Halley's comet 1985-86: space exploration

A coordinated program to explore Halley's comet in 1985 to 86 is proposed. The program employs a variety of observational systems for remote observations and utilizes spacecraft encounters with the comet to obtain in-situ measurements. Included in the observational network are groundbased observatories, the Space Telescope, a Spacelab cometary observatory, small astronomical satellites, and experiments carried on airborne observatories and sounding rockets. It is assumed that a ballistic flythrough technique will be used to carry out the spacecraft encounters. The proposed strategy calls for the simultaneous launch of two spacecraft towards an intercept with Halley in March 1986. Following the Halley encounter one spacecraft is retargeted to intercept comet Borrelly in January 1988, while the other spacecraft proceeds to an encounter with comet Tempel 2 in September 1988

Opportunities for ballistic missions to Halley's comet

Alternative strategies for ballistic missions to Halley's comet in 1985-86 are described. It is shown that a large science return would be acquired from a ballistic Halley intercept in spite of the high flyby speeds of almost 60 km/sec that are associated with this mission mode. The possibility of retargeting the cometary spacecraft to additional comets after the Halley intercept also exists. In one scenario two cometary spacecraft of identical design would be used to carry out four separate cometary encounters over a three-year period. One spacecraft would intercept Halley before its perihelion passage in December 1985 and then go on to comet Borrelly witn an encounter in January 1988. The other spacecraft would be targeted for a post-perihelion Halley intercept in March 1986 before proceeding towards an encounter with comet Tempel-2 in September 1988. The flyby speeds for the Borrelly and Tempel-2 intercepts are 21 and 13 km/sec, respectively

Mathematical specifications of the Onboard Navigation Package (ONPAC) simulator (revision 1)

The mathematical theory of the computational algorithms employed in the onboard navigation package system is described. This system, which simulates an onboard navigation processor, was developed to aid in the design and evaluation of onboard navigation software. The mathematical formulations presented include the factorized UDU(T) form of the extended Kalman filter, the equations of motion of the user satellite, the user clock equations, the observation equations and their partial derivatives, the coodinate transformations, and the matrix decomposition algorithms

Mid-Infrared Spectrophotometric Observations of Fragments B and C of Comet 73P/Schwassmann-Wachmann 3

We present mid-infrared spectra and images from the GEMINI-N (+Michelle) observations of fragments SW3-[B] and SW3-[C] of the ecliptic (Jupiter Family) comet 73P/Schwassmann-Wachmann 3 pre-perihelion. We observed fragment B soon after an outburst event (between 2006 April 16 - 26 UT) and detected crystalline silicates. The mineralogy of both fragments was dominated by amorphous carbon and amorphous pyroxene. The grain size distribution (assuming a Hanner modified power-law) for fragment SW3-[B] has a peak grain radius of a_p ~ 0.5 micron, and for fragment SW3-[C], a_p ~ 0.3 micron; both values larger than the peak grain radius of the size distribution for the dust ejected from ecliptic comet 9P/Tempel 1 during the Deep Impact event (a_p = 0.2 micron. The silicate-to-carbon ratio and the silicate crystalline mass fraction for the submicron to micron-size portion of the grain size distribution on the nucleus of fragment SW3-[B] was 1.341 +0.250 -0.253 and 0.335 +0.089 -0.112, respectively, while on the nucleus of fragment SW3-[C] was 0.671 +0.076 -0.076 and 0.257 +0.039 -0.043, respectively. The similarity in mineralogy and grain properties between the two fragments implies that 73P/Schwassmann-Wachmann 3 is homogeneous in composition. The slight differences in grain size distribution and silicate-to-carbon ratio between the two fragments likely arises because SW3-[B] was actively fragmenting throughout its passage while the activity in SW3-[C] was primarily driven by jets. The lack of diverse mineralogy in the fragments SW3-[B] and SW3-[C] of 73P/Schwassmann-Wachmann 3 along with the relatively larger peak in the coma grain size distribution suggests the parent body of this comet may have formed in a region of the solar nebula with different environmental properties than the natal sites where comet C/1995 O1 (Hale-Bopp) and 9P/Tempel 1 nuclei aggregated.Comment: 31 pages, 5 figure, accepted for publication in A

