Light weight nuclear reactor, updating Mars Direct

SpaceNut · 2014-02-10 22:02:08

For building block parts of the ITV design have you looked at possible existing modules from the ISS such as the node 3 that the waste water recovery is located in and the Habitation Extension Module

http://www.nasa.gov/audience/formedia/p … heets.html

Quaoar · 2014-02-11 11:39:22

Why not to rebuild mission architecture sending firstly in LMO an unmanned lander-tanker with a SAFE 400 nuclear reactor and a lot of empty propellent depots?

The lander-tanker will land in place with known ice pack in high latitude like this ( http://www.space.com/1371-ice-lake-mars.html ); melt the ice and use the water for ISPP (LOX-LCH4 or LOX-LH2 if it is possible to produce LH2 with a compact hardware); when the tank is full, the lander will take-off, dock with a propellant depot, fill it and land again to produce more propellant. When all the propellent depots will be full, an orbiter vehicle with the astronaut, two lander and a landing habitat will departure from Earth, aerocapture in LMO, then dock with propellant depots and use the propellant to explore multiple sites.

When the astronaut will find a site in low latitude with a big buried ice reserve, they will land there the landing habitat, that will be the first module of a scientific base.

louis · 2014-02-11 15:20:25

Why bother with a nuclear reactor that might malfunction when we have operated Rovers safely for several years on Mars using PV energy?

RobertDyck · 2014-02-11 15:56:08

Not enough. You can't make return propellant with power from PV. Besides, Curiosity has an RTG right now.

Besides, why do you fall into the Hollywood fiction of saying nuclear = fail? That's like asking why use a Space Shuttle Main Engine when it might malfunction?

Last edited by RobertDyck (2014-02-11 16:13:40)

louis · 2014-02-11 17:16:55

RobertDyck wrote:

Not enough. You can't make return propellant with power from PV. Besides, Curiosity has an RTG right now.
Besides, why do you fall into the Hollywood fiction of saying nuclear = fail? That's like asking why use a Space Shuttle Main Engine when it might malfunction?

I don't say an RTG is not possible - just that if you go with one reactor and it fails, you've could have a dead crew on your hands. It's all very well to say they have a 100% record but we need a failsafe plan if we are sending humans.

I don't know why you say PV can't power propellant manufacture. Perhaps you aren't working with a pre-lander element in your mission architecture, but there's no reason why you can't begin propellant manufacture years before the humans land.

RobertDyck · 2014-02-11 22:53:05

This discussion thread is about updating Mars Direct, not redesigning it. I discussed an alternate mission architecture in another thread. With Mars Direct, the idea is land an ERV with no humans, produce fuel, and ensure the radio signal indicates full propellant tanks before crew even leave Earth. If there's a problem, send a replacement ERV. Furthermore, a second ERV will follow the hab. If something goes wrong, the second ERV will land at the first mission site. If everything is Ok, if astronauts walk over to the pre-landed ERV and inspect it to find everything is working, then the second ERV will land at a new site. That new site will start the second mission. So if the reactor fails, there are backups.

PV on Mars will accumulate dust. As the solar panes are covered, they get less light. That generates less power. Opportunity was lucky, it had several dust devils clean its PV panels. With a human mission, you have crew who can erect multiple panels. You won't have that for the ERV. And if the PV panels get dusty, crew can walk over with a broom. Again, you won't have that with the ERV.

Quaoar · 2014-02-12 02:59:16

RobertDyck wrote:

This discussion thread is about updating Mars Direct, not redesigning it. I discussed an alternate mission architecture in another thread. With Mars Direct, the idea is land an ERV with no humans, produce fuel, and ensure the radio signal indicates full propellant tanks before crew even leave Earth. If there's a problem, send a replacement ERV. Furthermore, a second ERV will follow the hab. If something goes wrong, the second ERV will land at the first mission site. If everything is Ok, if astronauts walk over to the pre-landed ERV and inspect it to find everything is working, then the second ERV will land at a new site. That new site will start the second mission. So if the reactor fails, there are backups.
PV on Mars will accumulate dust. As the solar panes are covered, they get less light. That generates less power. Opportunity was lucky, it had several dust devils clean its PV panels. With a human mission, you have crew who can erect multiple panels. You won't have that for the ERV. And if the PV panels get dusty, crew can walk over with a broom. Again, you won't have that with the ERV.

