The Ephemerality and Reality of the Jetpack

First time accepted submitter Recaply writes "Here's a look back at the 1960's Bell Aerosystems Rocket Belt. 'Born out of sci-fi cinema, pulp literature and a general lust for launching ourselves into the wild blue yonder, the real-world Rocket Belt began to truly unfold once the military industrial complex opened up its wallet. In the late 1950s, the US Army's Transportation Research Command (TRECOM) was looking at ways to augment the mobility of foot soldiers and enable them to bypass minefields and other obstacles on the battleground by making long-range jumps. It put out a call to various aerospace companies looking for prototypes of a Small Rocket Lift Device (SRLD). Bell Aerospace, which had built the sound-barrier-breaking X-1 aircraft for the Army Air Forces, managed to get the contract and Wendell Moore, a propulsion engineer at Bell became the technical lead.'"

Comments

Almost as if

[Anonymous Coward]

the technological fantasies of the past don't always make sense. But space elevators and asteroid mining totally make sense.

Re:Almost as if

[phantomfive]

Jetpacks make sense if you can get them to work. If you can get one to every person in your army, imagine the mobility you would have. Think of the kinds of flanking maneuvers you could perform. The same would be true for flying cars. Of course, the barriers are cost, controllability, range.....things like that.

Space elevators and asteroid mining can make sense too, but in those cases (assuming the space elevator can actually be built, which it can't with today's materials) it becomes a cost/benefit analysis. Is it cheaper to mine asteroids, or get the same materials here on earth? As soon as it's cheaper to get them from asteroids, we will get them from asteroids. Is it cheaper to get things into orbit via space elevator? We don't know yet, but if it is, then we will build a space elevator.

Re:Almost as if

[Anonymous Coward]

Jetpacks make sense if you can get them to work. If you can get one to every person in your army, imagine the mobility you would have. Think of the kinds of flanking maneuvers you could perform. The same would be true for flying cars. Of course, the barriers are cost, controllability, range.....things like that.

Flanking maneuvers? "Hey everybody, shoot the loud flying things over there!" I don't know what place they would have on a modern battlefield. At best, if there was a miniature, silent version, there could be some use for special forces, but that violates laws of physics, so ... yea, seems pointless.

Re:Almost as if

[phantomfive]

Flanking maneuvers? "Hey everybody, shoot the loud flying things over there!"

A flanking maneuver doesn't need to be a surprise. It just needs to be fast enough to get into position before the defenders can rearrange themselves.

I don't know what place they would have on a modern battlefield.

Whether they have a place on the modern battlefield is equal to the question of whether infantry has a place on the modern battlefield. If they do, then having a mobile infantry is an advantage.

Re:Almost as if

[Anonymous Coward]

You know Batman isn't real, right? If the ability to fly is important, as opposed to traveling over the ground, you're close enough to get shot while you're flying. If not, give everyone motorcycles in your imaginary world.

Re:Almost as if

[Anonymous Coward]

Um, you're joking, right? You have to be kidding.

Re:Almost as if

[phrostie]

but no one mentions the Martin http://www.youtube.com/watch?v...

Re:Almost as if

[phantomfive]

If the ability to fly is important, as opposed to traveling over the ground, you're close enough to get shot while you're flying

Don't fly so close to the guns!

Re:Almost as if

[fahrbot-bot]

Jetpacks make sense if you can get them to work.

As would many, many other things, like Warp Drive and the G Spot.

Re:Almost as if

[ColdWetDog]

G-spot? That's crazy talk.

Re:Almost as if

[plover]

I think the biggest problem with jetpacks is the logistics of carrying them when you're not actually jetting about with them. They were simultaneously bulky, fragile, and extremely combustible. Plus, the things weighed 60 kg when fueled, and this would almost double the normal amount of weight the average infantryman is required to carry. Even if they had a specific military purpose, getting them to the soldiers who need them at the exact time they need them is problematic.

Re: Almost as if

[Anonymous Coward]

no, it is "get out of range of those guns"

Re:Almost as if

[AK Marc]

Flanking works great in today's wars because the armor goes at the front and the squishies in the back. If you come at them from the side/back, you get to take out more of their squishies than they get of yours. If you get them directly from both sides in a crossfire, then they must split their forces for a 2-front defense, greatly reducing their defensive effectiveness.

Re:Almost as if

[AK Marc]

For the military, I'd go with jump-jets. The "launch" is taken care of by a catepult. The jet pack needs half the fuel and only turns on at the apex. Parachute as backup for pack failure. You strap in at launch points (in a jump vehicle) and get shot out like meat-artillery. You then "glide" to the earth, maybe with a small gliding device and the pack for more lift.

How about an army of autogyros, droned with the human shooting from it as a flying weapon platform? That sounds like an evolution of the flying infantryman. Or whatever they call it when you have a parachute, and a huge fan on your back, giving you thrust and the chute lift, so you have the ability to climb or go long distances. That's more practical than the jump packs.

Re:Almost as if

[gmhowell]

Whether they have a place on the modern battlefield is equal to the question of whether infantry has a place on the modern battlefield. If they do, then having a mobile infantry is an advantage.

