If You Want a Job at SpaceX, Solve This Riddle

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The latest biography of Elon Musk, by technology journalist Ashlee Vance, provides an in-depth look into how the entrepreneur and tech titan built Tesla Motors and SpaceX from the ground up, often in the face of enormous personal and professional challenges.

For those coders and developers who’ve always dreamed of participating in the space industry in some capacity, and want to work for SpaceX at some point, the biography offers some key insights into the rocket company’s hiring processes. For starters, given the highly specialized nature of the work, SpaceX is understandably rigorous when it comes to recruiting, often targeting engineers and researchers based on their published work; it also sends HR staff to trade shows and conferences to hunt for the best of the best.

As with many other tech firms, SpaceX subjects its job candidates to a battery of rigorous quizzes and tests. “Companies will typically challenge software developers on the spot by asking them to solve problems that require a couple of dozen lines of code,” Vance writes at one point. “The standard SpaceX problem requires five hundred or more lines of code.”

If that wasn’t challenging enough, SpaceX tries to separate those candidates who’re just looking for a job from those with a genuine passion for spaceflight by asking all of them to write an essay for Elon Musk “about why they want to work at SpaceX.”

But the last step might prove the most challenging of all: an interview with Elon Musk himself. Despite SpaceX’s rapid growth, Musk still manages to meet with key personnel before they come onboard. Often branded as mercurial and brilliant, he reportedly suffers no fools, and likes to pick every brain in the vicinity. “The tales of engineers who have interviewed with Musk run the gamut from torturous experiences to the sublime,” Vance writes. “He might ask one question or he might ask several.”

During that interview, Musk likes asking candidates a particular brainteaser:

“You’re standing on the surface of the Earth. You walk one mile south, one mile west, and one mile north. You end up exactly where you started. Where are you?”

If you can answer that riddle successfully, and pass all of SpaceX’s other stringent tests, you may have a shot at launching rockets into orbit.

121 Responses to “If You Want a Job at SpaceX, Solve This Riddle”

  1. C L Couch

    I think maybe you’re at the magnetic North Pole. If you’re using a traditional compass to set your direction(s).

    I tried posting this before, and it didn’t appear to work. So I apologize if this comment, here, is redundant.

  2. Start 1 mile + (1 mile / 2pi) north of the south pole, where there is land to walk on. You walk 1 mile south and can now walk west in a circle with circumference of 1 mile to get back where you started walking west, and walk 1 mile north to stop where you started.

  3. The North Pole is partially correct, but I suspect if you gave that answer you’d not get the job. There are also an infinite number of places near the South Pole: If you started a mile North of the place where the circumference of the Earth is exactly a mile, then your mile long walk West circumnavigates the Earth and the walk back takes you back to where you started. Then there are the circle where you circumnavigate twice, thrice, and so on, right down to the point where you nearly get to a mile North of the South Pole, and it’s arguable about whether you can spin on the spot for a mile going West before getting back to where you started.

  4. Ryan M

    Anywhere on earth, if you are using a non eucledian surface, like the surface of the earth, you can make a triangle with 3 right angles, walking the path described, and end at your starting location.

  5. There are other solutions…..

    If you start about 1.318 miles north of the south pole, you can go south 1 mile, do a 1 mile loop around the south pole, then go north 1 mile, and you’re where you started. So “North Pole” is A correct solution but not the ONLY correct solution.

  6. Scott Norris

    There are an infinite number of circles around the south pole whose circumferences are (1/n)th of a mile, where n is an integer. Walking one mile west along these circles will cause you to circle the south pole n times, bringing you back to where you started. *Any* position one mile to the north of *any* of these circles is a valid solution.

  7. Payne

    “You’re standing on the surface of the Earth. You walk one mile south, one mile west, and one mile north. You end up exactly where you started. Where are you?”