To produce 100 KW on Mars orbit we need 1000 m2 of PV. On Mars surface we need even more. A SAFE-400 nucear reactor will be much lighter and compact than a very large solar array that may be difficoult to deploy automatically. SAFE-400 weight is only 512 Kg: why not to send the ERV with two of them?
The second recator will be a very safe backup and it may produce an excess of propellant that may be use for an hopper.

Last edited by Quaoar (2014-02-12 03:00:57)

RobertDyck · 2014-02-12 06:39:00

In understand the argument for a backup. However, nuclear reactors are generally reliable. Contrary to the usual Hollywod trope. If the extremely unlikely event happens, if the reactor fails, then just don't send the hab with crew. Instead send a second ERV, and crew are postponed by 26 months. That's when Earth and Mars will allign for the next launch opportunity.

louis · 2014-02-12 19:16:42

RobertDyck wrote:

This discussion thread is about updating Mars Direct, not redesigning it. I discussed an alternate mission architecture in another thread. With Mars Direct, the idea is land an ERV with no humans, produce fuel, and ensure the radio signal indicates full propellant tanks before crew even leave Earth. If there's a problem, send a replacement ERV. Furthermore, a second ERV will follow the hab. If something goes wrong, the second ERV will land at the first mission site. If everything is Ok, if astronauts walk over to the pre-landed ERV and inspect it to find everything is working, then the second ERV will land at a new site. That new site will start the second mission. So if the reactor fails, there are backups.
PV on Mars will accumulate dust. As the solar panes are covered, they get less light. That generates less power. Opportunity was lucky, it had several dust devils clean its PV panels. With a human mission, you have crew who can erect multiple panels. You won't have that for the ERV. And if the PV panels get dusty, crew can walk over with a broom. Again, you won't have that with the ERV.

I take your point about not looking for a redesign. But on the specific point I don't think there would be any problem with putting on the planet a small maintenance robot that would patrol up and down the lines of PV panels and blow away dust. Also there are designs that could mitigate the dust problem.

louis · 2014-02-12 19:18:23

RobertDyck wrote:

In understand the argument for a backup. However, nuclear reactors are generally reliable. Contrary to the usual Hollywod trope. If the extremely unlikely event happens, if the reactor fails, then just don't send the hab with crew. Instead send a second ERV, and crew are postponed by 26 months. That's when Earth and Mars will allign for the next launch opportunity.

If you go with RTG I do think you need two - and well separated. Meteorite strikes are probably the greatest danger. We saw that rock pop up out of nowhere on Mars recently - could have been a nearby meteorite strike.

louis · 2014-02-12 19:22:34

Quaoar wrote:

RobertDyck wrote:
This discussion thread is about updating Mars Direct, not redesigning it. I discussed an alternate mission architecture in another thread. With Mars Direct, the idea is land an ERV with no humans, produce fuel, and ensure the radio signal indicates full propellant tanks before crew even leave Earth. If there's a problem, send a replacement ERV. Furthermore, a second ERV will follow the hab. If something goes wrong, the second ERV will land at the first mission site. If everything is Ok, if astronauts walk over to the pre-landed ERV and inspect it to find everything is working, then the second ERV will land at a new site. That new site will start the second mission. So if the reactor fails, there are backups.
PV on Mars will accumulate dust. As the solar panes are covered, they get less light. That generates less power. Opportunity was lucky, it had several dust devils clean its PV panels. With a human mission, you have crew who can erect multiple panels. You won't have that for the ERV. And if the PV panels get dusty, crew can walk over with a broom. Again, you won't have that with the ERV.
To produce 100 KW on Mars orbit we need 1000 m2 of PV. On Mars surface we need even more. A SAFE-400 nucear reactor will be much lighter and compact than a very large solar array that may be difficoult to deploy automatically. SAFE-400 weight is only 512 Kg: why not to send the ERV with two of them?
The second recator will be a very safe backup and it may produce an excess of propellant that may be use for an hopper.

