embrittlement and cracking at about 2300 F, and a meltpoint pretty close to 3200 F. It's square-woven of yarns, close weave, but still porous. It's very much like fiberglass boat cloth, when you handle it.
Up to a point, you can handle stagnation heating at Mars, even in the essentially "white" color. But maybe not for direct entry from interplanetary transfer, that's getting to be too fast, the re-radiating surface temperatures are getting very high. Once you heat it and cool it, that's when the embrittlement and shrinkage cracking occur. For one shot use only, you might tolerate stagnation zone material surface temperatures between the 2300 and 3200 F limits.
The properties and usage limitations are very similar to my ceramic composite heat shield. All the alumino-silicate materials have essentially the same characteristics at high temperatures. I have some curves on this posted over at "exrocketman". They should be a good ballpark guide.
As for Dragon's heat shield, it wasn't originally designed for a free return from the moon, it was designed for a free return from Mars. That's much tougher, being around 17 km/s at entry. It's also why they could fly the same capsule back from LEO unrefurbished 4+ times if they want to. And they probably will.
The Orion guys sneer at it to deflect the knowledge that Dragon is more capable in many ways, just smaller, and therefore much easier to launch. 7 crew in Dragon would be about as cramped as Gemini was. 2 weeks was too much for Borman and Lovell on Gemini 7.
GW

Would you want to be in a Gemini capsule all the way to Mars? Do you think it would make sense to incorporate an Orion capsule as part of an Earth return vehicle for Mars direct?

RobertDyck · 2014-02-07 14:59:27

The architecture I described elsewhere includes a larger spacecraft, dedicated for ISS to Mars orbit and back. Aerocapture at both ends. I included a space capsule as an emergency escape pod in case aerocapture fails. At one point I was thinking 2 Soyuz, just descent and service modules, no orbital module. But Dragon is the perfect escape pod; you only need one. Why would you use Orion? It's too heavy.

GW Johnson · 2014-02-07 19:15:51

I have never advocated riding anywhere more than a week away in a space capsule. Any space capsule. Orion is no more suitable for a Mars mission than Dragon is. Or Gemini. Capsule is not equal to habitat. Not even close. NASA's Transhab design is also inadequate for Mars missions. It just takes more than that.

GW

RobertDyck · 2014-02-07 21:03:05

I laid out my mission plan in Yet another Mars architecture. The Interplanetary Transit Vehicle (ITV) would be about the size of a single module of ISS. If you flatten that out, say a Mars Direct hab with a just a single floor, we can estimate that mass by taking the Mars Direct hab and deleting open rovers, pressurized rovers, and field science equipment, and spares and margin. The result is 19 metric tonnes. Now delete all structure and shell for the lower deck. I said launch the ITV with full food and supplies on a single Falcon 9, but separate launches for TMI stage, escape pod, and lander/rover. It would have to include self-rendezvous with ISS. Below is the floor plan for the Mars Direct hab. The ITV wouldn't have a lab, and life support equipment would have to be on this deck. Or make the hab it little smaller in diameter and put equipment in a "basement" beneath the centre of the living space deck. Or a loft on top, docking port for Dragon above, and another docking port for the lander beneath. Could you do it?

Falcon 9 is designed for a 5.2 metre outside diameter fairing. Could it handle an 8 metre hab? Could a Bigelow hab expand from 5 metres to 8?

Another question: could you add artificial gravity? Use a tether to connect the propulsion state to the ITV. Again, the idea was an expendable propulsion state both ways, so the stage could be discarded when it's time to de-spin prior to aerocapture. But eventually the propulsion stage would be replaced by a reusable one. Could the stage be reeled in during de-spin?

RobertDyck · 2014-02-07 21:04:25

This is already getting off-topic. The purpose for this discussion thread is to update the Mars Direct ERV. That's all; not debate whether Mars Direct is a good architecture. Let's limit out-of-scope debate.

Tom Kalbfus · 2014-02-08 08:41:50

GW Johnson wrote:

I have never advocated riding anywhere more than a week away in a space capsule. Any space capsule. Orion is no more suitable for a Mars mission than Dragon is. Or Gemini. Capsule is not equal to habitat. Not even close. NASA's Transhab design is also inadequate for Mars missions. It just takes more than that.
GW

Have you ever considered a virtual reality suit? It can project a space around the astronaut that is much larger than the inside of a space capsule. The suit would be designed to provide resistance, so the astronaut could walk around the inside of a palatial virtual room, he would only realize he is in a space capsule when he takes off the suit. How does that sound?

