I'm unsure of your logic there, ngunn. During Skylab, which IIRC was pressurized to about 5psia with pure oxygen, the crews found that they could not be heard by other crew members once they were more than about 5 meters away. Also, squawk boxes that were installed to provide comm through out Skylab weren't numerous enough, and even caution/warning klaxons became impossible to hear a very few meters away from one of them.

At lower pressures, sound attentuates faster. The pressure wave may move as far regardless, but its energy (i.e., ability to excite an eardrum) falls off faster. Thus, sound becomes inaudible at a much smaller distance. That's not speculation, it's empirical, observed fact.

-the other Doug

The ECO sensors are indeed capacitance sensors. I don't have data at the moment as to whether or not they're AC-excited, but they're definitely capacitance sensors.

-the other Doug

Moon dust smelled like burned gunpowder to the astronauts, so the story goes, because the dust had sharp rock facets that had never been exposed to enough gas to interact with the facet surfaces. That made the surfaces of the dust particles slightly more chemically reactive than they would become once they had been immersed in gases for a bit. (Especially oxygen.) Gunpowder is also more chemically reactive than most other terrestrial substances (certainly more than dirt), and so our sense of smell perceives the two substances similarly. As soon as Moon dust is kept in an atmosphere for a while, it loses its odor.

Now, as for Mars... I have been thinking for some time that Mars dust might actually have a rather nauseating aroma. Add the obvious sulphuric element to the peroxides that are postulated to make up at least some of the soils, and you get something that would stink and burn your nasal passages, all at once. It would be a hell of a note if we lost the first humans on Mars because they couldn't keep food down...

-the other Doug

As a tech support rep for Comcast, I can tell these guys exactly how to fix their problem:

1) Unplug everything.

2) Leave everything unplugged for a good 30 seconds.

3) Plug everything back in, in sequence from upstream to downstream (in terms of signal flow).

Works every time...

-the other Doug

I always thought that the ultimate in scan platforms was Galileo, which, IIRC, was a spinning spacecraft with a central bus that was entirely despun. All of the control cabling, instrumentation data flow and power flow between the spinning portion and the despun bus had to connect along continually moving surfaces.

I'm still amazed it worked.

-the other Doug

Looks like a passing rocket left a hole in the cloud deck...

-the other Doug

My thoughts exactly -- it's going to be a very energy-intensive process. Just bringing on a few electric heaters isn't going to get it done. We're talking about *extremely* cold ice here, for the most part. Ice, like any other material, needs to be raised all the way to its melting point before it will melt. You can't just ignore the hundred-plus degrees of heat that you have to apply just to get the ice up to its liquifaction point.

This is going to be harder and more energy-intensive than, say, melting ice cubes that are already within 10 degrees of their melting point.

-the other Doug

I don't think I'd be good with just opening up a hole and creating a geyser to study. There is a whole wide range of assumptions we can make about what's in that ocean -- but if there are living organisms, I think it's incumbent on us to explore without endangering them.

After all, we don't want UMSF to get the bad reputation that the military had at one point -- you know, the reputation reflected in the old slogan, "Join the Army, go to strange new places, meet strange and interesting people -- and kill them."



-the other Doug

I would say that not only is it imperative that a melt-hole reseal itself, it's really unavoidable. The extreme cold of the ice surrounding the melt-hole will refreeze any liquid water very quickly, for the first 80% of the hole at least, so if you don't keep re-heating the walls of the hole, it'll freeze solid again within hours of the passage of the ocean probe.

I'm tempted to think that the first 20 or 30 meters of the hole might have to be drilled "dry", the probe dropped in, and the whole thing filled in with the excavated shavings. You then very *slowly* melt out enough liquid water around the probe to *seep* up through the shavings, consolidating them and establishing a pressure-tight seal.

You think that's going to be an engineering feat? That's not even the biggest challenge -- the biggest problem is how to maintain communications through the ice crust between the probe as it descends (and of course after it reaches the ocean) and the lander on the surface, which is of course the comm link between the probe and the outside Universe.

You can't just lower the thing on a cable -- the cable would probably have to be a few km long at the shortest, which would be pretty massive on a spacecraft which will likely have an extremely tight mass budget. Not to mention avoiding snag and jam issues on whatever payout device you design, and the fact that 99% of your cable would be frozen into the resealed hole for most of the descent. You'd have to keep the cable heated for its entire length for it to move through the ice as it pays out, and that wouldn't let you truly seal the melt-hole and avoid that nasty geyser that will otherwise spray your entire mission into a Europan sub-orbital trajectory.

