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Microthrusters For Small Satellites

Soulskill posted about 2 years ago | from the or-install-50,000-of-them-for-large-satellites dept.

Space 75

An anonymous reader writes "A research team led by Paulo Lozano at MIT's Space Propulsion Lab and Microsystems Technology Lab have shown off a microthruster array capable of powering small satellites. The tiny, flat design could obviate the need for bulky propellant tanks. 'To explain how the thruster works, Lozano invokes the analogy of a tree: Water from the ground is pulled up a tree through a succession of smaller and smaller pores, first in the roots, then up the trunk, and finally through the leaves, where sunshine evaporates the water as gas. Lozano's microthruster works by a similar capillary action: Each layer of metal contains smaller and smaller pores, which passively suck the ionic liquid up through the chip, to the tops of the metallic tips. The group engineered a gold-coated plate over the chip, then applied a voltage, generating an electric field between the plate and the thruster's tips. In response, beams of ions escaped the tips, creating a thrust. The researchers found that an array of 500 tips produces 50 micronewtons of force — an amount of thrust that, on Earth, could only support a small shred of paper. But in zero-gravity space, this tiny force would be enough to propel a two-pound satellite.'"

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Satellites in zero-gravity? (3, Interesting)

jdastrup (1075795) | about 2 years ago | (#41028283)

Do we have satellites in zero-gravity? Hmmm.

Re:Satellites in zero-gravity? (0)

Anonymous Coward | about 2 years ago | (#41028381)

Nope. Only anti-gravity ones.

Re:Satellites in zero-gravity? (4, Informative)

PDF (2433640) | about 2 years ago | (#41028403)

From Wikipedia [wikipedia.org] :

"zero-gravity" is usually used synonymously to mean effective weightlessness, neglecting tidal effects.

So, yes, there is plenty of gravity acting upon satellites in orbits, but they are in free fall, so there isn't a significant gravitational force experienced by the components of the satellite due to their accelerating reference frame. Thanks to our somewhat sloppy terminology, this is zero-gravity.

Re:Satellites in zero-gravity? (0)

Anonymous Coward | about 2 years ago | (#41028437)

Did you look for them in the Lagrange Points yet ?

Re:Satellites in zero-gravity? (1)

koan (80826) | about 2 years ago | (#41030327)

'zero-gravity" No such thing.

"microgravity"

Re:Satellites in zero-gravity? (1)

Immerman (2627577) | about 2 years ago | (#41036707)

If we're going to be pendantic though, is that really much better a term for satellites? Sure, something as far out as the Moon is only experiencing ~0.0003g due to Earth, and that probably qualifies (as milli-gravity at least...). But a satellite in LEO is less than 30% further from Earth's center of mass than we are, and will be experiencing over 0.5g, which I think clearly does not.

Personally weightlessness gets my vote since weight is a sloppy term to begin with, a measurement of mass-scaled gravitational acceleration versus a reference frame - and in the local reference frame of a passive satellite there's minimal gravitational acceleration. Tidal forces will generally be minimal unless the satellite is quite large, as will the mico-scale (nano? pico?) effects of the satellite's own mass. Very little noteworthy unless you're dealing with *extremely* precise instrumentation

Re:Satellites in zero-gravity? (0)

Anonymous Coward | about 2 years ago | (#41032005)

I was curious too. Where can we find this wonderful spot in the universe that lacks one of the four fundamental forces?

Re:Satellites in zero-gravity? (1)

Immerman (2627577) | about 2 years ago | (#41036785)

God only knows, and He's not telling 'cause he's got a sweet zero-G spa set up and doesn't want to have to start clearing out vermin.

On a more serious note, it's at least theoretically possible there are points (geometric of course) in the universe where the sum total of all gravitational forces is exactly zero. Somewhere near the epicenter of the Big Bang would be one likely spot to look.

I'm in a nitpicking mood. (0)

Anonymous Coward | about 2 years ago | (#41028353)

"The tiny, flat design could obviate the need for bulky propellant tanks."

This is like saying a 25cc engine obviates the need for a large fuel tank.

