Structures

The spacecraft's structure is built around a rectangular equipment deck that supports engineering components and the science instruments. The medium-gain antenna is on the underside, and the low-gain antennas are mounted on the solar wings. All the equipment is mounted directly onto the equipment deck except for the canister, the concentrator and the collector arrays, which are mounted inside the sample return capsule, which in turn is mounted on the equipment deck.

The structures subsystem weighs 98.6 kilograms (217.4 pounds).

Genesis Spacecraft Configuration Diagrams

Sample Return Capsule

The sample return capsule is a blunt-nosed cone with a diameter of 152 centimeters (60 inches). It has five major components: a heat shield, backshell, sample return canister, parachute system and avionics.

The total mass of the capsule, including the parachute system, is 205 kilograms (420 pounds).

A hinged clamshell mechanism opens and closes the capsule. The science canister housing the solar wind collector arrays and ion concentrator fits inside, with a central rotating mechanism to extend the collector arrays. The capsule is encased in a carbon impregnated material known as carbon-carbon and an ablative material called SLA- 561 to protect the samples stowed in its interior from the heat of reentry. A parachute activated by a mortar unit is carried inside the capsule and will be used to slow its descent.

Genesis Heatshield

The heat shield is made of a graphite-epoxy composite covered with a thermal protection system. The outermost thermal protection layer is made of carbon-carbon. The capsule heat shield remains attached to the capsule throughout descent and serves as a protective cover for the sample canister at touchdown. The heat shield is designed to remove more than 99 percent of the initial kinetic energy of the sample return capsule.

Genesis Backshell

The backshell structure is also made of a graphite-epoxy composite covered with a thermal protection system: a cork-based material called SLA-561V that was developed by Lockheed Martin for use on the Viking missions to Mars, and have been used on several missions including Genesis, Pathfinder, Stardust and the Mars Exploration Rover missions. The backshell provides the attachment points for the parachute system, and protects the capsule from the effects of recirculation flow of heat around the capsule.

The science canister is an aluminum enclosure containing the specialized collector arrays and ion concentrator. On the inside of the lid of the science canister is a bulk solar wind collector array. The specialized collector arrays are rotated out from inside the science canister. Underneath the stowed collector arrays, the ion concentrator forms the bottom of the science canister. The canister is inside the sample return capsule, which is mounted to an equipment deck suspended between the backshell and heat shield on a set of support struts.

The parachute system consists of a mortar-deployed 2.1-meter (6.8-foot) drogue chute to provide stability at supersonic speeds, and a main chute 10.5 by 3.1 meters (about 34.6 by 12.1 feet).

Inside the canister a gas cartridge will pressurize a mortar tube and expel the drogue chute. The drogue chute will be deployed at an altitude of approximately 33 kilometers (108,000 feet) to provide stability to the capsule until the main chute is released. A gravity-switch sensor and timer will initiate release of the drogue chute. Based on information from timer and backup pressure transducers, a small pyrotechnic device will cut the drogue chute from the capsule at about 6.7 kilometers altitude (22,000 feet). As the drogue chute moves away, it will extract the main chute. At the time of capture, the capsule will be traveling forward at approximately 12 meters per second (30 miles per hour) and descending at approximately 4 meters per second (9 miles per hour).

The solar arrays were stowed during launch and then released. Mechanisms under the wings allowed them to unfold and move on a hinge until two latches per wing engaged and locked the wings in place.

The sample return capsule has a separation and release system, made of three two legged struts that hold the sample return capsule in place. The sample return capsule is mounted on its struts with its heat shield atop six spring-loaded cans. The springs push on a ring that presses against the heat shield and gently shoves the capsule away from the spacecraft when pyrotechnic bolts are cut.

The sample return capsule's lid opens and closes on a main hinge, and all the electronic signals that control the collector arrays and concentrator are passed through a wire harness from the spacecraft to the capsule that passes through the hinge. In order to keep the hinge from damaging the sample return capsule as it plunges through Earth's atmosphere, the hinge is retracted away from the capsule before reentry.