The best design I've seen (and it's likely been discussed here) was one in which the descending probe would leave relays every few tens of meters, each relay capable of talking with the two above it and the two below it. (It's easier to transmit across 30 meters of ice than it is to transmit across a few km... and you want to be able to lose one or two and, as long as they're not next to one another, you still maintain your overall link to the surface.)

The bigger issue, of course, is that any such ocean probe is going to have to literally sink the entire way through the ice crust. That means that the probe is going to have to create a bubble of superheated (for its environment) liquid water that will unfailingly *sink* through the entire crust. Given the likelihood (almost certainty) that the ice is likely not homogenous but will have impurities (such as, oh, I dunno, maybe house-sized rocky boulders), this is going to be very, very difficult to pull off. The whole descent process is going to be extremely energy-intensive, and the probe will have to take that energy down with it -- no cables, remember? And each comm relay is going to have hefty power requirements, too. (And, of course, in such an eternally dark ocean, we'll need to bring some awfully bright lights all the way down into it, just to see what's there...)

The odds are that this isn't going to work the first time we try it. It may not work the first several times we try it. It may be almost impossibly difficult to do.

Whatever the odds, though -- we simply must try.

-the other Doug

Really? What do you think the P stands for in the P6 truss? Or the S in the S4 truss?



-the other Doug

In a microgravity environment, your feet and toes dramatically gain usefulness. I read a breakdown somewhere of how various Skylab and early ISS crew adapted to microgravity, and a certain percentage ended up going barefoot a lot, using their toes to grab onto little "toeholds" in their environments and help stabilize their lower bodies when stopping to do some transient activity for which strapping in or down is way too much activity overhead.

One of the more interesting results of the Skylab experience that was actually taken into account in the design of the ISS modules was the breakdown of how people orient themselves within a microgravity environment. Going entirely from memory, I believe it was something like a third who felt comfortable no matter what direction their heads were pointed at any given time, guys who would have happily tossed workstations anywhere on a floor, ceiling or wall. Then there was a third that preferred to have a sense of local vertical congruent to their surroundings, people who liked to keep their feet pointed towards a "floor" and their heads towards a "ceiling", but who could easily work in odd angles if they needed to. And finally, there was a third who really strongly needed the local vertical, people who got physically uncomfortable in locations like the Multiple Docking Adapter, which had no local verticals but literally plastered the interior with equipment and control consoles.

Because of this, the third who would be happy hanging any which way were outvoted, and the ISS modules are all built with a pretty strong sense of local vertical. And most of the eventual labs will share the same local vertical, minimizing disorientation going from module to module. So, this is one instance where it would seem lessons were indeed learned and applied to later programs.

-the other Doug

How effectively, given current materials technology, can we insulate the "ground" where we would locate a Titanian habitat from the heat within the hab?

Seems to me we're going to have to limit heat leakage from the hab *very* selectively, or else the "ground" (or at least some of it) will become liquid where in direct contact... thereby alleviating your worries, Nick. No matter what we do, she'll eventually end up afloat, regardless!



-the other Doug

I dunno, Aussie -- there are a lot of late-middle-aged baby boomers (like me) who were raised with the American versions of the old Imperial units, and we (well, at least I) have a hard time thinking in metric. I can *translate* into metric in my head (even conversationally), but I can't really think in it easily.

The more recent generations have been well exposed to metric, far more well exposed than my own generation. I mean, hey, when I think of changes in velocity for spacecraft, my "gut level" frame of reference is still feet per second, OK? But the kids these days -- they can think better in metric than I can.

That said, the purveyor of the recent update isn't having problems thinking in metric -- as far as I can tell, he/she is just having a problem thinking...

-the other Doug

As we all know, Martian meteorite ALH84001 has interesting structures that have now been debated endlessly as to their origins. The more interesting point, however, is that these structures occur within carbonate inclusions in the rock.

Carbonate Martian rocks have generally not been found from orbit by remote sensing equipment. And in ALH84001, the carbonate "nuggets" are rather tiny inclusions.

If there *are* carbonate rocks on Mars, how the heck do we find them? And if they tend to exist merely as tiny inclusions in other rocks, how do we analyze them (or even see that they're there) in situ?

-the other Doug

And let's not forget the many manned spacecraft that have borne names of naval tradition -- Yankee Clipper, Intrepid, Endeavour (2), Challenger (2)... and Enterprise.

