Comet Encounter Research Articles

Ion formation by high- and medium-velocities dust impacts from laboratory measurements and Halley results

The ion formation processes by dust impacts have been studied qualitatively as well as quantitatively by dust accelerator laboratory measurements. Iron, carbon and metallized glass particles in the femto- to nano-gram mass range had been impacted on various metal targets in a velocity regime of υ = 2 – 64 km/s. In the high velocity regime as relevant for the (retrograde) Halley encounter more than 99% of the ions produced are singly charged atomic, the rest molecular ones. The ion/atom ratios are apparently modified SIMS yields, the modification parameter being impact velocity dependent. A semiempirical formula was deduced for the determination of mass and density of the impacting particle from target and projectile ion yields. When evaluating the Halley encounter results, the elemental distribution of p/Halley dust appeared nearly to be solar; the organic fraction (CHON) could be characterized in a rough manner as fairly unsaturated. Oligomers of the monomers C 2H 2 (65%), CH 2O (25%), and HCN (10%) are probable. With medium velocities (for prograde comet encounter), i.e. υ = 15 – 30 km/s molecular ion types govern the mass spectra. Consequently, more chemical information of the projectile can be expected in this case, additional to the elemental distribution. Mass and density of the impinging dust particles can be determined as well.

The nature of punctuational crises and the spenglerian model of civilization

Mankind's essentially untroubled state of mind in the presence of comets during the last two centuries has been fortified by the overall relative brevity of cometary apparitions and the calculated infrequency of cometary encounters with planets. During the course of the Space Age, however, the fact of cometary splitting has also become increasingly secure and there is growing appreciation of the fact that mankind's state of mind can never be altogether relaxed. Indeed a watershed in the modern perception of cometary facts has evidently been reached with the most recent and devastating example of cometary splitting, that of the fragmentation of Comet P/Shoemaker-Levy 9 and its subsequent bombardment of planet Jupiter. Thus there is a recognized tendency now amongst comets, especially those in short-period orbits, due to the occasionally excessive effects of solar irradiation, planetary tides and small body impacts, which gives rise to individual swarms of cometary debris, and it is the resulting repeated penetration of such dispersed swarms by our planet which apparently increases the danger to mankind from time to time. The danger comprises global coolings, atmospheric pollution and super-Tunguska events, the cometary debris being responsible for both high-level dust insertions and low-level multimegaton explosions in the Earth's atmosphere along with a generally enhanced fireball flux. Historically, the presence of such danger was drawn to mankind's attention by the observed bombardments over several decades due to “blazing stars threatening the world with famine, plague and war; to princes death; to kingdoms many curses; to all estates many losses; to herdsmen rot; to ploughmen hapless seasons; to sailors storms; to cities civil treasons.” The sense of cosmic destiny aroused by these bombardments evidently involved degrees of fatalism and public anxiety which were deplored by both ecclesiastical authorities and secular administrations with the result that acknowledged dispensers of prognosis and mitigation who endorsed the adverse implications of ‘blazing stars’ (astrologers, soothsayers etc.) were commonly impugned and censured. Nowadays, of course, we are able to recognise that the Earth's environment is not only one of essentially uniformitarian calm, as formerly assumed, but one that is also interrupted by ‘punctuational crises’, each crisis being the sequence of events which arises due to the fragmentation of an individual comet whose orbit intersects the Earth's. That even modest crises can arouse apprehension is known through the circumstances of the nineteenth century break-up of Comet Biela. Indeed it seems that these crises are rather frequently characterized by relatively violent (paradigm shifting) transmutations of human society such as were originally proposed by Spengler and Toynbee more than sixty years ago on the basis of historical analysis alone. It would appear, then, that the historical fear of comets which has been with us since the foundation of civilization, far from being the reflection of an astrological perception of the cosmos which was deranged and therefore abandoned, has a perfectly rational basis in occasional cometary fragmentation events. Such events recur and evidently have quite serious implications for society and government today. Thus when cosmic danger returns and there is growing awareness of the fact, we find that society is capable of becoming uncontrollably convulsed as ‘enlightenment’ spreads. A revival of millenarian expectations under these circumstances, for example, is not so much an underlying consequence but a deviant manifestation of the violent turmoil into which society falls, often to revolutionary effect.

