Electric powered engines.

Gibbon · 2003-06-27 06:24:57

I asked this about a year ago and I was never able to check the reply and I can't seem to find the thread (forgot where I posted it!)
I'm just wondering if there are any engines that are currently available, or on the horizon, that are electric powered and could be used to either get from Earth into space and/or get from Earth to Mars?
Power supply isn't a problem, I'm just wondering if the actual propulsion is there.
Also, I heard that ION engines are electric powered but in one report I heard that they still require fuel, albeight very little.
Anyway, thanks for any help.

RobertDyck · 2003-06-27 11:45:21

All thrust is based on action/reaction. That means you must push on something. A rocket accelerates propellant out the back. If it accelerates M mass of propellant at once and A acceleration that will require M*A force. That will produce an equal but opposite force on the engine, and presumably the engine is attached to the spacecraft. If F is the force applied by the engine and the spacecraft has mass Ms (Mass Spacecraft) then the acceleration applied to the spacecraft will be F/Ms. The longer the propellant is in the engine, the greater the total propellant mass to be accelerated. The greater the propellant mass the greater the propulsive force, but the greater the mass of propellant you must carry. The real key is to increase the exit velocity of the propellant. That can be accomplished by either keeping propellant in the engine longer or increasing the acceleration applied to the propellant. Propellant for a chemical rocket is the spent fuel, and the chemical reaction only creates enough energy to accelerate the exit velocity so far. Different fuel mixtures produce different energy, cryogenic hydrogen/oxygen seams to have the greatest.

With an ion engine the propellant does not undergo chemical reaction. Instead it is ionised and pulled with an electric field. A grid is charged with static electricity and the ionised gas is pulled toward it. Some of the gas will impact the grid, causing electric discharge and no propulsive force. Some of the gas will pass through the holes of the grid causing it to exit the engine; that gas provides propulsion. Xenon or Krypton gas is used since they have a high mass to electric charge ratio. That increases propellant mass per unit of electric charge. Notice, increasing propellant mass increases thrust force but also increases mass of propellant to be carried. In terms of reducing propellant mass to get to your destination, that cancels out. The key with Xenon and Krypton is they reduce electricity required. Also, if charged gas density in the engine is too high the positive charge of the gas at the acceleration grid will negate the force of negative charge on the acceleration grid. In other words, if gas density is too high the charges will "jam up" the engine causing reduced efficiency. Heavy gasses like Xenon and Krypton are a way to increase gas mass without increasing the number of ions.

The numbers to measure fuel efficiency for an engine in space is Specific Impulse, designated by the letter "I" with a subscript "SP", such as (Isp). It is measured in seconds; that is one pound of fuel can produce one pound of thrust for how many seconds. Or in metric, one kilogram mass of fuel can produce one kilogram force of thrust for how many seconds. Here kilogram force is defined as one kilogram mass multiplied by one standard gravity of acceleration. One standard gravity is the acceleration on Earth at sea level, or about 9.78 metres per second squared.

As a comparison, the solid rocket boosters of the space shuttle have an Isp of about 269 seconds. The main engines of the space shuttle are the most efficient chemical rockets every built, they produce 455 seconds in vacuum; their efficiency isn't quit as high at sea level. The ion engines used on Deep Space One had a nominal efficiency of 3,100 seconds, but the exact Isp depended on throttle setting. This demonstrates that ion engines are much more fuel efficient. However, electric engines are weak. The thrust produced by the engine on DS1 was about equal to the force of a single sheet of paper resting on your hand in normal Earth gravity. That is obviously not enough to lift the spacecraft off the ground. In space you keep going at whatever speed you have, so a low thrust can gradually increase speed over months. A low-thrust high-efficiency engine is great once you are in space, but it won't get you off the ground.

Today the Glenn Research Center where the engine for DS1 was developed is working on a larger version. They have produced an Isp of 5,600 seconds and are working on a still larger one that they hope will produce 8,300 seconds. A researcher at the Johnson Space Center is working on a Variable Specific Impulse Magnetoplasma Rocket (VASIMR) that will use hydrogen gas instead of xenon or krypton and permit either high-efficiency and low-thrust, or low-efficiency and relatively high-thrust. It still won't produce enough thrust to launch off the ground, but should exit Earth orbit quickly using high-thrust then cruise toward Mars using continuous thrust with high-efficiency and low thrust.