Mobile infantry made me the man I am today.

Re:Almost as if

[Anonymous Coward]

Flanking works great in today's wars because the armor goes at the front and the squishies in the back. If you come at them from the side/back, you get to take out more of their squishies than they get of yours. If you get them directly from both sides in a crossfire, then they must split their forces for a 2-front defense, greatly reducing their defensive effectiveness.

You in the army? Because my understanding is that's completely backwards for even WWII-era thinking, and since then combined arms has been transformed by the use of air power. So unless you're fighting for the Serbian army, this sounds like computer game logic, not military thinking. Or perhaps military thinking for late WWI, early WWII.

Re:Almost as if

[AK Marc]

Nope, flanking is still a good idea. It's just that with air power, you flank from above. Or so says your link, which does agree with me.

this sounds like computer game logic, not military thinking.

Wars are games. Like Risk or Chess, but with real people. Many of the tactics used were thought up in game-like ways.

Re:Almost as if

[pepty]

In today's wars only one side has any armor or an air force to speak of. If not at the beginning then at least by the time the winning side's "squishies" are brought forward.

Re:Almost as if

[pepty]

miniature silent version

Ah.

That would be called a drone.

Re:Almost as if

[Anonymous Coward]

"Flank from above"? Seriously? We call those planes. And they're easier to automate than soldiers on foot, hence UAVs. Dear god, I hope you're not actually in charge of people's lives.

Can't you visualize these flying people you speak of? They won't be moving fast, so they'll be easier to hit than the slowest of planes, and they won't have a stable platform to shoot from like a helicopter. If they have any altitude worth a jetpack, they'll be extra visible. If they are far enough from the front line for that not to matter, who gives a damn whether it's a jetpack or a jeep?

Wars are games. Like Risk or Chess, but with real people. Many of the tactics used were thought up in game-like ways.

Well, you import an army of jetpack people into a modern wargame which could realistically simulate them, and I'll gladly kick your ass.

Re:Almost as if

[LordLimecat]

Alernatively, imagine how many more soldiers you could pay for and equip instead of issuing these jetpacks to all of them. You essentially have a choice between more soliders with more versatile gear and better mobility, or rocket soldiers who get one 20 second instance of unstable flight before needing to refuel-- not to mention the tax on their mobility all the rest of the time.

Yea, Ill take more soldiers, thanks. If you need air support, thats what the air force is for.

Re:Almost as if

[LordLimecat]

Whether they have a place on the modern battlefield is equal to the question of whether infantry has a place on the modern battlefield.

No, its not.

Infantry are mobile, versatile, able to perform precision strikes, able to adapt to many situations.

Rocket belts are heavy, unwieldy, unreliable, expensive, noisy, and incredibly niche. Im sure there are circumstances where it happens to be the right tool for the job, Im just not sure what that might be or why youd want to weigh all of your infantry down with it for that one circumstance.

Re:Almost as if

[LordLimecat]

Youre still carrying a massive extra load just for that one time you happen to need jumpjets.

We have a lot of other ways of accomplishing the things a jumpjet does without all of the ridiculous complexity and logistics it requires.

Re:Almost as if

[phantomfive]

You clearly missed the part where we're talking about hypothetical future jetpacks. Context man, context!

Re:Almost as if

[gIobaljustin]

That might be the case, but it might also not be the case.

Re:Almost as if

[Anonymous Coward]

miniature silent version

Ah.

That would be called a drone.

You know that they're anything but "silent", right?

Re:Almost as if

[AK Marc]

"Flank from above"? Seriously?

That was a direct quote from the person I was responding to (well, their link).

Re:Almost as if

[AK Marc]

But it'd be cool.

Re:Almost as if

[delt0r]

Jetpacks from a 100% efficient physics perspective can't work unless you have an arc reactor. They will always have very poor range, and huge jet/prop blast. As for military applications, well its not going to be too far into the future where it won't be fleshy meat bags doing the shooting.

Space elevators proponents always miss one very important detail. If you have the material to make the elevator, you can use that material to make traditional rockets too. And it may well make rockets cheaper than a elevator.

Re:Almost as if

[rgbatduke]

There are a few minor practical problems with jet packs, or more properly, rocket packs as these devices are rockets, not turbojets, and it matters. It matters because there are some pretty fundamental limits on how much fuel/reaction mass a soldier can carry, especially when they have to carry other stuff like body armor, weapons, helmets, ammunition, food, shelter. Let's imagine that a stripped down soldier carrying little but armor, ammo and a rifle has a mass of 100 kilograms, 90 kilograms of which are the actual soldier. The rocket pack described above had a mass (full) of 57 kilograms and required the pilot to wear heat-protective clothing -- let's call it 60 kilograms. So wearing it and suitable armor and carrying weapons would be a roughly 70 kilogram burden on a 90 kilogram soldier, sort of like wearing a liquid nitrogen and hydrogen-peroxide-filled teen-ager on your shoulders as you wade into battle.