    If you are at the Utah Salt Flats, and you walk one mile south, then one mile west, then one mile north, you will approximately 1 mile west of the starting position, but this distance is not approximate you would need to use calculus in conjunction with each sq. footage of the radius of that exact point on earth then factor that into the distance equation but would be very close to 1 mile west on flat ground. if you were on mountainous terrain and walked south,west,north for one mile each the change in distance from starting position would put you somewhere between 0-3 miles away from the starting point. If each cardinal direction had radically different terrain then the point will always be within 180-270 Degrees. Another consideration is the utility of direction finding. If someone were to use a map in an environment with visual depictions of cardinality etched into the environment and said environment was flat terrain then a walk from point A1 to B1, then point B1 lies approximately 1 mile west of point A1. Then based on the the Magnetic poles the distance to point A2 to B2, B2 would be roughly within the same region as B1, but with each attempt B2 would be at different points on the earth because of a variety of different reasons but, not limited to instrument error and changes in magnetic field. Using a Global Positioning Device with a high gain antenna would yield different results than B1,B2. Since most GPS clients ignore factoring in the terrain that would need to be walked B3 would be a rough estimation of the walking distance but, would be within 350* feet of the location and (A3 to B3) 180-270 degrees away. There are always exceptions to the conjecture. At any arbitrary point the following will be defined for a topography, “C” is flat as the salt flats in Utah moving south to point “D”, D is the highest point of the terrain which is a hill with a diameter of 2 miles, walking west down the hill to “E” which resembles the flatness of “C”, then north to “F” which is equal to both “E” and “C” the direction from “C” to “F” would be somewhere between 90-270 degrees assuming that point “D” has an elevation of a half mile to a mile. so stating that you could end up south or north the starting point is a real possibility if “D’ has an elevation higher than a half mile. So saying that it is also true for any change in cardinal direction that there could be an elevation change that could put the direction from the starting point to the end point anywhere within an approximate 1 mile diameter thus, being the best case scenario, the worst case scenario assumes that you’ll travel 1cm (within the diameter at any fixed point) from point AB due to unknown elevations with sinusoidal topography. There are infinitely many solutions to the problem that are within 1 mile pointing west of the end point and any topographical deviation from that point shrinks the diameter and changes the cardinal direction from A to B.

    topics not explored: temporal disturbances in magnetic poles, curvature of the earth, pole shifts, paths of least resistance, (Reimann sums or Integrals or Optimization) for each square inch traveled, ignoring gravity,

    “Climbing is unadulterated hard labor. The only real pleasure is the satisfaction of going where no man has been before and where few can follow.”
    -Annie Smith Peck

  8. George

    Still stuck on Earth. Elon’s goal is to get us off this planet and by being a member of the SpaceX team, you share this idea and understand that the human goal should be to explore beyond the gravity of our birth planet.

  9. Deepak

    the answer is : on the surface of earth.
    Explanation : surface of earth is flat. 1 mile south means you are going 1 mile below the surface. Then 1 mile west inside below but parallel to surface. Finally , 1 mile north means you are coming up to the surface. So i started from surface of earth and came back to surface again.

  10. Chris

    I don’t believe that it is possible to end up “exactly where you started,” and even if it were it is certainly not calculable with the information provided. I suppose that depends on your definition of “where you started” and the level of precision implied by “exactly.” If ending “exactly where you started” implies absolute position vs relative position, any “walking” done would need to counteract the rotational velocity of the earth’s surface, orbital velocity of the earth relative to the sun, moon and other objects having mass, translational velocity of the ever expanding universe, as well as a host of other factors. Unless of course you are “walking” at the speed of light and leveraging time dilation to force the magnitude of the displacement caused by any outside velocity to zero. Depending on the level of precision implied by “exactly” one could argue that even at the speed of light you would still experience time (~1.61×10^-5 Seconds) as you transit three miles and in that time the sub atomic particles that make up the atoms that make up the molecules that make up the … that make up you can change their orientations and thus you are not “exactly” where you started.

  11. Ravi C

    You can be anywhere on Earth. All you need is walk in such a way that you make an equilateral triangle. Just 3 sides of equal 1 mile each. You will end up back at same place. But its a good question Elon !! Loved it !!

  12. Greg B.

    “anywhere on Earth” is wrong. If you are 0.5 miles from the south pole you cannot even go 1 mile south. I believe the north pole is the correct answer.

  13. answer: three (3) miles from your starting point.

    explanation: assuming the earth rotates 1 mile per hour towards the east, each mile you make puts you exactly one mile to the west so by the time you move to west, south, and north, you would’ve travelled three miles to the west.

  14. Don Kingery


  15. Clint Staley

    It’s an old riddle, of course, and many people already have the
    trick-answer “The North Pole” memorized.

    Interestingly, there are a lot of other such locations at various distances from the South Pole. Any location that is 1 + 1/(2*pi*n) miles north of the South Pole will also work (where n is any positive integer). Walk one mile south from such a location, and you’re 1/(2*pi*n) miles from the pole. At this very nearly polar location, the circumference of the planet is just 2*pi * (1/(2*pi*n) = 1/n miles. Walk west one mile, and you’ll circle the pole *exactly* n times, ending back up at where you started circling. If you then walk north the final mile, you’ll be at your starting point, after having made n “trips around the world”.

