Built on Facts

Physics, Rockets, and Iron Man

I’m not quite convinced Iron Man is entirely realistic.

i-8d068023428e723356163f039947500d-IronMan.png

“Proposterous!”, you say, “Hollywood makes its superhero films to near-documentary accuracy!” No, hear me out. Iron Man can fly, using rockets in his hands and feet. We know from the commercials that the suit can in fact fit in a briefcase and be carried around by hand, so as an estimate let’s say the Iron Man suit + Tony Stark weighs 200 pounds even. In more proper physics-style units, that’s 889.6 newtons. Just to hover, let alone fly into the air at high speed, his rockets are required to generate at minimum 889.6 newtons of force.

Force, as we know, is equal to the rate of change of momentum. Momentum is conserved, so the force required to keep Tony aloft is equal to the change of momentum of the rocket exhaust as it leaves his thrusters:

i-1a518f2655b02f9d30ddb0c8226ad8eb-1a.png

And the momentum is just mass times velocity:

i-88516ca505d84f969b7ab15a965c3fb3-2.png

But we’re interested in dp. the rate of change of momentum. The exhaust velocity v is constant, so dp = v dm, where dm is the amount of mass the rocket spits out in the time interval dt. In other words, we can rewrite the force equation with that substituted in, and dm/dt will be the rate at which the rocket spits out its fuel through the thrusters:

i-d18063683dcc0d42b9be45451a84d1e3-3.png

So what’s the exhaust velocity? Based on the fact that he doesn’t deafen everyone standing near him when he takes off, I’d say it’s subsonic, but let’s be generous and say v = 330 m/s, which is about the speed of sound in air under normal circumstances. Solving for dm/dt, I get:

i-8d7070ce28f0af28047c7a5fb8246d53-4.png

Which is a pretty darn hefty burn rate. We know from the fact that the suit is portable that there aren’t all that many kilograms of fuel in the suit to begin with, and even if there were then the thrust (and the burn rate) would have to be higher to get the stored fuel off the ground as well. It’s diminishing returns, and one of the reasons rocketry is so expensive. It looks like in real life Tony Stark would probably take off dramatically before ignominiously sputtering out and crashing in a heap. This, incidentally, is one of the major reasons personal jet packs never became practical. (That and the whole “certain death” thing if anything goes wrong.)

Switching to rocket fuel with a higher v is a possibility. A good rocket fuel might have an exhaust velocity of 4000 m/s, with a corresponding burn rate of 0.22 kg/s, which is better. Maybe Iron Man then has a couple minutes of flight before having to call a refueling time out in the heat of battle. The noise factor would be tremendously antisocial to everyone in the vicinity, but that might be an acceptable price to a superhero saving the day. Or showing off at sporting events, whatever.

Alternately the suit might not use rockets at all. Instead it could be a jet engine, pulling in air from the environment, heating it and spitting it out the rocket thrusters. With an appropriate energy source, this could go indefinitely so long as there’s air around. The suit doesn’t seem to have visible air intakes though, and if the suit has been shown working in space in the comics (confirm/deny, Marvel fans?) then that explanation is right out.

But I have to admit if someone did manage to invent and market a personal rocket suit I’d be the first in line.

Comments

  1. #1 Winawer
    April 29, 2010

    It seemed to me that the first film vaguely implied that the propulsion was electrical – ion / plasma drive? I could be wrong on that, though.

  2. #2 Steve
    April 29, 2010

    The glowing doohicky on his chest generates extremely high circulating currents in the suit, which is made from a high-temperature superconductor. Iron-man is, in effect, a powerful electromagnet. Tony wrote a complex algorithm that lets the suit hover through interaction with the earth’s magnetic field (much like a maglev train). The jets in his hands and feet are for steering.

    This same principle explains why he doesn’t visibly recoil while shooting rockets at the bad guys.

  3. #3 Jody
    April 29, 2010

    I think that the latest explanation for Iron Man’s flight abilities are that it’s an outgrowth of his “repulsor” technology, which utilizes some kind of charged particle field to push things out of the way. Directed at an enemy and they go hurling away. Directed at the ground and he can fly through the air.

    Of course I have no idea of how any of that works.

  4. #4 Andrew S.
    April 30, 2010

    Yeah, Iron Man flies with his ‘repulsors’, whatever that means. It’s not typical jet propulsion.

    Also, the suit in the briefcase is an emergency-use variant – it’s visibly less bulky than the normal one.

  5. #5 Matt Springer
    April 30, 2010

    Repulsors make more sense from an in-universe perspective, but you wonder why they leave a trail of rocked exhaust (as in the screenshot above) and make a traditional “rocket” sound.