Re:I'm in a nitpicking mood. (3, Informative)

WhiplashII (542766) | about 2 years ago | (#41028783)

Not really - ion propulsion trades "energy squared" for "propellant flow rate". So the large fuel tank (100 kg, say) has been replaced with a much smaller one, around 1 kg, for the same thrust. Here's the trade details:

1. Trading a 350 Isp Hydrazine thruster for a 35,000 Isp ion drive - it uses 1/100th the propellant for the same total impulse (thrust*time)
2. The thrust decreases dramatically typically - but for small satellite station-keeping that doesn't matter
3. The power requirement/N thrust gets ridiculous - from about 3.5KW/N to 350KW/N

Nanotube Array (1)

sanman2 (928866) | about 2 years ago | (#41029671)

Actually, I'd been wondering if an array of large-diameter nanotubes could be used to eject ions faster and more efficiently.

Re:Nanotube Array (0)

Anonymous Coward | about 2 years ago | (#41030433)

To be honest, the current ion drives are pretty good - we can basically achieve arbitrary efficiency and Isp. The real issue is the crazy power requirement, which unfortunately is basic physics. The only place to really focus on is making the engine weigh nothing.

Re:I'm in a nitpicking mood. (0)

Anonymous Coward | about 2 years ago | (#41029699)

So you trade a simple metal tank for a complex and heavy power supply?

Re:I'm in a nitpicking mood. (1)

ChrisMaple (607946) | about 2 years ago | (#41033587)

The trade is getting energy from substantial mass of fuel which also acts as reaction mass, for energy from the sun and a small reaction mass. Whether the power supply is heavy depends on how much thrust is produced. Granted the sun is heavy, but for satellite uses you don't have to take it with you.

Re:I'm in a nitpicking mood. (0)

Anonymous Coward | about 2 years ago | (#41028879)

Or, you could NOT read it as "the design is flat and tiny, *thus* it could obviate the need for bulky propellant tanks"

Re:I'm in a nitpicking mood. (0)

Anonymous Coward | about 2 years ago | (#41029057)

Try as I might, it's impossible to do so.

Thank You, Captain Obviate (1)

sanman2 (928866) | about 2 years ago | (#41029351)

But this thruster seems to be just a new variant on the ion thruster, albeit in a compact form

Re:I'm in a nitpicking mood. (1)

X0563511 (793323) | about 2 years ago | (#41029625)

If the analogy doesn't fit, you must (shut the hell up)

2 pounds in zero-gravity? (4, Funny)

sylvandb (308927) | about 2 years ago | (#41028359)

How large, in zero-gravity, is a 2 pound satellite?

Re:2 pounds in zero-gravity? (0)

Anonymous Coward | about 2 years ago | (#41028447)

Do you mixup units for a living?

Re:2 pounds in zero-gravity? (0)

Anonymous Coward | about 2 years ago | (#41029771)

Do you mix up nouns and verbs for a living?

Re:2 pounds in zero-gravity? (0)

Anonymous Coward | about 2 years ago | (#41030783)

You take yourself too seriously for a living.

Re:2 pounds in zero-gravity? (0)

Anonymous Coward | about 2 years ago | (#41028459)

When I tried to calculate this my calculator called me an invalid.

Re:2 pounds in zero-gravity? (0)

Anonymous Coward | about 2 years ago | (#41028507)

It has a mass of 2 pounds in zero gravity.

Re:2 pounds in zero-gravity? (2)

Roachie (2180772) | about 2 years ago | (#41028775)

$7.23

Re:2 pounds in zero-gravity? (1)

sylvandb (308927) | about 2 years ago | (#41030579)

Thank you. :)

Re:2 pounds in zero-gravity? (1)

roman_mir (125474) | about 2 years ago | (#41028941)

I think it is as large as a comparable satellite in normal gravity.

here's a hint for you... (0)

Anonymous Coward | about 2 years ago | (#41029665)

I think it is as large as a comparable satellite in normal gravity.

if you had a working knowledge of physics, you would know that the pound is actually a unit of force - not of mass. without force - or gravity - 2 pounds doesn't make sense as a measurement.