I would concede that there is some mass advantage to a nuclear reactor. However, if you have to take two that is a doubling of mass. And if you have to locate it well away from the hab, you of course are building up cable mass.

PV panels have a number of advantages. We do know they work well on Mars. A meteorite strike will not put the whole of the energy generation out of action. It can be split up - so if you want to set up a mining operation a few kms away you don't need to import another nuclear reactor.

SpaceNut · 2014-02-12 19:52:05

Just a quick reference for the solar http://en.wikipedia.org/wiki/Sunlight look at the table below the header Intensity in the Solar System this is the sine function of the angle which is related to distance to the sun and the diameter of the planet but the issue for it comes back to we are trying to make up for the energy being less than that to which we see for the difference that we take for granted. When you must put additional energy into making oxygen, water, and then for fuels we really can not use the much lower level of solar for the high energy needs of those processes.

RTG's have staying power...

http://www.patentstorm.us/patents/52465 … ption.html

The RTG is subject to two significant power degradation mechanisms. One is radioactive decay of the plutonium isotope that has a half-life of 88 years. This inevitable power loss is about 1% per year. The other mechanism is degradation of the unicouples. The electric power loss due to the unicouple degradation is also about 1% per year.

The only thought I have on backups would be with the ability to keep them turned off until needed but wonder if one can be turned off once started as well. The next would be maintaining them if they are not working quite to specifications, what are the possible ways to repair?

RobertDyck · 2014-02-12 20:45:39

What I described is launch the backup if it's needed. If it isn't needed, don't launch it. That is the lowest cost solution.

louis wrote:

We saw that rock pop up out of nowhere on Mars recently - could have been a nearby meteorite strike.

That isn't a meteorite. As I posted elsewhere, my belief is it's salt. Look carefully, the shape exactly matches the dirt it the crack beneath. It's even turned the same way, with a point to the lower left. That can't be a coincidence. Salt water extruded up through a crack from weight of the rover sitting on the rock. Then water evaporated. So no need to panic about meteorites.

SpaceNut · 2014-02-14 00:46:27

Human Rating Mars EDL

http://trs-new.jpl.nasa.gov/dspace/bits … 5-3869.pdf

Just how do we get 40 to 80 tons on the surface as that means its lots more than that since you must add in the fuel for landing, heat shield and parachutes.

http://www.nasa.gov/pdf/637595main_day_ … irhead.pdf

We talked about the fact to save money and mass we need to make the right choices such as not sending an extra RTG not only to say mass but to save on funding of this future mission.

http://trs-new.jpl.nasa.gov/dspace/bits … 9-3642.pdf

Highlighted in this document is all the previous Design Reference mission plans. Lots of what we are talking about using in this DRA-5 plan.

http://www.marspapers.org/papers/Brown_Ed_2004.pdf
CHALLENGES IN HUMAN-RATING THE CREW EXPLORATION VEHICLE
TO MARS
OR
WHY HUMAN SPACEFLIGHT IS SO DAMNED EXPENSIVE

But there are alternatives to the cost possibly in the Red Dragon
http://www.lpi.usra.edu/meetings/marsco … f/4315.pdf

What new tech do we truely need? Some say due to huge mass of the landing elements that we need to Development of Supersonic Retro-Propulsion for Future
Mars Entry, Descent, and Landing Systems

http://www.ssdl.gatech.edu/papers/confe … 0-5046.pdf
Mars edl comparisons are made for the misions we have done thus far. But where do we stand with the tech that we have and the matuity needed.

GW Johnson · 2014-02-14 16:59:43

Landing 100+ ton vehicles on Mars is not that big a deal from an engineering standpoint, if you use supersonic/hypersonic retro-propulsion. Period. Chutes are useless with ballistic coefficients that high.