The problem with electric engines is electric power. The more thrust you want from them the more electric power they need. Solar power provides continuous power during the trip but it really isn't much. The high-power electric engines that some people hope to use to leave Earth orbit for Mars will require 10 megawatts or more. That will either require a giant solar array 700 metres wide or a nuclear reactor.

Shaun Barrett · 2003-06-27 18:33:32

That was a very interesting post, Robert. You've put a lot of complicated stuff into easy-to-understand language.
I like the sound of the 8,300 second engine. What's the best Isp figure and the best thrust for the VASIMR engine?

RobertDyck · 2003-06-27 19:35:04

That was a very interesting post, Robert. You've put a lot of complicated stuff into easy-to-understand language.
I like the sound of the 8,300 second engine. What's the best Isp figure and the best thrust for the VASIMR engine?

The goal of VASIMR is 9,000 second Isp. It uses a slightly different principle. It heats hydrogen gas in a chamber by exposing it to radio waves of a certain frequency. That heats hydrogen the same way that microwaves heat water in a microwave oven.

By the way, a microwave oven is tuned to the frequency that will be absorbed by water. It heats the water in food which then conducts the heat to the rest of the food. All food is wet so it works well.

In a VASIMR engine the hydrogen is heated so hot that it could melt the engine. It is contained with a magnetic containment bottle. A magnetic choke at the exit controls how much hydrogen gets out. If you open the choke wide it provides high fuel flow rate. That can produce high thrust but at low fuel efficiency. Closing down the choke will hold the hydrogen in until it reaches very high pressure. Higher pressure results in higher exit velocity. Choking it down reduces flow rate so that produces high efficiency but at low thrust.

One advantage of VASIMR over ion engines is that high gas density doesn't produce reverse force, so it doesn't reduce engine efficiency. This permits VASIMR to use hydrogen, which is light, cheap and abundant. However, high pressure could cause the hot gas to get through the magnetic containment bottle and melt the inside of the chamber. The key with VASIMR is the containment system. The guy at Johnson Space Center is still working on the prototype. JSC is having difficulty convincing the budget guys to maintain funding for this research.

Free Spirit · 2003-06-27 20:31:23

Shaun if you get a kick out of high ISP motors that could be built with current technology, you should check out this very politically incorrect, 1,000,000 ISP beast. It's kinda like your garden variety ion engine overdosing on crack. I decided to paste in a segment of the article below. If you already know about this just ignore.

"Fission-fragment propulsion involves permitting the energetic fragments produced in the nuclear fission process to directly escape from the reactor; thus, the fission fragments, moving with a velocity of several percent of the speed of light, are the propellant working fluid. Because these fragments are heavily ionized, they can be directed by magnetic fields to produce thrust for propulsion. Specific impulse in excess of 1 million lbf-s/lbm is possible."

Shaun Barrett · 2003-06-28 01:44:56

Thanks fellas!
So many wondrous contraptions we could be using to cruise around the solar system!
Too bad it's so hard to get past the budget committees and the environmental zealots.

Gennaro · 2003-06-28 04:11:15

Couldn't help it. This subject is too fun. Especially when you get such a informed down to earth lecture on thrust, Isp and a few of the propulsion concepts out there as the one by RobertDyck!

Free Spirit, I've read that article before and it sure is an amazing concept. I suspect though it may not be all that developed above the level of theory. Most of these ideas aren't. The best bet to my knowledge - from a various set of standpoints - would be some sort of Nuclear Thermal Reactor Propulsion.

In a VASIMR engine the hydrogen is heated so hot that it could melt the engine. It is contained with a magnetic containment bottle. --- However, high pressure could cause the hot gas to get through the magnetic containment bottle and melt the inside of the chamber. The key with VASIMR is the containment system. The guy at Johnson Space Center is still working on the prototype. JSC is having difficulty convincing the budget guys to maintain funding for this research.