Re:here's a hint for you... (2)

roman_mir (125474) | about 2 years ago | (#41029753)

if you had a sense of humour, you'd be familiar with the sound a 2 pound satellite makes over your head (even in a low earth orbit)

Re:here's a hint for you... (0)

Anonymous Coward | about 2 years ago | (#41030303)

don't go trying to write off your lack of intellect as an attempt at humor, you won't fool anyone with that act.

Re:here's a hint for you... (1)

udachny (2454394) | about 2 years ago | (#41034417)

you know what's funny, it's how stupid you are while thinking that you have said something intelligent or insightful.

There is pound-mass and there is pound-force, but that is irrelevant even, because the joke had nothing to do with it, so you are also very dim.

Re:here's a hint for you... (0)

Anonymous Coward | about 2 years ago | (#41061713)

try to backtrack all you want, you're still wrong. just because your sock puppets are laughing doesn't mean you're funny.

Re:here's a hint for you... (1)

davester666 (731373) | about 2 years ago | (#41033791)

It depends Is 2 pounds the satellites mass or its weight?

Re:here's a hint for you... (0)

Anonymous Coward | about 2 years ago | (#41029887)

If you had any practical experience working with physics, particularly any place that uses American equipment or older equipment form places that used to use customary units, you will find that there is both a force unit called a pound and a mass unit called a pound. Just as many places that use metric units will from time to time end up with a kilogram force unit instead of Newtons in some situations. The identically named force and mass units are related by the defined standard gravity, a roughly middle of the range value for acceleration experienced by a frame attached to the surface of the Earth.

While the SI system is great, in the real world of science work, you all too often find yourself stuck with odd ball units. MKS vs CGS is annoying enough, kg-force and lbm are more annoying... and just be thankful you don't have to use a poundal.

Re:here's a hint for you... (0)

Anonymous Coward | about 2 years ago | (#41032691)

Or a slug. ( no kidding... a "slug" is the unit for mass in the English system, however no one ever seems to use it. Can you imagine asking your butcher for a half decislug of beef? )

If we butchered physics in the MKS world the way we butcher physics in America, they would order their beef by the kilonewton.

No wonder a lot of American students find physics so daunting. It takes a long time before one finally understands that what the teachers said and what they really mean are not the same thing at all. Not to bag on teachers - its just the misuse of units of force and mass is so ingrained in American usage that by this time its hard to correct.

In practical use, its accepted because gravity is nearly constant everywhere on this planet, however in the physical sciences, misunderstandings of what is force and what is mass has severe consequences.

Re:here's a hint for you... (0)

Anonymous Coward | about 2 years ago | (#41033953)

In the end, people use whatever units are most convenient, scientist and engineers not excluded. Even in the "metric" world, you end up with force units like the newton, dyne, and stene for the MKS, CGS and MTS systems respectively. Then there is the oddball hyl and pond combo, that is still metric based, but not one of those more convenient systems. The use of the "pound" for both mass and force goes far enough back in history, it is not surprising we have both a pound-mass and a pound-force, along with the slug to differentiate it. Alternatively, if you want to assume the pound is a unit of mass and derive a unit of force from it, you end up with the poundal. Kind of goes something like lbf:slug::poundal:lbm. And this leaves out all the fun of other mass units still used in science and technical work: eV/c^2, the dalton, and so on.

I've never had much trouble teaching the difference between force and mass units to American students. If anything, the fact they use pounds in everyday life, and then learn new units like newtons for a physics class helps them start with a blank slate. They keep the units pretty straight, and even the lower students can immediately point out there should be a force of mg pointing downwards when on the Earth's surface. The only odd failure is to connect that downward force with the word weight. You can ask for what the downward force is, get an expression/number, then ask for what the weight is, and get a blank look. Sometimes you can even ask for what the difference between mass and weight is right after that and get a reasonable answer.

Re:here's a hint for you... (0)

Anonymous Coward | about 2 years ago | (#41047325)

Re:2 pounds in zero-gravity? (0)

Anonymous Coward | about 2 years ago | (#41028967)

9.975 Qubic-Liters.

Re:2 pounds in zero-gravity? (1)

TubeSteak (669689) | about 2 years ago | (#41028991)

I'd say that it depends on if the satellite is made out of 2 pounds of feathers or 2 pounds of lead.

