Call me crazy, but... is there *layering* in some of those crater walls?????

-the other Doug

I wish I had specific references that refer to it in detail. There are references to the trans-lunar trajectories in the Apollo press packages and mission guides (which are available at various sites on the internet)... but the gist of it is:

Apollos 8, 10 and 11 used free-return trajectories. If there had been no LOI burn, these spacecraft would have returned to Earth. (Some minimal mid-course corrections, well within the capability of the SM's RCS engines, might have been required to trim up the corridor on such lunar flyby trajectories, but correction into the corridor was *always* within the RCS capabilities.)

Starting with Apollo 12, and for Apollos 12 through 16, the trajectory was called a "hybrid." The initial trans-lunar trajectory was free-return; with no other action, the spacecraft would remain within RCS capability of correction into the entry corridor. This trajectory usually took the spacecraft to a pericynthion of between 150 and 300 nautical miles.

On the second day of translunar coast, the SPS engine was fired to adjust the approach trajectory to place it into the desired inclination in relation to the lunar equator, and to phase the arrival time for optimal lighting conditions during landing. They had to do this to get the spacecraft into the desired lunar orbit -- it was simply not possible to get to certain orbits from Apollo's parking orbit at various times of the year and *also* assure a free return. The resulting trajectory would result in the spacecraft missing Earth by as much as 10,000 miles had the LOI burn not taken place.

The rationale for leaving the free return trajectory was that, first, by leaving it you prove that you have a good SPS engine that can get you back on a free return path if anything goes wrong. Second, you had the LM attached and your return to a free return path was always within the capability of the LM's DPS engine. So, the risk of leaving a free return path was deemed acceptable.

Of course, on Apollo 13, the SPS engine that had proved it was good enough to get them back on the free return path was disabled, along with the rest of the CSM, a day after they left the free return trajectory. Since the CSM/LM was accelerating towards the Moon at that point, they needed to fire the DPS to get back onto a free return path before they rounded the Moon, to minimize the amount of delta-V that would be needed to get back to an acceptable entry corridor.

The first DPS burn on Apollo 13 got the spacecraft back on a free return trajectory that would have ended in a splashdown some four days later, in the Indian Ocean. A longer firing after they rounded the Moon simply added speed to the trajectory, resulting in a Pacific landing only three days later.

Finally, Apollo 17 didn't use a free return trajectory at all. It was the first, and only (if memory serves) flight in which there was simply no trans-lunar trajectory that could be adjusted into the desired lunar orbit that would result in a free return. It was still a hybrid; they injected into a trajectory that was within SPS capability of attaining a free return path, and adjusted it to the desired lunar approach on flight day two. (The hybrid maneuver on Apollo 17 also served to make up for the launch delay, adjusting the trajectory so they arrived at their LOI point within a minute or two of the pre-planned time, even though they launched some two hours and forty minutes late.) By then, they simply had confidence that either the SPS or the LM's DPS would be able to get them back on a return path in case of abort.

-the other Doug

Ummm... I think that's what is referred to as "a willing suspension of disbelief." In other words, the pun is the whole point of the story, and the author (knowingly or not) disregarded real-world physics in order the deliver his punchline.

However, if a third Martian moon *had* been discovered orbiting at a lower altitude than Phobos, I would have been in favor of using the name Bottomos. Because, like the referenced author, I'm an incorrigible punster, myself...

-the other Doug

The architecture of the proposed return-to-the-Moon missions clearly says something about the way in which the same vehicles would be used for manned missions to LEO and further out into the Solar System.

For one thing, the CEV itself is basically the return "pod" more than the massive, primary "mothership" that the CSM represented in Apollo. As such, it will *not* carry the majority of consumables that the crew will use over the course of a mission. I'm getting the feeling that the crew will actually inhabit the lunar lander as their primary quarters on the outbound journey (though possibly using CEV-based consumables such as oxygen and water). On a Mars mission or an asteroid mission, you would include a habitation/logistics module that would carry the consumables for longer mission durations, with lander and propulsion modules attached on the far end of the hab/CEV combo.

Secondly, if we're going to leave the CEV unmanned in lunar orbit, it's going to have to be capable of fine-tolerance remote control. We'll have to be able to maneuver the CEV, both translationally and in attitude, as well as or better than a human pilot. Without any crew on board.