The impact of comet Shoemaker‐Levy 9 on the Jovian magnetosphere

By the time of the impact of comet P/Shoemaker‐Levy 9 with Jupiter, the freshly‐broken surfaces of the accompanying rubble will have been outgassing for about two years, and will have produced an expanding and co‐moving cloud of gas hundreds of RJ across. Much of this gas, escaping from the cometary fragments at low (≤ 1 km/s) speed, will arrive in the Jovian magnetosphere contemporaneously with the comet and drift through the magnetosphere. This gas, as it is photoionized, will be picked up primarily in the outer magnetosphere and the resulting high‐energy ions should intensify magnetospheric processes, such as Io plasma torus and auroral emissions, that are thought to be powered by outer magnetospheric mass loading. If the composition of the comet is similar to that of P/Halley, the power available from mass loading should be comparable to that driving the aurora (1014W) and at least an order of magnitude larger than that exciting the plasma torus for several weeks or months. Measurement of these emissions during and after the cometary encounter may constrain the mechanisms for energization of magnetospheric charged particle populations and magnetospheric transport processes.

Initial results from Giotto comet flyby

The European Space Agency's Giotto spacecraft became the first probe to fly by two comets on July 10 when it flew to within 200 km of the nucleus of Comet Grigg‐Skjellerup. Giotto's previous comet encounter passed to within 600 km of Comet Halley in March 1986.Eight of the 11 instruments onboard were operating during the encounter and returned data. At a distance of 600,000 km from the nucleus, the first presence of cometary ions was detected by the Johnstone Plasma Analyser (JPA). The JPA and the Reme Plasma Analyser detected a bow shock or a bow wave that was much more distinct than had been predicted for such a weak comet.

The Evolution of Jupiter Family Comets over 2000 Years

The orbital evolution of the whole sample sample of short-period comets was computed by numerical integrations for a time interval of 2000 yr centered on the present epoch. This data base is intended to serve in various studies involving the statistics of orbital evolution and correlation with physical parameters or discovery circumstances. We present some results concerning the following aspects: the evolution of the orbital elements and their past-future asymmetry, statistics on the discovery of comets and on the encounters of comets with Jupiter.

The February 1986 solar activity: A comparison of GIOTTO, VEGA-1, and IMP-8 solar wind measurements with MHD simulations

Large disturbances in the interplanetary medium were observed by several spacecraft during a period of enhanced solar activity in early February 1986. The locations of six solar flares and the spacecraft considered here encompassed more than 100° of heliolongitude. These flares during the minimum of cycle 21 set the stage for an extensive multi-spacecraft comparison performed with a two-dimensional, magnetohydrodynamic (MHD) numerical experiment. The plasma instruments on the European Space Agency (ESA)'s GIOTTO spacecraft, on its way to encounter Comet Halley in March 1986, made measurements of the solar wind for up to 8 hours per day during February. We compare solar wind measurements from the Johnstone Plasma Analyzer (JPA) experiment on GIOTTO with the MHD simulation of the interplanetary medium throughout these events. Using plasma data obtained by the IMP-8 satellite in addition, it appears that an extended period of high solar wind speed is required as well as the simulated flares to represent the interplanetary medium in this case. We also compare the plasma and magnetometer data from VEGA-1 with the MHD simulation. This comparison tends to support an interpretation that the major solar wind changes at both GIOTTO and VEGA-1 on 8 February, 1986 were due to a shock from a W05° solar flare on 6 February, 1986 (06:25 UT). The numerical experiment is considered, qualitatively, to resemble the observations at the former spacecraft, but it has less success at the latter one.

Advances in laser-pumped helium magnetometers for space applications (abstract)

Recently tunable lasers have been developed which are suitable for use as pumping sources in optically pumped helium magnetometers. This advance in laser technology is leading to a new generation of improved laser-pumped resonance magnetometers for use in geophysical and space applications. The history of optically pumped resonance magnetometers in space exploration will be reviewed, in order to describe the anticipated benefits of laser pumping. Experiments will be described which have demonstrated signal strengths in laser-pumped helium magnetometers which are 45 times greater than those observed in the same sensor pumped with a conventional rf electrodeless discharge helium lamp. This was a collaborative effort with the Magnetics Group at the Jet Propulsion Laboratory and Professor L. D. Schearer’s group at the University of Missouri at Rolla. The impact of the laser pumping technique on sensitivity, accuracy, and versatility of space magnetometers will be discussed. Proposed laser-pumped magnetometers will be described including the vector helium magnetometer for interplanetary field measurement, the scalar helium magnetometer for earth orbital applications, and the vector/scalar hybrid magnetometer for planetary and cometary encounters. Recent developments in miniaturized turnable laser sources will be presented. This was supported by the Jet Propulsion Laboratory/NASA.

