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The Solar Wind Electrons Alphas and Protons (SWEAP) Investigation on Solar Probe Plus is a four sensor instrument suite that provides complete measurements of the electrons and ionized helium and hydrogen that constitute the bulk of solar wind and coronal plasma. SWEAP consists of the Solar Probe Cup (SPC) and the Solar Probe Analyzers (SPAN). SPC is a Faraday Cup that looks directly at the Sun and measures ion and electron fluxes and flow angles as a function of energy. SPAN consists of an ion and electron electrostatic analyzer (ESA) on the ram side of SPP (SPAN-A) and an electron ESA on the anti-ram side (SPAN-B). The SPAN-A ion ESA has a time of flight section that enables it to sort particles by their mass/charge ratio, permitting differentiation of ion species. SPAN-A and -B are rotated relative to one another so their broad fields of view combine like the seams on a baseball to view the entire sky except for the region obscured by the heat shield and covered by SPC. Observations by SPC and SPAN produce the combined field of view and measurement capabilities required to fulfill the science objectives of SWEAP and Solar Probe Plus. SWEAP measurements, in concert with magnetic and electric fields, energetic particles, and white light contextual imaging will enable discovery and understanding of solar wind acceleration and formation, coronal and solar wind heating, and particle acceleration in the inner heliosphere of the solar system. SPC and SPAN are managed by the SWEAP Electronics Module (SWEM), which distributes power, formats onboard data products, and serves as a single electrical interface to the spacecraft. SWEAP data products include ion and electron velocity distribution functions with high energy and angular resolution. Full resolution data are stored within the SWEM, enabling high resolution observations of structures such as shocks, reconnection events, and other transient structures to be selected for download after the fact. This paper describes t, United States. National Aeronautics and Space Administration (contract NNN06AA01C (Task NNN10AA08T))

The Time and Frequency Laboratory at the Johns Hopkins University Applied Physics Laboratory (JHL/APL) provides support to multiple current and upcoming NASA/APL missions that span our solar system from the study of the Sun's coronal mass ejections to the examination of the outer planets and the Kuiper Belt objects. This support includes providing precise time and frequency to the integration and testing of new hardware, frequency reference for spacecraft ranging and communications via the APL satellite communications facility, and the time-stamping of ground-receipt telemetry packets from various spacecraft. The Lab's ensemble of three high-performance cesium standards and three hydrogen masers are integrated to form the APL timescale, which is the basis for estimating UTC - UTC (APL) and for evaluating the performance of our clocks. Traceability to USNO, NIST, and UTC is maintained via GPS common-view and all-in-view time transfer. The Lab's clocks are also incorporated into the computation of International Atomic Time (TAI)., Presented at the Annual Precise Time and Time Interval (PTTI) Systems and Applications Meeting (41st), Santa Ana Pueblo, NM, 16-19 Nov 2009 and published in proceedings of the same p253-260. The original document contains color images.

Our master clock accuracy goal at the Time and Frequency Laboratory of the Johns Hopkins University Applied Physics Laboratory (JHU/APL) is to maintain UTC (APL) within plus-or-minus 20 nanoseconds of UTC. This is a challenging goal, because it requires the estimation of the future character of UTC - UTC (APL) up to 6 weeks beyond the latest issue of Circular T from the BIPM. Furthermore, the accuracy of our timescale-based estimation is challenged by the environmental influence on our ensemble of six clocks and the statistical limits to the dynamic characterization of these sources. This paper will describe the estimation algorithm used to determine the steering of UTC (APL). We will describe how the residual drift within the JHU/APL timescale affects our ability to estimate UTC - UTC (APL) and how we have modified the algorithm to remove this drift from the timescale prior to computing the estimation., See also ADM002186. Presented at the Annual Precise Time and Time Interval (PTTI) Systems and Applications Meeting (40th) held in Reston, Virginia on 1-4 December 2008. Published in the Proceedings of the Annual Precise Time and Time Interval (PTTI) Systems and Applications Meeting (40th), p219-226, 2008. The original document contains color images.

In the past years, we have reported on continuous improvement in the capability of our Time and Frequency Laboratory at the Johns Hopkins University Applied Physics Laboratory and its contribution to the TAI. We have discussed our ensemble of hydrogen maser and cesium beam atomic clocks into a time scale that enables UTC (APL) to be steered within plus or minus 20 nanoseconds per month of UTC. A significant element to the control of UTC (APL) has been the use of our autonomous time scale algorithm, reported in 2005 at the combined PTTI and IEEE FCS. In our laboratory report this year, we will discuss experimentation using this time scale algorithm to investigate the timekeeping capability of an ensemble of three quartz ultra-stable oscillators (USO). This experimental ensemble could represent the frequency references of a system of spacecraft, similar to those proposed in deep space missions of long duration. Although these spacecraft would likely be in regular communication with the ground segment controllers, it may be necessary that they operate autonomously for periods of time ranging from a few days to several weeks. To make this possible, we are considering improvement in the frequency stability of the onboard timing reference that will act as a fly-wheel when frequency corrections from mission controllers have been temporarily interrupted. We present experimental data and examine the compliance of the ensemble of three USOs to a frequency stability of better than plus or minus 1x 10(exp -11) per week., See also ADM002029. Presented at the Annual Precise Time and Time Interval (PTTI) Meeting (38th), held in Reston, VA, on 5-7 Dec 2006. Published in the proceedings of the meeting, p361-372, 2007. The original document contains color images.

In past years, we have reported on continuous improvement in the operation of the master clock of our Time and Frequency Laboratory at the Johns Hopkins University Applied Physics Laboratory. We have discussed our ensemble of hydrogen maser and cesium beam atomic frequency standards into an autonomous timescale that maintains UTC (JHU/APL) within + or - 20 ns per month of UTC. This year, since completing the major aspects of our laboratory refurbishment, we have undertaken systems analysis toward optimization and improved timekeeping. In our paper, we will describe the system of clocks, control mechanisms, and their relationship that maintain our laboratory's accuracy. One outcome will describe the determination of our worst performing clock through frequency characterization and the performance improvement in the UTC (JHU/APL) timescale through selectively weighting its contribution., Presented at the Annual Precise Time and Time Interval (PTTI) Meeting (39th) held in Long Beach, CA on 26-29 Nov 2007. Published in the Proceedings of the Annual Precise Time and Time Interval (PTTI) Meeting (39th), p131-138, 2007. The original document contains color images.