I'm back from the Europa Focus Group meeting... Options

[Bob Shaw]

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.

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

[Guest_BruceMoomaw_*]

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.

[Bob Shaw]

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

[dvandorn]

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

[Guest_BruceMoomaw_*]

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.)

[edstrick]

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.

[helvick]

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

(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.

[edstrick]

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

[gpurcell]

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?

[centsworth_II]

...why couldn't you use the JUPITER atmosphere in an aerobraking manuever for the PROBE before it begins its descent to Europa?

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

[JRehling]

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 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...

[Bob Shaw]

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.

Er... ...Ranger A?

Bob Shaw

[odave]

think of the Ask The Eight Ball

...ask again later

[edstrick]

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.

[Guest_BruceMoomaw_*]

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.)