An engine that can conjure thrust from thin air? We speak to the designer Will satellites be capable of generating their own thrust with propellant created out of thin air one day? Scientists at the George Washington University (GWU) and Princeton Plasma Physics Laboratory reckon so. They have been awarded more than $1 million from the US government boffinry nerve center DARPA to build prototype air …
There are different human definitions for the start of space. 50 miles and 100km are both popular. Earth's atmosphere does not suddenly vanish at either altitude. It just gets thinner and thinner until it approaches the pressure of the sun's atmosphere. Likewise the sun's atmosphere doesn't suddenly disappear. It gets thinner and thinner until it approaches the pressure of the galaxy's atmosphere.
"There are different human definitions for the start of space. 50 miles and 100km are both popular."
The internationally recognized beginning of space is 100km. Virgin Galactic uses 50 miles since they have a problem going higher with Space Ship 2 and advertising rides "almost" to space isn't as enticing.
Yeah, I was confused by the original article and read this hoping for some clarification, but the interviewee still seems to mix and match "fuel" and "propellant". It still sounds as though the energy input is electricity which is used to create a plasma to generate thrust. So the electricity is the fuel and the propellant is air turned to plasma. I'd like to be contradicted if anyone can do it at no more than high school physics level so I can try to understand what is really revolutionary here :-)
These are just electric-powered ramjets.
The game has been played at low airspeeds, with a model flown by MIT a few years back, the main difference being that the ionisation and acceleration took place outside the airframe, above the wing. Also, the plane used a DC electrode to ionise the air, not an electron beam.
The Wiki article on ABEP (sic) notes the use of a radio-frequency (RF) magnet to ionise the plasma, just as I did professionally for some years when engineering waferfab stuff (Not that we launched the wafers like UFOs, sadly they lived in tightly-confined chambers).
As any designer of high-altitude ramjets will tell you, you have to get up to hypersonic speeds to achieve sufficient airflow. If you rely on superhigh exhaust velocities, your thermodynamics become inefficient, so you try to shift as much air as possible, as slowly as you can get away with. The trouble is, from a flow-rate perspective there is naff all mass in the air at these near-space altitudes. So you are looking at slightly higher air densities, and hence lower altitudes, in order to maintain efficient thrust.
Also, you have to get up to around Mach 20 before you gain enough centrifugal lift to think of your craft as orbiting rather than flying.
So you end up with a hypersonic ramjet and all the problems of airframe heating that brings. This is the real killer: to get in enough air to generate the required thrust, you have to punch through so much of it that your airframe melts in a few minutes. Your only hope is hypersonic aerodynamics to reduce the thrust required, and new heat-resistant materials and techniques.
Next, we get onto the rate of energy delivery, aka engine power. It is phenomenal. Think of the rocket thrust needed to sustain Mach 20 flight at such altitudes. All that has to come from the electron gun, and any other field-enhancing gadgets you can come up with. You should see the power supplies we built just to sustain a pretty light above a 6" wafer for 30 secs or so. Battery drain would be staggering, recovering ambient energy a drop in the ocean. Increasing the exhaust velocity to allow reduced mass flow would drain the batteries even faster. This is not a satellite but a short-range cruise missile.
The history of electromagnetics has been full of horse shit and snake oil since the days of Nikolai Tesla, and the tradition shows no sign of slowing down.
Well, his statement "...because you are tens times closer to the earth compared to geostationary satellites in low Earth orbit." is, to quote Wolfgang Pauli, "This isn't right. This isn't even wrong." . So it makes one wonder what else is ill-conceived. I've had plenty of DARPA funding in my career. The quality of the projects funded is strongly dependent on the DARPA grant officer, who have a huge amount of discretion over what they fund, and they tend to fund a lot of garbage in the hopes that something useful will be learned. It's not a bad strategy in terms of yielding new solutions that would never be uncovered via peer reviewed grants, it's just inefficient. So we'll see...
he's just an indian who hasn't gotten all the space lingo down yet. yes it seems unprofessional but the poster you are replying to has literally no idea wtf he's talking about.
this isn't a supersonic ramjet, this is a micro-jet. there is no ram physics here. no high speed required. it is using the low density at that altitude and electricity to accelerate the gas in the duct. idk how badly informed you must be to confuse this micro-propulsion with a supersonic combusting ramjet. one wonders what else in his comment history is poorly thought out.