Elbow joints at the top of the hinge have separation bolts and cable cutters that separate and retract the hinge assembly. The ion and electron monitors each had a door mechanism that exposed the sensors inside by using pyrotechnics to expand small metallic balloons to open the door.

Four mechanical latch/hook assemblies worked to grab the lid of the sample return capsule and hold it in place throughout launch. The science canister mechanisms are: the lock ring device, sealing lid, canister lid mechanisms, and solar collector array deployment mechanism.

All of the canister mechanisms combined weigh 17.0 kilograms (37.5 pounds)

Genesis receives its commands and sequences from Earth and translates them into spacecraft actions. The flight software is capable of running multiple concurrent sequences, as well as executing immediate commands as they are received.

The software used during the collection mission interpreted data from the ion and electron monitors to deploy the proper collectors depending on the type of solar wind. The flight software is also responsible for a number of autonomous functions, such as attitude control and fault protection, which involve frequent internal checks to determine whether a problem has occurred. If the software senses a problem, it will automatically perform a number of preset actions to resolve the problem or put the spacecraft in a safe mode for the ground to respond.

Most systems on the spacecraft are fully redundant. This means that, in the event of a device failure, there is a backup system to compensate. A software fault protection system is used to protect the spacecraft from reasonable, credible faults but also has resiliency built into it so any faults not anticipated can be accommodated without placing the spacecraft in a safe state.

Command and Data

All of the spacecraft's computing functions are performed by the command and data handling subsystem. The heart of this subsystem is a RAD6000 computer, a radiation hardened version of the PowerPC chip used on some personal computers and videogame systems. With 128 megabytes of random access memory and three megabytes of non-volatile memory, which allows the system to maintain data even without power, the subsystem runs Genesis' flight software and controls the spacecraft through interface electronics. Interface electronics are used to communicate with external peripherals. They allow the use of redundant, identical sets of computer and interface electronics, so that if one fails the spacecraft can switch to the other. Communication with Genesis' sensors that measure the spacecraft's orientation in space, or "attitude," and its science instruments is done via another interface card. A master input/output card collects signals from around the spacecraft and also sends commands to the electrical power subsystem. The interface to Genesis' telecommunications subsystems is done through another card called the uplink/downlink card. There are two other boards in the command and data handling subsystem, both internally redundant. The module interface card controls when the spacecraft switches to backup hardware and provides the spacecraft time. A converter card takes power from the electrical power subsystem and converts it into the proper voltages for the rest of the command and data handling subsystem components.

The entire command and data handling subsystem weighs 11.9 kilograms (26.2 pounds).

Genesis' telecommunications subsystem is composed of both a radio system operating in the S-band microwave frequency range and a system that operates in the ultra high frequency (UHF) range. The S-band system provides communication capability between Earth and the spacecraft throughout all phases of the mission. The UHF system is located in the sample return capsule; after parafoil deployment, it provides a backup tracking capability.

The spacecraft's radio system communicates with Earth though a medium-gain antenna. The medium-gain antenna is spiral-shaped, about 10 centimeters (4 inches) in diameter, about 12 centimeters (4.87 inches) tall and weighs 105 grams (about 4 ounces). The spacecraft also houses four low-gain antennas, located on the underside of the craft. These are patch antennas, which sit on a coaster-size square (10 by 10 by 1 centimeters (4 by 4 by 0.4 inches)). These have a much wider field of view.

The low-gain antennas will be used to make initial contact with the spacecraft after it leaves Earth's atmosphere, and afterwards only for emergencies. The medium-gain antenna will be used for most of the spacecraft's communication with Earth.

The telecommunication subsystem weighs 10.1 kilograms (22.3 pounds).

