Secondary Payload Research Articles

Regeneratively Cooled Multiple-Use Plug Hybrid for Nanosatellites

The multiple-use plug hybrid for nanosatellites prototype thruster is being developed to fill a niche application for nanosat scale spacecraft propulsion. The prototype thruster uses safe-handling and inexpensive nitrous oxide and acrylonitrile-butadiene-styrene as propellants. The thruster system provides attitude control using secondary-injection thrust vectoring and allows large-impulse and small-impulse attitude control and proximity burns to be performed with the same system. To ensure survivability during extended duration burns, the multiple-use plug hybrid for nanosatellites incorporates a novel regenerative cooling design in which the nitrous oxide oxidizer flows through a cooling path embedded in the aerospike nozzle, before being injected into the combustion chamber near the nozzle base. Digital manufacturing was used to fabricate the nozzle components. Fused deposition modeling was used to fabricate the solid fuel grain from the acrylonitrile-butadiene-styrene thermoplastic. When fully developed, the multiple-use plug hybrid for nanosatellites thruster could provide an enhanced propulsive capability that would enable multiple nanosatellites to be independently repositioned after deployment from the parent launch vehicle. Because the environmentally benign propellants are mixed only within the combustion chamber after ignition, the system is inherently safe and can be piggybacked on a secondary payload with very little overall mission risk increase to the primary payload.

Radio Aurora Explorer: A Mission Overview

The primary objective of the Radio Aurora Explorer mission is to study plasma instabilities that lead to magnetic field aligned irregularities of electron density in the lower polar ionosphere (80–400 km). These irregularities are known to disrupt communication and navigation signals. The Radio Aurora Explorer mission uses a bistatic radar configuration; the spacecraft is the radar receiver and the transmitters are several worldwide incoherent scatter radars of which the primary radar is located in Poker Flat, Alaska. The satellites are 3 kg, university-class CubeSats with a primary payload of a direct-conversion radar receiver operating in the frequency range from 426 to 510 MHz. The satellite bus has a novel configuration of processing, attitude control, and antenna design that met the physical constraints of the CubeSat form factor and the one-year schedule constraint imposed by launch dates. Two satellites have launched: RAX-1 on 19 November 2010 onboard a Minotaur-IV rocket from Kodiak, Alaska, and RAX-2 on 28 October 2011 onboard a Delta-II rocket from Vandenberg U.S. Air Force Base, California. RAX-2 has detected and measured irregularities during multiple experiments over Alaska and Canada. Preliminary analysis indicates unprecedented characterization of the irregularities.

Abstract P6-11-11: Multistage Delivery of Paclitaxel: Increased Drug Stability and Sustained Release Results in Enhanced Efficacy in Breast Cancer

