Neat Tech

Scientist are looking at replacing Xenon propellant with Iodine for ion drive.

The advantage to Iodine is that it is a solid, and hence is far denser when stored, and does not required a pressure vessel to store.

Unlike the noble gas Xenon though, Iodine, a halogen, is rather corrosive, and so requires some attention to materials.

Basically, the Iodine is boiled off (at 184.3°C) and then ionized and accelerated to very high velocity to provide a highly efficient low thrust source:

Most people are probably familiar with iodine through its role as a disinfectant. But if you stayed awake through high school chemistry, then you may have seen a demonstration where powdered iodine was heated. Because its melting and boiling points are very close together at atmospheric pressures, iodine will readily form a purple gas when heated. At lower pressures, it'll go directly from solid to gas, a process called sublimation.

That, as it turns out, could make it the perfect fuel for a form of highly efficient spacecraft propulsion hardware called ion thrusters. While it has been considered a promising candidate for a while, a commercial company called ThrustMe is now reporting that it has demonstrated an iodine-powered ion thruster in space for the first time.

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The current efficiency champion is the ion thruster, which has now been used on a number of spacecraft. It works by using electricity (typically generated by solar panels) to strip an electron off a neutral atom, creating an ion. An electrified grid then uses electromagnetic interactions to expel these from the spacecraft at high speed, creating thrust. The ions end up being expelled at speeds that can be an order of magnitude higher than a chemical propellant can produce.

Only a relatively small amount of material can be accelerated at once, so this can't generate anything close to the amount of thrust produced in a short period of time by a chemical rocket. But it uses far less material to produce the same amount of thrust and, given enough time, can easily produce an equivalent acceleration. Put differently, if you can be patient about your acceleration, an ion engine can do the equivalent amount in a form that uses less mass and less space. And those are two very important considerations in spacecraft.

Critical to making this work on a spacecraft's energy budget is a material that can be ionized without requiring much energy. Right now, the material of choice is xenon, a gas that's easy to ionize and resides several rows down the periodic table, meaning that each of its ions is relatively heavy. But xenon has its downsides. It's relatively rare (it's only one part per 10 million in our atmosphere) and must be stored in high-pressure containers, which cancel out some of the weight savings.

Iodine seems like an ideal alternative. It's right next to xenon on the periodic table and normally exists as a molecule composed of two iodine atoms, so it has the potential to produce more thrust per item expelled. It's even easier to ionize than xenon, taking 10 percent less energy to lose an electron. And, unlike xenon, it happily exists as a solid under relevant conditions, making storage far simpler. Just a bit of heating will convert it to the gas needed for the ion engine to work.

The big downside is that it's corrosive, which forced ThrustMe to use ceramics for most of the material that it would come into contact with.

By way of comparison, an ion drive can provide a little under a millinewton of thrust with an ISP (fuel efficiency) of about somewhere between 1,500 and 10,000 seconds.

By comparison, the Space Shuttle Main Engine (SSME) produces about 2.3 meganetwons of thrust and an ISP of 363 seconds.

It's a lot less thrust, but it can provide thrust for weeks and months, and in the vacuum of space over long distances, say much beyond the moon, it will significantly shorten travel time.

One Way to Deal With Limited Launcher Capacity

Israel is looking at advanced propulsion technology to maximize the capability of what are necessarily small reconnaissance satellites:

Israel is working to sharpen its eyes in space, enlisting Israel Aerospace Industries (IAI) to improve the optical and radar payloads of the spy satellites serving the nation’s intelligence community.

The company is developing a new generation of satellites for even more complex missions, using nanosatellite production and electric propulsion concepts.

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In addition to the imagery, Doron says the low weight and a unique set of reaction wheels in IAI’s satellites enable them to capture more usable images of an area of interest in every pass. Special reaction wheels also enable Israeli satellites to carry a smaller amount of hydrazine gas, usually used to enable the satellite’s maneuvers in space and to keep it at the designed altitude.

