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Posted by: BruceMoomaw Mar 1 2006, 07:33 AM

...which I decided to attend literally at the last possible minute, which is why I didn't alert you guys in advance. Very interesting -- both the discussions about the likely design of the mission (and how to retrieve it from cancellation), and many of the actual science presentations (which aren't on the Web yet, although they probably soon will be). I'll give you some more information tomorrow -- although I can't resist telling Alex that Tom Spilker's subgroup took my ideas about a Europa penetrator, and the printed information I gave them on the subject, seriously enough to recommend making further inquiries to NASA HQ on it. (And without my browbeating them, either. Nyaah.) The case for it, however, is still extremely far from certain.

As I say, more tomorrow.

Posted by: nprev Mar 2 2006, 01:43 AM

Standing by for that update, Bruce... ...

...and, while I'm dreaming, how about a broad-spectrum "geophone" as part of the penetrometer science package? Imagine the acoustical effects of Europa's tidal stress used as a multipurpose data source for ice crust property determination...to say nothing of noises made by any Europan whale-analogs propagating through the ice...

Posted by: edstrick Mar 2 2006, 09:01 AM

Viking Lander 2 provided essentially no information on martian seismicity, but it did provide essential data on how to design a seismic network optimized for Mars.

Any experiment, even single-channel, short-lived data, that can provide as broad-band as possible data on Europa's seismic/acoustic spectrum and it's variations with time will similarly provide essential data for a future penetrator-based seismic/geophysical net.

Posted by: BruceMoomaw Mar 2 2006, 02:11 PM

One advantage of a penetrator is precisely that it provides better seismic coupling -- although, in the case of Europa, this is probably the least of its fringe benefits. More important is that it:

(1) Is the only conceivable type of lightweight hard lander that can punch down below Europa's radiation-scrambled surface layer to reach possible recognizable biological remains.

(2) Can use the ice itself to shield itself from Jupiter's radiation for a fairly long lifetime.

(3) Is much lighter than a full-fledged soft lander -- or even an airbag hard lander.

(4) Can land on rough surfaces.

The big catch with a penetrator, however, is whether it can (1) point itself nose downward accurately enough without an atmosphere to avoid hitting the surface with its nose pointed at a slew ("angle of attack"), and (2) deal properly with hitting a sloping surface ("incidence angle"). Europa seems to have a very rugged surface; its AVERAGE surface slope seems to be about 12 degrees. This was the continuing point of dispute at the conference -- quite rightly -- and it remains uncertain to me, too (although it turns out that the Deep Space 2 probes were designed explicitly to deal with this problem, and their solution might work at Europa too).

Anyway, more on all this shortly. As I say, it was a VERY interesting conference, with a definite sprinkling of new scientific news (notably on Europan surface composition) -- and it seems to have reached some genuine initial conclusions about the feasibility, purpose and design of any lightweight piggyback lander that might possibly be carried on the Europa Orbiter.

Posted by: ugordan Mar 2 2006, 02:20 PM

IIRC, someone recently mentioned that (2) is not an issue at all. A penetrator could survive a wide range of incidence angles as long as point (1) held, that is -- the axis of the penetrator is precisely aligned with its velocity vector.
Whether or not the surface impact is at an oblique angle is apparently much less of a factor.

Posted by: djellison Mar 2 2006, 02:52 PM

I'm having difficulty imagining a Europa impactor.

You'd have to have active attitude control, thus either hydrazine thrusters, or perhaps some cold-gas thrusters to maintain attitude for the nose-first impact.

You've not got the budget, I assume, for much delta V to slow the thing down before impact - so we're talking a very VERY fast impact - are we talking straight in from approach, or a deorbit manouver after arrival? The former might be several km/s - the later is going to be a very low angle of impact. ( I assume you want the later so some sort of targetting can be planned from high res imagery )

A 355km Europa Orbit is something like 1.3 km/sec orbital speed.

If you do a deorbit manouver of say, 100m/sec, your impact would be at about 5 degrees and more like 1.5 km/sec

Given that attitude control would require some sort of pressure vessel, be it cold gas or liquid prop, you're going to have an explosion on impact of some sort.

DS2 heritage is 1) not too great because let's not forget, DS2 was a failure for whatever reason. 2) the speed of impact is going to be an order of magnitude higher unless you take some sort of decelleration propulsion, in which case the mass is going to be an order of magnitude higher. 3) DS2 was passively orientated and required no active attitude control for entry or impact.

We're talking RTG (as you mention a long life span) which means a fairly heavy craft before we even think about anything else, and the rtg's going to have to be built like the proverbial brick out house to survive the thing going in. Plus the fact that we're talking about highly sensitive biological experiments - which don't really like hundreds of G.

I'd really really like to see something like this - but I struggle to see how an impactor probe would work out there.

I have to say - it's a very very long shot - the sort of long shot that'd I'd expect you to lambast for being totally outside the realms of sensibility Bruce

If there are specific design details around, I'd love to see some - see how they're proposing this thing.