Re:2 pounds in zero-gravity? (1)

camperdave (969942) | about 2 years ago | (#41030015)

I don't know about lead, but 2 pounds of feathers is much heavier than 2 pounds of gold, even though two ounces of feathers is lighter than two ounces of gold... Stupid non-SI system.

Weight vs.s. mass (1, Informative)

seifried (12921) | about 2 years ago | (#41028449)

Something that weighs 2 pounds in orbit would have to have a huge amount of mass. I'm pretty sure they meant 1 kilogram which is a unit of mass. Science writing is really going downhill it seems.

Re:Weight vs.s. mass (1)

Daniel Dvorkin (106857) | about 2 years ago | (#41028483)

So do you complain when people give their weight in kilograms instead of newtons?

Re:Weight vs.s. mass (2)

seifried (12921) | about 2 years ago | (#41028577)

Depends on the application. Day to day when I'm buying lunch meat not really, but if it's a technical issue or article then yes, it would be a problem. Technical and scientific articles have a much greater need for correctness. Getting these things wrong can lead to significant and expensive problems.

Re:Weight vs.s. mass (3, Informative)

Urza9814 (883915) | about 2 years ago | (#41028533)

http://en.wikipedia.org/wiki/United_States_customary_units#Units_of_mass [wikipedia.org]

The pound avoirdupois, which forms the basis of the U.S. customary system of mass, is defined as exactly 453.59237 grams by agreement between the U.S., the U.K. and other English-speaking countries in 1959. Other units of mass are defined in terms of it.

The avoirdupois pound is legally defined as a measure of mass[15], but the name pound is also applied to measures of force. For instance, in many contexts, the pound avoirdupois is used as a unit of mass, but in some contexts, the term "pound" is used to refer to "pound-force". The slug is another unit of mass derived from pound-force.

Re:Weight vs.s. mass (1)

sjames (1099) | about 2 years ago | (#41029051)

A satelliote with a MASS of 2 pounds is fairly small though.

Pound can refer to the pound avoirdupois, a unit of mass OR to a unit of force. So which one do you figure is more applicable in free fall?

Re:Weight vs.s. mass (0)

camperdave (969942) | about 2 years ago | (#41030323)

A satelliote with a MASS of 2 pounds is fairly small though.

That all depends on what the satellite is made of. An aerogel satellite would be 0.907 cubic metres. If it's made out of lead... not so much.

Re:Weight vs.s. mass (1)

RockClimbingFool (692426) | about 2 years ago | (#41029161)

From the summary (and the article):

But in zero-gravity space, this tiny force would be enough to propel a two-pound satellite.

Its doesn't say "weigh" two pounds, its says a two-pound satellite. In that context, it pretty easy to see that the implication is its a 2 lbm satellite. Its slightly ambiguous, but not wrong. I don't know why its hyphenated. Any by some magical coincidence, it would happen to weigh 2 lbf pretty much anywhere on the surface of the Earth.

Also, this isn't from the text of peer reviewed, journal quality technical paper. It's an article trying to related cutting edge research to anyone who cares to read about it. Properly relaying the concepts is the important part.

Re:Weight vs.s. mass (1)

Deadstick (535032) | about 2 years ago | (#41029189)

The word "pound" is used for both weight and mass. One pound-force (lbf) is the weight of an object whose mass is one pound-mass (lbm) under standard gravity. In popular usage, they're both just called pounds.

The same situation exists in the SI (metric) system: one kilogram-force (kgf) is the weight of an object whose mass is one kilogram (kg) under standard gravity.

Is it confusing? Yes. Does it excuse public ignorance of science? Yes. Is it going away? Not bloody likely. Live with it.

Re:Weight vs.s. mass (1)

trout007 (975317) | about 2 years ago | (#41030403)

I am a mechanical engineer and this is how I keep it straight in my head.
Just remember F=m a
SI is easy.
N = kg*m/s^2
English is trickier you need a constant
1 lbf = 1lbm * 32.2 ft/s^2
so the constant gc is 32.2 lbm*ft/lbf*s^2
F=m a / gc
The slug is used to get rid of the constant
1lbf = 1 slug * 1 ft/s^2

Hooray for meaningless "facts"! (1)

wonkey_monkey (2592601) | about 2 years ago | (#41028787)

But in zero-gravity space, this tiny force would be enough to propel a two-pound satellite.

