Engineering topics

Gilchrist, Brian

Publications and source records attributed to Gilchrist, Brian.

6 records

NASA NTRS2012

The PROPEL Electrodynamic Tether Mission and Connecting to the Ionosphere

The exponential increase of launch system size.and cost.with delta-V makes missions that require large total impulse cost prohibitive. Led by NASA's Marshall Space Flight Center, a team from government, industry, and academia has developed a flight demonstration mission concept of an integrated electrodynamic (ED) tethered satellite system called PROPEL: "Propulsion using Electrodynamics". The PROPEL Mission is focused on demonstrating a versatile configuration of an ED tether to overcome the limitations of the rocket equation, enable new classes of missions currently unaffordable or infeasible, and significantly advance the Technology Readiness Level (TRL) to an operational level. We are also focused on establishing a far deeper understanding of critical processes and technologies to be able to scale and improve tether systems in the future. Here, we provide an overview of the proposed PROPEL mission. One of the critical processes for efficient ED tether operation is the ability to inject current to and collect current from the ionosphere. Because the PROPEL mission is planned to have both boost and deboost capability using a single tether, the tether current must be capable of flowing in both directions and at levels well over 1 A. Given the greater mobility of electrons over that of ions, this generally requires that both ends of the ED tether system can both collect and emit electrons. For example, hollow cathode plasma contactors (HCPCs) generally are viewed as state-of-the-art and high TRL devices; however, for ED tether applications important questions remain of how efficiently they can operate as both electron collectors and emitters. Other technologies will be highlighted that are being investigated as possible alternatives to the HCPC such as Solex that generates a plasma cloud from a solid material (Teflon) and electron emission (only) technologies such as cold-cathode electron field emission or photo-electron beam generation (PEBG) techniques.

Gilchrist, Brian↗

NASA NTRS2001

Langmuir Probe Spacecraft Potential End Item Specification Document

This document describes the Langmuir Probe Spacecraft Potential (LPSP) investigation of the plasma environment in the vicinity of the ProSEDS Delta II spacecraft. This investigation will employ a group of three (3) Langmuir Probe Assemblies, LPAs, mounted on the Delta II second stage to measure the electron density and temperature (n(sub e) and T(sub e)), the ion density (n(sub i)), and the spacecraft potential (V(sub s)) relative to the surrounding ionospheric plasma. This document is also intended to define the technical requirements and flight-vehicle installation interfaces for the design, development, assembly, testing, qualification, and operation of the LPSP subsystem for the Propulsive Small Expendable Deployer System (ProSEDS) and its associated Ground Support Equipment (GSE). This document also defines the interfaces between the LPSP instrument and the ProSEDS Delta II spacecraft, as well as the design, fabrication, operation, and other requirements established to meet the mission objectives. The LPSP is the primary measurement instrument designed to characterize the background plasma environment and is a supporting instrument for measuring spacecraft potential of the Delta II vehicle used for the ProSEDS mission. Specifically, the LPSP will use the three LPAs equally spaced around the Delta II body to make measurements of the ambient ionospheric plasma during passive operations to aid in validating existing models of electrodynamic-tether propulsion. These same probes will also be used to measure Delta II spacecraft potential when active operations occur. When the electron emitting plasma contractor is on, dense neutral plasma is emitted. Effective operation of the plasma contactor (PC) will mean a low potential difference between the Delta II second stage and the surrounding plasma and represents one of the voltage parameters needed to fully characterize the electrodynamic-tether closed circuit. Given that the LP already needs to be well away from any near-field disturbances around the Delta II, it is possible to use the same probe with a simple reconfiguration of the electronics to measure potential with respect to the ambient plasma. The LP measurement techniques are outlined in the following text and discussed in detail in the Appendix. The scientific goals of the investigation, the physical and electrical characteristics of the instrument, and the on-orbit measurement requirements are also discussed in this document.

