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

[Guest_BruceMoomaw_*]

...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.

[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.)

[JRehling]

The Kremlin, which wasn't used to having to publicly admit so many space failures in a row, was apoplectic at this point
[...]
At this point Korolev died due to his botched surgery

Things that make you go "Hmmmm."