Doug

Posted by: BruceMoomaw Mar 2 2006, 05:48 PM

What we're talking about is similar to Paul Lucey's design for his "Polar Night" lunar penetrator mission. (It's no accident that he shares my enthusiasm for the possibility of a Europa penetrator.) To wit: you put the penetrator into an orbit with a periapse only 2 km or so above Europa's surface, use a liquid-fueled retropackage to cancel out ALL of its orbital velocity at that point (about 1.8 km/second for both Luna and Europa), use gas jets to point the penetrator nose-down and spin it up for stabilization, then detach the propulsion module and simply let the penetrator drop, to hit the surface at about 75-100 meters/second. (The simpler "Jovian Moon Impactor", aka the "bowling ball" -- which seems to be the Penetrator's main rival now as a piggyback lander concept for Europa Orbiter -- would do exactly the same thing, except that it wouldn't bother with attitude control after the deorbit engine shut off.) They refer to the technique as "stop-and-drop".

Clearly you need both a lot of deorbit fuel (ALL vehicle concepts that descend and land from Europa orbit are about 50% fuel, with full-fledged soft-landers requiring only slightly more), and a good guidance and control system. The latter may be the catch -- you need to cancel out the penetrator's forward orbital speed very accurately, AND point it nose-down with high accuracy. Lucey thinks it's doable for acceptably low cost -- and the Discovery review board that appraised his concept reached a similar conclusion -- but obviously this is still open to debate. The sources I've read say that a 5 degree error in angle of attack (e.g., the penetrator's nose is slewed up to 5 degrees from straight down) is acceptable -- but Europa's surface may be much harder than the regolith that lunar and Martian penetrators must cope with. William Moore said he'd heard that "1 or 2 degrees" was a more accurate estimate of the acceptable pointing error -- and of course you must also make sure you totally cancel out the penetrator's forward orbital velocity as precisely as possible.

Even if your penetrator is going straight down, you also have the problem of hitting a sloping surface ("incidence angle"), which as I say may also be a good deal more likely on Europa than for the Moon and Mars. This problem is indeed lesser, although it is by no means trivial. But I discovered just yesterday that the Deep Space 2 penetrators were explicitly designed to deal with these problems, and the fact that they were cruddily constructed and tested does not mean that their solution is unworkable. You use a wide, flat surface contact plate with a hole in its middle, and the penetrator perched in a cylindrical sleeve above that hole. If the vehicle hits the surface at a moderate angle, one side of the plate will hit the surface first, and the plate will then of course instantly tip so that it's lying flat against the surface -- and only then does the plate come to a stop (with the penetrator being pointed normal to the surface), and the penetrator's own inertia then carries it through the hole and down into the surface. There's a picture of the concept at http://www.nasatech.com/Briefs/Oct98/NPO20295.html . Depending on which Web document you read, the DS-2 penetrators were intended to deal with surface slopes up to 20, 27 or 30 degrees, and angle of attack errors of 9, 10 or 12 degrees -- at which point we're in the range needed for a Europa penetrator.

There is another problem: the possible sheer hardness of Europa's surface. I hadn't appreciated until the meeting just how shallow Europa's regolith layer is thought to be, since the satellite apparently resurfaced itself only about 60 million years ago and has only been re-accumulating impact regolith since then. The regolith is likely to be no more than a meter or so deep anywhere on the surface, and in the freshest parts of the surface -- which are just where we want to land -- it will be a good deal shallower than that. Such areas may even be virtually bare, solid ice -- and ice at Europa's cryogenic temperatures is as hard as concrete.

The DS-2 penetrators were designed to survive crashing into permafrost, but not into solid rock. However, they were also deliberately blunt-tipped -- presumably to minimize their burial distance -- and a sharper-nosed penetrator could be a good deal more durable. One 1979 test in which penetrators were crashed onto solid rocks found that "Only large single rocks greater than 10 times the penetrator diameter caused deflections appreciably greater than 10 degrees...No catastrophic failure of the penetrator occurred during these tests." And a 2004 Sandia Labs document says that "Penetrators have recently been successfully tested into concrete targets at striking velocities approaching the rigid body limit of approximately 4000 ft/sec."

Another problem may be the penetrator's afterbody, containing its relay antenna, which you want to leave on the surface, connected to the penetrator by a cable. In the case of the general DS-2 type design, the afterbody would actually be the cylindrical sleeve through which the penetrator would slide to go into the ground -- probably a short sleeve, wrapping only the penetrator's front end. But if you hit a hard enough surface, the afterbody's going to bounce seriously. However, it might be possible to give it a bottom lip, protruding through the contact plate and equipped with a sharp lip and maybe even short spikes; and make the contact plate itself brittle (like the aeroshells on the DS-2 probes) -- or even make it a radiating array of breakable outrigger rods -- so that the contact plate would shatter on impact and the afterbody would tend to anchor itself into even a hard surface.

Clearly there's a huge swarm of questions and uncertainties about the concept, and it may well turn out to be unworkable. But if the impact problem can be solved, it has very definite benefits. For one thing, it's much lighter than any other possible lander except the bowling ball. (Lucey's lunar penetrators, even including their deorbit and attitude packages, weighed only 135 kg apiece -- and survived crashing into a 3-foot layer of plywood with an onboard mass spectrometer and neutron detector working fine afterwards.) Its biggest selling point, though, is one of the conclusions reached by the Group meeting: it's the only possible concept for a small piggyback Europa Orbiter lander that has any chance of doing meaningful biological studies. Europa's regolith layer is virtually certain to have had any biological remains that it held fried beyond recognition by Jupiter's radiation, and also contaminated by incoming carbonaceous meteoroids. You need to get about a meter below the surface to get good biological samples, and any soft lander that could drill or carry a little short-range cryobot to do that is absolutely certain to weigh far more than the 340 kg which is all the extra payload margin the current design for Europa Orbiter can carry. (Even the frequently mentioned "Europa Pathfinder" concept -- a hockey-puck type rough lander using airbags -- has now been firmly rejected; its airbags, even if their weight alone is raised to 225 kg, are probably too fragile to work on Europa's rough and supercold surface.)

