Click here for Objectives, Structure, Payload, Power and Electrical, Command and Data Handling, Telemetry, Testing

Objectives

The primary objective of the Icarus Endmass is to serve as a stabilizing anchor for the ProSEDS tether system. The physical dimensions of Icarus are based off of the Endmass from the SEDS experiment. In order to maximize science return, Icarus will collect and transmit data on tether deployment and dynamics as well as Endmass attitude using the on board aspect magnetometer and GPS receiver. The Endmass GPS data acts as back-up for ProSEDS position tracking.

Once the Delta-II second stage performs its last depletion burn placing it into the ProSEDS orbit, power to the ProSEDS experiment is initiated. Pyrotechnic bolts release the Icarus Endmass from the Payload Attach Fitting deploying the entire 15 km of tether. Other than the mechanical non-electrical tether connection, there are no electrical or functional connections between Icarus and the rest of the ProSEDS experiment.

Icarus will transmit data continuously for the first four orbits of the mission. After that time, data will be transmitted only when the Endmass is within view of a ground station as determined by GPS location. The ProSEDS project is using ground stations from the DSN, GSFC, and AFSCN located in Goldstone, CA, Canberra, Australia, Madrid, Spain, Santiago, Chile, Wallops Island, VA, Guam, Hawaii, and Vandenberg AFB, CA. Hardware timers turn off the transmitter after 21 days due to NTIA frequency licensing restrictions.

Icarus and its Components
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Structure

Icarus is a 10.25" x 13.65" x 18.75" structure with a mass of 21.3 kg fully assembled. The shell is made of alodined aluminum panels with Kapton coating. The center of mass of the system is positioned at the center of the structure to reduce the risk of tumbling during tether deployment.

Thermal control of Icarus is provided by a passive thermal switch developed by Starsys Systems, Colorado. In addition, a blanket of Multi-Layer Insulation (MLI) is added around all electrical components that require warmer operating temperatures.

Payload

Icarus is equipped with an aspect magnetometer and GPS receiver for tether dynamics and attitude data. The magnetometer chosen was the Billingsly Model TFM 100G-2 which has a high enough accuracy to provide a +/-5 degree accuracy on the Endmass attitude. The Rockwell-Collins MPE-I was chosen for the GPS receiver due to its low power consumption and low cost. The unit is identical to the receiver located on the Delta-II side of ProSEDS.

Power and Electrical

Power to the Endmass is supplied using rechargeable Energizer NiCd E3200D batteries. Average power required by the system is 12.5W for the primary mission (100% transmitter duty cycle) and 8.6W for the secondary mission (%20 transmitter duty cycle). Twelve strings of Si solar cells located on all six panels recharge the Icarus batteries extending the total mission lifetime.

Command and Data Handling

Control functions of the Endmass are provided by an industrial grade CPU, the Octogon Systems 386 processor running MS-DOS 6.22. The C&DH subsystem to parse and determine the validity of GPS data. To supplement the MPE-I's searching capability, an orbital propagator is programmed into the software to approximate position based on a previous known position and time.

Data relating to the Endmass attitude is sampled at a 1 Hz rate with GPS being sampled as 0.5 Hz rate. Health data composed of voltage, current, temperature sensors is sampled once per minute. Data is organized into telemetry frames in compliance with the IRIG standard 106-96. A UART chip internal to the transmitter adds start and stop bits to the beginning and end of each byte to verify the quality of data transmission at the ground stations.

Telemetry

Data transmission to ground stations is performed via a S-band Southern California Microwave telemetry transmitter. A custom built patch antenna transmits the signal to ground stations around the world. The downlink rate is 115.2 kbits/sec. The entire on-board memory of telemetry, holding three orbits of data is cycled through the transmitter and takes approximately 72 seconds to downlink.

Testing

Since its delivery of the Endmass to Marshall Space Flight Center in September 2000, Icarus has been through four major systems tests- mechanical vibration and shock, thermal cycle, thermal vacuum, and a 48-hour hardware/software verification.