Microsatellites To Study Earth's Atmosphere From Low Orbit

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. 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 belonging to the Air Force 20th Space Control Squadron, a principal resource for tracking low-Earth orbiting space satellites.

The primary goal of the ANDERR mission is to test and verify the capabilities of the deployment mechanism that will be used on the shuttle for the actual ANDE mission. Secondary goals for ANDERR include spin axis and orientation measurements, space qualification of the backup communications system, and space qualification of copper-indium-gallium-diselenide (CIGS) photovoltaic arrays.

ANDE's particular design requirements led to the ANDERR mission, which evolved as a way to test the new deployment technique before the launch of the ANDE mission. 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. 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 ANDERR and ANDE microsatellites are each spherical spacecraft, and 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. The ANDERR satellites, called Mock ANDE Active (MAA) and Fence Calibration (FCal), underwent testing and integration at NRL in 2006.

Each 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.

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 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. MAA will be added to the amateur radio satellite network used globally by ham radio operators. MAA subassemblies have been 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 operated by the Air Force 20th Space Control Squadron. 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 ANDE project was conceived and developed at NRL, by Andrew Nicholas of NRL's Space Science Division. He envisioned two microsatellites sent into orbit at the same time; one satellite completely passive, the other carrying active instruments: a miniature wind and temperature spectrometer to measure atmospheric composition, cross-track winds, and neutral temperature; a Global Positioning Sensor; a thermal monitoring system to monitor the temperature of the satellite; an electrostatic analyzer to monitor plasma density; and a spacecraft charging sensor developed by the U.S. Air Force 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's Remote Sensing and Optical Sciences Divisions. 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.

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.