Sadly, this model would not work at all for the current rocket pack designs -- they provide less than 1500 N of thrust, and our soldier now has a weight of 1600 N. He would burn half of his fuel (give or take) waiting for the fuel levels in the tank to drop to where he could take off at all. The troop of rocket-equipped soldiers would all have to be "feather merchants" -- mass 70 kg or less -- and be armed with plastic squirt guns to get off of the ground at all.

Even with modern improvements, nobody has been able to increase flight time beyond around 30 seconds. The practical range in 30 seconds is perhaps 200 to 300 meters, at a height of ten meters -- a height great enough that it is already dangerous to fatal if one falls from it wearing an explosive, superheated massive outfit on your back. One cannot expect to increase their range or flight time because rockets eject mass backwards at high speed in order to provide thrust forward. The backward speed of the reaction mass is determined and limited by thermodynamics and chemistry and the need not to cook the soldier to extra crispy in a 30 second flight. There isn't that much variation in what's available to use for thrust in this context -- one could probably improve on the 740 C exhaust temperature, but only at the expense of adding a lot more shielding (and weight) and much more protective clothing.

The more interesting possibility is to build an actual jet pack -- jets of course use air for thrust mass and use fuel just to heat and compress the air, so they potentially have a much greater range. Small jet engines are mostly hobbyist stuff at the moment, but can produce order of a kilonewton of force at a mass cost of maybe 20 kilograms for the engine itself. One would need two, still further efficiency improvements, serious hearing protection, better shielding in the clothing (jet exhaust is still hotter than the "rocket" exhaust of hydrogen peroxide catalysis to water and oxygen). There is even military technology associated with cruise missiles that could be adapted.

We could learn another lesson from cruise missiles as well. Wings help. Wingsuits, for example, increase the glide ratio of skydiver to six. Hang gliders can achieve 17 to 20. Equipping a small hang glider with a small jet engine (one engineered to run without overheating for indefinite periods of time, unlike many of the powered hang glider engines currently available that tend to be based on two stroke chainsaw motors) could conceivably result in a wearable harness with a comparatively small wingspan in which a fully equipped soldier would have a range of tens of kilometers in tens of minutes at heights ranging from 10s of meters to a thousand meters or so. After powering up and attaining height, the engines could be shut off and the gliders could passively and silently descend from a height of a kilometer to a target 10 kilometers away.

The wings would have to be designed to be "compressible" to a comparatively small pack and quickly and easily erected into a structurally stable functional form, and would probably ma

Re:Almost as if

[Anonymous Coward]

If you have them, the enemy has them. Your flanking supposition doesn't include for that.

Re:Almost as if

[phantomfive]

Space elevators proponents always miss one very important detail. If you have the material to make the elevator, you can use that material to make traditional rockets too. And it may well make rockets cheaper than a elevator.

I always thought the most expensive component of a rocket was the fuel, but who knows

Re:Almost as if

[mrchaotica]

Space elevators proponents always miss one very important detail. If you have the material to make the elevator, you can use that material to make traditional rockets too. And it may well make rockets cheaper than a elevator.

Although making rockets out of nanotube carbon fiber would certainly reduce the weight, it wouldn't reduce it that much. You forget that the bulk of a rocket's weight is fuel; eliminating that is the "big win" a space elevator provides.

Re:Almost as if

[hey!]

Jet packs make sense if you can get them to work.

There's the rub right there. Feasibility is a prerequisite of "making sense", and in the real world you have to deal with physics and the physical limitations of human beings. Antigravity would "make sense" if you could get it to work.

The physics of a jet pack are governed by the rocket equation: V = Ve * ln(Mt/Mp). You need to carry enough mass, ejected at a sufficient speed, to produce 9.8 m/s v every second.

The upshot is that to counterbalance the weight of a soldier and his gear you can either have your rocket eject a lot of mass at low velocity or a small amount of mass at high velocity. That's why the rocket belts thus far have only had a very, very short burn time. To increase the burn time you'd need to carry more fuel than a man could lift.

A typical infantry solider or marine carries over a hundred pounds of gear into battle. Even accounting for things he could dispense with if he had greater mobility, he can't carry much fuel to power his rocket belt. A practical battlefield air transport machine would be a small vehicle which carries more weight than an individual solider can. In other words: a helicopter.

Similar concerns attach to asteroid mining. You *can* physically go out there and return materials from asteroids, just like you *can* strap a rocket belt on a soldier. The question isn't whether physics permits it, but rather whether physics permits economically feasible retrieval of asteroid material, and that's a lot tougher than it sounds. Even the "asteroid belt" is practically empty by terrestrial standards; your chance of randomly encountering anything larger than a dust speck while crossing it is less than hitting the lottery. So prospecting for nuggets of stuff like platinum is physically possible, but not feasible. Unless we hit the jackpot with a near earth object like 433 Eros, we won't see asteroid mining until v in space becomes much, much cheaper.

Re:Almost as if

[phantomfive]

To increase the burn time you'd need to carry more fuel than a man could lift.

Nah, all you really need is an arc reactor. Then you're good.

Re:Almost as if

[hey!]

You know, you touch on something that bugged me when I watched the Iron Man movies. Where is the reaction mass for Iron Man's flight coming from? Even a lightweight, unlimited power source wouldn't solve the problem of reaction mass. The Iron Man suit obviously uses some kind of reactionless drive -- not inconceivable, given that it also has "repulsor" technology which has no plausible physical explanation and violates classical physics.

