Author Topic: Power Supply for VASIMR  (Read 30376 times)

Offline wingod

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Power Supply for VASIMR
« on: 11/29/2007 04:38 AM »
I thought about this when I saw the article yesterday but someone has gone for it and written one about using this new "Nuclear Battery" technology to power a VASIMR engine

Really really REALLY interesting.

http://advancednano.blogspot.com/2007/11/vasimr-engines-plus-200-mw-of-nuclear.html



Offline A_M_Swallow

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Re: Power Supply for VASIMR
« Reply #1 on: 11/29/2007 05:50 AM »
Seven nuclear power "batteries" to get to Mars in 39 days sounds like the manned version.   The cargo version will probably take 100 days using 2 nuclear "batteries" or possibly use 50 MW solar arrays to power the VASIMR.  The trips are sufficiently short that the spacecraft can be reused.

At these sort of speeds we no longer need to use the shortest route.  I wonder how long the trip will take at maximum separation between the Earth and Mars?  All year round trips to Mars will make a Mars colony much more viable.

If a small VASIMR SEP is going to the Moon in 2010 then a version can be sent to Mars in say 2012.

Offline pippin

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Re: Power Supply for VASIMR
« Reply #2 on: 11/29/2007 08:59 AM »
Just 10 ARES V flights to assemble one... Sounds a bit big to me.
Oh, and burying the "battery" is probably also not an option for spaceflight ;-)

Offline meiza

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Re: Power Supply for VASIMR
« Reply #3 on: 11/29/2007 01:15 PM »
Physics!!

How does the "nuclear bathtub" work? I've heard very sceptical mentions from nuclear engineers, saying how reactors have to have a big surface area to move the heat out - something that the nuclear bathtub doesn't have.
And you need a temperature difference (if you don't have a direct conversion system), something which requires big big radiators in space. When you see a picture of JIMO, most of that stuff is *radiators*.

So you can't just take "hey 200 MW, let's stick it on a spacecraft".

Gah.

Offline neviden

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Re: Power Supply for VASIMR
« Reply #4 on: 11/29/2007 03:20 PM »
It's all about cooling.

Getting power in space is easy. You can get 100 MW of thermal power to one spot with big lightweight mirror or hot reactor.

The hard part is using 100 MW of thermal power but at high isp. If you just use the heat to directly heat the propellant you get low isp in the range of 800s (NTP). Once you calculate the cost and weight of the whole ship (reactor, shields, plumbing,..) you are no better then the simple chemical rocket. VASIMR is good since you can get very high isp. The problem is that you need electrical power. You can’t use thermal power. And to get it you need to run some kind of thermal to electric conversion. And that basically means that to get your 100 MW VASIMR running, you must reject 200 MW of thermal power (very optimistically) in what is big thermos bottle (vacuum).

VASIMR is useful only when you have lightweight electric power generator (with the radiators) so that it can actually make a difference. Unless of course the VASIMR is only part of the fusion drive in that case it’s not really VASIMR, is it..

Offline khallow

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Re: Power Supply for VASIMR
« Reply #5 on: 11/30/2007 02:44 AM »
Even if dumping heat directly to propellant isn't that useful, it's still a way to dump heat. One could use that as a way to preheat propellant that is to be ionized (the assumption being that heating will help lower the energy threshhold for ionization).
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Offline Lampyridae

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Re: Power Supply for VASIMR
« Reply #6 on: 11/30/2007 03:29 AM »
I've come across one white paper that proposed used a gasdynamic laser as a radiator, which could then be used to heat propellant. Well, actually it wasn't the gasdynamic laser doing the heating - that had a negative temperature, and it fires back into the working gas, resulting in a standard blackbody radiation (albeit very bright and in a small space) that could be dumped through an optical window. A mirror could focus that radiation into a propellant. At least that's what I gathered from reading the thing. Apparently it doesn't violate entropy laws, either - but the idea's gotten no farther than that white paper.

Liquid droplet radiators could dump the heat a lot better, but that's still mass and bulk that needs on-orbit deployment and assembly...
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Offline neviden

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Re: Power Supply for VASIMR
« Reply #7 on: 11/30/2007 07:04 AM »
Quote
khallow - 30/11/2007  4:44 AM
Even if dumping heat directly to propellant isn't that useful, it's still a way to dump heat. One could use that as a way to preheat propellant that is to be ionized (the assumption being that heating will help lower the energy threshhold for ionization).
Heating propellant directly is useful to get to about 1000s isp. Anything above that is not possible since your support structure will melt. While it is a good boost it doesn’t really matter if your target isp is in the thousands of seconds. That is why you need electric power. At high isp levels the flow rate of propellant is measured in grams per second. Not something that would be enough to cool it. It would be good if you had low isp and it is already used that way (chemical rocket) but once you go to high isp (VASIMR) then it doesn’t really help that much.

Let me put it another way. Space shuttle has 12 GW engines at liftoff with isp in the area of 400 s. It is 95% propellant, burns its engines for few minutes and gets the maximum of 10 km/s delta-v. If we had one in orbit we could easily get to Mars orbit and back. The problem is, that we don’t have free 2,000,000 kg propellant depot in LEO so that we could refill our Space Shuttle once in orbit.

If you could get engines with higher isp you would not have to carry that much propellant in the first place even if you had to burn them for longer. And while you do need that much power to actually get from the ground (to fight the gravity), that power isn’t needed once you are in freefall (in orbit). Sure it would be mightily helpful if you would have 12 GW thrust engines in orbit. If you had isp that would be high enough so that you could actually carry enough propellant (that means you would not burn it in few minutes) you would be able to use it to get to Mars and back in few days. Even better would be if you had 12 GW thrust engines with high isp, but once you look how big that ship would be you get to understand the problem..

Offline advancednano

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RE: Power Supply for VASIMR
« Reply #8 on: 11/30/2007 03:47 PM »
I exchanged email with Hyperion Power Generation (the maker of the new power generator. They indicate that the Sante Fe reporter made a mistake. The output is about 25-17 MW ELECTRIC [This statement was also consistent with the patent which talked about tens of MW in electricity.] They also said that the containment vessel will be dense enough that no radiation will escape even if it is not buried in the ground.

So in addition to the regular electric generation there would be probably double that amount of thermal power. Which could be partially converted to electricity using thermoelectronics. 30-66% with better technology like powerchips

Lighter radiation shields are possible.

I have asked them about weight of the reactor and different heat pipe configuration, and they are considering whether to answer me about it. I believe that they may have more heat piping and just are not showing it in the diagrams.

Offline meiza

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Re: Power Supply for VASIMR
« Reply #9 on: 11/30/2007 04:58 PM »
I still don't see the power extraction mechanism.
Current reactors have fuel in thin rods and water circulates around them, extracting the heat. Then it's turned into electricity in a steam turbine.


Offline neviden

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RE: Power Supply for VASIMR
« Reply #11 on: 11/30/2007 05:20 PM »
Quote
advancednano - 30/11/2007  5:47 PM
I have asked them about weight of the reactor and different heat pipe configuration, and they are considering whether to answer me about it. I believe that they may have more heat piping and just are not showing it in the diagrams.
That is the most critical point. How much would everything weigh on a spaceship. Radiators, shielding, structure, reactor, piping, electrical conversions for specific thrusters (if they need different voltage for example), cables, controls..

You take the weight, divide it by how much power you get and you get nice KW/kg number. That is the most important thing that you need to know if you want to make any comparison. Higher it gets, faster, lighter and more capable your spaceship will be.

VASIMR itself is useless without some very capable electrical system to power it.

Edit: Oh I see I have missed that magical 70% - 80% lightweight 200 MW “powerchip” conversion. That is why there is no need for radiators that you would otherwise need to dump 500+ MW of heat in vacuum..

Without them your spaceship would look something like this (only bigger, since this one is only 10 MWe):
http://gltrs.grc.nasa.gov/reports/2003/TM-2003-212349.pdf

Oh, yeah, that company that makes those “powerchips” will be big, better buy it now. ;)

Offline advancednano

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RE: Power Supply for VASIMR
« Reply #12 on: 11/30/2007 06:42 PM »
It is only the size of a hot tub. 8 cubic meters. Even at max avg density of 8. That would be 64 tons. There is only about 600-1200 kg of uranium hydrate.

I believe that for a space ship lighter radiation shielding could be used.

I discuss the recent thermoelectric advances which are part of a quite well funded program to raise the efficiency of cars and trucks. This could be used in place of heavier power conversion. Should be ready in 2014 (actually the first versions will be in BMW car in 2010. Crude versions are already used for beer refridgerators and are used for car seat warmers). Could boost the electric power conversion by 60%. Pushing electrical power from 25MW to 40MW per unit. Only 5 units would be needed to achieve 200MW.

With electrostatic radiation shielding and advanced thermoelectronic heat to electricity conversion then I believe each unit could be brought down to ten tons. Most of the weight is the tons of fuel that the Vasimr would be using as reaction mass.

Vehicle efficiency technology gets about 176 million per year The new thermoelectronics is not magic tech.

Offline meiza

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Re: Power Supply for VASIMR
« Reply #13 on: 11/30/2007 07:37 PM »
Note that the quantum dot graph has T_Cold = 50 C. I don't know how big radiators you need for that in space...
Pressurized water nuclear reactors run around 350 C on the hot side but have the advantage of being on earth where your cold side can be cooool. And they use high efficiency steam generators and end up being around 30% efficient.
So what we need:

1) hot side temp of the tub reactor system (or is there a lower limit for coolant coming in to the reactor? The Greenspan paper uses fancy metal coolants which mean the incoming coolant has to be hot too to stay molten, and thus the delta T is only 150 C)
2) mass of a certain tub size with certain power
3) we can calculate a reasonable cold side temp of a reasonable mass radiator
4) from these we get delta-T and can calculate the conversion efficiency

Only THEN can we estimate the mass of the system. That's a first order thing.

