Mark Frauenfelder at 6:35 pm Thu, Apr 4, 2013
ADVERTISE AT BOING BOING!
D.S. Deboer says "Check this out! It's neat and really helped me grasp how far away Mars is. (Hint: It's really, really, really far away.)"
How Far is it to Mars?
(Ben shared this in the Google + Boing Boing Community. Join us there for fun link sharing and conversation!)
*starts drawing up plans for hyperpixel drive*
Need to add animated file of astronaut climbing out of landing module, looking around, saying, “Meh,” and turning around to head back.
Shoulda taken a left turn at Albuquerque.
Bugs pronounces it, “Albukoikie”.
I don’t think Pismo beach is quite this wide
Very cool! Needs Phobos and Deimos. Since our moon is represented.
No use. At this scale they would be less than 1/5th of a pixel and 1/10th of a pixel respectively.
It’s so far I closed the tab before i got there
You just ruled yourself out as a candidate for the Mars mission. You clearly don’t have the patience to make the trip.
Are you kidding? He just perished in the vacuum of space. Or she.
I like using marbles for this. 3 marbles, each one twice the diameter of the one before it.
Earth is 30 marble diameters away from the moon, and mars is 142 times that distance away. prop the marbles up on a signpost or a mailbox, and the model fits within a city block.
(It’s fun to find a tiny grey marble, a normal sized red marble and a big blue marble. You could then use beach balls for the gas giants if you wanted)
On the other hand how far away is it in energy terms? If I took eight months to drive a boat to the US, and it takes eight months to fly a spacecraft to Mars, which vehicle uses less energy for the same mass?
It depends on the starting conditions but I reckon you could get to Mars with less energy, because there are fewer losses along the way.
I could go into the physics, but let’s think about it with common sense–let’s ask how much fuel is needed (since the point of having fuel is to convert as much of it as you can to work). For a manned mission, it is expected that multiple rockets on the scale of the Saturn V will be needed to assemble and fuel the spacecraft. We are talking about several 100 m+ sized rockets filled to the brim with rocket fuels. A boat of an equivalent size as the finished spacecraft would be able to fit into the fuel tanks. So unless the boat needed several refueling in the middle of the ocean, there is no chance that the energy values are even comparable.
But consider vehicles like the Voyagers. The ability to conserve momentum in space means that they ultimately make better use of their initial load of kinetic energy.
That initial load of kinetic energy is the key. You don’t get to escape velocity without a bigass rocket pushing you there. And any fuel you carry has to be pushed up with other fuel. For the Voyager example, a less than one tonne probe required a 630 tonne rocket.
And as far as the Voyager probes, I’m not sure what you mean by conserving momentum. The momentum of the Voyager probes have changed significantly over their missions as they have interacted with different gravitational potentials (and used slingshot maneuvers).
You don’t get to escape velocity without a bigass rocket pushing you there.
Thats an implementation detail. For sure there is an energy cost in achieving Earth and partial Solar escape velocity, but there are better ways to do that which we are finding. If you total up the cost imposed by gravitational fields (remembering that potential energy is yours forever), and compare that with losses to friction into the future, you might still be ahead.
And as far as the Voyager probes, I’m not sure what you mean by conserving momentum.
If I pushed a voyager probe into the Pacific, its initial momentum would be lost in a second or two. In space that momentum would not be lost to friction.
Okay, let’s ignore the rocket equation and pretend we have a magical system that, without violating the conservation of energy or using the rocket equation, can with 100% efficiency put an object at escape velocity, which is 11.2 km/s. Using KE = 1/2 m v^2, we have 62.7 MJ/kg or 62.7 GJ/tonne. Let’s have a 100 tonne spacecraft, so the total enegy needed is 6.27 * 10^12 J.
Now, let’s pretend we have a petrol engine on a 100 tonne ship. Isooctane has a standard enthalpy of combusion of around 5.46 MJ/mol. Converting to mass and volume, we have 33 MJ/L. What would 6.27 * 10 ^ 12 J buy us in fuel? 190,000 liters. And that fuel would have a mass of 131 tonnes, more than that of the ship itself.
Conclusion: your point is refuted by absurdity.
Escape velocity is purely a measure of the amount of gravity to be overcome. It would only apply to objects fired from a gun or other device at ground level, where the object has no fuel/motor/balloon to apply further upward force.There is no need to reach that escape velocity to get into space, you just have to keep going up/out.
