Aerospace and Electronic Systems - August 2018 - 10

Proposed Landing on Europa
Table 1.

Maximum Continuous Rates for Collecting Data for Transmission to Earth
Qty

Samples

Unit

Rate/
Instrument
(bits/s)

Maximum
Data Rate
(bits/s)

Cameras

images/h

7,282

14,564

16-bit pixels, 1,280 ×
1,280 pixels

Seismometers

250

s−1

6,000

24,000

@ 24 bits/sample

Magnetometers

600

2,400

@ 24 bits/sample

Laser spectrograph

400

Temperature
sensors

Radiation sensors

Instrument

−1

Comments

8,000

@ 20 bits/sample

min

−1

0.33

10.67

@ 20 bits/sample

min−1

0.33

1.33

@ 20 bits/sample

−1

NOTES: Maximum rate = 48,976 bits/s. Maximum storage in an hour = 22,039,202 bytes. Maximum storage in a day = 528,940,836
bytes.

Some requirements for a spectrograph are as follows: a range
of atomic and molecular mass of 1 to 200, a sample range to 100
m, and a SNR of at least 75 dB (ENOB > 12 bits).

TEMPERATURE SENSORS
Knowing the temperature distribution and the temperature of each
instrument is important for interpreting the data and maintaining
the integrity of both the spacecraft and the lander. Stability and
low-temperature performance will be requirements for these sensors; these should probably be glass-bead thermistors [21].
Assuming two sensors per instrument case, four for the lander
superstructure, and two per motor, at least 30 thermistors will be
needed. Requirements for the temperature sensors are as follows:
a range from −190°C to +45°C, accuracy of ±0.2°C, stability (resistance to change) < 0.07% per year, and SNR at launch of at least
74 dB (ENOB > 11 bits).

RADIATION MONITORS
Understanding of the geochemical processes on Europa requires
understanding of the radiation environment of Europa. Correlating the radiation and magnetic environments with measurements
of chemical compounds will help elucidate these processes.
The lander should contain at least two radiation monitors or
counters, one on the superstructure and the other in the instrument
pod. The radiation monitor in the pod will provide an indication of
the ice shielding for the pod. It can be used as a feedback sensor to
control the time of heating and melting the pod into the ice. Both
monitors will give an indication of the radiation flux on the surface
of Europa. Current technology provides for small and low-power
(< 0.25 W) sensors [22]; we doubled this value for the worst case.
We measured the mass of one model of Geiger-Mueller tube; it was
35 g. Consequently, 100 g (0.1 kg) for both tube and electronics
should be achievable.
10

METHOD TO DEVELOP SOLUTIONS FOR MASS, POWER,
AND VOLUME
Table 1 gives estimates of bandwidth that would reasonably allow
the lander's instruments to collect definitive data. The maximum
bandwidth is approximately 49 kb/s; this value occurs only when
the transmission bandwidth is available to the lander or there is
remaining storage in memory. The maximum bandwidth for transmission between Jupiter and the Deep Space Network (DSN) is
337 kb/s, but the availability will be less than this value, which will
reduce the cumulative bandwidth.
Table 2 contains the estimates for mass, volume, and power
consumption of all instruments to give a final, maximum cumulative value for each parameter. We estimate that the instrument suite
will have a mass of 27 kg, a volume of 0.019 m3 (assuming a packing density of 50% gives 38,000 cm3 or about 34 cm on each side
of a cube), and 83 W maximum power consumption (assuming all
instruments are operating continuously at the worst case).

LANDER ARCHITECTURE
The spacecraft is a combination of a fourth-stage booster plus a sky
crane and a lander. The fourth-stage booster will deorbit the sky
crane and lander and then fly away to destruction in Jupiter. The
sky crane will place the lander on the surface of Europa and then
also fly away to destruction in Jupiter. If the Space Launch System
(SLS), which is currently mandated for use, is not available, then a
Centaur booster will boost the fourth-stage booster, the sky crane,
and the lander toward Europa.
The sky crane will have its battery charged from the SRG on
the lander during the long cruise to Europa. When the SRG power
connection separates from the sky crane, the battery will maintain
the control circuitry of the sky crane and power the pulleys and reel
to lower the lander. The sky crane's battery will also maintain the
circuitry while the sky crane flies to destruction in Jupiter.

IEEE A&E SYSTEMS MAGAZINE

AUGUST 2018

Aerospace and Electronic Systems - August 2018

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