All of the spacecraft's power is generated, stored and distributed by the electrical power subsystem. The system obtains its power from an array of standard silicon solar cells arranged on two panels on either side of the equipment deck. The two solar panel wings, made of silicon and aluminum, are fixed in place. They hold grids of silicon cells which generate 265 watts at Earth's distance from the Sun. A power distribution and drive unit contains switches that send power to various loads around the spacecraft. Power is also stored in a 16-amp-hour nickel hydrogen battery.

The electrical system also contains a pyro initiator unit which fires small explosive devices that configure the spacecraft following launch, performing such tasks as extending Genesis' solar array and opening covers on science instruments. The pyrotechnic system also releases the sample return capsule by actuating cable cutters to allow the heat shield and back shell to separate from the spacecraft's body.

The electrical power subsystem weighs 36.5 kilograms (80.5 pounds).

Genesis maintains its orientation in space, or "attitude," by continuously spinning in space. The attitude control system will keep Genesis spinning at a rate of 1.6 revolutions per minute. During the science mission, the axis of spin pointed 4 degrees ahead of the Sun, so that ion and electron monitors would face directly into the oncoming solar wind. The slow spin helps maintain inertial pointing at the Sun, and minimizes pointing errors due to solar radiation pressure torques. Genesis determines its orientation at any given time using a star tracker and Sun sensors.

Genesis is the first robotic spacecraft to fly this particular system to determine its orientation, or "attitude." The star tracker can track stars of third magnitude or fainter; in combination with the digital Sun sensor, it can identify stars and generate information on the spacecraft's attitude. Using both the angles of the Sun and of nearby stars, on-board software can determine the spacecraft's orientation and spin rate. As long as the spacecraft is spinning between 1.6 and 2 revolutions per minute, it can identify stars. During the maneuvers when the spacecraft is spinning faster than 2 rpm, the spacecraft will use its spinning Sun sensors to determine its orientation. There are two star trackers, two digital sun sensor and two spinning sun sensors onboard as redundant backups.

The guidance, navigation and control subsystem weighs 10.0 kilograms (22.0 pounds).

The propulsion subsystem features sets of two kinds of small thrusters. The larger are used to make major trajectory correction maneuvers, and the smaller to continually maintain the spacecraft in its orbit.

Firing the thrusters changes the spacecraft's orientation. Two clusters of four small hydrazine thrusters each are mounted on the spacecraft, providing 0.88 newtons (0.2 pounds) of thrust each for small maneuvers to keep the spacecraft in orbit and to increase or reduce the rotation rate. Four more thrusters are also mounted on the spacecraft, each providing 22.2 newtons (5 pounds of thrust) for major trajectory correction maneuvers. These thrusters are only used when the sample return capsule's lid is closed in order to avoid contaminating the solar samples.

In addition to miscellaneous tubing, latch valves and filters, the propulsion subsystem also includes two 55-centimeter-diameter (22-inch) fuel tanks, each containing hydrazine, pressurized with gaseous helium. The outlets of tanks are metered together and will draw together equally.

The propulsion subsystem weighs 36.6 kilograms (80.7 pounds).

The thermal control subsystem is responsible for maintaining the temperatures of each component on the spacecraft to within their allowable limits. It does this using a combination of active and passive control elements. The active components are the heaters. The passive components are thermal paint, blankets of black kapton on the backside of the spacecraft and blankets of indium-10 oxide on the sunward side.

The thermal control subsystem weighs 15.9 kilograms (35.1 pounds).

Genesis is sponsored by NASA's Discovery Program, which competitively selects lowcost solar system exploration missions with highly focused science goals. The Jet Propulsion Laboratory, Pasadena, Calif., manages the Genesis mission for NASA's Office of Space Science, Washington, D.C. Lockheed Martin Astronautics, Denver, Colo., designed and built the spacecraft and will operate it jointly with JPL. JPL is a division of the California Institute of Technology, the home institute of the principal investigator. Major portions of the payload design and fabrication were carried out at Los Alamos National Laboratory.

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