he next-generation commercial imaging satellite of DigitalGlobe Inc. (Longmont, CO, USA) is called WorldView-1, a successor of QuickBird-2 (launch Oct. 18, 2001 - and fully operational as of 2007). In ... Oct. 2003, DigitalGlobe was awarded a sizeable contract by NGA (National Geospatial-Intelligence Agency) of Washington DC, formerly NIMA (National Imaging and Mapping Agency), to provide high-resolution imagery from the next-generation commercial imaging satellites.
The NGA requirements call for imagery with a spatial resolution of 0.5 m panchromatic and 2 m MS (Multispectral) data. The contract award was made within NGA's NextView program, designed to give the US commercial imaging satellite operators the financing to build their satellites for high-resolution imaging. The WorldView mission is intended to provide imaging services to NGA as well as to the commercial customer base of DigitalGlobe.
BATC (Ball Aerospace and Technologies Corporation) of Boulder, CO, is the prime contractor and integrator of the spacecraft, providing the S/C bus (Ball Commercial Platform BCP-5000) and a WorldView-60 camera. A new feature of the WorldView spacecraft are CMG (Control Moment Gyroscopes) actuators for precise and highly responsive pointing control. The BCP-5000 bus provides increased power, stability, agility, data storage and transmission (over the BCP-2000 bus) as the demand for Earth remote-sensing information becomes more comprehensive.
The S/C is 3-axis stabilized. The ADCS (Attitude Determination and Control Subsystem) employs star trackers, IRU (Inertial Reference Unit) and GPS for attitude sensing, and CMGs as actuators. A S/C body-pointing range of ±40º about nadir is provided corresponding to a FOR (Field of Regard) of 775 km in cross-track. An instantaneous pointing accuracy of ≤ 500 m is provided at any start and stop of an imaging sequence. On the ground, the geolocation accuracy of the imagery is 5.8 to 7.6 m without GPCs (Ground Control Points) and 2 m with GPCs (3σ). The agile S/C provides retargeting at a rate of 4.5º/s with an acceleration of 2.5º/s2; it takes 9 s to slew the S/C over a ground distance of 300 km.
S/C power of 3.2 kW (EOL) is provided by the solar panels; the battery capacity is 100 Ah. The solar arrays are being articulated into the sun (normal pointing into the sun). The rotational drive assemblies and drive control electronics, referred to as QuAD (Quiet Array Drive), are being provided by Starsys, a subsidiary of SpaceDev, Poway, CA. Unlike traditional stepper motor solar array drives, the QuAD technology provides low disturbance actuation, allowing spacecraft images to be captured at the same time that the solar arrays are being pointed.
The S/C bus has dimensions of 3.6 m (high) and 2.5 m in diameter, the span of the deployed panels measures 7.1 m. WorldView-1 has a launch mass of 2500 kg. The mission design life is 7.25 years.
Launch: A launch of the WorldView-1 spacecraft took place on Sept. 18, 2007 on a Delta-2920 vehicle from VAFB, CA.
Orbit: Sun-synchronous circular orbit, altitude = 496 km (nominal), inclination = 97.2º. The equator crossing time is at 10:30 hours on a descending node. The period is 94.6 minutes. Note: While the low-altitude orbit selection offers better spatial resolutions than a higher one, it requires also more frequent reboosts to maintain the low orbit due to atmospheric drag influences.
RF communications: The command data are in S-band at 2 or 64 kbit/s. The housekeeping telemetry and tracking is in X-band at 4, 16, or 32 kbit/s of real-time data, or 524 kbit/s of stored data. The imagery is downlinked in X-band at 800 Mbit/s. The S/C provides a data storage capacity of 2.2 Tbit in solid state memory with EDAC (Error Detection and Correction). A total of 331 Gbit of imagery per orbit may be collected. In addition, direct (real-time) downlinks to customer sites are available using the same high-speed 800 Mbit/s X-band link.
Mission status: In early January 2008, DigitalGlobe announced the general availability of WorldView-1 imagery to its customers after all check-out aspects of the spacecraft and its payload had been completed. 6)
• DigitalGlobe delivered its first sample set of high-resolution images on Oct. 15, 2007 and began supplying imagery to the National Geospatial-Intelligence Agency (NGA) on Nov. 26, 2007 (the S/C reached already full operating capacity on Nov. 17. 2007).
Informaiton obtained from http://www.eoportal.org/