Do parachutes help when you lose control 50ft off the ground? Deploy time is probably too short. Also lateral speed may be fatal enough with a jetpack.
Still needs a certain minimum height to be effective, >= 400 ft in straight and level flight, 920 ft in a spin [1]. Don't think it would be much use in a jetpack (apart from the fact that the article states that they haven't found a way yet to attach both a jetpack and a parachute, let alone a ballistic one).
Yes, that will work. It's how Spirit and Opportunity landed on Mars. Many people will die in airbag deployment failures before it works reliably, some of whom would have survived without the airbags, and they will be prohibited in the sort of repressive jurisdictions that prohibit bulletproof vests and gas masks.
> Yes, that will work. It's how Spirit and Opportunity landed on Mars.
What do you know that makes you say "that will work"? A planned and controlled landing for a rover (engineered from metal and stuff) on a planet with a gravity 38% that of earth is rather different from this hypothetical emergency system for fragile humans on earth.
Ok, let's do the math. The result is easy: When you fall from h meters (accelerating), and then decelerate over s meters cushion, your deceleration is (if it is nice and uniform) h/s. So, when you want to decelerate with at most 5g, your cushion needs to be 1/5th of the free fall distance.
For example: Velocity from a 100 metre (300 ft) free fall is v = sqrt(2gh) = 44 m/s = 160 km/h = 100 mph.
Now let's say we might survive 5g to 50g (Astronauts pull 5g routinely, Lady Di in her car crash had about 70g).
So, to brake a fall from 100m somewhat comfortably, you need a 20m cushion. To brake it such that you have a small chance of survival, you need at least a 2m cushion. This scales linearly with height you fall from, until you approach terminal velocity.
Interestingly, terminal velocity is around 200 to 300 km/h (depending on position), or 125 to 185 mph, or 54 to 80 m/s, requiring a 3m to 30m cushion.
A 30m airbag in a jetpack strikes me as unlikely. A 2m airbag in a jetpack that achieves constant deceleration may be feasible, though not soon, and certainly not something I want to experience.
For reference, these Fall-Pac units at 1.2 metres cushion promise fall protection up to 3-5 metres.
https://en.wikipedia.org/wiki/John_Stapp#Work_on_effects_of_... shows that 50 gees is survivable, at which speed you need 120 ms and 3.6 m to decelerate from 60 m/s. Not pleasant but still safer than a car crash. If the airbags inflate before you hit the ground your terminal velocity is much lower, decreasing roughly in inverse proportion to your hydraulic diameter (√(2mg/ρ/A/Cd)), so a 1.5-meter-radius cocoon of airbags around you will cut your terminal velocity to about 20 m/s, at which point you need 40 ms and 400 mm to stop safely. For this you need something like 4-12 1.5-meter-diameter airbags, 7 m² of surface each; at 20-μm thickness that's 140 cc, and if it's mostly something like gel-spun UHMWPE fiber or polyimide film, it's also about 140 g each, so 0.5-1.7 kg total bag weight --- plus conventionally 2 kg of nitrogen per airbag in the form of 3 kg of sodium azide, which is another excellent reason to perform the inflation well before you hit the ground, so you can use atmospheric air instead.
Suppose you weigh 100 kg. To stop you at a safe 20 gees max when you hit, the bag needs to exert 2000 kg max force or 20 kN, so the pressure in a bag acting over something like 1 m² of your body needs to peak at 20 kPa, about 0.2 atmospheres or 2.8 psi. Approximating hoop stress as ½Pr/t we get a bit under 400 MPa stress in the bag, too much for unaided polyimide but an order of magnitude lower than what UHMWPE fiber can handle. So you can make the bag thinner than that, lowering the weight further, perhaps to 40 g per airbag. There are whiplash shock loading problems conventionally handled in automotive airbags by generous safety factors that can be reduced by origami design and judicious addition of thicker compliant material like nylon.
A 30m airbag would need to be 20x thicker and would have 400x as much area, so it would weigh 8000x as much, 320 kg. This would indeed be unwieldy for a backpack.
You can closely approximate constant deceleration by connecting the airbag under you with other, more voluminous airbags on the other side of you, just as a car tire closely approximates constant pressure when traveling over bumps in the road. But it's not necessary; what's necessary is acceptable peak deceleration and, probably, minimal jerk. It's true that constant deceleration is the best case of minimal distance and time for a given peak deceleration, but even linearly increasing deceleration, like from a Hookean spring, only doubles the time needed to stop when holding the peak deceleration constant, thus multiplying the distance by √2.
So, you see, all the materials and mechanisms necessary are already available, though only in the last few decades. There's no technical risk. It's "just" a question of engineering the thing to not kill people all the time when it fails, based on experience with what the deadly failure modes are. It'll require a lot of work and many deaths, but if people put in the work, it will definitely work.
Let me know if I got any of the calculations wrong!
If only that invention wasn't supposed to be strapped to the same part of the person's anatomy as the jetpack, with the result being that no practically working implementation combining the two exists...
It's also not the solved problem your snark implied. I mean, someone's been working on it for decades and his solution is fly over water as much as possible!
(As other posters have alluded to, parachutes won't save you at low altitudes. In the mean time, it's further weight on your back on a device which is already difficult to control, and not really optimal for releasing next to jets of hot kerosene either)
Tens of person-years of work is not as much investment as you are implying in the context of manned heavier-than-air flight. Boeing spends ten person-years on developing flight every 40 minutes on average. Since you wrote your comment 4 hours ago Boeing has spent about 60 person-years on developing flight.