Offline advancednano

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Re: Power Supply for VASIMR
« Reply #14 on: 11/30/2007 08:44 PM »
The hyperion device runs at 400-800 degrees using uranium hydrates and can run at 1900 degrees using thorium hydrates.

We can look at other spacecraft designs that have heat radiators. Those are separate technologies from the main hyperion nuclear reactor.

Here is some info on other heat radiators for rockets

Here were some weights for a nuclear fission system.

BTW: on the topic of the people who are making light of the powerchip company, You can also mock general electric, general motors, john Deere, Delphi Automotive Systems, Dow Corning, Caterpiller, Argonne National Laboratory, and Oak Ridge National Laboratory and Virginia Polytechnic Institute and Ames National Laboratory and the other companies working on advanced thermoelectronics.

Offline meiza

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Re: Power Supply for VASIMR
« Reply #15 on: 11/30/2007 09:15 PM »
That is a remarkably efficient thermionic system and will change a huge amount of things on earth too.

Okay here is the calculation with a huge amount of assumptions:

-The coolant enters the tub at 400 C and leaves at 800 C.
-The thermionic quantum dot system has a ZT of 4.5 which means efficiency of 22% at 400 K delta T.
-For 200 MW electric power we need thus about 1000 MW thermal power.
-To radiate 1000-200 = 800 MW at 400 C = 700 K means
P = Re * 6E-8 * A * T^4
8E8 W = 1 * 6E-8 W/(m^2*K4) * A * (700 K )^4
A = 8E8 m^2 / (6E-8 * 700^4)
A = 55000 m^2.
Or a square with a side of over 200 meters.

On the other hand, if you accept a lower efficiency and lower delta T, you can run with a higher radiator temperature and that makes it smaller. If we want a 100 m square, the area drops to 1/4, T^4 grows to 4, T^2 to double and T to 700 K *(sqrt(2)) = 1000 K or 700 C.
Thus the delta T drops to 100 K and thermionic efficiency to about 10%. Meaning the whole system (reactor, converter, radiator area) must grow to 2X. That means the radiators are 1/4 * 2 = half the area, or about 140 m a side. There is a certain optimal low end temperature which depends on the specific radiator, converter and reactor masses.

Offline neviden

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Re: Power Supply for VASIMR
« Reply #16 on: 11/30/2007 09:45 PM »
You are missing the point. You don’t have to prove that NEP would work. It is a known and a good concept.

It is the matter of facts. How much would everything weigh and what could you do with it.. Even if you increase power conversion efficiency to 80% you still need to look at the whole picture. How heavy would reactor be? How heavy would that powerchip conversion be? What about structures? Tanks? Cables? Shields? Thrusters? Cryogenic stuff for your propellant?

What is the realistic kW/kg estimate. How big would everything be if you designed your ship to have and use 200 MWe thrusters? How much would it cost?

Offline meiza

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Re: Power Supply for VASIMR
« Reply #17 on: 11/30/2007 10:22 PM »
We simply don't have that data as the reactor concept is so vague as is the data about the thermiionic systems. I just showed that radiator area is pretty big even with very favorable assumptions.

Offline neviden

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Re: Power Supply for VASIMR
« Reply #18 on: 11/30/2007 10:53 PM »
I agree with meiza. But the whole NEP concept doesn't even need 200 MWe to be useful. Even 10 MWe with present technology would work almost as good as chemical/NTP and allow reusable spaceship capable of reaching Mars orbit and returning back.

Anything with more power and better kW/kg ratio would only shorten transit times, increase payloads and increase capabilities.

Offline advancednano

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Re: Power Supply for VASIMR
« Reply #19 on: 11/30/2007 11:22 PM »
I did not say that vasimr needed the Hyperion reactor to be useful. Vasimr is proceeding with its 200kw device.

However, the Hyperion reactor had a bunch of confused information online at slashdot and Sante fe reporter. I was providing more accurate info from the patent and from direct correspondence with the company.  I was also considering how it might help the Vasimr if it did get developed. I do not see any other relatively small solid core reactor nuclear projects with any funding.

The vasimr - hyperion reactor is a speculation based on limited info.

From the patent (section 58)

At the rate of power production assumed for the reactor, 50 to 100 W/cm**3.

If the density is 8. then it would seem to work out to 7-14KW per kg.

Offline wingod

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Re: Power Supply for VASIMR
« Reply #20 on: 12/01/2007 07:32 PM »
Quote
neviden - 30/11/2007  5:53 PM

I agree with meiza. But the whole NEP concept doesn't even need 200 MWe to be useful. Even 10 MWe with present technology would work almost as good as chemical/NTP and allow reusable spaceship capable of reaching Mars orbit and returning back.

Anything with more power and better kW/kg ratio would only shorten transit times, increase payloads and increase capabilities.

yes but what it does is open the entire solar system to human exploration and development.  If this turns out to work it is civilization changing!!

The problem with low power VASIMR is that it has very low efficiency.  It needs the power to get into the best operating regime.

I am really stoked about this development!!





Offline neviden

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Re: Power Supply for VASIMR
« Reply #21 on: 12/02/2007 09:43 AM »
I agree that VASIMR could use lots and lots of power and that more power at lower weight will improve capabilities. Better reactors and more efficient power conversions will do both of those things.

But the thing that is holding VASIMR back is that it is used in the wrong way. It is almost like NASA always asks themselves: “OK, how will this technology help us in going to Mars. You know, something like Apollo.. “.

So that means that is not absolutely needed is “impossible”..

Reuse? “impossible”..
Existing launchers? “impossible”
Space refueling? “impossible”
Long term space flight? “impossible”
Growing food? “impossible”
Artificial gravity? “impossible”

So all plans for VASIMIR start at LEO, they must race to Mars at full speed (you know, because it is “impossible” to create 1 g environment in space or carry enough shielding to protect the crew) and return back. That means 200 MW space propulsion with minimum mass.. Reuse? Oh, that will come after that.. when they throw everything in the trash and start on completely new design in 50 years or so..

Offline TyMoore

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Re: Power Supply for VASIMR
« Reply #22 on: 12/02/2007 05:54 PM »
Just a few points:

1) The nuclear 'battery' concept is a possibly good choice for a stationary power supply, but as a flight weight reactor--it is unnecessarily heavy. A better choice of reactor power system would be a compact tungsten core with U-Zirconium alloy fuel rods (U-235 enriched to 90% or better) cooled with Helium gas run through a Brayton Cycle gas-turbine conversion system. Using two units counter rotating will eliminate undesirable gyroscopic effects. It's still heavy--but the conversion efficiency will approach 50%. The Uranium-Zirconium alloy fuel system is currently mature technology used aboard any US nuclear submarine (although they use pressurized water cooling and not helium gas!)

2) Thermodynamic efficiency isn't everything--because more efficient systems tend to expell heat at lower temperatures the size of the radiator increases inversely with the fourth power of the temperature of heat rejection. Because of this fact, a slightly less thermodynamically efficient power conversion system may actually end up being more mass-efficient (lighter weight) than it otherwise would have to be. In otherwords, it is sometimes O.K. to take a heat-efficiency hit if it means saving a lot of mass--you have to look at the system as a whole and identify and eliminate as many penalties as you can...

3) Electrostatic radiation shielding--works o.k., but it works better in conjunction with a strong magnetic field. And it won't work at all for shielding the eminations from a nuclear reactor. Why? Because the majority of the most dangerous radiation components are neutrons and gamma-rays--both of which are neutral and extremely penetrating. Only two things will help here: mass and distance. You put mass between yourself and the reactor--and you get the reactor as far away from you as you can. Unfortunately these operational requirements are at odds with the usual smaller, lighter design philosophy of spacecraft design. So the designer must then see if there is a way to use the reactor for another purpose--like as counter weight for a spinning artificial gravity system. The spacecraft designer will put much effort into attempting to solve more than one problem with the same solution!


Offline wingod

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Re: Power Supply for VASIMR
« Reply #23 on: 12/02/2007 06:26 PM »
Quote
neviden - 2/12/2007  4:43 AM

I agree that VASIMR could use lots and lots of power and that more power at lower weight will improve capabilities. Better reactors and more efficient power conversions will do both of those things.

But the thing that is holding VASIMR back is that it is used in the wrong way. It is almost like NASA always asks themselves: “OK, how will this technology help us in going to Mars. You know, something like Apollo.. “.

So that means that is not absolutely needed is “impossible”..

Reuse? “impossible”..
Existing launchers? “impossible”
Space refueling? “impossible”
Long term space flight? “impossible”
Growing food? “impossible”
Artificial gravity? “impossible”

So all plans for VASIMIR start at LEO, they must race to Mars at full speed (you know, because it is “impossible” to create 1 g environment in space or carry enough shielding to protect the crew) and return back. That means 200 MW space propulsion with minimum mass.. Reuse? Oh, that will come after that.. when they throw everything in the trash and start on completely new design in 50 years or so..

Oh I agree that trying to use VASIMR deep in a gravity well is not the best idea out there.  

Remember Babylon V and the Earth starships?  A VASIMR would be the first step down that road.



Offline neviden

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Re: Power Supply for VASIMR
« Reply #24 on: 12/02/2007 08:21 PM »
Quote
wingod - 2/12/2007  8:26 PM
Remember Babylon V and the Earth starships?  
Babylon V style space station would actually be quite a good idea to have in LEO or even better in HEO. And it would not require anything high tech that we would not be able to do right now. All we would have to do is create a thick (crude) metal cylinder and rotate it. After that you can fill it with air and you have a safe place just like Earth.

Earth starships that would look like Omega class destroyers or Leonov from 2010 are also quite possible and something that would actually work (without hyperspace stuff of course).

