I do understand your point, John. The problem with just inventing better rockets to drop the mass from Mach 5 down to zero is that, as the mass of what you're landing goes up, the total amount of its entry velocity that can be shed solely through atmospheric drag becomes less and less. And the more velocity you need to shed using rockets, the more propellant you need to carry, and the less effective drag slowing becomes. It's a vicious circle.

And besides, if you're going Mach 5 and you're a kilometer above the surface, and you have no more than about 30 seconds to remove the remaining velocity, just how many G's would you have to pull to avoid crashing? A 50-G deceleration would probably be outside the limits for Mission Success in any manned or unmanned mission I can imagine, and I can't imagine the required deceleration being much less than that.

If you use chemical rockets, you're going to keep coming up against the isp limits we've already identified as barriers to growth. We need truly revolutionary advances in propulsion technology, not just engineering tweaks of known technologies, to get the performance-to-mass ratios required for an effective MSR, much less for manned landings. IMHO.

If you look at it as a Venn diagram, I'm just afraid that the set that contains what's possible to do with chemical rockets, and the set of the mass of vehicles required for MSR, are sets which do not overlap...

-the other Doug

p.s. -- please bear in mind that I'm qualifying all of this when I say we need an EDL breakthrough for an *effective* MSR. I do not consider spending 15 billion dollars to bring back less than a kilogram of samples to be effective. That's an awful lot of money to return, frankly, far less material than we already have to analyze from Martian meteorites. -dvd

I can, however, imagine an impactor large enough to succumb to tidal break-up as it approaches Mars.

Bring a body the size of one of the larger asteroids across Mars just within the Roche limit. As the body breaks up, the release of the outer pieces would fling them into escape velocities, and breakup dynamics would allow some pieces to fall into stable orbits. The rest of the body would, of course, impact Mars.

In such a break-up scenario, I can well imagine pieces the size of Deimos and Phobos coming out of the process as relatively intact chunks of rock. Collisions with other pieces of the original parent body during the break-up would knock off the roughest edges, and accretion of smaller chunks over the months and years after the break-up would provide craters and regolith.

Perhaps Phobos looks like it has stretch marks because it was literally stretched in the process of the break-up on the original body? Subsequent mantling and alteration has not been enough to wipe the striations off the face of the little moon, since the cracking also controls impact-shock faulting and reinforces the surface expression of the cracks.

On a gestalt level, it hangs together... at least, for me.

-the other Doug

In actuality, I truly don't think the issue is really designing a MAV -- no offense, John, but it's really not that hard to design a rocket that can do the job. You don't need revolutionary new propulsion technologies to get off Mars and into MEO.

The problem is that with most any existing rocket technology, you have to land a very large mass onto Mars to make MSR work. Not as large a mass (or set of masses) as for a manned landing and exploration, but a very large mass, indeed. And the problem is that we've maxed out the amount of mass we can land on Mars with something roughly the mass of MSL. Much heavier and you run smack into the Mach 5 problem that has been discussed here extensively; the mass required for a MAV is large enough that friction with Mars' thin atmosphere isn't enough to slow it to a speed from which rocket braking can take over and reduce it to a landing velocity before the vehicle crashes.

Let's face it, it's probably just not possible to build a MAV powerful enough to do the job and that is yet light enough that it can be landed (even in pieces) with our current ability to do a successful EDL.

So, the EDL challenge would seem to me to be the limiting factor. If we can beat the Mach 5 problem, then it just becomes a matter of spending the money needed to get that mass to Mars in the first place.

-the other Doug

The original plan was to bring Hubble back, actually. It went away after the Columbia accident, mostly because mooring the Hubble properly (and prepping it for return) requires EVAs, and all of the Shuttles except for Columbia had their built-in airlocks removed. For ISS operations, the airlock is part of the docking adapter, which extends into the payload bay.

The add-on airlock makes the remaining space in the payload bay shorter than Hubble -- so none of the Shuttles currently flying can fit both an airlock *and* the Hubble in their payload bays.

Without Columbia, you'd have to do an expensive re-fit of one of the existing orbiters to add back the internal airlock in order to bring Hubble back. And that's just not cost-effective by any stretch of the imagination.

-the other Doug

Yeah -- there are great challenges to getting ISS out of LEO, and while it could be made feasible with a huge amount of money, it will never be cost-effectively so.

