# Tag Info

16

The harpoons are intended to hold the lander to the surface long enough to get the ice screws on the lander's legs in securely. The ice screws are intended as the more permanent hold-down solution. Bear in mind that the comet offers essentially no gravity; imagine trying to drive a wood screw into the ceiling without pushing the screwdriver upward at all. ...

16

There isn't any limit to how small bodies can orbit each other (gravity-wise) until you get to atomic scale where one of the remaining three fundamental forces (weak force, strong force and electromagnetism) take over and gravity becomes largely irrelevant. With smaller bodies, gravitational potential will only be that much smaller and required centrifugal ...

13

Indeed the presence of water has been confirmed. The late 1980s mission Giotto confirmed the existence of water on a comet well-known to mankind - Halley's Comet. Wikipedia states: Measured volume of material ejected by Halley 80% water, 10% carbon monoxide 2.5% A mix of methane and ammonia. Other hydrocarbons, iron, and sodium were ...

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 ...

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

There are a total of 4 Martian spacecraft that have promised to attempt a photo, according to this article. Mars Express- Will look for a total of 2 weeks, it started this week (On Monday) MRO- HiRISE camera will take 3 photos, at closest approach and the day before and after. Curiosity and Opportunity will both attempt a photo as well. In fact, at least ...

9

Yes No (see update). From ESA's 15 November 2014 update on the Rosetta mission: Pioneering Philae completes main mission before hibernation 15 November 2014 Rosetta’s lander has completed its primary science mission after nearly 57 hours on Comet 67P/Churyumov–Gerasimenko. After being out of communication visibility with the lander since ...

8

Rosetta's approach and odd orbit (described well in the question and answer here: Is this really Rosetta's orbit around 67P?) are designed to gather the necessary information needed to achieve a safe orbit and eventually land Philae. The landing site is being selected now: "As many as five possible landing sites will be identified by late August, before ...

8

Indeed it's extremely difficult to accurately determine the mass of a comet without flying something past it at close range. Even if you assume an average density (which is not particularly safe, as little is yet known about the internal makeup of comets and how that varies from body to body), no earthbound telescopes (including Hubble) were able to resolve ...

8

Taking q = 0.2531011 AU (perihelion radius) and e = 1.1937160 from the latest ephemeris for A/2017 U1, we get a semimajor axis of $$a = \frac{r_p}{1-e} = -1.3065575~\textrm{AU}.$$ Using the definitions of 1 AU and $\mu_{\textrm{Sun}}$ from here, we get the heliocentric velocity at perihelion of v_p = \sqrt{\mu_{\textrm{Sun}}\left(\frac{2}{r_p} - \frac{1}{a}...

7

Since my question didn't yet receive an answer, I did some digging around of my own. This should be considered as a temporary answer, before more precise ones will be actually possible. The answer is, that for the time being, we don't know yet, because we don't yet know what orbit around 67P/Churyumov–Gerasimenko will be first attempted, or is indeed the ...

7

TildalWave's answer is good when only considering the two bodies, but as Pepijn and mart note, for many purposes it is also important to consider the other forces at work, which brings me to one of my favorite learnings about orbital dynamics. In many practical scenarios, we need to consider the influence of the Sun, which exerts tidal forces that become ...

7

It turns out that scientists thought the same thing very recently. According to this Anatomy of a Comet article at NASA Jet Propulsion Laboratory's website, related to the Rosetta mission, "Scientists used to think that it was solid and firm, but NASA’s Deep Impact mission (2005), in which Rosetta participated, surprised them. They found that the ...

7

Agreed, orbiting can happen at pretty much any scale. To give an idea, 67P/Churyumov–Gerasimenko has an escape velocity of about 1 m/s. (removed reference to ISS experiment because that didn't rely on gravity) A quick experiment: for bodies that weigh 1 kg each and a radius of 1 m, the formula given by @Tildalwave yields an orbital speed on the order of \$...

6

I did some research, and according to this source, Philae has only one, upward-pointing, thruster, the "Active Descent System". It has no downward-facing thrusters that could kick up dust. This thruster will likely only be used when Philae is already on the ground to keep it there while it anchors itself, not for course correction. Rosetta contains a ...

