Aerospace and Electronic Systems - August 2018 - 18

Proposed Landing on Europa

The lander will need a self-righting mechanism should it
land on an uneven surface.
The lander will eject the four instrument pods with cables
uncoiling behind each.

ESTIMATES

LAUNCH AND TRAJECTORY TO JUPITER

MASS
Combining an estimate for the lander of 85.1 kg with the estimated
mass of the instruments of 30 kg yields a total mass of the instrumented lander of 115.1 kg. The energy to deorbit and land the lander is 2.36 × 108 J. The sky crane will have a mass that depends on
the fuel load, probably liquid oxygen and liquid hydrogen (LOX/
LH2). The dry mass of the sky crane is 28.9 kg.
Combining all these values allows first-order calculations to
estimate velocity profiles and determine feasibility. With a total
dry mass of 141 kg for the lander and sky crane, 170 kg of propellant will be needed, for a total wet mass of 311 kg. The sky crane
will lower the lander to the surface of Europa and then fly away
at escape velocity. The sky crane will then follow a decaying orbit
into Jupiter and be destroyed, which will provide some planetary
protection for Europa.
Deorbiting the lander and sky crane requires a fourth-stage
booster that has a dry mass of 40 kg, along with 800 kg of fuel.
The combined total mass of the booster, sky crane, lander and fuel
is 1,151 kg. The fourth-stage booster, sky crane, and lander will
need a Centaur third-stage booster [37] if an Atlas V 551 or a Delta
IV Heavy is the launch vehicle.

COST
We estimate the combined design, development, and mission
cost to be about US$950 million [6]. Should the proposed mission launch with the orbiter on SLS, it will decrease the mission
costs by US$26 million (caused by the significantly shorter time
required of mission control staff) and eliminate the Atlas V 551
launch and its cost of US$400 million, and the Centaur third-stage
booster and its cost of US$75 million; this would put the lander
mission at US$452 million. This becomes a 21% cost added to the
US$2 billion estimated for the Europa flyby mission.

SCHEDULE
Using the Atlas V 551 or the Delta IV Heavy will drive the schedule
to consume 16 y, divided roughly into 2 y for conceptual definition; 3
y for design and development; 1 y for manufacturing, assembly, test,
and integration; 7 y for launch and cruise; and finally, 3 y for landing
and collecting data from the surface of Europa. These phases overlap
somewhat: design and development will begin before the end of the
conceptual definition, and manufacturing will begin before design
and development are finished. The current proposed launch date is
May 2022. This proposed mission might fit that window.
The SLS would shorten the cruise by 4 y but is riskier because
of the unknowns with the new boosters. Its schedule would take 12
18

y, divided roughly into 2 y for conceptual definition; 3 y for design
and development; 1 y for manufacturing, assembly, test, and integration; 3 y for launch and cruise; and finally, 3 y for landing and
collecting data from the surface of Europa. The current proposed
launch date is July 2022. This proposed mission fits that window.

Assuming launch on an Atlas V 551 or a Delta IV Heavy with a
Star 48 second-stage booster, a Centaur third-stage booster would
accelerate the spacecraft (fourth-stage braking booster, sky crane,
and lander) to 16 km/s from Earth [32]. Gravity assists by Venus
and Earth will provide Δv to place the spacecraft in a trajectory to
be captured by Jupiter.

DEORBIT SEQUENCE AROUND JUPITER AND EUROPA
Orbital capture by Jupiter and Europa will decelerate the spacecraft. From the estimates of mass and thrust of the fourth-stage
braking booster, the sky crane, and the lander, we simulated the
speeds, altitudes, and times for landing on Europa. Table 4 gives
our estimates for these parameters.

DISCUSSION
SEVERAL TRADEOFFS
The biggest concern and tradeoff in this proposal is the power
source. We felt a photovoltaic (PV) array large enough to adequately power the lander and melt the ice for burying the instruments would be too massive. Again, we estimate that the lander
will need 1,100 W to melt the ice and bury the instruments in a reasonable time. Juno's PV array is the largest ever flown, and it generates between 420 and 480 W [6]. The PV panels are also massive,
which makes for a heavy spacecraft. However, RTGs and SRGs
are nuclear-fueled plants, which must overcome huge political obstacles to fly. In the end, flying an SRG will require approval and
expediting at the highest levels of government; it becomes a matter
of national will to move forward with a nuclear-fueled plant.
Another area of tradeoff in the lander is data-transmission
bandwidth. The electronics and processors could perform digital filtering, potentially wavelet analysis, on the seismic data and
transmit only seismic events, not continuous data. If the bandwidth
of the seismic data is reduced, then each camera might send up to
3 images/h, instead of only 1 image/h. Burst-mode imaging could
snap and store multiple images per second and then slowly transmit the stored data to Earth.
Another area of consideration for tradeoff is the mission configuration. This proposal is only for a lander; coordination with
an orbiter, which could survey Europa's surface before the lander
descends, would be beneficial in selecting a more suitable landing
site.
While redundancy, as in the architecture of New Horizons, is
fault-tolerant, it also increases the mass of the circuitry [24]. The
lander cannot have a dual C&DH unit because of the limited volume available within the instrument pod.

IEEE A&E SYSTEMS MAGAZINE

AUGUST 2018

Aerospace and Electronic Systems - August 2018

Table of Contents for the Digital Edition of Aerospace and Electronic Systems - August 2018