Now, Skylab -- *that* would have been far more suited to lunar orbital use. Remove the ATM, use the EREP to study the lunar surface instead of the Earth's surface... that would have been useful. And far, far easier overall to get out of LEO.

-the other Doug

I'm unsure of that radon report -- the Moon doesn't follow the same rules as worlds that accreted more slowly and melted from the inside out.

The Moon melted more from the outside in. Some decent information developed from study of lunar volcanic glasses, and the gasses and traces of volatiles found on and in the glasses, strongly indicates that the Moon's core is an unmelted, undifferentiated mass of chondritic material. There seems to be a still-molten lower mantle in which the core moves *separately* from the outer mantle and crust; The Moon's core actually seems to move and librate within at different rates, and with different motions, that the outer mantle and crust, even today.

But in a system where the entire body didn't melt, very heavy elements like uranium would sink to the bottom of the lower mantle and then stop. That inevitably means that uranium and other heavy radioactive elements would be located non-uniformly. I can imagine quite well enough local melting from radioactive "hot spots" to keep the lower mantle liquid and create just enough sluggish movement in the mantle to allow the progression of gasses up through to the surface. But in widely scattered spots.

See -- the Moon, to me, is still a puzzling place where the rules seem to have been turned upside-down, a place that still offers an awful lot for us to learn about how planetary bodies form. There have been many tantalizing hints of processes we'd never, ever have suspected. The old "been there, done that" attitude about studying the Moon is just not a rational attitude, to me... *sigh*...

-the other Doug

Why not? Three words: global magma ocean.

The energy of the final accretion of the Big Whack impact fragments melted the entire "crust" of the Moon. Any water that outgassed as vapor from the interior at that time would have been so highly energized by the high temperatures of the magma ocean that it would likely have had enough energy to escape out of the Moon's gravity well. Heck, some of that energy, combined with the chemical composition of the outgassing lunar crust and mantle, might well have dissociated some of the water molecules into other chemical forms.

By the time the surface cooled to the point where liquid water could actually exist (assuming a temporary atmosphere that would provide enough pressure for liquid water), the vast majority of the water that was "releasable" would already have been released, lost from the lunar gravity field, or altered into other chemical forms. So, the largest remnant of water would have been retained in the mantle. (Remember, the Moon's crust and mantle must have remained molten for long enough for a fairly high degree of differentiation, in which the relatively iron-rich magmas sank into the mantle and the relatively light aluminous feldspathic magmas floated to the top. It's not like the crust cooled to hardness in a matter of days or weeks after the final phases of that initial accretion.)

As for snowflakes, that's a different matter. At the very least, a fair amount of the water vapor that remained unaltered as it escaped the Moon's gravity had to have coalesced into tiny icy particles, which might have amalgamated into structures reminiscent of snowflakes. Some of that ice may well have settled back onto the Moon, and considering how long such particles might have hung around the Earth-Moon system, there's a chance some of it might well have accumulated at the lunar poles, in permanently shadowed locations. However, the time it took for the Moon and Earth to sweep up ice particles was probably less than the time from the Moon's crustal cooling to the end of the Late Heavy Bombardment, which probably scattered most of the accumulated ice back into space, or at least redistributed it into non-shadowed locations.

My feeling about the amount of water postulated for the lunar mantle is that, even during the most extensive periods of mare volcanism, the total amount of water available for liberation would have been so small (and the surface conditions now so near to a perfect vacuum) that deposition of liquid water would have been impossible, and only a tiny fraction of the liberated water would have ended up deposited in polar shadows.

Hopefully, all that made some degree of sense...

-the other Doug

I'm sure that most people won't notice this kind of thing, but this is the kind of thing that always captures my attention...

Apollo 11 was launched on Wendesday, July 16, 1969 and landed on the Moon on Sunday, July 20.

Next Wednesday is July 16, and the following Sunday will be July 20.

39 years later, and the dates land on the same days of the week as they did during the actual flight. That's only happened six times since 1969, including this year.

Just a little oddity... sort of makes you wonder just what goes on in this cesspit I call my mind, doesn't it?



-the other Doug

Yeah -- there are very few pieces of film in the documentary I had never seen The only thing I know I had never seen before was film of the escape tower and boost protective cover jetting off the vehicle, taken from inside the spacecraft.

Still, I think the best thing about this film is the commentary by Mike Collins, the best writer and most interesting storyteller of the first five astronaut groups.