The ONLY issue is exactly how to implement retro-propulsion. It has been studied before, just not very seriously, by NASA itself, ca. 1960. We do know from those test then that vehicle drag is reduced by the presence of a retro plume, in an amount dependent upon the massflow of that retro plume. A very simple wind tunnel test at Mach 2 told us that long ago.

The only real issue is retro plume(s) stability, because a plume that flip-flops from one side to the other as it reverses, may very well induce large destabilizing forces on the vehicle.

But, if you use multiple engines, and cant them off centerline, the retro plumes are pre-oriented toward one side. That should provide a stable flow field. The only question is how much cant is enough, and what variables does that depend upon?

That basic answer is determinable from supersonic to low hypersonic wind tunnel tests in very sub scale, with a 6-d.o.f. force balance holding your model. That is quite inexpensive to do: well under $1M at multiple universities with aero engineering departments, and their wind tunnels.

From there, it goes to subscale model tests high in our atmosphere on sounding rockets or via the suborbital spaceplane operators. All very cheap to do.

Then you build a full scale prototype, and launch it into the thin air with existing launchers.

Land one of those unmanned on Mars for final checkout. Program total should be under $50M, or somebody is stealing the money.

Then use it: land some men on Mars, for cryin' out loud!

GW

SpaceNut · 2014-02-15 11:39:20

So from an engineering standpoint of supersonic/hypersonic retro-propulsion, what happens with an engine goes out or does not start; what then when you are already on the way down.

Quaoar · 2014-02-15 12:35:05

SpaceNut wrote:

So from an engineering standpoint of supersonic/hypersonic retro-propulsion, what happens with an engine goes out or does not start; what then when you are already on the way down.

IMHO, the lander has to be projected with multiple rocket and with engine out capability.

Quaoar · 2014-02-15 12:42:14

louis wrote:

PV panels have a number of advantages. We do know they work well on Mars. A meteorite strike will not put the whole of the energy generation out of action. It can be split up - so if you want to set up a mining operation a few kms away you don't need to import another nuclear reactor.

There are variants like Mars Oz that use PV panels instead nuke, but they use a little Mars Ascending Vehicle for rendez-vous with an orbital Earth Return Vehicle. To produce almost one hundred tons of LOX-LCH4 to fill the tanks of a landing ERV, PV are not enough.

louis · 2014-02-15 13:12:28

Quaoar wrote:

louis wrote:
PV panels have a number of advantages. We do know they work well on Mars. A meteorite strike will not put the whole of the energy generation out of action. It can be split up - so if you want to set up a mining operation a few kms away you don't need to import another nuclear reactor.
There are variants like Mars Oz that use PV panels instead nuke, but they use a little Mars Ascending Vehicle for rendez-vous with an orbital Earth Return Vehicle. To produce almost one hundred tons of LOX-LCH4 to fill the tanks of a landing ERV, PV are not enough.

It's a crazy way to go about things landing a big ERV. The Apollo method is much better. There should be a small lander/ascent craft.

You land the Mars Hab separately. Then all the crew need to do is transfer from the lander to the hab. I think the Apollo ascent craft had something like 2.6 tonnes of propellant. Scaling up for a 3 man ascent craft, maybe we'd be talking about 10 tonnes fuel being required.

Quaoar · 2014-02-15 16:32:58

louis wrote:

It's a crazy way to go about things landing a big ERV. The Apollo method is much better. There should be a small lander/ascent craft.
You land the Mars Hab separately. Then all the crew need to do is transfer from the lander to the hab. I think the Apollo ascent craft had something like 2.6 tonnes of propellant. Scaling up for a 3 man ascent craft, maybe we'd be talking about 10 tonnes fuel being required.

Sure, but Mars Direct was planned in 1989, when automatic orbital rendez-vous and docking procedures were not well developed like now. Zubrin avoided orbital rendez-vous because pilots would be out of training, after spending 500 days on Mars surface. Probably he was right.

