Europa Hard Landers and Penetrators

I have a new post on Europa Hard Landers and Penetrators at http://futureplanets.blogspot.com/2009/04/europa-hard-landers-and-penetrators.html

Russian Europa Lander

See http://futureplanets.blogspot.com/2009/04/russian-europa-lander-concept.html for the blog entry. Blogspot lists posts in the order written, not published, so this latest entry isn't at the top of the page.

Russian Planetary Plans

In preparation for a trip, I've been writing blogs ahead of time. It turns out that blogspot lists the entries in order of writing, not posting. So just in case you check in here to see what's new, click here to see the post on future Russian planetary missions.

http://futureplanets.blogspot.com/2009/04/last-several-posts-on-this-blog-have.html

Europa Hard Landers and Penetrators

This blog entry continues looking at presentations from the Russian-sponsored conference last January on Europa landers. The last entry looked at a proposal for a highly capable lander. This entry looks at proposals for two smaller landers.

Concepts for planetary landers fall into three classes. The first is for soft landers like the Mars Phoenix or MER rover craft. Combinations of parachutes, rockets, and or airbags soften the landing force. As a result, highly sophisticated craft and instruments can be delivered to the surface.

The other two classes of landers only partially spell the energy of descent and as a result do what can be termed as a controlled crash with style. Hard landers simply hit the surface, bounce and eventually come to a stop. Penetrators look like small rockets and burrow, nose first, into the ground and use the friction of ground penetration to stop some distance beneath the surface. Both classes of landers require hardened instruments and system electronics, which limit their capabilities. There isn't room for complicated masts to hoist imagers or robot arms to gather carefully identified samples for analysis. Instead, one or two simple instruments are carried. The landed mission lasts until the small batteries are exhausted.

The conference had presentations proposing both types of landers. The hard 'stop and drop' lander was discussed by a team from the Jet Propulsion Laboratory, one of NASA's centers. The team presented a number of possible instruments, but focused on an accelerometer (presumably to study the surface hardness but possibly also to measure some seismic activity), a gas-chromatograph/mass spectrometer, and a camera. The goal would be to conduct measurements for a full Europan day (84 hours) plus an additional 12 hours for additional data relay to the orbiter. Approximately 14 to 24 Mbits of data would be returned, depending on the altitude of the orbiter.

The penetrator presentations was done by the UK Penetrator Consortium. Here a small penetrator, perhaps 60 cm in length, would carry around 2 kg of instruments. Possible instruments include a seismometer, mass spectrometer, soil/environment package, simple surfve and descent cameras. Penetrators are used in a number of terrestrial studies, especially when dropped from airplanes. They have been studied for planetary missions for decades. Except for the doomed Deep Space 2 probes, none that I remember have flown. The Japanese space agency came close to flying penetrators to the moon, but canceled the mission due to development problems.


The hard lander presentation showed that for the nominal 2020 launch date and current mass estimates for the Jupiter Europa orbiter (JEO), 260 - 320 kg spare mass margin. (Note: spacecraft have a nasty tendency to grow in weight as design progresses and right now the JEO exists only as preliminary computer files.) No weight estimate is given for the hard lander plus descent system; presumably it would fit within the mass margin. One chart suggests a lander mass of 100 kg plus 35 - 65 kg of propellant. The penetrator presentation showed a mass of 30 kg or less for the penetrator and descent system. This would potentially allow several penetrators to be carried.

Editorial Thoughts: A number of problems exist with hard landers and penetrators. First, they require miniaturized desent craft that kill the orbital speed and possibly some of the descent speed. In the case of the penetrators, the descent craft also must ensure that the penetrator is pointing down for its impact. Another issue is the tight space in within the landers or penetrators -- every system must be miniaturized and hardened against impact, which reduces capabilities (including battery life). It is also hard to build miniaturized sample devices to bring material into the craft for analysis. This is especially true for hard landers which must be capable of acquiring samples no matter which side ends up being in contact with the surface. Europa would also poise a special problem for small surface landers -- there's not much mass to provide shielding against the radiation that will be present. Here, penetrators would have the advantage because the surrounding ice would provide some shielding.


