Technical Sessions

Session X: Mission Enabling Technologies 1

Chair: Johan Leijtens, TNO Science and Industry

Wednesday, August 11, 2010

3:45 p.m.Smart Propellant

Siegfried Janson – The Aerospace Corporation

ABSTRACT: It costs thousands of dollars to put a kilogram of anything into orbit, including propellant. For many missions, one can significantly reduce the required on-orbit propellant mass by replacing cheap, “dumb” propellant with more expensive “smart” propellant composed of individual pico-, or nanospacecraft. The key is to use controlled ejection velocities and orbital mechanics to put these spacecraft on precise trajectories that eventually return them back to the host spacecraft for re-use. Each “smart propellant” spacecraft has on-board navigation, attitude control, and propulsion systems that enable fine-tuning of their trajectories for recapture. The ejected spacecraft mass, minus the expended on-board propellant mass for trajectory modification, can be re-used again and again. Smart propellant applications include orbit rephasing, orbit raising and lowering, and landing (plus subsequent take-off) on airless bodies. Required smart propellant ejection velocities range from tens of meters per second for rephasing to tens of kilometers per second for orbit raising in low Earth orbit. This paper presents results from orbital analyses of the above applications, their impact on smart propellant spacecraft design, and the potential use of mass-produced smart propellant pico- and nanospacecraft for human and robotic exploration of the Moon in the next decades.

4:00 p.m.YUsend-1 Solid Propellant Microthruster Design, Fabrication and Testing

Kartheephan Sathiyanathan, Regina Lee, Hugh Chesser – York University; Charles Dubois, Robert Stowe, Rocco Farinaccio, Sophie Ringuette – Defence Research and Development Canada (DRDC)

ABSTRACT: At the YUsend laboratory at York University, we have developed a solid propellant microthruster (SPT) design, developed with conventional materials and processes with future plan for MEMS fabrication. The proposed SPT design will be demonstrated on-board the YUsend-1 satellite. The objective will be to perform a technology demonstration in space conditions. The YUsend-1 prototype SPT consists of 36 individual thrusters with chambers 1.5 mm in diameter and approximately 3 mm in length. The propellant is a formulation of glycidyl azide polymer (GAP) and ammonium perchlorate (AP) with reduced viscosity for easy chamber filling. Impulse and thrust values were determined using a ballistic pendulum for no-nozzle, sonic and supersonic nozzle configurations. Throat diameters were approximately 600-700 μm. In all three configurations, ignition was successful. For the sonic and supersonic nozzles, a concentrated plume was visible for a burn duration of 1.3-1.6 s resulting in pendulum displacements of 1.2-1.8 mm. Observed thrust range was 0.15-0.28 mN which is consistent with existing SPT designs.

4:15 p.m.Towards Star Tracker Only Attitude Estimation

John Enright, Geoff McVittie, Tom Dzamba – Ryerson University; Doug Sinclair – Sinclair Interplanetary; C. Cordell Grant – Space Flight Laboratory/University of Toronto

ABSTRACT: Star trackers can provide full information about satellite attitude information from a single sensor. In this paper, we examine the feasibility of designing attitude determination systems using only star trackers. Star trackers can provide direct inertial attitude estimates without the need for sensor fusion, but current sensors are not robust enough to provide effective attitude estimates in all mission scenarios. Specific technical capabilities must be developed before star tracker only schemes could be practical. To this end, we discuss the performance, robustness, and survivability requirements that would be demanded of a star tracker only system and illustrate important developmental milestones delivered by the recently developed S3S star tracker. To illustrate the star tracker only approach, we present a case study showing variant designs for the CanX-4/5 satellites.

4:30 p.m.Real-Time, Near Global, Low Earth Orbit Communication Using Geostationary Inmarsat BGAN System as a Relay

Christian Lenz, Chris McCormick – Broad Reach Engineering Company; Rob Goldsmith – COM DEV Europe; Eyal Trachtman – INMARSAT

ABSTRACT: This paper describes a new service and related communications hardware that provides continuous, near global access to and from Leo Spacecraft utilizing the existing geostationary INMARSAT BGAN Satellite System as a data relay. This new communications link for LEO platforms will provide full duplex data rates from as low as 100kbps up to 475kbps with near-real time latencies and near global coverage. A team of Broad Reach Engineering (US), COM DEV Europe (UK), and INMARSAT (UK) is developing the terminal and service for use on LEO Spacecraft.