    These rings of locations are infinite in number, approaching solid density as you reach the ring one mile from the South Pole. Whether the ring exactly one mile from the pole qualifies is left as an exercise in real analysis 🙂

  16. Punnisher

    Actually my first thought was the north pole but that did not make sense , so you must be at the equator because of the earths rotation , going south then west all while the earth is rotating and your walking at about 1mph so thats 1 hr south 1hr west and 1hr north , that is 3hrs of earth rotation or 45 degrees of rotation in 3hrs which will put you right where you started 3hrs ago

  17. Robert miller

    The only possible answer is the north pole. If you started 1 mile north of the south pole and went south for one mile then yes you are now at the south pole. But now you cannot go east or west. The only way you can go is back north in any given direction.

  18. Larry B

    The answer is – My House. I just tried this late last night – and I ended up at my neighbor’s house with his wife while her husband was at work. Her husband came home and caught us – he called the cops – and the police came and drove me back to my house ( I did not walk) – ending up right where I started

  19. where am I? On top of a mountain. That and still standing in front of you in your office answering these silly questions. Now lets figure out how to control gravity.

  20. Either Vegas or Jersey.

    Thousands of people, trying to get out of Jersey, who can’t. And, what happens in Vegas, STAYS in Vegas.

    Seriously, though? The answer requires you to ask Musk what he means. To take the forbidden step of clarifying what he is looking for. More than anything, he probably doesn’t want people who THINK they know what he wants expending time and resources. When in doubt, always clarify. THEN make the magic happen!

    Such errors in understanding are why the Hubble Space Telescope was launched into orbit with a screwy mirror!

  21. You’re at magnetic North Pole. If you were at the South Pole, you simply couldn’t go South as required in the first step 🙂 When standing on the South Pole, anywhere you walk would be considered North; you can’t go “more South”. Conversely, if you are instead at the North Pole, you can indeed go South in step 1, turn to the West and walk, then turn North and walk to return to your original location. Since you’d be tracking your direction with a compass, rather than just turning ~90 degrees, you’d have walked in a triangle.

  22. garthbock

    It all depends on who is walking……
    A man…..lost…….
    “I am not going to ask for directions I know where I am going !”
    A woman….delayed…..
    “I would have been there but I saw a sale going on and I just had to stop !”

  23. You’re, on the North Pole.

    You can only go south, after that east or west makes no difference. When you turn north you are headed back from where you started.

    You walked in a triangle.

  24. Walker Moon

    I figured the North Pole. I didn’t realize some of the other answers also apply, like the ones near the South Pole. That’s pretty cool and I learned something.

    But there are also constraints regarding the question, like walking around a couple of miles implies you are able to walk – i.e., the place has to be on land or on enough ice to traverse by walking.


  25. Sherman Adams

    My starting point being the “surface of the earth” nowhere specific ,do all my walking in all directions,no matter where I end up ill still be right where I started” the surface of the earth”

  26. Chris B.

    I believe that with the information given the only correct answer is “on the surface of the Earth” since that was implicitly stated as being the starting condition. Because no coordinate system was specified, there is no way of knowing if simply returning to the same point on the Earth’s surface constitutes returning to “exactly” where you started relative to the coordinate system being used. If for instance the coordinate system selected is relative to Earth’s motion around its axis or Earth’s orbit around the Sun or heck even the solar system’s motion through space around the center of the galaxy, returning to the exact same point in spacetime is impossible. Remember, time is a dimension too. So I think given the specifics of the problem it is not possible to resolve it any better than “on the surface of the Earth” which has to be correct as it was implicitly stated as a presumption in the beginning of the problem.

  27. Zaphod

    The only way I’d be interested in the job would be if:
    A. I get to work from home. (AKA not Mars.)
    B. I get to choose my hours.
    C. The job must come with unlimited vacation time.
    D. I get full and comprehensive health benefits including dental.
    E. The job must pay more than 160K.
    F. I’m not required write more than 120 lines of code an hour.
    G. I need to have a decent retirement package.
    H. I want a 5 million dollar life insurance benefit.
    I. SpaceX must pursue me.

    The best answer I could come up with was, 90° North.

  28. “Where are you?”
    I am in your office applying for a position at SpaceX and since you make statements that use antiquated British units of measurements instead of the internationally accepted SI Metric units maybe SpaceX is not the company for me.