An ion thruster or drive is a form of electric propulsion used for spacecraft. It creates thrust by accelerating positive ions with electricity for satellites with optical and synthetic aperture payloads. The resolution will be improved, and the way the images are processed on the ground also will be enhanced with very advanced ground stations.

Reaction wheels are basically gyroscopes, and it means that there is no propellant expired to change orientation.

They are also looking at adding electric propulsion for orbital maneuverability:

To further prolong the life of full-size Israeli satellites, the division is evaluating the use of electric propulsion to replace the use of hydrazine. The system will use xenon gas to operate on thrusters, he says. According to Doron, the use of xenon will enable the satellite to orbit the Earth at a lower altitude but give it enough power to correct any loss of altitude that will be caused by greater friction with the atmosphere.

An ion thruster or drive is a form of electric propulsion used for spacecraft. It creates thrust by accelerating positive ions with electricity for satellites with optical and synthetic aperture payloads. The resolution will be improved, and the way the images are processed on the ground also will be enhanced with very advanced ground stations.

An ion drive provides much less thrust than a rocket or a thruster, but it's ISP (basically fuel economy) is far greater, with about 250 seconds for a thruster, and 3000 seconds for an ion thruster, which means a lot more delta-V with a lot less propellant, which means greater maneuverability and greater time on station.

It Looks Like Ion Drive is Going Commercial

Following the success of the Dawn Spacecraft in exploring the asteroids, I suppose that it was inevitable that ion propulsion would hit the commercial satellite industry:

It’s no secret that Boeing’s space systems unit is aggressively pricing bids in an effort to grow its commercial business segment as government spending flags. But even the most bullish observers were taken aback by an estimated $400 million deal just signed with Asia Broadcast Satellite (ABS) and Satellites Mexicanos (SatMex) to build the first all-electric commercial telecom spacecraft intended for launch to geostationary orbit.

The technology—which uses light-weight xenon-fueled ion thrusters rather than conventional chemical propulsion to maneuver a spacecraft into position—is promising. Imagine cutting in half a satellite’s weight, and subsequently its launch costs, which can top $100 million depending on the size of the spacecraft. All-electric satellites could potentially save fleet operators hundreds of millions of dollars in annual launch expenditures, with potentially no impact to their satellites’ capability or performance.

The downside is that while most commercial communications spacecraft are expected to be on station and making money within a few weeks of launch, new all-electric satellites could spend up to six months using slow pulses from ionic propulsion systems to maneuver into their final orbital slot—months when the spacecraft is not generating any revenue. This might not pose a problem for large operators with established revenue streams who can accommodate the lag in revenue as they incorporate new satellites into fleet-replenishment programs. But it could put small companies at a disadvantage as they sacrifice up to half a year’s income waiting for the spacecraft to enter service.

In either case, employing an all-electric spacecraft requires getting an early start on the capital-spending cycle to accommodate the lengthy orbit-raising process.

“It is easier for a company with a large fleet that has to anticipate replacement satellites several years in advance to tolerate the several months it takes for an electric satellite to reach position once it has separated in orbit,” says Romain Bausch, chief executive of Luxembourg-based SES, the world’s second-largest fleet operator by revenue.

Basically, chemical maneuvering thrusters have something like a hundred times more thrust, but have about 100x lower ISP (fuel efficiency).

The downside to ion propulsion close to earth is time, but the lines cross for anything farther the earth-moon system.

Russia Planning Nuclear Rocket

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Bimodal Nuclear Thermal Rocket

From the report, we are not talking about Orion, or direct thrust from nuclear heating, but rather some sort of electric propulsion system using electricity from a reactor for a proposed mission to Mars.

Something like ion drive, or plasma drive would likely cut transit time by at least ¾ for a manned trip to Mars, and if a ground base were established, a nuclear power supply would handle the reduced solar energy levels there.

I'd take this with a grain of salt, because the cost quoted for this is a bit over US $¾ billion, which sounds like a quote from Never Land.

Ion Drives for Spy Sats

DARPA is looking at ion-drive spy satellites. Truth be told, this is not surprising.