Gilchrist, Brian↗

NASA NTRS1999

Propulsive Small Expendable Deployer System (ProSEDS) Experiment

ProSEDS is a secondary (i.e. piggyback) payload on a Delta-11 GPS 8 mission scheduled for launch in August 2000. It will test the feasibility of generating generate electrodynamic thrust without propellant using a 5 kilometer conducting wire (tether). The ProSEDS obtains thrust as the tether cuts across the magnetic field, a voltage is induced across the wire. Electrons are attracted to the positively based far end of the wire. Electrons flow downward through the conductive tether. Earth's magnetic field exerts a drag force on the current in the tether segments, that is mechanically transferred via the wire to the stage. The primary objective for the ProSEDs mission is to demonstrate that a significant, measurable electrodynamic thrust through a tether in space. The primary mission will last one day, as the primary battery assures at least three orbits of data will be collected, the remaining power will be provided by the secondary battery, which uses tether generated power to recharge. The extended mission begins using the power provided through the tether, and wil terminate when a system ceases to function; (i.e., either degradation of the tether,through Atomic Oxygen contact, a micrometeoroid or other debris impact, or another malfunction.) The technology has many potential applications. Amongst the applications, which are reviewed in detail, are: (1) satellite deorbit, (2) reboost of the International Space Station, (3) propellantless reusable Orbit Transfer Vehicles, (4) Propulsion and power generation for future Jovian missions.

Johnson, Les↗

NASA NTRS1998

Electrodynamic Tether Propulsion for Spacecraft and Upper Stages

Relatively short electrodynamic tethers can use solar power to 'push' against a planetary magnetic field to achieve propulsion without the expenditure of propellant. The groundwork has been laid for this type of propulsion. Important recent milestones include retrieval of a tether in space (TSS-1, 1992), successful deployment of a 20-km-long tether in space (SEDS-1, 1993), and operation of an electrodynamic tether with tether current driven in both directions (PMG, 1993). The planned Propulsive Small Expendable Deployer System (ProSEDS) experiment will use the flight-proven Small Expendable Deployer System (SEDS) to deploy a 5 km bare copper tether from a Delta II upper stage to achieve approximately 0.4 N drag thrust, thus deorbiting the stage. The experiment will use a predominantly 'bare' tether for current collection in lieu of the endmass collector and insulated tether approach used on previous missions. The flight experiment is a precursor to utilization of the technology on the International Space Station for reboost and the electrodynamic tether upper stage demonstration mission which will be capable of orbit raising, lowering and inclination changes, all using electrodynamic thrust. In addition, the use of this type of propulsion may be attractive for future missions at Jupiter.

Johnson, Les↗

NASA NTRS1998

Overview of Future NASA Tether Applications

The groundwork has been laid for tether applications in space. NASA has developed tether technology for space applications since the 1960's. Important recent milestones include retrieval of a tether in space (TSS-1, 1992), successful deployment of a 20-km-long tether in space (SEDS-1, 1993), and operation of an electrodynamic tether with tether current driven in both directions-power and thrust modes (PMG, 1993). Various types of tethers and systems can be used for space transportation. Short electrodynamic tethers can use solar power to 'push' against a planetary magnetic field to achieve propulsion without the expenditure of propellant. The planned Propulsive Small Expendable Deployer System (ProSEDS) experiment will demonstrate electrodynamic tether thrust during its flight in early 2000. Utilizing completely different physical principles, long non-conducting tethers can exchange momentum between two masses in orbit to place one body into a higher orbit or a transfer orbit for lunar and planetary missions. Recently completed system studies of this concept indicate that it would be a relatively low-cost in-space asset with long-term multi-mission capability. Tethers can also be used to support space science by providing a mechanism for precision formation flying and for reaching regions of the upper atmosphere that were previously inaccessible.

Johnson, Les↗

NASA NTRS1998

Propulsive Small Expendable Deployer System (ProSEDS) Space Experiment

The Propulsive Small Expendable Deployer System (ProSEDS) space experiment will demonstrate the use of an electrodynamic tether propulsion system. The flight experiment is a precursor to the more ambitious electrodynamic tether upper stage demonstration mission which will be capable of orbit raising, lowering and inclination changes-all using electrodynamic thrust. ProSEDS which is planned to fly in 2000, will use the flight proven Small Expendable Deployer System (SEDS) to deploy a tether (5km bare wire plus 15 km spectra) from a Delta II upper stage to achieve approximately 0.4N drag thrust, thus demonstrating deorbit thrust. The experiment will use a predominantly 'bare' tether for current collection in lieu of endmass collector and insulated tether approach used on previous missions. ProSEDS will utilize tether-generated current to provide limited spacecraft power. In addition to the use of this technology to provide orbit transfer of payloads and upper stages from LEO to higher orbits it may also be an attractive option for future missions to Jupiter and any other planetary body with a magnetosphere.

Johnson, Les↗