Microsatellites: Definitions and Technologies
Microsatellite projects typically involve rapid developmental timetables for experimental missions, with initiation to launch schedules in months to a few years. Often, commercial-of-the-shelf (COTS) technology is used and modified for microsatellite projects, even for military systems. Using COTS technology helps with the plug-and-play approach to microsatellite construction. By having pre-made, interchangeable components, microsatellites can be assembled to order and launched in a relative short time, sort of like Legos.
DARPA, the Pentagon’s R&D arm, has been working on a number of microsatellite technologies designed to reduce their weight and improve reliability and performance. These technologies include lightweight optical space surveillance/situational awareness sensors; lightweight power, chemical and electric propulsion systems; advanced lightweight structures; advanced miniature RF technology, including micro crosslink and use of COTS approaches; active RF sensor technology; COTS processor and software environment; miniature navigation technologies, including the use of starfields for deep space navigation; and autonomous operations technology.
Microsatellites are cheaper to make and launch. Smaller launch vehicles can be used to launch multiple microsatellites into orbit, or microsatellites can piggyback on rockets blasting larger payloads into space.
In addition to being faster and cheaper, microsatellites can be used for missions that larger satellites can’t perform, such as setting up a constellation of communication nodes or conducting in-orbit inspection of larger satellites. They could even be used as anti-satellite weapons to destroy key satellites of opponents. Some observers have judged that the BX-1 microsatellite deployed by China in 2008 was an experimental anti-satellite weapon.
The slogan for the small satellite approach is “faster, better, smaller, cheaper” – a slogan that the Pentagon has embraced with gusto.
Pentagon’s TacSat Program
 |
| TacSat program implementation schedule – 2007 |
In its 2007 report to Congress, the Pentagon said that the ORS effort had three goals: “first, to rapidly exploit and infuse space technological or operational innovations; second, to rapidly adapt or augment existing space capabilities when needed to expand operational capability; and third, to rapidly reconstitute or replenish critical space capabilities to preserve operational capability.”
These goals drove the ORS concept “to improve the responsiveness of existing space capabilities (e.g., space segment, launch segment, ground segment) and to develop complementary, more affordable, small satellite/launch vehicle combinations and associated ground systems that can be deployed in operationally relevant timeframes.”
To oversee this effort, DoD set up the ORS Office in 2007 at Kirtland Air Force Base, NM. The office was tasked to integrate the ORS program; one of its focuses has been development and deployment of TacSat microsatellites. The TacSat program, which includes 8 TacSat, involves participation from the Naval Research Lab (NRL), the Air Force Research Lab (AFRL), the Army’s Space and Missile Defense Command, and the Air Force Space Command, as well as the ORS Office.
During 2003 and 2004, TacSat-1 was developed, produced, and tested for less than $10 million. The satellite was a 220 pound-class microsatellite with electronic intelligence capabilities, including specific emitter identification (SEI), visible and infrared imaging, and cross-platform capabilities. Both the SEI and cross-platform mission payload used a low-cost receiver (LCR-100) design.
The TacSat-1 bus, based on Orbital Sciences’ Orbcomm FM29 satellite, was designed to carry three payloads into low earth orbit: an infraSPOT Indigo Omega infrared camera, a HanVision HVDUO-F7 visible camera, and a Copperfield-2 payload capable of detecting, tracking, and identifying pulsed radio frequency signals. The satellite had the capability to task and disseminate data through the Pentagon’s secret SIPRNET network.
However, the launch of TacSat-1 aboard the SpaceX Falcon rocket, set for March 2006, was postponed because of problems with the Falcon. After a number of launch delays, the Pentagon decided to cancel the TacSat-14s launch in 2007 because TacSat-2 had already been successfully launched.
TacSat-2 was an imaging and RF satellite that provided tactical CDL and UHF links and used a Fairchild Imaging CCD 583 Time Delay Integration (TDI) Line Scan array. The TDI process enabled the satellite to scan the earth at high speeds and provide a high resolution image to ground commanders. Unlike TacSat-1, TacSat-2 was successfully launched Dec 16/06 aboard an Orbital Sciences’ Minotaur 1 rocket from the Mid-Atlantic Regional Spaceport at the southern tip of NASA’s Wallops Flight Facility, VA.
For TacSat-3, partners included ONR, AFL, and the Army Space and Missile Defense Command; ATK was the satellite manufacturer. TacSat-3 is an imaging satellite that consists of three payloads: the ARTEMIS hyper spectral imager (HSI), the Ocean Data Telemetry Microsatellite Link (ODTML), and the Space Avionics Experiment (SAE).TacSat-3 was launched on May 19, 2009, aboard a Minotaur-1 rocket from the Mid-Atlantic Regional Spaceport and became operational in May 2010 after completing testing and a mission demonstration in the field.
