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Hi Everyone,
I was going back thru some old posts and found some good ones by Hop. I'm bringing them forward and making a thread for talking about the delta vee and orbits needed to create artifical impacts on Mars.
I'll make several posts on this subject later, first what Hop has to say:
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I would use the asteroids at Jupiter-Sun L4 and L5 points (aka Trojans)
These are far enough from the sun to be ice rich.
Delta vee to send them on a Hohmann journey to Mars is 4.27 km/sec. Likely the asteroid's own resources can provide fuel and reaction mass.
When a Trojan arrives in Low Mars Orbit, it is traveling 7.6 km/sec. If Mars' atmosphere sheds 2.8 km/sec or more, the body is captured into elliptical orbit. Then each periapsis the body would again graze the atmosphere, gradually losing angular momentum Until finally the Trojan penetrates the Martian atmosphere one last time at about 3.5 km/sec.
For one body of Trojans, Hohmann windows occur each 2.24 years. But Mars could receive Trojans twice as often since there are two populations (the leading and trailing or L4 and L5). It takes a Trojan about 3.1 years to fall to Mars from it's original 5.2 AU orbit.
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Hop
>>> also... <<<
Another possibility is the outer Main belt. There is a healthy population at 3.15 AU and these also may be volatile rich.
Delta vee to send it to Mars is 3.23 km/sec. Velocity at arrival in Low Mars Orbit is 6.2 km/sec. The atmosphere would need to shed 1.4 km/sec or more to capture the asteroid to an elliptical orbit.
The synodic period is 2.83 years, but I don't think you'd need to wait that often to send asteroids Mars way since these asteroids are scattered in a ring about the sun. These take about 1.8 years to fall to Mars from their 3.15 AU orbit.
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Hop
>>> and... <<<
If I remember right, Kim Stanley Robinson terraforms his Mars with KBOs. To send bodies at 40 AU to Mars you'd need 3.4 km/sec. Velocity on reaching Low Mars Orbit is 10.5 km/sec Sad. It would take about 47 years for a KBO to fall to Mars from a 40 A.U. orbit. Getting to KBOs would be very hard. We still haven't sent a Discovery mission to Pluto so far as I know.
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Hop
Thanks Hop for your interesting posts. Are you still active? I've not seen anything receint by you.
Warm regards, Rick.
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Why might we want to drop asteriods or comets on Mars?
1) Add mass to Mars & increase its gravity. (This is so small an advantage as to be almost zero.)
2) Add volitiles to Mars. Mars has been slowly losing water to space for billions of years. From what I've read, a comet 1 km cubed in size would last tens of millions of years before its water was lost. More Nitrogen, Argon and the like will help Mars perminantly.
3) Start volcanos. This is a good thing bad thing. Impacts large enough to start up volcanos will also blow away a fair bit of atmosphere. By the time we start dropping giant comets on Mars the local population likely won't appreciate impact this large.
4) Land on Carbonates / Nitrates rock formations. It is looking like Mars does not have much in the way of Carbonate rocks (too acidic?) but likely it has plenty of Nitrates caused by lighting reacting with nitrogen in the atmosphere. If we drop a iceteroid with 5% NH3 on Mars on top of a nitrate bed we might get a nitrogen boost double what is in the comet itself. (This is all speculative but likely in my view.) If we don't have carbonate beds, we might be able to drop the comet on CO2 Clathrates and get a simular effect. Basically by picking the impact points we can leverage the amount of mass in the comet.
5) Adjust the spin of the planet. Again this result would be so small as to be almost zero unless we are talking about unreasonably huge numbers of rocks of very large sizes.
6) Adjust the albedo of Mars. In another thread I calculated that if we darkened Mars with a carbonaceous chondrite asteroids to a depth of 1mm we would get a 5 degree C warming. This might be enought to be significant for terraformers.
7) Melting the ice caps. No question this would work but the problem is that water (or CO2) vaporized / melted will just refreeze. Even the energy of fair sized asteriods would be dwarfed by the sunlight reflected by a 200 km^2 mirror hovering over the poles for a year or two.
Anyway those are the main reasons I see for dropping rocks. If people would like to argue that we shouldn't drop rocks on Mars, perhaps we can move that question to a new thread? In this thread the working assumption is that someone might want to do this and we will talk about how expensive it will be.
Warm regards, Rick.
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Hi Everyone,
Hop had shown in his posts above that the Hohmann journey to Mars from the Trojan asteriods requires a delta vee of 4.27 km/sec. In Jupiter's oribt they are cold enough to have plenty of water. However, I am not enchanted by the Trojan asteroids as they are too warm to keep their NH3 which is the volitile that Mars really wants more of. So how much more would it cost us to go to the outer solar system?
Not much (in terms of delta vee)...
(By the way, most of the numbers in this post are from "Entering Space: Creating a Spacefaring Civilization" by Robert Zubrin.)
Objects far out from the sun orbit at a slower speed. It thus takes less delta vee to change their orbit from circular to eliptical. Nor do you have to make the elipse reach Mars at one end (that is expensive). All you have to do it give it a new orbit that moves it close to an outer gas giant and then use that body as a gravity assist to slow your iceteroid so it will fall into the inner solar system.
Robert Zubrin suggests moving an asteriod in a 25 AU circular orbit so it gets a gravity assist at Uranus. This will require a delta vee of 0.3 km/s!
The down side of this is after falling so far towards the sun, the body will have picked up a lot of speed. (We generally prefer nice small, slow impacts...)
This can be handled two ways: one we can move small bodies so that even when they hit Mars hard, the impacts are minor and don't splash large amounts of atmosphere, etc. Since it is MUCH easier to move small bodies than large ones, this is my choice.
If you wanted to move a huge body (say because you decided you just had to build a good sized moon), then you could use another gravity assist at Jupiter to slow the fall towards the inner system and circularize the asteriod's orbit.
Large gravity wells are in many ways like free fuel when it comes to plotting orbits around the solar system. We were lucky enough to get 4 huge gravity wells in the outer solar system. It seems a shame not to use them.
Warm regards, Rick.
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How feasible is dragging a 1 km asteroid into Mars orbit? (For All Mankind Spoiler Alert)
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