One of the limiting factors on many spy satellites is the amount of propellant available, and if you can use a very high impulse (rocket fuel economy) for station keeping and scheduled moves, you can either make a lighter vehicle, which means more for the same price, or one with much hhigher flexibility and operational life.

NASA Launches Dawn Probe to Asteroid Belt

The Dawn mission to Ceres and Vesta has been launched.

It's the first mission to renedez vous with more than one body, and an ambitious application of ion drive technology.

For more on the tech, see here

OK, I am Now Mildly Excited

I've been hearing about the EM drive for some time.

It's a space propulsion system which requires no reaction mass or fuel.

I've been dubious, but NASA has published a favorable report in a peer reviewed journal, which means that the concept is credible on a mainstream level.

I look forward to the tests:

NASA scientists have been daydreaming about a new kind of engine that could carry astronauts to Mars in 70 days without burning any fuel. Now, in a new paper published in the peer-reviewed Journal of Propulsion and Power, they say that it might really work.

The paper, written by astrophysicists at NASA's Eagleworks Laboratories, tested a electromagnetic propulsion system, or “EM drive,” that generates a small amount of thrust simply by bouncing microwaves around a cone-shaped copper chamber. No propellant goes in, no exhaust comes out, and yet, somehow, the engine can make things move.

If you think that news sounds too good to be true, you've got good instincts — it just might be. This “impossible” fuel-less engine appears to violate one of the fundamental laws of physics.

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That's Newton's third law of motion. It's the principle that explains why pushing against a wall will send an ice skater zooming in the opposite direction. It also explains how jet engines work: As hot gases are expelled out the back of the plane, they produce a thrusting force that moves the plane forward.

But the EM drive doesn't work that way. Its thrust seems to come from the impact of photons on the walls of the copper cavity. That would be like moving a car forward by just banging against the windshield.

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According to the new paper, yes. The Eagleworks scientists report that their machine generated 1.2 millinewtons of thrust per kilowatt of electricity pumped in. (That electricity could come from solar panels in a hypothetical spaceship.) That's a fraction of thrust produced by the lightweight ion drives now used in many NASA spacecraft, National Geographic noted, but it's a lot more than the few micronewtons per kilowatt produced by light sails, a proven technology that generates thrust using radiation from the sun.

I'd like to see some orbital testing, and a theoretical model explaining how it works, but I am now officially intrigued.

Vasimr Electric Propulsion System Heading Out to ISS

NASA will be sending the variable specific impulse magnetoplasma rocket (Vasimr) up to the International Space Station (Paid subscription required) for tests and validation. (Earlier posts)

It's expected to put out about 5.7 Netwons, about a pound, with an ISP (fuel economy) of somewhere between 10 and 30 times that of chemical propellants.

While a pound does not seem like much thrust, it's more than enough for station keeping and orbital, or for that matter interplanetary, maneuvering, as you can get the thrust for months, rather than hours, and compared to other electric thrusters systems, like the ion drive used on the Dawn Probe, it provides a lot more thrust. (Dawn has a thrust of only 90mN, about 1/50 that of the Vasimr).

Space nuke boffin: NASA Moonbase needs nuclear rockets | The Register

If you reference some of the links off this page, a nuclear powered engine of this type does give a higher ISP 875 vs 350 for the very efficient SSMEs.

Of course, other technologies, Ion and plasma are much higher (a quick google gives an ISP of 3300 for early ion drives).

Of course, Ion and plasma are low thrust, and cannot be used for ascent or descent, but neither can NERVA class motors, as their exhaust is radioactive.

Space nuke boffin: NASA Moonbase needs nuclear rockets
By Lewis Page
Published Saturday 30th June 2007 07:02 GMT

One of America'a top nukes-in-space boffins says it's time to consider nuclear-powered rockets again. He reckons atomic boosters could cut the cost of NASA's upcoming Moonbase plan.

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This guy runs the premier RTG battery (nuclear batteries) manufacturer in the US, The Center for Space Nuclear Research, and he is someone who has a hammer, and sees everything as a nail.

