Kalman filter orbit improvement from Kootwijk laser range observations

Modern satellite ranging lasers emit short pulses at a low beam divergence and therefore require accurate satellite position predictions. To reach these accuracies the application of a Kalman filter orbit improvement technique has been investigated. Using laser observations acquired at only one groundstation the filter scheme provides real-time satellite position prediction updates, and also yields better predictions for subsequent passes over that station.     

Coordinated optical-EXOSAT-tenma observations of a burst from 2S1636-536

During a coordinated observations of 2S1636-536 with EXOSAT, Tenma and the 1.4 metre Danish telescope at La Silla, a single burst was detected at all three observatories. The burst was bright with a peak flux of 6 × 10^-8 ergs/cm ² /s and rapid expansion of the blackbody radius. EXOSAT and Tenma agree closely in the values of blackbody radius, temperature and flux which are very similar to the three bursts recently reported by Tenma which appear to reach the Eddington flux limit at their peak. Preliminary analysis of the X-ray and optical timing data reveal that this burst is unusual in having a sharp leading edge in both X-ray and optical data and a very short X-ray-optical delay compared with those previously observed. If confirmed, this result puts significant restraints on the location of the optical reprocessing site.     

Study of CME transit speeds for the event of 07-NOV-2004

Several methods for CME speed estimation are discussed. These include velocity derivation based on the frequency drifts observed in metric and decametric radio wave data using a range of coronal density models. Coronagraph height–time plots allow measurement of plane-of-sky and expansion speeds. These in turn can enable propagation speeds to be derived from a range of empirical relations. Simple geometric e.g., cone, models can provide propagation velocity estimates for suitable halo or partial halo events. Interplanetary scintillation observations allow speed estimates at large distances from the Sun detecting in particular the deceleration of the faster CMEs. Related interplanetary shocks and the arrival times and speeds of the associated magnetic clouds at Earth can also be considered. We discuss the application of some of these methods to the transit to Earth of a complex CME that originated earlier than 16:54 U.T. on 07-NOV-2004. The difficulties in making velocity estimates from radio observations, particularly under disturbed coronal conditions, are highlighted.     

MESSENGER Mission Design and Navigation

Nearly three decades after the Mariner 10 spacecraft’s third and final targeted Mercury flyby, the 3 August 2004 launch of the MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and Ranging) spacecraft began a new phase of exploration of the closest planet to our Sun. In order to ensure that the spacecraft had sufficient time for pre-launch testing, the NASA Discovery Program mission to orbit Mercury experienced launch delays that required utilization of the most complex of three possible mission profiles in 2004. During the 7.6-year mission, the spacecraft’s trajectory will include six planetary flybys (including three of Mercury between January 2008 and September 2009), dozens of trajectory-correction maneuvers (TCMs), and a year in orbit around Mercury. Members of the mission design and navigation teams optimize the spacecraft’s trajectory, specify TCM requirements, and predict and reconstruct the spacecraft’s orbit. These primary mission design and navigation responsibilities are closely coordinated with spacecraft design limitations, operational constraints, availability of ground-based tracking stations, and science objectives. A few days after the spacecraft enters Mercury orbit in mid-March 2011, the orbit will have an 80° inclination relative to Mercury’s equator, a 200-km minimum altitude over 60°N latitude, and a 12-hour period. In order to accommodate science goals that require long durations during Mercury orbit without trajectory adjustments, pairs of orbit-correction maneuvers are scheduled every 88 days (once per Mercury year).     

Astronaut-induced disturbances in microgravity

This Note describes the dynamic load sensors (DLS) spaceflight experiment that measured middeck astronaut-induced disturbances during the 14-day STS-62 Space Shuttle mission in March 1994. The DLS experiment was flown in conjunction with the reflight of the Middeck 0-Gravity Dynamics Experiment (MODE). The objective of MODE was to investigate effects of the microgravity environment on large space structures. Where Skylab experiments focused on measuring the forces exerted during vigorous soaring activities, the DLS experiment quantified the reaction forces and moments exerted by the crew going about their normal on-orbit activities. The objective of this Note is to present DLS force data and frequency analysis that characterize astronaut-induced loads during spaceflight.     

Structural development of the X-ray limb flare of 30 April 1980

We describe the development of the limb flare of 30 April 1980, 20:20 UT, as observed by the Hard X-ray Imaging Spectrometer (HXIS) aboard the Solar Maximum Mission (SMM). It consisted of a short-lived bright nucleus (FWHM < 10,000 km), just inside the Sun's limb; a longer lasting tongue, extending to a height of 30,000 km, and a more complicated feature, approximately situated at the Sun's limb. The tongue was a pre-existing magnetic structure that started emitting X-rays only a few seconds after the bright nucleus, and which had a slightly higher temperature than the nucleus; its X-ray emission may be caused by electrons escaped from the nucleus.     

Rapid short-term pulse-period variations in Vela X-1 (4U 0900-40)

Results are presented of an analysis of 83 days of 2–12 keV X-ray observations of Vela X-1 (4U 0900-40) obtained during three separate pointings with the ESA COS-B satellite. The pulsation period is shown to undergo very rapid intrinsic changes, at a rate of up to during intervals of a few days. The lower values of which were previously observed over longer intervals, appear to result from an averaging-out of these rapid changes. It is argued, that the transfer of angular momentum to the neutron star by the accreting matter is very unlikely to be sufficient to explain these pulsation-period changes. An alternative explanation is suggested.