Well, his statement "...because you are tens times closer to the earth compared to geostationary satellites in low Earth orbit." is, to quote Wolfgang Pauli, "This isn't right. This isn't even wrong." So it makes one wonder what else is ill-conceived.
My reaction exactly. I stopped reading at that point.
And kudos for the Pauli quote.
I'm not too keen on referring to air as "fuel" in this context either. To me, that implies air is the source of the energy used to produce thrust. It isn't, it's just reaction mass (or working mass).
We need to see evidence in the thermodynamics here.
All the energy sources involved need to be listed and accounted for. Otherwise, it just doesn't work.
"For a successful technology, reality must take precedence over public relations, for Nature cannot be fooled." - Richard Feynman.
I agree with your conclusion (this isn’t practical), but not your reasoning. “If you rely on superhigh exhaust velocities, your thermodynamics become inefficient”. Yes, but you’re making the assumption that thermodynamic inefficiency is unacceptable. However, today spacecraft use ion engines routinely with exhaust velocities 30+km/s upwards, and the thermodynamics *are* inefficient. The atmosphere is sufficiently thin that the thrust required is low enough (milliNewtons), that the spacecraft tradeoff is in favour of over-provisioning power to save stored reaction-mass, up to a point.
The reason that *I* don’t think this will work is: one has to allocate a large fraction of the frontal area to the intake ram. Because even at 30kps exhaust velocity, drag is a fixed large fraction of thrust. The solar panels have a massive area, so they have to be aerodynamic, ie edge-on to direction of travel. But you can’t just fix the solar panels like this. The spacecraft is orbiting and constantly turning relative to the Sun. It *must* point them separately towards the Sun, otherwise for large fractions of the orbit you have no power, and no thrust.
Now, there’s a bodge, which the designers of this might be aware of but not understood properly. If you choose a sun-synchronous (polar) orbit, you can have the panels fixed and edge-on to direction of travel. But only a small range of orbits can be Sun-synchronous. That orbit relies on a coincidence due to the earths equatorial bulge, which needs an orbital altitude 250km+, otherwise it’s unstable. As low as they want it to be (within the upper atmosphere) the simple orbit equation naively seems to allow it, but you’d need to use an unthinkable amount of delta-v to keep the inclination stable at 96degrees over the year. I think what happened is that they’ve *seen* an existing operating example, but not understood it. GOCE satellite indeed does have low altitude, uses electric-propulsion, and has fixed aerodynamic solar panels. And that does work….because GOCE is in a Sun-synchronous orbit! But GOCE orbit altitude intrinsically isn’t low enough to gather sufficient propellant to maintain orbit, so it has onboard propellant. There’s just no overlap between the constraints “propellant collection rate”, “solar panel power / area / pointing” and “sun-synchronous orbit”.
I think a (military) spacecraft operating on Nuclear Thermal Battery, plus aero-ram, plus ion engine, could work though….
I worked in the space industry for over twenty years, designed and led several payload equipments, and later overall Program Management responsible on two spacecraft.
Apparently, you can’t read. That was exactly what I said: there’s a hidden assumption on the solar panel config that needs it to be in sun-synchronous, but it can’t be.
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“ 70 to 90 kilometers”. At 80km, pressure is about 0.01mbar. No, I don’t think “airbreathing engine” is the correct perspective. It’s an ion thruster, backed by an air ram as a propellant source (instead of xenon tank, as per norm), and powered by solar panels.
