The Clementine Mission —
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The Clementine mission – A 10-year perspective Trevor C Sorensen1,∗ and Paul D Spudis2 1University of Kansas, Lawrence KS, USA. 2Applied Physics Laboratory, Laurel MD, USA. ∗e-mail: [email protected] Clementine was a technology demonstration mission jointly sponsored by the Department of Defense (DOD) and NASA that was launched on January 25th, 1994. Its principal objective was to use the Moon, a near-Earth asteroid, and the spacecraft’s Interstage Adapter as targets to demon- strate lightweight sensor performance and several innovative spacecraft systems and technologies. The design, development, and operation of the Clementine spacecraft and ground system was per- formed by the Naval Research Laboratory. For over two months Clementine mapped the Moon, producing the first multispectral global digital map of the Moon, the first global topographic map, and contributing several other important scientific discoveries, including the possibility of ice at the lunar South Pole. New experiments or schedule modifications were made with minimal constraints, maximizing science return, thus creating a new paradigm for mission operations. Clementine was the first mission known to conduct an in-flight autonomous operations experiment. After leaving the Moon, Clementine suffered an onboard failure that caused cancellation of the asteroid ren- dezvous. Despite this setback, NASA and the DOD applied the lessons learned from the Clemen- tine mission to later missions. Clementine set the standard against which new small spacecraft missions are commonly measured. More than any other mission, Clementine has the most influ- ence (scientifically, technically, and operationally) on the lunar missions being planned for the next decade. 1. Introduction operations. The Lawrence Livermore National Laboratory (LLNL) provided lightweight imaging The Ballistic Missile Defense Organization cameras developed under the sponsorship of the (BMDO) informed NASA in January 1992 of its BMDO, the Goddard Space Flight Center pro- intention to test lightweight miniature sensors and vided trajectory and mission planning support to components by exposing them to a long duration the NRL for the lunar mission phase, and the Jet space environment while obtaining imagery of the Propulsion Laboratory (JPL) provided asteroid Moon and the near-Earth asteroid, Geographos encounter planning and the Deep Space Network (Worden 1992). NASA agreed to provide science (DSN) for deep space communications and orbit support in return for access to data collected dur- determination. Besides the parts suppliers, sev- ing the mission. The result was the Deep Space eral contractors were used by NRL during the Program Science Experiment (DSPSE) Clementine project. mission. The BMDO selected the Naval Research Clementine was launched on a Titan IIG expend- Laboratory (NRL) as its executing agent with able launch vehicle from Vandenberg Air Force responsibility for mission design, spacecraft engi- Base into low Earth orbit (LEO) on January 25th, neering, spacecraft manufacture and test, launch 1994. Eight days after launch, it executed a Trans- vehicle integration, terrestrial support, and flight lunar Transfer Injection (TTI) burn that placed it Keywords. Polar deposits; Clementine; bistatic radar; Moon; mineral mapping. J. Earth Syst. Sci. 114, No. 6, December 2005, pp. 645–668 © Printed in India. 645 646 Trevor C Sorensen and Paul D Spudis into a lunar phasing loop orbit with two Earth fly- camera with its single filter. The objectives of the bys. The STAR 37FM Solid Rocket Motor (SRM) LWIR global mapping were to and ISA, collectively referred to as the Inter- stage Adapter Subsystem (ISAS), separated from • derive surface roughness and ‘beaming’ proper- the spacecraft during the first phasing orbit. The ties, ISAS remained in a highly elliptical orbit for three • understand LWIR calibration through observa- months collecting and transmitting radiation data tion of the Apollo landing sites, and from the Van Allen belts (Regeon et al 1994). • assist interpretation of other data. On February 19th, 1994, a 460 m/s burn of the spacecraft’s bi-propellant propulsion system The tracking data from the Clementine space- put the spacecraft into a highly elliptical polar craft can be used to help determine and refine the orbit with an 8-hour period. This was the first lunar gravitational potential field model, especially time an American spacecraft had been in lunar when combined with the earlier lunar missions orbit since Apollo 17 in 1972. Two days later and the subsequent Lunar Prospector mission. a burn put Clementine into a 5-hour period The Apollo missions were very useful in defin- elliptical orbit for mapping. Clementine spent ing the lunar potential field, but