A manned mission, I agree. An unmanned mission, maybe not, as you can use the moon's gravity for the trip. But I don't know.bdewoody":21h46isw said:
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I have heard it said that delefecting an asteroid requires much more detailed imformation about its structure and composition than are readily opbtained from even the most sophisticated unmanned mission. Therefore crewed missions are desirable to obtain the level of knowledge neccessary to guide mitigation of asteroid hazards. The same might be said for the technology needed to deflect one.
The probability of Earth being hit by a large asteroid in the next 100 years is minuscule.
So, there is no need to develop the capacity now. It will come automatically as a spin-off of space exploration as advances are made. Which doesn't mean asteroids are not interesting.
So, there is no need to develop the capacity now. It will come automatically as a spin-off of space exploration as advances are made. Which doesn't mean asteroids are not interesting.
In all that I have read concerning this subject I have never seen anything claiming that manned missions to asteroids were needed Each asteroid is unique so I don't see where a manned mission to one that will never hit the earth will be useful in deflecting one we haven' even discovered yet. I'd like to see some references to papers citing the need for a manned mission for the reasons you state.JonClarke":310h5c7z said:
MeteorWayne":1ukl5erp said:
I think you are setting up a "straw man." Apollo 11 spent 21 hours on the surface of the moon. So you could have a rocket go 1.67 LDs, which we easily have the technology to do. Spend two days on the asteroid -- over TWICE the time Apollo 11 spend on the moon (or spend one day and only travel .83 LDs). And then return a LD of 1.67 LDs, which again is well within our current abilites. Based on Apollo technology, it would take about four days to get to 1.67 LDs, plus the same to get back. Now, what would take quite a bit of time, would be to match the speed of Adophis and then lose that speed. But obviously that is within our capabilites since we just had a more or less successful sample return mission from an asteroid. So the ONLY issue for such a mission is how long it would take to match the speed and then lose that speed because the rest of the mission need only take about 10 days, including two days on the surface of the asteroid. So, even if it would take a matter of months to gain and lose that speed, such a mission is feasible today with current technology, let alone the technology of 2029.
I don't understand why people here are so negative to such a mission. Is it a case of political bias: If Obama is for it, it must be bad?
I'm not negative about it at all, it's just not the cake walk that some seem to think.
Yes, a shorter mission makes it a lot more feasible, but that's more of a flags and bootprints type of mission, which isn't what I thought the objective is.
Of course, what the objectives are has never been made particularly clear
Yes, a shorter mission makes it a lot more feasible, but that's more of a flags and bootprints type of mission, which isn't what I thought the objective is.
Of course, what the objectives are has never been made particularly clear
Nasa speaks of 150 days. I think they are more interested in a shakedown of the tech to orbit Mars than a specific destination. A few weeks won't be enough. It has to be a significant part of the way to Mars (in miles and/or dV) to prove it can be done.
And I think the velocities required since there will be no gravity assist to slow down or speed up are way beyond what we are currently capable of in a manned space craft. Everything we have done so far is basically a coast after the initial boost stage.
You are COMPLETELY wrong. Apophis is traveling around 16,000 mph relative to earth. Apollo 11 reached 17,380 mph in a MERE 11 MINUTES after liftoff, with absolutely no gravity assist. So 40 years ago, we had the ability to accelerate to 17,000 mph in 11 minutes and to successfully decelerate from that same speed, WITHOUT gravity assists. But you are not the only one who was wrong. I WAY overstated the time necessary for an Apophis mission. It could easily be done in not much more than a two week mission, INCLUDING the time it takes to gain and lose 16,000 mph. Also, if NASA wants a longer mission, just meet Apophis further away and spend more time on Apophis. A mission to Apophis is easily within our technical capabilities and I hope NASA proceeds with such a mission. (As long as NASA can be sure that landing on Apophis won't increase the likelihood of impacting earth in 2036.)bdewoody":3j26i6lj said:
robnissen":16p7uokt said:
Sorry, it is you that is wrong...though I won't say completely. The difference is that the moon is in orbit around the earth, so that the overall relative velocity is zero. Also, the moon has 1/6 the earth's gravity which aided the deceleration required to enter lunar orbit. Aphophis has effectively no gravity to help. Also it is moving 16,700 mph relative to the earth, look at it as sideways across the sky, while the moon remains the same distince from earth (roughly) all the time. Look carefully at my post on page 1. During a two week landed mission, you must intersect the asteroid at > 11 LD, decelerate to match the speed, then 2 weeks later you have to shed the speed from 11 LD away and delta V your way back to earth.
