TacSat 2 (JWS D1, ST 6ISC)

JWS D1 [MicroSat Systems]

The TacSat-2 is a small technology mission of the Air Force Research Laboratory. It will build upon the experience gained with TacSat 1.   TacSat 2 has now been renamed JWS D 1 (Joint Warfighting Space Demonstrator)

The spacecraft Road Runner bus is being developed by MSI (MicroSat System's Inc.) of Littleton, CO, using the spare bus and parts of the TechSat-21 program (which was cancelled in early 2003) with minor modifications. The bus structure consists of composite facesheets over an aluminum honeycomb core, comprising only 13% of the spacecraft mass. The basic structure is an irregular octagon with a "payload" and a "separation" deck. The platform is 3-axis stabilized capable of providing a pointing accuracy of < 0.15º. The ADCS (Attitude Determination and Control Subsystem) employs 3 reaction wheels (Dynacon MW-1000) and 3 torque rods as actuators. A star camera provides high-precision attitude measurements. An IMU (Inertial Measurement Unit), analog sun sensors, and a magnetometer complete the ADCS sensor suite. Electric power of up to 550 W is provided by the solar array. The Li-Ion battery has a capacity of 30 Ah. The bus power system is based on a direct energy transfer topology (tied directly to the battery via a set of FETs) delivering unregulated 28 V switched power to the loads. The C&DH (Command and Data Handling) subsystem employs a Power PC. Bus communication is provided by a Mini-SGLS (Miniature Space-to-Ground Link Subsystem), using 2 pairs of patch antennas for full spherical coverage and an encryption device. The spacecraft has a mass of 415 kg.

Following experiments are on board:

• ESI (Earth Surface Imager) developed by AFRL and SAIC (Science Applications International Corporation). ESI is the prime instrument of TacSat-2 (pushbroom imager). The objective is to provide high-resolution imagery at < 1 m GSD (Ground Sample Distance). The instrument features a Pan band and 3 multispectral bands in the visible range across a swath of 6144 pixels (5 km swath width). The optics subsystem employs a COTS telescope of 50 cm aperture of RC Optical Systems.
• TIE (Target Indicator Experiment). The objective is to locate targets based on RF signatures and in conjunction with P3 aircraft. A version of this payload is flown on the TacSat-1 satellite. TIE uses a total of 11 antennas. This payload needs only 7W instead of 70W on TacSat 1.
• CDL (Common Data Link) is an AFRL experimental communication system. The objective is to use it in combination with a ground-based CDL terminals. This high-performance system permits downlink data rates of up to 274 Mbit/s.
• ROPE (Roadrunner On-orbit Processing Experiment). This payload consists of an array of FPGAs (Field Programmable Gate Array) designed to process imagery into standard military imaging formats. ROPE supports also event processing to identify likely targets, and JPEG data compression for real-time data transmission to the ground segment.
• HET (Hall Effect Thruster), provided by AFRL at Edwards AFB, CA. This demonstration ion engine is based on the Busek Tandem Hall Thruster BHT-200-X3 (Busek Co. Inc., Natik, MA). HET features an Isp of up to 1600 s, variable thrust levels, and variable power usage. The nominal 200 W thruster has an operating envelope ranging from 50 to 300 W. The thrust range is 4-17 mN with nominally 12.4 mN. The instrument has a mass of < 1 kg and a size of 100 mm diameter and a length of 105 mm. HET is an experiment, it's main use is to maintain orbit against drag.
• IGOR (Integrated GPS On-orbit Receiver), developed by Broad Reach Engineering, Tempe, AZ. IGOR is of BlackJack heritage of JPL. The objective is to conduct ionospheric reflection and transmission experiments. In addition, IGOR provides the spacecraft with a precise navigation solution in support of high-precision imaging observations.
• ADS (Atmospheric Density Specifications). ADS consists of two complementary experiments to characterize the neutral wind of the upper atmosphere.
  • ACME (Anemometer Cross-track Measurement Experiment). ACME measures the cross-track component of the very rarified atmosphere at the orbital altitude of 350 km; it requires precise pointing knowledge to remove the spacecraft in-track velocity component from its measurement. ACME is being developed by the University of Texas at Dallas, TX. (now removed)
  • ADMS (Absolute Density Mass Spectrometer). ADMS measures the atomic mass of the prevailing species in the wind in the range from 1 to 50. ADMS is being developed at AFRL, Hanscom AFB, MA.

  The coordinated ADS package measurements permit a better understanding of the dynamic processes that affect the variability of the upper atmosphere.

• MVIS (Miniaturized Vibration Isolation System). The objective of MVIS is to demonstrate damping of spacecraft jitter - in support of higher-quality observation measurements. MVIS consists of a series of actuators placed at the imager telescope assembly center of gravity.
• ESA (Experimental Solar Array), developed by MSI. The experiment consists of a flexible thin film photovoltaic array designed to demonstrate two different cell technologies and two different deployment mechanisms. ESA is supported by the patented FITS (Folded Integrated Thin film Stiffeners) of MSI, providing improved stiffness. These arrays offer the potential to drastically reduce the storage volume needed for high-power microsatellites.
• AE (Autonomy Experiment), developed by ICS (Interface & Control Systems). The AE consists of two subsystems:
  • OOCE (On-Orbit Checkout Experiment) features an enabling technology for autonomously commissioning the spacecraft (checkout) during its first day of orbital life.
  • ATE (Autonomous Tasking Experiment) permits non-expert users in the battlefield to send data requests to the spacecraft (example: "image a particular region in latitude and longitude") and to receive the response directly, if possible with regard to the current spacecraft location in orbit. ATE also serves as long-term and short-term experiment scheduler for all the payloads.

The ACME payload has been removed from the spacecraft to save weight.

Additionally a NASA New Millennium Payload has been added: The Inertial Stellar Compass (ISC) enables a spacecraft to continuously determine its attitude or the direction in which it is pointing. It also enables a spacecraft to recover its orientation (direction and pointing) after a temporary malfunction or power loss. This is done by the "marriage" of a miniaturized star camera and gyro system. Although this is not a new concept, the small size and low power consumption are revolutionary and an important feature for the new, smaller spacecraft and satellites of the future. ISC technology uses an active pixel sensor in a star-tracking camera and a three-axis system of microelectromechanical gyros. Draper Laboratory is the technology provider.

Source: Signal Magazine, January 2004 issue

Last update: 27.09.2009
Contact: gunter.krebs@skyrocket.de
© Gunter Dirk Krebs