Neither presentation gave more than passing mention to the radiation environment, suggesting -- as with the soft lander discussed in the last blog entry -- that these are preliminary concepts. I have my doubts about whether either would actually fly. On paper, the landers seem reasonable. As we learned from the Deep Space 2 and Beagle 2 landers, however, building and testing craft that would actually survive is hard and requires substantial financial resources.

However, should either concept make it to flight, I have a slight preference for the penetrator. I believe that it would be the lighter of the solutions, perhaps allowing 2 -3 to be carried. I suspect that crashing into the surface of Europa could be fatal a high percentage of the time. Redundancy would be nice.

If a lander is designed for Europa, then in theory it could be modified to also fly on ESA's Jupiter Ganymede Orbiter (JGO). The primary difference that I see would be the need for a heftier descent system to account for the greater mass of Ganymede.

Resources:

Hard lander presentation: http://arc.iki.rssi.ru/conf/2009elw/presentations/presentations_pdf/session2/Hand_ELW.pdf

Penetrator presentation: http://arc.iki.rssi.ru/conf/2009elw/presentations/presentations_pdf/session7/Gowen_ELW.pdf

Deep Space 2: http://en.wikipedia.org/wiki/Deep_Space_2

Beagle 2: http://en.wikipedia.org/wiki/Beagle_2

Russian Europa Lander Concept

At the Russian sponsored Europa lander meeting last January, the Russian space agency presented a concept for a Europa orbiter. This presentation focused on the spacecraft hardware. Other presentations looked at possible scientific instruments.

The mission outlined is an ambitious one. The mission consists of a series of stacked stages and spacecraft. The first stage would be a solar electric propulsion unit that would help deliver the orbiter stack to Jupiter following a three years cruise. A propulsion stage brakes the stack into Jupiter orbit where gravity assists allow the eventual Europa orbit insertion in early 2024. The stack then separates into a Europa orbiter and a highly capable soft lander.



The science potential of the mission could be substantial. During the Jupiter system tour, the spacecraft would perform thirteen Ganymede and four Callisto flybys. The orbiter would carry 50 kg of scientific payload. That is sufficient for capable studies during the flybys and while in Europa orbit. The lander would host 70 kg of instruments. Both the orbiter and lander would be powered by RTG's, providing the mission with considerable operational flexibility.



Editorial Thoughts: The mission concept certainly is ambitious. Left unmentioned is the elephant in the room for any Europa mission -- the radiation environment. This seems a curious oversight. NASA has spent a decade developing technology that can withstand the radiation at Europa. Perhaps considerable work is underway to develop the technologies to solve this problem and simply wasn't included in the presentation. It appears that the time in Europa orbiter may be limited to a small number of months, which would help. Without this issue being addressed, however, I am left wondering whether or not this mission is merely a pipedream or a serious proposal. If anyone reading this blog attended the mission, your clarification would be very welcome.

Even without the issue of radiation, the mission is technically ambitious, especially for a first flight by the Russian space agency beyond the orbit of Mars. The presentation does point out that the Europa lander concept builds upon technologies that will be used in the Phobos sample return and the lunar lander missions. I don't doubt that the Russians are capable of developing the technologies needed -- they are the only nation to have landed on Venus. The Venus program, however, built up capabilities over time with missions becoming more sophisticated as technologies were developed and concepts proven. Going directly from Phobos and the lunar surface to Jupiter and the surface of Europa seems a large step.

I also think that the time frame for the mission seems wrong. It would seem more logical to me to have the lander arrive after NASA's Jupiter Europa orbiter has mapped the moon and identified both safe and scientifically interersting locations. This would delay arrival to 2029. The extra five years also could provide more time for the Russian space agency to hone the technologies for a Europa mission.

I hope that my skepticism is unfounded. A Europa lander would be an excellent addition to the 2020's exploration of the Jovian system.

Resources:

Europa lander concept presentation: http://arc.iki.rssi.ru/conf/2009elw/presentations/presentations_pdf/session2/martynov_ELW.pdf

Website with all presentations. Look towards the bottom for a number of presentations on potential instruments. http://arc.iki.rssi.ru/conf/2009elw/presentations/