Quote
wingod - 2/12/2007  8:26 PM
A VASIMR would be the first step down that road.
VASIMR is not the only propulsion technology. There are many plasma drives possible. I think it would be better to start with smaller, cheaper spaceships that would not cost that much (200 MW seems like an overkill) and upgrade them later.

What is important is to actually start using those new things. NASA will get $15 billion to spend no matter what it does. While it may seem like a good idea to throw money at Ares I and V, I think that this is complete waste of money. Even Ares V that might even make sense is a waste of money, since it will promote “hey, why bother with refueling and all that stuff! Let’s just build it, launch it and dump it.. “. There are plenty of perfectly good launchers already operating and completely underused.

20 MW electric spaceship would be more then able to do basic things and would be (more then 200 MW) price competitive with chemical option. That is the thing that is important, not what kind of reactor you have or how much time you spend in ship.. or at least.. it should be..

Offline advancednano

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Re: Power Supply for VASIMR
« Reply #25 on: 12/02/2007 10:48 PM »
Neviden

The topic of how NASA or the other space or government programs should spend there money is a separate topic.

Part of my recommendation on that is related to my suggested plan for winning the google Xprize for lunar robot landing.

http://advancednano.blogspot.com/2007/09/outline-of-how-to-win-google-lunar.html

We should not spend a bunch of money on another big chemical rocket.

Nasa should use existing rockets like the russian Dnepr or SpaceX rockets ($10 million per rocket) and send a constant stream of rockets to the moon using low energy orbital transfers. Get 3000-4000lbs to earth orbit and then spend 10% of the weight to get to lunar orbit in 5 months. Help armidillo finish new lunar landers. They should land robots there like the Carnegie Mellon mining robot. Robotics should be used to build up facilities and resources for people to exploit later. We could start landing $30-50 million missions every week. About 2000 lbs on each trip to the lunar surface. Once all the facilities are built up we can look at when it makes sense to  send people.

For new vehicle development, we should only be paying for radical improvement.

A ram accelerator launch system looks like it could be put together for $500 million and that it could send hardened payload into orbit for $500/kg.
http://advancednano.blogspot.com/2007/08/cheaper-space-launch-500kg-or-less-ram.html

Skylon or the plasma hypersonic vehicle might work and could make sense if the military wanted to help foot the bill. For Nasa, I would stick with nuclear and laser arrays. If the once a week 2000 lbs to the lunar surface worked out starting next year. Then I would look at using the lunar facilities to build simple nuclear rockets and power systems (plus solar). We need hundred of MW and GW for a real space infrastructure.

Offline Lampyridae

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Re: Power Supply for VASIMR
« Reply #26 on: 12/02/2007 11:37 PM »
What is really needed is a change in directive, as well as management in NASA. Bush said "go back to the moon, and then go on to Mars." That's exactly what they're doing, although flawed thinking and a lack of plain old common sense has landed them with the Ares problem. What would have been the easiest thing? Build a SDLV with oodles of power by banging on engines to the external tank. But no, NASA's doing the complicated thing because it looked easy at the time - and to carry out their directive given to them by the boss (George 2.0).

If George 2.0 had said "develop a sustainable lunar architecture," then NASA would have done it in a sub-optimal way, because they're about science and tech, not space economics. What NASA is doing right now with COTS and what's going on with the various X- and Google-prizes is in my opinion the best thing.

Sending cargo to the moon with low-cost, existing rockets would be far more expensive than doing it the NASA way. This has been discussed many times over:
1. Massive infrastructure upgrades needed to support required launch volume
2. Minimum mass requirements of systems which do not scale down well mean smaller payload fraction (e.g. avionics - you can't have 1/10 of an avionics box; also minimum thickness for fuel lines, nozzles etc)
3. Minimal economies of scaling
4. Fixed per-launch support costs (e.g. mission control requires almost the same staff for big rocket as a small one)

With all this a Dnepr could land maybe a 10kg payload on the moon for $10 million. A Falcon 9, OTOH, maybe 1 tonne for $100 million? That's an order of magnitude $/kg costs. Rather go with big commercial rockets, build up the robotic infrastructure as you suggested, and then land crew using dirt-cheap rocket chairs from orbit, much like the private lunar base plan. But leave NASA out of it, except to provide competition money. Further down the road, if someone invests $10 billion and 10 years into Skylon, then maybe after another 10 years we'll have a system which can do $1000/kg. Note that Skylon is only slightly more cost-effective as Falcon 9 Heavy, but has a lower payload mass. Hypersonic SSTO will only be an outgrowth of suborbital / hypersonic travel, nobody's going straight from A to Z.
SKYLON... The League of Extraordinary Gentlemen's preferred surface-to-orbit conveyance.

Offline wingod

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Re: Power Supply for VASIMR
« Reply #27 on: 12/02/2007 11:54 PM »
Quote
Lampyridae - 2/12/2007  6:37 PM

What is really needed is a change in directive, as well as management in NASA. Bush said "go back to the moon, and then go on to Mars." That's exactly what they're doing, although flawed thinking and a lack of plain old common sense has landed them with the Ares problem. What would have been the easiest thing? Build a SDLV with oodles of power by banging on engines to the external tank. But no, NASA's doing the complicated thing because it looked easy at the time - and to carry out their directive given to them by the boss (George 2.0).

If George 2.0 had said "develop a sustainable lunar architecture," then NASA would have done it in a sub-optimal way, because they're about science and tech, not space economics. What NASA is doing right now with COTS and what's going on with the various X- and Google-prizes is in my opinion the best thing.

Sending cargo to the moon with low-cost, existing rockets would be far more expensive than doing it the NASA way. This has been discussed many times over:
1. Massive infrastructure upgrades needed to support required launch volume
2. Minimum mass requirements of systems which do not scale down well mean smaller payload fraction (e.g. avionics - you can't have 1/10 of an avionics box; also minimum thickness for fuel lines, nozzles etc)
3. Minimal economies of scaling
4. Fixed per-launch support costs (e.g. mission control requires almost the same staff for big rocket as a small one)

With all this a Dnepr could land maybe a 10kg payload on the moon for $10 million. A Falcon 9, OTOH, maybe 1 tonne for $100 million? That's an order of magnitude $/kg costs. Rather go with big commercial rockets, build up the robotic infrastructure as you suggested, and then land crew using dirt-cheap rocket chairs from orbit, much like the private lunar base plan. But leave NASA out of it, except to provide competition money. Further down the road, if someone invests $10 billion and 10 years into Skylon, then maybe after another 10 years we'll have a system which can do $1000/kg. Note that Skylon is only slightly more cost-effective as Falcon 9 Heavy, but has a lower payload mass. Hypersonic SSTO will only be an outgrowth of suborbital / hypersonic travel, nobody's going straight from A to Z.

You know I don't buy this at all.  Bush in his speech specifically said that the ships that go to Mars could do it with propellants made on the Moon.  This implies a robust ISRU capability that NASA has ignored so far as ISRU propellant production is not anywhere near the baselines for the Lunar DRM.

Also, EELV's will be critical for the RTM.  The Ares V is going to be a billion dollars a launch and there are few payloads that need that kind of system.  The Delta IV or Atlas V heavies can put 4500 kg on the lunar surface and the small ones can put 1500 kg.  This is plenty for resupply, for a lot of hardware, and a much higher delivery rate than just a single cargo mission per year.

Also, it is not true about the infrastructure.  Today in Decatur AL there is the ability to manufacture 23 booster cores per year with the existing tooling and facilities.  That is plenty to support lunar missions and this does not count the production capacity in Colorado which is probably another 15 more cores per year.  

A sustainable architecture will have more than just the Ares system, no matter how it is built out.



Offline wingod

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Re: Power Supply for VASIMR
« Reply #28 on: 12/02/2007 11:56 PM »
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neviden - 2/12/2007  3:21 PM

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wingod - 2/12/2007  8:26 PM
Remember Babylon V and the Earth starships?  
Babylon V style space station would actually be quite a good idea to have in LEO or even better in HEO. And it would not require anything high tech that we would not be able to do right now. All we would have to do is create a thick (crude) metal cylinder and rotate it. After that you can fill it with air and you have a safe place just like Earth.

Earth starships that would look like Omega class destroyers or Leonov from 2010 are also quite possible and something that would actually work (without hyperspace stuff of course).

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wingod - 2/12/2007  8:26 PM
A VASIMR would be the first step down that road.
VASIMR is not the only propulsion technology. There are many plasma drives possible. I think it would be better to start with smaller, cheaper spaceships that would not cost that much (200 MW seems like an overkill) and upgrade them later.

What is important is to actually start using those new things. NASA will get $15 billion to spend no matter what it does. While it may seem like a good idea to throw money at Ares I and V, I think that this is complete waste of money. Even Ares V that might even make sense is a waste of money, since it will promote “hey, why bother with refueling and all that stuff! Let’s just build it, launch it and dump it.. “. There are plenty of perfectly good launchers already operating and completely underused.

20 MW electric spaceship would be more then able to do basic things and would be (more then 200 MW) price competitive with chemical option. That is the thing that is important, not what kind of reactor you have or how much time you spend in ship.. or at least.. it should be..

I am thinking about their large transportation vehicles that had the spinning section for the humans.  The B-V space station is a bit down the road.

Offline neviden

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Re: Power Supply for VASIMR
« Reply #29 on: 12/03/2007 08:56 AM »
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advancednano - 3/12/2007  12:48 AM
The topic of how NASA or the other space or government programs should spend there money is a separate topic.
It is, but VASIMR and things like that don’t get used because of the way money is spent. There is nothing wrong with technology or the concept.

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advancednano - 3/12/2007  12:48 AM
Nasa should use existing rockets like the russian Dnepr or SpaceX rockets ($10 million per rocket) and send a constant stream of rockets to the moon using low energy orbital transfers.
You can’t get things from LEO to Moon via low energy orbital transfers (ITN I presume). You need 3 km/s delta-v to come anywhere near the place where you could enter ITN and by then you are already at the Moon. You could use SEP/NEP to cut down the fuel requirements though.