Apparently the only possible alternative to a penetrator for a lander on Europa Orbiter is the "bowling-ball" type lander -- which has viewports for cameras, and even a bunch of little sharp-edge sampling cups mounted on it that could allow it to pick up ice samples on impact for non-biological chemical analyses. But since biology is the raison d'etre for Europa landings, is such a lander even worth the trouble? Or should we instead pour that 240 kg of added orbiting payload into more orbital experiments, a faster data rate, and above all more radiation shielding to allow a longer lifetime for the Orbiter? (The current concept for the Orbiter gives it a minimum of 3 months in Europa orbit -- but for each month longer that you want it to work, about 100 kg more shielding is required.)

Interestingly, there was a growing feeling expressed at the meeting that a small piggyback lander may be worth doing, not so much for science as for engineering data on Europa's surface that will be crucial to design the later big Astrobiology Lander that will be the follow-up to the Europa Orbiter. You want to make damn sure that something that expensive and long-term survives landing. Even given a very high-powered HiRISE-type camera on the Orbiter, that means that you want very close-range descent images (which must be played back after landing) and/or surface images, to gauge the small-scale roughness and feature types of this moon's strange surface. (Lucey's lunar penetrators carried descent cameras.)

You may want (as Ed Strick suggests) a short-lived preliminary seismometer just to get the data on Europa's seismic behavior that will be needed to design a later, better one. You may want to measure the acidity of the ice if it's really high, to make sure that cryobots and ice-analysis gear can survive it. And (as Tom Spilker told me) you may also want to measure the debris content of the ice, to see if there are so many meteorites and other rocks, pebbles and grit in it that a Cryobot would have trouble melting its way through without a grinding head as well. (It looks as though by far the best surface sampler for an Astrobiology Lander will be a short-range cryobot that melts its way 10-100 meters through the surface, which can melt and filter two orders of magnitude more ice than a drill can.) Spilker suggests sonar on a little preliminary lander -- or at least a speed-of-sound experiment, like that on Huygens, to measure the overall rock content of the immediate surface ice that the piggyback lander is sitting on. (You may also want to measure the ice's salt content -- if it's really concentrated, an ice-melting cryobot might eventually build up a lump of concentrated salt ahead of it that would also stop it without a grinding head.) These are the sorts of things that even a tiny hard lander of the Bowling Ball type could get.

Anyway, this is how the Europa Focus Group's overall discussions of a Europa lander seemed to be tilting. (And at least I gave them a little useful input, since I was the one who brought up the penetrator concept to Spilker's subgroup that was discussing the engineering design of a lander, and they were genuinely interested in it and recommended some further inquiries to NASA and JPL about its possible feasibility. They also want to get in touch with Lucey -- although Torrance Johnson remains highly skeptical about the whole idea. One guy named Paul Holland seems to have turned into a flat-out fan of the idea.) Coming up next: my summary of the actual scientific talks at the meeting -- which were a good deal more interesting overall than I'd figured they would be.

Posted by: PhilCo126 Mar 2 2006, 06:13 PM

Interesting post !
Post Scriptum: aren't we supposed to stay away from Europe ( 2001 a space odyssey ... )

Posted by: helvick Mar 2 2006, 07:07 PM

Well - if so then you, me, Doug and about a third of the crew here are all in trouble already.

Posted by: BruceMoomaw Mar 2 2006, 08:16 PM

If I had a nickel for every time that joke was used at the meeting...

By the way, it WAS emphasized that as yet we don't know how to build a full-sized RTG that can endure more than 40 G -- but we do have some very small units that can endure 600 G. So the possibility of a long-lived version of the EO piggyback lander can't quite be ruled out, but is indeed unlikely -- we're more likely talking about batteries and a lifetime of just a few days.

Posted by: vexgizmo Mar 3 2006, 01:19 AM

Believe it or not, Torrence Johnson addressed this in his talk. He pointed out that at the Europa Ocean Conference (1995), Arthur C Clark dialed in by video-phone and gave his okay.

Posted by: djellison Mar 3 2006, 10:12 AM

I make a 2km drop to Europa a 72 m/sec impact after a fall of 52 seconds.

I'm guessing you want the forebody at least 2m down, and thus that's, I THINK - 124G.

The afterbody, you want it to stop very quickly, perhaps 25 cm, thus that's, again, if my maths is right - approx 1000G

Doug

Posted by: BruceMoomaw Mar 3 2006, 07:14 PM

Yep. The "bowling ball" lander is supposed to endure 4000 to 10,000 Gs -- with sophisticated science instruments onboard. JPL says they're confident they can engineer it. The real question with the afterbody on a penetrator, I'd think, is how to eliminate the bouncing problem if it hits a hard surface.