Abstract Background: A significant challenge for effectively treating cancer is overcoming biological barriers that reduce circulation times and increase degradation of possible treatments. We established an innovative approach to address this issue by embedding drug-containing nanoparticles within the pores of a larger mesoporous silicon particle (MSP) in order to optimize site-specific localization and release of therapeutic agents. The objective is to develop a nanotherapeutic-based multistage platform for breast cancer treatment, wherein paclitaxel, a mitotic inhibitor used in the treatment of breast tumors, will be loaded into polymeric micelles, which in turn will be loaded within MSPs. We hypothesize that this nested incorporation of drugs within MSPs, combined with enhanced tumor transport, will result in a more pronounced and sustained antitumor effect. Materials and Methods: Micelles were assembled from amphiphilic block copolymers consisting of poly(ethylene glycol)-poly(∈-caprolactone) (PEG-PCL, MW = 5k-5k). Nanoparticle size, zeta potential, and morphology was determined, and PTX loading and release kinetics from micelles analyzed. Drug-containing micelles were incorporated into MSPs by a previously established dry-loading method, wherein nanoparticles were incorporated into pores via capillary action. Loading of fluorescent micelles was used to verify loading within MSPs via fluorescence microscopy and flow cytometry analysis. Sulforhodamine B assays were used to evaluate the in vitro antitumor efficacy of the platform in MCF-7 and MDA-MB-468 breast cancer cells. In vivo efficacy was evaluated in MDA-MB-468 breast tumors in female nu/nu mice. Results: Resulting micelles had an average size of 20 nm, as confirmed through TEM, with paclitaxel loaded into micelles very effectively. Release kinetics showed that 50% of the drug was released within 4 hours and 80% released within 24 hours. Loading of micelles into MSPs depended largely on electrostatic interactions, with micelles loading better within pores of MSPs displaying increased positive charge. Micelle loading into MSPs was successful as demonstrated by flow cytometry, and release was significantly retarded (< 30% of drug released over 4 d). Incubation of micelle-containing MSPs with breast cancer cells in vitro showed that MSPs could be internalized by cells, after which a sustained and delayed release of the payload was observed in cells. Breast tumors treated with MSPs demonstrated sustained tumor suppression (169 mm3 compared to initial starting volume of 200 mm3) at day 35 following a single injection. It is important to note that sustained tumor efficacy was achieved with nanoparticle and free drug formulations, however, with the caveat of repeated administrations. Discussion: A novel multistage approach to chemotherapy effectively allows a secondary payload to be loaded and preserved within the MSPs until reaching the tumor site. This prevents premature release of the drug and allows for a sustained release which may potentially result in fewer patient side effects. Future studies will involve loading of multiple nanoparticle types into MSPs and addition of targeting and diagnostic components. Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P6-11-11.

Focusing on Size and Energy Dependence of Electron Microbursts From the Van Allen Radiation Belts

Focusing on Size and Energy Dependence of Electron Microbursts From the Van Allen Radiation Belts

A global geographical survey of received signal strength in the VHF band

Sumbandila (SO-67) is an 81kg LEO satellite launched on 17 September 2009. Its primary payload is a multi-spectral imager with a ground sampling distance of 6.25m at an orbit altitude of 500km. Its two command transceivers operate in the commercial and amateur radio VHF and UHF bands and one of them provides a VHF to UHF repeater service to radio amateurs. This paper presents initial results of a global three week monitoring period of two VHF frequency ranges. The data is obtained by executing on-board flight control procedures to select the frequencies to measure. The existing on-board telemetry gathering system is employed to record the data, most notably the received signal strength for the selected frequency. The data is downloaded using an adaptation of the imagery data download path. We determine regions of high signal levels by distributing individual measurements over cells in the satellite footprint before averaging over the cells. The data is then plotted on a geographical signal strength heatmap. We compare our results with that of a similar study of the late 1990s and point out changes since then. The data provides useful information for selecting future ground station locations for minimum interference. It further gives an indication of frequencies to use for command and telemetry communication at existing ground stations. We propose that including a receiver capable of measuring frequency interference across a desired frequency range is very useful to future missions for selecting communication frequencies from this range for ground station locations.

A Novel Satellite Mission Concept for Upper Air Water Vapour, Aerosol and Cloud Observations Using Integrated Path Differential Absorption LiDAR Limb Sounding

We propose a new satellite mission to deliver high quality measurements of upper air water vapour. The concept centres around a LiDAR in limb sounding by occultation geometry, designed to operate as a very long path system for differential absorption measurements. We present a preliminary performance analysis with a system sized to send 75 mJ pulses at 25 Hz at four wavelengths close to 935 nm, to up to 5 microsatellites in a counter-rotating orbit, carrying retroreflectors characterized by a reflected beam divergence of roughly twice the emitted laser beam divergence of 15 µrad. This provides water vapour profiles with a vertical sampling of 110 m; preliminary calculations suggest that the system could detect concentrations of less than 5 ppm. A secondary payload of a fairly conventional medium resolution multispectral radiometer allows wide-swath cloud and aerosol imaging. The total weight and power of the system are estimated at 3 tons and 2,700 W respectively. This novel concept presents significant challenges, including the performance of the lasers in space, the tracking between the main spacecraft and the retroreflectors, the refractive effects of turbulence, and the design of the telescopes to achieve a high signal-to-noise ratio for the high precision measurements. The mission concept was conceived at the Alpbach Summer School 2010.