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advancednano - 3/12/2007  12:48 AM
Once all the facilities are built up we can look at when it makes sense to  send people.
I think you underestimate the size of the problem. Dnepr size chunks would be too small to make them into a base for humans (you can’t make humans smaller). You would probably need 20 mT size chunks.

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Lampyridae - 3/12/2007  1:37 AM
Sending cargo to the moon with low-cost, existing rockets would be far more expensive than doing it the NASA way. This has been discussed many times over:
And that thinking is the reason why it costs $100 billion to send 4 men to Moon/Mars..

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Lampyridae - 3/12/2007  1:37 AM
1. Massive infrastructure upgrades needed to support required launch volume
Seriously? You believe that?

There is no reason why you would need anything more massive then you have now. Sure, you would have to build few more factories that would mass produce those rockets, but that is about it. Ask the Russians if it is possible to launch one rocket every week and how hard would that be..

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Lampyridae - 3/12/2007  1:37 AM
2. Minimum mass requirements of systems which do not scale down well mean smaller payload fraction (e.g. avionics - you can't have 1/10 of an avionics box; also minimum thickness for fuel lines, nozzles etc)
So? Who cares.. all that it matters is that you can bring some reasonable payload into LEO for certain price.

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Lampyridae - 3/12/2007  1:37 AM
3. Minimal economies of scaling
Not surprising since you must support everything even if you build and launch few rockets.. try building hundreds of rockets then come back to me with economies of scale..

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Lampyridae - 3/12/2007  1:37 AM
4. Fixed per-launch support costs (e.g. mission control requires almost the same staff for big rocket as a small one)
And whose fault is it that you must have few thousand people for every launch instead of few dozens? How about if you automate some of that work, eh?

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Lampyridae - 3/12/2007  1:37 AM
With all this a Dnepr could land maybe a 10kg payload on the moon for $10 million. A Falcon 9, OTOH, maybe 1 tonne for $100 million?
Try looking at the problem in terms of containers. You make things in some factory in China, you put them into big box. After that you use trucks, rail, ship, rail again, ship and at the end you get your things delivered to your door in wherehouse in some city in US. Only there you open your box to get the things.

Dnepr and Falcon 9 would launch containers. “Trucks, rail, ship and stuff” would also launch on those rockets but on a separate occasions.

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wingod - 3/12/2007  1:56 AM
I am thinking about their large transportation vehicles that had the spinning section for the humans.
http://en.wikipedia.org/wiki/Leonov_%28fictional_spacecraft%29
http://en.wikipedia.org/wiki/EAS_Churchill (Omega)

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wingod - 3/12/2007  1:56 AM
The B-V space station is a bit down the road.
It shouldn’t be. All you would need to know is how to create big plates out of some metal (how do you get them and where is the hard part. Easiest would be to get materials from NEOs since that has the lowest delta-v to get to HEO, or even melted down upper stages from rockets in LEO), weld them together and spin them up. After that you can use any technology that you use on Earth since you have 1 g.

Radiation and temperature protection?
Put some of the material on the lowest floor (outer most floor). Concrete, dirt, water, propellants… whatever..

Food and air?
http://ag.arizona.edu/ceac/research/SouthPoleChamber/index.htm

Offline advancednano

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Re: Power Supply for VASIMR
« Reply #30 on: 12/03/2007 09:30 PM »
I had believed that low energy orbital transfers would work better considering how well the Hiten did. Checking it again I guess the Belbruno Transfer is only 18% better than Holmann.

I guess then some kind of electrical propulsion tug would be needed to move things from low earth orbit to ITN entry to achieve what I envision. Which is get most of what we stick in LEO over to the moon. Then the chunks would become bigger.

People don't get smaller but if we are only sending people after we have stuff built out then the cost and number of trips would go way down.

Offline neviden

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Re: Power Supply for VASIMR
« Reply #31 on: 12/03/2007 10:13 PM »
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advancednano - 3/12/2007  11:30 PM
People don't get smaller but if we are only sending people after we have stuff built out then the cost and number of trips would go way down.
20 mT is the payload of the cargo Ares V to the Moon surface. It is also maximum payload for quite a few rockets that fly. It is probably the best number to plan things around. Number of landings until you get “ready for humans” would also be lower with higher weight.

VASIMR could probably be quite useful here, but it would need somewhere in the neighborhood of 1 - 10 MW of electricity to move things in some reasonable timeframe. Van Allen belt would mean that you need quite robust solar cells, but SEP would be quite feasible. Starting LEO orbit would have to be a little higher then NEP, but then again everybody would get very nervous if NEP got to close to Earth.

STP (solar thermal propulsion) would be an option also but its isp is quite low (around 800 s) and it would not be that much faster then high power SEP with far smaller propellant requirement. I wouldn’t even consider NTP. Chemical would probably be preferable for fast manned transfer to Moon orbit.

Offline clongton

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Re: Power Supply for VASIMR
« Reply #32 on: 12/03/2007 10:38 PM »
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neviden - 3/12/2007  6:13 PM

{snip} Starting in LEO orbit would have to be a little higher than NEP, but then again everybody would get very nervous if NEP got to close to Earth. {/snip}
Slightly off topic, but people seem to have this morbid fear of an EXTREMELY overblown danger of the NEP. People appear to think that the earth is MUCH smaller than it really is, and that the NEP power supply is MUCH bigger than it is. It is a completely irrational and thoroughly overblown and unfounded fear. If a spacecraft with a NEP power source actually "exploded", the NEP power source would drop most likely into the ocean, completely intact, with NO radiation leak. That's how they would be designed because they wouldn't be allowed to fly in any other condition.

I personally would have absolutely no fear of a NEP or even an NTP powered spacecraft going over my head. They are, or would be safe, completely safe.
Chuck - DIRECT co-founder
I started my career on the Saturn-V F-1A engine

Offline neviden

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Re: Power Supply for VASIMR
« Reply #33 on: 12/03/2007 11:06 PM »
I don't think that is off topic since the topic is "Power Supply for VASIMR"..

I do agree that nuclear fear is overblown, but that is politics. Solar is clean, nuclear isn’t and will get protests or worse. Deep space NEP missions could possibly get less attention, but LEO - Moon orbit - LEO tug would always stay near the Earth.

I would dismiss NTP even without that fear consideration based only on performance. It delivers small improvement over chemical, with bunch of extra problems and costs.

Offline superczar

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RE: Power Supply for VASIMR
« Reply #34 on: 01/26/2008 07:20 PM »
:cool:
Let's hear it for some of the Vasimr power supply posters but I think we'll have to admit that the Vasimr concept is not one of a propulsion system if it dosen't include what's been gone over in many of the posts, i.e power densities, launch costs, overall mission ISPs. Plus there isn't alot to recommend Vasimr. for instance what are the actual specs not the hype I've had to swallow. There's no reason that an ion propulsion engine couldn't be devised that was superior to Vasimr and didn't use what I consider its downfall - magnetic fields, or more specifically the gimmicky way they're touted for varying specific impulse. It certainly dosen't seem possible that its the best way to vary ISP. Frankly, I think we all got robbed on this one. Varying the ISP of an ion discharge is as easy as changing the accelerating voltage - not a major project in my estimation. There are some fairly efficient ways to ionize matter too, i.e hollow cathodes as in a few successful missions which have already flown. Or how about small radius-of-curvature ionization. It seems feasible that a powerful enough lightweight engine could easily be constructed using one of these concepts or even helicon waves which Vasimr uses and which I explored independently of Vasimr knowledge some years ago.

Anyway the general high ISP-NEP concept is sound and would seem the way to go in pushing forward exploration (including interstellar), asteroid deflection,and other apps. Also any push to develop a decent power supply would have spinoff benefits. I think this is most easily achieved with a particle bed design (fission) although there has been some bad press and a debacle in relation to it. Certainly all of the claims dealing with technology that tries to cut the edge where there's no edge to cut shouldn't be funded. There is reason to hope that a non-Carnot heat engine principle could be developed to eliminate bulky heat rejectors. An MHD or similar conversion system seems the best hope. Powerchips (whatever they are) are most likely not designed to function efficiently or at all in this app (basically they're looking like a puddle of goo). By the way the efficiency was listed as 70-80% of the Ideal Carnot efficiency which does not imply anywhere near 70-80% efficiency.

Since there already have been high ISP missions flown  and the only place to go is to augment with a superior power supply the death-knell for the cutting-edgedness of Vasimr was sounded long ago. Cheers.

Offline advancednano

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many small cheap rockets
« Reply #35 on: 02/05/2008 04:37 PM »
Using fuel depots in low earth orbit would increase the payload that could be delivered to the moon by 3-15 times. This would make the many smaller cheaper approach more feasible and effective

Offline clongton

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RE: many small cheap rockets
« Reply #36 on: 02/05/2008 04:44 PM »
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advancednano - 5/2/2008  12:37 PM

Using fuel depots in low earth orbit would increase the payload that could be delivered to the moon by 3-15 times. This would make the many smaller cheaper approach more feasible and effective
And this relates to Vasimr power supply how?
Chuck - DIRECT co-founder
I started my career on the Saturn-V F-1A engine

Offline advancednano

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RE: many small cheap rockets
« Reply #37 on: 02/05/2008 10:49 PM »
As part of the thread (this thread) about Vasimr there was a discussion about how money is currently spent on space (whether Vasimr should be funded or other things). I mentioned that a lot of cheap rockets would be better than spending many billions developing just another chemical rocket like Nasa is doing now. Then it was pointed out that cheap rockets would not be able to deliver much payload to the moon. The space fuel depot would be an affordable system and architecture which would help enable the use a bunch of cheap rockets to do more in space approach. Relating to Vasimr in that any advanced system is within the context of doing more in space cheaper and sooner.