The paper highlights some of the key features and advantages compared to traditional communications architectures and presents missions and applications, some previously impossible, that are enabled by the system. The development progress is described along with some of the challenges and solutions related to implementing the 3G based BGAN technologies on a space flight capable platform. The business case and decisions leading up to the development are discussed and the timeline for completing the development is shown.

4:45 p.m.Automatic Generation of SDM Application Source Code From xTEDS

Jacob Christensen, Scott Cannon – Utah State University; Bryan Hansen – Space Dynamics Laboratory; Jim Lyke – Air Force Research Laboratory/RVSE

ABSTRACT: The Satellite Data Model (SDM) developed at Utah State University (USU) is a plug-and-play software system for satellites. An xTEDS must be written for each component that participates with the SDM. Software applications can query the SDM for data products, commands, and services that components provide. The application can then subscribe, command, and use services from a devices that it has never seen before. The extra functionality required of an SDM application can be difficult to develop. This paper presents a technique for automatically generating SDM application source code by extrapolating information from xTEDS. This technique has been implemented in a tool called the SDM App Wizard. The SDM App Wizard reduces the time and effort required to develop a software application that participates with the SDM.

5:00 p.m.Deployable Booms and Antennas Using Bi-Staple Tape-Springs

Thomas Murphey – Air Force Research Laboratory; Sungeun Jeon – CSA Engineering; Adam Biskner, Gregory Sanford – LoadPath, LLC

ABSTRACT: Utilizing the orthotropic properties of composite materials, tape-spring structural elements can be made that exhibit the unique behavior known as bi-stability. Tape-springs with this behavior display a controlled and deterministic deployment path of simply unrolling once initiated; they do not bloom. Deployable booms and multi-element antennas have been conceptualized based on these tape-springs and are reported on within. Both inventions occupy approximately ¼U of a CubeSat volume (50 x 50 x100 mm) when packaged and self-deploy to lengths of several meters. The boom concept employs four tape-springs arranged so that the boom tips separate linearly (without any rotations). It is intended to be used as a gravity gradient stabilization boom, camera boom or sensor boom. A damper element can be used to control deployment rate. The antenna concept uses multiple elements in a log periodic configuration and is deployed without rate control.

Alternate Space and Ground Segments Link Performance Verification for Small Satellite TT&C Transponders

Ahmed Maghawry – National Authority for Remote Sensing & Space Sciences (NARSS); Magdi Fikri – Cairo University

ABSTRACT: Verification of low earth orbit (LEO) satellite communication links is required for evaluation and acceptance purposes. Telemetry and telecommand transponder’s bit error rate (BER), which is the main communication link parameter to be evaluated, is required to be verified by measurement rather than by analysis. This paper introduces a novel algorithm for measuring the BER of both space and ground segments. BER could be determined only if a received pattern is compared with a locally generated one. This feature exists for those transponders that utilize direct sequence spread spectrum (DS-SS) technique for purposes of range and range rate measurements, spreading the spectrum, or for security. In this work the space and ground segments’ BER verification by measurement is achieved by exploiting the inherent locally generated pseudo random sequences (PRS). The application of this algorithm for measuring the BER of the space segment necessitates sending the information as a telemetry parameter just before the end of the communication session. This algorithm requires measuring BER over a large sample of the received chips due to the randomness of the errors. The high chip rate of the employed PRS (around 0.5MHz) and the period of the communication session (7-10 minutes in average) satisfy this condition. This algorithm is applied for measuring the BER for a digitally implemented coherent MSK DS-SS modem and the results for measuring the BER against E_b/N_o are presented.

Alternate Cost-Effective End-of-Mission Disposal of LEO Microsatellites: The Terminator Tape

Robert Hoyt, Jeffrey Slostad, Ian Barnes, Nestor Voronka, Michael Lewis – Tethers Unlimited, Inc.

ABSTRACT: To provide a cost-effective means for satellite operators to comply with 25-year post-mission orbital lifetime restriction, Tethers Unlimited is developing a lightweight de-orbit module called the “Terminator Tape™”. The Terminator Tape is a small module that bolts onto any side of a spacecraft during satellite integration. At the completion of the satellite’s mission, the satellite will activate the Terminator Tape module, which will then deploy a fifty-meter length of thin conducting tape. This tape will not only significantly enhance the aerodynamic drag experienced by the system, but will also generate electrodynamic drag forces through passive interactions with the Earth’s magnetic field and conducting ionospheric plasma, de-orbiting the satellite within 25 years. Two modules are currently in development, one sized for microsatellites operating at altitudes of less than 900 km, and the other sized for CubeSats operating at altitudes of up to 1100 km. Deployment of prototype modules has been successfully demonstrated in a microgravity environment.