I would say rather that despite the fact that it is measured in units of velocity, it doesn’t represent an actual speed. Rather it is acceleration multiplied by the time over which that acceleration occurs. So you get t times X / (t squared) The t on the top of the fraction cancels one of the t’s on the bottom. So the UNITS are X/t or velocity.
What matters is the kinetic energy. You need to escape the gravitational well of the Earth. Escape velocity is one easy way to describe this. But in any case, the energy requirement is the same.
Particularly with a boat that takes eight months to drive to the US from anywhere on this planet.
Rowboats are faster than that.
It better be far away or our orbit would’ve been perturbed a long time ago.
The app nicely demonstrates the distance to Mars, but there’s also a difference in velocity.
If the app were to show that, the image of Mars would track to the right and be gone by the time you got there.
* * *
The one “fun” course I took at CMU was a policy course on space exploration. The professor gave us an accelerated grounding in the physics and technology of space travel so we could actually make informed decisions. You know, instead of wanking about Final Frontiers and Great Destinies and Not Letting China Get There First and such.
As best I recall after fifteen years: Going to Mars means entering an elliptical orbit around the Sun the intersects Mars’ orbit and Earth’s orbit. You make a “burn” to reach escape velocity and enter the transfer orbit, another to exit it when you arrive at Mars, with more velocity changes required to actual get into an orbit around Mars.
You have a wide variety of orbits to choose from; the one traditionally considered the most efficient — requiring the least change in velocity — is the Hohmann orbit. An ellipse with Mars’ orbit at the maximum distance from the Sun and Earth’s orbit at the other end. We plotted a Hohmann orbit based trip to Mars in class. We came up with a total velocity change of 20 km per second.
In practice NASA uses complex slingshot orbits to take advantage of other body’s orbital velocities. And on arrival, aerobreaking is used to match Mars’ orbital velocity and get into orbit with a minimum of actual fuel usage.
If you want to get to Mars fast, for example so your crew spends less time in microgravity and exposed to solar flares, you use a faster, more elliptical orbit. Getting into and out of that orbit takes a great velocity change.
Yep. Minimum energy tends to be maximum time. And yes, in general, heat shields to leverage atmospheric drag are usually lighter than fuel for the same change in velocity. For most missions, getting there is only part of the problem. It take approximately as much energy to go from Earth orbit to an orbit that intercepts mars as it does to slow down from that speed to Martian orbit.
I didn’t realize how many stars there were between Earth and Mars
And why are we (h sapiens) going there? The coolest (and most appropriate) way to explore other planets is via unmanned probes-exactly what Curiosity is doing at this instant on Mars! Besides, prolonged 0 G and ambient gamma radiation will be murder-literally-for unfortunate space travellers (calcium resorption; regarding radiation, the incidence of cataracts for Apollo astronauts (voyages<1 fortnight) is almost 100% http://science.nasa.gov/science-news/science-at-nasa/2004/22oct_cataracts/
Of course, people should just stay at home and let the robots have all the fun. And, while we’re at it, what was with those fools who would go on long sea voyages of exploration? Scurvy, weird diseases from other countries, shipwrecks… what were they thinking?
Probably thinking that there wasn’t really an alternative to them or people like them going personally. The point is that isn’t the case anymore. It’s like saying we don’t really need anesthesia to amputate limbs because in the Olde Heroick Days patients used to just take a slug of whiskey.
Along the way, half way to Mars, the screen turned white.
I think my space ship exploded.
It’s happened to me twice now, in Firefox. I like to think it’s that the travel velocity is so fast that the very fabric of space suddenly tears.
Thank the gods I don’t have to scroll to Mars. What a drag.
7000 pixels/sec is roughly three times the speed of light at that scale.
The space between the planets is not the only issue, what people always forget is the radiation out there.
Curiosity had a system to record the amount during the trip, I never heard how dangerous for humans it might be…
Someone should edit the code and have it show wealth inequality in the USA.
That’s awesome! I built something like this (sans the sweet animation) years ago for school that set the diameter of Pluto to 1 pixel and based everything off that. http://kevinfreitas.net/projects/solarsystem/
…Before they kicked Pluto out of the club like Ceres, I’m guessing.
I want a version that shows the distance to the nearest star. So when people get so very excited about another discovered exoplanet they have some real idea of how far away they actually are…
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