Nuclear propulsion for rockets.

[Satanic Mechanic]

I figure this is a good technical topic for discussion-  Use of nuclear power as a propulsion system.

Of course the ship will have to be assembled in orbit.  I am convinced that this is the way to go to the moon for ferry missions and to Mars.  I have read some NERVA papers in the past and came across this twenty year old paper recently from Los Alamos about the benefits of going nuclear: http://www.lascruces.com/~mrpbar/Mars%20NTR%2085.pdf

I have heard many different designs- gas, solid and torodial reactors.  I have also heard of many different numbers for specific impulse.

Your thoughts please.


SM

[LunarOrbit]

I'm going to look at that link you provided first, SM. I admit I don't know much about nuclear propulsion.

It's obvious, though, that we can't go far using chemical rockets, at least not as we know them today.

[rcable1]

Cannot comment scientifically or technically, but if that is the power needed in the future, then I say go for it.As this is a contraversial issue, I'm sure it won't be easy.

[skyjim]

I suspect that we'll start with nuclear power systems  for outer planet missions and possible lunar base apps - but it looks like the early lunar base work is going to be done with chemical propulsion.

The first nuclear propulsion system will probably be nuclear electric power for deep space missions...NEP can give extremely high impulse and much more thrust than the little ion thrusters we've played with so far.  Deep space missions also will need serious power generation once they get to their destinations so they can do more science and/or carry out crewed missions.  Prometheus looked geared to define proper reactor sizes for both robotic and crewed spacecraft - hopefully it will yield results in time to get a crew to Mars when the time comes, and to do it under low-gee constant boost so transit times come way down.

Wouldn't be surprised to see the first crewed Mars mission leaving Earth-Moon on a big chemical stage  for initial oomph, though.  If we really do go and work on lunar oxygen generation, why not?  

I know that NEP systems aren't as sexy as big honking Nuclear Thermal Rockets - but consider this: they are much closer from a political standpoint (Prometheus plus existing electric thruster programs = NEP.  We're already started!)and can yield Mars ships capable of boosting at, say, 1/1000th gee.  Pretty wimpy-sounding number- but a 1/1000th gee constant-boost ship will get to Mars in around 10 weeks!  (That's back of the envelope figures from Robert Heinlein's "Expanded Universe" - assumes boost to midpoint, flip over and decelerate to destination, Mars at average opposition, NOT an unusually close one like we just had.  Windows open every 26 months...)  

Jim

[LunarOrbit]

10 weeks! That's a heck of a lot better than 6-9 months. Thanks for the info, Jim.

[Satanic Mechanic]

Funny you should mention the big honkin NTR's... I have always imagined the design of the nuclear spacecraft like the "Discovery" in Clarke's 2001.  But alas I know the ship will not have the streamlined design.  I just want the damn thing to be reusable.

I know that the astronauts will be happy with 1/1000th of a G.  Plus with a short trip, we will not have to worry much about the body's muscle/bone atrophy.

SM

[skyjim]

SM, I always loved the Discovery design, too!

Something that Heinlein pointed out in that same piece: that 10 weeks is about the time it took the MAYFLOWER (or any typical merchant vessel of the time, I guess)to cross the Atlantic in 1620. Round trips to the outer solar system at 1/1000 gee would take roughly the time that trade voyages required in the 18th and 19th centuries - and the canniest of the  traders got RICH!  The resources of the solar system are open to us if we have the will to explore.  

I need to do some more homework on electric thrusters.  We've got a great deal of work to do to build this  imaginary 1/1000 G ship.  Won't be easy, but to the best of my knowledge there are no basic breakthroughs required to make it happen. Just big reactors and big thruster arrays.  They would look decidedly odd to our eyes, basic structure perhaps like a dinner plate with a skinny cylinder standing upright on it - a big inverted "T", the bottom serif of the T" being crew accomodations.  Maybe you use the bottom section (with reactor shielding and reaction mass/water tanks, etc) as a shadowing device in the event of a big solar event - suspend boost, orient the thruster array toward the flare, ride it out for a few hours or days.

