Aerospace and Electronic Systems - August 2018 - 21

Fowler and Dyer

Figure 9.

Various configurations to bore the pod and probes straight down: (a) gravity drive and an alignment rod, (b) motor drive on the alignment rod, and (c)
boring bit and pump to move ice and water.

we did not take any deep dives into details; we attempted only to
show feasibility for the proposal.
We did not simulate a detailed mission trajectory; mission
planning was beyond our expertise. Both fuel margins and trajectory calculations must be studied in much greater detail before
an actual mission. The number of missions, either underway or
planned, shows that this effort is tractable.
We did not go into detailed plans for program management.
There are good examples to follow in current missions; developing
the plans would require a large effort.
We did not suggest new instrument designs. Suitable designs
are already available and proven; their mass and power consumption either are acceptable or can be decreased for the mission that
we propose. Furthermore, our understanding of geochemistry, geology, and geophysics is limited enough to not know what requirements would be appropriate beyond the current designs.
We did not suggest new schemes for communications. The
DSN and current designs are already available and proven; their
mass and power consumption are acceptable for the mission that
we propose.

OPTIONS NOT CHOSEN
We did not consider distributing CubeSats above Europa. CubeSats would add complexity to the mission, with lower return on
investment than a lander. One of the missions, the Europa Multiple
Flyby mission, is now studying both an orbiter with CubeSats and
an orbiter with a lander [46], [47]. A lander can have significant
AUGUST 2018

longevity over CubeSats and can carry more-sophisticated instruments.
We did not select a rover for the surface of Europa. This was
a judgment call on our part; we felt that a rover would add too
much mass and complexity for the mission; additionally, it would
be a challenging design effort because of the unknown terrain on
Europa. A rover may be severely limited by cliffs, escarpments, or
abutments in the ice crust. Two recent papers have proposed mobile landers [46], [47]. These would extend the utility of a lander
by reaching various parts of Europa and sampling points of interest. The main concerns are mass, power, and autonomy to navigate
large obstacles. An additional concern would be that of contaminating the environment if propellants other than LOX/LH2 were
used. We have decided to not consider a mobile lander because of
these concerns.
Finally, we decided not to propose burying a mass spectrograph
or laser spectrograph. They are simply too large, which increases
the power or the time required to melt the ice and bury the instrument pod. The access tubes (from the ice surface to the buried pod)
needed for the instruments would be difficult to keep clear of ice
and too complex for unreeling or telescoping.

CONCLUSION
We have proposed a spacecraft and lander for studying Europa,
along with the lander instruments and the parameters needing consideration to obtain useful data [6], [7]. We also described the lander configuration to shield against radiation and to provide plan-

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Aerospace and Electronic Systems - August 2018

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