Time to Mars, rather shocking

[KASASpace]

So, using modern technologies it would take quite a while to get to Mars......

However at constant acceleration, even at 1 foot per second per second, you can get there within a month.

Now, this equation assumes Uniform forces, which I know is not true, but it is close.

d is distance

g is acceleration

t is time

According to the equation d=1/2gt^2 we can solve for time:

(2d/g)^1/2=t

Now, assuming that Mars is at its closest distance, which is more or less 35 million miles, we can discover how long it takes at 1 foot per second per second.

However, we must convert miles to feet first. Multiply 35,000,000 by 5,280, than by 2.

35,000,000 * 5280 = 184,800,000,000. 184,800,000,000 * 2 =369,600,000,000.

Since acceleration is 1, just leave it alone.

Find the square root....

~607947.3661428265

Now, divide by 86,400.

You get about 7. That's only counting acceleration, no deceleration. So you need to multiply it by 2, but it is a little bit over that....

2 weeks to our neighbor!

Edited March 11, 2014 by KASASpace

[Camacha]

Have you calculated the amount of fuel that would take?

[jwenting]

why shocking? It's been known for decades that a torch ship can do the trip in that time. Just that we don't have the engine and fuel technology to make it work. Needs far more TWR than we can manage.

Plus of course you'd be splattered against the nearest internal bulkhead in a thin layer of protoplasma.

[Faark]

Yes, and if you travel with light speed, it will take less than most plane flight's here on earth. There isn't anything shocking about typing made-up numbers into a calculator. Accelerating 0.3m/s for 2 weeks would mean your rocket has to have about 360km/s² delta-v. Feel free to build something like that out of cola bottles + mentos and we'll see you on mars.

[Rakaydos]

You get about 7. That's only counting acceleration, no deceleration. So you need to multiply it by 2, but it is a little bit over that....

2 weeks to our neighbor!

You need to multiply by 4. Not only do you need to slow down, but you need to start slowing down when you're only at half speed (halfway there)

[Camacha]

You need to multiply by 4. Not only do you need to slow down, but you need to start slowing down when you're only at half speed (halfway there)

Depending on how you plan to slow down, of course. You could employ aerobraking or an aerocapture, but the thin atmosphere and high speeds will limit your options a bit.

[CalculusWarrior]

If you were going to accelerate constantly towards Mars, (assuming you had the delta-v required), then I suggest accelerating at ~10 m/s², or 1 g. This would allow you to build your spaceship in a vertical sort of manner, and for most of the trip, you would be simulating standard Earth gravity (which would eliminate the problems of weightlessness in humans).

This has the added benefit of shortening your travel time!

Mars is (on average) 1.5 AU from the sun. Since Earth is, by definition 1 AU from the sun, we assume that Mars is about 0.5 AU from the Earth at our closest approach.

I made a slight tweak to our initial equation, as we can only accelerate halfway to our destination. We then need to turn around halfway and start slowing down, otherwise we'll make a crater in the already-scarred Martian surface.

I multiplied by 2 at the end there because we only calculated the time it would take until our turn-to-decelerate maneuver.

As such, accelerating at 1 g would be likely the method of choice for an interplanetary ferry, as not only does it let its passengers enjoy the same gravitational pull as at home, but it gets to its destination in 2 days, rather than in 2 weeks.

Of course, the math is the easy part. Now we actually need to design and build an engine that has the ability to accelerate at 1 g for 2 days straight. Someday it'll happen!

EDIT:

Depending on how you plan to slow down, of course. You could employ aerobraking or an aerocapture, but the thin atmosphere and high speeds will limit your options a bit.

While those methods are certainly usable for the speeds which current interplanetary spaceships travel at, the velocities which our hypothetical torchship would be travelling at are significantly faster than that:

Entering any sort of atmosphere while travelling at this speed would likely destroy your spacecraft.

Edited March 11, 2014 by CalculusWarrior

[magnemoe]

Depending on how you plan to slow down, of course. You could employ aerobraking or an aerocapture, but the thin atmosphere and high speeds will limit your options a bit.

Aerobraking from hundreds of Km/s will give you some temperature and g-force issues. For the temperature you could just as well aerobrake on the sun

I sent an probe into Eve atmosphere at 1000 km/s once, it faced 70.000 g at peak, this is comparable with getting shout out by an modern cannon.

[Camacha]

Entering any sort of atmosphere while travelling at this speed would likely destroy your spacecraft.

Aerobraking from hundreds of Km/s will give you some temperature and g-force issues.

I know, that is exactly what i meant Mars is already a problem due to its thin atmosphere - too thick to ignore, to thin to really use. Add a lot of speed and your issues will only get worse.

You might of course bleed off a lot of speed by aerobraking, but chances are you are still escaping after the first pass and, of course, you will spend a lot more time slowing down than actually travelling. Not very practical and quite counterproductive.

[Seret]

OP reported to mods for doing physics in imperial units.

[Camacha]

OP reported to mods for doing physics in imperial units.

That's how you get to Imperial Mars.

[DonLorenzo]

Well, if you're going to mars and can choose arbitrary accelerations, I'd say go with mars gravity of ~ 0.3g

[Sirrobert]

However, we must convert miles to feet first. Multiply 35,000,000 by 5,280, than by 2.

Thank you for demonstrating why you imperial system sucks.

Now apart from that.

Basicly you just told us that if you have an engine with an ungodly high ISP and Thrust, you can get to mars really fast. BIG WOOPING SUPRISE

[KASASpace]

Thank you for demonstrating why you imperial system sucks.

Now apart from that.