Or a one-pound satellite. Or a ten-pound satellite. Or a hundred-kilogram satellite. Or a planet.

Re:Hooray for meaningless "facts"! (3, Informative)

RockClimbingFool (692426) | about 2 years ago | (#41029357)

All satellites need station keeping thrusters to maintain a stable orbit. Because the Earth is shaped like an oblate spheroid [wikipedia.org] , orbits are not stable. There is a particular amount of thrust needed per pound of satellite to maintain the orbit. Their calculations probably assumed some typical orbit and the station keeping thrust needed.

What is the specific impulse? (2, Insightful)

tp1024 (2409684) | about 2 years ago | (#41029221)

There are three factors that are important for any propulsion system:
1) Thrust - check
2) Wheight - probably very low, hopefully not too important
3) Specific impulse - how much fuel do you need to get that thrust? The higher the velocity of the exhaust, the less fuel you need for a given thrust. And that is exactly what is missing from all sources. Who knows what they had to compromise with in order to scale the whole thing down?

Mod parent up (2)

fiannaFailMan (702447) | about 2 years ago | (#41029355)

Thank you for being the first person to post something useful and constructive on the thread. Shame I had to scroll through the usual pedantic know-it-all minutiae about units and mass and weight to get to it.

I swear, /. is going severely downhill in the quality of discussion these days.

Re:Mod parent up (1)

tp1024 (2409684) | about 2 years ago | (#41030153)

It went downhill far enough that somebody moded the "mod parent up" post up, but neglected to mod the parent up ...

Anyway ... unfortunately my questions still wants an answer.

Re:What is the specific impulse? (1)

Anonymous Coward | about 2 years ago | (#41029485)

Also: Power requirements (covered vaguely in TFA), efficiency, and thermal requirements, since this is an electric ion thruster. There are a lot of SEP designs, although I don't recall any others quite this small.

What I also didn't see in the article is whether they have or need some sort of MEMs equivalent of valves... will the ionic fluid boil off in vacuum without the voltage applied? At what rate? Does the ionic fluid degrade with storage, and will it clog the capillaries like an inkjet printer? How big are the pores, and are they sensitive to cosmic radiation like silicon?

-R C

Re:What is the specific impulse? (1)

Zarquon (1778) | about 2 years ago | (#41029541)

Also: Power requirements (covered vaguely in TFA), efficiency, and thermal requirements, since this is an electric ion thruster. There are a lot of SEP designs, although I don't recall any others quite this small.

What I also didn't see in the article is whether they have or need some sort of MEMs equivalent of valves... will the ionic fluid boil off in vacuum without the voltage applied? At what rate? Does the ionic fluid degrade with storage, and will it clog the capillaries like an inkjet printer? How big are the pores, and are they sensitive to cosmic radiation like silicon?

-R C

Forgot to log in. Ah well.

-R C

Re:What is the specific impulse? (1)

Anonymous Coward | about 2 years ago | (#41030947)

This was presented at the Small Satellite conference in Logan, UT, and I was in attendance. The Isp (specific impulse) was on the order of 2000-3000 seconds. It's basically a new way of doing a standard ion engine, only with less dry mass and less power; it's a really good thing for applications where that low a thrust is tolerable. It also has issues with how much propellant can be stored, as of right now, putting a definite limit on usable lifetime (though this wasn't specified). Another drawback is the need for extremely precise machining; they have to make a grid of hundreds of micron-large precisely contoured bumps on a plate, and THEN they have to make a plate with hundreds of precise holes cut in it to the exact same scale, and THEN they have to align it perfectly... it's going to be a nightmare making that small a size practical let alone the scaleup the authors mentioned. Despite that, it's still an exceptionally promising technology. There were others at the same conference; I talked with one company that has a solid propellant that can be turned on, TURNED OFF, and throttled only with electricity and otherwise cannot be lit on fire, making it extremely safe, while not giving up any performance from current state of art... so that's got its own niches. As do the people who showed up with a prototype of a 3-D printed hybrid rocket that they're planning to fly in I believe 2013, which is its own little revolution.