Offline clongton

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RE: many small cheap rockets
« Reply #38 on: 02/06/2008 03:23 AM »
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advancednano - 5/2/2008  6:49 PM

As part of the thread (this thread) about Vasimr there was a discussion about how money is currently spent on space (whether Vasimr should be funded or other things). I mentioned that a lot of cheap rockets would be better than spending many billions developing just another chemical rocket like Nasa is doing now. Then it was pointed out that cheap rockets would not be able to deliver much payload to the moon. The space fuel depot would be an affordable system and architecture which would help enable the use a bunch of cheap rockets to do more in space approach. Relating to Vasimr in that any advanced system is within the context of doing more in space cheaper and sooner.
I follow your thinking but the thread is about the VASIMR Power Supply, not about other ways to do things with other kinds of rockets.
Chuck - DIRECT co-founder
I started my career on the Saturn-V F-1A engine

Offline Patchouli

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RE: Power Supply for VASIMR
« Reply #39 on: 02/13/2008 05:34 PM »
The nuclear battery sounds like what we have been waiting for as it solves the issues with the size of the radiators you'll still need them but they can be much smaller now also maybe see if you can get a few more tens of KW out of said nuclear battery by making it's cooling system a Rankine organic cycle turbine which do work well with small temperature gradients.
Heck maybe also include some thermoelectric devices on the batts just to squeeze that last bit of power out of the system but only after it's found they will not add more mass then what the extra delta V you'll get from the extra power can move.

the ORC turbine http://en.wikipedia.org/wiki/Organic_Rankine_Cycle

I believe producing lots of electric power in space is likely the most important engineering breakthrough needed for crewed deep space missions even HLLVs like ares V are optional as most things can be launched in pieces if needed but energy dense power sources are not optional as there is no way around it.

Offline A_M_Swallow

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RE: many small cheap rockets
« Reply #40 on: 02/13/2008 06:19 PM »
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clongton - 5/2/2008  5:44 PM

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advancednano - 5/2/2008  12:37 PM

Using fuel depots in low earth orbit would increase the payload that could be delivered to the moon by 3-15 times. This would make the many smaller cheaper approach more feasible and effective
And this relates to Vasimr power supply how?

"Possible fuels for the VASIMR engine could include hydrogen, helium, and deuterium."
from
http://www.nasa.gov/vision/space/travelinginspace/future_propulsion.html

Reusable VASIMR spacecraft can also be refuelled by a fuel depot.

Offline TyMoore

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RE: many small cheap rockets
« Reply #41 on: 02/14/2008 04:07 AM »
...and perhaps most importantly, VASMIR can be refueled "insitu" by capitalizing on volatile resources already found in space: namely dormant or extinct comets; volatiles on or in near earth crossing asteroids; and quite possibly by using lower performance, but more readily available oxygen reaction mass--an expected by product of metal extraction from lunar and asteroid regolith processing.

Offline neviden

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Re: Power Supply for VASIMR
« Reply #42 on: 02/17/2008 04:00 PM »
VASMIR could be useful if it could use one interesting propellant with high isp: water. Space storable, non-toxic, cheap, easily extractable ISRU.. Or more specifically.. any SEP/NEP concept that could use that as propellant would be very attractive. That doesn't solve the Power requirement, but it could enable the same mission with less power/lower isp if the quantity of propellant would not be an issue (water bearing NEOs, Moon, maybe even Phobos or Deimos).

Offline lambda0

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Re: Power Supply for VASIMR
« Reply #43 on: 02/18/2008 02:37 PM »

A few years ago, I thought that a nuclear reactor was clearly the best solution to power a VASIMIR, but now, solar panels seem to have a better improvement potential. Current or near term technology can reach 4-5 kg/kW.  With advanced technology, 1 kg/kW, or even less, could be possible. I am not sure that nuclear power can reach those performances, at least with standard technologies.
Of course, nuclear power would be necessary beyond Mars, but for a martian mission, I think that both solutions should be carefully evaluated. A solar power plant could also have a longer lifetime and could be reusable, may be less costly, etc.









Offline khallow

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Re: Power Supply for VASIMR
« Reply #44 on: 02/18/2008 04:22 PM »
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lambda0 - 18/2/2008  7:37 AM


A few years ago, I thought that a nuclear reactor was clearly the best solution to power a VASIMIR, but now, solar panels seem to have a better improvement potential. Current or near term technology can reach 4-5 kg/kW.  With advanced technology, 1 kg/kW, or even less, could be possible. I am not sure that nuclear power can reach those performances, at least with standard technologies.
Of course, nuclear power would be necessary beyond Mars, but for a martian mission, I think that both solutions should be carefully evaluated. A solar power plant could also have a longer lifetime and could be reusable, may be less costly, etc.

As I recall, solar power is halved at Mars' distance from the Sun. Are you taking that into account? I gather aerobraking will be the primary form of deceleration. So not so much thrust is required on that end. Second, it seems to me that solar panels would either need to be jettisoned or packed away prior to aerobraking manuevers. Heat sinks would too, but high temperature reactors can have heat sinks much smaller for the power output than the same amount of solar.
Karl Hallowell

Offline clongton

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Re: Power Supply for VASIMR
« Reply #45 on: 02/18/2008 06:38 PM »
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khallow - 18/2/2008  12:22 PM

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lambda0 - 18/2/2008  7:37 AM


A few years ago, I thought that a nuclear reactor was clearly the best solution to power a VASIMIR, but now, solar panels seem to have a better improvement potential. Current or near term technology can reach 4-5 kg/kW.  With advanced technology, 1 kg/kW, or even less, could be possible. I am not sure that nuclear power can reach those performances, at least with standard technologies.
Of course, nuclear power would be necessary beyond Mars, but for a martian mission, I think that both solutions should be carefully evaluated. A solar power plant could also have a longer lifetime and could be reusable, may be less costly, etc.

As I recall, solar power is halved at Mars' distance from the Sun. Are you taking that into account? I gather aerobraking will be the primary form of deceleration. So not so much thrust is required on that end. Second, it seems to me that solar panels would either need to be jettisoned or packed away prior to aerobraking manuevers. Heat sinks would too, but high temperature reactors can have heat sinks much smaller for the power output than the same amount of solar.
It would seem to me that it would be far better to power half way out, then turn around and decelerate the remaining way to Mars orbit. In this way, capture into Mars orbit can be accomplished almost with maneuvering thruster use alone. Return home can be the reverse, accelerate half way home and decelerate the last half, entering EML2 capture with just thrusters. This eliminates having to use aero breaking and having to design a spacecraft to stand up in that kind of structurally stressful maneuver.
Chuck - DIRECT co-founder
I started my career on the Saturn-V F-1A engine

Offline neviden

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Re: Power Supply for VASIMR
« Reply #46 on: 02/18/2008 06:47 PM »
Aero braking is not needed with NEP/SEP. You need it with chemical or NTR to compensate for low isp, so you can reduce IMLEO.

Mars only gets about 40% of solar radiation around the Earth, but your return ship has a lot less weight to push around, since it already used half of the propellant. If we couldn’t get more illumination on solar cells by some kind of concentrator, then we can simply use lower isp propulsion mode that would use up more propellant but would give more thrust per watt. Once we would get closer to the sun power output would rise accordingly.

Offline RanulfC

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Re: Power Supply for VASIMR
« Reply #47 on: 02/18/2008 08:29 PM »
One concept I came across at one point for an SEP deep space craft was a 2000 concept called "POWOW"
(Since my adobe reader is giving me problems let me post the google-search results page)
http://www.google.com/search?hl=en&q=POWOW+A+Modular+High+Power+Spacecraft+Concept

The idea being to combine a vehicle with a solar power system capable not only of traveling to Mars orbit by electric propulsion but once there acting as a solar power satellite and beaming power down to ground stations.

Randy
From The Amazing Catstronaut on the Black Arrow LV:
British physics, old chap. It's undignified to belch flames and effluvia all over the pad, what. A true gentlemen's orbital conveyance lifts itself into the air unostentatiously, with the minimum of spectacle and a modicum of grace. Not like our American cousins' launch vehicles, eh?

Offline lambda0

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Re: Power Supply for VASIMR
« Reply #48 on: 02/19/2008 05:40 AM »
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khallow - 18/2/2008  11:22 AM
As I recall, solar power is halved at Mars' distance from the Sun. Are you taking that into account? I gather aerobraking will be the primary form of deceleration. So not so much thrust is required on that end. Second, it seems to me that solar panels would either need to be jettisoned or packed away prior to aerobraking manuevers. Heat sinks would too, but high temperature reactors can have heat sinks much smaller for the power output than the same amount of solar.

The best achieved power density with thin films panels is 4200 W/kg = 0.24 kg/kW, for Sun-Earth distance. Around Mars, that would translate to about 0.5 kg/kW.
It is advanced technology, not yet flight proven, but this means that 1 kg/kW doesn't seem to be impossible.
Excepted maybe the highly speculative vapor core reactor, I don't think that nuclear reactors can reach this value.
And why aerobreaking ? Not necessary with electric propulsion.





Offline neviden

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Re: Power Supply for VASIMR
« Reply #49 on: 02/19/2008 12:05 PM »
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lambda0 - 19/2/2008  7:40 AM
The best achieved power density with thin films panels is 4200 W/kg = 0.24 kg/kW, for Sun-Earth distance. Around Mars, that would translate to about 0.5 kg/kW.
It is advanced technology, not yet flight proven, but this means that 1 kg/kW doesn't seem to be impossible.
To do some reasonable (= equal or better then chemical) transit from HEO to Mars orbit and back you need 6 - 20 MW of power. That would make SEP more then adequate for such a mission, not to mention “politically acceptable”, since it wouldn’t include the N-word (Nuclear of course).