Posted by: nprev Mar 4 2006, 12:40 AM

4-10K Gs, huh? Gotta admit, the sheer survivability of the thing sure adds a lot of mission success sex appeal, which has got to be more important than ever these days...

What kind of instruments are under consideration for this concept? I can see some interesting possibilities, provided that the ball can "unfold" or otherwise deploy sensors after coming to rest.

Posted by: stevesliva Mar 4 2006, 04:23 PM

If at your penetrators' 4km periapse it's connected to a 4km tether with a counterweight that smacks into Europa first, will the penetrator fall straight down? I guess if the tether breaks, you fall up, though. Doh.

Posted by: Bob Shaw Mar 4 2006, 05:40 PM

Somehow, all these plans - the 4kG penetrator, the bowling ball, and now long bits of string - remind me inexorably of the Wiley E Coyote school of physics. I hope there are plans for sound effects, though hopefully not a b'wah, b'wah, b'wah one!

Bob Shaw

Posted by: BruceMoomaw Mar 4 2006, 10:39 PM

The tether idea, alas, would work about as well as one of Wile E.'s schemes (but would be a lot more costly -- after all, he always survives somehow). The moment the lower end of the tether brushes the surface, the penetrator gets flung downwards -- in an entirely uncontrolled way -- on the top end.

As for the Bowling Ball's instrumentation: it would unfold nothing. What it would have on its surface is a number of little camera ports and patch antennas, and about half a dozen little sharp-edged "sample cups" that could scoop up surface samples as a result of the impact itself -- after which electrodes in the cups would analyze the ice's pH, salinity and redox content, and a fiber-optic lead from the cups to an onboard Raman spectrometer would provide further composition analysis. Add an onboard short-lived seismometer or geophone, and that's the total instrument payload of the current model (although an active pulse generator might allow the geophone to double as a simple sonar system to help measure the rock content of the ice, as Spilker thinks is wise).

I'm starting to think that the biggest problem with a penetrator might be not its impact angle, but its remaining horizontal drift on landing -- which a broad surface-contact foreplate couldn't correct on impact, especially if the edge of the plate in the direction of the horizontal motion was also tilted slightly downwards. That is, the penetrator might "trip" and thus "flip". It may be that the only way to solve that problem is to absolutely minimize remaining horizontal motion during the deorbit burn -- which, in turn, might require a forward-facing Doppler radar sensor. (The Bowling Ball, by contrast, has tremendously more tolerance for horizontal landing velocity.)

It starts to look as though the only question is whether the possibility of getting some astrobiological data on the very first landing -- using a sample from a still quite shallow depth, and involving the analysis of a very small amount of ice collected by the penetrator -- would be worth the considerably increased complexity of the Penetrator as opposed to the Bowling Ball. In short, I'm starting to acquire new serious doubts about my Brilliant Idea.

Posted by: Bob Shaw Mar 4 2006, 10:56 PM

Bruce:

The ACME Space Science Corporation ™ Bowling Ball © has certainly got the virtue of establishing an initial ground truth...

...it's just the bit about the Road Runner jumping off a nanosecond before impact that gets to me!

Bob Shaw

Posted by: dvandorn Mar 5 2006, 03:59 AM

If we're going to delve into the realm of Looney Tunes physics, the answer for *any* lander is perfectly obvious.

You put your lander on a scale automobile. You put a very precisely measured amoutn of gas int he automobile. The car runs out of gas just an inch before crashing into the surface, stops dead (but perfectly intact) that one inch above the ground, your lander hops off, and the car *then* continues on to crash into smithereens.

I think we're researching the wrong propulsion fields -- we need to investigate alternate physics, concentrating on Looney Tunes physics. There are so many things to take advantage of there!

-the other Doug

Posted by: BruceMoomaw Mar 5 2006, 05:57 AM

Well, you know, Bugs once stopped a crashing airplane just a few feet above the ground by putting on its Air Brakes. (This was after his previous attempt to stop the crash by activating the plane's Robot Pilot had failed when the Robot Pilot dashed out of a compartment in the cockpit wall, took one look at the situation, grabbed one of the parachutes and bailed out.)

If we're going to think along these lines, though, why not simply recruit a few of the Warner Brothers cartoon characters to personally pilot expeditions to other worlds? After all, they're virtually indestructible: they routinely survive swallowing lighted sticks of dynamite, having half-ton safes fall on their heads, etc. As such, they represent an invaluable national resource which has been sadly underutilized. (Their price is low, too: Sylvester would cheerfully lead an expedition into the bottommost depths of Hell for a canaryburger, and even the normally sensible Bugs, as we know, will do almost anything for a carrot.)

Posted by: edstrick Mar 5 2006, 07:41 AM

For those that don't know it... look for the on-web document: The "Cartono Laws of Physics".

You're glasses <assuming you have> will fog over repeatedly as you read it.

Posted by: helvick Mar 5 2006, 09:03 AM

(cleans glasses)
Clearly then the Europa lander needs to be an Anvil (Law IX) as that will fall slower than anything else. All delta-v can be provided by Spontaneously Created Dynamite (Amendment E) saving mass. We can do away with traditional instrumentation too and replace with a cat - it's ability to actually provide any calibrated scientific data is a small problem but it will prove to be indestrutible (Law VIII) and the NIR capability is not to be sniffed at. Amendment D (Gravity in C-Space is transmitted by slow moving waves of large wavelength) and a descent imaging system that simply watches the cat will give us some very detailed data about the internal structure of Europa during the descent.
Even better throw a dog wielding a knife into the equation and the combination of Law V, Law VIII, Law X,Amendment A and Amendment E should make sample return a piece of cake.