Spacecraft observations of the interaction of active comets with the solar wind

In 1985 and 1986, six spacecraft encountered two comets and obtained a wealth of new data about the plasma processes at work in the interaction of an active comet with the solar wind. This paper summarizes those data and their interpretations. The interaction process starts millions of kilometers from the nucleus where the solar wind first picks up cometary ions. The cometary ions not only slow down the wind but also create disturbances which are ultimately responsible for the surprisingly high fluxes of energetic particles detected at comets. After passing through a structure that is arguably called a bow shock, the plasma continues to slow down as it accretes more cometary ions. The deceleration of the wind causes the interplanetary magnetic field to pile up and drape around the comet's ionosphere, as predicted by Alfvén in 1957. It is this draped field that defines the geometry of a comet's plasma tail. At Halley the Giotto spacecraft detected a well‐defined boundary separating the mixture of solar wind and cometary plasmas and the interplanetary magnetic field from the field‐free, nearly pure cometary plasma in the inner coma. Other unexpected features in the inner coma were a flux of fast “granddaughter” ions and high densities of negative ions. For all the comet encounters, the region between the bow shock and the field‐free cavity was distinguished by several sudden changes in the properties of the plasma; the natures and causes of these features are subjects of intense debate.

Trajectories for spacecraft encounters with comet Honda-Mrkos-Pajdušáková in 1996

Early in 1996, the relatively bright short-period Comet Honda-Mrkos-Pajdušáková (HMP) will pass only 0.17 astronomical unit (AU) from the Earth, providing both an unusually favorable apparition for ground-based observers and an opportunity for spacecraft to reach Comet HMP on relatively low-energy trajectories. The Japanese Institute of Space and Astronautical Sciences' (ISAS's) Sakigake spacecraft is expected to fly by Comet HMP on February 3, 1996, after utilizing four Earth swingbys to modify its orbit. If the camera on the European Space Agency's (ESA's) Giotto spacecraft is inoperable, Giotto may also be sent to Comet HMP. In addition, 1-year Earth-return trajectories to Comet HMP are described, along with some that can be extended to encounter Comet Giacobini-Zinner (GZ) in 1998.

Dinosaurs victims of cyanide poisoning?

The Eos article, Comets and Life (March 28, 1989), reports on the work of Paul Thomas, Christophere Chyba, Carl Sagan and Leigh Brookshaw on cometary impact production of cyanides and other organics that may have been precursors of life. The article was based on material presented at the 20th Lunar and Planetary Science Conference [Thomas et al, 1989].As pointed out in the article, comets may contain 20% organic matter in the form of a complex interbonded mass. This kerogen‐like material contains CN bonds as well as CC and CO bonds. Evidence for cyanide protection from light‐element “CHON” solids was observed in the recent Halley's comet encounter in the form of CN plumes [Eberhardt et al., 1986; Schlosser et al., 1986]. An additional, and possibly more important source of cyanide, is HCN, which was observed [Schloerb et al., 1986] to be emitted from Halley's comet as part of the normal neutral gas emission with an abundance equal to 10−3 that of H2O. H2O is the dominant volatile species in comets and appears to constitute 80% or more of the total molecular release [Mendis, 1986].

Halley’S Comet (Part I): Ground-based Observations

AbstractSince the recovery in October 1982, an extensive, international programme to observe Comet Halley with ground-based instruments has been co-ordinated by the International Halley Watch (IHW), and a comprehensive archive is now in the final phases of preparation. The observations were carried out at more than 150 observatories and with all available methods. A special effort was made to support the space missions during the comet encounters in early March 1986. Whereas the spacecraft provided detailed in-situ measurements over a short time interval, ground-based observers have so far followed the development of the comet over a period of nearly six years, and a number of spectacular events near the nucleus and in the tail have been documented in great detail. These observations still continue. This article gives an overview of the most important results obtained from the ground and also mentions the prospects for further observations with large telescopes during the next years.