RobertDyck · 2014-02-08 21:37:15

I found a report to NASA for the Oxygen Generation Assembly, dated 1995. It says the system package weight was 383 lb, and power supply cart 291 lb.

The Wikipedia article lists components. I missed the Urine Processing Assembly, which is separate from the Water Processing Assembly. I found a report for that too, dated 2003. Unfortunately it doesn't include mass, but it does document power.

The UPA is designed to process a nominal load of 8.45 kg/day (1 8.6 Ibs/day) of wastewater consisting of urine, flush water, and a small amount of waste from, Environmental Health System water samples. At a maximum load, the UPA can process 13.6 kg (30 Ibs.) of wastewater over an 18-hour period per day. It operates in a batch mode, consuming 424 W power when processing, and 108 W during standby (current projections).

Articles from 2011 and 2013 state performance in space was not as good. It was supposed to recover 85% moisture, and did for ground tests. But in space, astronaut bone decalcification resulted in high calcium in urine. That reduced efficiency, and clogged the system. Pre-treatment with an ion exchange medium could fix that. They talk about resins and gypsum. This does demonstrate the need to test life support equipment on ISS before going to Mars. But we're doing it!

It's also interesting that the Russian side has a sink and a shower, and their water recovery system can process that water. Equipment in Zvezda normally routes that water to their oxygen generator, but could be used as drinking water in an emergency. But in interviews, astronauts always say they just wipe themselves down with a wet washcloth. Why? They don't want to use the Russian shower? Skylab had a shower. The US Habitation module was supposed to have a sink and shower. NASA's media document says water from the sink and shower would go to the existing Water Processing Assembly.

I wrote that recycling life support equipment would be housed in the Dragon trunk. Instead, put it in an aluminum skin or inflatable small module on top. Connected to the docking hatch. Soyuz connects its descent module to orbital module with light-weight hatch. Same inside diameter as an APAS hatch, but no shock absorbers or other latches. In fact, it has only one door: the descent module side. When the orbital module is ejected, the open hatch depressurizes the module. After all, it's just discarded. Do the same with Dragon. Give it a light-weight hatch instead of CBM. This allows for housing life support in a pressurized module, that astronauts can access. ISS has had enough problems with life support that I think astronauts require access.

The Soyuz descent module has 20 minutes of life support, just enough for atmospheric entry and landing. The orbital module originally had 2 weeks of life support, but they may have reduced that for ISS operation. This ERV module would have 6 months of life support. How long for Dragon itself? Just 20 minutes, or a little longer?

Or just use a Bigelow BEAM. That is 13 feet/4 metres long, and 10.5 feet/3 metres long. It weighs 3,000 lbs / 1,360 kg. But the question is how well it would withstand Mars atmospheric entry and landing, while filled with equipment. Could a hard jolt when the parachute opens cause the soft wall to push against life support tubing, causing a tear? And how to support the equipment? A hard wall module could allow bolting equipment to the walls.

Another concern is if Dragon is launched with a life support module attached to its nose, then when it launches from Earth it will require a fairing. Not just the small dome over the hatch that Dragon normally uses, but a full fairing. Or would it? The Russian Soyuz does, but it also has an open truss between spacecraft and launch vehicle. We don't want parts to rip off during hypersonic flight, like the solar panel wing of Skylab. But if the life support module has a smooth hard wall shell, could it just sit on Dragon during launch? I'm sure it could on Mars, but when launching from Earth?

SpaceNut · 2014-02-08 23:35:13

http://www.nasa.gov/centers/marshall/pd … _eclss.pdf
http://science.ksc.nasa.gov/shuttle/tec … eclss.html
http://www.ntrs.nasa.gov/archive/nasa/c … 093339.pdf
What you are looking for was in the crashed section of the ISS thread...

RobertDyck · 2014-02-08 23:50:55

Thankyou. However, I don't see mass for the Urine Processing Assembly in any of that.

