Episode #125 of the Stack Overflow podcast is here. We talk Tilde Club and mechanical keyboards. Listen now
39

The United States (along with Russia, China, Japan, India, and most other space-faring nations) did not sign (or in some cases, ratify) the Moon Treaty, and so companies that are registered in any of these countries are also not bound by it. So, that treaty is essentially pointless for anyone who actually has the ability to get to the moon in the first ...


35

NASA has actually published a study on this. This study was the primary motivator for Planetary Resources to start its work on mining an asteroid. And there is more work being done by NASA to learn more as well. And there's the approach that Planetary Resources has set in place, which seems to be the best overall approach. The first thing that should be ...


34

There are three factors which contribute to the difference in “apparent crateredness” between Earth and Mars. By far the most significant is ongoing erosion from weather. In Mars’ thin atmosphere, a crater can last for hundreds of thousands of years if not millions. On Earth, small craters are buried or worn away relatively quickly. The second factor is ...


28

Caves Any large body where you can survive on the surface to begin with can be used for caves, artificial or natural. This observation isn't off-topic because you ask about holding in atmospheric pressure. Moon caves can hold 1 atmosphere of pressure about 60 meters below the surface with no stresses on the surrounding rock. I'm using very simple math ...


27

Definitely not in current shape, as it depends on tightly packed soil/rock to provide an opposing force to resistance of the ground/rock against the drill. Asteroids, with low gravity, will be far less stable and this sort of forces could easily break apart smaller ones. Also, starting the tunnel would be a serious problem, as instead of 1g to keep the ...


26

No spacecraft has been yet lost to the asteroid belt. In fact, we have the opposite example of missing an asteroid when it was even targeted, like was the case with MINERVA lander of the JAXA's Hayabusa deep space probe, missing the 25143 Itokawa asteroid. Why haven't we lost any spacecraft due to collision with asteroids in the asteroid belt is also pretty ...


25

This report shows that Mars is hit over 200 times a year by meteorites big and/or fast enough to leave a crater of typically 12.8 feet diameter. Earth strikes of this size are thankfully much rarer, so yes: Mars is more at risk. Possible reasons for this are: a) Mars is "only" 100 million km from the asteroid belt, whereas Earth is 180 million km away; b)...


20

The Voyager probes are outside the Kuiper belt now, and have a very long way to go before entering the Oort cloud. They are now in a place that is almost completely devoid of matter. Or at least I couldn't find any estimates as to how dense the solar system is there. But what about when they where still in the Kuiper belt? If Wikipedia is to be believed, ...


20

It does not have any known objects. It seems unlikely that it would happen, although it could theoretically happen for a short period of time. There are few stable orbits around the Moon, and even fewer that are likely to remain stable for any length of time. Even Lunar orbiting missions don't remain stable, and they have a better chance than a random object ...


19

Finding macroscopic (i.e., big enough to actually use) pure-iron meteoroids appears to be extremely low-probability. Certainly the bulk composition of the metals in Earth (good references here, here, and here) and metallic meteorites is iron plus nickel, a siderophile, and a few also-rans, like sulfur and oxygen, and other siderophile metals like cobalt. ...


18

With all the hype in the news this was surprisingly hard to research for specifically 2011 UW158. I never did find a source for the claim on the value, though the Slooh Community Observatory put the claim at "\$300 billion to as much as \$5.4 trillion dollars worth of precious metals and minerals". The answer basically seems to come down to: we've analyzed ...


18

The asteroid belt isn't nearly as dense as popular media makes it out to be. An answer from the Dawn Mission's FAQ, specifically "What is the average distance between individual asteroids? (6/13/10)", helps here. Asteroids are not distributed uniformly in the asteroid belt, but could be approximated to be evenly spaced in a region from 2.2 AU (1 AU ...


15

I just want to add that a lot of work goes into predictions of abundance, for objects including those we have not detected so far. There is some similarity to exoplanets - where we know that a method has a detection bias. If you can quantify the detection bias perfectly, then you can get the total abundance for different sizes. One source gives a pretty ...


15

The asteroid belt is roughly 6 Astronomical Units wide, and so when it is drawn only 600 pixels wide with each asteroid a handful of pixels wide, you end up with each asteroid being five times bigger than the Sun! I've borrowed a small piece of the image used in @jos' excellent answer to show what I mean. As pointed out in this answer, Wikipedia says: ...


14

Our Moon makes this possible. An asteroid with a low $V_\infty$ with respect to Earth making a close flyby of the Moon in the right direction could get into a distant orbit around the Earth. That object would likely continue to encounter the Moon, and could be ejected again.


