Obama/McCain and space exploration

CrackerBarrel · #1 10-21-2008, 04:26 PM

Quote:

Originally Posted by cheerfulgreek

I think we could go now. We have the technology, so why not?

Well, I really don't think anyone is fighting to see who goes first anymore. When the Cold War died, the space race died with it. If the Cold War was still going on, I'll betcha we would have landed someone on Mars 8 years ago. The Soviet space program attempted two launches in 1988 to explore Mars and it's moon Phobos that met with disappointment, continuing a streak of bad luck that pretty much has plagued every Soviet or Russian Mars mission. So because of that also, I don't think we've really been that pressed to go. It's funny how after the launch of Sputnik, we went to the moon soon after. I guess our government now sees it as since we have no one to compete against, why go?

Because we don't have the technology. Not anywhere close. The moon is 240,000 miles away. If we wanted to go back to the moon, we probably could. Mars is 50,000,000 miles away. It's 208 times farther away than is the moon. The shortest time period possible to get from the earth to mars is 9 months, and that is if you time it exactly right at an opportunity that comes every 1.6 years. Here's a quote from a kids astronomy page about the difficulty of a mission to Mars.

Quote:

Just like you have to wait for Earth and Mars to be in the proper postion before you head to Mars, you also have to make sure that they are in the proper position before you head home. That means you will have to spend 3-4 months at Mars before you can begin your return trip. All in all, your trip to Mars would take about 21 months: 9 months to get there, 3 months there, and 9 months to get back. With our current rocket technology, there is no way around this. The long duration of the trip has several implications.
First, you have to bring enough food, water, clothes, and medical supplies for the crew in addition to all the scientific instruments you will want to take. You also have to bring all that fuel! In addition, if you are in space for nine months, you will need a lot of shielding to protect you from the radiation of the Sun. Water, and cement make good shielding but they are very heavy. All together, it is estimated that for a crew of six, you would need to have 3 million pounds of supplies! The Shuttle can lift about 50,000 pounds into space, so it would take 60 shuttle launches to get all your supplies into space. In the history of the Shuttle, there have only been about 90 launches, and there are less than ten launches per year... So with the shuttle, it would take six years just to get the supplies into space. For this reason, you would probably need to develop a launch system that could lift more than 50,000 pounds into space. Even with a better launch vehicle, it is unlikely that you could launch the Mars mission all at once. You will have to launch it in several pieces and assemble them in orbit.

It's obviously a little outdated too since it's still saying we are making less than 10 shuttle launches a year. Yeah, much less now.

cheerfulgreek · #2 10-22-2008, 10:23 AM

Quote:

Originally Posted by CrackerBarrel

Because we don't have the technology. Not anywhere close. The moon is 240,000 miles away. If we wanted to go back to the moon, we probably could. Mars is 50,000,000 miles away. It's 208 times farther away than is the moon. The shortest time period possible to get from the earth to mars is 9 months, and that is if you time it exactly right at an opportunity that comes every 1.6 years. Here's a quote from a kids astronomy page about the difficulty of a mission to Mars.

It's obviously a little outdated too since it's still saying we are making less than 10 shuttle launches a year. Yeah, much less now.

I disagree. I also thought the kiddy astronomy post you posted was cute.

I'll respond to that too. I guess.

