Do we currently have the technology to land men on Mars?
I wanted to open this up on the great debates thread, because we have
been discussing this at great length in the General Discussions thread, and
there are vastly differnt opinions being stated.
My answer is emphatically, NO. We can’t afford a Mars mission, with our current technology, so we really haven’t yet developed the technology needed for a
Mars mission.
Let me explain in detail. 3 decades ago today, we sent a command module , complete with LEM, to the moon and back. Although our rocket engines may be
more powerful now and more efficient, than those used on the Saturn V rockets, Mars is 1000 times farther from the earth than the Moon. This means that to
go to Mars at the same speed would take 1000 times longer. So with our current methods of propulsion, it would take almost ten years - one way. Way too long
for a manned mission to mars. But we do have a savior in this case. The earth is traveling around the sun at approximately 20 times the speed at which we
first journeyed to the moon. If we use Earth’s velocity to slingshot our spacecraft, a one-way trip would take only six months to a year.
So, what’s the problem? The law of physics called the Conservation of Motion. Because of the length of our voyage to Mars, we are going to have to utilize a much heavier spacecraft. While the increase in speed mentioned above, doesn’t seem like much, when we can slingshot our craft towards Mars, the weight of the spacecraft means that small increase comes at very high cost.The speed at which a rocket is propelled forward depends on three things: the speed at which the propellant leaves the rocket, the mass of the expelled propellant, and the combined mass of the rocket and the remaining fuel. So… if we want our rocket to move faster, we have to expel more propellant out the back: but if we have to expel more propellant, we must start out with more propellant. But if we start out with more propellant, we must expel a little more the we would have to get the spacecraft (plus propellant) moving in the first place. But that means we have to bring along more propellant, which means we need a bigger ship, which means… you see where this is going.
As our final velocity begins to exceed the speed of the propellant that is expelled, things change quickly. Increasing the velocity of our spacecraft form 1 to 2 times the speed of the propellant shooting out the back, requires 4 times as much fuel. Increasing final velocity to 4 times that with which our propellant leaves the spacecraft requires us to increase the required amount of propellant by a factor of more than 30. In this particular example, the initial mass of the ship plus propellant would be about 55 times the mass of the ship without fuel.
Now we must consider, that since a ship designed to carry such a large amount of propellant will have to be sturdier than it would otherwise have to be, it will weigh more than the type of spacecraft designed for the Apollo missions, or our current shuttle program. So this in turn limits our final velocity. With our current methods of propulsion, it is generally impossible to move a spacecraft faster than 3 or 4 times the velocity of the propellant. Remember, since this round trip to Mars may take a year or more, during which we have to adequately feed and house our astronauts, our spacecraft will weigh substantially more than an Apollo capsule. Since the total amount of propellant is a fixed multiple of the spacecraft weight, our net fuel requirement will be many times that associated with a trip to the moon, even if faster speeds were not required.
And, it just keeps getting worse… there is this matter of getting back. Mars has a stronger gravitational field than the moon. To achieve a trajectory back to Earth you have to carry a comparable amount of propellant for the return trip. This means the ratio of propellant needed for trip back, relative to mass of the now lighter spacecraft, is almost what would be needed for the initial journey to Mars. But, then this fuel must be added to the initial mass of the spacecraft, before we can calculate the initial propellant requirements. This becomes our main problem.
So, basically the Conservation of Motion laws, and our voyage duration limitations, dictate that the propellant required to achieve a sufficient velocity for a trip to Mars is 5 times the mass of the spacecraft with an empty storage tank. If you need a comparable ratio for the return trip, then you would need to land on Mars with a spacecraft that weighed 6 times the mass of an empty spacecraft - that is, the mass of the empty spacecraft plus 5 times the mass of the spacecraft in fuel required for the return trip. Here’s the rub. This would mean that the mass our spacecraft plus propellant at the time of takeoff from Earth would have to be 36 times the mass of the empty spacecraft. We basically end up with a Star Wars battle cruiser. Most of the above was explained in detail in a great book by Lawrence M. Krauss. I plagerize his work often - but only on discussion threads.
The above scenario more or less covers why NASA first considered a manned mission to Mars in '89, and then quickly decided against it. The price tag back then was $450 billion!! Mars in our life time is a pipe dream. Show’s how little research the Bush administration did, before once again bringing up the prospect of going to Mars.
