Yes and No. If your jetpack could have enough fuel to take your astronaut all the way down to the surface, then fine. It lets you hover, so it can accelerate the astronaut at 1 g.
Since g is 9.8 meters per second, if you can sustain it, then you can reach 10 km / second after 1020 seconds of acceleration, so after about 17 minutes of constant 1 g acceleration.
So, if your jet pack can last for 17 minutes, and can supply you with 2g, not just 1 g (use two packs if one isn't enough), you could in principle use it to go into orbit.
Then get a refuel up there, and return to Earth, the way you came. Just slow down and then hover and descend back to Earth, like a typical Earth launch but in reverse.
But - no that doesn't work. The problem is that the amount of fuel you need goes up exponentially depending on the delta v needed. Though you can fly around for a few seconds, even a minute or two, with a jet pack no problem, nobody will ever build one that can keep you aloft for 17 minutes, not using a pressurized tank or ordinary rocket motors.
They could do it, perhaps, if it had vasts amount of power (say micro fusion if that was ever possible) and used the air as propulsion - or some very advanced ion thruster that can take a small amount of fuel and expel it at huge speeds, again requiring huge amounts of power.
Or some revolutionary new technology (such as Roger Shawyer's projections for the EM-Drive though his optimism is not shared by other researchers of his invention).
Right now, no. You'd run out of fuel first.
If it wasn't for the atmosphere and aerobraking, then returning from orbit would have been extremely difficult to do. You would have to launch all the fuel needed for a typical lift-off into orbit first, to use to return back to Earth and you'd need that whole thing of first, second and third stages (or much more powerful single stage) again in orbit, to get back to the surface safely. Probably would need dozens of launches to put all the fuel and machinery in orbit just to prepare for a safe return to Earth of your first astronaut.
It's lucky we could use aerobraking instead :).
In case you wonder about SpaceX - some people seem to have got the impression they plan to decelerate all the way from orbit. But no, that's totally impractical with present day technology. They would need to decelerate to terminal velocity by aerobraking, same as everyone else returning from orbit. Even with recovery of the first stage, most of the deceleration is through aerobraking - even though it doesn't have a parachute but it still has enough air resistance to have quite a low terminal velocity when nearly empty. They just use the rocket engines for the last part of the landing - they take the place of the parachute phase of a normal landing.
It could work on the Moon though. The escape velocity is much less and because the amount of fuel goes down so much with only a small reduction in the delta v - the astronauts could easily get into orbit with quite a small rocket motor.
In principle you could convert the engine for the lunar module, or a modern version of it, into a rather large jet pack, and use that to go into orbit around the Moon from its surface.
It weighed 180 pounds, and had a length of 47 inches and nozzle diameter 34 inches. And that was to propel the entire lunar module and two astronauts and all their equipment into orbit.
Reference Spacecraft Engines
It's quite a dramatic illustration of the rocket equation that you only need that much to get off the Moon while they needed a whole Saturn V rocket to escape Earth to get to the Moon.
Since g is 9.8 meters per second, if you can sustain it, then you can reach 10 km / second after 1020 seconds of acceleration, so after about 17 minutes of constant 1 g acceleration.
So, if your jet pack can last for 17 minutes, and can supply you with 2g, not just 1 g (use two packs if one isn't enough), you could in principle use it to go into orbit.
Then get a refuel up there, and return to Earth, the way you came. Just slow down and then hover and descend back to Earth, like a typical Earth launch but in reverse.
But - no that doesn't work. The problem is that the amount of fuel you need goes up exponentially depending on the delta v needed. Though you can fly around for a few seconds, even a minute or two, with a jet pack no problem, nobody will ever build one that can keep you aloft for 17 minutes, not using a pressurized tank or ordinary rocket motors.
They could do it, perhaps, if it had vasts amount of power (say micro fusion if that was ever possible) and used the air as propulsion - or some very advanced ion thruster that can take a small amount of fuel and expel it at huge speeds, again requiring huge amounts of power.
Or some revolutionary new technology (such as Roger Shawyer's projections for the EM-Drive though his optimism is not shared by other researchers of his invention).
Right now, no. You'd run out of fuel first.
If it wasn't for the atmosphere and aerobraking, then returning from orbit would have been extremely difficult to do. You would have to launch all the fuel needed for a typical lift-off into orbit first, to use to return back to Earth and you'd need that whole thing of first, second and third stages (or much more powerful single stage) again in orbit, to get back to the surface safely. Probably would need dozens of launches to put all the fuel and machinery in orbit just to prepare for a safe return to Earth of your first astronaut.
It's lucky we could use aerobraking instead :).
In case you wonder about SpaceX - some people seem to have got the impression they plan to decelerate all the way from orbit. But no, that's totally impractical with present day technology. They would need to decelerate to terminal velocity by aerobraking, same as everyone else returning from orbit. Even with recovery of the first stage, most of the deceleration is through aerobraking - even though it doesn't have a parachute but it still has enough air resistance to have quite a low terminal velocity when nearly empty. They just use the rocket engines for the last part of the landing - they take the place of the parachute phase of a normal landing.
It could work on the Moon though. The escape velocity is much less and because the amount of fuel goes down so much with only a small reduction in the delta v - the astronauts could easily get into orbit with quite a small rocket motor.
In principle you could convert the engine for the lunar module, or a modern version of it, into a rather large jet pack, and use that to go into orbit around the Moon from its surface.
It weighed 180 pounds, and had a length of 47 inches and nozzle diameter 34 inches. And that was to propel the entire lunar module and two astronauts and all their equipment into orbit.
Reference Spacecraft Engines
It's quite a dramatic illustration of the rocket equation that you only need that much to get off the Moon while they needed a whole Saturn V rocket to escape Earth to get to the Moon.
About the Author
Robert Walker
Writer of articles on Mars and Space issues - Software Developer of Tune Smithy, Bounce Metronome etc.Studied at Wolfson College, Oxford
Lives in Isle of Mull
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