Wonder if a breakthrough on the containment system of VASIMR could have any effect on the development of Gas Core Nuclear Propulsion? The problem here, or so I'm told, is likewise managing the tremendous heat levels produced that needs to be contained somehow.
Unlike VASIMR of course, the Gas Core Nuclear Reactor has enough thrust to be ground launchable. A strategic advantage in my mind, because then it can be utilized to build a Single Stage to Orbit system that is also fully landable on Earth, the Moon, an asteroid or a space station and back.

RobertDyck · 2003-06-28 09:24:43

The problem with fission fragment or a Gas Core Nuclear Thermal Rocket is that the fission fragments are exhausted. The fission fragments are far more radioactive than uranium or plutonium. In fact, before it goes into a nuclear reactor you can handle uranium with just the same plastic gloves you get with oven cleaner. The fission fragments, however, are so radioactive that you want a lead wall a foot thick between you and any spent nuclear fuel rods. So fission fragment engines or GCNTR wants to expel those highly radioactive fragments in gas form directly into the atmosphere?! Once you are in space the radiation would be like adding a teaspoon of water to the ocean, it would be nothing compared to radiation from solar wind or cosmic radiation, but in the atmosphere!? I don't think so. The nuclear activists can get panicky and fear the word "nuclear" with religious dogman. However, expelling highly radioactive gasses into the atmosphere would finally give them something real to protest against.

Nuclear Thermal Rockets designed as launch vehicles are careful to contain those fission fragments. Because of their radioactive hazard they have to be held inside the engine and contained so well that if the rocket was destroyed the fission fragments would still be contained. Nerva contained its uranium in ceramic capsules so strong that they could fall all the way out of orbit and hit the ground without cracking. That would keep the radioactive waste inside the capsules. Nerva was designed as an upper stage; it would be turned on after safely in orbit. If the launch vehicle had a catastrophic failure, cleanup would require bar-B-Q tongs and the same plastic gloves you get with oven cleaner, and a plastic garbage bag. Just be careful not to place more than a couple capsules close to each other. Timberwind was designed as a launch vehicle. It was a pebble bed reactor so its nuclear fuel was small balls the size of a marble. Since the reactor would operate during launch, let guys in hazard suits collect the marbles; they would be highly radioactive. If a Timberwind upper stage were used on a conventional rocket, then you have the same safety: just use bar-B-Q tongs and plastic gloves and don't put the marbles together.

But you want to use fission fragments in the atmosphere!? Um, no; not safe. Yes, it could be very efficient but you don't want to poison the atmosphere with more radiation that 3 Mile Island with every launch.

Gennaro · 2003-06-28 09:41:00

But you want to use fission fragments in the atmosphere!? Um, no; not safe. Yes, it could be very efficient but you don't want to poison the atmosphere with more radiation that 3 Mile Island with every launch.

Hm, I never proposed launching a Fission-Fragment viechle from terra firma.
Moreover, I thought that in a Closed Cycle GCNR (a form of NTR), the fissionable material did not get into direct contact with the hydrogen working fluid.

Fission Fragment:
http://www.islandone.org/APC/Nuclear/10.html

Gas Core Nuclear Rocket:
http://www.islandone.org/APC/Nuclear/08.html

Also see here:
http://www.nuclearspace.com/a_liberty_ship7.htm
http://www.nuclearspace.com/images/articles/mauk2b.jpg

RobertDyck · 2003-06-28 13:41:58

Ah, the nuclear light bulb. When talking about GCNR I think of the open-cycle engine. That uses a vortex to contain the nuclear fuel in the engine, and liquid hydrogen injected through the core of the vortex. That results in direct contact between the nuclear fuel and propellant. That is the most efficient heat transfer, but some nuclear fuel is lost with the exhaust. From an efficiency stand point, that means you are leaking fuel; not good. It also means the fission fragments (nuclear waste) are exhausted with the propellant; very dirty.

A nuclear light bulb contains the nuclear fuel and its waste products within a transparent quartz capsule. Radiant heat literally shines through the transparent capsule, hence the name "light bulb". The drawing on your link indicates the capsule would be internally cooled. If that capsule separates the nuclear fuel from propellant, you don't want the capsule to be cooled by anything other than the propellant itself. Any other cooling would take heat away from the propellant. But that does mean the capsule must be made of a material that can get hotter than propellant exhaust temperature and retain its structural strength.