The arc reactor idea actually is interesting to think about. Suppose you had an unlimited energy source with negligible weight. Could you build something like a rocket belt? I think you could, say by driving a turbine or some more exotic method of accelerating air. Technically it wouldn't be a "rocket" belt, but it would fit the bill. Even you'd still be limited in how small you could make the thruster due to the hazards the high velocity of the exhaust would present to the user and the surroundings.

Re:Almost as if

[phantomfive]

The arc reactor idea actually is interesting to think about. Suppose you had an unlimited energy source with negligible weight. Could you build something like a rocket belt? I think you could, say by driving a turbine or some more exotic method of accelerating air.

My guess is yes. I feel like one of these approaches at least would be able to take advantage of a massive energy source.

Re:Almost as if

[crunchygranola]

miniature silent version

Ah.

That would be called a drone.

You know that they're anything but "silent", right?

"Silent" is a relative term, depending on how close you are and how sensitive your pick-up. A drone can be made as quiet as anything with powered flight can be made, and with sufficient altitude you won't be able to hear it.

There is abundant evidence that with suitable operation many U.S. reconnaissance drones routinely operate without audible detection.

Re:Almost as if

[crunchygranola]

For the military, I'd go with jump-jets. The "launch" is taken care of by a catepult....

Where I have seen this before? Oh, right. "Run away, run aw-a-a-y...".

Re:Almost as if

[crunchygranola]

And you need to bring up your man-catapults before attack.

Re:Almost as if

[crunchygranola]

Space elevators proponents always miss one very important detail. If you have the material to make the elevator, you can use that material to make traditional rockets too. And it may well make rockets cheaper than a elevator.

I always thought the most expensive component of a rocket was the fuel, but who knows

This has the matter completely upside down. For rockets the fuel is essentially free (compared to the rocket itself). Honest!

Consider the Delta 7000, an inexpensive launcher that cost $70 million to launch in 2006 dollars. The whole launch system weighed at least 180,000 kg and it burned (except for the boosters) LH2/LOX. Assume as a limiting case that the entire launch weight is fuel - in that case the fuel is 20,000 kg of hydrogen and 160,000 kg of oxygen. How much does LH2 and LOX cost? For LH2 it is about $3/kg, and for LOX $0.25/kg, so the total cost is $60,000 + $40,000 = $100,000. The fuel cost is thus 0.15% of the total launch cost, barely round-off error.

Re:Almost as if

[AK Marc]

You install them in every Humvee, as ejection seats.

Or just make the Humvees fly.

Re:Almost as if

[phantomfive]

Cool, good to know.

Re:Almost as if

[phantomfive]

They really did mess up then, not making the space shuttle fuel tank reusable

Re:Almost as if

[Anonymous Coward]

but no one mentions the Martin

That's not a jetpack, it's a lightweight VTOL craft that you strap yourself to, not a pack you wear on your back. Quit whoring for views, moron.

Re:Almost as if

[FunkDup]

Suppose you had an unlimited energy source with negligible weight.

Pratt and Whitney's impressive trimodal nuclear rocket seems relevant (sorry about the weird links, this engine has largely disappeared from the internet). Some of the ideas and materials in this design would not doubt be applicable to a rocket belt regardless of the nuclear capability.

Re:Almost as if

[delt0r]

You are also forgetting that a rockets performance is empty weight to full weight ratio. So if you can make a fuel tank half as light you just double the ratio and that makes a huge difference. But also there is cost. Currently getting the needed ratio is expensive. A stronger lighter material could well make it much cheaper to achieve the required ratios.

sound-barrier-breaking X-1 aircraft

[Deadstick]

...as opposed to the rocket belt, which was merely eardrum-breaking...

This Day on Slashdot

[Anonymous Coward]

I know it's offtopic and all, but is it just me, or has this not changed in like a week or more?

Re:This Day on Slashdot

[Soulskill]

We had to disable updates to most of the Slashboxes, including 'This Day on Slashdot' in order to fix an underlying issue in the code. The work should be completed soon, at which point we'll re-enable everything. Apologies for the inconvenience!

Re:This Day on Slashdot

[ObsessiveMathsFreak]

I am detecting a significantly elevated level of story quality and of course, beta changes, in the last week or so. I guess you guys really did listen...eventually.

Can we discount the possibility that the

[rmdingler]

Chuck Taylor's weren't responsible for the gain in vertical leap?

Re:Can we discount the possibility that the

[rts008]

No.

Kids these days...*sigh.

Chuck Taylor's couldn't hold one of the PF Flyers shoestrings!

PF Flyers even came with a 'Magic Ring' that done encoding and decoding...Johnny Quest would never lie to me.

Ankles are lousy landing gear

[Animats]

A big problem with jetpacks is that human ankles are weak landing gear. You can't do a parachute landing fall while wearing a jetpack; you have to do a standing landing. With all the mass of the gear on your back.