6

(Consider this a spaceholder until I get around to the hard part of the answer) Principally there's no lower size above atom scale. But I would say that for stable orbiting, the gravitational force should be the dominant force compared to solar wind etc. This would depend qualitavly on these factor: Mass of the 'central' body - the heavier the less relative ...

6

According to Google Translate version of The Wayback Machine cached copy of the now expired domain: "Small bodies exploration Forum" is a group that joins us from various positions for the next small bodies exploration of "Hayabusa" mission, followed by the public debate by using the Internet, etc.. In this site, I would like to introduce ...

6

The existence of water on comets is not really news, we can detect it by many means, for example by mass spectrometry analysis of comets' tails and coma using ground based or orbited observatories, so I'll rather point out maybe a bit more interesting fact that we have actual direct evidence through the collected and returned to Earth samples taken by the ...

6

Comets are typically on much higher energy trajectories compared to the asteroids looked at for mining. I suspect that that alone would make them un-economic.

6

Assuming that our vaporization is at least as effective as a rocket engine (ISP 500) that gives 2.5m/s delta v Unlikely - the rocket engine uses a shaped engine bell tuned to give the best thrust (put simply) over a several minute burn. Whereas vaporised material from the comet itself would consist mainly of low energy expanding gas and its "exhaust angle" ...

6

The only form of ice that we see naturally in bulk on Earth is Ice I, all within the sub-h variety. There's no place on Earth that gets cold enough for any other form--but that's not necessarily true for the rest of the solar system. Unfortunately for this question, there is nowhere in the solar system that we could ever find any type of ice that depends ...

6

I used the JPL Horizons database and downloaded the predicted positions (state vectors) of Earth and Comet 67P at 10 day intervals from 1600-Jan-01 to 2500-Dec-01. edit: As @pericynthion pointed out in comments, since comets are subject to various non-gravitational forces, including "propulsion" by gasses vented unevenly and unpredictably by the rotating (...

6

These are all space probes that have visited or investigated comets throughout history, mostly from the Halley Armarda, a group of probes launched to investigate Halley's Comet during its 1986 approach. Bear in mind the portraits are very stylised so certain identification is kind of difficult. Across the top from left to right: Sakigake/Susei Japan's ...

6

It is a “Fast Mission” opportunity. These are missions that address an opportunity in the near future that would possibly be missed with the normal mission development timeline. Historically, ESA missions are classified as Large (L), Medium (M) or Small (S). The distinction is not on size of the payload, but on the technology development required for the ...

5

The advantage of asteroid mining is that there's very little mining involved; almost all of the resources are exposed, free to take. It's "bringing them home" that's the problem. What is most expensive in space? Air can be reused. Solar power is abundant as long as you don't fly too far away. The resources are there free for picking. What is most expensive ...

5

Well, to know that question, someone would have had to track it in the last 20 years, and that hasn't been done. It is fair to say it will still be somewhere in the vicinity of Earth, and I tracked through a few rumors that it might be heading back to Earth around 2016, but the general consensus is that it isn't well known where the spacecraft in fact is. ...

5

I'm going to interpret your question as "is it feasible to change a large comet's orbit to one we can easily access?" The short answer is no, we cannot with current technology. In order to move something as massive as Chury (100 Billion metric tons) in a controlled way you need a rocket that can produce a great deal of power, and you'd need an enormous ...

5

There are two specific things that we have to have to get pictures in this case: Communication: PearsonArtPhoto already talked about this. If we can't receive information from the probe we can't get pictures. The instruments cannot have been damaged: Take a look at this picture of Philae: (Note: instruments are described on the Wikipedia page) The ...

5

According to this SETI Talk 2014 Dec 16 by Jens Biele at German DLR, the "grabbing mechanisms" failed in several ways. The cold gas thruster that should've pushed it down gave an error indication even before landing. But since there was nothing they could do about it they landed as planned anyway. They had wired the harpoons wrong so they did not fire on ...

5

There are a number of reasons: When it's near the Sun (anything less than a few AU) a comet evaporates quickly, so it's not a safe place to be in. If you put the probe in the wrong place, evaporation below it can blast it off the comet. When the comet is further out that reduces, of course, but it takes a long time for the comet to become completely ...

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