“You have no idea what plasma systems eat or why”. Ad hominem, and not useful. It’s clear that we come from different industries, you are from the aero side; whereas I come from the space angle. Almost all the latest class of geo satellites are now electric thruster. The mass saving from reducing the chemical propellant tank is sufficient to compensate for the several months of orbit-raising via ion thruster. But if I take say a Eurostar E3000 EOR variant, it has 5kW thrusters fitted. The total bus power budget is up to 25kW, with 15-20kW payload power now routine. So, no, the electrical power draw of the thruster is not the be-all-and-end-all, it’s just one consideration in a large tradeoff matrix.
My apologies for that remark. I was in a bad mood for other reasons at that moment. Once I cooled down I redacted it.
But as a spacer, you are wrong about what an airbreathing engine is: it draws in ambient, and applies some power source to accelerate it backwards, that is all. "Backed by an air ram" is known in the trade as a ramjet. This is why NASA's aim is to demonstrate an atmospheric thrust/drag ratio and not some space-related thrust parameter. Call it an airbreathing ion thruster if you will.
> high altitude ramjets
At about 70 to 90 kilometers (citation from the article) there is no ramjet effect. 'cause there is not enough air.
As I understood that engine is not designed to work at lower altitudes or even to get the satellite there, it is designed to keep the satellite up there by using the few molecules around. And it does not need to do a constant push, a few hours per day with sun on the solar panels might be enough. This is where the experimental reality must follow, cause if it works as planned it will be a huge step forward.
All you say applies to altitudes far below where a normal ramjet effect actually works, which seem to max out at 25 km to 30 km. Unless you choose a parabolic flight where you get above that altitude where a ramjet works. You can add extra 10 km altitude as "future buffer" if you like, still a bit distance to where those satellites are planned to fly.
“A few hours per day with sun on the solar panels might be enough”
I’m afraid the orbital mechanics for this don’t work. Firstly, the orbital period is about 90 minutes, that’s the length of your light cycle period. But if you only thrust on the half of the orbit when you are in the sun, you don’t maintain orbit altitude. Instead, you push the height of the orbit up, on the opposite side of the Earth where you are thrusting. Very quickly you get an elliptical orbit. And the bit of the orbit opposite the dark side just decreases in height without being held up at all, and hits the ground quite quickly.
Well, I suspect some of the things have to stay hidden for now, like the plans to the device and actual photos or renderings.
It is not even clear whether it accelerates particles to let them ram something to move forward, or whether accelerating the particles cause a push on "thing" which supplies the acceleration into the particles. It sounds a bit like the latter to me, but how should we know?
Still the article was an interesting read, made me curious. Like the other article a short while ago where Ion thrusters used solid metal as propulsion mass source instead of xeon gas, easier to transport into space - but I've lost the link to that interesting artice.
MAD I say, MagnetoAerodynamic Drive, the Red October of Low-Orbit Space! Conjure that stealth caterpillar stuff close to your own Earth's thin air please -- Here on Mars, we value our hot-tub privacy way too much for such (presumably innocent) "very high resolution imaging" enablement! </extra-terrestrial-rant>
(cool interview though!)
What powers the electric gun? Where does that *fuel* come from?
What's the expected thrust output? Early in the article it mentions ion drives, which this isn't/can't be, as those have notoriously low thrust (but can work in actual space when you burn them over long periods of time). Is this intended as an intermediary step that takes over from the launch rockets and then acts as a sort of "shuttle" to get them through the "Karman line plus/minus some dozen km"? I confess, I don't know what the "lowest useful orbit" is for satellites. Real ones, not Jebediah when I'm jubilatin' that I barely made it in KSP.
A lot more question could/should have been asked by the interviewer.
The *designer* hasn’t necessarily got it wrong, it’s just not what it is presented to be. He’s just a PhD student, he’s got a technical idea that he’s working through, butdoesn’t have the breadth of industry knowledge or systems experience, nor should we expect them to.
The *funding agency* is DARPA. This is a military program in disguise. They know what the true use case is, and why even if the Conference Poster is rubbish, it might have a useful outcome to them. But they certainly aren’t explaining that in public, and almost certainly neither the PhD student nor his department professor know.
