1 - Virginia Tech



1.0 Executive Summary

2 Brief overall description of Lander/Probe

In Greek mythology, Europa is a mortal concubine of Zeus. Zeus carried Europa off to a remote island and had several demigod children with her. Our probe takes the name of Zeus in the spirit of life which is embodied in this story. Life forming on a distant deserted island is exactly what may have occurred on Jupiter’s moon Europa. Along the same lines as in mythology, it is hoped that the union of the moon Europa with our Zeus spacecraft will present to the world the fruits of nature in the form of life on another world.

According to the 1997/98 AIAA Undergraduate Team Space Design Competition RFP, “The objective of this project is to produce a complete system design for a spacecraft that can land on the surface of Jupiter’s moon Europa and examine the ice and water of which it is made.” To accomplish this objective, the lander/orbiter and the ice/water probe need to possess certain instruments and experiments. The spacecraft needs to re-map certain areas of Europa that have been selected from data from the previous Europa Orbiter mission. This mapping will be done from a 20km orbit and will include photography and surface topography. Once the spacecraft lands, surface tests must be conducted to determine the physical and chemical properties of Europa. Photography and seismic testing are also essential portions of the lander/orbiter’s mission. Once the spacecraft lands, the ice/water probe can be released. This probe has the duty of providing chemical analysis, taking photographs, and determining the pressure and temperature distribution beneath the surface of Europa, as well as conducting life detection experiments.

The Zeus spacecraft is furnished with the RIEGL Laser Altimeter LD90-31K to aid in mapping the surface of Europa. The lander is equipped with 1024x1024x24-bit CCD cameras, which are also used for surface mapping from orbit, as well as providing photographs of the surface once the spacecraft has landed. The lander carries a robotic arm, which is modeled after the Mars Surveyor 2001 lander. An optical spectrometer is attached to this arm to perform chemical analysis of the Europa’s surface. To observe the ice shifting and “Moonquakes,” a JPL Microseismometer is imbedded in one of the feet of the landing gear to perform these measurements. Before any of the scientific operations can occur, the spacecraft must be able to maneuver to an orbit around Europa. Zeus’s three main engines provide a maximum thrust of 488 N and use monomethelhydrazine and nitrogen tetraoxide propellants. The ten monopropellant hydrazine thrusters on this spacecraft provide a maximum thrust of 6.15 N each. The power is generated by a Radioactive Power Source (RPS), which converts thermal energy to electrical power. The communications system consists of a parabolic high gain antenna constructed out of an aluminum honeycomb. A low gain antenna is used for low data rate communications and in case of high gain antenna malfunction. The spacecraft guidance and navigation is performed by autonomous star trackers, Fine Sun Sensors from the Swedish Space Corporation, an Analog Devices/ ADXL05 accelerometer, and a Litton LN-200 Fiber Optic Inertial Measurement Unit. To organize all of these instruments, a redundant computer is used to conduct the operations of the spacecraft.

The ice/water probe, like the lander/orbiter, is also required to perform scientific operations. The chemical analysis is executed by capillary electrophoresis system. This system separates molecules based on their movement through a fluid under the influence of an applied electric field (Weinberger, 1993). A set of cameras is used to take pictures near the ice/water boundary. The cameras are equipped with halogen lamps to provide the light within the underdwellings of Europa. These cameras view the inside of the moon through ports provided for the transducers used to measure the pressure and temperature distribution of Europa. The ice/water probe contains instruments vital to the success of this portion of the mission. Like the lander/orbiter, the ice/water probe houses an RTG for power. In addition to the RTG, the probe contains radioactive heating units (RHU) which aid in melting the ice for its journey to the ice/water boundary. Once the probe has melted its way down to about 30 m from the ice/water boundary, the Probe Arresting Sub-System (PASS) is activated. This system consists of titanium blades that, when released, hold the upper portion of the probe in the ice while the lower portion continues to fall into the hopefully present water.

The purpose for the PASS is to ensure contact with the ice for the communications between the ice/water probe and the lander. The communications system between the probe and the lander uses sonar through the ice. This system consists of hydrophones and an acoustic modem. Sound, instead of an electrical impulse, is sent through the ice. This means that a cable between the probe and the lander is not necessary. The sonar system can also be used to determine the depth of the ice and the distance from the probe to the lander.

1.2 Mission Events Sequence

1.3 Mission Time-Line

The following is a time-line explaining the order and date of key aspects of the mission.

1. 2.0 Introduction

The exploration of the world and universe has always been a preoccupation for humans. Since the dawn of our species, as we traveled across continents to settle into different territories, to the modern space age, we have spent tremendous resources on expanding our horizons. In the last few years of the 20th century, we are on the cusp of discovering life outside of our planet. New telescopes are able to see planets forming around distant stars, and planets and moons in our own solar system show promise of having what it takes to form life as we know it—liquid water. With the discovery of oceans covered by a thick ice crust on Europa, the possibility of finding life is more imminent than at any other time.

As part of this study of our solar system, and our quest for life outside of our planet, NASA has proposed a possible mission to Europa. This mission is going to do a detailed analysis of the surface and subsurface of Europa. No probe prior to this one will have probed these features in as much detail. This will be the first time a probe will be landed on a Jovian moon. The choice of Europa is based on the interest surrounding the liquid water, which is theorized to be present.

As a moon of Jupiter, Europa is brought under the gravitational forces of the second largest body in the solar system. Since Jupiter comprises as much mass as all other bodies in orbit around the sun, any object which comes in close proximity to this planet experiences huge tidal forces. These huge tidal forces continually oscillate through Europa’s orbit, due to the oblateness of Jupiter. Further tidal forces are encountered as nearby moons are passed. This motion continually generates heat in the center of Europa. It is theorized that this heating is what causes the liquid ocean under the crust to exist.

The scientific community has only recently accepted the concept of a floating ice shell. The first real evidence of this situation has come from high resolution, ................
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