World's largest space arena to be developed

On 2 July 1985, the European Space Agency (ESA) launched an interplanetary probe to encounter Halley's Comet on the night of 13/14 March 1986 at a distance of 0.98 AU from Earth. The mission to Halley's Comet was the Agency's first venture into deep space. The tracking stations necessary to support such a mission were not directly available to ESA at the initiation of the GIOTTO project although facilities operated by NASA's deep space network were later made available for certain phases of the mission, together with the 30-m Weilheim antenna of the DFVLR. ESA's European Space Operations Centre, ESOC therefore developed the new deep space tracking stations especially for support of the GIOTTO mission. One of these stations, the 15-m antenna facility at Carnarvon, West Australia, was designed and installed by ESA as a dedicated S-band and X-band tracking, telemetry and command station. The second station at Parkes, New South Wales, Australia, a 64-m radio telescope owned by the Commonwealth Scientific and Industrial Research Organization (CSIRO) was modified to provide X-band telemetry reception using cryogenic MASER low-noise amplifiers. This station operated by CSIRO with assistance from a ESA engineering and operations team, provided support to the GIOTTO mission for reception of the 46 kbs high speed telemetry format which is vital to success of the GIOTTO mission at time of Cometary Encounter. Additionally, the DFVLR Weilheim station was modified to include the newly developed ESOC deep space tracking system which was also installed at the Carnarvon Station. The paper discusses in some detail the network of tracking stations which provided the Control Centre at ESOC in Darmstadt, F.R.G. with the data which was vital to the success of the mission. Because the launch date of GIOTTO was a date which could not be rescheduled, the design installation, integration and testing of the complete GIOTTO mission operations system was an extremely time critical activity. Without the “ground segment” in a fully functional state, the launch of GIOTTO could not take place. The activities leading to the successful completion of the GIOTTO mission operations system are described in some detail with emphasis on the final testing carried out in early 1985. One important factor which is sometimes overlooked by authors describing the GIOTTO mission is that, whereas NASA has had for many years a world-wide deep space network available for its deep space missions, ESA had to start from scratch in its task of building a system capable of controlling the GIOTTO mission to Halley's Comet. The task of spacecraft operations can never be discussed separately from the system required to provide the necessary control of the mission. This paper will concentrate to some extent in this aspect as experienced during the flight to the comet and the rendezvous on the night of 13 March 1986.

Giotto—The mission operations system

On 2 July 1985, the European Space Agency (ESA) launched an interplanetary probe to encounter Halley's Comet on the night of 13/14 March 1986 at a distance of 0.98 AU from Earth. The mission to Halley's Comet was the Agency's first venture into deep space. The tracking stations necessary to support such a mission were not directly available to ESA at the initiation of the GIOTTO project although facilities operated by NASA's deep space network were later made available for certain phases of the mission, together with the 30-m Weilheim antenna of the DFVLR. ESA's European Space Operations Centre, ESOC therefore developed the new deep space tracking stations especially for support of the GIOTTO mission. One of these stations, the 15-m antenna facility at Carnarvon, West Australia, was designed and installed by ESA as a dedicated S-band and X-band tracking, telemetry and command station. The second station at Parkes, New South Wales, Australia, a 64-m radio telescope owned by the Commonwealth Scientific and Industrial Research Organization (CSIRO) was modified to provide X-band telemetry reception using cryogenic MASER low-noise amplifiers. This station operated by CSIRO with assistance from a ESA engineering and operations team, provided support to the GIOTTO mission for reception of the 46 kbs high speed telemetry format which is vital to success of the GIOTTO mission at time of Cometary Encounter. Additionally, the DFVLR Weilheim station was modified to include the newly developed ESOC deep space tracking system which was also installed at the Carnarvon Station. The paper discusses in some detail the network of tracking stations which provided the Control Centre at ESOC in Darmstadt, F.R.G. with the data which was vital to the success of the mission. Because the launch date of GIOTTO was a date which could not be rescheduled, the design installation, integration and testing of the complete GIOTTO mission operations system was an extremely time critical activity. Without the “ground segment” in a fully functional state, the launch of GIOTTO could not take place. The activities leading to the successful completion of the GIOTTO mission operations system are described in some detail with emphasis on the final testing carried out in early 1985. One important factor which is sometimes overlooked by authors describing the GIOTTO mission is that, whereas NASA has had for many years a world-wide deep space network available for its deep space missions, ESA had to start from scratch in its task of building a system capable of controlling the GIOTTO mission to Halley's Comet. The task of spacecraft operations can never be discussed separately from the system required to provide the necessary control of the mission. This paper will concentrate to some extent in this aspect as experienced during the flight to the comet and the rendezvous on the night of 13 March 1986.