"The *funding agency* is DARPA. This is a military program in disguise. "
There's not even a disguise. DARPA is the Defense Advanced Research Projects Agency and the sorts of things they fund are those that have direct military usage. Occasionally, they will fund some science if it might lead to engineering they can use. A low altitude satellite they can move around would be very useful if it was small, low mass and had lots of Delta V. Low cost and quick deployment from a very basic launch site would also be handy.
Ah, there's more detail in the previous article that we link to. The electric gun could be solar powered or from a nuclear device. Or any other way you want to make electricity.
And I've added some more links at the start of this latest piece to more info about the tech.
C.
There are NACA reports on this sort of stuff.
Essentially it's offering "orbit maintenance" for a very low orbiting satellite by scooping some air, ionising it and squirting it out the back. Making it a funnel to give ram compression is not necessary. The acceleration is done electrically.
The power source is likely to be solar cells.
Boosting velocity at this high an altitude will also mean the "air" will thin further until the thrust falls off. So basically you're satellite "porpoises" up and down in the atmosphere.
It'll be interesting to see if he can make it work.
>> "...something out of science fiction." **** "A.T.: The concept of ion engines is pretty old. I think during the '60s there was some talk....."
The ion talk was mature when I was a lad in the 1960s. One science fair project was a pin in a straw on a string with a high voltage power supply. The differential ion-push between blunt head and pointy end gave a teeny thrust, and if you pulsed it to match the pendulum swing it "worked". (And as a lad I could see that the power supply mass was millions of times larger than the available thrust, so this was not a fire-free jet-pack.)
Campbell, Asimov, and Chandler are not answering my call. An 'interplanetary ion rocket' was painted-up for a 1959 book: https://www.projectrho.com/public_html/rocket/images/enginelist/ionEngine04.jpg seen at https://www.projectrho.com/public_html/rocket/enginelist.php#ion But before that you would not have to explain "ion drive" to any wide-awake audience, because "tubes" (gas and vacuum) had ions good and bad. (Thyratron works by ions. Vacuum tube stops working when ions clog it.)
Low-orbit ion drive was not (AFAIK) in Science Fiction. Clearly it can't work very well. SciFi likes the Big Rockets, not hummingbird farts.
Taploo may be right that there is a narrow swath of near-space and low-orbit and limited corrections where ionized air boost may save a few grams over N₂H₄. Simply losing the mission-size gas tank for BYO gas propulsion saves kilograms.
As orbiting debris increases - keep in mind a exponential increase threshold exists - lower orbits may become more economical because of their lesser space junk density (because junk falls fast at lower altitudes).
One thing about this project is: given it appetite for electric power it will need big solar panels, but big solar panels will incur more drag, especially at lower altitudes. I expect somebody is thinking of nuclear powered low orbit satellites - but I wouldn't recommend it.
Ion drives don't need that much amps, they need high voltage. Wikipedia says "typically consume 1–7 kW of power", whereas the 100 Watt version exist too. But even with 1 kW and more: Using batteries to store the charge, and then go when needed. Sounds all doable to me. The actual engineering is the interesting part.
Ask Anmol Taploo who invested years. Maybe we will get another interview, but maybe those are details he has to keep a bit quiet about. I am by far not expert enough, but I am close enough to understand the principle, the idea itself.
Or at least it doesn't say what a lot of people will read the headline to say. This is about reaction mass, not propellant, which people generally understand to be fuel. An energy source. This is probably going to capture the extremely thin air and accelerate it out the back using electric power from solar cells. So why not be explicit and say reaction mass? Well then it's not as attractive because there's no mystery.
If the satellite were just using a source of electricity (solar etc) and accelerating electrons out the back for thrust, the craft would have an increasingly net positive charge which is going to make it harder and harder to shove negative electrons out the exhaust.
The trick is to shove the same number of +ve and -ve ions out the exhaust (the more massive the better.)