But Howe reckons that there's more to nukes in space than just providing electricity. He says that nuclear power should be used for propulsion, too. According to an article in New Scientist, his plan is to update a 1960s design called Nuclear Engine for Rocket Vehicle Application (NERVA) to carry payloads from Earth orbit to the Moon.

NERVA-type rockets use a fission reactor to heat up hydrogen and blast it out of the thrust nozzle at extremely high speed, faster than can be achieved by normal chemical-powered boosters. This allows a nuclear-driven spacecraft to achieve more with a given amount of liquid fuel, or "reaction mass." The NERVA test programme had its problems - not least the fact that the reactor tended to come apart and fire itself out of the exhaust - and was terminated in 1972 during NASA budget cuts.

Howe and his team reckon that the greater efficiency of nuclear drive would allow each Moon shot to carry an additional eight tons of payload, which would mean fewer launches being needed. He thinks the savings from a lower number of launches would more than offset the cost of updating the original NERVA design, perhaps yielding overall savings of as much as $2bn.

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VASIMR Plasma Drive Hits Rated Power in Bench Test

I've mentioned the technology before, and now it appears that the VASIMR plasma drive has hit a major milestone in the lab. The first stage (helicon) of the system has hit its rated 30 KW power.

Thrust levels are relatively low, though they are high compared to something like Ion, around 10N in low ISP mode, and in the 100mN range in high ISP mode.

The developer of this technology, Ad Astra Rocket Company, hopes to get a space-rated model to the ISS in the next few years to validate performance in space.

Picture pr0n:

Lab picture


VASIMR Space Craft Concept

I believe that the spacecraft shown uses nuclear power for propulsion requirements.

Interesting Concept

People are looking into using metals for reaction mass in electrical spacecraft propulsion. (Alternate link)

We are talking about things like Hall Effect Thrusters, Ion Drives, and Plasma Drives.

They are looking at replacing various noble gasses, like xenon, krypton, and argon, with cheaper and denser metals, like zinc, bismuth, and the like.

I do recall that cesium was favored as a reaction mass a few decades ago, but that is corrosive and difficult to handle:

Move aside, xenon, krypton and argon. There is a new, heavier-weight class of spacecraft propellant: metals.

This year, several startups are testing electric thrusters that run on metal propellants. The companies say the hard stuff packs a greater punch for its volume and is cheaper and easier to handle than conventional gases.

In March, propulsion company Benchmark Space Systems launched its Xantus plasma thruster system, which uses molybdenum as a propellant, on Orion Space Solutions’ 12U cubesat. In August, Neumann Space and the University of Melbourne announced the successful completion of on-orbit tests of the Neumann Drive, an ion thruster that also uses molybdenum, on a nanosatellite. And in January, Starlight Engines plans to test its Crucible Hall-effect thruster on orbit using zinc propellant.

Metal propellants work inside electric propulsion systems in a similar way to gaseous propellants: After being vaporized, they are ionized and then accelerated out the back of the system using an electrical field. Because metal propellants have greater atomic weight, the elements require less storage volume to generate equivalent thrust.

Typically such systems provide very low thrust, from the 10s of micronewtons to a few millinewtons, but they provide somewhere between 4 and 10 times the ISP (Fuel efficiency) meaning that for station keeping in orbit or long duration missions, they can offer significantly better performance once in space.

I'm keeping my eye on this.

Neat Tech: Radio Plasma Drive

NASA Ad Astra Ink Second Space Act Agreement in “Vasimr” Engine (subscription required)

NASA is working with Ad Astra Rocket Co. on it's Vasimr engine. It uses radio waves to heat electrically charged fluids to extremely high temperatures for fuel efficiency, controlling the resulting plasmas for thrust and insulating nearby structures with magnetic fields.

ISP appears to be in the 5K-12K seconds range (PDF), or more than 10 to more than 30x that of chemical rockets.

Unlike Ion, it's supposed to support higher thrust levels, on the order of 100+ N, compared to the millinewton levels for Ion drives.