Planning Mars Direct now, probably may be a better option sending empity orbital propellant depot and two unmanned lander-tanker with a nuclear recator. So the big ERV will refuel on orbit and two reusable lander can be used to explore multiple sites in the same mission, plus a landing on Phobos.

Last edited by Quaoar (2014-02-15 16:39:58)

RobertDyck · 2014-02-15 16:39:00

In Yet another Mars architecture I talked about parking a reusable Interplanetary Transit Vehicle in Mars orbit. However, the Mars Ascent Vehicle would carry enough propellant to be the Trans-Earth Injection stage for the ITV. That requires a lot of propellant. But that's how all return propellant is produced with ISPP. The alternative is to bring return propellant from Earth. Once you do that, launch weight from Earth increases so much that cost becomes prohibitive. My mission architecture uses a fabric umbrella-like heat shield to aerocapture into orbit at both ends: Mars and Earth. Leave it parked in highly elliptical, high Mars orbit. That way it is barely in Mars orbit at all, so minimum propellant to depart. But once in Earth orbit, further aerobrake down to ISS. This has the advantage that the ITV is dedicated for interplanetary transit. Also when crew depart Earth, they do so in the ITV that is intended for transit both ways, and the surface habitat goes with them. That means all food for the entire trip, from Earth to Earth, goes with astronauts. If free return is necessary, they have all the food right there. And if necessary, life support equipment in the surface hab can act as backup for life support equipment in the ITV. A Dragon would be docked to the ITV as an emergency escape pod aka lifeboat. As long as it's not used, the Dragon would stay attached for the next mission.

In this architecture, the MAV is only used to transfer astronauts, Mars samples, and propellant from Mars surface to Mars orbit. That's a short trip. Instead of a pressurized cabin with life support, it could use an unpressurized fairing with seats. Let astronauts stay in suits until they're safely in the ITV. That reduces weight. However, launching from Mars surface with enough propellant to be the TEI stage? And for an ITV as large as a single module of ISS with a Dragon attached? That's a lot of propellant.

And you do want to land all crew on the surface. Orbit has zero gravity, and a lot of radiation. Remember Mars does not have a magnetosphere. ISS is in LEO, so inside Earth's magnetosphere. MARIE instruments on Mars Odyssey measured radiation in Mars orbit as roughly twice that of ISS. So you want to land all crew on Mars surface. This means designing the MAV for 4 crew.

But this is off-topic. We should discuss this on the other thread.

Last edited by RobertDyck (2014-02-16 09:21:01)

Quaoar · 2014-02-15 16:51:22

RobertDyck wrote:

But this is off-topic. We should discuss this on the other thread.

OK excuse me to go OT.
In the classic Mars Direct, for refueiling a big ERV on Mars surface, the ISPP-unit was powered by a 100 KW nuclear reactor. To get the same amount of energy of a 100 KW 512 Kg Safe-400 operating continously, a PV array has to be very huge and massive: 3000-4000 square meters (plus buffer batteries for the night). Astronauts can easly asseble it in a week of work, but I dont know if such large array can be stowed and deployed automatically by an unmanned vehicle.

Last edited by Quaoar (2014-02-15 16:54:04)

SpaceNut · 2014-02-15 18:00:40

What was the reason for the 5 k w solar in the initial post table.

The only other update from that table is to change materials to lighter alloy's for constructing the ERV or Hab and that includes the furniture.

RobertDyck · 2014-02-15 18:26:19

SpaceNut wrote:

What was the reason for the 5 k w solar in the initial post table.

In case the Hab lands far from the ERV. That 5 kilowatt electric (5 kWe) solar array is for life support, and other power in the Hab.

SpaceNut · 2014-02-15 20:39:25

Here is the copy that I found for Mars Driect

http://wp10988215.server-he.de/MSE/wp-c … _19911.pdf

So how does the crew get from landing in the second ERV to a Hab that is far off....Just how far off could it be?

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