Time to Mars, rather shocking

[Sirrobert]

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.

GREAT.

Just one tiny little problem

We don't have such an engine

[KASASpace]

GREAT.

Just one tiny little problem

We don't have such an engine

Oh no!

You just ruined the universe.

Now seriously, just one tiny little actual factoid, it is called R&D for a reason, and I never said let's do it now, I said eventually when we have the technology.

[Rakaydos]

Oh no!

You just ruined the universe.

Now seriously, just one tiny little actual factoid, it is called R&D for a reason, and I never said let's do it now, I said eventually when we have the technology.

And if we have warp drive technoligy, we could get there in minutes. Your point?

[Camacha]

Wait a minute.

Edited March 12, 2014 by Camacha

[KASASpace]

Yes, logic. There is a good reason they take as long as they do right now. You consistently ignore that. You dream up some fantasy ship without justifying all the other factors and think we go along with it.

Proof it. Do the calculations. Show us we are wrong. I would love to be proven wrong, though I think I will be disappointed.

Very hypothetical, to the point that with modern or feasible future technology it is pure fantasy Without some advance or breakthrough, this is simply not going to happen.

How do you think everything starts? You are the one being ignorant here. Everything starts as an idea, it is not fantasy, it is more based in reality than your belief that you can't make ideas without designing the entire thing.

Now, if we can build a space station, we can build a ship, however, the problem in this case is the propulsion, not the ship itself.

In fact, by your logic all any space program ever did is fantasize.

[KASASpace]

And if we have warp drive technoligy, we could get there in minutes. Your point?

We're closer to NTR than warp.

[Camacha]

Now seriously, just one tiny little actual factoid, it is called R&D for a reason, and I never said let's do it now, I said eventually when we have the technology.

Allright, I will do you one better. The distance between Earth and Mars is at most 401 million kilometer. We know that we can not go faster than light and we know that going close to 1c takes a lot of energy, so we will schale it down a bit to 0,9c. Still an incredible amount of juice, but what are you going to do. The speed of light is 299.792.458 m/s or 299.792,458 km/s. 401 million/ (299.792,458 km/s * 0,9) is roughly 1486 seconds or about 24 minutes and 42 seconds.

Mars is just around the corner!

Then again, if I go by bike and average 25 kilometers an hour it will take me a little under two millenia. Imagine that, Mars is suddenly very far away. Maybe my grand^grand children will make it if I pack enough lunches.

[KASASpace]

Allright, I will do you one better. The distance between Earth and Mars is at most 401 million kilometer. We know that we can not go faster than light and we know that going close to 1c takes a lot of energy, so we will schale it down a bit to 0,9c. Still an incredible amount of juice, but what are you going to do. The speed of light is 299.792.458 m/s or 299.792,458 km/s. 401 million/ (299.792,458 km/s * 0,9) is roughly 1486 seconds or about 24 minutes and 42 seconds.

Mars is just around the corner!

Then again, if I go by bike and average 25 kilometers an hour it will take me a little under two millenia. Imagine that, Mars is suddenly very far away. Maybe my grand^grand children will make it if I pack enough lunches.

Now that is fantasizing.

Remember, distance is relative, as is everything else.

[Camacha]

How do you think everything starts? You are the one being ignorant here. Everything starts as an idea, it is not fantasy, it is more based in reality than your belief that you can't make ideas without designing the entire thing.

Conveniently ignoring the unfortunate parts is not making plans, it is simply not being realistic. I agree that doing new things starts with dreaming impossible things, but you are a little too optimistic in ignoring everything that works against you.

Please refrain from using ad hominems in your arguments, as it does not make them any better.

[KASASpace]

Conveniently ignoring the unfortunate parts is not making plans, it is simply not being realistic. I agree that doing new things starts with dreaming impossible things, but you are a little too optimistic in ignoring everything that works against you.

Please refrain from using ad hominems in your arguments, as it does not make them any better.

Ignoring? No, just not brought up as of yet. This thread started by saying that it is possible to get to mars in less than one month.

I'm not going to design the ship, but I know that R&D exists for a reason.

Now, you see, I am being quite realistic based on my original post, as this entire thing should be.

And I simply referred to the implied ignorance you said earlier.

[Camacha]

Ignoring? No, just not brought up as of yet.

I could use some extra money, so I will buy a lottery ticket. That way I will win 20 million euro. I am not ignoring the fact that it is very unlikely that I will win for some time to come, I just did not bring it up yet.

And I simply referred to the implied ignorance you said earlier.

What you think is implied is your responsibility, what I say is mine

[Ralathon]

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.

Yea there are multiple things that limit your dV. Just look at the Tsiolkovsky equation. But if you actually track them down they all come back to fuel.

You have Isp,

Which depends on how much energy your fuel contains. The theoretical maximum Isp you can eke out of H2-O2 reactions is around 480 if I'm not mistaken.

mass ratio,

Depends on the fuel density. Lower density fuel requires bigger tanks thus causing a lower mass fraction.

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.

And why don't we cover it in fairy sprinkles while we're at it? NASA would sacrifice their firstborns for an engine like that. The problem is that high ISP + high thrust is a very difficult problem to tackle. Isp depends on exhaust velocity, since you are well above the theoretical maximum for chemical propulsion this means electrical or nuclear propulsion. That kind of ISP is out of the question for nuclear until we invent gas core NERVAs, or fusion engines. So this means some electric design. But since you want a high TWR you'll need a massive power supply, way more than solar can provide. This means a nuclear reactor (running into the same issues as before) or some form of beamed power. Even if you somehow manage to pull a reactor like that out of your ass, or plaster halve the earth in transmitters your craft will need a very elaborate cooling system. Since space has no air this means you have to radiate all that energy away.