The other big problem is that rocket systems have a short flight time, and jet engine systems are too expensive. The jet engine powered backpack worked well, but cost too much. That used a small Williams jet engine. Williams International has tried and tried to make small jet engines cheaper. So have many others. Unfortunately, that's a very hard problem, which is why general aviation is still piston-powered. Below small-bizjet size, jet engines don't seem to get much cheaper as they get smaller. There was a big effort about a decade ago to develop "very light jets", but they ended up costing well over $1 million, most of that being engine cost.

So it can be done, and it has been done, but it just doesn't work very well.

Re:Ankles are lousy landing gear

[phantomfive]

That's a great video

Re:Ankles are lousy landing gear

[phantomfive]

Price will lower when they will be able to simply print it.

Pretty sure 3-D printing is more expensive than other mass-manufacturing processes (injection molding). The advantage of 3-D printing is, you can do it at home, and in single quantities, it is cheaper.

But if you're expecting 3-D printing to eventually make everything cheaper, you'll probably be disappointed. The most that could be expected is to bring the costs of custom items be the same as mass-manufactured items. Which is still a good thing.

Re:Ankles are lousy landing gear

[Recaply_]

Great video thanks for sharing. Added it into the post..

Re:Ankles are lousy landing gear

[wisnoskij]

That and stabilization.

It is easy to launch someone into the air with just a moderate amount of explosives, or a jet engine strapped to your back, doing so in a slow controlled manner when we are talking at least 300 pounds of human, their gear, and the jetpack itself is a whole lot harder. Add to that this engine or rocket has to be in direct contact with a living human being for an extended period.

Practically, you are not going to create a solution light enough to carry around just in-case it is needed. Maybe you could create something that is usable, but it will be so heavy that, best case scenario, it would just be carry-able by a single man without too much extra gear, and more likely it would be a very limited range vehicle that needed to be transported to where it was to be used by plane or truck.

Re:Ankles are lousy landing gear

[jafac]

Based on the prices of some programs, I don't think that "too expensive" is an issue.

When killing people is concerned, I think that no price is too high for our military.

Re:Ankles are lousy landing gear

[ColdWetDog]

Anyone expecting printed materials to survive environments typically found inside jet or rocket engines needs to be awfully patient.

Re:Ankles are lousy landing gear

[plover]

I think they could solve stabilization with modern electronics. Kid's toy quadcopters are already self leveling, and as they weigh much less thank a kilogram, they're far more "twitchy" than 150kg of inertia carried about by the humans and their gear.

As you mentioned, it's the soldier who has to carry the additional 60kg pack that is the real limit.

Re:Ankles are lousy landing gear

[50000BTU_barbecue]

Well, selective laser sintering seems to be at that stage, however from what I understand, it's still a huge machine, a slow process and requires as much if not more skill and knowledge as machining from stock.

You aren't going to see huge improvements in designs anymore IMO, just some tweaks in manufacturing processes. SLS can do things like progressively blend from one alloy to another in one part. How much that helps I don't know.

Re:Ankles are lousy landing gear

[AK Marc]

One of the ways 3D printing makes everything cheaper is easier prototyping and drops in the cost of tooling, when you can make moulds out of 3D printed things, rather than by hand, then use those moulds to make the tooling, cutting retooling costs and time, dropping production cost.

Re:Ankles are lousy landing gear

[Anonymous Coward]

Practically, you are not going to create a solution light enough to carry around just in-case it is needed. Maybe you could create something that is usable, but it will be so heavy that, best case scenario, it would just be carry-able by a single man without too much extra gear, and more likely it would be a very limited range vehicle that needed to be transported to where it was to be used by plane or truck

Which is why we still use helicopters. We haven't really figured a way to scale that type of mobility down to a single person. And frankly speaking, unless we get moving on actual mechanized battle-suit technology, we won't. The ultimate problem is your power source, getting it small and light enough while maintaining enough power to be useful.

Re: Ankles are lousy landing gear

[Em Adespoton]

Two words:

Robotic Exoskeleton

Re:Ankles are lousy landing gear

[phantomfive]

That will be better when they can do that.

Re:Ankles are lousy landing gear

[Anonymous Coward]

In high performance parts like turbofan blades, you absolutely must control the microstructure of the steel to within extreme tolerances. I don't believe laser sintering can accomplish that. From everything I've read, the tensile strength of sintered steel, for example, is several times weaker than cast steel. And that's using state-of-state, very expensive printing techniques (in nitrogen vacuum, etc). You can improve strength by subsequent annealing, but you still can't match existing techniques.

Given the performance demands of something like a jet engine, I'm going to go out on a limb here and guess that it'll be one of the very last applications for 3D printing, many decades from now, if ever. I can just imagine a whole plane being printed, with hollow cavities for the engines.

Re:Ankles are lousy landing gear

[AK Marc]

Or when they can build per atom with any material. They can call them "replicators". Even better if they have a fission/fusion power source that can assemble any element/compound that's atomically stable (the other excluded for safety reasons, though ordering up a 3l jug of HF or SbHF6, or some other relatively dangerous chemical

Re:Ankles are lousy landing gear

[phantomfive]

Yeah, once you have near infinite energy for cheap, then lots of other things become cheap as well.

