Q

The Qweak experiment, which took data at Jefferson Lab in the period 2010 - 2012, will precisely determine the weak charge of the proton by measuring the parity-violating asymmetry in elastic e-p scattering at 1.1 GeV using a longitudinally polarized electron beam and a liquid hydrogen target at a low momentum transfer of Q2 = 0.025 (GeV/c)2. The weak charge of the proton is predicted by the Standard Model and any significant deviation would indicate physics beyond the Standard Model. The technical challenges and experimental apparatus for measuring the weak charge of the proton will be discussed, as well as the method of extracting the weak charge of the proton. The results from a small subset of the data, that has been published, will also be presented. Furthermore an update will be given of the current status of the data analysis

Pulsed Plasma Thruster Systems for Spacecraft Attitude Control

Pulsed Plasma Thrusters (PPTs) are finding renewed user appeal due to the growth in small satellite applications. PPTs are especially well suited to small satellite applications because they are simple, low-mass, and high Isp propulsion systems. The solid Teflon fuel allows for a self-contained, inert and stable propellant system. With a power draw of only 0.1 to 150 W and a very small (50 - 800 µNs) impulse bit, PPT technology makes it possible to consider a revolutionary attitude control system (ACS) concept providing stabilization and pointing accuracies previously obtainable only with reaction wheels, with reduced mass and power requirements. NASA Lewis Research Center (LeRC) and Olin Aerospace Company (OAC) are working together to develop an advanced PPT system with twice the total impulse capability and half the mass of the previous best PPT system. The two key factors to accomplish these goals are: 1 ) significantly improving thrust efficiency - the ratio of thrust power to input electrical power and 2) improving the energy density and life of the energy storage capacitor. Typically, PPTs provide relatively low efficiency, with the LES 8/9 PPT delivering a little more than 7 percent. OAC has tested a matrix of configuration parameters with improvement in the efficiency by a factor of 1.5 to 2.0. To achieve the LeRC goals, the capacitor must be capable of 20 million pulses at an energy level of 40 J, ideally with a mass of no more than 1 kg. LeRC and OAC have embarked upon a two-step process to demonstrate the capacitor technology, with benchtop testing at OAC and integrated PPT/capacitor life testing at LeRC to be conducted in the development phase. The program provides for design, fabrication and qualification of a flight PPT, which is then slated to fly as an orbit raising demonstration aboard the Air Force Phillips Lab MightySat II.1 in early 1999. A second unit, configured for ACS functions, is planned for flight on the NASA New Millennium EO-1 spacecraft in mid-1999. With a light, high performance PPT in development for flight applications, it becomes possible to consider replacement of momentum wheels with PPTs. Typical momentum wheel attitude control systems consume 10\u27s of W power and weigh 0.1 kg per kg of spacecraft weight, including the momentum desaturation devices. Mission analysis to be presented shows the PPT to be very competitive with these systems, with the advantages of lower cost, lower mass, extension of ACS capability to very small (nano) satellites, and simplicity in replacing both the wheels and the desaturation devices

Pulsed Plasma Thruster (PPT) Development and Ground Testing in Support of PPT Flight Demonstrations on MightySat

The Pulsed Plasma Thruster (PPT) Space Demonstration is a cooperative effort between the US Air Force, Phillips Laboratory and the NASA-Lewis Research Center. The purpose is to investigate the orbit-raising capability and overall performance of the PPT system on-board a spacecraft and to determine the effects of plume contamination from the thruster on spacecraft instruments. The PPT is scheduled for a January 2000 launch on the MightySat II.1 spacecraft. The MightySat program is managed from the Space Experiments directorate of Phillips Laboratory technology in a timely and cost-effective manner. The MightySat program office has selected the Orbital/Sub-Orbital Platform (OSP) as the launch vehicle for flight II.1, which has been named Sindri. While mission analysis shows that for OSP insertion at nominal solar flux conditions it is unnecessary to do any orbit raising to maintain a one year mission life for Sindri. The PPT design and testing effort, conducted jointly with NASA Lewis Research Center and Primex Aerospace Corporation, will continue to focus on the critical orbit raising mission from a Space Shuttle insertion orbit

Advanced Pulsed Plasma Thruster Demonstration On MightySat Flight II.1

This paper describes the progress associated with a joint effort to demonstrate an advanced pulsed plasma thruster (PPT) on MightySat Flight II.1 to be launched in January, 1999. The PPT currently being developed for this flight represents a significant leap in technology compared to previous flight models. Although the MightySat II.1 launch vehicle is yet to be determined, the Space Shuttle Hitchhiker Eject System is the primary option under consideration. With this launch option, the PPT will be used to extend MightySat 11.1 life from about 1-3 months to over one year by raising its operational orbit. The PPT is an ideal propulsion system for extending small satellite life because of its high specific impulse (\u3e 1000 sec), low system wet mass \u3c 5 kg), and inert nature when unpowered (thus minimizing Shuttle integration issues). In addition to the life enhancement mission, the on-orbit operations have been specifically designed to rigorously test the PPT and to demonstrate its compatibility with the MightySat II.1 spacecraft in order to validate it for future DoD, NASA, and commercial satellites