Nanosatellite Cluster Launch Collision Analysis

AbstractNanospacecraft are usually launched in clusters from a single launch, in which they are hosted as secondary payloads. The nanospacecraft, e.g., CubeSats, are usually released simultaneously in small groups from one single container, to simplify the launcher interface manufacturing and the launch operations. The release sequence must be designed to minimize the risk of collisions among the nanospacecraft themselves. Considering the increasing number of micro- and nanosatellites in recent space activity, a collision risk analysis and a release systems configuration optimization are of interest. This paper describes a collision probability analysis for a nanosatellite cluster deployment, performed by a series of Monte Carlo simulations, comparing results obtained with different release mechanisms, procedures, and orbital dynamics modeling assumptions. The collision risk in the first orbits after launch depends mostly on the in-orbit injection initial conditions, such as relative initial position and ...

The dynamics and control of the CubeSail mission: A solar sailing demonstration

The CubeSail mission is a low-cost demonstration of the UltraSail solar sailing concept ( Burton et al., 2005; Botter et al., 2006; Hargens-Rysanek, 2006; Pukniel, 2009), using two near-identical CubeSat satellites to deploy a 260 m-long, 20 m 2 reflecting film. The two satellites are launched as a unit, detumbled, and separated, with the film unwinding symmetrically from motorized reels. The conformity to the CubeSat specification allows for reduction in launch costs as a secondary payload and utilization of the University of Illinois-developed spacecraft bus. The CubeSail demonstration is the first in a series of increasingly-complex missions aimed at validating several spacecraft subsystems, including attitude determination and control, the separation release unit, reel-based film deployment, as well as the dynamical behavior of the sail and on-orbit solar propulsion. The presented work describes dynamical behavior and control methods used during three main phases of the mission. The three phases include initial detumbling and stabilization using magnetic torque actuators, gravity-gradient-based deployment of the film, and steady-state film deformations in low Earth orbit in the presence of external forces of solar radiation pressure, aerodynamic drag, and gravity-gradient.

Small Space Weather Research Mission Designed Fully by Students

1 of 2 Copyright 2011 by the American Geophysical Union Students at the University of Colorado at Boulder are building a satellite to study the space weather generated by high-energy particles near the Earth. The Colorado Student Space Weather Experiment (CSSWE) is a CubeSat mission funded by the U.S. National Science Foundation, scheduled for launch into a low-Earth polar orbit in June 2012 as a secondary payload under NASA’s Educational Launch of Nanosatellites (ELaNa) program. CSSWE will observe energetic particles for a minimum of 3 months with two goals: to relate the location, magnitude, and frequency of solar flares to the timing, duration, and energy spectrum of solar energetic particles (SEP) reaching Earth and to determine the evolution of the energy spectrum of radiation belt electrons. To accomplish these objectives, CSSWE will measure energetic ions and electrons coming directly from the Sun while it traverses the polar regions, where Earth’s magnetic field lines are directly connected to the interplanetary magnetic field. CSSWE will also measure radiation belt particles at lower latitudes. These types of radiation can affect the operations and life spans of Earth-orbiting spacecraft. Solar particles incident over the polar caps also produce ionospheric disturbances that can affect radio frequency communications. CSSWE (see Figure 1) consists of three stacked CubeSat units, each 10 × 10 × 10 centimeters, that together will contain a single science payload, the Relativistic Electron and Proton Telescope integrated little experiment (REPTile). REPTile is a miniaturization of the Relativistic Electron and Proton Telescope (REPT) currently being built at University of Colorado’s Laboratory for Atmospheric and Space Physics (LASP) for the NASA Radiation Belt Storm Probes (RBSP) mission, which consists of two identical spacecraft scheduled to launch in May 2012 that will go through the heart of the radiation belts in a low-inclination orbit. REPTile is designed to measure the directional differential flux of protons ranging between 10 and 40 megaelectron volts and electrons ranging between 0.5 and 3 megaelectron volts. These energetic particle measurements will be used in conjunction with flare measurements from other spacecraft, such as the Extreme Ultraviolet Variability Experiment on NASA’s Solar Dynamics Observatory and the Solar X-Ray Imager on NOAA’s Geostationary Operational Environmental Satellite