Re:Ankles are lousy landing gear

[pepty]

The goal isn't to kill people; the goal is to distribute the project to as many congressional districts as possible. More moving parts, more better.

Re:Ankles are lousy landing gear

[AK Marc]

We should start with covering the moon in solar panels and transmission stations.

Re:Ankles are lousy landing gear

[LordLimecat]

transmission stations

Also known as "death rays". Dont let China see you pointing it at you or you may see your solar panels destroyed.

Re:Ankles are lousy landing gear

[Anonymous Coward]

I can just imagine a whole plane being printed, with hollow cavities for the engines.

And crew, hopefully.

Re: Ankles are lousy landing gear

[Anonymous Coward]

Two words:

Additional weight

Re:Ankles are lousy landing gear

[delt0r]

Printing does not the crystal structure they way you need it for high temperature metals and materials. Most metals in use today, including that outside casing on iPhones need non trivial heat treatments. In fact using the iPhone as an example, its forged then machines precisely because it was the only way to get a metal with the properties it required. In short, you can't print it.

Re:Ankles are lousy landing gear

[delt0r]

Laser sintering gets you sintered material with different properties than say single crystal material. http://www.appropedia.org/Sing...

Re:Ankles are lousy landing gear

[delt0r]

And it has been used for this for decades.

Re:Ankles are lousy landing gear

[Confusador]

Anyone expecting printed materials to survive environments typically found inside jet or rocket engines needs to be awfully patient.

Or, you know, NASA.

Re:Ankles are lousy landing gear

[Chris Mattern]

One notes that this part is not *inside* the engine, but is a port cover for a secondary system. Pump exhaust covers/baffles, yes. Turbine blades? Not so much.

Re:Ankles are lousy landing gear

[jstults]

GE is going to production with 3D printed fuel injectors and uses 3D printed turbine blades for testing right now.

Re:Ankles are lousy landing gear

[AK Marc]

What 3D printers were used in the 80s? My recollection is that "decades" ago, we were still crafting prototypes by hand, and casting those for moulds, and tooling was largely built by hand.

Re:Ankles are lousy landing gear

[Animats]

What 3D printers were used in the 80s?

3D Systems was founded in 1986. Stereolithography is older than many people think it is. Early systems produced rather fragile objects, but product designers in the late 1980s were using them to make product models.

Williams WASP X-Jet

[OzPeter]

This is the reality of how to make a single man fly.

Williams WASP X-Jet

It worked, it flew, there was no military justification for it, it disappeared.

Re:Williams WASP X-Jet

[phantomfive]

It worked, it flew, there was no military justification for it, it disappeared.

Specifically, with fuel lasting only 30 minutes, it didn't have much practical application.

Re:Williams WASP X-Jet

[aliquis]

As I understood it the designer behind that one is a one which worked with Moore until he died (at age 54?) and later continued with the work.

I'm not all that surprised there wasn't much interest for that can though. Then again maybe it was awesome to avoid branches, offer some protection, let you carry gear / rifle, .. Maybe it just looked worse :)

They all controlled great :)

Re:Williams WASP X-Jet

[Anonymous Coward]

This is the reality of how to make a single man fly.

Williams WASP X-Jet

It worked, it flew, there was no military justification for it, it disappeared.

Ya, I've seen that one before, it's brought up in a lot of Conspiracy-type books/videos.
It's not a jet pack- you can't carry it around until needed, which is the idea that would make a jet-pack useful. It's a light vehicle, and if you're going to go through everything needed to support it you may as well just scale it up a notch and go with a helicopter.

Re:Williams WASP X-Jet

[ObsessiveMathsFreak]

To be fair, it could be defeated completely by wearing the crocodile mask.

Starship Troopers

[rossdee]

"Whether they have a place on the modern battlefield is equal to the question of whether infantry has a place on the modern battlefield. If they do, then having a mobile infantry is an advantage."

There is a big difference between what the jet pack can do, and what the armored suits of the "Mobile Infantry" could do. For a start they had nuclear power, so could keep flying for hours not minutes. And of course they were fighting in alien worlds, there were no civilians around to worry about collateral damage.

Re:Starship Troopers

[phantomfive]

There is a big difference between what the jet pack can do,

Yes, that is why the discussion is about what a jet pack could do if the practical limitations were overcome. Context is important.

Checkout the Martin Jetpack

[Anonymous Coward]

http://www.martinjetpack.com/

Re:Checkout the Martin Jetpack

[Anonymous Coward]

http://www.martinjetpack.com/

Sigh. Calling shit like this a "jetpack" is highly misleading at best. It's not a pack, it's a light-weight vehicle with an open cock-pit that you strap yourself to.
The entire point of calling something a "jetpack" is that it's a PACK which you can strap to your back, pickup with one hand, and hike around with until such a time as you need to use it.

Re:Checkout the Martin Jetpack

[crunchygranola]

http://www.martinjetpack.com/

Sigh. Calling shit like this a "jetpack" is highly misleading at best. It's not a pack, it's a light-weight vehicle with an open cock-pit that you strap yourself to.