-the other Doug

And, of course, the Star Trek universe's Starfleet is a quasi-naval organization. It certainly borrows more from naval traditions than any other service traditions.

-the other Doug

I hate to disagree with your reasoning, Ed, but I do. Astronaut bootprints and otherwise disturbed soils only appeared dark in the immediate vicinity of the LMs, where the descent engine plumes had swept loose dust from the surface and brightened it. Every LM landing site imaged by the J-mission pancams showed a brightened "splash patch" of soil extending 50 or so meters out from the actual landing points.

Extensive review of the TV and film record, and accounts of the astronauts' impressions on the scene, confirm that footprints, rover tracks, etc., did not generally darken the soils at any reasonable distance from the LMs. In fact, in some places (especially at highland sites), footprints and other soil disturbances actually brightened the soil, since in some areas a dark gray surface covered brighter deposits.

That said, some hardware impact sites that have been imaged do display dark rays -- notably some of the S-IVB craters. I've wondered if that might not have something to do with the composition of the impactors, however...

-the other Doug

What still concerns me about any operations on Titan (manned or unmanned) is the rather phenomenal temperature difference at which terrestrial machines and organisms (i.e., us) can operate versus Titan's natural environment.

Any terrestrial outpost or machinery is going to add *significant* amounts of heat to the Titanian environment. If ever there was a situation where observing a phenomenon affects that phenomenon, this is it.

We may have to figure out how to develop robots that can operate entirely at Titanian temperatures before we set out to study the place at close range, because the heat our current technology would be pumping into the local materials will change them in innumerable ways, and we won't see them as they've developed in situ.

-the other Doug

This, along with many other ISS traditions (including its informal radio callsign, Alpha) was established more than seven years ago by the first expedition crew, commanded by Bill Shepherd.

Shepherd was USN, of course. An ex-Seal, to be specific. But it was Shepherd who brought the ship's bell to ISS, and who instituted the "ringing in" of all new and visiting crew.

-the other Doug

Oh, I understand -- uranium has a higher potential energy density than a lithium battery. I'm just thinking in terms of logistics. Any plan that requires bringing along enough fissile materials to support a manned base is going to be harder to accomplish (in terms of just getting everything to Titan and setting it up) than a plan that can actually draw enough power for its operations from indigenous sources.

Titan is just so energy-poor... you'd need to cover hundreds of square kilometers of landscape with solar cells to get anything useful at that distance from the Sun and through that thick haze. And you just can't extract heat out of a system that doesn't have any...

-the other Doug

I was actually thinking about the extremely high mass of fissile materials. Takes a lot more energy to send a cubic mile of uranium to Saturn than sending a cubic mile of, say, lithium batteries.

-the other Doug

All in all, though, Nick, Titan offers more of the raw materials humans would need to create a self-sustaining colony than just about any other body in the Solar System (except for Earth).

There are all the elements we need to survive -- specifically, carbon, hydrogen, oxygen and nitrogen -- in great abundance. The only thing in short supply is a good power source. Yes, if you crack enough oxygen from the water ice you'd be able to burn a lot of the hydrocarbons, but that burning would generate less energy than what you'd need to crack that much oxygen out, I fear.

The one thing we'd need to import from Earth is a good energy source to make Titan a good place for human habitation. Unfortunately, the only thing I can think of that would work well there would be nuclear energy, and you don't want to have to transport megatons of fissile materials all the way out to Saturn! (You think you have issues with the anti-nuke crowd *now*...)

-the other Doug

This view is almost identical to the view televised from Apollo 16 immediately after transposition and docking, which was by far the best image of global Earth ever transmitted via television from an Apollo spacecraft.

-the other Doug

I knew it had to be from one of three missions -- Apollos 10, 11 or 15 -- due to the amount of the North Pole illuminated by the Sun. Since we appeared to be further from solstice than July, my best guess was Apollo 10 (which, of course, flew in May).

Nice to see I was right!

-the other Doug

I've noted that two Navy CDRs on Apollo flights (Conrad and Young) both used the word "started" when context would indicate they meant "targeted." Conrad says it when he spots Surveyor Crater during final descent ("It's started right for the center of the crater!") and Young uses it when praising the targeting after his landing ("You guys just started us right in there.").

I bet we have a few ex-Navy types out there. Any of you have a clue as to whether "started" in Navy terms means "targeted"?

-the other Doug