BTW, Aldrin has said elsewhere that his First Whizz on the Moon took place just after he set foot on the surface, not just prior...

-the other Doug

Well, it makes a certain amount of sense. If the Moon was created in the Big Whack, you'd have to think that the bodies involved (proto-Earth and the impactor) would have a fair amount of water built up already. I always found it unsatisfying to believe that *none* of that water would end up in the mass that accreted into the Moon. Small amounts, to be sure -- but I always felt that *some* water ought to have been incorporated.

Seems my gut-level feeling was correct.

-the other Doug

Not for me. Not even getting the redirect, now -- just your basic 404 error.

-the other Doug

I quote this post to illustrate a rather important change in the Phoenix website.

Note the base URL above -- http://phoenix.lpl.arizona.edu.

Guess what? If you go to the home page based on that URL, you get redirected to:

http://phoenix-web.jpl.nasa.gov/

The University of Arizona seems to no longer be hosting their own Phoenix website!

And by the way -- this makes every single link we have in here to images at the original URL base broken.

-the other Doug

Very nice, Phil!

Just one caution (and I know, this is so obtuse it's beyond belief) -- your southwest "safe" landing zone at the Descartes site, located just west of Survey Ridge and just north of Wreck and Stubby, was reported by Young and Duke to be a pretty deep depression in the local lurrain. While the sides of this old depression are shallower than the sides of the larger craters in the area, the topo maps are a little misleading. Survey Ridge (just west of the return leg of the EVA-2 plot) was a very steep slope on its east side, and at the one point where the crew could look over to the other side (south of the beginning of the ridge), they estimated the western side of the ridge dipped down quite a bit further than the east side they traversed. This general impression is also borne out by the pans taken from up the side of Stone Mountain.

Unfortunately, their plan to climb to the top of the ridge and head back north along it had to be scrapped when they discovered the power to the rover's rear wheels was off. With only the front wheels powered, the rover was actually unable to climb the east side of the ridge, even angled north along it. Tells you just how steep that ridge actually was.

(Good thing that, at their next stop, the crew found the power problem to the rear wheels was due to a circuit breaker misconfiguration...)

-the other Doug

I wouldn't be at all surprised to see clouds around the Phoenix site. In fact, I'm pretty certain Phoenix herself captured some images of clouds from the ground. Here's a highly downsampled image from Sol 5:



This is just one of several sky images from that sol. They all show patterning in the sky that seems to suggest clouds, to me.

Besides, we're in the Land of the Polar Hood Clouds. This latitude on Mars has been observed from Earth as developing cloud decks which regularly obscure the scene from telescopic observers.

-the other Doug

I dunno -- look at the semi-regular spacing. Personally, I think you've discovered the dust clouds kicked up by the annual thoat drives into the great abattoires of Helium...

-the other Doug

Let us hope that ESA doesn't do the same thing with Rosetta's Steins images as it did with the crescent Mars images that Rosetta supposedly acquired... *heavy sigh*...

-the other Doug

You'll do great! You obviously have a good command of the material. And, most important, you're enthusiastic and you care.

I've always found that you can't argue or educate people into enthusiasm. You have to catch it, be contagious, and let other people catch it from you -- simply by being unabashedly enthusiastic.

So, like I say... you'll do great!

-the other Doug

One very short phrase: Lunar Surface Gravimeter.



-the other Doug

There is a good example in NASA history as to what happens when you try to enforce a no-time-off work schedule on even highly motivated individuals.

The Skylab 4 crew (third resident crew) had been aboard Skylab for about 6 weeks and had not yet gotten a single day off. Houston just kept finding more and more activities to fill their "free time" schedule blocks. So, one fine morning, the crew woke up and told Houston they were taking a day off. Period. End of discussion.

It was called a "mutiny" in the American press, and I know several people in NASA considered it such. Certainly Jerry Carr, the Skylab 4 mission commander, was never offered another space flight.

One of the hardest lessons learned from Skylab revolved around this incident, and the mission managers eventually realized that they, and not the crew, were at fault. No matter how motivated, people can't be expected to just push hard for weeks and months at a time. You have to give them time off, for a psychological break (if nothing else) from the work.

So, I have no problem with the Phoenix team taking a day or two off. In the long run, it's good for the team, and thus good for the mission.

-the other Doug

Group hug!



-the other Doug

Well... I see the greatest resource challenge upcoming the challenge in energy resources. Everything else is based on energy -- with enough cheap energy, you can overcome any and all of the remaining resource issues.