The bottom line is that there's a LOT of exciting work going on in spacecraft propulsion- it's just that there's nothing on the horizon that can hit the holy grail of high-thrust and high-Isp at the same time, so there's not enough publicity of it.

(Posting as AC to protect the reputations of the guilty- I see you, attendees of the SpaceX party on the balcony!)

Re:What is the specific impulse? (1)

tp1024 (2409684) | about 2 years ago | (#41034239)

Thanks.

Well, depending on how long the actual lifetime will be and what the propellant storage looks like, this seems like it's just what the doctor ordered for cube sats. But beyond that, they will need a way to recharge those capillaries and they'll need to mass-produce those things to get the costs down - which is kind of hard given the limited numbers of cube sats currently being launched. (Afaik, there are still fewer cube sats being launched each year than regular ones ...)

Re:What is the specific impulse? (0)

Anonymous Coward | about 2 years ago | (#41032457)

There are three factors that are important for any propulsion system:
1) Thrust - check
2) Wheight - probably very low, hopefully not too important
3) Specific impulse - how much fuel do you need to get that thrust? The higher the velocity of the exhaust, the less fuel you need for a given thrust. And that is exactly what is missing from all sources. Who knows what they had to compromise with in order to scale the whole thing down?

All of this is irrelevant, did you look at the picture of the device in TFA? It's rectangular. Everyone knows that Apple designed the rectangle after centuries of careful research and they will certainly not allow their patented monopoly on this shape to go unchallenged in court!

Slashdotters are not rocket scientists... (2, Informative)

Anonymous Coward | about 2 years ago | (#41029689)

In the torque-free environment of space, any amount of force will overcome inertia in an appreciable way. Gravity gradients, solar pressure, lunar and solar gravitational influences, atmospheric drag.

All they're saying is that 50 microNewtons is about the right size for small satellites, regardless of how many pounds-force that satellite might be at sea level. More than likely this is intended for attitude control maneuvers rather than orbit changes, but even in the latter case, small thrusts for long periods in space can be used.

And yes, I am an aerospace engineer.

Re:Slashdotters are not rocket scientists... (0)

Anonymous Coward | about 2 years ago | (#41030987)

50 microNewtons is actually kind of shrimpy for effective attitude control; that's the regime of the forces you listed above, and will only really compensate for them plus atmospheric drag above 500 km, so this isn't useful for LEO. You really want at least 1 millinewton for LEO applications, though you can get by in half that in a pinch.

TAANSTAFL (1)

DerekLyons (302214) | about 2 years ago | (#41030467)

"The tiny, flat design could obviate the need for bulky propellant tanks."

And instead, replaces them with bulky electrical power sources. There's no free lunch - whether the thrust comes from electricity or from reacting chemicals, it's got to come from somewhere.

Though, if you actually read TFA, you find there actually is a "fuel tank" built into the thruster... But, as the tank is very small, means a very limited lifetime.

Re:TAANSTAFL (0)

Anonymous Coward | about 2 years ago | (#41031335)

Don't most satellites already have electrical power sources? The key question here is if the additional size for the electrical power source is more than the savings in size for the fuel tank. If not, this would seem to be a good tradeoff. If they can use the existing power source without any capacity increase (because thrust is only needed when the satellite is not performing its primary purpose), then this might be a very good tradeoff.

Re:TAANSTAFL (1)

GodfatherofSoul (174979) | about 2 years ago | (#41032093)

These satellites don't have to carry the sun.

Re:TAANSTAFL (1)

DerekLyons (302214) | about 2 years ago | (#41032903)

Solar panels are still heavy and bulky. Duh.

Re:TAANSTAFL (0)

Anonymous Coward | about 2 years ago | (#41038381)

They are, yes, compared to magic unicorn power. But Dawn is cruising the asteroid belt right now on solar-powered ion propulsion, and has accumulated more delta-v than any other spacecraft made, proving that there is a greatly-reduced-price lunch.

Re:TAANSTAFL (1)

evilviper (135110) | about 2 years ago | (#41033389)

And instead, replaces them with bulky electrical power sources. There's no free lunch

Nuclear power sources can be extremely high power, for relatively little size and weight. Hence, nuclear submarines.

