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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.'"
...as opposed to the rocket belt, which was merely eardrum-breaking...
I know it's offtopic and all, but is it just me, or has this not changed in like a week or more?
Chuck Taylor's weren't responsible for the gain in vertical leap?
Happiness in intelligent people is the rarest thing I know.
Ernest Hemingway
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.
"First they came for the slanderers and i said nothing."
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.
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.
"First they came for the slanderers and i said nothing."
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.
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but no one mentions the Martin http://www.youtube.com/watch?v...
"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.
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!
"First they came for the slanderers and i said nothing."
Jetpacks make sense if you can get them to work.
As would many, many other things, like Warp Drive and the G Spot.
It must have been something you assimilated. . . .
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.
Like the problem with a functional 5 megawatt laser, it is about a power source
"When life gives you lemons, don't make lemonade. Make life take the lemons back!" -- Cave Johnson
G-spot? That's crazy talk.
Faster! Faster! Faster would be better!
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.
Have gnu, will travel.
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.
John
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.
Learn to love Alaska
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.
Learn to love Alaska
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!!
Violence is the last refuge of the incompetent. Polar Scope Align for iOS
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.
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.
Jesus was all right but his disciples were thick and ordinary. -John Lennon
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.
Learn to love Alaska
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.
miniature silent version
Ah.
That would be called a drone.
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.
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.
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.
You clearly missed the part where we're talking about hypothetical future jetpacks. Context man, context!
"First they came for the slanderers and i said nothing."
That might be the case, but it might also not be the case.
Thank you Dave Raggett
"Flank from above"? Seriously?
That was a direct quote from the person I was responding to (well, their link).
Learn to love Alaska
But it'd be cool.
Learn to love Alaska
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.
If information wants to be free, why does my internet connection cost so much?
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.
GP didn't say they aren't possible, he said they aren't practical.
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"
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
Even when the experts all agree, they may well be mistaken. --- Bertrand Russell.
http://www.nasa.gov/press/2013/august/nasa-tests-limits-of-3-d-printing-with-powerful-rocket-engine-check/#.UxSiDvRdU9c
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.
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
"First they came for the slanderers and i said nothing."
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.
"[Regarding the 'cloud,'] ownership was what made America different than Russia." -- Woz
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.
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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.
"First they came for the slanderers and i said nothing."
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.
Post may contain irony: discontinue use if experiencing mood swings, nausea or elevated blood pressure.
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.
"First they came for the slanderers and i said nothing."
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.
Second class citizen of the New Gilded Age
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...".
Second class citizen of the New Gilded Age
And you need to bring up your man-catapults before attack.
Second class citizen of the New Gilded Age
WANTZ tehze CHUCKs, with ZIP on SIDEZ!
"Flyin' in just a sweet place,
Never been known to fail..."
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.
Second class citizen of the New Gilded Age
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.
Second class citizen of the New Gilded Age
You install them in every Humvee, as ejection seats.
Or just make the Humvees fly.
Learn to love Alaska
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).
Second class citizen of the New Gilded Age
Cool, good to know.
"First they came for the slanderers and i said nothing."
They really did mess up then, not making the space shuttle fuel tank reusable
"First they came for the slanderers and i said nothing."
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.
Great spirits have always encountered violent opposition from mediocre minds -- Albert Einstein
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.
If information wants to be free, why does my internet connection cost so much?