Offline clongton

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Re: Power Supply for VASIMR
« Reply #50 on: 02/19/2008 12:30 PM »
Politically correct be damned!

Why are people afraid to use the word? It’s not “the N-word”; it’s NUCLEAR.
The key to the solar system past Mars is not SEP, it is nuclear. The farther we get from our star, the less efficient SEP will be. It’s already on the tricky edge at Mars in terms of power density and is not likely to get much better. I for one believe that we are just about at the point of diminishing returns for SEP technology. It is also not very efficient in the inner solar system if you need to get somewhere reasonably quickly. It’s power density just isn’t high enough.

Now please do not take that as me “nay saying” SEP, because it’s not. SEP is going to be extremely useful for the inner solar system and should be exploited for electric propulsion. There is no argument from me on that point. But SEP electric propulsion is slow over small distances because its power density just isn’t high enough. So if you want to get anywhere fast, electric propulsion will need to be NEP; which will allow you to build bigger and more powerful engines.

I believe that BOTH should be developed in parallel because both will be needed.

Please come out of the shadows and quit skirting around the media-hyped scare tactics of nuclear. They do that, not because it’s a bad thing that the public is afraid of, but because it sells copy, and for no other reason at all. They make a profit every time they scare you with the “N-word”. Don’t be taken in. The word is “nuclear”, and it is the KEY to the solar system. I live in the shadow of a nuclear power generator which runs my lights and refrigerator and kitchen range in my home, and I make my living building nuclear powered ships. Nuclear is like all other powerful energy sources; dangerous UNLESS you mitigate the danger. We have been plying the oceans for almost 60 years with nuclear powered ships and there haven’t been any “nuclear” accidents, because the reactor designs mitigate the danger. There has been one commercial accident (TMI) caused primarily by staff that didn’t know what they were doing. Chernobyl is different. That was a bad design that should never have been built.

Nuclear. Nuclear. Nuclear. It’s not an “N-word”; it’s a “Good-word”. Get used to using it because it is going to open the solar system.
Chuck - DIRECT co-founder
I started my career on the Saturn-V F-1A engine

Offline TyMoore

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Re: Power Supply for VASIMR
« Reply #51 on: 02/19/2008 12:47 PM »
Clongton--I completely agree with you. We need both nuclear and solar power systems. When it comes to the highest delta-V missions or the deepest space explorations, or both, especially if they are manned, they will need reliable, copius, compact power--nuclear is about the only thing that will fit the bill for any manned missions beyond Mars.

SEP will work very well for missions to Venus and Mercury, and I imagine that ion or MPD thrusters could be quite effective RCS for solar power satellites--but where people are concerned, you want to cross the radiation belts as quickly as possible, and cross the interplanetary gulfs as quickly as possible as well.

VASIMR for large, manned spacecraft will demand upwards of 50MWe-250MWe or more...and will only be slightly 'faster' than a 'conventional' ion craft. The big problem is the power conversion system--not only do you need a reactor, and shielding, but some means of cooling the reactor and converting that heat into electrical power, probably in a Brayton-cycle gas turbine cycle, and then dumping most of the rest of the heat in a radiator--which is the single biggest item.

For some missions it might be easier to take the Isp performance-hit and go with a bi- or tri-modal nuclear thermal rocket--


Offline lambda0

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Re: Power Supply for VASIMR
« Reply #52 on: 02/19/2008 12:50 PM »
20MW, maybe less, should be enough for a "short stay" mission (450 days, with 30-60 days on Mars). With more power, 200MW, a 8-9 months round trip is possible.
Even without any political consideration, just from cost and performances point of view, solar power is becoming an attractive option for high power VASIMR, because performances improvements on lightweight solar panels seem to be faster than for nuclear reactors.
I don't think it's so clear now that SEP would be slower than NEP, a solar power plant could be lighter than a nuclear reactor.

This document should be interesting :
http://www.hapcos.org/DOCS/download.php?id=81&type=pdf


Offline meiza

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Re: Power Supply for VASIMR
« Reply #53 on: 02/19/2008 12:56 PM »
Solar has just so much less initial headaches than nuclear that even with significant mass disadvantages it could be a preferable choice for Mars missions.

Now, beyond that of course it's probably out of the question.

Offline TyMoore

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Re: Power Supply for VASIMR
« Reply #54 on: 02/19/2008 01:06 PM »
Thanks for posting that link--I've seen the initial reports on this technology and it is quite impressive--printing solar cells directly onto surfaces. Initially they used Mo foil, I think. A buddy of mine has been hand building Very Small UAV's for reconnaissance for the US Marine Corps on an experimental basis--and I suggested that he consider "skinning" the upper surface of his craft with these thin film cells--ought to work well in the Iraq.


SEP can work--no argument there. And I have no doubt that it could be lighter because you don't need the inert mass of  radiation shielding, nor do you need the bulky and heavy radiators to reject heat.

I'm not sure how interactions with the solar cells with Solar Wind will affect their performance and life--I know that proton doping can be a problem with the semiconductors...

And as far as nuclear goes--I tend to look very long term: manned missions to and beyond Jupiter are going to get too little sunlight to consider SEP for manned missions.

Also, the higher 250MWe figure I mentioned--that's for a 'pet' project: Asteroid and comet nuclei mining--heat and power for processing materials...not just propulsion.

Offline RanulfC

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Re: Power Supply for VASIMR
« Reply #55 on: 02/19/2008 01:38 PM »
Chuck;
The actual word is the "A" word or "Atomic" as in "Atomic Rocket Cruisers of the Space Patrol!"

:::sigh:::: I really, really want my DUMBO SST-just about anywhere rocket ship....

Randy
From The Amazing Catstronaut on the Black Arrow LV:
British physics, old chap. It's undignified to belch flames and effluvia all over the pad, what. A true gentlemen's orbital conveyance lifts itself into the air unostentatiously, with the minimum of spectacle and a modicum of grace. Not like our American cousins' launch vehicles, eh?

Offline lambda0

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Re: Power Supply for VASIMR
« Reply #56 on: 02/19/2008 02:23 PM »
Quote
TyMoore - 19/2/2008  8:06 AM
...
And as far as nuclear goes--I tend to look very long term: manned missions to and beyond Jupiter are going to get too little sunlight to consider SEP for manned missions.
Also, the higher 250MWe figure I mentioned--that's for a 'pet' project: Asteroid and comet nuclei mining--heat and power for processing materials...not just propulsion.

I agree with that. Anyway, nuclear reactor will be required beyond Mars.
And there may be also some real progress on nuclear reactors : a futuristic vapor core reactor with MHD conversion could have a specific mass as low as 0.3kg/kW for a 100-200MW class reactor.

I've not seen yet a manned martian mission analysis with solar+VASIMR, but Chang-Diaz presented a paper at IEPC 2007 for a lunar cargo solar plant+VASIMR :
http://www.adastrarocket.com/Tim_IEPC07.pdf

Offline neviden

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Re: Power Supply for VASIMR
« Reply #57 on: 02/19/2008 04:01 PM »
Quote
clongton - 19/2/2008  2:30 PM
Politically correct be damned!
Well.. I just tell as I see it. Nuclear is still a dirty word. God forbid that one activated nuclear reactor should fall back onto Earth. That is a “political reality” that we can’t change and I am only pointing that fact out.

Saying that, I agree that SEP is unworkable beyond the Asteroid belt, but I don’t see any manned mission to the Titan in my lifetime. Moon, Mars and NEOs are the only targets in the next 50 years, and they are quite simply cheaper with SEP then with NEP.  Both technically and even more politically. Nobody would care if one SEP would crash to Earth (especially if there would be nobody onboard). NEPs would soon get few Hollywood scare movies about the end of the world and I am sure you all know what would do that to any NASA NEP plans..

NEPs share the same technology with SEP. That means that the way is always open for “upgrade” from SEP to NEP. Kind of like: We would use the sun to power our craft to Jupiter, but it’s too far away, but look.. all those SEPs have performed nicely and we would only change the power source.. It would be safe.. We promise!

Offline alexterrell

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Re: Power Supply for VASIMR
« Reply #58 on: 03/09/2008 10:55 AM »
Quote
lambda0 - 19/2/2008  12:40 AM

The best achieved power density with thin films panels is 4200 W/kg = 0.24 kg/kW, for Sun-Earth distance. Around Mars, that would translate to about 0.5 kg/kW.
It is advanced technology, not yet flight proven, but this means that 1 kg/kW doesn't seem to be impossible.
Excepted maybe the highly speculative vapor core reactor, I don't think that nuclear reactors can reach this value.


A quick play with Stefan's law gives the following radiator output (with emissivity=0.9):
T (K)   P (W/m2)
270    268
320    528
370    945
420    1,568
470    2,459
520    3,685

At a temperature of 540K, the radiator will dump 4200W / m2. Assuming overall efficiency of 50% (a tall order at 540K cold temperature), can 1m2 of radiator be done for 1kg. (actually, 0.5m2, since it'll be 2 sided)?

I don't think it can be if liquid needs to circulate in the radiator. Hence I can't see NEP getting remotely close to SEP in Earth orbits.

(For Larry Niven, this would have been no problem. A sail of black superconducting cloth would do the trick).


Offline A_M_Swallow

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Re: Power Supply for VASIMR
« Reply #59 on: 03/09/2008 12:59 PM »
Quote
alexterrell - 9/3/2008  12:55 PM
At a temperature of 540K, the radiator will dump 4200W / m2. Assuming overall efficiency of 50% (a tall order at 540K cold temperature), can 1m2 of radiator be done for 1kg. (actually, 0.5m2, since it'll be 2 sided)?

I don't think it can be if liquid needs to circulate in the radiator. Hence I can't see NEP getting remotely close to SEP in Earth orbits.