TacSat-4 is a communications satellite that provides 10 UHF channels that can be used for communication, data collection and transmission, and/or Blue Force Tracking. The project is led by the NRL with participation from the Pentagon, the Air Force, Army, Marines, and US Strategic Command. TacSat-4 provides communications-on-the-move capabilities for existing radios without requiring antenna pointing and provides a wideband MUOS-like channel for early testing.
TacSat-5 is being led by AFRL and will test plug-and-play technology for all internal and external bus interfaces. This is intended to enable the rapid assembly of microsatellites to meet commanders’ urgent needs. In October 2009, 11 contracts were let for development of TacSat-5. TacSat-6 is expected to be a communications satellite; TacSat-7 and TacSat-8 are still in the mission planning stage.
A spinoff of the TacSat program is the ORS-1 microsatellite, which is designed to provide continuous battlefield ISR. The ORS-1 satellite, built by ATK, grew out of the success of TacSat-3. ATK used the TacSat-3 bus to build the ORS-1 satellite with the addition of a propulsion module.
In June 2010, the Pentagon requested reprogramming of $3.9 billion in appropriations for the ORS program; $15.7 million of that was redirected to fund the launch of the ORS-1 microsatellite, which is set for April 2011 aboard a Minotaur-1 rocket from the Mid-Atlantic Regional Spaceport.
MiDSTEP Program Of DARPA
Under its Microsatellite Demonstration Science and Technology Experiment Program (MiDSTEP), DARPA is developing advanced technologies and capabilities to demonstrate a suite of lightweight technologies integrated into high-performance microsatellites.
One of the MidSTEP’s projects is the Microsatellite Technology Experiment (MiTEX). MiTEX is actually 2 microsatellites, one built by Lockheed Martin and the other by Orbital Sciences. The NRL built the upper stage kick motor for both satellites.
The satellites were successfully launched into geostationary orbit on June 21/06 aboard a Delta II rocket from Cape Canaveral Air Force Station (AFS). Over the next few years, they conducted experiments in autonomous operations and maneuvering and station-keeping. Both MITEx satellites maneuvered close to the defunct DSP early warning satellite. The first made a flyby on Dec 23/08 and the second on Jan 1/09.
DARPA has been reticent about what specific capabilities MiTEX was supposed to demonstrate. In its budget justification for the project, the agency said:
“The Microsatellite Technology Experiment (MiTEx) technology demonstration investigated and demonstrated advanced high-payoff technologies from a variety of potential candidates, including: lightweight power and propulsion systems, avionics, structures, commercial off-the shelf (COTS) components, advanced communications, and on-orbit software environments. MiTEX flight tested a new, experimental upper stage, and demonstrated small COTS technologies to support a fast-paced, low-cost, lab-like, build-to-launch satellite approach in a shared industry/government environment.”
Not very specific. At least one pundit wonders if the MiTEX microsatellites were designed to demonstrate anti-satellite warfare capabilities.
Another DARPA innovate microsatellite program is Systems F6 (Future, Fast, Flexible, Fractionated, Free-Flying Spacecraft), which aims at removing the constraints of traditional satellite programs. The F6 program rides on a number of trends, including the rapidly changing face of computing, and a steady rise in mini- and microsatellites.
System F6 will divide up the tasks performed by a large satellite (power, receivers, control modules, etc.) and assign each task to a dedicated micro-satellite. By communicating with each other in a cluster, the idea is that the cluster would provide the same overall capability as a traditional satellite.
By allowing the various functions of a spacecraft to be developed and launched separately, this type of “fractionated” system reduces overall program risk, provides budgetary and planning flexibility, speeds initial deployment, offers greater survivability – and allows future technologies to build on existing efforts, in order to create something totally new.
The program requires development of open interface standards to enable the emergence of a space “global commons.” A program goal is the industry-wide promulgation of these open interface standards for the sustainment and development of future fractionated systems.
RAFAEL's LiteSat
 |
| RAFAEL's LiteSat, a micro-satellite will weigh less than 100 kg to be used for 'Responsive Space Operations' by deploying reconnaissance satellites by airborne or ground launched satellites on missions supporting operational requirements on quick notice. Drawing: Rafael |
The core of the system is based on Rafael’s LiteSat design, a new micro-satellite platform designed for a maximum weight of 100kg, facilitating airborne launch methods. Leveraging on relatively low-cost airborne launch (from aircraft such as teh F-15) the concept calls for the deployment of several satellites in a constellation enabling high revisit frequency and rapid ‘Operationally Responsive Space’ deployment ORS.
The satellite is designed to operate in a Low earth Orbit (LEO) at an altitude of 300-350 km for missions lasting up to seven years. Rafael is planning to equip the LiteSat with an EO payload offering ‘sub-metric’ resolution, with the same mission management, image processing, enhancement and optimization handled by field deployable IMILITE imagery processing systems currently supporting aerial recce and UAV platforms.
The Litesat platform is designed with ultra-light structures manufactured by Rafael’s space qualified composite material labs. The company has also developed lightweight propulsion methods, based on cold gas and elctrical propulsion (HAL effect), facilitating long operation using minimal fuel storage.
No comments :
Post a Comment