9 months? Yeah, maybe if you travel at an Apollo era velocity. I think we do have the technology, and we would be moving at a much greater speed than that. Also, I agree, Mars is indeed far away, much farther than the Moon. But what you have to look at is the fact that at its closest approach, when it stands directly on the opposite side of the Earth from the Sun, it actually never gets nearer than 38 million miles, that's about 55 million kilometers. At it's farthest, when it stands behind the Sun as seen from the Earth, it lies about 400 million kilometers distant. As far as I know of, there actually isn't any propulsion system, that can push directly away from the Sun and perform the transit between Earth and Mars in a straight line when the two are in oppostion. This is because a spacecraft leaving Earth posseses the velocity of the Earth, some 30 kilometers per second and unless massive amounts of propellant are expended to alter the course, the spacecraft will continue to circle the Sun in the same direction as the Earth. I think you're looking at the distance between the two planets alone. That's not the way to look at the picture. I think the best time to travel from Earth to Mars should occur when the two planets are in conjunction with each other. This goes back to what I was saying ealier. Opposition means when Mars is standing directly on the opposite side of Earth from the Sun. At conjunction, Mars stands behind the Sun as seen from Earth. So anyway, at their "maximum" distance from each other on opposite sides of the sun, is the best way. It's the easiest way to go, because if you take this path, you can actually travel along an ellipse which is tangent to the Earth's orbit at one end, and tangent to Mars' orbit on the other, thus minimizing the course change. You can disagree if you want, but we can agree to disagree, because neither one of us are astrophysicists. If you disagree with me, that's fine, but if you deviate from such a flight plan, the harder your propusion job, and the costlier the mission.

In repsonse to your comparrison with the the Moon's distance relative to Mars, Apollo astronauts traveled between the Earth and Moon with an average speed of about 1.5 kilometers per second, and this speed limit was set not by the limits of the propulsion technology of the time. Actually, the 3rd stage of the Saturn V could have rocketed the Apollo spacecraft toward the Moon at double or even triple this velocity, by the nature of the mission geometry, and I think this is what you're not seeing. The Apollo astronauts launched off at the Moon at about 4 kilometers per second and reached it in a single day. What you also have to look at is with that speed headed towards the Moon they wouldn't have been able to stop. Because of weak Lunar gravity, a spacecraft's propulsion system has to do nearly all the work required to capture a trans lunar spacecraft into lunar orbit.

Mars on the other hand, has substantial gravity and an atmosphere, both of which can assist in facilitating a deceleration maneuver. So a spacecraft can reach Mars with a much greater approach velocity and still manage to capture itself into orbit. More importantly, a spacecraft leaving Earth with a departure velocity of I'm thinking about 3-5 kilometers per second does not fly across the solar system with a mere 3 km/s speed.

Rather, in leaving the Earth, the spacecraft is launching off a very fast moving platform, and since it's moving in the same direction, it picks up (based on physics) an extra 30 km/s of velocity from the Earth as it goes around the Sun. You have to also look at the fact that the spacecraft would be moving across space with an initial velocity NOT of 3 km/s, but 33 km/s. That's more than 20 times the speed of an Apollo command module. Also you can't use this moving platform effect to help you reach the Moon, because the Moon is moving about the Sun in company with the Earth. As it leaves the Sun's gravity to move outward from the orbit of Earth to that of Mars, it actually would trade some of the kinetic energy associated with this velocity into potential energy, and so slows down a bit, but it's still moving very fast. I could be wrong, but I think I'm right or pretty close, because we had this same discussion in my P&A club and some agreed with me, some didn't. The members who disagreed with me were not looking at the fact that Mars will be cruising along its orbit, with a velocity of about 25 km/s in roughly the same direction of the spacecraft. I told them just like I'm telling you, that when the spacecraft reaches Mars' orbit, its velocity relative to Mars will be only 3 km/s, since it's moving at about 21 km/s. At 3 km/s, that's slow enough to allow orbit capture. What you're not understanding, is by the time the spacecraft reaches Mars, its traveled 1000 times farther than the Apollo astronauts, but on average 20 times faster. So, if you do the math, 1000 times farther divided by 20 times faster gives us a travel time that is a factor of 50 greater than the three day transits for the Apollo astronauts, so I'm thinking about 150 days. That's about 5 months from Earth to Mars. Of course this is a rough estimate of the travel time for a one way transit to Mars using using Apollo era or present day technology for propulsion. I don't think it's a bad estimate either, because we (my P&A members) got into this discussion based on a Discovery Channel documentary on Mars, and astronomers approximated about 6 months one way travel time. 9 months would be pretty close if we were taveling using technology from the Apollo era. But again, I have no problem agreeing to disagree with you.