And the ridiculous thing about that is that we're awash in a great ocean of energy. There is energy everywhere around us -- it is one of the most common things in the Universe.

The problem is, we don't have enough ways of converting that energy into the useful *work* that our technological society requires. At least, not in economical ways.

I see umsf as a means to a greater understanding of the Universe, and thereby a greater understanding of how mass and energy interact at grand scales. Just as important is the particle physics research being conducted around the world, which grants us a greater understanding of the same interaction at tiny scales. We need to continue to improve our understandings of mass/energy interactions in order to reach new quantum improvements in our energy technology.

I see msf as a driver to find applications that allow human exploration of the Solar System. I mean, what are the challenges of human exploration at present?

- First, it's incredibly expensive to climb out of a gravity well (particularly our own), due to the speeds at which energy must be added to, or subtracted from, your vehicles. After all, there is enough total energy in a 747 at take-off to launch its entire mass into orbit. It simply lacks the ability to apply that energy fast enough to increase its speed to that required for orbit. It's not the amount of energy so much as the speed with which you can add it. And, of course, when landing or going into orbit around other planets, it's how fast you can shed it.

- Second, we'll need a way of manipulating energetic cosmic particles to keep them from penetrating our spacecraft and crews, if we want them to survive long interplanetary flights (an application of managing the mass/energy interface that has truly abundant implications for terrestrial technologies).

- Third, we'll soon want a way to travel from planet to planet in days and weeks, not months and years. Advanced propulsion technologies may well drive breakthroughs in energy production, conversion and management.

So, I see these "unprofitable" activities of umsf and msf as technology drivers that can lead a path to a truly Utopian world. But I fear that we may hit the energy wall before we've put enough resources into the sf infrastructures to allow those drivers to generate the breakthroughs we need.

There -- I don't think I was political in that whole explanation!

-the other Doug

The current financial strains are only going to get worse, I fear. The world is facing a near-future resource crisis, which is going to create a *lot* of financial strains.

I'm firmly convinced that both msf and umsf can be powerful tools in overcoming this resource crisis, but we need to have the infrastructure for both a little more established before the crisis really starts to hit, or else these powerful tools may be lopped out of human endeavour as being "too wasteful" by those who just can't make themselves think longer-term than right now.

Now, while we can still make a good case for developing these tools, is when we should push for as much to be put into them as we can possibly manage.

IMHO.

So, I'm happy to see this move by France. And in the end, I think they have a point -- any costly human endeavour that requires planning and execution over years and decades becomes, ipso facto, a political decision. Put another way, when something very much needs to be done but will never generate a profit, that thing has to be done by a government. And anything a government does is, almost by definition, a political decision.

-the other Doug

If there is something there, I would venture it would be more like gegenschein or something along those lines. I can imagine the Earth-Moon system has some dust and gas entrained in it, there may well be a very faint torus of "stuff" that has been sputtered off of the Moon by direct interaction withthe solar wind, and other "stuff" sputtered off of Earth's upper atmosphere by interactions with its own magnetic field. At least some of this stuff would stay in the near area for millions if not billions of years, I would think.

At various angles, the remnant dust and gas in the plane of the ecliptic demonstrates back-scattering effects resulting in fog-like luminsecences. One of those is the famous gegenschein. The dust and gas in the ecliptic and in cislunar space might be visible under the right lighting conditions.

But yes, I severely doubt we're seeing a lunar atmosphere here. After all, keep in mind that each Apollo landing, with the exhaust from the LM descent engine, added more gas to that lunar atmosphere than had been there to begin with, i.e., an increase greater than 100%. Now, spread out the gas from about 18,000 lbs of propellants all around the Moon, and you get an idea of just how thin that stuff has to be...

-the other Doug

That's sort of a matter of degree, isn't it, Nick? In the great range of like to unlike, Mars is far more like Earth than it is, say, like Jupiter. Or Neptune. Or even Titan.

-the other Doug

Ah, yes -- I do recall living from one edition of AW&ST to the next. It was the only regular publication that carried news of the aerospace industry, including the upcoming manned and unmanned space flights. (The magazine Missiles and Rockets, unfortunately, had gone the way of the dodo by the late 1960s.)

I can still recall Xeroxing the edition that had the first line drawing I had ever seen of the layout of instruments in Apollo 15's SIM bay. That must have been in April or May of 1971.

-the other Doug