  29. joe dechant

    you have to be at the north pole if you are at the south pole any direction you walk will be north and at the north any direction will be south then if you walk west or east either way will work then back north at the north region you will end up back at the north pole you can rule out the south pole because you cant walk south from there

  30. Not Elon

    For not it’s worth, I think Oni’s answer is closest to the mark,

    I believe what Mr. Musk is looking for is not only the logic to find the solution but the awareness to ask for clarification of vagaries when necessary. What I mean by that is that there is no frame of reference explicitly stated for what “You end up exactly where you started” means. The question begins with “You’re standing on the surface of the Earth” so we can probably assume that’s the frame of reference but I would still ask for clarification. Of course asking such a question might also be a disqualifier because even though unwarranted assumptions can be killers you have to accept some level of assumption to get anything done. The trick is to find the right balance.

    If the frame of reference is the surface of the earth, then the (rotational) North Pole, and the “one mile plus distance to circles with whole integer divisors of a 1 mile circumference from the (rotational) South Pole, both work. Even in this case, we are making assumptions (ignore that the earth is not a perfectly oblate sphere ,blah, blah, blah) but for a problem at this level it’s a reasonable one.

    If the frame of reference is not the surface of the earth then the answer is undefined (from a practical standpoint nowhere). Then, “the surface of the Earth” is the only answer I can see.

  31. Phillip kabler

    You are at the north pole. To the The folks who indicated the south pole ,Damn hard to go south from the south pole,Going east or west is a red herring because it makes no difference,it,s a circular route.Think aviation

  32. good lord, I think humanity is in trouble. I think we need to go back to the original theory of teaching people something while we are still in school. lol.

    There is a lot of thinking going on here, and at least that is good.

    anyone get a job there yet?

  33. michael crum

    you are still on the surface of the earth were you started ! what happens when a celestial being in organic form go’s back to being celestial ? . or what happens when beings from the stars go back to the stars ? these are the questions I hope he answers soon.

  34. sherri

    What some are not understanding is that even though the earth moves, WE are also moving with it! I don’t know the answer but just wanted to add that tidbit of information in. I think people are over-thinking this…lol. I do know that I wouldn’t be at home if I were to do that walk from my house.

  35. the answer is………….given to you in the question and is different for everyone, unless 2 are standing in exactly the same place when they begin.

    Always understand the question before you try to answer it.

    I would love to see the author develop a web site dedicated to this kind of stuff. It is sorely needed. human minds are not being challenged enough today, we just accept what we hear or read.
    Thinking and deducing is becoming a lost art

    I did join a site online that is meant to sharpen up the mind, but I just can’t remember the name of it at the moment!
    When can I apply or should I wait to be invited?

    lov you guys…allan

  36. We need more information to solve this don’t we.

    what direction and speed does the earth rotate?
    How fast do you walk?
    Do you stop anywhere to eat or drink or take a nap along the way?
    The real stickler is… does the earth wobble?
    And lastly…. Can you remember where you started from? This is critical information and should be memorized prior to beginning this ,because there are sooo many other variables that enter into it.
    This is important for life lessons too. Always remember where you started from. It keeps us humble.


  37. Terrance van gemert

    “You’re standing on the surface of the Earth. You walk one mile south, one mile west, and one mile north. You end up exactly where you started. Where are you?”

    North or south pole it does not matter which..

  38. While there are “correct” answers, I believe, along with others, that the one being sought is “on the surface of the Earth.” Why? because every person being interviewed will be familiar with the question and either jump to “the North Pole” or “somewhere North of the South Pole, where….” I believe the question is meant to test whether the person is stuck in the box overthinking a simple question in order to prove their genius, or can step back out of the box and see the simplicity in the big picture…with so many possible “mathematically correct” answers, the only single answer that works is “on the surface of the Earth.”

  39. KCKunnanz

    “On the surface of the Earth” is barely more accurate than saying in the Solar system. Or a vague reference to the present time in, if considering both time and space.

  40. brandon kinnear

    Did anyone read the article!?
    I did, thanks for writing it!
    The question in the riddle is “where are you?”, Which is answered just before the question…
    ….”you are were you started,” and depends on where you started.

    It’s a philosophical question, and it’s response is a look through a window, in the “resume”, intended to expose the Being within.

  41. Siddharth

    I think the truth must be fundamental and original .However,the roads built -up upon that truth can be different depending on choice.In that case ,and by this riddle you are probably playing with different sets of quadratic equations ( may be linear ) whose both roots are 1.

  42. You are on a treadmill that every 30.7 minutes rotates by 90 degrees clockwise and going at a speed of 1.96 miles per hour on the international space station. Obviously the best answer.