PDS_VERSION_ID = PDS3 RECORD_TYPE = STREAM LABEL_REVISION_NOTE = " 20070830, G.A. Neumann Initial Version; 20071201, G.A. Neumann Changed references to be PDS compliant; 20080324, G.A. Neumann Plain text from unicode, added MOLA reference SMITHETAL2001B; 20080325, J.G. Ward Added SMITHETAL2001B reference as INSTRUMENT_REFERENCE_INFO object; 20080429, J.G. Ward Reformatted; 2008-05-006, EN:bsword, reformatted; 2010-03-10, G.A. Neumann added SMITHETAL2009 reference." OBJECT = INSTRUMENT INSTRUMENT_HOST_ID = "LRO" INSTRUMENT_ID = "LOLA" OBJECT = INSTRUMENT_INFORMATION INSTRUMENT_NAME = "LUNAR ORBITER LASER ALTIMETER" INSTRUMENT_TYPE = "LASER ALTIMETER" INSTRUMENT_DESC = " INSTRUMENT OVERVIEW =================== The LOLA instrument was designed, built and tested by the NASA Goddard Space Flight Center (GSFC). The principal investigator is David E. Smith (GSFC), and the deputy PI is Maria Zuber (MIT). LOLA has two primary objectives. First, it will produce a high-resolution global topographic model and geodetic framework that will assist with precise targeting, safe landing, and surface mobility for future scientific and exploration activities. LOLA will also characterize the polar illumination environment and image the Moon's permanently-shadowed regions (PSRs) to identify possible locations of surface ice crystals in shadowed polar craters. To achieve these primary objectives, LOLA will make three measurements: 1) the distance between the surface and the spacecraft, 2) the spreading of the returned laser pulse, and 3) the transmitted and returned laser energies. LOLA is a pulse detection, time-of-flight laser altimeter. LOLA transmits a 5-spot pattern that measures the precise distance to the lunar surface at multiple points simultaneously, thus providing 5 profiles across the lunar surface (Figure 1). Each spot within the five-spot pattern has a diameter of five meters; the spots are 25 meters apart in the form of a cross canted by 26 degrees counterclockwise to provide five adjacent profiles. The 5-spot pattern enables the surface slope to be derived in the along- track and across track directions. LOLA's instrument design is similar to the designs of the Mars Orbiter Laser Altimeter (SMITHETAL2001B) and the Mercury Laser Altimeter (CAVANAUGHETAL2007), augmented by a novel diffractive optic element (DOE) (SMITHETAL2009). It has five beams and five receiver channels, the first of which is also fiber-optic-coupled to a Laser Ranging (LR) telescope mounted on the High- Gain Antenna. Because LOLA makes global observations, the LOLA altimetry data can be used to improve the spacecraft orbit and our knowledge of far side lunar gravity, which is currently extremely poorly known but is required for precise landing and low-altitude navigation. Timing of one- way pulses fired from Earth to the LR will also improve navigation and gravity determination. The five received laser pulses are time stamped with respect to the spacecraft mission elapsed time using a set of time-to-digital converters at <0.5 ns precision. LOLA measures the transmitted and received pulse energies by integrating the pulse waveforms. The on-board science algorithm, running on an embedded microprocessor, autonomously adjusts the receiver detection threshold levels, detector gain, and range window for the lunar surface returns. ---- #4 #5 #1 ---- # shot 3 #3 #2 @4 @5 @1 ---- @ shot 2 @3 @2 *4 *5 *1 ---- * shot 1 *3 *2 Figure 1. Spot pattern generated on lunar surface by three successive laser shots. INSTRUMENT HARDWARE =================== The main technical details regarding the instrument are given below. Mass: 13 kg Power: 33.5 W (at CDR 7/06) Telescopes: Receiver 18x Beam Expander ---------- Objective Sapphire BK7G18/fused silica DOE Aperture Diameter (cm) 14 3.24 Focal length (cm): 50 16.2 Area: 0.015 m^2 8.245 cm^2 Field of view 1/e2 400 urad 100 urad Optics transmission >70% >95% Bandpass filter: lambda = 1064.45nm dlambda = 0.7nm FWHM LR Bandpass filter: lambda = 532.15 nm dlambda = 0.3 nm Detector/preamplifier: Si-Avalanche photodiode (APD) Detector diameter 0.7 (mm) Quantum efficiency 40% Noise equivalent power 0.05 pW/Hz1/2 Electrical bandwidth 100 MHz Pulse timing independent leading and trailing edge times from TDC-S1 ASICs, combined with 5 MHz coarse count. Energy monitor Gated charge-time measurement circuit with digitizer. Performance: Timing resolution <0.5 ns Clock freq. uncertainty <1eE-7 Laser pulse epoch acc. <3 ms Link margin, 50 km: 5.4 dB (P.D. ~85% at 100 