Posted by: edstrick Mar 5 2006, 09:30 AM

(notices he can't even spell "Cartoon") <sigh>

Posted by: gpurcell Mar 5 2006, 03:52 PM

Just a silly little idea, but why couldn't you use the JUPITER atmosphere in an aerobraking manuever for the PROBE before it begins its descent to Europa?

Posted by: centsworth_II Mar 5 2006, 04:13 PM

The velocity toward the surface is already zero (initially) for a probe dropped from an orbiter.

Posted by: JRehling Mar 6 2006, 07:04 PM

I wonder, qualitatively speaking, how many different ways the Bowling Ball idea could be tweaked to something intermediate between a hard-smash lander, a penetrator, and an airbag lander.

Could a spherical instrument package be placed inside a larger sphere with free capacity to rotate and a bottom-loaded center of gravity so that when the outer sphere makes first contact, the instrument sphere would rotate into a desired orientation while the outer sphere crumples? It seems like if it were desirable to end up with a constrained (but not tightly constrained) final orientation of the instrument package, something like this could be designed to happen automatically during the crumple/deceleration phase of landing.

It seems to me a penetrator is designed to be destroyed simultaneous with its initial compression and to have destruction exceed compression (leaving a lot of Gs for the instrument-bearing portion to absorb). An airbag is designed to compress fully with no destruction (Gs are still experienced by the instruments in each bounce, especially the first, but not as part of the lithobraking). Wouldn't the ideal design balance these exactly, like an airbag that fails precisely at the instant when it would begin to decompress on the bottom surface (and thus bounce)? There's nothing about the bounce up that you particularly desire (if you have another means to orient the instrument package), and the ability to do so means redundant springiness/durability. With the airbag representing the redundant-spring design and the penetrator representing the partial-spring design, is it feasible to try to design a system that gets the spring/destruction phase Just Right?

With a self-orienting instrument package (think of the Ask The Eight Ball), it seems like that's the ideal design if the margins can be predicted precisely. There's no atmosphere of varying density to screw up that aspect of the landing...

Posted by: Bob Shaw Mar 6 2006, 07:42 PM

Er... ...Ranger A?

Bob Shaw

Posted by: odave Mar 6 2006, 07:55 PM

...ask again later

Posted by: edstrick Mar 7 2006, 08:17 AM

Actually, Ranger A or I think more accurately the Block 1 series were Rangers 1 and 2, engineering test missions with a full load of science instrumentation to be placed in a highly eccentric orbit with apogee beyond lunar orbit. Both were stranded in low parking orbit due to Agena re-ignition failures, could not maintain proper attitude control or communications due to 90 min day-night orbits, and re-entered rather promptly.

Ranger Block 2 was Rangers 3 -5, with a payload including the balsawood cushioned capsule. Yes, the seismometer instrument package was cushioned in fluid, was to right itself inside the impact capsule after impact, then fire "bullets" to drain the fluid and let the seismometer to settle with "down" down. Block 3 was the 6-TV camera Rangers, while a block 4 or D series were to have been an improved version of the Block 2 missions, but was cancelled early in development.

Point of Terminology:

Impact missions are un-braked or insufficiently braked and are destroyed on impact.

Descent probes are atmosphere descent probes that may or may not survive to reach a planetary surface. They are not required, expected, or instrumented to survive impact. If they do, like the Pioneer Venus Day probe, they are defacto hard landers. Early Soviet Venera missions were instrumented for atmosphere descent with the hope/expectation they'd reach the surface and survive, but they were crushed by the atmosphere before impact.

Hard landers are landing vehicles that are protected against impact damage on all sides and are not required or expected to maintain attitude control or stable contact with a surface after impact. Ranger Block 2 impact capsules, early Luna landers (9 and 13 succeeded), early Venera landers (7 and 8), Pathfinder and MER rovers are hard landers.

Soft landers are required to maintain controlled attitude during landing. They may simply impact at low speed in a controled orientation, like Huygens, on a landing ring like the large Venera and Vega landers, or on legs like the Surveyors, Viking, Luna heavy landers, and Phoenix.

Penetrators are required to maintain attitude control after impact as they penetrate the surface and embed themselves below the surface, usually leaving an afterbody (very hard lander) on the surface.

Posted by: BruceMoomaw Mar 7 2006, 11:32 AM

The trouble with Rehling's idea is that all the instruments on the Bowling Ball (or, to give it its correct name, the Jovian Moon Impactor) -- except for the seismometer -- are supposed to peer through ports in the outer hull. There's no way to do that if the outer layer is crushable; the idea seems to be simply to make all the components inside the Ball extremely shock-resistant. Unless, that is, you do what was seriously considered for a seond-generation Ranger hard-landing capsule and have the shock-absorbing outer layer (the "impact limiter") in the form of petals that can unfold after impact (and, in the process, also prop the capsule upright). That is, a smaller version of the Pathfinder and MER landers. This might be doable for the Europa Ball, but it would add weight -- apparently for not much benefit beyond what the current design provides.