NASA is upgrading RTG to more efficient Stirling radioisotope generators (SRG), and full-fledged nuclear reactors are sometimes used, with an even better power to weight ratio.

Re:TAANSTAFL (1)

DerekLyons (302214) | about 2 years ago | (#41033803)

And instead, replaces them with bulky electrical power sources. There's no free lunch

Nuclear power sources can be extremely high power, for relatively little size and weight.

Maybe you should actually look up the weight of some actual spaceborne nuclear power sources, they're quite heavy for any significant power. (Curiosity's weigh over 100lb each, with an output on only 150 watts.) Not to mention that none exist down in the size range of the satellites this thruster system is designed for.
 

NASA is upgrading RTG to more efficient Stirling radioisotope generators (SRG), and full-fledged nuclear reactors are sometimes used, with an even better power to weight ratio.

NASA has some pie-in-the-sky research to build SRG's, true. But they aren't flying anytime soon.
 
Not to mention that regardless of efficiency, they're very expensive - and, again, not going to be used on the small cheap satellites this thruster array is designed for.

Re:TAANSTAFL (0)

Anonymous Coward | about 2 years ago | (#41038225)

And instead, replaces them with bulky electrical power sources. There's no free lunch

Nuclear power sources can be extremely high power, for relatively little size and weight.

Maybe you should actually look up the weight of some actual spaceborne nuclear power sources, they're quite heavy for any significant power. (Curiosity's weigh over 100lb each, with an output on only 150 watts.) Not to mention that none exist down in the size range of the satellites this thruster system is designed for.

... Huh? GP points out that nuclear power sources, in general, can be rather mass efficient, and cites a fission reactor as an example, and your "rebuttal" only addresses decay-heat generators? Both US and USSR programs have flown fission reactors decades ago, so you can't pretend RTGs are the only thing going.

GP then points out that NASA is making progress toward the maximum, and you basically handwave it by saying that the progress isn't finished. So we can't research two complementary technologies, because neither one is "a free lunch" until the other is developed?

Re:TAANSTAFL (1)

evilviper (135110) | about 2 years ago | (#41042723)

Maybe you should actually look up the weight of some actual spaceborne nuclear power sources

Okay!

SNAP-10A: Output 30 kW; weight 650 lbs.

NASA has some pie-in-the-sky research to build SRG's

That's completely inaccurate.

they're very expensive - and, again, not going to be used on the small cheap satellites this thruster array is designed for.

Nuclear power sources are just about as cheap as solar panels. Much cheaper than hauling up lots of fuel.

Re:TAANSTAFL (1)

DerekLyons (302214) | about 2 years ago | (#41043217)

Maybe you should actually look up the weight of some actual spaceborne nuclear power sources

Okay!

SNAP-10A: Output 30 kW; weight 650 lbs.

That's 30kw thermal - only about 500w electrical. Learn to read you moron.
 

NASA has some pie-in-the-sky research to build SRG's

That's completely inaccurate.

OK, you have me there, it's been a while since I looked into them.
 

Nuclear power sources are just about as cheap as solar panels. Much cheaper than hauling up lots of fuel.

Not wrong on both counts... rather utterly disconnected from reality on both counts.

You bet (0)

Anonymous Coward | about 2 years ago | (#41030599)

I microthrust into your wifes anus while you sleep.

I want to know one thing: (1)

subreality (157447) | about 2 years ago | (#41033417)

Specific Impulse. Discussing a new thruster without giving Isp is about as useful as announcing a "revolutionary networking technology" without giving a bits per second figure: interesting hack, but is it vaguely practical?

Re:I want to know one thing: (0)

Anonymous Coward | about 2 years ago | (#41034081)

As I mentioned upthread, since I was there when this paper was presented a few days ago: They cited in the presentation 2000-2500 seconds.

Re:I want to know one thing: (1)

subreality (157447) | about 2 years ago | (#41034241)

Sweet! That's completely respectable for such a tiny and lightweight design. It's good enough to make maneuvering possible in tiny satellites, and perhaps make stationkeeping more efficient in moderate sized ones assuming it's reliable and has a good service life.

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