km). Range measurement acc. <0.1 m at 50 km. Transmitted energy relative accuracy (shot to shot): 2% (1 sigma). Received energies Er relative accuracy, 0.1fJ< Er <3 fJ: 12% (1 sigma). Laser Oscillators: Two Cr:Nd:YAG slab cross-Porro resonators. Diodes: Two 2-bar arrays with thermoelectric cooler (TEC). Pumping: 60 A and 140-160 microsecond duration. Spatial mode: TEM00 Trigger: Passive Cr4+:YAG q-switch Operating range: 5 degrees C to 28 degrees C. Pulse width and rate: 6 ns FWHM, 28 Hz. Pulse Energy: 2.7 +/- 0.3 mJ Wavelength: 1064.30 +/- 0.1 nm Beam divergence: 100 urad. Beam separation: 500 urad. Fiber optics: LR fiber-optic bundle parameters: 7 fibers, 400um core, 0.22NA, 1.28mm bundle Receiver Fiber: 200 um core, 0.22NA INSTRUMENT MODES ================ The LOLA instrument has four modes, with the following hardware states: MODE TELEMETRY LASER DETECTOR ---- --------- ----- -------- MEASUREMENT HK, Science Firing enabled, Active-lunar return counts 28 Hz triggers STANDBY2 HK, Science Firing enabled, Active-LR and noise counts no trigger pulses STANDBY1 HK, Science Laser TEC active, Active-LR and noise counts capacitors not charged OFF Analog temps Survival heaters Inactive enabled These modes are controlled by the following ground commands: Mnemonic APID Fn Code Data (Check these bits) -------- ---- ------- ---- LRO_LOLA_PWR TBD TBD 0=off; 1=on LOLA_LASER_ENABLE 104 2 bit 0 = 0, ON; bit 0 = 1, OFF LOLA_LASER_SELECT 104 2 bit 1 = 0, Laser 1; bit 1 = 1, Laser 2 LOLA_LASER_FIRE 104 2 bit 2 = 0, Laser fire; bit 2 = 1, Laser disable LOLA_TEC_ENABLE_1 104 2 bit 3 = 0, enable TEC; bit 3 = 1, disable TEC LOLA_TEC_ENABLE_2 104 2 bit 4 = 0, enable TEC; bit 4 = 1, disable TEC LOLA_RESET_ENABLE 104 2 bit 5 = 1 LOLA_RESET 104 2 bit 6 = 1 LOLA_ALG_ENABLE 104 2 bit 7 = 0, hold 80K85 prime reset; bit 7 = 1, enable LOLA_DIAG_ALG_ENABLE 104 2 bit 8 = 0, hold 80K85 redundant reset; bit 8 = 1, enable LOLA_EEPROM_PROTECT 104 2 bit 9 = 0, inhibit EEPROM writes; bit 9 = 1, allow There are also commands to override thresholds, gains, and range gates that are nominally controlled by the FSW algorithm. The algorithm seeks to maximize the probability of detection under varying background noise conditions, by utilizing hardware noise counters in a fashion similar to that employed on the MOLA and MLA instruments. A variable range gate setting opens only during the window of time that returns are expected from the surface according to the FSW return histograms. To accomodate the large dynamic range of lunar return strength, a variable gain amplifier is implemented in hardware prior to the discriminator input. The gain is set according to tables of range setting - gain setting, one for each detector. Earth laser ranges are recorded by detector 1 during the 8 ms window preceding each laser fire, approximately 1-9 ms after the start of each 28-Hz cycle. The Earth window uses the same threshold and gain settings as for lunar ranges. Owing to higher background earth counts, especially during New Moon phases, the detector 1 thresholds are likely higher than those of the detector 2-5 channels. --------------- The data are downlinked to the Ground Data System in the Mission Operations Center and are transferred to the LOLA SOC at the end of each downlink pass. LOLA ground software assembles the telemetry files into EDR data tables, each covering a ~10-minute time period. A housekeeping telemetry data stream, which is a subset of the science telemetry, is sent to the LOLA SOC in realtime during tracking passes. The realtime housekeeping provides energy and signal processing information for the pulses generated by the LR component. The LOLA Measurement Team, Institution, and responsibilities David E. Smith GSFC Lunar coordinate system Maria T. Zuber MIT Exploration and altimetry Oded Aharonson Caltech Surface roughness, rock sizes James W. Head Brown Landing sites, geology Frank G. Lemoine GSFC Orbit and gravity Gregory A. Neumann GSFC Altimetry, radiometry Mark Robinson ASU Polar ice, landing sites Xiaoli Sun GSFC Instrument performance " END_OBJECT = INSTRUMENT_INFORMATION OBJECT = INSTRUMENT_REFERENCE_INFO REFERENCE_KEY_ID = "CAVANAUGHETAL2007" END_OBJECT = INSTRUMENT_REFERENCE_INFO OBJECT = INSTRUMENT_REFERENCE_INFO REFERENCE_KEY_ID = "SMITHETAL2001B" END_OBJECT = INSTRUMENT_REFERENCE_INFO OBJECT = INSTRUMENT_REFERENCE_INFO REFERENCE_KEY_ID = "SMITHETAL2009" END_OBJECT = INSTRUMENT_REFERENCE_INFO /* repeat as necessary for references */ END_OBJECT = INSTRUMENT END