A quote from the above:
"One of the closest of those 16 is of course Apophis in 2029, and it's big (~270 m), but the relative velocity is 7.42 km/s, which means that each day it moves 1.667 times the average earth-moon distance. That means for a two week surface mission, it will move 23 times the lunar distance or 9 million km. So you have to travel 12 times the distance to the moon, match speeds with it (unless you like that bug on a windshield feeling, and it's gravity is too feeble to help) then hop off 12 LD away, and get rid of all that speed to return to earth.
MeteorWayne":2vlspvg4 said:
No, you miss the point. The whole reason why Apollo had to decellerate is because the relative earth-moon speed is zero. The moon is 250,000 miles away, so to GET to the moon, Apollo had to ACCELERATE to about 24,000 mph (seeing as how the earth and moon are not collocated) and then DECELERATE to 0 mph, because as you pointed out the relative speed of the earth and the moon is zero.
To travel to Apophis on the other hand, a spaceship could accelerate to say 24,000 mph, but then it would only need to decellerate to 16,000 mph, since the RELATIVE speeed of earth/Apophis is 16,000 mph. Losing 8,000 mph is not an insurmountable task. (Granted at 8,000 mph relative speed, it will take your ship longer to get to Apophis, but that is still one LD about every 30 hours.) Then on the return to earth, you start off with 16,000 mph of speed (if you exit before Apophis reaches earth), which puts you ahead of Apollo which started on its return trip with 0 mph of speed (that whole relative speed = 0 thingy again). And then you use the earth's gravity to slow down, just like Apollo did. This is VERY dooable.
BTW, I do not understand your fixation with a two-week surface mission. Are you aware that EVERY Apollo moon landing was less than three days, with the exception of Apollo 17, which was 3 hours over three days. Surely, it is not your position that no useful science was conducted in the Apollo program because the landings were only three days. Thus, for a three day surface mission, it would be necessary to travel only about 5 LDs, stay on Apophis for three days, and then exit Apophis BEFORE it reaches earth (well under 1 LD), and the ship would be starting with 16,000 mph of speed (as opposed to Apollo, which was starting with relative speed of 0). Then use the rockets to get a gravity assist from earth (the ship would be close enough that there would be no reason to get any additional speed, although of course some propulsion would be necessary to leave Apophis and not miss earth on the way back.) Once again, this is highly doable and I believe would capture the world's attention, especially because some day we may have to do something to a NEO asteroid.
"To travel to Apophis on the other hand, a spaceship could accelerate to say 24,000 mph, but then it would only need to decellerate to 16,000 mph, since the RELATIVE speeed of earth/Apophis is 16,000 mph"
But in the opposite direction! If you are meeting it on the way toward earth (at a relative velocity of 17,000 mph), you are hitting it head on. So you must lose your 17,000 mph and turn around to match it's speed (another 17,000 mph). When you get off in 2 weeks, you are heading AWAY from the earth at 17,000 mph, so you must dissipate that speed and turn around to head back toward earth. Another 34,000 mph change in velocity. Trust me, draw it out on a piece of paper.
But in the opposite direction! If you are meeting it on the way toward earth (at a relative velocity of 17,000 mph), you are hitting it head on. So you must lose your 17,000 mph and turn around to match it's speed (another 17,000 mph). When you get off in 2 weeks, you are heading AWAY from the earth at 17,000 mph, so you must dissipate that speed and turn around to head back toward earth. Another 34,000 mph change in velocity. Trust me, draw it out on a piece of paper.