As for penetrators, they aren't supposed to be crushable at all (except perhaps for a shock absorber on the afterbody) -- the penetrator's solid-metal nose literally plows through the soil or rock on impact until the penetrator has been braked to a stop. Where lander airbags are concerned, there have been proposals to have them deflate instantly on impact so that they absorb the impact shock without the vehicle bouncing after landing, but this design has not yet been used and may be too complex.

By the way, I was under the impression for decades that the early Soviet Luna landers used just the same scheme (especially since they were ejected from their braking modules at much lower altitude and hit the surface at much lower speed than the Ranger capsules would have). It was only a few years ago that I learned that they also used a pair of hemispherical airbags that wrapped the capsule, and then deflated after landing and before the petals unfolded. And it was only a few weeks ago that I stumbled across a 2000 article in "JBIS" detailing the history of the intermediate-phase Soviet Luna lander and orbiter missions (1963-68), and learned that all four unsuccessful missions in 1965 (Luna 5 through 8) came progressively closer and closer to success, with the Soviets correcting the cause of failure each time only to have a separate failure occur later on -- and with the airbags themselves being the cause of the final failure on Luna 8.

Specifically, the computerized autopilot on the Lunas -- which was originally also supposed to control all the booster stages except the first one, to save weight -- was the bane of the program; it had failure after failure (causing 4 of the 8 launch failures they had during this part of the Luna program), until they finally surrendered and switched control of the rocket to a separate computer (which oddly, they had done from the start in the Venera and Mars launches, whose launch failures were from other causes). And even then it failed again on Luna 5, forcing cancellation of the midcourse maneuver (which is why that one landed in the Sea of Clouds instead of the Ocean of Storms, as it was supposed to). While it later recovered, the second maidcourse maneuver attempt was also botched due to a ground command error; and then the autopilot itself malfunctioned again shortly before the final braking maneuver was about to be attempted anyway, causing the craft to tumble so that it never attempted to brake itself. They finally got rid of the problem once and for all on Luna 6, but during that midcourse maneuver another botched ground command caused the engine to fail to shut off until it had burned all its fuel, causing the craft to miss the Moon by fully 160,000 km. Luna 7 was thus the very first Soviet Moon mission to successfully carry out a midcourse maneuver; but during its final orientation before retrobraking one of its optical sensors was unable to lock onto Earth (due to a design error in its pointing direction!), and so again the craft was improperly stabilized and made no attempt to brake itself. (This system of optical sensors had failed completely on Luna 4 back in 1963, causing that mission to cancel its midcourse maneuver and fly by the Moon at about 8000 km range.) The Kremlin, which wasn't used to having to publicly admit so many space failures in a row, was apoplectic at this point, and Korolev had to personally talk them out of cancelling the program -- but then, while Luna 8 oriented itself properly for landing, as soon as the airbags inflated one of them was punctured by a sharp bracket that had been improperly installed on the craft by a single worker, and the resultant gas jet threw the craft into an uncontrollably fast tumble that yet again ruined the planned retrofire. At this point Korolev died due to his botched surgery, just before he would have seen success at last on the 12th attempt at a survivable landing with Luna 9. (All this is totally irrelevant to Europa, but it seems historically interesting and so I've been waiting for a chance to put it on this blog.)

Posted by: edstrick Mar 7 2006, 12:46 PM

And of course the real story only marginally matches the old story about one of the last 2 failures retrofiring early and the other late, due to timing errors relative to the range-radar's "mark" signal.

I've never seen (should go brousing Encyclopedia Astronautica etc) pics showing the airbags. They've been completely missing in every pic and model I ever saw, and I'm surprised there's no obvious trace of them in either the Luna 9 or 13 panoramas.

Posted by: JRehling Mar 7 2006, 03:44 PM

Things that make you go "Hmmmm."

Posted by: Bob Shaw Mar 7 2006, 03:56 PM

These comments about the airbags disturb me to some extent, as they simply *don't* appear in the historical record. What *do* appear are 'sleeves' around the lander ball itself, and yes, they do appear to split into two sections. Whether or not these are 'airbags' in the sense we now use them is, I think, open to dispute. The illustrations I've seen of the landing sequence didn't have a traditional Pathfinder airbag deployment, but did go into such details as the radar, the rod which struck the ground first, and so on, so I wonder if the airbag story is a little bit of modern gloss!

Have a look at the image!

Bob Shaw

Posted by: JRehling Mar 7 2006, 05:49 PM

Something crushable could provide ports as well -- you would just have to have the inner sphere end up using whichever ports happen to end up on top, and either have big ports (like the face mask of a football helmet, but in multiple locations) and some tolerance for the orientation not being guaranteed to match precisely when everything comes to a halt. How this might play out in terms of affordable mass, I don't know.

Posted by: BruceMoomaw Mar 7 2006, 08:51 PM

The Europa Ball has little teeny camera ports -- of the sort that could easily be concealed by a crushed outer layer -- and it carries 16 of them to maximize the chances that some will be pointed in the right direction for both close-up and longer range Post-landing photos. (It seems to have no provision for descent photos -- something else, I think, that needs to be changed and easily could be, even given its lack of attitude stabilization.) One could, I suppose, put the camera lenses outside the crushable layer and run optical-fiber lines to them (which do, in fact, run from the camera ports on the current version to a single CCD, with other optical-fiber lines running from the 12 sample cups to a single Raman spectrometer) -- but I'd assume that such O.F. lines would be extremely vulnerable to damage when the layer is crushed.

