Europa mission concepts under study. Credit: JPL
At today's Outer Planet Analysis Group (OPAG) meeting, more
details of NASA's study of cheaper Europa flagship missions were
presented. The attendees also had a
lively discussion of which of three mission concepts NASA should concentrate on
for further analysis.
At the last OPAG meeting last Fall, the study team presented
a flyby spacecraft that would focus on remote sensing studies requiring power
and data hungry instruments and an orbiter that would conduct those studies
that could only be done from Europan orbit. (See this post for a description of the orbiter and multiple-flyby concepts.) At that meeting, early ideas for a Europa lander were presented. (See this post for both background on the earlier concept and a description of a high priority location to land at.)
Members of the study team today presented a more mature
concept for an Europan lander. The early
ideas included a very simple carrier craft that would deliver two landers into
orbit about that moon. Two landers
provided redundancy in case one crashed.
With further analysis, the study team members have concluded that high
resolution imaging is needed to find a safe landing site. Europa is so rough that simple redundancy
isn't a viable plan.
The new concept has a much more capable orbiter with a high
resolution camera to image the surface at sub-meter resolution (which
would put it in the class of the HiRISE camera currently in orbit about Mar). Images would quickly be acquired of a small
number of preselected possible landing sites to find at least one area 100x100
meters that would be flat enough to enable a safe landing.
Advanced precision landing technologies would be used to guide the
lander to a landing location as small as a hectare (2.5
acres) and then further analyze that target location during descent to find the safest spot within that location. Once the lander was
safely down, the orbiter would act as a communications relay (although the
lander would have its own backup communications capability)
The lander would conduct three types of studies. It would image the local site to enable
scientists to select sampling locations and to understand the processes that
created the surface. A robot arm
would drill into the surface to collect samples from as deep as 10 cm to get at ice that had not been altered by Jupiter's intense radiation field. A mass spectrometer and possibly a Raman
spectrometer would be used to analyze the sample composition. Seismometers and a magnetometer would be used
to study Europa's interior by measuring seismic activity and the induced magnetic field created by the subsurface ocean's interaction with Jupiter's
magnetosphere.
After the lander concept was presented, the overall study's
team leader, Bob Pappalardo of JPL, presented the wrap up. The two key slides were the estimated cost
and risk of each concept and a checklist of questions that each of the concept
missions could address about Europa.
The estimated costs of each mission, not including a launch
vehicle that would add approximately $275M to the total, were:
Europa orbiter - $1.6B (low risk)
Europa multiple-flyby - $1.9B (low risk)
Europa lander - $2.8B-$3.5B (high risk)
The multiple flyby craft's higher cost compared to the
orbiter results from both requiring more capable instruments and spacecraft
systems and from the much longer mission duration creating higher operating
costs. A group at Aerospace
Corporation did independent costs analyses for the orbiter and multiple-flyby
missions and came up with similar estimated costs.
They study team recognized that at best NASA will at some
future time go forward with only one of these concepts. None would answer all the high priority
questions by itself. For example,
characterizing Europa's ocean and its interface with the overlying ice shell
and underlying rocky core requires either the orbiter or the lander. Understanding the structure and composition
of the ice shell would require either the heavy, data hungry instruments of the
flyby craft for global studies or the lander to characterize conditions at one
location.
The meeting attendees spent almost an hour discussing which
of these missions they believe would provide the greatest advance in the study
of Europa. No clear answer emerged, in
part because OPAG is chartered by NASA to analyze plans and proposals but not
to provide advice. (Note: It's not clear
to me how you can cleanly separate the two.)
Pappalardo stated that he felt that the multiple-flyby spacecraft would
provide the most Europa science for the dollar.
Most of the participants also seemed to lean towards the multiple-flyby
option as their preference. (While it
was not discussed, the multiple-flyby spacecraft with its highly capable remote
sensing instruments also should be better able to study Jupiter and the other
moons than the less capable instruments planned for the orbiter.)
Examples of a possible set of flyby ground tracks at Europa for the multiple-flyby spacecraft. Credit: JPL
Editorial Thoughts: The study team has shown that there are
two small Flagship (<$2B) class missions that are low risk that could start
development without additional technology development. This is in
sharp contrast the previously planned Jupiter Europa Orbiter with its >$4B
estimate. Various strategies such as
using solar panels instead of plutonium power supplies or international
collaboration might reduce the cost to NASA for either the orbiter or
multiple-flyby missions.
The studies also show that viable mission concepts are
outside the $1B budget cap of the New Frontiers program. This isn't surprising. The Juno New Frontiers mission that is en route
to orbit Jupiter has a cost of $1.1B.
The proposed European JUICE Ganymede orbiter (which would also flyby
Europa and Callisto) would have a cost of at least $1.3B. (I've read that ESA increased the cost caps
for its Large mission proposals, but don't know by how much.) Other studies have found similar costs for minimal Titan and Europan missions. The outer planets are expensive to reach and study.
Unfortunately, NASA's projected budgets do not include beginning
funding for any planetary flagship missions until at least the end of this
decade. We remain dependent on the selection of the Discovery Titan TiME lake probe and/or the European JUICE proposals to continue the
exploration of the outer solar system once the Cassini and Juno missions end in
2017.
In the meantime, I hope that NASA will select one of the
Europa mission options for continued low level study so that when the budget
situation eventually improves, it can be ready to begin development.