Permutation/Silence Coding in Partially Under-Utilized Cellular Networks

We consider a cellular system where (i) wireless spectrum is divided into resource blocks in time and frequency, (ii) each wireless receiver is assigned one or more resource blocks as the exclusive (primary) user of these blocks, (iii) some of the resource blocks are under-utilized due to the mismatch between the primary user's application payload and the capacity of the dedicated resources, and (iv) there are users with backlogged traffic that cannot be fully served by only utilizing their own dedicated resource blocks. We show how partially utilized resource blocks in a given cell can be reutilized by conveying extra information to the backlogged users in the system (secondary users) by coding over the transmission patterns of the primary users. Specifically, we propose to create on-off transmission patterns (referred to as silence coding), where during on periods the base-station sends primary user's symbols and during off periods the base-station keeps silent. Distinct transmission patterns in return are used to carry different messages for a given secondary user. We first analyze the achievable rate region for primary and secondary users from an information theoretical point of view for randomly generated codebooks. Then, we propose practical schemes that use permutation codes for silence coding with and without forward error correction. Finally, we evaluate the performance of these practical schemes.

Feasibility of performing space surveillance tasks with a proposed space-based optical architecture

Under ESA contract an industrial consortium including Aboa Space Research Oy (ASRO), the Astronomical Institute of the University of Bern (AIUB), and the Dutch National Aerospace Laboratory (NLR), proposed the observation concept, developed a suitable sensor architecture, and assessed the performance of a space-based optical (SBO) telescope in 2005. The goal of the SBO study was to analyse how the existing knowledge gap in the space debris population in the millimetre and centimetre regime may be closed by means of a passive optical instrument. The SBO instrument was requested to provide statistical information on the space debris population in terms of number of objects and size distribution. The SBO instrument was considered to be a cost-efficient with 20 cm aperture and 6° field-of-view and having flexible integration requirements. It should be possible to integrate the SBO instrument easily as a secondary payload on satellites launched into low-Earth orbits (LEO), or into geostationary orbit (GEO). Thus the selected mission concept only allowed for fix-mounted telescopes, and the pointing direction could be requested freely. Since 2007 ESA focuses space surveillance and tracking activities in the Space Situational Awareness (SSA) preparatory program. Ground-based radars and optical telescopes are studied for the build-up and maintenance of a catalogue of objects. In this paper we analyse how the proposed SBO architecture could contribute to the space surveillance tasks survey and tracking. We assume that the SBO instrumentation is placed into a circular sun-synchronous orbit at 800 km altitude. We discuss the observation conditions of objects at higher altitude, and select an orbit close to the terminator plane. A pointing of the sensor orthogonal to the orbital plane with optimal elevation slightly in positive direction (0° and +5°) is found optimal for accessing the entire GEO regime within one day, implying a very good coverage of controlled objects in GEO, too. Simulations using ESA’s Program for Radar and Optical Observation Forecasting (PROOF) in the version 2005 and a GEO reference population extracted from DISCOS revealed that the proposed pointing scenario provides low phase angles together with low angular velocities of the objects crossing the field-of-view. Radiometric simulations show that the optimal exposure time is 1–2 s, and that spherical objects in GEO with a diameter of below 1 m can be detected. The GEO population can be covered under proper illumination nearly completely, but seasonal drops of the coverage are possible. Subsequent observations of objects are on average at least every 1.5 days, not exceeding 3 days at maximum. A single observation arc spans 3° to 5° on average. Using a simulation environment that connects PROOF to AIUB’s program system CelMech we verify the consistency of the initial orbit determination for five selected test objects on subsequent days as a function of realistic astrometric noise levels. The initial orbit determination is possible. We define requirements for a correlator process essential for catalogue build-up and maintenance. Each single observation should provide an astrometric accuracy of at least 1”–1.5” so that the initially determined orbits are consistent within a few hundred kilometres for the semi-major axis, 0.01 for the eccentricity, and 0.1° for the inclination.

