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3 days to Mars. How fast?

ImmaStegosaurus!
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ImmaStegosaurus!

ImmaStegosaurus!

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I have ran into claims that new witchcraft engines could get us to Mars in three seconds*. These claims do not care to mention if three days include deceleration or if it's just a fly past. I'm not smart enough to calculate acceleration required or final velocity near Mars but I feel brain matter is very much present on these forums.

So, assuming that 3 days claim includes deceleration for half the distance and that things go wrong at worst possible moment in mid way I'd ask how fast would a spacecraft shoot past Mars if braking was not possible? How far would this velocity take the craft and would it escape our solar system?


* Typo but too funny to fix!

Edited by ImmaStegosaurus!
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PB666

PB666

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  On 3/27/2016 at 1:54 AM, ImmaStegosaurus! said:

I have ran into claims that new witchcraft engines could get us to Mars in three seconds. These claims do not care to mention if three days include deceleration or if it's just a fly past. I'm not smart enough to calculate acceleration required or final velocity near Mars but I feel brain matter is very much present on these forums.

So, assuming that 3 days claim includes deceleration for half the distance and that things go wrong at worst possible moment in mid way I'd ask how fast would a spacecraft shoot past Mars if braking was not possible? How far would this velocity take the craft and would it escape our solar system?

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100,000,000,000 meters over 300,000 seconds = ~ 1/3 million m/s If earth transects mars. If mars is on the opposite side of the sun then its around a million meters per second. speed of light is around 300 million meters per second.

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UmbralRaptor

UmbralRaptor

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  On 3/27/2016 at 1:54 AM, ImmaStegosaurus! said:

I have ran into claims that new witchcraft engines could get us to Mars in three seconds. These claims do not care to mention if three days include deceleration or if it's just a fly past. I'm not smart enough to calculate acceleration required or final velocity near Mars but I feel brain matter is very much present on these forums.

So, assuming that 3 days claim includes deceleration for half the distance and that things go wrong at worst possible moment in mid way I'd ask how fast would a spacecraft shoot past Mars if braking was not possible? How far would this velocity take the craft and would it escape our solar system?

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Er, which is it?

In any case, assuming a 3 day (259200 s) brachistochrone, one can get get reasonable numbers by playing with the kinematic equations:

t == 259200/2 == 129600 s (we only need to work out half-way)

x == 5.46e10 m (opposition with Mars at perihelion and Earth at aphelion) to 4.013e11 m (conjunction with both planets at aphelion)

a == 2*t-2*x/2 == t-2*x == 3.25 m/s2 to 23.89 m/s2

vmax == a*t == 421 km/s to 3096 km/s (0.0014 c to 0.0103 c)

Δv == 2*vmax == 843 km/s to 6193 km/s.

Sure, the acceleration in the first case is low enough that gravity sort of matters, but given the absurd ΔV, not as much as one might think. If there's a coast phase, expect higher accelerations to keep within the time limit.

Assuming some sort of impulsive accelerations, the speeds run from 211 km/s to 1548 km/s (with expended ΔVs of 421 km/s to 3096 km/s.)

Edited by UmbralRaptor
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Mitchz95

Mitchz95

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  On 3/27/2016 at 1:54 AM, ImmaStegosaurus! said:

I have ran into claims that new witchcraft engines could get us to Mars in three seconds.

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  On 3/27/2016 at 1:54 AM, ImmaStegosaurus! said:

could get us to Mars in three seconds.

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  On 3/27/2016 at 1:54 AM, ImmaStegosaurus! said:

three seconds.

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Uh...

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WestAir

WestAir

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He obviously meant 3 days, as per the Thread Title and the entire rest of his OP. No need to dig into an obvious mis-type. ^_^

That said, I doubt we'll ever see 3 days to Mars. That's how long it takes to get to the moon.

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Mitchz95

Mitchz95

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  On 3/27/2016 at 4:29 PM, WestAir said:

He obviously meant 3 days, as per the Thread Title and the entire rest of his OP. No need to dig into an obvious mis-type. ^_^

That said, I doubt we'll ever see 3 days to Mars. That's how long it takes to get to the moon.

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I was just poking fun at it. No insult intended. ;)

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fredinno

fredinno

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  On 3/27/2016 at 8:40 PM, hendrack said:

Russians haven been developing a new nuclear engine, claiming to reach Mars in 45 days. http://sputniknews.com/russia/20160302/1035657122/engine-rosatom-space.html

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And Americans have been developing an ION engine called VASMIR capable of reaching Mars in 3 Days :D

Neither is going to happen, because there is literally no point right now for such a fast Mars transfer.

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RocketSquid

RocketSquid

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  On 3/28/2016 at 7:52 AM, UmbralRaptor said:

@ImmaStegosaurus! *did* say it was powered by witchcraft.

I'd still be suspicious of any flight that claims to get to Mars in a few weeks and isn't an Orion or Zubrin drive, though.

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I think he's talking about the cannae drive/EmDrive, which don't carry their own propellant, leading to a very light ship.

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Kerbart

Kerbart

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  On 3/27/2016 at 1:54 AM, ImmaStegosaurus! said:

I have ran into claims that new witchcraft engines could get us to Mars in three seconds. These claims do not care to mention if three days include deceleration or if it's just a fly past. I'm not smart enough to calculate acceleration required or final velocity near Mars but I feel brain matter is very much present on these forums.

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I'm pretty sure that the acceleration required for a 3 second trip (ignoring unimportant issues like breaking the speed of light) will ensure that there will not be a lot of brain matter left after arriving.

Yes; I know you meant 3 days. But that wouldn't make it nearly as funny. :) 

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WestAir

WestAir

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  On 3/28/2016 at 9:21 PM, Kerbart said:

I'm pretty sure that the acceleration required for a 3 second trip (ignoring unimportant issues like breaking the speed of light) will ensure that there will not be a lot of brain matter left after arriving.

Yes; I know you meant 3 days. But that wouldn't make it nearly as funny. :) 

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Technically 3 seconds to Mars from the crews perspective is still within the realm of plausible physics. The crew would only experience the first milisecond, however, because they'd be dead after that. :lol:

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  • 3 weeks later...
Monsterlunch

Monsterlunch

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How to travel to Mars in 3 seconds:

Step 1: Create a local gravitational field not affecting anything but your spacecraft orbiting around it.

Step 2: Send your spacecraft to mars using conventional propulsion.

Step 3: Un-create the gravitational field

Due to the habit of gravitational fields bending space-time, time passing for our admittedly VERY brave astronauts could be reduced to three seconds without actually violating the laws of physics. Just have to get around the problem of our gravitational field swallowing planets and stuff...

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