Aerospace and Electronic Systems - August 2018 - 15

Fowler and Dyer
needed when using the SLS. In addition
to supporting and boosting the fourthstage booster, the sky crane, and the instrument lander, the propulsion vehicle
would have the following subsystems:
C

Communications link to Earth
for receiving command sequences and sending status
Booster (we suggest a Centaur
third-stage booster, assuming a
launch vehicle other than SLS)
Thruster system for attitude control
Separate C&DH unit from the
fourth-stage booster, sky crane,
or lander for simplicity of development
Connection via cable-wire harness with the sky crane and
lander to receive power from the
SRG and data from the instrument, giving its status

Figure 7.

Outline of the structure of the sky crane and the lander.

The communications link to Earth would be either X-band or
Ka-band to the DSN. Further study is needed to select the frequency and modulation scheme.
If the SLS is not used, the booster (again, potentially a Centaur
third-stage booster) would need to be sized to boost itself, the fourthstage brake or booster, the sky crane, and the lander to Jupiter; it will
require a trajectory that is called Venus-Earth-Earth gravity assist
(VEEGA) for the necessary boosts to gain Δv. A Centaur third-stage
booster would begin with 20,830 kg of fuel, which leaves 1,154 kg
for unexpected maneuvers. This is a margin of 5.5%.

FOURTH-STAGE BOOSTER
The fourth-stage booster would decelerate the sky crane and lander
toward Jupiter and Europa. After decelerating the spacecraft, the
booster would then fly away to destruction in Jupiter's atmosphere.
It will need an initial propellant load of 800 kg, which leaves 22.2 kg
of propellant for unexpected maneuvers. This is a margin of 2.8%.

SKY CRANE
The sky crane will lower the lander with the instruments and
probes to Europa's surface. It will have technology similar to that
of the Mars Exploration rover mission. It will require the following
components and parameters:
C

Propellant load of 170 kg to brake the lander, with a combined mass of 311 kg, to less than 0.25 m/s [28]
Remaining propellant to fly away from the landing site,
achieve the escape velocity of 2.025 km/s, and crash into
Jupiter to avoid contamination of Europa

AUGUST 2018

Motor and battery (estimated ≤35 Ah) with pulley, reel, and
control electronics to lower the lander
C&DH unit to sequence the operations

It will need an initial propellant load of 170 kg, which leaves
7.3 kg of propellant for unexpected maneuvers. This is a margin
of 4.3%. Figure 7 illustrates the concept for the structure of the
sky crane and the lander. The SRG umbilical will separate as the
lander begins to lower; the battery will maintain the power in the
sky crane. Table 3 lists the estimated masses.

BURYING ELECTRONICS IN ICE FOR RADIATION
SHIELDING
The electronics need to burrow into the ice for protection from radiation. We estimate that a depth of 1 m, possibly 2 m for a margin
of safety, will provide protection [29]. The instrument and probe
enclosures, or pods, would have heaters that would melt the ice.
The mass of the pods would aid in driving the pods into the melting
ice. The thermodynamics and hydrodynamics of this operation will
need extensive calculation, simulation, and testing in ice.
The lander has two types of heaters: a low-power resistive element that warms the electronics, and a high-power resistive element for melting ice to bury the pod and probes. The size of the
warming heaters is to be determined; it depends on the thermal
conductivity of the potting compound and the insulation effectiveness of the titanium thermos bottle.
The melt heaters are sized to bury the pod and probes in 13 h or
less. The melt heater for the pod dissipates 500 W. The melt heaters
for the probes each dissipate 150 W. The total power required for
melting the instrument pod and four probes would be 1,100 W. On

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Aerospace and Electronic Systems - August 2018

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