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Assumptions for the story: The rocket pack is not unlike the scenario of the movie when I was little, "Rocketeer," in terms of viability. I have hand-waved it in my story.

  • The rocket pack should be assumed for this question to be unlimited in fuel and power without subjecting harm to the character.
  • There is a maximum of 10 minutes of oxygen within the helmet apparatus, and my character can wear anything from slacks to ski gear.

Given an unlimited rocket without direct effects from the rocket onto the hero: In my story, I would like the character to achieve (1) very fast travel; and (2) very high travel.

For instance, I have a part where the hero rockets to a height of an airplane, but then descends. Also, must travel distances. While the rocket is hand-waved, the limitations to the human body aren't. The hero has access to clothes you'd find in the closet (including ski gear), the 'hand-waved' rocket, and the helmet allows for 10 minutes of oxygen and protection from exhaust of the hand-waved rocket. But not space gear and not protection from effects of speed, height, pressure, or anything else.

I can handle the storyline for logistics, politics, psychology, the rocketpack, etc.; this if about survivability. For the story, what are the speed and height constraints that my hero can survive, given that she can wear warm clothing, have oxygen for up to ten minutes and needs to fly around a lot. She will have to go far and high.

Wardrobe is considered modern day, household items, upper-income western lifestyle. The hero has a credit card and knows how to use it, but is no Elon Musk. The only sci-fi is the safe, hand-waved rocket-pack and helmet with oxygen.

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  • $\begingroup$ Explain the size of the rocket, fuel type, speed and steering mechanism. $\endgroup$ – Youstay Igo Sep 23 '15 at 6:39
  • $\begingroup$ Note that atmospheric pressure "at the height of an airplane" is not the same that you feel inside such airplane; modern planes are pressurized and airlines keep the pressure equivalent to (IIRC) 8000 feet. So do not assume your hero may breath normally at 10 km high because he cannot. For comparation, the summit of the Everest is already defined as a "death zone" (you do not get enough oxygen to support all of your body functions). I would put the height limit due to lack of oxygen approximately at those altitudes. $\endgroup$ – SJuan76 Sep 23 '15 at 7:59
  • $\begingroup$ Your super hero would die from altitute sickness long before he reached that height (or be crushed by the acceleration should he rise fast enough so the gas embolics don't kill him). So, unless he has a pressure suit, he cannot rise to these heights and live. It' not jsut the lack of oxygen that kills him. $\endgroup$ – Burki Sep 23 '15 at 12:18
  • $\begingroup$ @SJuan76 - there is oxygen available. $\endgroup$ – Mikey Sep 23 '15 at 17:17
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    $\begingroup$ @Mikey With oxygen provided your rocketeer should be able to safely manage something like 15'000 feet, but i don't have any robust figures at the moment. Without oxygen, a quick climb to 10'000 feet can - depending on some factors, like personal fitness, but also weather (ambient air pressure) - become problematic (i tested that in a cessna on a hot day: as a regular smoker, you already become disoriented, hardly able to read a map, hands and feet tingling...) $\endgroup$ – Burki Sep 24 '15 at 6:46
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Aerodynamic drag, temperature and breathable air are the primary limiting factors. Even with a handwaved rocket pack, the rocketeer has significant challenges at high altitudes and high speeds. High speed-high altitude flight for an unprotected human is going to be uncomfortable at the least and deadly at the worst.

Air

Ten minutes isn't that long of a flight time. If you try to compensate for this by going faster, the strain (as a result of drag) on the rocketeer increases with the square of velocity.

Temperatures

It's really really cold at high altitudes. WW2 bomber crews flying between 20,000 and 27,000 feet regularly encountered temperatures of -30 to -50 F. As you can see from the below table, flesh freezes very quickly in cold temperatures without a breeze. Since the rocketeer wants to fly both very high and very fast, any exposed flesh is going to fresh instantly.

NOAA Windchill Table

(Note that windchill is a measure of how fast your exposed flesh would freeze at that temperature, not the temperature your flesh would actually reach.)

Wrapping the rocketeer up in "windproof" fabrics such as Gore-Tex won't work either because such fabrics are only windproof to a certain windspeed. If the rocketeer is going hundreds of miles per hour, those fabrics won't work. A full body leather windsuit might work though great care must be taken to avoid exposing any flesh to the windstream.

Even with a perfect windsuit, the rocketeer must still insulate themselves against the -30 to -50 F temperatures. Extremities such as toes and fingers are especially difficult to insulate.

Rocketeer Fatigue

Holding one's shoulders square to a 400 mph wind is going to be very tiring, very quickly. There's at least two knock-on effects of this kind of strain. Oxygen use goes up because muscles increase oxygen use when under heavy load thus reducing oxygen stores down from their 10 minute estimate. Second, the higher the rocketeer goes, the more their metabolism will have to kick in keep itself warm.

Given this the physical labors of flying, it's unlikely that the rocketeer will be fresh and spry when he lands.

Realistic Flight Conditions

Have a look at ultralight aircraft. They have relatively low service ceilings and their unprotected cockpits preclude speeds above 100mph.

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At 6000 meters she would begin to need oxygen and at 8000 human life becomes unsustainable, The speed is a bit more solid and will be the focus of my answer. humans can survive up to 9 G's for a few seconds. Astronauts go through 3 G's during take off, but most of us can live going through 4-5 G's. 6 G's or higher for any long amount of time will kill a human. Sorry for the briefness

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  • $\begingroup$ You need oxygen at substantially lower altitudes, since the rocketeer does not spend hours or even days climbing, but minutes at most. $\endgroup$ – Burki Sep 24 '15 at 11:06

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