Lunette: A network of lunar landers for in-situ geophysical science

Over the last 3 years, a team at JPL has worked to design a new concept for a small, low cost lander applicable to a variety of in-situ lunar exploration activities. This concept, named Lunette, originated as a design which would exploit potential excess capacity of EELV launches by being compatible with the EELV Secondary Payload Adapter (ESPA). The original Lunette mission concept would have allowed up to six low cost landers to be delivered to a targeted region of the moon, with landings separated by a few km, allowing establishment of a regional network with a single, shared launch. The original concept faced limits in the extent of regional distribution of landing sites since all six landers were dependent on a single solid rocket braking motor. In the last year the Lunette team has focused on a modification of the original ESPA-based concept to a design that would allow launch of multiple individual landers (each with its own braking stage) on a single launch vehicle, where each lander would be capable of independent targeting and landing. With such an implementation, the entire lunar surface could be accessed for establishment of network nodes that could enable high priority geophysical measurements on a scale not seen since Apollo. The present paper discusses the current state of the design of the Lunette geophysical network lander, as well as describing mission design, science operations, and an innovative design solution allowing the lander to take critical data continuously, even over the lunar night, without the need for radioisotope power systems.

Design of low mass dimensionally stable composite base structure for a spacecraft

Reduction of spacecraft structure mass is an important design goal as it helps to increase the payload fraction, improve agility and also reduce launch cost. The spacecraft is subjected to mechanical loads during launch and thermal loads during on orbit operations. A typical spacecraft contains a main load bearing base structure, which supports all primary payloads and connects the satellite with the launch vehicle. The dimensional stability and tolerance requirements of the payload interfaces are very stringent and there is a need to improve these under the specified thermal environment. This paper explains a novel design consisting of a bonded assembly of metal and laminated composites to achieve a dimensionally stable, low mass base structure without altering the interfaces and overall dynamic behavior of the spacecraft. The design was checked for its performance under all critical loading conditions and was found to meet all requirements including stiffness and stability. Thermal distortion analysis showed that radial distortion is an order of magnitude lower than that of the existing design. The structure was fabricated and it showed compliance to dimensional accuracy requirements. The new base structure weighed 7.54kg achieving a mass saving of 35% on the existing structure.

Airborne Electro-Mechanical Actuator Test Stand for Development of Prognostic Health Management Systems


 
 
 With the advent of the next generation of aerospace systems equipped with fly-by-wire controls, electromechanical actuators (EMA) are quickly becoming components critical to safety of aerospace vehicles. Being relatively new to the field, however, EMA lack the knowledge base compared to what is accumulated for the more traditional actuator types, especially when it comes to fault detection and prognosis. Scarcity of health monitoring data from fielded systems and prohibitive costs of carrying out real flight tests create the need to build high-fidelity system models and design affordable yet realistic experimental setups. The objective of this work is to build an EMA test stand that, unlike current laboratory stands typically weighing in excess of one metric ton, is portable enough to be easily placed aboard a wide variety of aircraft. This stand, named the FLEA (for Flyable Electromechanical Actuator test stand), allows testing EMA fault detection and prognosis technologies in flight environment, thus substantially increasing their technology readiness level – all without the expense of dedicated flights, as the stand is designed to function as a non-intrusive secondary payload. No aircraft modifications are required and data can be collected during any available flight opportunity: pilot currency flights, ferry flights, or flights dedicated to other experiments. The stand is currently equipped with a prototype version of NASA Ames developed prognostic health management system with models aimed at detecting and tracking several fault types. At this point the team has completed test flights of the stand on US Air Force C-17 aircraft and US Army UH-60 helicopters and more experiments, both laboratory and airborne, are planned for the coming months.
 