13

At this point in time it seems doubtful that we could intercept and deflect an asteroid large enough to justify being deflected. This is simply a matter of momentum, a large asteroid has a great deal of momentum and the puny little spaceships we can presently intercept an asteroid with can impart only very little momentum. The only way we can substantially ...


13

The challenge here is getting the pusher plate into position. The potential impactor is not generally traveling on an orbit that can be reached with low DV. So the only way with current(ish) technology to get 100-1000 tons of pusher plate alongside and stationary to an asteroid is if it uses an Orion drive. And if you have a fully working Orion then you can ...


12

Both questions are really hard to answer. You can only estimate how often this happens. There is no monitoring system, which constantly observes the entire sky. There is an unknown number of asteroids and comets in the solar system. Right now, the rate of newly discovered objects increases exponentially (due to better and better technology). Today's number ...


12

Yes. Planetary Differentiation is the key here. When enough smaller asteroids smash together and form a big enough body, the heavy stuff sinks to the bottom (iron and other metals), middle layers tend to be formed of silicates (i.e. sand and rocks), and the lighter stuff floats on top (water, methane). (Mind you, the examples here are based on the ...


12

Let's break your question into separate tasks: Autonomous orbit determination (autonomous because the DSN won't be there to help you when you need it) Autonomous attitude determination Situational awareness for formation flying (relative positions, velocities, attitudes and attitude rates), most efficiently done in a cooperative manner Cooperative collision ...


12

Unlike chemical rockets such as hydrazine (a monopropellant, which doesn't require separate oxidizer and fuel to burn), water is just the reaction mass — not the energy source. The Comet-1 thruster that the DSi Prospector series is using is electrothermal, so it requires a substantial electrical power supply in order to energize the water (presumably ...


11

The prior answer cleared up the issue I was having. It is true that with only the absolute magnitude (H) and albedo (p) you can estimate the size. The formula is the following: $$D(km) = \frac{1329}{\sqrt{p}}10^{-0.2H}$$ For objects in my search range, here are some examples: (object name) (JPL diameter estimate) (formula result) Aten 1.1 km 1....


11

It would take vastly more $\Delta V$ to get it to a low-Earth orbit. The targets selected are close enough to Earth's orbit about the Sun that it only takes around $200\,\mathrm{m/s}$ to get it into a distant retrograde orbit about the Moon. To get the thing to a low Earth orbit would be around $3\,\mathrm{km/s}$. The tyranny of the rocket equation makes ...


11

It depends on the size of the asteroid. According to this article, if the asteroid's diameter is more than 8 km, you can walk on it without the fist step sending you flying off. When the asteroid is smaller, the article proposes to loop a cable loosely around the asteroid. Astronauts can tether themselves to this cable and walk around. Of course this limits ...


11

There is a lot that the two missions you mentioned--Stardust and Hayabusa--have taught us about sample return. Sample Contamination: Serious measures were taken with Stardust to control for the possibility of sample contamination, but notable problems were still encountered: However, despite these precautions the Stardust spacecraft outgassing was ...


10

Dawn uses an ion drive which is very efficient but does still require xenon as a reaction mass. Dawn started with 425kg of xenon and used about 275kg to get to Vesta and will use about 110kg to get to Ceres. The remaining 40kg is for stationkeeping and margin. Dawn does not, nor was it planned to have, enough xenon left after arriving at Ceres to depart ...


10

There is one such article here, based on a NASA paper: Most Earth mining depends upon gravity to hold the cutting edge against the ore. (However, for many Earth mining operations this is not enough, and other means are employed, e.g., cables and reels.) Scraping away at the surface of the asteroid requires holding the cutting edge against the outer ...


10

There are entities that hope to mine asteroids, Planetary Resources and Deep Space Industries. The proposed Asteroid Retrieval Mission is based upon the Keck Report, a paper outlining how a small Near Earth Asteroid (NEA) could be parked in lunar orbit. Co-authors of the Keck Report include Chris Lewicki (Chief engineer of Planetary Resources), J. S. ...


10

The general idea behind this is as follows. After a certain size of impact, there isn't really much that will increase the devastation. So if you take two rocks, each half the size of the first, and toss it, you will quite likely have 2 large impacts, instead of 1 large impact. If you manage to make all of the pieces small enough, then there would be less ...


10

The main problem is that the Moon has many mascons, not a uniform sphere. Close orbits around it tend to get perturbed. They keep the same semi-major axis but become more and more elliptical until they hit the Moon. Early satellites sometimes hit the moon within weeks, while others lasted for months or longer, and it took them a while to figure out why. ...


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