So the plan, to repeat, is to make the whole thing so rigid and solid-state that it can survive up to 10,000 G -- as with the most sophisticated penetrator designs. (NASA's tests in the late 1970s included repeatedly crashing penetrators even into solid boulders, with a whole variety of scientific instruments onboard, including seismometers 100 times more sensitive than Apollo's -- and the only one that suffered any problems was a CCD camera on the afterbody.)

As for the history of Luna, the JBIS article (Sept. 2000, by Asif Siddiqi et al) is extremely thorough in its sources, and cites both the most recent and detailed Russian accounts and recently declassified US tracking of the Luna probes to confirm that Lunas 5 and 7 didn't brake at all, while Luna 8, during its tumbling final descent, fired its braking engine for only 9 seconds and then in the wrong direction. There's also a lot of detail on the airbags (including Soviet documents grousing about their design problems) -- the Soviets may have kept silent about them at the time to try to make the landings look more like the more sophisticated full-fledged Surveyor soft landings. The article is co-authored by Timothy Varfolomeyev, who's done somc excellent earlier stuff for JBIS in digging up, archaeologist-style, the true space past of his own nation's former secretive tyranny -- including an earlier JBIS article on the first block of Luna missions (1958-60), which I may report on later over in our "Moon" section.

Posted by: Phil Stooke Mar 7 2006, 09:07 PM

Here's a diagram of the Luna 9-style landers' landing sequence, showing the discarded padded shell... I'd prefer to call it that. The expression 'airbags' was never used by the Soviets until Pathfinder, when Russian sources started referring to the Luna 9 padding in the same way. I don't want to say it's intentionally misleading, it is probably a translation issue. But there was no sudden inflation as we would think of in airbags.

We have no idea how far the landed capsule rolled after being ejected from the carrier stage. The padded shell and the carrier rocket may be close by but hiddem by the tilt of the camera, or just too far away to be sen clearly. I have suggested that a big 'rock' (mapped as such by the Soviets) near Luna 13 might be its shattered carrier rocket stage.

Phil

Posted by: BruceMoomaw Mar 7 2006, 09:13 PM

The article is extremely explicit that there WERE inflatable airbags, and that they were the cause of the Luna 8 failure. (The craft began tumbling at 2 rpm 13 seconds after the inflation began.) The precise cause of the leak was discovered 5 days later. One letter from a co-worker describes Korolev -- who valued this program very highly -- as seemingly teetering on the verge of slitting his own throat after the failure.

Quoting the description: "During flight to the Moon, the Automatic Landing Station [aka the lander capsule] was covered in a thermal blanket. Within the blanket, there was a second covering, this one comprising an expandable rubber chamber with a a protective Kapton shell. Compressed gas from a spherical bottle mounted on the separable Compartment #1 [one of the two side equipment pods jettisoned from the main craft during retrofire] would inflate this second covering into two independent cushioning airbags which would protect the actual lander cocoon moments before impact....

"After the Luna 8 accident... Babakin's engineers introduced changes primarily related to the sequence of operations before landing. In the Ye-6 [previous design], inflation of the shock absorbers was carried out before main engine ignition. But as two senior engineers from the Lavochkin Design Bureau later noted, the sequence was changed for the 'Babakin variant': 'It was established that it was essential to carry out the inflation of the shock absorbers after ignition of the braking engine, to prevent harmful rotating moments that arose when the shock absorbers were inflated before braking engine ignition.' This reasoning seems to be supported by at least two contemporary accounts of the Luna 9 mission from 1966 in which the authors note that the airbags 'were prepared for landing while the engine was working.' Because the compressed-gas bottle for the shock absorbers was in a container attached to Compartment #1 which separated before engine ignition, Babakin's engineers moved this bottle to the side of the I-100 control system compartment on the main bus. One source notes that another difference on Luna 9 was that the attitude control thrusters were used in a continuous mode rather than intermittently to stabilize the spacecraft after airbag inflation."

There is an accompanying diagram of the Luna 9 design from a Soviet technical magazine showing Luna 9, complete with the new position for the airbag gas bottle, and there are very extensive bibliographic notes for all of this -- including the 1966 articles that mention the airbags. The thermal cover over the entire capsule-airbag assembly was jettisoned at the very start of the landing sequence. (The I-100, by the way, was also the spacecraft control system that was the bane of the whole program from Jan. 1963 through May 1965.)

Posted by: Bob Shaw Mar 7 2006, 09:17 PM

Phil:

Yes, that's the illustration I'd seen somewhere before, I think in one of the old Novosti Press propaganda booklets from the late 60s - with all the photos ludicrously airbrushed to death for no real reason, even the ones of cosmonauts looking really pleased at having been given lots of, er, flowers.

It's a bit like the Prop-M Mars 3 rover-on-a-string being 'remembered' once Sojourner came along. All very interesting, but indicative of a certain degree of spin...