 

Post mission life plan for FORMOSAT-2

This paper presents the enhancement in mission operations, the mission life state-of-health (SOH) trending analysis, and the post mission life plan of the FORMOSAT-2 (or FS2, Formosa satellite #2, was called ROCSAT-2, or RS2, Republic of China satellite #2, previously) during its five years mission life from 20 May 2004 to 20 May 2009. There are two payloads onboard FS2: a remote sensing instrument (RSI) with nadir ground sampling distance (GSD) of 2m for panchromatic (PAN) and GSD of 8m for multi-spectral (MS, 4 bands) as the primary payload, and an imager for sprite and upper atmospheric lightning (ISUAL) as the secondary payload. It was launched on 20 May 2004. The design life is 7 years while the mission life is 5 years. In other words, the end of mission life date of FS2 is 20 May 2009. Generally speaking, FS2 is still at very good condition in its SOH. Post mission life plan for FS2 consists of: the practice of orbit transfer for global coverage and better resolution, the development of gyroless attitude control, and the method for life extension. It is expected that the working life of FS2 can be extended 3–5 years.

TerraSAR-X Mission Planning System: Automated Command Generation for Spacecraft Operations

On June 15, 2007, TerraSAR-X was successfully launched from Baikonur, Kazakhstan. On board TerraSAR-X, a high-resolution X-band synthetic aperture radar (SAR) instrument is being operated as the primary payload. The user community requesting SAR products is composed of commercial and scientific partners as documented in a public-private-partnership agreement. The operations of the TerraSAR-X bus as well as payload operations are performed by the Mission Operations Segment (MOS). The Mission Planning System (MPS), which is a part of the MOS, has been designed to handle complex payload and standard bus operations in an automated manner. The purpose of this paper is to describe the concepts and the TerraSAR-X realization of the MPS.

New Passive Instruments Developed for Ocean Monitoring at the Remote Sensing Lab—Universitat Politècnica de Catalunya

Lack of frequent and global observations from space is currently a limiting factor in many Earth Observation (EO) missions. Two potential techniques that have been proposed nowadays are: (1) the use of satellite constellations, and (2) the use of Global Navigation Satellite Signals (GNSS) as signals of opportunity (no transmitter required). Reflectometry using GNSS opportunity signals (GNSS-R) was originally proposed in 1993 by Martin-Neira (ESA-ESTEC) for altimetry applications, but later its use for wind speed determination has been proposed, and more recently to perform the sea state correction required in sea surface salinity retrievals by means of L-band microwave radiometry (TB). At present, two EO space-borne missions are currently planned to be launched in the near future: (1) ESA's SMOS mission, using a Y-shaped synthetic aperture radiometer, launch date November 2nd, 2009, and (2) NASA-CONAE AQUARIUS/SAC-D mission, using a three beam push-broom radiometer. In the SMOS mission, the multi-angle observation capabilities allow to simultaneously retrieve not only the surface salinity, but also the surface temperature and an “effective” wind speed that minimizes the differences between observations and models. In AQUARIUS, an L-band scatterometer measuring the radar backscatter (σ0) will be used to perform the necessary sea state corrections. However, none of these approaches are fully satisfactory, since the effective wind speed captures some sea surface roughness effects, at the expense of introducing another variable to be retrieved, and on the other hand the plots (TB-σ0) present a large scattering. In 2003, the Passive Advance Unit for ocean monitoring (PAU) project was proposed to the European Science Foundation in the frame of the EUropean Young Investigator Awards (EURYI) to test the feasibility of GNSS-R over the sea surface to make sea state measurements and perform the correction of the L-band brightness temperature. This paper: (1) provides an overview of the Physics of the L-band radiometric and GNSS reflectometric observations over the ocean, (2) describes the instrumentation that has been (is being) developed in the frame of the EURYI-funded PAU project, (3) the ground-based measurements carried out so far, and their interpretation in view of placing a GNSS-reflectometer as secondary payload in future SMOS follow-on missions.