Of course, reality is that if we are in a real hurry to send a crew to Mars, we'll probably try to do it in free fall orbits using chemical propulsion and take a couple of years to do the whole mission.  Rad shielding gets more important (and massive) with longer mission durations, and we wind up with either a truly gigantic set of solar arrays or reactors for electrical power.  Hmmm - how many reactors do you put on a spacecraft which is going to carry people for a couple of years?  Do you build a photovoltaic array capable of powering basic life support and essential ship functions as a backup?  How much in-service testing do you do to establish reliability numbers?  What type and mass of rad shielding package is enough to protect the crew from cosmic and solar radiation, as well as local emissions from the reactors?

All sorts of nuts and bolts questions need to be addressed.  It's one of the reasons I'm anxious to go back to the Moon.  

I think it's a good place to learn.

Just for fun, imagine a system capable of 1/100 G constant boost...way beyond any current technology I'm aware of save Orions.

Earth-Mars in 23 days!

[rcable1]

Quote:The resources of the solar system are open to us if we have the will to explore.

I agree fully. The only thing I think of is should these valuable resources be brought back to Earth, someone(s) will get exceedingly, filthy wealthy while the average Joe has to pay through the nose to enjoy or benefit from such resources.
In other words we are now being robbed,IMHO, everyday for the resources we now have so wyhy would that change?

I do not want to sound negative on this subject, I am just concerned with such things.

[skyjim]

Rusty, I don't think that hummanity is likely to change its stripes.  There will still be greed, and the predatory types always exploit.  But I would rather be exploiting the asteroids for raw materials than a living biosphere.

What we think of as a high living standard is very resource-intensive. Not to mention energy-intensive. If we are able to tap into sustainable energy and increased raw materials, is it not one possibility that the overall lot of humans might improve?  More wealth to go around might improve the range of human options.  What we do with those options is doubtless going to run the gamut from inspired to depraved, just like humanity.  Are we worth perpetuating?  I guess that is the fundamental question.

  I think expanding into space, especially for energy and industrial activities, might actually SAVE the Earth's biosphere in the long view.  Might make us a worthier species in the process.  Hell, I'm a glass half-full type.  But I see a future where we are essentially trapped on a planet with dwindling resources and increasing mouths to feed if we don't get off the rock sometime soon.

Jim

[Satanic Mechanic]

A great step forward for nuclear propulsion.  I can't think of a better organization to build the reactor than the Navy.  When I lived in Idaho (northern part), the Navy use to build all their reactor prototypes outside of Idaho Falls (INEL).

http://www.space.com/businesstechnology/technology/jimo_fin_040219.html

[Dingo1]

Nuclear proposion is a good idea for interplanetary travel, just a bad idea for ground launches.  As for bases on the moon and such, Solar energy collection is the better idea, as long as you insure having collectors located around the moon for continuous power supply

[Satanic Mechanic]

I would rather go with a nuclear source of energy than solar.  More kW/kg.  More waste created from making high output photovoltaics than a nuclear reactor.  A lot of people think reactors put out a lot of waste but most of the nuclear waste you see is from enriching to make weapons grade material (80-99% pure).

[Dingo1]

SM...Long term this is correct, short term, solar makes sense on a $$$$ basis

One reason nuclear power is cost effective on Earth is the abundance of a cooling material...aka water.  Pocket Nuclear power plants that are in development in Russia for spaceflight still need a cooling mechinism..generally heat radiation on the dark-side of the vehical.

[Satanic Mechanic]

Making or should I say growing the photovoltaics cost more per once than that of gold.  
You can use radiators to dissipate the heat.

[Dingo1]

SM...agreed currently photovoltaics do cost more per ounce than gold, with current technology, yet research continues towards finding a much lower cost process.

What I am refering to is the cost of launches.  Radiators weigh quite abit in comparison to solar cells, so that solar cells on a pound per pound bases pay for themselves in launch cost savings.

I am just looking at using solar cells initially, until we have established a small working base on the moon that can build the nessisary infrastructure for nuclear energy generation.  It also loks like a viable energy source for remote sites until they can be hooked into the power grid.  Also keep in mind that in time there will be independant colonests on the moon, who will not want to have anything to do with government or coorporate controls