The reference has been made to “landing on an asteroid”. I don’t know the exact figures, but even on a very large asteroid, a person would weigh about one gram. Unlike the movie Armageddon, people wouldn’t be walking around on an asteroid. A misstep could easily result in the person exceeding escape velocity. Everything would be so close to weightless, it would be no test for any systems that would be used for either Moon landings or other planets such as Mars.
As noted, there is virtually nothing that could be learned by humans on an asteroid that could not be learned with robotic missions which would be a LOT less expensive and would not present any danger to humans. Robotic missions wouldn’t have to worry about radiation, food, water, or any of the other life support issues. Robotic missions could last for decades, gathering information the entire time. In fact, a robotic mission hitching a ride on an asteroid with a highly elliptical orbit, could send back information from beyond Mars and possibly close to the Sun.
As noted, there is virtually nothing that could be learned by humans on an asteroid that could not be learned with robotic missions which would be a LOT less expensive and would not present any danger to humans. Robotic missions wouldn’t have to worry about radiation, food, water, or any of the other life support issues. Robotic missions could last for decades, gathering information the entire time. In fact, a robotic mission hitching a ride on an asteroid with a highly elliptical orbit, could send back information from beyond Mars and possibly close to the Sun.
SDC : Asteroid Mining: Key to the Space Economy
SDC : Asteroids Data Sheet
By Mark Sonter
National Space Society
posted: 09 February 2006
06:51 am ET
The Near Earth Asteroids offer both threat and promise. They present the threat of planetary impact with regional or global disaster. And they also offer the promise of resources to support humanity's long-term prosperity on Earth, and our movement into space and the solar system.
The technologies needed to return asteroidal resources to Earth Orbit (and thus catalyze our colonization of space) will also enable the deflection of at least some of the impact-threat objects.
We should develop these technologies, with all due speed!
SDC : Asteroids Data Sheet
MeteorWayne":n9ihgnpq said:
No, that's another straw man. Obviously, you would not go in a straight line head on collision course towards the asteroid at 17K mph, put on the brakes (i.e. fire rocket in the opposite direction), go to 0 mph and then 17k mph in the opposite direction. Instead you would leave earth in a large eliptical orbit so that the spaceship and the asteroid would intersect going approximately in the same direction.
Second point, I said to exit the asteroid BEFORE it got to earth, so the 17K speed is sending you towards earth, NOT away from it. That is why I said to meet it at about 5 LD, so that there could be 3 days of science done, and still exit the asteroid before it passed earth.
"Trust me, draw it out on a piece of paper."
First, you are using the term “strawman” incorrectly. At worst, MeteorWayne’s calculations might be inaccurate, which they are not. If you are going to use a term to bash someone, you really should learn what it means first.robnissen":133za9ym said:
Second, MeteorWayne is quite correct. The alternate “large elliptical orbit” you presented would be practical for a long duration robotic mission, but impractical for humans. The extra consumable provisions alone would add considerable mass to the mission, and the months of wasted time in transit would be counterproductive.
In addition, there is nothing that people could do on an asteroid in three days surface time, that a robotic mission could not do far better in months or years on the surface.
mental_avenger":35dkmwms said:
1. Definition of "straw man" from Wikipedia: "A straw man argument is an informal fallacy based on misrepresentation of an opponent's position. To 'attack a straw man' is to create the illusion of having refuted a proposition by substituting a superficially similar yet weaker proposition (the 'straw man'), and refuting it, without ever having actually refuted the original position."
I can't imagine a better definition of a "straw man" argument than to claim I was suggesting that a ship approach an asteroid head-on, come to a dead stop...and then accelerate in the opposite direction to 17K mph.
2. They are not "months of wasted time in transit," the one thing MW and I agree on is that the ship must match the asteriod's speed, the only practical way to do that is to approach the asteroid from an elliptical orbit.