A 0.5 millimetre thick graphite sheet would fit the weight.
http://en.wikipedia.org/wiki/Graphite

The Graphene form has a thermal conductivity of between (4.84±0.44) ×10^3 to (5.30±0.48) ×10^3 W/m/K
http://en.wikipedia.org/wiki/Graphene

Offline meiza

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Re: Power Supply for VASIMR
« Reply #60 on: 03/09/2008 06:15 PM »
Quote
alexterrell - 9/3/2008  12:55 PM

Quote
lambda0 - 19/2/2008  12:40 AM

The best achieved power density with thin films panels is 4200 W/kg = 0.24 kg/kW, for Sun-Earth distance. Around Mars, that would translate to about 0.5 kg/kW.
It is advanced technology, not yet flight proven, but this means that 1 kg/kW doesn't seem to be impossible.
Excepted maybe the highly speculative vapor core reactor, I don't think that nuclear reactors can reach this value.


A quick play with Stefan's law gives the following radiator output (with emissivity=0.9):
T (K)   P (W/m2)
270    268
320    528
370    945
420    1,568
470    2,459
520    3,685

At a temperature of 540K, the radiator will dump 4200W / m2. Assuming overall efficiency of 50% (a tall order at 540K cold temperature), can 1m2 of radiator be done for 1kg. (actually, 0.5m2, since it'll be 2 sided)?

I don't think it can be if liquid needs to circulate in the radiator. Hence I can't see NEP getting remotely close to SEP in Earth orbits.

(For Larry Niven, this would have been no problem. A sail of black superconducting cloth would do the trick).


Of course, you need two numbers: the exit temperature of the heat engine working fluid, say T_3 and the cool input temperature T_1 too. In the radiator the liquid slowly cools from T_3 to T_1. The end temperature T_1 mostly determines the size of the radiator. (With power ie flow of course.)
In the heat engine, the working fluid expands from T_1 to T_2, work is extracted and T_3 is reached.

Now, you could get an upper limit estimate by assuming the whole radiator to be at the low end temperature, and the actual number could be quite close because of the T^-4 thing.

Very simplified of course. :)

With a solid radiator like Swallow proposed, it's harder, you have to take into account the thermal conductivity as the rest of the radiator will be cooler than the base so it needs to be bigger.

Offline alexterrell

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Re: Power Supply for VASIMR
« Reply #61 on: 03/09/2008 06:39 PM »
Quote
A_M_Swallow - 9/3/2008  8:59 AM

Quote
alexterrell - 9/3/2008  12:55 PM
At a temperature of 540K, the radiator will dump 4200W / m2. Assuming overall efficiency of 50% (a tall order at 540K cold temperature), can 1m2 of radiator be done for 1kg. (actually, 0.5m2, since it'll be 2 sided)?

I don't think it can be if liquid needs to circulate in the radiator. Hence I can't see NEP getting remotely close to SEP in Earth orbits.

A 0.5 millimetre thick graphite sheet would fit the weight.
http://en.wikipedia.org/wiki/Graphite

The Graphene form has a thermal conductivity of between (4.84±0.44) ×10^3 to (5.30±0.48) ×10^3 W/m/K
http://en.wikipedia.org/wiki/Graphene

That's amazing conductivity, but how would you arrange it?

With some kind of thermocouple generator, the cold ends could go to multiple points on a graphite sheets. With a more conventional reactor, distributing heat to the radiator will be a problem.

Offline A_M_Swallow

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Re: Power Supply for VASIMR
« Reply #62 on: 03/09/2008 07:00 PM »
Quote
alexterrell - 9/3/2008  8:39 PM

Quote
A_M_Swallow - 9/3/2008  8:59 AM

Quote
alexterrell - 9/3/2008  12:55 PM
At a temperature of 540K, the radiator will dump 4200W / m2. Assuming overall efficiency of 50% (a tall order at 540K cold temperature), can 1m2 of radiator be done for 1kg. (actually, 0.5m2, since it'll be 2 sided)?

I don't think it can be if liquid needs to circulate in the radiator. Hence I can't see NEP getting remotely close to SEP in Earth orbits.

A 0.5 millimetre thick graphite sheet would fit the weight.
http://en.wikipedia.org/wiki/Graphite

The Graphene form has a thermal conductivity of between (4.84±0.44) ×10^3 to (5.30±0.48) ×10^3 W/m/K
http://en.wikipedia.org/wiki/Graphene

That's amazing conductivity, but how would you arrange it?

With some kind of thermocouple generator, the cold ends could go to multiple points on a graphite sheets. With a more conventional reactor, distributing heat to the radiator will be a problem.

Since Graphene is pure carbon its melting point is probably in the 3,800 K range.

Guessing.
The walls of the reactor could be made out of Graphene with fins stuck on them.
Or the reactor's cooling liquid could be pumped through a pipe made of Graphene with large fins sticking out of it.

Offline Peacekeeper

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Re: Power Supply for VASIMR
« Reply #63 on: 05/12/2008 08:57 AM »
Is it possible to liftoff with VASIMR?
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Offline meiza

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Re: Power Supply for VASIMR
« Reply #64 on: 05/12/2008 12:01 PM »
No. Bad t/w (much less than 1) and the nozzle doesn't work in the atmosphere.

Offline meiza

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Re: Power Supply for VASIMR
« Reply #65 on: 05/12/2008 12:02 PM »
Actually the whole engine insides probably doesn't work in the atmosphere as air gets in through the nozzle.

Offline clongton

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Re: Power Supply for VASIMR
« Reply #66 on: 05/12/2008 12:11 PM »
Quote
meiza - 12/5/2008  8:02 AM

Actually the whole engine insides probably doesn't work in the atmosphere as air gets in through the nozzle.
That's too bad, because we need a new way to get off the planet.
Chuck - DIRECT co-founder
I started my career on the Saturn-V F-1A engine

Offline meiza

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Re: Power Supply for VASIMR
« Reply #67 on: 05/12/2008 12:30 PM »
VASIMR was never intended for high thrust or atmospheric propulsion. It's like trying to plough a field with a Ferrari.

I also think it's one of the most misunderstood propulsion technologies. It's not an engine in the sense like an F-1 or RD-180 are: just add fuel and they produce thrust. VASIMR needs a power source that doesn't exist of yet for it to be very useful, and even then, it's not very different from hall thrusters or ion engines that have already lots of operating experience.

Offline clongton

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Re: Power Supply for VASIMR
« Reply #68 on: 05/12/2008 12:35 PM »
Quote
meiza - 12/5/2008  8:30 AM

VASIMR was never intended for high thrust or atmospheric propulsion. It's like trying to plough a field with a Ferrari.

I also think it's one of the most misunderstood propulsion technologies. It's not an engine in the sense like an F-1 or RD-180 are: just add fuel and they produce thrust. VASIMR needs a power source that doesn't exist of yet for it to be very useful, and even then, it's not very different from hall thrusters or ion engines that have already lots of operating experience.
I understand that. My comment was rhetorical.
Chemically fueled rocket engines are the only way off the planet that is practical for now.
It works but is inefficient. Like I said, we need a new way off the planet.
But that gets off topic
Chuck - DIRECT co-founder
I started my career on the Saturn-V F-1A engine

Offline meiza

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Re: Power Supply for VASIMR
« Reply #69 on: 05/12/2008 12:45 PM »
I don't think VASIMR would even get off the moon. Depends on some assumptions on VASIMR and power source's tech I guess. From an asteroid it could lift off...

I think themical engines are probably good enough if you are smart with them (you reuse the launcher) and you use in-space resources very much. No sizable fraction of Earth's inhabitants will ever leave Earth. There might be people living in space though.

With extraterrestrial resource use, huge things get possible. Like interstellar travel.

Offline clongton

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Re: Power Supply for VASIMR
« Reply #70 on: 05/12/2008 01:32 PM »
Quote
meiza - 12/5/2008  8:45 AM

I don't think VASIMR would even get off the moon. Depends on some assumptions on VASIMR and power source's tech I guess. From an asteroid it could lift off...

I think themical engines are probably good enough if you are smart with them (you reuse the launcher) and you use in-space resources very much. No sizable fraction of Earth's inhabitants will ever leave Earth. There might be people living in space though.

With extraterrestrial resource use, huge things get possible. Like interstellar travel.
What kind of performance is possible with VASIMR per unit of power?
Can you provide a simple chart/spreadsheet?
Chuck - DIRECT co-founder
I started my career on the Saturn-V F-1A engine

Offline Namechange User

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Re: Power Supply for VASIMR
« Reply #71 on: 05/12/2008 02:13 PM »
Quote
meiza - 12/5/2008  7:30 AM

VASIMR needs a power source that doesn't exist of yet for it to be very useful

That is incorrect.
Enjoying viewing the forum a little better now by filtering certain users.

Offline meiza

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Re: Power Supply for VASIMR
« Reply #72 on: 05/12/2008 02:26 PM »
So you say VASIMR is very useful when coupled with solar cells?

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Re: Power Supply for VASIMR
« Reply #73 on: 05/12/2008 02:37 PM »
Quote
meiza - 12/5/2008  9:26 AM

So you say VASIMR is very useful when coupled with solar cells?

I'm saying the technology does exist to power VASMIR, both solar and otherwise, to power VASMIR.
Enjoying viewing the forum a little better now by filtering certain users.

Offline Peacekeeper

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Re: Power Supply for VASIMR
« Reply #74 on: 05/12/2008 05:22 PM »
Quote
meiza - 12/5/2008  3:30 PM

VASIMR was never intended for high thrust or atmospheric propulsion. It's like trying to plough a field with a Ferrari.