He should have cited the Bell Jet Flying Belt - a flight pack that incorporated a turbofan engine, not a rocket. It could fly up to 25 minutes, with the far more efficient use of fuel (air was essentially the propulsion fluid).

The entire point of calling something a "jetpack" is that it's a PACK which you can strap to your back, pickup with one hand, and hike around with until such a time as you need to use it.

Or not. Did you check out the rocketpack weight? It was 57 kilograms. No one is going to do much hiking "around with until such a time as you need to use it" with that much deadweight - the guy is grossly-overloaded without carrying anything else. The U.S. Army's recommended combat load limit for a soldier is only 33 kilograms and the Army normally wants the soldier to carry less.

Me, me, me...I want to name it.

[Anonymous Coward]

Sky Segway.

1950s

[djupedal]

I suspect they ran the numbers and decided that rather than making medicore-range quasi-flyers out of ground soldiers, the smart money was on just getting it over with and develop better helicopters, instead. Better speed; longer flights; bigger payloads - all much cheaper than adding limited flight capabilities to the individual.

Re:1950s

[delt0r]

Jet packs are like flying cars. Everyone thinks they are awesome and would make like better, but no one knows how or why it would be better. Logic is hardly going to work with these fans.

Also the way things scale means its easier and cheaper to make some of these things bigger. So its cheaper to make a 2 man-4 man helicopter than a one man jet pack. Range is always a problem with smaller things because of the cube law.

Re:1950s

[Anonymous Coward]

I'm stuck in traffic. The sky is empty. If I had a flying car, I wouldn't be stuck in traffic.

I have to get across town, could walk for an hour, catch a bus or three, take a train, take a car through traffic, none of which are quick or direct. If I had a jet pack, I could go direct and quickly.

Re:1950s

[Wolfrider]

--Jet packs will likely be much more feasible if/when we start colonizing other planets. If you can get to 60-70% of Earth's gravity or lower, it will be much easier to fly.

Re:1950s

[delt0r]

Only your jet pack doesn't have enough range. And its raining.

Like another problem

[TheRealMindChild]

Like the problem with a functional 5 megawatt laser, it is about a power source

Re:Like another problem

[phantomfive]

So many uses for Mr Fusion. Sigh.

Re:Like another problem

[Anonymous Coward]

Well, yes, but when this happened there were still fantasies of nuclear powered cars ....

So, not so stupid other than the wishful thinking.

It is a reality - Check out the Martin Jetpack

[Anonymous Coward]

Jetpacks are better for civilian rather than military use, e.g. search & rescue;

http://www.martinjetpack.com/

Re:It is a reality - Check out the Martin Jetpack

[PPH]

For the search part, a UAV would probably be a cheaper way to put sensors in the air. For the rescue part, you need to hover and lift quite a bit of weight. Consider that many victims need some medical attention or at least assistance in getting aboard the rescue craft. So that means a crew of several people plus rescue gear (basket, stretcher, etc.). Well beyond the capabilities of a jet pack and even some small helicopters.

Re:It is a reality - Check out the Martin Jetpack

[Anonymous Coward]

Jetpacks are better for civilian rather than military use, e.g. search & rescue;

http://www.martinjetpack.com/

That's not a jetpack, it's a lightweight vehicle.
A Jet PACK is something you can pick up with one hand and carry around on your back. This shit isn't it, so stop whoring for page hits asshole.

Re:It is a reality - Check out the Martin Jetpack

[coofercat]

Although, much like the paramedics on bicycles or motorbikes, getting somewhere first, even if you can't get back out again is sometimes useful.

As someone above said though, lugging a couple of these about the place, just in case you need to get one person somewhere really quickly seems like an awful overhead for a one-time, niche use.

Re:It is a reality - Check out the Martin Jetpack

[crunchygranola]

Jetpacks are better for civilian rather than military use, e.g. search & rescue;

http://www.martinjetpack.com/

That's not a jetpack, it's a lightweight vehicle. A Jet PACK is something you can pick up with one hand and carry around on your back. This shit isn't it, so stop whoring for page hits asshole.

So the rocket belt was NOT a "jet PACK" by your criteria since at 57 kg you could NOT pick it up with one hand (unless you were perhaps a professional body builder).

Re:It is a reality - Check out the Martin Jetpack

[Anonymous Coward]

So the rocket belt was NOT a "jet PACK" by your criteria

More or less, yes. In the case of this "rocket belt" you keep bringing up, it might be appropriate to call it a "jetpack" but it's certainly not a useful one because you can't pack it around.
But both this post and the previous ones were a response to this guy whoring for page hits for something which is not at ALL a pack of any sort, it's a massive frame you strap yourself into.

Holy Crap!

[Ecuador]

I saw that when I was a kid in the 80's on some TV program and as I grew up I was pretty sure that I had either watched something fictional, or I was too young and misunderstood. I mean, if they had that working in the 70s, they would have something even better in the 90s, 00s etc, instead of, ehm, pretty much nothing. Thanks for that! You verified my childhood memory and solved what was a "mystery" to me!!

Re:Holy Crap!

[LordLimecat]

AFAIK power density hasnt really changed that much. You have a pretty fundamental limit on how long flight lasts given a fuel density and a payload.