The European Student Moon Orbiter (ESMO): A lunar mission for education, outreach and science

ESMO is the fourth mission within ESA's Education Satellite Programme and builds upon the experience gained with SSETI Express (a micro-satellite launched into LEO in 2005), the YES2 tether experiment (launched into LEO on the Foton-M3 mission in 2007) and the European Student Earth Orbiter (a micro-satellite planned for launch in 2011/2012). The ESMO project is performed in order to attract and train the next generation of lunar and planetary engineers and scientists. The 250 kg ESMO mini-spacecraft is designed to be launched into geostationary transfer orbit (GTO) as a secondary payload in the 2012/2013 timeframe. An onboard liquid bi-propellant propulsion system will be used to transfer the spacecraft from its initial GTO to the operational lunar orbit via the Sun–Earth L1 Lagrange point over a period of 3 months. A miniaturised payload consisting of a narrow angle camera for optical imaging of the surface, and a subsatellite for global gravity field mapping would perform measurements over a period of 6 months. Alternative payloads under consideration include a biological experiment, and a passive microwave radiometer. The paper presents the scientific, educational and technical aspects of the ESMO project, including a description of the payload, the spacecraft design and mission profile.

CALIPSO Lidar Calibration Algorithms. Part I: Nighttime 532-nm Parallel Channel and 532-nm Perpendicular Channel

Abstract The Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) mission was launched in April 2006 and has continuously acquired collocated multisensor observations of the spatial and optical properties of clouds and aerosols in the earth’s atmosphere. The primary payload aboard CALIPSO is the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP), which makes range-resolved measurements of elastic backscatter at 532 and 1064 nm and linear depolarization ratios at 532 nm. CALIOP measurements are important in reducing uncertainties that currently limit understanding of the global climate system, and it is essential that these measurements be accurately calibrated. This work describes the procedures used to calibrate the 532-nm measurements acquired during the nighttime portions of the CALIPSO orbits. Accurate nighttime calibration of the 532-nm parallel-channel data is fundamental to the success of the CALIOP measurement scheme, because the nighttime calibration is used to infer calibration across the day side of the orbits and all other channels are calibrated relative to the 532-nm parallel channel. The theoretical basis of the molecular normalization technique as applied to space-based lidar measurements is reviewed, and a comprehensive overview of the calibration algorithm implementation is provided. Also included is a description of a data filtering procedure that detects and removes spurious high-energy events that would otherwise introduce large errors into the calibration. Error estimates are derived and comparisons are made to validation data acquired by the NASA airborne high–spectral resolution lidar. Similar analyses are also presented for the 532-nm perpendicular-channel calibration technique.

Lunette: A low-cost concept enabling multi-lander lunar science and exploration missions

The development of low cost missions for lunar exploration has emerged as a topic of increasing interest. Recently a study team from JPL was tasked to consider potential high-value lunar surface science and exploration missions that could be performed with small, low cost landed assets, with particular emphasis on missions that could be flown as secondary payloads on evolved expendable launch vehicle (EELV) launches. A mission concept and flight system design was developed in the course of this study that would deliver a network of up to six individual landers to a local lunar region, utilizing the full capabilities of the EELV secondary payload adapter (ESPA). The braking burn of the six landers would be performed by a single solid rocket motor integral with the ESPA ring, following which the landers would separate from the ESPA and perform final descent and precision landing using their own onboard propulsion systems. The six landers would initiate a one year mission, performing site survey and environmental science measurements including illumination, temperature, radiation, soil mechanics, and seismometry. Additional payload accommodation would be available on each lander to include unique experiments. The lander design was constrained to fit within the requirements for accommodation on the ESPA. These include a wet mass of no more than 180 kg, and dimensions that fit in an envelope of 61×71×96 cm. The total landed mass of the conceptual spacecraft is ∼140 kg which would deliver a total of ∼15 kg of payload mass to the lunar surface, per lander. In addition to the multi-lander ESPA-based design, a single lander flight system variant was developed that could enable globally distributed network science at very low cost. This paper discusses the mission concepts, flight system designs and numerous system engineering challenges that led to the development of this uniquely flexible and cost effective lunar mission concept.