SpaceNut · 2014-02-09 10:42:54

One way to get the mass for the Urine Processing assembly is to inferr from data that you may already have with the rack mass minus the mass for the sections that you have for the items contained in rack 2 that the shuttle brought to the station back in 2007.

RobertDyck · 2014-02-09 11:30:32

The equipment would probably have to be redesigned anyway. If we use the Shuttle toilet in the lower part of Dragon, then a bottle of urine would have to be carried up to the processor. To make the equipment smaller and lighter, build it as an integrated unit, with each step immediately adjacent, to reduce or eliminate connecting tubes.

RobertDyck · 2014-02-09 18:55:07

The space toilet has equipment to separate urine from air. After all that, putting it in a normal bottle, without gravity to separate liquid from air? You could just fill a plastic bag; with all air removed. Handling that is "ew". Another option is a Playtex Nurser baby bottle. It has a plastic bag within a hard plastic bottle. Replace the nipple with a quick release valve.

RobertDyck · 2014-02-10 10:52:22

All this tells me life support will be bigger and heavier than originally estimated. The nuclear reactor will be smaller and lighter. The light truck can be smaller because it has to carry a smaller reactor, it can be the mobility section of Curiosity rover. But if you use Dragon, add the aluminum hull module for life support, plus all the life support equipment from ISS, it adds up to more weight. That basically consumes weight saving from the reactor. Now if the part that launches from Mars is heavier, then the fuel tanks have to be bigger. What can we do to reduce launch mass from Mars? One option is the propellant tanks.

Mars Direct included aluminum lithium alloy, known by the brand name Weldalite. The external tank of the Space Shuttle used that; from the time ISS construction began until Shuttle was decommissioned. But we now know how to make carbon fibre / epoxy composite tanks. They're even lighter. You can't store liquid oxygen in them, because carbon fibre burns in liquid oxygen. But you can add a plastic film liner. In 2005 I met a representative from XCorp, he was looking at exactly that. I asked which polymer they were considering using. After all, it has to withstand the cold of liquid oxygen. He refused to say which one, but did say they looked through the entire catalogue from Dupont and chose the best one. Ah hah! I'm familiar with that catalogue. That means they chose Teflon FEP. That's a good polymer, but not the best. PCTFE is more impermeable to water, and more importantly more impermeable to oxygen. And it can withstand cold better, it's embrittlement temperature is -240°C while liquid oxygen boils at -182.96°C at one atmosphere pressure. They keep LOX as close as possible to the boiling temperature to reduce energy consumed to heat propellant. PCTFE used to be sold by 3M with brand name Kel-F, but they stopped making it in 1995. Now it's made by Honeywell. They sell it with two brand names: Clarus targeted to military and aerospace applications, and Aclar to the pharmaceutical industry as blister packs for pills. Yes, I told the guy from XCorp all this. Yet another piece of engineering advice given away free. But this means a carbon fibre epoxy LCH4 tank, and the LOX tank would also be carbon fibre epoxy with a liner of Clarus film.

Another lesson learned: development of X-33 tried to use carbon fibre epoxy tanks. Unfortunately someone made the last minute decision to replace the solid wall composite tank with a hollow wall, honeycomb structure. They tested it with liquid nitrogen. It worked until they drained the tank. When it warmed, the tank came apart. The paper thin walls developed micro-fractures, enough for liquid nitrogen to seep into the cells of the hollow wall. When they drained the tank, the LN2 in those cells did not drain out. When the tank warmed, thermal expansion caused the micro-fractures to seal shut. Then the liquid nitrogen boiled. With no where to go, the nitrogen gas created pressure in the cells until they ruptured. This caused the tank to self destruct. They also discovered a student who helped assemble the tank used a piece of tape to hold the paper thin carbon fibre sheet. After epoxy was applied, that tape was still there. The tape formed a weak spot. So when the tank started to come apart, it ruptured at the weak spot. Would have come apart anyway, but the tape caused it to explode. Reports are it was dramatic. Ok, so lesson learned. Paper thin walls of a hollow wall composite tank are not compatible with cryogenic propellants. They should have gone back to a solid wall composite. But they didn't. Rather than further belabouring the past, let's just accept the lesson that we need a solid wall tank.

The DC-XA used a carbon fibre / epoxy composite tank for liquid hydrogen. It worked. Again, the key is a solid wall tank. But it worked, it has been demonstrated. So let's use it.

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