Now how do you ensure nuclear fuel and its waste products stay contained even in the event of a catastrophic loss like Columbia?

TJohn · 2003-06-30 06:43:46

This has been one of the most interesting topics in the past couple of weeks! Keep it up! I agree with Shaun, wholeheartedly.

I'm all for nuclear propulsion but Ion propelled and VASMIR is might nice too.

Gennaro · 2003-06-30 11:29:55

RobertDyck,
according to that article about the "Liberty Ship" from Nuclear Space at least, the principle of the "nuclear lightbulb" was tested in the 70's and made to work. Not being aware of any further details, I wouldn't be surprised though if the separation 'glass plate' is a source of trouble with this system for the reasons you're pointing out.
Nevertheless, I would personally like to see R&D continue with the closed cycle GCNR. It has interesting potential from a space industrial expansion point of view.

"Now how do you ensure nuclear fuel and its waste products stay contained even in the event of a catastrophic loss like Columbia?"

Well, to put it bluntly, I guess I don't. The dangerous part is the waste products. On the other hand, ground control can be put into radiation proof bunker shelters during launch and provided it's done from a desolate place, I hardly see why a catastrophic event would be much dirtier than an atmospheric nuclear bomb test. Naturally, the system should be designed to be as rugged and reliable as is possible.

Speaking of safety, you previously outlined why the solid core NTR was superior in this regard. Do you know if it could be updated? The ceiling for NERVA typically ranged an Isp of 900 and used a graphite reactor. Is it possible to improve on this system at all?

RobertDyck · 2003-06-30 12:34:56

The idea I came up with this year is a combination of solid core NTR and VASIMR. The current design philosophy for VASIMR is to use a nuclear reactor to generate electric power, then use that electricity to create radio waves in the primary propulsion chamber. What if you use a Nuclear Thermal Rocket that preheats cryogenic hydrogen, then injects hot hydrogen gas into the VASIMR chamber. Neutron moderation will generate electromagnetic radiation, often gamma radiation. Could you tune the design to moderate neutrons in such a way that it generates radio waves in just the right frequency for VASIMR, and shape the nuclear reactor (possibly with wave guides) to direct the radio waves into the VASIMR chamber. This would reduce energy conversion to a minimum. You would still need some electricity to power the magnetic containment bottle, so the excess heat of the nuclear reactor would have to have some sort of power generation. This has the potential for the high thrust of an NTR engine, and high Isp of an electric engine.

Of course, this is combining an NTR engine, a nuclear reactor, and a VASIMR engine. The VASIMR hasn't even been completed yet, and space nuclear reactors are just under development now. This may be future technology, but it has the potential for an engine for a ground launch vehicle with a 4-digit Isp. Do we know anyone with a Ph.D. in nuclear engineering and a M.S. in Aeronautics and Astronautics? (Hint, Hint) For those who don't know, I'm saying Dr. Robert Zubrin has those qualifications.

prometheusunbound · 2003-07-04 14:58:48

I freaking love that idea. Let one of us ask zubrin what he thinks. . . . :;):

Gibbon · 2003-07-05 23:32:45

So, RobertDyck, what you are saying is that VASIMR is electric powered, it just needs alot of it?
Perhaps that could be a goal, create an extremely efficieant power source that is small enough and strong enough to survive a trip on a ricket whilst producing power.

Free Spirit · 2003-07-06 00:25:25

Do we know anyone with a Ph.D. in nuclear engineering and a M.S. in Aeronautics and Astronautics? (Hint, Hint) For those who don't know, I'm saying Dr. Robert Zubrin has those qualifications.

I didn't know that Zubrin had a Ph.D. in nuke engineering. I remember reading somewhere that he worked on fusion projects for awhile, which I thought was odd for an aerospace engineer. All is revealed.

Gibbon · 2003-07-15 03:54:31

With the ION engine, would it be able to work in an atmosphere infinitely? (assuming infinity power of course.)

Gennaro · 2003-07-22 05:04:05

This has the potential for the high thrust of an NTR engine, and high Isp of an electric engine.