3. That is a different argument, the argument you make here, is that humans should not engage in manned space flight, if they are only going to visit an extra-terrestial body for three days. That is a legitimate argument, but then you must also believe that the Apollo landings were useless, since humans were only on the moon for at most three days for each mission. I disagree, I believe that the Apollo landings were not a waste ot time, and neither would be a landing on an asteroid.
robnissen":1erxfph0 said:
And that's the crux of the reason why what I was saying is not a straw man. As you and MA pointed out, the only way to match the speed is to basically be in the asteroid's orbit before then. That means being in an orbit with roughly the same orbital parameters...semimajor axis, inclination, eccentricity, and the resultant period of the orbit. In order to do that, you will need to already be in the same orbit as the asteroid well before your 3 day surface sortie.
So pick your asteroid (with it's real orbit), and look at the propellant and/or the time required to actually get into that orbit from earth. You can't just in magically be in that orbit at 5 LD; you probably have to already close to it at 100 LD or more, or you're going to miss the bus. If you think 100 LD is too far away, pick your own asteroid and show me how you match the asteroid orbit in advance. How much delta V, or how much time?
MW
Ok. That is a fair argument and I agree that argument is not a straw man. 1 comment and 1 question.MeteorWayne":3mvvrrw6 said:
The comment is that you do not need to be in the same orbit as the asteroid, because unlike the asteroid, the rocket ship can change its speed. So what is needed is the tangent of the elliptical orbit of the space ship...must intersect the tangent of the elliptical orbit of apophis. (Sortof the north side of the space ship's orbit...intersecting the south side of apophis' orbit.) By changing the speed of the rocket ship to speed up to or slow down from or to 17kmph, when the two bodies intersect they could have a relative speed of 0...even though they are in different orbits. But I certainly am not saying that the geometry and propulsion necessary for such a rendevous would not be complicated, merely that it would be doable.
The question: Do you now agree that at least the return from Apohphis would not be terribly difficult as long as the ship left Apophis before it passed earth, so that the 17k mph was sending the ship towards earth and not away frrom it?
All I can say for now is maybe. I'll have to look at the orbit in more detail tomorrow. I'm pretty tired, it's 2 AM, and I had a strenuous day, and a lot of "fluid intake" watching the Dodgers-Yankee game. Sleep is calling Now maybe if Mighty Mo can throw the spacecraft.....
I'll look into it tomorrow.
MW
Now maybe if Mighty Mo can throw the spacecraft.....I'll look into it tomorrow.
MW
MW was merely using the only really practical way for humans to rendezvous with an asteroid without spending months in a long intersecting orbit, coming up from behind. For instance, Apophis has a solar obital period of about 324 days. To come up from behind it to rendezvous, you would have to catch up to it after it passed Earth, which could take 2-3 months. Then it would be on its way out. The only way to leave Apophis as it approached Earth, would be to remain on it for the majority of the rest of the orbit, perhaps 180 days.robnissen":228mtlpx said:
The months in transit would be wasted because there is very little useful work that could be done during that time. Also, every day in space uses consumables which add more mass to the ship which requires even more thrust which requires more fuel which requires more thrust…………….robnissen":228mtlpx said:
No, that was your argument, not mine. You are the one offering a three day surface mission by humans. I merely said that robots could do the same thing easier, a lot cheaper, and a lot safer. Comparing it to the Apollo landings is a Strawman. Those missions were short because our technology was so relatively primitive then, and the purpose of those missions was so much different than contemporary missions.robnissen":228mtlpx said:
Well I am going to reiterate that all the manned space advocates should rally behind the best most do-able project for the near future and that is building a base on the moon. Long term stays by scientists and engineers who can determine whether safe habitats can be constructed and maintained while actually performing good science in the astronomy field.
The Moon is not, and never will be a suitable test bed for developing systems for use on such planets as Mars. The first colony should be on Mars. The only use for a Moon base is to provide materials and propellant for space missions once the need is established. Until then, the Moon is not a practical use of resources.bdewoody":15sbov76 said:
I strongly disagree with your conclusions Mental Avenger. Is a discussion of our actual reasoning likely to be profitable?
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