Basicly you just told us that if you have an engine with an ungodly high ISP and Thrust, you can get to mars really fast. BIG WOOPING SUPRISE

I'm saying even with a TWR of 10/322, you can get to Mars in just over 2 weeks, I discovered this quite recently, and due to the best part of rockets:

TWR increases over time.

So you would actually get there much much faster with it on one throttle setting.

Now, on to the ship, I was thinking something the size of a few XTs powered by a Nuclear Lightbulb.

[guto8797]

Also we must think of something passenger wise. The reversing maneuver would be quite... harsh. Either engines on the fron (which would also increase Delta-V need), or turning the ship around, it would mean that the passengers would have to be strapped on to some kind of safety device (even more delta-v costs). For now, the problems aint the engine. It is hauling so much fuel.

[Whirligig Girl]

2 weeks is not shocking, and the acceleration would be destructive anyway. A Hohmann Transfer Orbit would take several months, but even that's not that bad. You don't have to do a Hohmann Transfer either. Imagine you had enough Delta-V to sundive, but you bring your Perihelion up to a safe distance, then do a correction burn, you could get to Mars even quicker.

[Ralathon]

I'm saying even with a TWR of 10/322, you can get to Mars in just over 2 weeks, I discovered this quite recently, and due to the best part of rockets:

TWR increases over time.

So you would actually get there much much faster with it on one throttle setting.

Now, on to the ship, I was thinking something the size of a few XTs powered by a Nuclear Lightbulb.

Have you actually played Kerbal Space Program?

The limiting factor for spaceflight is not TWR, it's fuel. Sure, if you build a craft with 2000km/s of dV you can get to Mars and back pretty quickly. But you will need a lot of fuel for that, and to push that fuel you need more rocket engines, which in turn eat more fuel. That's when you crash headlong into the Tyranny of the rocket equation. You'll probably end up with a completely impractical ship the size of the moon.

[MBobrik]

You'll probably end up with a completely impractical ship the size of the moon.

Or just with a ship propelled by a nuclear engine with seven digit Isp

[Firov]

I think the best, quasi-realistic, estimates I've seen to get to Mars fast use an electric propulsion system, specifically a VASIMR plasma drive, coupled with a massive 200 megawatt nuclear fission reactor. Such a vessel could, in theory, complete a trip to Mars in just under 40 days. However, that would require putting a stupidly large nuclear reactor into orbit. Plus, even as efficient as VASIMR plasma drives are, it would still need a fair amount of fuel for the trip.

From what I've read about this proposal we do have the technology to build it, but it would be amazingly expensive, and we'd need to figure out a way to put such a large nuclear reactor into orbit. Keep in mind, the largest reactors put into orbit so far have been in the tens of kilowatts range.

[SargeRho]

Fusion pulse propulsion is the way to go for fast intra-system travel IMO. Daedalus-type beam confinement for trips to the furthest reaches of the solar system (read: Uranus, Neptune and beyond), and the fusion driven rocket for the inner system. 30 days transit time wouldn't be a problem with them.

[MBobrik]

and we'd need to figure out a way to put such a large nuclear reactor into orbit.

don't put into, build there.

[KASASpace]

Have you actually played Kerbal Space Program?

The limiting factor for spaceflight is not TWR, it's fuel. Sure, if you build a craft with 2000km/s of dV you can get to Mars and back pretty quickly. But you will need a lot of fuel for that, and to push that fuel you need more rocket engines, which in turn eat more fuel. That's when you crash headlong into the Tyranny of the rocket equation. You'll probably end up with a completely impractical ship the size of the moon.

Yes, I have played.

I say its shocking because it proves that things aren't that far.

And plus, there is no limiting factor, there are MULTIPLE limiting factors. Now get your facts straight.

You have Isp, mass ratio, and the fuel you're using (determines the actual SIZE of the ship).

Now, XTs are Shuttle external tanks, and I mean quite a few, at least five, powered by an engine with 1500 to 3000 Isp.

TWR matters because in this scenario it is constant acceleration, with a TWR of 10/322. 0.3048 meters per second per second. Not fast, but like an Ion engine it builds up over time, so you get there quickly.

[KASASpace]

Also we must think of something passenger wise. The reversing maneuver would be quite... harsh. Either engines on the fron (which would also increase Delta-V need), or turning the ship around, it would mean that the passengers would have to be strapped on to some kind of safety device (even more delta-v costs). For now, the problems aint the engine. It is hauling so much fuel.

Actually, not. If you have a trailer system, you can just flip the engines, not with rotors or anything, but like how the Soyuz rotates its solar panels, thrusters.

Of course, probably a tractor trailer system, so it would be better.

[Camacha]

I say its shocking because it proves that things aren't that far.

We know. Space is not even an hour's drive away in a car. Yet it is almost impossibly far away. If you ignore some basic limitations of physics and current or near future technology, going to space is easy stuff - just a shortish commute. Sadly, reality does not work like that.

I mean, if I was going to break logic with an imaginary scenario, I would come up with something better than two weeks travel time

[KASASpace]

We know. Space is not even an hour's drive away in a car. Yet it is almost impossibly far away. If you ignore some basic limitations of physics and current or near future technology, going to space is easy stuff - just a shortish commute. Sadly, reality does not work like that.

I mean, if I was going to break logic with an imaginary scenario, I would come up with something better than two weeks travel time

Excuse me? Break logic? 2 weeks is better than 6 months! Less radiation, not much of a storm shelter, less life support. Sure, it would take quite a while to build the system to get there, but with what we have, we can build the SHIP, just not the engine. It's actually more hypothetical, too.