The First Europa Lander, What can be done first, cheapest & best? |
The First Europa Lander, What can be done first, cheapest & best? |
Dec 31 2005, 12:08 AM
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Merciless Robot Group: Admin Posts: 8789 Joined: 8-December 05 From: Los Angeles Member No.: 602 |
I think that many people in this forum would agree that somebody's going to have to land on Europa someday before the rather elaborate schemes to penetrate the outer ice layer will ever fly, if for no other reason than to get some relevant ground truth before committing to such an elaborate, expensive, and risky mission.
EO seems to have ruled out any surface science package for that mission (though it would be nice to change their minds! ), but I think that there is a valid requirement at some point to directly assess the surface properties of Europa in an inexpensive yet creative way. Some candidate instrument payloads might be: 1. A sonar transducer/receiver set embedded within a penetrometer to determine crust density and examine the uniformity of the ice layer within the operational radius of the instrument (looking for cracks and holes, in other words). 2. A conductivity sensor again embedded inside a penetrometer to measure the native salinity of the surrounding material and possibly derive some constraints on the composition of metallic salts in the European crust (saltiness has a major effect on ice properties, in addition to the obvious need to derive the salt content of any underlying ocean). 3. A seismometer for all sorts of reasons. How does this sound? Any critiques, additions, or subtractions? I omitted a surface imager not only because of bandwidth/extra complexity considerations but also because it seems desirable to penetrate the crust in order to minimize as much as possible reading any contaminants from Io during surface measurements. The orbiter data could be used to sense and subtract this from the penetrometer readings. -------------------- A few will take this knowledge and use this power of a dream realized as a force for change, an impetus for further discovery to make less ancient dreams real.
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Jun 27 2006, 04:07 AM
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#2
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Member Group: Members Posts: 172 Joined: 17-March 06 Member No.: 709 |
It seems that at the November 2005 COMPLEX meeting there were 4 options presented for a Europa Lander that could be included as part of the Europa Explorer mission. Each of these options assumes the same plan for initial descent. First, the lander arrives, eventually, with the Orbiter in a circular 100-km orbit around Europa. Second, after separation, the lander fires a thruster to decrease velocity by 22 m/sec. This puts the lander into a 100 x 1.5 km orbit around Europa. Third, a large rocket burn takes place at periapsis to decrease velocity by 1,500 m/sec. This essentially stops the lander cold and it begins to free-fall the last 1.5 km to the surface. This is the Stop and Drop maneuver. The remainig descent to Europa's surface is where the designs diverge. These are details of each of the 4 proposed lander designs. 1. JMI - Jovian Moon Impactor - This probe falls all the way to the surface, impacting it at 62 m/sec. It is designed to withstand 5,000 - 10,000 g's and looks to heritage from the Deep Space 2 Mars penetrators. This is where a precursor mission like DS-2 has its payoff. JMI Mass = 65 Kg 2. EPF - Europa PathFinder - After the Stop and Drop, EPF free falls to the surface, but cushions its landing with 3 airbags, similar in size to the Beagle 2 design. The EPF itself is desinged to withstand 600 g's and is saucer-shaped. EPF Mass = 220 Kg 3. ESSP - Europa Surface Science Package - After the Stop and Drop, the ESSP utilizes thrusters to slow its descent. The thusters cut-off at about 10 meters and ESSP freefalls to semi-soft landing at about 40 g's or somewhat greater. ESSP Mass = 350 Kg Each of these first 3 landers is designed to have payload masses of about 7 - 8 Kg, a lifetime of 3 days, power levels of about 10 W, with a total science data transmission of 200-300 MBits. 4. IML - Icy Moon Lander - A true soft lander, using thrusters all the way to the surface after Stop and Drop. Landing at less than 40 g's and using an RTG. TMI Mass = 825 KG The TMI is designed to last for 30 days, to have a power level of 100 W, to have a payload mass of 40 Kg, and to transmit a total of 7 Gbit of data. I think that the IML and/or the ESSP may use crushable materials to cushion the landing on Europa. Also, these landers are able to be considered since the new mission design for the Europa Explorer envisions using the Delta 4 Heavy as the launch vehicle and the use of a VEEGA trajectory. The VEEGA trajectory design utilizes 1 Venus and 2 Earth flybys and enables 7,000 Kg to be sent on the way to Jupiter. This contrasts with the original Europa Orbiter design that contemplated a payload of only 1,500 Kg to Jupiter. Another Phil |
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Guest_Richard Trigaux_* |
Jun 27 2006, 07:16 AM
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#3
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Why to limit the life time of a surface lander? if it has no RTG, it is understandable that the battery limits the lifetime (when it is exhausted). But a RTG has a theoretical lifetime of 30 years or more.