[zxczxczbfg]

Something with such a short travel time like this implies a sort of "cruise" or "sightseeing" trip; two weeks is a bit short, and rather economically inefficient, for a colony. Which implies, good luck bringing the fuel to get back as well, my friend.

Edited March 12, 2014 by zxczxczbfg

[Ravenchant]

This thread started by saying that it is possible to get to mars in less than one month.

Er...no one is denying that, and your math seems to mostly check out. So the thread basically started as stating a fact that is interesting but not very useful because the tech needed to achieve comparable delta-v doesn't exist outside of speculative science fiction, and likely won't for a long time

[KASASpace]

I could use some extra money, so I will buy a lottery ticket. That way I will win 20 million euro. I am not ignoring the fact that it is very unlikely that I will win for some time to come, I just did not bring it up yet.

How does that example have anything to do with this discussion.

Edited March 12, 2014 by KASASpace

[KASASpace]

Yea there are multiple things that limit your dV. Just look at the Tsiolkovsky equation. But if you actually track them down they all come back to fuel.

Which depends on how much energy your fuel contains. The theoretical maximum Isp you can eke out of H2-O2 reactions is around 480 if I'm not mistaken.

Depends on the fuel density. Lower density fuel requires bigger tanks thus causing a lower mass fraction.

And why don't we cover it in fairy sprinkles while we're at it? NASA would sacrifice their firstborns for an engine like that. The problem is that high ISP + high thrust is a very difficult problem to tackle. Isp depends on exhaust velocity, since you are well above the theoretical maximum for chemical propulsion this means electrical or nuclear propulsion. That kind of ISP is out of the question for nuclear until we invent gas core NERVAs, or fusion engines. So this means some electric design. But since you want a high TWR you'll need a massive power supply, way more than solar can provide. This means a nuclear reactor (running into the same issues as before) or some form of beamed power. Even if you somehow manage to pull a reactor like that out of your ass, or plaster halve the earth in transmitters your craft will need a very elaborate cooling system. Since space has no air this means you have to radiate all that energy away.

Uh huh. Yep, sure.

But fuel is just a factor, mass ratio ultimately comes down to how much cargo you want.

Plus, a TWR of 10/322 is not high thrust, it's tiny and quite comparable to modern engines. However NASA would never get a Nuclear Lightbulb, just because of the name.

[KASASpace]

Something with such a short travel time like this implies a sort of "cruise" or "sightseeing" trip; two weeks is a bit short, and rather economically inefficient, for a colony. Which implies, good luck bringing the fuel to get back as well, my friend.

This is more for shipping TO Mars, like equipment for the colony, habitats, etc.

[KASASpace]

Er...no one is denying that, and your math seems to mostly check out. So the thread basically started as stating a fact that is interesting but not very useful because the tech needed to achieve comparable delta-v doesn't exist outside of speculative science fiction, and likely won't for a long time

It's interesting to people who would like to see us

*puts on shades*

Take on Space.

[KASASpace]

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)

Yeah...

about that....

You see, I got the multiply by 2 from an actual rocket scientist.

[vger]

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.

At that speed, I wonder what kind of G's you'd be doing in orbit? I think it'd only be slightly more agonizing than the initial acceleration.

As for possible transfer times, I'll just leave this here. http://www.lpi.usra.edu/meetings/marsconcepts2012/pdf/4181.pdf

Edited March 12, 2014 by vger

[KASASpace]

At that speed, I wonder what kind of G's you'd be doing in orbit? I think it'd only be slightly more agonizing than the initial acceleration.

As for possible Mars speeds, I'll just leave this here. http://www.lpi.usra.edu/meetings/marsconcepts2012/pdf/4181.pdf

IF you got into orbit (somehow) you shouldn't really feel G's.

[Camacha]

IF you got into orbit (somehow) you shouldn't really feel G's.

Any change in speed will cause the subject to experience G's, in orbit too.

[CalculusWarrior]

At that speed, I wonder what kind of G's you'd be doing in orbit? I think it'd only be slightly more agonizing than the initial acceleration.

As for possible transfer times, I'll just leave this here. http://www.lpi.usra.edu/meetings/marsconcepts2012/pdf/4181.pdf

What this thread is proposing is constant acceleration. Rather than burn for a while when you leave, then burn to slow down when you arrive, you simply accelerate at a set value. The OP chose the value of 1 ft/s², while I chose a value of 9.81 m/s² in my example. This has the side-effect of producing a uniform 'gravitational field' in the direction of the ship's motion, so a cleverly-designed ship could make use of this to provide passengers with Earth-like accommodations for the trip, rather than have to deal with zero gravity.

[KASASpace]

What this thread is proposing is constant acceleration. Rather than burn for a while when you leave, then burn to slow down when you arrive, you simply accelerate at a set value. The OP chose the value of 1 ft/s², while I chose a value of 9.81 m/s² in my example. This has the side-effect of producing a uniform 'gravitational field' in the direction of the ship's motion, so a cleverly-designed ship could make use of this to provide passengers with Earth-like accommodations for the trip, rather than have to deal with zero gravity.

I thought of that, but I just wanted to show that even at ~0.3 m/s^2 (~1ft^2) you could get to Mars quick. I, being a space enthusiast, find this fact amazing and shocking.

*Is that the Doctor?

[KASASpace]

Any change in speed will cause the subject to experience G's, in orbit too.

A change, yes, but you said what you would be doing in orbit, which I assumed meant after you braked.