their orbits were 73 days in lunar orbit, during which time it restricted to the equatorial region. Two of the accomplished the goal of a complete global mul- Lunar Orbiter spacecraft of the mid-1960s were tispectral mapping of the Moon, a gravimet- placed in polar orbits, but the tracking resolution ric map, and the first global topographic map, of the time was sufficient only to provide a fairly and making several other important scientific coarse potential field model. discoveries. Additional science objectives included a lumi- nescence experiment, a lunar horizon glow (LHG) 1.1 New technologies experiment, stereo mapping, a high resolution stereo camera (HRSC) experiment, a bi-static The primary new technologies that BMDO wanted radar (BSR) experiment, and various tests to to test during the lunar mission were the aid in the calibration of the images. These tests lightweight sensors: Ultraviolet/Visible (UV-Vis) also included engineering and calibration sequences camera, High Resolution (HiRes) camera, Near that included dark field imaging, flat field imag- Infrared (NIR) camera, Long Wave-length Infrared ing, stray (scattered) light, point spread function, (LWIR) camera, and two star tracker cameras infrared camera temperature response (deep space (STCs); spacecraft subsystem components, e.g., stare), data compression, and radiometric cali- NiH Common Pressure Vessel (CPV) battery, bration using stars and lunar calibration sites as lightweight solar arrays, lightweight reactions targets. wheels and inertial measurement units (IMUs), and a R3000 RISC processor; and innovative soft- 2. Clementine spacecraft ware, e.g., Spacecraft Command Language (SCL), autonomous position estimation, autonomous atti- The spacecraft consisted of hardware and soft- tude determination, and autonomous operations ware subsystems, a payload subsystem, and the scheduling software (Rustan 1994). ISAS. The spacecraft was designed, integrated, and tested by the NRL. Table 1 provides an overview 1.2 Science objectives of the spacecraft system characteristics and fig- ure 1 shows the Clementine spacecraft in its launch The lunar mapping science objective was to obtain configuration with the ISAS and also in its oper- topographic imaging, altimetry data, and multi- ational configuration. Figure 2 illustrates Clemen- spectral imaging of the lunar surface (Nozette et al tine’s configuration. A more detailed description of 1994). The topographic imaging and altimetry data the spacecraft subsystems can be found in Regeon were to be obtained for as much of the Moon’s et al (1994). surface as possible, but due to the limitations of the HiRes camera and the laser ranger, 100% 2.1 New spacecraft technologies coverage was not possible. Two camera (UV-Vis camera, NIR camera) multispectral imaging with One of the primary objectives of the Clementine wavelengths specifically selected for lunar mineral mission was to demonstrate advanced lightweight identification was planned for 100% of the Moon’s BMDO components technology (Regeon et al surface. 1994). Some of the technologies flown for the Thermal mapping was desired for the sunlit first time on Clementine were (Horan and Regeon areas. This was to be accomplished by the LWIR 1995): The Clementine mission 647 Table 1. Clementine spacecraft characteristics. Subsystem Characteristics Attitude control subsystem • 3-axis stabilized for all modes except spin stabilized TTI burn (ACS) • 0.05 degree control; 0.03 degree knowledge; 6 degrees maximum rotational acceleration • Two STCs, one interferometric fiber optic gyro (IFOG), and one ring laser gyro (RLG) IMUs for attitude determination • Reaction wheels (4) and thrusters (12) for attitude control Electrical power subsystem • Gimbaled (single axis) GaAs/Ge solar array (2.3m2; 360 W@ 30 Vdc) (EPS) • 1.21 m2 GaAs/Ge solar array coverage on ISA assembly • Maximum solar eclipse (2 hours) Propulsion • SRM auxiliary kick motor; STAR 37FM • Bi-propellant (N2O4/MMH) for delta-V; monopropellant (N2O4) for momentum dumping, orbit maintenance, nutation control and spin-up/down Structures • Conventional (Aluminum) longerons with honeycomb skins • Composite interstage adapter, solar array panels and high-gain antenna • Space vehicle (launch adapter, kick motor, interstage and spacecraft) Command, telemetry, and • Primary controller - MIL-STD-1750A radiation-hardened processor data handling (CT & DH) • Image processor and backup controller - R3081 processor subsystem • 2.0 Gb (200 Mb) dynamic random access memory (DRAM) solid state data recorder Communications subsystem • S-band transponder; 125 b/s and 128 kb/s forward error correction (FEC) down- link; 1 kb/s uplink • 1.1 m diameter directional high rate antenna • S-band omni-directional transmit and receive antennas Payload and sensors • Payload interface electronics