Aerospace and Electronic Systems - August 2018 - 16

Proposed Landing on Europa
Table 3a.

Table 3b.

Estimated Mass and Thrust for the Spacecraft for
Simulations of Acceleration Profiles
Parameter

Value

Unit

99,200

20.0

SRG

50.0

Thermal radiator

5.0

RF antenna

2.0

Specific impulse

450.5

Fuel consumption

46.24

kg/s

Dry mass

2,247

Motor drive of instrument swivel

0.1

Fuel mass

20,830

Instrument swivel ring +
bearings

3.0

9,000

Cable harness

2.0

Fuel consumption

4.6

kg/s

Pod lowering reel and motor

3.0

Dry mass

Total

85.1

Fuel mass

800

Sky crane wet mass +
lander

311

Europa insertion wet
mass

1,151

Total wet mass

24,228

Fourth-stage braking booster
Thrust

the surface of Europa, we assume no atmosphere pressure, so p =
0. Consequently, the heat of fusion is just the internal energy, U, or
232.3 kJ/kg. (Calculations for heat transfer and ice displacement
derive from the enthalpy for a homogeneous system, given by H
= U + pV [30].)
If the instrument pod has dimensions of 10 cm wide × 10 cm
long × 20 cm high (a volume of 2 L), and the heater dissipates 500
W to warm and melt the ice from an initial temperature of −180°C,
then it will take 1.1 h for the pod to sink 0.2 m. Extrapolating from
this simple calculation predicts that it will take 5.5 h to sink 1 m
or 11 h to sink 2 m.
If each probe has dimensions of 6 cm wide × 6 cm long × 10 cm
high (a volume of 0.36 L), and the heater dissipates 150 W to warm
and melt the ice from an initial temperature of −180°C, then it will
take 0.65 h to sink 0.10 m. Extrapolating from this simple calculation predicts that it will take 6.5 h to sink 1 m or 13 h to sink 2 m.

PLANETARY PROTECTION
Planetary protection is a risk area that must be approached without a lot of previous experience by anyone in the space business.
About the only way to ensure a sterile lander is with an autoclave,
which heats objects with pressurized steam [31]. We propose that
the lander, with its instruments installed, a docking plate for the
sky crane, and an open bag of Kapton or mylar be sterilized in an
autoclave for 1 h. Following sterilization of the lander, technicians
will run a built-in test. Afterward, a sterile bag must be raised to
cover the lander, which requires remotely controlled manipulators.
16

Mass (kg)

Superstructure

Centaur third-stage booster
Thrust

Lander Structure (Dry Mass, Not
Including Instruments)

NOTE: Instruments add 26.7 kg to the lander structure; see Table 2.

Table 3c.

Sky Crane Structure (Dry Mass)

Mass (kg)

Superstructure

10.0

Reel and motor/brake

4.0

Electronics of the C&DH

0.4

C&DH case

0.5

Battery (35 Ah)

4.0

Thrusters (8 @ 0.5 kg)

4.0

Fuel piping and valves

2.0

Fuel tank

4.0

Total

28.9

NOTES: C&DH = command and data handling. Sky crane
fuel mass = 170 kg. Europa insertion wet mass = fourth-stage
booster, sky crane, lander, fuel. Total wet mass = Centaur,
fourth-stage booster, sky crane, lander, fuel. To calculate
acceleration profiles, assume Europa's gravitation constant =
1.314 m/s2 and Europa's mean radius = 1,560,800 m. Altitude
above Europa to begin fourth-stage braking = 270,000 m.

Then, technicians will seal the collar of the bag around the docking
plate that clamps the top of the lander, providing suspension from
the sky crane; the docking plate has the motor-and reel-assembly
for lowering the lander and a hermetically sealed connector that
connects power and data communications between the lander and
the sky crane. Once the bag's collar is sealed (or welded) to the
docking plate, the technicians can run a built-in test of the lander
through the connector on the docking plate. Anytime up to when
technicians attach the shroud on the launch vehicle, they can run
a built-in test of the lander; should a failure occur, technicians can

IEEE A&E SYSTEMS MAGAZINE

AUGUST 2018

Aerospace and Electronic Systems - August 2018

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