My guess is that the satellite is intended to scoop up the very thin air by its rapid passage through that air (by virtue of its orbital velocity - very considerable at 50km to 90km), then ionizing the captured gases into a plasma, separating the -ve and +ve ions with static magnetic field(s)*, then accelerating☆ these two ion streams out the exhaust. Once accelerated the two ion streams could be recombined, or not, before leaving the exhaust as its only the total momentum (mass×velocity) that matters.
The $64 question is whether the whole propulsion system can ever produce more thrust than the drag the craft experiences. If you could produce oodles more thrust then you could have powered flight outside the constraints of purely orbital motion. Even hover or linger over a particular geographical location. :)
The whole idea isn't all that different from the various interstellar ram scoop drives of my childhood scifi reading.
* charged particles moving in a static magnetic field experience a force perpendicular to both the field and direction of motion (the force experienced by +ve ions is opposite to that of -ve ions) note no work is done by the magnetic field.
☆ I think a pair of any type of presumably linear particle accelerators would suffice.
"I heard about air-breathing plasma engines, it sounds really cool, interesting, and something that could be potentially novel. So [my PhD advisor] said: Why don't you do this as a project? So for the last five to six years, this has been my PhD topic"
Choose your own research topic and take six years? Here in the UK PhDs are three years unless you over run, which is just about time to bone up on the subject, make a small contribution and write up. Furthermore, pretty much every PhD research topic is pre-defined for you -- usually your supervisor's pet topic or the one they landed a grant for. So essentially a PhD bursary is a cut price Research Assistant post, as the monthly bursary is typically half the pay of an RA. I sometimes wish I'd gone to the US.
I don't see this working at all.
Either you need some sort of ram system to get a lot of volume through your thruster (and thus take the drag penalty this implies) or you need a massive intake to gather massive amounts of very thin atmosphere and use massive amounts of power to push against molecules already moving at a relative speed of some mach 20. In either case you are going to need very big solar panels that are going to further increase your drag (if you can even keep them intact at those kinds of drag scenarios). Not to mention the problems of keeping anything cool while screaming through the atmosphere at those kinds of speeds.
Most of the very obtuse methodolities for creating "special" new discoveries of assemblage are not operational on the planet. I am a member of the original satellite company who pioneered the origins of stable applications of the tech. We used liquid fuel originally and still do, but much better capabilities these days for the seven we have in space at this time. Our company does not need new fuel logic as we just fly up and refuel when our office reports that we need to refuel soon. So count us out for a customer, we are doing really great. Our aircraft at Hughes Aircraft that do the job for us have great capabilities as we make all of our own tech. Thanks for your understanding. Dr.Hughes
"refuel our satellites" whaaaat? Yes, they did refuel some, but those missions were FAR from cheap. But with your experience: How is it done, do the satellites need to be prepared/constructed be able to refuel? How many were/are in geostationary orbit? And my next level of curiosity asks: How many of those refuel missions were for military, and how many for civilian?
Wait, why is there no article from you on The Reg... If you are among those who actually executed those missions it would be an interesting read!
Finally the old technology, the "Ram-scoop" has found a niche! (Ram-scoop: big nuclear reactor creates a massive magnetic field to funnel the Inter-Stellar Medium into it as fuel to thrust out the back).
How does he neutalise the positive ions it will emit? (Biggest problem with ion-drives, they must not become negatively charged as a consequence, as this reduces the thrust and, more importantly, will eventually destroy the elwctronics on board.) Is the exo-atmosphwre used for this purpose? i.e. the neutralisation is indirect, due to that exo-atmosphere? If so, Very smart: no neutralisation grids in the way of the exhause-flow (which reduce the speed of the emitted ions, thus loses thrust.)
Look at the pictures of the linked article (and other searchengine-of-your-choice results): All current ion drives in actual operation, AFAIK, do take the electrons back. And the rest of the accelerated, then neutal, atoms makes their way out. But not with neutralization grids, they are not needed with the current drives since the exhaust-slit-ring is already quite narrow.
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