  6. #6 WcT
    April 30, 2010

    @Matt at 5

    They do that because it looks cooler. Duuuh!

  7. #7 nanoAl
    April 30, 2010

    They push the air so hard that it lights on fire of course!

  8. #8 wfr
    April 30, 2010

    Just to hover, let alone fly into the air at high speed, his rockets are required to generate at minimum 889.6 newtons of force

    Are you implying that, in order to fly, your thrust-to-weight ratio must be greater than one? Hmmm.

  9. #9 Uncle Al
    May 1, 2010

    If you saw the movie… Stark as prisoner cast a palladium wire loop at a critical moment. Iron Man is powered by cold fusion. Energy is no problem. Working fluid is a problem.

    That Iron Man can raise a palm and repulse a tank without Newtonian reaction or counter-thrust suggests the suit is rooted in vacuum zero point fluctuations. Reaction thrust is then fine tuning with air as the working fluid and perhaps coolant. Don’t drive a brad with a sledge hammer.

    Two big questions: 1) How does the man inside get pounded without transforming into a particuarly poor grade of ground chuck like an asstronaught taking a Байконур/Baikonur sleigh ride atop an Ares booster? 2) How does he pee? One sees a lot of sharp edges OTOH and a lot of wiring OTOH.

  10. #10 Carl Brannen
    May 1, 2010

    “you wonder why they leave a trail of rocked exhaust”

    That must be the plume of waste heat from his energy generator. That’s a lot of energy. It’s directed downwards so it doesn’t get in his view. Plus there could be some residual force.

  11. #11 Matt Springer
    May 2, 2010

    @8: For the scenes where he’s flying vertically upward, anyway. In other cases he can improve on this, especially with wings.

  12. #12 Riley
    May 7, 2010

    “you wonder why they leave a trail of rocked exhaust”

    As is so often the case when faced with the task of evaluating the technological genius, Thomas Edison, Steve Jobs, Tony Stark, we under evaluate the role showmanship as an essential component of success. Clearly, Tony Stark recognizes the importance of product branding.

  13. #13 Aaron
    May 11, 2010

    @#9: I suppose he has some sort of “inertial dampening”. Considering the other crap he pulls off, this is right up his alley.
    They bring up the “How do you pee?” question in the movie. It was rather funny.

  14. #14 Ben
    May 11, 2010

    I also always figured it was jet propulsion. I mean, he’s got megajoules of energy coming out of his chest, why not?

    I’ll ignore heat issues…

  15. #15 Peter
    May 14, 2010

    It’s an Arc Reactor you fool! They made up a fictional power source precisely so fans wouldn’t over analyze it.

    In the 2nd movie, he makes a new element. Get over it.

  16. #16 edward
    June 2, 2010

    can analysis about the movie iron man 2 to me by using the phyiscs?

  17. #17 rogers kiome
    June 2, 2010

    send me messages

  18. #18 Anonymous
    September 7, 2010

    gay

  19. #19 Anonymous
    September 7, 2010

    NERDS. get out of ur moms basement. get a girl and a life

  20. #20 Anonymous
    October 29, 2010

    suck penis u fagit

  21. #21 <-This guy
    January 15, 2011

    Ok, arc reactor = TFTR = Tokamak fusion test reactor. Just a little guy though… and actually the model that is in Tony’s chest in the movie looks strikingly similar to the new ITER diagrams as in here: http://4.bp.blogspot.com/_q1YbG78HW6A/TI5CGeMqnrI/AAAAAAAAAHU/gpD7rxHDzdU/s1600/iter-reactor-layout.jpg

    Also, “rocket trails” = condensation? vapor trails?

    And lastly – why do this to yourselves? You will NEVER wear IM armor, nor will you see anyone else wear it in your lifetime. This is fiction, and for entertainment purposes only. As some have stated already, get a life. But also – don’t lose your imagination and creativity!

  22. #22 ^-That guy
    February 8, 2011

    “Also, “rocket trails” = condensation?” Vapor Trails FTW! Rush at Bell Center Montreal, April 20th!!

    “Stark Industries new repulser technology” if it’s “new” to Tony Stark, than I’m willing to bet it’s not something that your feeble minds can grasp. And at that stage it was a top secret military weapons sale (for the Jericho missile). But whatever. I would imagine that the “repulsers” he uses, take alot of energy to run, due to the fact that Tony initially gets the palladium from 12 seemingly generic “Stark Industries” rockets that supposedly use repulsers in the cave of the first movie. My point being, each of the rockets use repulsers, and I would guess they weigh alot more than Tony and his suite, yet they use 1/12th of the palladium even less than that when he gets his MK2 chest piece. While yes, missiles are 1-use explosive devices, their weight is still an incremental factor.