I know what the limiting factor is: radioactivity, which will quickly destroy any electronics. However there would be some strong interest into having a long lived probe on Europa surface: -long run seismometre recording (a lone seismometre is not very useful, but a further mission may bring another one, so that they could work as a network and explore inner Europa structure, provided that the first is still working 10 or 20 years later). -use it as a beacon or GPS emitter for a further mission or landing -detecting underground SOUNDS on Europa, which may help to understand the oceanic properties. So what I propose would be that the lander may have a pod, which would use the excess RTG heat to bury a small emitter/seismometre deep enough into the ice, so that it would be protected against radiations and could work for 20 or 30 years. Could there be alternative power sources other than RTG? -solar panels could still have some efficiency on Europe, but they would quickly degrade with radiations. -a long wire left on the ground may gather enough electricity to feed a small circuit, with an emitter working in burst mode. On Earth, during magnetic storms, continuous currents can appear into power lines, strong enough to disturb their normal operation. On Europe, which moves into Jupiter magnetic field, a large copper loop laid on the ground may gather enough energy to feed a small aparatus, without all the hassle and problems of a RTG, insensitive to radiations, and for a virtually infinite time. A large capacitor battery would store the energy for emission bursts, of during magnetic storms (the current may be sometimes zero), without a limited lifetime like batteries. |
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Jun 27 2006, 07:04 PM
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#4
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Senior Member Group: Members Posts: 2530 Joined: 20-April 05 Member No.: 321 |
Why to limit the life time of a surface lander? Mainly with an eye towards the mass budget. There are time-varying phenomena on Europa, and there are non-time-varying phenomena (at least, on cycles of greater than 30 Earth days). Only a magnetometer and seismograph would be useful over long time scales; other than the diurnal changes in light and those two experiments, the only requirement for a long lifetime will be to grab samples near the craft... and that might be rather homogeneous itself. Some of the time variation the magnetometer will go looking for would repeat many times in 30 days anyway. So the question is how much mass is it worth (taking it away from surface composition instruments, or orbiter instruments) to get a long life out of a seismometer? |
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Jun 28 2006, 01:30 AM
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#5
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Merciless Robot Group: Admin Posts: 8789 Joined: 8-December 05 From: Los Angeles Member No.: 602 |
Mainly with an eye towards the mass budget. There are time-varying phenomena on Europa, and there are non-time-varying phenomena (at least, on cycles of greater than 30 Earth days). Only a magnetometer and seismograph would be useful over long time scales; other than the diurnal changes in light and those two experiments, the only requirement for a long lifetime will be to grab samples near the craft... and that might be rather homogeneous itself. Some of the time variation the magnetometer will go looking for would repeat many times in 30 days anyway. So the question is how much mass is it worth (taking it away from surface composition instruments, or orbiter instruments) to get a long life out of a seismometer? I would say that a long-lived seismometer would be worth quite a bit. Consider all the variables (potentially) involved: sub-shell oceanic tidal effects on the crust, undersea vulcanism, crustal structural failure events, resonance flexing from the other big moons...the seismic environment on Europa might be quite complex indeed, and thus would require long-term data acquisition. Of course, you really need a lot more than one seismometer in one location to get a really useful dataset. -------------------- A few will take this knowledge and use this power of a dream realized as a force for change, an impetus for further discovery to make less ancient dreams real.
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