Bob Shaw

Posted by: BruceMoomaw Mar 7 2006, 09:51 PM

Additional notes:

(1) The braking engine was shut off at 250 meters altitude (actually not very much lower than the optimal but very flexible planned burnout altitude of the 1962 Ranger retromotor), and "seconds later" the lander capsule was ejected. In the case of Luna 9, it landed "halfway up the inner slope of a 25-meter crater." Luna 13, by contrast, touched down on a plain, so I suppose it's conceivable that it did see its braking stage at a distance. (One of Alexei Leonov's space paintings shows the Luna 9 braking stage lying on its side just a short distance from the capsule, but of course this is poetic license.)

(2) Luna 8's "airbags had been pierced by a plastic mounting bracket of the stabilization petals that were supposed to be opened after landing. The bracket had broken off and the sharp edges had punctured one of the rubber airbags. The entire sequence of events could be perfectly reproduced in the laboratory. In the end, the problem was traced back to one single worker who had made a mistake during the manufacturing part of the process." Lucky for him that Stalin wasn't still around.

(3) There's also a photo of a model of the Luna 9 braking stage in the Tsiolkovskiy Museum that clearly shows the inflation bottle for the airbags in its new position.

(4) The 10-cm shift in Luna 9's post-landing position occurred "possibly because the diminishing water supply in its thermal control system had changed its weight distribution."

Any further notes I have on the Luna program will be moved over to the Moon section where they properly belong.

Posted by: BruceMoomaw Mar 7 2006, 10:12 PM

Getting back to Europa: the most interesting purely scientific news to come out of the Focus Group meeting was three separate reports that converge pretty well on a likely surface composition.

John Spencer reported on several years' worth of near-IR spectra taken through Keck adaptive optics which have a spatial resolution of only 200 km, but a spectral resolution fully 66 times better than Galileo's -- and which, to the researchers' shock, nevertheless showed NO new spectral features beyond those seen by Galileo. The very smoothness of the Keck spectra indicates that the salts in the ice are in flash-frozen brine (e.g., amorphous) form rather than crystalline; I wonder whether the same Jovian radiation that breaks up Europa's ice into amorphous form may have randomly redistributed the dissolved salt ions through the same process.

All three reports (including two other studies by John Dalton and T.M. Orlando) indicate a good spectral match to ice mixed with large amounts of sulfuric acid, Mg sulfate and Na sulfate. Remove any of those three substances and the spectrum doesn't match nearly as well.

Posted by: Phil Stooke Mar 7 2006, 10:14 PM

Bruce, I hadn't known about the inflatable bladder. That's good to know. Thanks.

Phil

Posted by: Bob Shaw Mar 7 2006, 10:18 PM

Bruce:

If you get the chance to point us at some pictures it'd be rather good; is there any hint of the volume of this bladder? I think that's a far better word than air-bag, which conjures up the wrong associations these days...

Bob Shaw

Posted by: AlexBlackwell Mar 7 2006, 10:18 PM

I'll just note the Spencer et al. paper is currently http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6WGF-4JBGJ9D-1&_user=10&_handle=V-WA-A-W-ZV-MsSAYVW-UUW-U-AAVVBZAWVV-AAVAEVWUVV-DUYBWCWCY-ZV-U&_fmt=summary&_coverDate=02%2F24%2F2006&_rdoc=1&_orig=browse&_srch=%23toc%236821%239999%23999999999%2399999!&_cdi=6821&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=3a00c50526aea6cf5fcd9c9c4d815157 with Icarus.

Posted by: BruceMoomaw Mar 7 2006, 10:34 PM

Correction: the spectral resolution of the Keck spectra was only 18 times better than Galileo's -- not 66 times better. That's still a lot better, and Spencer said he's abandoned his hopes that New Horizons' long-distance spectra of Europa might tell us anything new about its composition.

Nope, I have nothing on the volume of the Luna airbags.

While, we're on the subject of salt, one EGU abstract ( http://www.cosis.net/abstracts/EGU06/04537/EGU06-J-04537.pdf ) says that Cassini's dust analyzer has pegged the composition of the dust particle streams being spewed out by Io -- while they contain some sulfur and potassium compounds, they're mostly just plain old NaCl. Io is sprinkling table salt all over the Solar System.

Posted by: AlexBlackwell Mar 7 2006, 10:35 PM

Since this had been one of your favorite hobby-horses, hammered into our brains with your now-familiar as-I-have-saids and I-repeats, I guess the more interesting question is have you abandoned it?

Posted by: BruceMoomaw Mar 8 2006, 01:17 AM

I wouldn't say it was my FAVORITE hobbyhorse; just my favorite one where the NH flyby of Jupiter is concerned. Yeah, I've abandoned it. (I'm also backing away from two of my much bigger Europa hobbyhorses simultaneously, in case you didn't notice -- although I haven't quite given up on either of those. I am not, however, going to back away from my belief that NASA should be "balkanized", as you put it, and that space-science spending should then compete on an equal level with other types of governmentally funded science spending. Cost effectiveness is cost effectiveness.)

Orlando, by the way, agrees with Spencer that the salts in Europa's ice are "flash-frozen" and therefore amorphous in structure, rather than crystalline. I don't think Dalton had anything to say one way or the other.

Posted by: BruceMoomaw Apr 28 2006, 09:26 AM

There's a short description (and external picture) of the Icy Moons Impactor (aka the "Bowling Ball lander") at http://www.lpi.usra.edu/meetings/jimo2003/pdf/9043.pdf .