Project ANDE Assembly and Testing Nears Completion at NRL for Fall Delivery to NASA
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A team of Naval Research Laboratory scientists and engineers is preparing two sets of microsatellites for the Atmospheric Neutral Density Experiment (ANDE). ANDE is a low-cost mission to study the atmosphere of the Earth from low-Earth orbit by monitoring total atmospheric density at 400 kilometers (km). ANDE data will be used to improve methods for the precision orbit determination of space objects and to calibrate the radar fence, a space surveillance system recently transitioned from the Naval Network and Space Operations Command to the Air Force 20th Space Control Squadron, the principal resource for tracking low-Earth orbiting space satellites.
The first set of ANDE microsatellites will fly on a Department of Defense Space Test Program (STP) risk reduction mission in early 2006 to test a novel deployment mechanism from the space shuttle cargo bay. The actual ANDE mission will be deployed during a later NASA space shuttle flight.
Significant advances in the miniaturization of space technology and cost reduction have resulted in the proliferation of much smaller spacecraft or microsatellites. The ANDE microsatellites, each 19 inches in diameter, are outfitted with instrumentation that will perform several interrelated mission objectives. These objectives include: providing high-quality satellites for calibration techniques and models for precision orbit determination; demonstrating a new concept for space to ground optical communications; and providing detailed atmospheric composition for validating new Air Force sensors.
Each ANDE satellite is a compact, nearly perfect sphere, which reduces shape and drag errors during the orbit determination process. The local density of the atmosphere will be determined by modeling position and velocity variations detected by high-accuracy laser and radar ranging techniques, whereby the satellites are the primary sensing instruments. The accuracy of the atmospheric density measurements inferred from the orbital tracking of ANDE satellites will be greater than that achieved by similar past experiments, due to the unique design of the spacecraft.
ANDE's particular design requirements gave way to the ANDE Risk Reduction (ANDERR) mission, which evolved from the desire to test the new deployment technique prior to the main ANDE mission. The first set of satellites, Mock ANDE Active (MAA) and Fence Calibration (FCal), will fly on the ANDERR mission and are currently being integrated and tested at NRL.
Many design challenges had to be overcome to meet the mission requirements. New methods for parts and assembly fabrication were sought out and implemented, and a unique payload ejection system had to be developed. To meet cost constraints, the command and telemetry links used inexpensive commercial off-the-shelf ham radio transceivers.
During the ANDERR mission, the MAA satellite will be used primarily as a technology demonstration and pathfinder mission. It will also be used as a proof-of-concept for a spherical antenna system being developed by the U.S. Naval Academy, and act as a pathfinder to determine conditions for space-based optical communications, such as the NRL-developed Modulating Retro Reflector in Space (MODRAS) experiment. The MAA satellite will be added to the amateur radio satellite network used globally by ham radio operators. Subassemblies of the MAA satellite are being used to educate the midshipmen at the U.S. Naval Academy in the design, analysis, fabrication, and testing of space-flight hardware.
The ANDERR FCal satellite is named for its intended use as a calibration target for the radar fence now operated by the Air Force 20th Space Control Squadron. However in an expanded role, the FCal satellite will also function as a satellite digital repeater for the amateur radio community and as an educational tool for satellite enthusiasts.
The deployment system for ANDE is unique in that there is no permanent mechanical interface between the system and the satellites. No existing space shuttle ejection system could deploy satellites of this design so the Air Force Space Test Program developed a new deployment system to meet mission requirements, the Canister for All Payload Ejections (CAPE). CAPE will be used for this mission as well as other future DoD missions.
Meeting the challenge for a single-ejection platform, CAPE will insert both satellites into orbit simultaneously. The decision to develop CAPE was made after an extensive review of all existing payload ejection systems. Researchers even studied an unconventional method of using the astronauts to "jettison" the satellites from either the International Space Station or the space shuttle. However this method was rejected due to safety concerns because accurate velocity and direction data were required for re-contact analysis.
CAPE is a cylinder that holds an internal cargo unit (ICU) for the two microsatellites. The ICU is a payload interface mechanism that serves as the unique payload carrier, totally enveloping the payload. The ICU-to-CAPE interface will be the primary separation system for ejecting the ICU from the CAPE Canister. The CAPE payload envelope is 21 inches in diameter and 53 inches long. The entire volume can be used to hold a payload, without affecting the ejection parameters of the CAPE system.
The ANDE project was conceived and developed at NRL, by a young scientist in NRL's Space Science Division, Mr. Andrew Nicholas, who envisioned two microsatellites sent into orbit at the same time; one satellite completely passive, the other carrying three active instruments: a miniature wind and temperature spectrometer (WATS) to measure atmospheric composition, cross-track winds, and neutral temperature; a Global Positioning Sensor (GPS); a thermal monitoring system (TMS) to monitor the temperature of the satellite; an electrostatic analyzer to monitor plasma density; and a spacecraft charging sensor developed by the USAF Academy.
The active satellite will telemeter data to the ground. Instead of an antenna, the active satellite will be fitted with MODRAS, a set of modulating retro reflectors, coupled with an electronics package, that will telemeter the data by modulating the reflected satellite laser ranging (SLR) laser interrogation beam. MODRAS was developed at NRL by Dr. Charmaine Gilbreath of the Remote Sensing Division and Dr. William Rabinovich of the Optical Sciences Division. MODRAS provides the ANDE program with a science enabling technology as it allows for a larger communications bandwidth without sacrificing the spherical geometry of the spacecraft.
Each satellite contains a small lightweight payload designed to determine the spin rate and orientation of the satellite from on-orbit measurements and from ground-based observations. The two microsatellites will slowly separate into lead-trail orbit to provide researchers an opportunity to study small-scale, spatial and temporal variations in drag associated with geomagnetic activity. The passive satellite will lead the active satellite in orbit, and will be observed by U.S. Space Surveillance Network (SSN) and domestic and international SLR sites. The variation in observed position will be used to determine in-track total density. The active satellite will trail in orbit, and will be used to test space-to-ground communications. Scientists will determine its position in relation to the passive satellite to compute total density and validate drag coefficient models. In addition, instrumentation on board this active satellite will measure density and composition.
To date, the hardware for the risk reduction satellites has been delivered. Mr. Nicholas' team is currently completing the testing the integration of the risk reduction payloads at NRL. In June, the ANDE risk reduction satellites are scheduled for integrated testing of the deployment system in launch configuration. Vibration testing of the whole package will be done at the Naval Center for Space Technology Vibration Facility at NRL.
Once the ANDE risk reduction satellites pass CAPE system level integrated testing, ground truth measurements of the satellites will be performed. In October 2005 the spacecraft will be delivered to Kennedy Space Center in Florida. The ANDERR mission is manifested on STS-116 flight scheduled for launch in February 2006.
Project ANDE is a cooperative effort, involving NRL, the DoD Space Test Program, the Air Force Research Laboratory, the U.S. Naval Academy, the U.S. Air Force Academy, Muniz Engineering, and the Stensat Group LLC.
|Integrating a retro reflector assembly into the FCal spacecraft. The MAA spacecraft is seen in the foreground.|
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