Which means that an aircraft also cannot use this propulsion on Earth?!  Then HOW in Star Wars and Star Trek ships liftoff with Ion and Plasma?!  Why can't we duplicate it here on this planet?
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Re: Power Supply for VASIMR
« Reply #75 on: 05/12/2008 06:11 PM »
Quote
Peacekeeper - 12/5/2008  1:22 PM

Quote
meiza - 12/5/2008  3:30 PM

VASIMR was never intended for high thrust or atmospheric propulsion. It's like trying to plough a field with a Ferrari.

Which means that an aircraft also cannot use this propulsion on Earth?!  Then HOW in Star Wars and Star Trek ships liftoff with Ion and Plasma?!  Why can't we duplicate it here on this planet?
Science Fiction is a good place to exersize the imagination and the worlds of make-believe. I enjoy both series, but then I return to reality.
Chuck - DIRECT co-founder
I started my career on the Saturn-V F-1A engine

Offline Peacekeeper

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Re: Power Supply for VASIMR
« Reply #76 on: 05/12/2008 06:14 PM »
Quote
clongton - 12/5/2008  9:11 PM

Quote
Peacekeeper - 12/5/2008  1:22 PM

Quote
meiza - 12/5/2008  3:30 PM

VASIMR was never intended for high thrust or atmospheric propulsion. It's like trying to plough a field with a Ferrari.

Which means that an aircraft also cannot use this propulsion on Earth?!  Then HOW in Star Wars and Star Trek ships liftoff with Ion and Plasma?!  Why can't we duplicate it here on this planet?
Science Fiction is a good place to exersize the imagination and the worlds of make-believe. I enjoy both series, but then I return to reality.
Science Fiction yesterday is Science Fact today, don't forget it ;)
Space - The Final Frontier!

Offline meiza

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Re: Power Supply for VASIMR
« Reply #77 on: 05/12/2008 07:14 PM »
Quote
OV-106 - 12/5/2008  3:37 PM

Quote
meiza - 12/5/2008  9:26 AM

So you say VASIMR is very useful when coupled with solar cells?

I'm saying the technology does exist to power VASMIR, both solar and otherwise, to power VASMIR.

I'm sceptical, with the high dry mass of VASIMR that it would be that better than some Hall thrusters or regular ion engines on a state of the art solar electric spacecraft.

Offline TyMoore

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Re: Power Supply for VASIMR
« Reply #78 on: 05/13/2008 02:43 AM »
One of the things that occurred to me when I was studying VASIMR was that the engine can be fairly easily 'tuned' to utilize different propellant streams. Why would you want to do that?

Well, suppose you wanted a fairy or freighter vehicle that could go back and forth from LEO to Lunar Orbit. Suppose that in lunar orbit you have a depot/processing station that uses solar energy to chemically reduce lunar regolith to its component elemetns: you'll get a lot of metals, and a lot of silicon, and a whole bunch of oxygen.

OK., what does that do for us? Our freighter in LEO departs on its maiden voyage using liquid hydrogen. It gets all the way to the lunar depot: it takes on a payload of metals and tons of liquid oxygen. An empty cryogenic tank can carry approximately 16 times the mass of liquid oxygen than it can carry in liquid hydrogen. So loading up a hydrogen tank (properly emptied and vented to space of course!) with liquid oxygen gives us a 16 times mass advantage. However a VASIMR engine processing oxygen will have a 16 times molecular weight penalty due to the fact the a single oxygen atom is approximately 16 times heavier than a single hydrogen atom. Because of this, the exhaust velocity of a oxygen fueled VASIMR will be approximately 1/4 as much as it would if it used hydrogen.

So what?

So: if the vehicle is carrying the same payload mass as it did on the outbound voyage then the oxygen fueled VASIMR could develop 4 times the delta-V of the hydrogen only VASIMR (payload constant.) Or it could carry four times as much payload, delta-V constant (same outbound as inbound.) Conceivably you could even use aluminum as the reaction mass and get an even larger performance spread...

The use of the same engine to process different propellant streams is totally unheard in just about any other engine system out there--and to me that makes VASIMR very unique!

Offline neviden

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Re: Power Supply for VASIMR
« Reply #79 on: 05/13/2008 07:40 AM »
Quote
Peacekeeper - 12/5/2008  8:14 PM
Science Fiction yesterday is Science Fact today, don't forget it ;)
Science Fiction does not have to follow the rules of physics or what is possible to build. It generally follows them as much as possible, since the writers don’t want to create the world that readers/viewers can’t believe in, but they can easily invent their own rules to make their story work. If they need to make space travel fast enough to make 45 minute show realistic, they will invent warp drive and that’s that. For anybody interested they can also invent technobable reasons on why things are how they are.

There is actually no physical reason why some type of ion propulsion would not be able to lift from the ground. You would just have to have pretty high power source and T/W of over 1. Maybe we will know how to build that in the future, but we don’t right now.

Quote
TyMoore - 13/5/2008  4:43 AM
So what?
Isn't the delta-V more related to energy input then the actual composition of ejected matter?

Chemical rocket gets both the energy and ejection mass from one process (chemical reaction). How fast it goes out determines the isp and is related to efficiency of engine and energy of reaction (H2 and O2 being the best). That isp is limited by energy released by the same reaction. You can increase the energy output by increasing the flow rate of propellant, but you can’t increase the energy density.

VASIMR and the rest of electric propulsions have power source separated from propellant rate. You can raise isp by lowering flow rate or raise thrust by raising flow rate of propellant. The actual power output stays the same. That means that you can increase delta-v by increasing time you thrust, thus increasing energy (as in KWh of electricity) used to accelerate propellant. That thrust divided by the weight of the whole craft determines how much spacecraft will accelerate and how much time it will have to accelerate to make the required delta-v. You build more efficient power plant, you get higher acceleration. You add more payload you get smaller acceleration. You use less efficient propellant  or use it less efficiently you get slower acceleration.

VASIMR doesn’t do anything magical in itself. It just allows you to convert electricity into thrust at specific isp that is the optimal for the mission (low for high thrust, high for long duration).  It’s the weight of the power plant and the energy it produces that determines what VASIMR can do and in what time. If you are in no hurry, then you can greatly increase the delta-v.

So shouldn’t we be talking about how much total energy do we need instead of how much propellant or which propellant do we need (like we do with chemical engines)? Shouldn’t the only metric be an acceleration (thrust to weight) of the whole craft at certain isp (for certain propellant)?

Offline TyMoore

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Re: Power Supply for VASIMR
« Reply #80 on: 05/13/2008 12:20 PM »
Given constant jet power, when utilizing a heavier molecular weight propellant stream, then all other things being equal, the speed of the ejected jet ought to be roughly proportional to 1/sqrt(m.w.) when compared hydrogen...

One of the greatest utilities of VASIMR is its inherent ability to be able to process different propellant streams--this allows us to contemplate the possibility of utilizing a less efficient but more plentiful and denser cryogen: oxygen.

I've actually written to Dr. Franklin Chang-Diaz (the inventor of the VASIMR concept) proposing this mode. According to him, the biggest hurdle in using oxygen as reaction mass is that singly ionized oxygen is probably one of the most chemically reactive species in the universe--as such, erosion of internal engine components from bombardment and sputtering of oxygen ions and neutral atomic oxygen will be a huge hurdle.

As far as performance metrics are concerned--that is a wide open field. There are multitudes of different ways to achieve the same thing. Each mission is different, and so a specific analysis needs to be made for a given mission and each engine operating mode would have to be explored--a complex undertaking to say the least.

However, in general, it is better to increase the Isp so that total mission delta-V is maximized for the available propellant. This can be achieved by dumping more energy into the exhaust stream. In the VASIMR concept this is done by dumping more power into the RF (radio frequency) ion-cyclotron resonance heater helicon antenna and thinning out (leaning) the plasma...though your Isp will increase, your thrust will decrease. And this begins a whole new level of optimization because long integration times at low thrust are slightly less propellant efficient than high thrust low integration times. It has to do with how much propellant is used to accelerate propellant still onboard--generally you want to reduce that as much as possible...

And again, this becomes a mission specific optimization--because at what point are the mission parameters satisfied (mission success: payload delivered) for a reasonable propellant expenditure. When is it good enough?

Offline lewis886

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Re: Power Supply for VASIMR
« Reply #81 on: 07/22/2008 12:05 AM »
did they ever do their test?  i have seen all kinds of things mentioning that they had a test planned for this year (early 2008, then changed to Q2 2008.)  just wondering if it's actually happened yet, or if we're still waiting on it.

Offline lewis886

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Re: Power Supply for VASIMR
« Reply #82 on: 08/06/2008 08:28 PM »
could a high power laser be a possible power supply?  or maybe be used in conjunction with other power supplies?  just wondering... because it seems that the power requirements are pretty steep... and combing VASIMR with Beamed Energy might be an interesting marriage....   then again i don't know if there's even a good efficient way to transform the beam into usable electrical energy.... dunno....
just a thought....

Offline iamlucky13

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Re: Power Supply for VASIMR
« Reply #83 on: 08/06/2008 11:06 PM »
Interesting development on the Vasimir front:

http://www.flightglobal.com/articles/2008/08/05/226329/nasa-to-test-plasma-engine-on-space-station.html

Hopefully this leads down the road to practical applications of the vasimir design. I've always thought the ISS ought to be a pretty good testbed for ion propulsion technology.

As nothing is mentioned about reboost, I'm assuming the prototype will be too small to make a meaningful dent in the ISS's delta-V needs.

Offline A_M_Swallow

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Re: Power Supply for VASIMR
« Reply #84 on: 08/07/2008 02:03 AM »

As nothing is mentioned about reboost, I'm assuming the prototype will be too small to make a meaningful dent in the ISS's delta-V needs.

The VF-200 can reboost the ISS but the burn would take several months.  The ISS would probably need extra solar panels to supply the 200kW of power.
http://www.adastrarocket.com/Plans.html

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