Re:Holy Crap!

[twosat]

I remember seeing this on a TV science program in the 1980's when I was at university in New Zealand. I'm pretty sure that it would have been mentioned in science magazines like "Popular Science" and "Popular Mechanics" - it was well-known at the time.

Jetpacks, flying cars - same problme

[joe_frisch]

We don't see jetpacks or flying cars for the very same physics reason. In order to hover against gravity you need to produce thrust > weight. Since thrust is proportional to (mass/second) X velocity, and power is proportional to (mass/second) X velocity^2, an efficient source of thrust you want to move a lot of material slowly (assuming you have unlimited reaction mass -> the atmosphere).

So, things that hover need to move lots of air, and have great big propellers. That is why helicopters work, and jet-reaction cars are too inefficient to be practical. It is why airplanes have big wings, not stubby lifting bodies. There may be a few spacial cases where you are willing to tolerate inefficiency, but they are rare.

Planes look like planes for a reason. Helicopters look like helicopters for a reason.

Re:Jetpacks, flying cars - same problme

[Jecel Assumpcao Jr]

Stubby lifting bodies can be practical at interesting cruise speeds, but you wouldn't want to take off or land at such speeds. Adding VTOL capability would solve that problem, but then we are back to the big and slow propellers issue you explained so well. I believe it is possible to convert a small, low thrust, high speed jet to a high thrust, low speed one with no moving parts. Air amplifiers actually increase thrust below 5cm in diameter but reduce it for larger sizes, so you have to figure out why it doesn't scale and fix that. The Dyson fan (http://www.dyson.com/Fans-and-heaters/cooling-fans.aspx), for example, is a terrible jet engine.

Re:Jetpacks, flying cars - same problme

[joe_frisch]

I didn't know that air amplifiers didn't scale, but also didn't know how efficient they were. Turbulent systems can be very non-intuitive - some airplanes have small vortex generators (tabs on the to of the wing that stick into the air flow) because they decrease drag. (they prevent boundary layer separation, but it still feels like exactly the wrong thing to do.....

Re:Jetpacks, flying cars - same problme

[Jecel Assumpcao Jr]

Fluids "love" to twist, so laminar flows (such as the curtain of air along the inner surface of air amplifiers) don't always get the best results. The laminar flows seem so quiet and smooth so it is hard for our intuition not to consider them to be the way to move mass with the least energy.

Vortices can scale very well. I always point to the Red Spot on Jupiter as an example. Can one be generated on a scale that could keep a car or a person suspended in mid air while using less fuel than a helicopter? I think it is possible, but haven't proved it yet.

no matter what, they fill fuck things up

[Anonymous Coward]

No matter how cool the device, they will find a way of fucking things up.

Just looks at the mall cops coasting around on their SHTs.

Infantry Soldier != Pilot

[Anonymous Coward]

Also consider that having an infantry of just barely high school graduates zipping around in 3 dimensions with jet packs and guns would probably be more dangerous to the home team than the enemy.

Re:You must be looking in the wrong place

[asylumx]

GP didn't say they aren't possible, he said they aren't practical.

Schlock says...

[Anonymous Coward]

Wisdom from http://www.schlockmercenary.com/2011-05-28
corporal: "Do you know what we call flying soldiers on the battlefield?"
private: "Air support?"
corporal: "skeet"

or just competent (of course being both patient an

[Anonymous Coward]

http://www.nasa.gov/press/2013/august/nasa-tests-limits-of-3-d-printing-with-powerful-rocket-engine-check/#.UxSiDvRdU9c

What if multiple contracts were awarded?

[RogueWarrior65]

I wonder how things would have been different if multiple identical R&D contracts were awarded to several companies so as to set up competition for the best technology. Basically, set aside R&D money to be given to a company so there is disincentive to risk their own money. I would also throw in there that R&D awards be given to startups rather than huge public companies.

Re:What if multiple contracts were awarded?

[crunchygranola]

Because contract competition in the early 1960s would have circumvented the fundamental limits of engineering and materials and produced something that cannot be made in 2014?

Note that there have been dozens of small "flying man" devices from the late 1950s to the present day, none of them practical for any important application. The limits of fuels and propulsion systems constrain everyone and even modern computers and composite materials aren't making flying belts practical today.

wrong

[Anonymous Coward]

Rocket belts make no sense and that's why they've never been used other than for research and demonstration purposes. They're incredibly expensive, heavy, offer no margin of safety since you're too low for a parachute to of any use in case of failure.

Oh and you can't ever fly longer than 30 seconds.

FUCKING DUH

Oh, the young ones...

[Anonymous Coward]

will have no clue how accurate that is. Bravo.

back on topic...

If we ever did perfect anti gravity via magnetic fields, we might be on to something. Seems like we have to be out of this 'fossil fuel' stuff first though.

Flying soldiers = SKEET

[Anonymous Coward]

Flying soldiers = SKEET!

http://www.schlockmercenary.com/2011-10-02

I DON'T HAZ ROKIT BELT

[Jeremiah Cornelius]

WANTZ tehze CHUCKs, with ZIP on SIDEZ!