Finally, with this remote-control capability in mind, it follows that the CEV will have to have a remote-controlled rendezvous and docking capability, to support ISS operations. I'm assuming that the CEV is going to have to serve as the crew rescue vehicle on the ISS if we're ever to expand the ISS crew size beyond three. And since, if it's going to support interplanetary missions, it will have to be able to be shut down and remain quiescent for months at a time, the CEV ought to be well-suited to serve as an escape capsule. So, go the full route and set it up such that a CEV could be launched unmanned to rendezvous and dock with ISS and provide both regular and emergency services, as needed, to support ISS operations. Sort of like a super-Progress/Soyuz.

So, if it's designed to take each of these capabilities into account, the CEV could really become a workhorse that can be used in a number of different mission configurations. We just need to make sure that it's designed from the start to have these needed capabilities.

-the other Doug

Reminds me of an infamous s.f. short story from long ago. It seems the first humans on Mars find some very strange features -- hilltops sheared off, long, perfectly formed tubular channels that run for hundreds of kilometers underground -- and are at a loss to explain them until they observe a small *moon* orbiting Mars at an average height of something like 20 meters above datum.

The punster-captain of this expedition, having discovered this third Martian moon, was given the discoverer's right to name it. And named it....

Bottomos.

-the other Doug

Yes, the reason the Apollo astronauts endured such a small radiation dose traversing the van Allen belts was simply that they only passed through them for a few hours, and indeed only passed through the most intense parts of them for a few minutes. One little-discussed reason why a farside landing was never attempted was that, in many cases, the trajectory to reach a farside landing site involved an outbound path that traveled along the Earth's magnetic tail, which entrains relatively high radiation levels (Of course, that depends on the location of the landing site and the Earth-Moon geometry during the selected flight month.)

One thing I'm unclear about -- the Apollo "skip" technique was discussed a lot before they flew to the Moon, but my understanding was that they never actually employed it. Instead of skipping entirely out of the atmosphere, the closest they ever got was to use the CM's small amount of lift to flatten out the trajectory relative to the Earth's surface, extending the heat pulse but lowering its greatest intensity. Is there any online resource that shows full skip flight paths for any of the returning Apollo CMs? I'd be interested in seeing them...

-the other Doug

I live in Minnesota. I've seen lots bigger snowdrifts than those dustdrifts. Like a lot of people, I stand a little less than two meters tall. Almost every winter here, there are places where snowdrifts are significantly taller than I am. Some probably reach three to four meters in height, in places, given the right dynamics.

Granted, I wouldn't want to try and drive Oppy through any of those snowdrifts, any more than I'd be tempted to drive her through these meter-tall dustdrifts.

-the other Doug

Here's a thought -- how hard would it be to use the Moons' gravity as a "brake" to reduce the speed of a CEV capsule returning from Mars to something closer to the speed of a return from the Moon?

-the other Doug

As you could with the Viking cameras. There is an official Viking Imaging Team portrait out there somewhere, taken with one of the Viking cameras. At least one person appears in the picture three times. Several others appear in it twice.

-the other Doug

One the negative side, these rocks are all jumbled up, just like they were at Fram and Vostok and outside of Endurance and, well, outside of every impact crater, large and small, we've driven by. Which means they're not in sequence -- they're just randomly jumbled (and highly shocked) pieces of the local evaporite layer.

On the positive side, these have to be remnants of the ejecta blanket from Erebus. And Erebus is a big crater, nearly as big as Victoria (if a lot older and more degraded). So, the closer we got to the rim, the deeper these blocks of finely layered evaporite were excavated from.

OK, guys -- these are the exposed evaporite outcrops of the Erebus rim. Not very impressive, are they...?

-the other Doug

I entirely disagree.

The land has a near-surface layer of layered sedimentary rock that is much lighter than the rockbeds below it and the upper layer of regolith. That layered rockbed is very visible in the crater wall. (In this, it resembles the craters at Meridiani, which have layered evaporite rockbeds just below a surface layer.)

Some kind of fluvial event has occurred after the crater was formed, which has stripped the upper layers off of the surrounding land, showing distinctive step-like patterns of erosion into flat, layered rockbeds. There are mesas topped with land that looks identical to the plains on the right side of the intact crater wall that occur within this scoured channel-like feature.