Impact of Special Collections in JGR Space Physics

Journals occasionally solicit manuscripts for special collections, in which all papers are focused on a particular topic within the journal’s scope. For the Journal of Geophysical Research: Space Physics, there have been 51 special collections from 2005 through 2018, with a total of 1,009 papers out of the 8,881 total papers in the journal over those years (11%). Taken together, the citations to special collection papers, as well as other metrics, are slightly higher than papers not in special collections. Several paper characteristics were examined to assess whether they could explain the higher citation and download values for special collection papers, but they cannot. In addition, indirect methods were conducted for assessing self‐citations as an explanation for the increased citations, but no evidence was found to support this hypothesis. It was found that some paper types, notably Commentaries and Technical Reports, have lower average citations but higher average downloads than Research Articles (the most common type of paper in this journal). This implies that such paper types have a different kind of impact than “regular” science‐result‐focused papers. In addition to having higher average citations and downloads, special collections focus community attention on that particular research topic, providing a deadline for manuscript submissions and a single webpage at which many related papers are listed. It is concluded that special collections are worth the extra community effort in organization, writing, and reviewing these papers.Plain Language SummaryJournals sometimes focus the attention of the research community by having a special collection, even an entire issue, devoted to a single topic. A reasonable question to ask is whether the extra effort of organizing, promoting, and maintaining the special collection is worthwhile. This paper examines paper impact in this journal, the Journal of Geophysical Research Space Physics, separating the special collection papers from those not in special collections. The short answer is, on average, yes, at least based on the metric of citations. Some characteristics of the paper were also assessed, such as the use of a colon in the title, the average author team size, the average number of references in each paper, and the paper type of the articles. None of these factors explains the higher average citations and downloads for papers in special collections. In this analysis, though, it was found that several paper types have lower‐than‐average citations but higher‐than‐average downloads, including Commentaries (personal perspectives articles) and Technical Reports (describing new methods or data sets). This implies that such papers are being read but perhaps not heavily referenced (yet). The overall conclusion is that special collections are worth the extra work.Key PointsJGR Space Physics published 51 special collections from 2006 to 2018, totaling 1,009 papers out of 8,881Average citations and downloads are slightly higher for papers in special collections compared to those not in collectionsPaper attributes thought to influence citations were analyzed, finding no statistically significant effect for special collection papers compared to othersPeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/153709/1/jgra55389.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/153709/2/jgra55389_am.pd

Dust Processing and Grain Growth in Protoplanetary Disks in the Taurus-Auriga Star-Forming Region

Mid-infrared spectra of 65 T Tauri stars (TTS) taken with the Infrared Spectrograph (IRS) on board the Spitzer Space Telescope are modeled using dust at two temperatures to probe the radial variation in dust composition in the uppermost layers of protoplanetary disks. Most spectra indicating crystalline silicates require Mg-rich minerals and silica, but a few suggest otherwise. Spectra indicating abundant enstatite at higher temperatures also require crystalline silicates at temperatures lower than those required for spectra showing high abundance of other crystalline silicates. A few spectra show 10 micron complexes of very small equivalent width. They are fit well using abundant crystalline silicates but very few large grains, inconsistent with the expectation that low peak-to-continuum ratio of the 10 micron complex always indicates grain growth. Most spectra in our sample are fit well without using the opacities of large crystalline silicate grains. If large grains grow by agglomeration of submicron grains of all dust types, the amorphous silicate components of these aggregates must typically be more abundant than the crystalline silicate components. Crystalline silicate abundances correlate positively with other such abundances, suggesting that crystalline silicates are processed directly from amorphous silicates and that neither forsterite, enstatite, nor silica are intermediate steps when producing either of the other two. Disks with more dust settling typically have greater crystalline abundances. Large-grain abundance is somewhat correlated with greater settling of disks. The lack of strong correlation is interpreted to mean that settling of large grains is sensitive to individual disk properties. Lower-mass stars have higher abundances of large grains in their inner regions.Comment: 84 pages, 27 figures, submitted to the Astrophysical Journal on 7 November, 200