    The repulsers may be focal points which simply channel immense quantities of energy (electricity) and like the ion propulsion system on the Deep Space 1 probe(?) would fire ions out in the opposite direction, but instead of using a heavy gas like Xenon, the repulser uses so much electricity that it can simply use the air in-front of, and around it while still creating a much more powerful thrust than the Ion engine previoulsy mentioned. In this case, we’re talking about ALOT of energy. Though while Deep Space 1 runs on solar panels, the Palladium Arc Reactor runs at 3gigajoules per second (aka 10,800,000,000,000 watt hour) approximately. That would run a city of over 150 thousand homes for over a year, and then some! Though my math may be off… Still, if I’m correct, that would be more than enough, if engineered properly, to easily propel a man through the air at mach whatever for X amount of time.

    I’m just trying to put into words what may be possible, and what is, for now, just science fiction. I hoe I’ve explained this thought of mine thoroughly enough. If you have a problem with it, please correct, but never cop out with a statement like “This is fiction, and for entertainment purposes only.” no matter how prefaced it may be, that’s just horse shit. Oh and try telling it to Martin Cooper, Friedrich Stradonitz, and the more obvious others. While not trying to be a super nerd who lives in his mom’s basement trolling on the physics forums, but never discourage the hashing about of thought and theory in any situation, no matter how frivolous or seemingly insignificant the topic. And not trying to be braggadocios or seem conceited (both are characteristics which I despise) but as I sit now at my computer, I am in a 2.5 million dollar house, one of many houses which I have earned by hard, long work, I am an active and avid long distance runner and all round sportsman, yet I read comics regularly, have finished Gears of war 1 and 2 consecutively twice! As well as Assassin’s Creed 1, 2, and brotherhood, Uncharted 1 and 2, and almost every game worth playing, I am a GAMER! And I am a NERD! I do not live in my mother’s basement, and certainly do not need to “get a life”. I’m not saying this in my personal defense, but in defense of all my inter web kinsmen, making such generalizations against us is insulting, and must be discouraged. POWER TO THE PLAYER! POWER TO THE NERD

    Thank you for your time.

    PS: Please do get out of your mom’s basement, and get a job.

  23. #23 Ayush
    March 12, 2011

    if the mass of suit can be brought less using a special element and better fuel can be used than ( noise reduction is not a hiccup any more it can be done easily )iron man can fly smoothly, so no problem!

  24. #24 Tony Edward Stark
    September 20, 2011

    These calculations are bit too simple for Iron Man…

    Itz gonna be me mAking the Suit =p

  25. man, you are too meticulous. that’s just a movie. have fun

  26. #26 Wow
    November 11, 2011

    I find it ironic when someone in their grubby boxers with no life has to pretend that everyone else has to be living in their mom’s basement and moreover, that they will obey the exhortations of this grubby little parasite and get out of this supposed mom’s basement.

    It’s amazing what morons will do to make themselves feel better, isn’t it?

    PS @25: this is fun too. Why do you think books like “The Physics of Star Trek” sell? Because it’s fun. Maybe you should take that stick out of your arse and get a sense of humour, hmm? Or at least realise that you are not the arbiter of what is fun and what isn’t.

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  28. #28 robin
    February 14, 2012

    above all leave iron man. Can we create a flying suit which can cover large distance like 10000+ km and able to land easily?
    Are u on facebook?

  29. #29 robin
    February 14, 2012

    above all leave iron man. Can we create a flying suit which can cover large distance like 10000+ km and able to land easily? And we can control it.
    Are u on facebook?

  30. #30 robin
    February 14, 2012

    above all leave iron man. Can we create a flying suit which can cover large distance like 10000+ km with great speed like jet and able to land easily? And we can control its direction and speed.
    Are u on facebook?

  31. #31 Sesli Chat
    February 20, 2012

    10000+ km with great speed like jet and able to land easily? And we can control its direction and speed.

  32. #32 Akshat
    April 6, 2012

    How can one explain all these facts by just classical physics? Considering the fact that everything inside the reactor on Tony’s chest was fusion…. an essential phenomenon exhibited by the quantum particles. And if you’ve passed your 12th grade… you would know well enough that classical physics are just not valid for quantum particles.
    But I guess with the technology we have right now, the suit is just a myth.

  33. #33 nick
    April 16, 2012

    It is not rockets it is repulser which is a neutron firing device, powered by the arc reactor which runs on cold fusion which a by product of cold fusion is neutrons