As the event that formed the fluvial feature broke through the left side of the crater wall, sediments carried along in the current spilled out sideways, leaving a fan of debris spilling into the crater. This deformed the left rim and probably washed a good deal of it further down the channel. I'd imagine that the crater filled with water as the flood rushed past, and that backflow against the main current caused the fine features we see in the channel boundary as it passes through the left third of the crater.

So, it seems obvious that what we're seeing is a crater that got in the way of a large flood or outflow. It's probably just a tongue of what was a larger, more massive outflow flood event of the kind that carved Chryse Planitia, Ares Valles, and many, many other places on Mars.

-the other Doug

Not bad, Doug! Looks like you can see an ice cap (the southern, I'd guess) at about the eleven o'clock position , near the limb. If that's the case, then the dark splotch might well be Syrtis Major.

-the other Doug

Well, the CEV is supposed to remain in lunar orbit, with a two-person crew, the entire time that the remaining four people are down on the surface. You gotta give them *something* to do for those two weeks or so.

Now, if you could just give the CEV enough delta-V to raise up to a high orbit (like 500 km), you could do some really good global science! That would have a lot of impact on abort options for the surface crew... but it would be worthwhile scientifically.

-the other Doug

From where do you get this? The Apollo CM worked marvelously well for lunar return. And at translunar speeds (and Mars-return speeds, as well) your entry corridor for a non-fatal entry would be identical for a winged vehicle that has a lot of cross-range capability as it would for a blunt re-entry body with only a limited amount of lift.

And you pay the weight penalty for taking those wings (or whatever extra mass you load on to achieve greater lift and greater cross-range capability) all the way to Mars and back. THAT is what would be crazy.

When you're coming back from Mars, you don't really want to have to worry about whether or not you can hit the centerline on a runway somewhere. You just want to get safely down onto any ocean or desert or prairie that's flat enough to allow for a safe landing.

Besides, the entry corridor on the Earth end of the trip is actually no more stringent in terms of accuracy than the MOI corridor -- especially if you use aerobraking to help you insert yourself into Mars orbit.

Again, what are your sources for insisting that the CM design "barely" survived lunar return and is incapable of surviving a return from Mars?

-the other Doug

That's no space station -- it's a small moon!

-the other Doug

So -- how is this any more stupid than having Daffy Duck and Marvin the Martian as the mascots of the MER Rovers?

I bet if they had turned Tethys into a soccer ball, our European cousins wouldn't have said a word.

Someone's bigotries are showing. And it's not a pretty sight.

-the other Doug

That's true, but every single manned spacecraft in history has taken longer to develop than originally planned.

Just in terms of American spacecraft -- the original plans called for the first Mercury manned launches in 1959. The first Gemini flights were originally scheduled for 1963. And the first Apollo flights were originally scheduled for 1965. (These "original" flight dates are all what were scheduled at the very beginnings of the spacecraft development programs.)

For the record, the first manned Mercury flew in 1961, first manned Gemini in 1965 and first manned Apollo in 1968.

And of course, the Shuttle was supposed to fly in 1978 -- and didn't fly until 1981.

I would hope that Mike Griffin is aware of all of this, and is trying to have realistic schedules put together for CEV.

As for the potential delay or cancelation of the Moon/Mars Initiative to fund Katrina relief -- unless those same Congress-critters are willing to withdraw America from manned space flight entirely, they need to spend money on either a new manned spacecraft or a re-certification of the Shuttle fleet. Neither option is cheap, and the former allows for an expanded program into the 2010s and 2020s. They may delay the heavy lift launchers and the lunar lander programs, but I bet the CEV is going to go ahead on schedule.

-the other Doug

Yes.

-the other Doug

In fact, people who are paid to investigate these things have found the the Moon is in a complete steady-state saturation state in all craters smaller than about one kilometer. There is a constantly maintained population of craters of all sizes below one kilometer -- including craters only microns in size. Lunar rocks feature "zap pits" which are the result of impacts from very tiny dust-mite-sized particles. So the instance of lunar craters from one meter to only a few microns in size is well-established as being maintained at its saturation point -- there are as many craters evident as is possible, considering the erasure of earlier craters by later cratering events.

The fact that the terminator regions of Itokawa do *not* show a saturation level of cratering, down to the resolution limit, is indeed a telling observation. This is in no way similar to lunar surface cratering in abundance or size distribution, even at the same scales.