See if I got this straight. Are you actually suggesting that we propel nuclear heated working fluid straight through a modified VASIMR magnetoplasma engine, which later on will switch on to an Ion stream as originally intended?
Otherwise, if you are simply using an alternative way of producing the fourth state of matter, I can't really see how you are supposed to get the high thrust during ascent. Of course, it could be something very basic about rockets that I don't understand. After all, I'm only a representative for the interested public.

prometheusunbound · 2003-07-22 06:08:37

(Gennaro Posted on July 22 2003, 07:04 )After all, I'm only a representative for the interested public.

Are you a senator or poltician?

Gennaro · 2003-07-22 09:58:39

I'm a citizen, yet not of the United States.

Sorry if I disappoint you.

Visited by moderator 2022/01/28

RobertDyck · 2003-07-22 10:11:27

This has the potential for the high thrust of an NTR engine, and high Isp of an electric engine.
See if I got this straight. Are you actually suggesting that we propel nuclear heated working fluid straight through a modified VASIMR magnetoplasma engine, which later on will switch on to an Ion stream as originally intended?
Otherwise, if you are simply using an alternative way of producing the fourth state of matter, I can't really see how you are supposed to get the high thrust during ascent. Of course, it could be something very basic about rockets that I don't understand. After all, I'm only a representative for the interested public.

I am not suggesting ion operation at all. The VASIMR engine uses radio waves to heat hydrogen the same way that a microwave oven uses radio waves to heat water (in this case in the microwave frequency band). The current approach for Nuclear-Electric Propulsion (NEP) is to use a separate nuclear reactor to produce the electricity required to supply the electric engine. I am suggesting fully integrating the nuclear reactor into the engine. Rather than keeping the electric engine and nuclear reactor as two separate distinct components, integrating them produces great improvements in efficiency. It also permits a fast reactor to produce a great amount of energy quickly and apply that energy directly to the engine, rather than multi-step energy conversion.

There are a few basic ideas. Rather than using only heat from the reactor and treating the radiation as something to shield against, use the radiation directly as an energy source. Rather than convert heat into electricity then convert electricity into radio waves, directly convert radiation into the required radio waves. In addition to using radiation that would otherwise be lost, we avoid losses from energy conversion. We also avoid having to deal with electric power on the order of a hundred megawatts. The means to produce high thrust is simply to provide a hell of a lot of power from the reactor directly to the engine.

To avoid melting down the reactor, I am suggesting running cryogenic liquid hydrogen through it. To ensure this isn't a loss of propellant, run the heated hydrogen into the engine. That makes the reactor a pre-heat chamber for the engine. Heating cryogenic liquid hydrogen in a nuclear reactor is the principle of a Nuclear Thermal Rocket (NTR) so this makes the reactor an NTR engine itself. So this system would run the exhaust from an NTR into a VASIMR engine. The key is to design the reactor to use neutron radiation to generate radio waves tuned to the requirements of a VASIMR engine, and then direct those radio waves directly into the VASIMR engine.

RobertDyck · 2003-07-22 10:13:36

...I'm only a representative for the interested public.

Are you a politician? Where are you and what office do you hold?

Visited by Moderator 2022/01/28

space_psibrain · 2003-07-25 17:56:55

Cook Inertial Propulsion

The Advantages of this System
1. It is nonpolluting- it can be electrically powered.

2. Initial cost is very low by comparison to other propulsion systems. A large rocket engine can cost well over $50,000,000. The estimated cost of a CIP engine of similar thrust is only several hundred-thousand dollars instead of millions.

3. Low operating costs- mainly because it can be powered electrically. The rocket engines use exotic fuels that can cost over $100 per gallon and are very dangerous to handle.

4. More durable and reliable than a rocket. The CIP engine should be able to run for years without major repairs. A large rocket's life is measured in SECONDS! This fast breakdown is caused by the extreme heat and cold the rocket components are subjected to. The CIP engine is not subject to this type of problem

5. Extremely quiet- it will make less noise than a good car engine.

Visited by moderator 2022/01/28

prometheusunbound · 2003-07-28 09:21:18

Sounds unrealistic. I don't see how it can work.

space_psibrain · 2003-08-15 18:58:58

it has to do with the splitting of masses to convert angular momentum to forward thrust...and this was demonstrated to companies like boeing, so i wouldn't be a critic right away

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