-the other Doug

I used to think that, too. But models show that debris would tend to hit both near and far sides of the Moon equally -- Earth slingshots debris into the near side as often as the Moon gets in the way of things headed for Earth. As evidence, basins are distributed fairly evenly across the entire Moon, near and far sides.

As far as the Moon's near side containing more of its mass than the far side, because of the Earth's gravity, as was once thought -- not true, either. The Moon's center of gravity (and mass) is actually a slight bit farther towards the farside surface than the nearside surface.

I imagine that the flooding of the nearside maria with basaltic lava flows had more to do with a short period of time defined by the dynamics of tidal lock than with the overall structure of the Moon. But, of course, I could be wrong... especially since laser ranging studies suggest strongly that the Moon's core is rotating at a slightly different speed, and at a slightly different inclination, from the rest of the Moon...

-the other Doug

I think it's pretty clear that the crater was not there nearly 30 years ago, that it was very fresh when first imaged by MGS, and that its ejecta has been significantly lightened in albedo since it was first imaged.

There is a lower-resolution image at this same site that shows the area at the same resolution available in the Viking image, and you can easily see the dark ejecta. And we can see that the dark ejecta has been lightened considerably between the first and second MGS images -- I can't imagine that this ejecta would get lighter, then darker, then lighter again. That's counter-intuitive to aeolian alteration; even when things are covered then uncovered, the fines would tend to remain, and the fine feathery ejecta pattern visible in the "fresh crater" image would be lost forever.

No, it's awfully obvious that this is a very fresh impact crater. And there's no reason to believe that such things don't continue to happen on Mars. It's a big planet, and it's closer to the asteroid belt than we are. There are more impactors nearby, and the thinner atmosphere promotes survival of impactors down to the surface.

-the other Doug

In my humble opinion, AI is a bit overblown. If you think we will make computers that can think and reason as well as human beings anytime within the next 20 years, I think you're being wildly optimistic.

Keep in mind, we have only the *tiniest* comprehension of how we, ourselves, think and reason. On an engineering level, anway. Yes, there are theories, but nothing that is accepted as "the whole story" of how biological information processing actually works.

And so, we have no model upon which to build microcomputer-based AI. So, we stumble along in AI research with menu-driven relational database lookup structuress and very limited abilities to judge events as anything except black or white. In other words, processes that obviously bear no relationship to how human (or other biological) information processing and reasoning operates.

And the more you build "fuzzy logic" into AI systems to try and expand beyond binary decision-making, the more frequently you get completely unexpected (and sometimes disastrous) results.

Rather like fusion power plants, I think that "truly intelligent AI" and "robots as smart as humans" will remain 10-25 years in the future for the next 50 to 100 years, at least... and postponing *true* exploration of the solar system until such things are successfully designed, built and operated means postponing such explorations until long, long after everyone here in this forum are safely and cozily dead and buried.

-the other Doug

I think that, while Itokawa is quite small, it's also massively uneven in its mass distribution. It took the guys controlling NEAR quite a while to be able to perform maneuvers in which they had any confidence of the resulting trajectory -- all because Eros' gravity field was extremely uneven.

At 25km, the small mass of Itokawa won't have much of a measurable effect on Hayabusa. As it approaches, the gravity effects become more noticeable -- and as the uneven field passes through Haybusa as Itokawa rotates, the *cumulative* accelerations (in all different vectors) will be difficult to predict.

I think they'll likely approach slowly and try to model the gravity field as they close in, so that they don't end up getting swatted badly out of position as they get *really* close.

-the other Doug

Manned spaceflight costs considerably less than what is spent on COSMETICS in the United States over the course of a year.

If you want to let your soul wither and die, then by all means, I suggest you make that choice for yourself. But as for myself, I'm going to the stars, or I'm going to die trying.

-the other Doug

I think what you're more likely to see are "SSME-equivalent" engines. For one thing, in many of the proposed configurations, you wouldn't need to throttle these engines, and could design and build cheaper, less complex engines with the same full-thrust capabilities as SSMEs.

And even for those configurations that require throttlable SSME-type engines (those which side-mount the payloads), you can make them somewhat less complex if you don't plan on recovering and refurbishing them.

If all they're planning to do is build a bunch of SSMEs based exactly on the current design, then I agree, that's not a smart way to go. But I have extreme doubts that that's what they're going to end up doing. It just doesn't make economic sense to build a bunch of engines designed for refurbishment when you know you're just going to use them once and throw them away.

-the other Doug