Observations of energetic water-group ions at comet giacobini-zinner: Implications for ion acceleration processes

Observations of energetic water-group pick-up ions made by the EPAS instrument during the ICE fly-by of comet P/Giacobini-Zinner are investigated for evidence concerning the processes which accelerate the ions from initial pick-up energies of around 10 keV up to energies of a few hundred kilo-electronvolts. The form of the ion spectrum in the ion rest frame is first investigated and compared with theoretical suggestions that exponential energy distributions might be produced by either first or second order Fermi acceleration in the cometary environment. It is shown that such distributions do not fit the data at all well, but that rather (over the EPAS ion bulk rest frame energy range of ∼30 to <300 keV) the observed distribution functions closely approximate an exponential in ion speed. The higher energy (> 50 keV) data also fit a power law distribution very well, but at lower energies the data tend to show a flattening below the power law form. It is also shown that the observed spectra are much softer than those calculated by Ip and Axford (1986, Planet. Space Sci. 34, 1061) for the G-Z ion pick-up region upstream of the bow shock, indicating that if these distributions are indeed due to second order Fermi acceleration as they propose, then the ion mean free path must be rather larger than used in their calculations (i.e. rather larger than 5 water-group ion gyroradii). Overall, it is concluded that at the present stage of theoretical development it is premature to draw firm conclusions about acceleration mechanisms from studies of the ion spectrum alone. However, from the general spectral analysis it is also possible to investigate the variations of ion intensity and spectral hardness which take place during the comet encounter, and to gain an indication of the degree of isotropy of the ion distribution in the rest frame of the flow. We find that a ∼.5 × 10 4km-wide region (∼ 35 min along the spacecraft trajectory) of rapid ion intensification and spectral hardening occurs immediately upstream from the turbulent mass-loaded region, suggestive of a first order Fermi process in which ions are successively reflected between the outer layer of the slowed, turbulent region and waves in the faster upstream flow. It is shown that within the turbulent region the ion distribution becomes rapidly isotropized in its own bulk rest frame, indicative of a sudden reduction in ion mean free path. Additional processes (possibly second order Fermi acceleration) must also occur in order to account for the further modest intensifications of the energetic ion fluxes observed within the turbulent mass-loaded region, as well as the presence of ions in the outer pick-up region which have energies well in excess of the local pick-up energy.

Energy diffusion of pickup ions upstream of comets

We present a steady state model of pickup ion energization upstream of a cometary bow wave in order to investigate the effects of quasi‐linear energy diffusion in the turbulence there. The model assumes that the ions are immediately isotropized at pickup, and it includes the effects of adiabatic acceleration in the slowing solar wind and of continual pickup of ions as the comet is approached. By taking all physical quantities to fall off as power laws with distance from the comet, an analytical expression is obtained for the distribution function of pickup ions in the reference frame moving with the solar wind. To illustrate the application of this model, we compare the model results to the observations of pickup ions at comet Giacobini‐Zinner. At present, this is the only cometary encounter for which sufficient quantitative information is available. The model does not compare well with these observations, but it is not clear whether the differences are due to artificial problems in the model or the data analysis or to the action of other energization processes at this comet. Preliminary results from the Halley encounters appear to agree more closely with this model.

The lightweight energetic particle detector EPONA and its performance on Giotto

A lightweight energetic particle detector system (EPONA/EPA) is described which was designed to operate in those novel environmental conditions (i) characterised by the varying solar aspect angles and temperatures pertaining during the cruise phase of the Giotto spacecraft and (ii) during the dust bombardment characterising closest approach ( approximately 600 km) to the nucleus of Comet Halley. Representative data, illustrating the functioning of EPONA during both the Giotto cruise phase and at comet encounter, are presented. The instrument has a wide range of applications to other space experiments where reliable plasma diagnostics are required. Data monitoring is also discussed together with data reduction.

The Giotto mission to Comet Halley

Giotto encountered Comet Halley on 14 March 1986, about four weeks after the comet's perihelion passage when it was most active. Giotto passed the comet nucleus at a distance of 600 km on the sunward side. Its scientific payload-comprising a narrow-angle camera, three mass spectrometers for the compositional and isotopic analysis of the neutral gas, ions and dust particles in the cometary coma, various dust impact detectors, a photopolarimeter and a set of plasma instruments-worked flawlessly and returned a wealth of data. The mission's scientific objectives, the spacecraft and the mission from launch to encounter are described. After the encounter Giotto was retargeted to return to the Earth. An Earth swing-by manoeuvre on 2 July 1990 will allow Giotto to encounter Comet Grigg-Skjellerup in July/August 1992.

What is SPAN?

SPAN is the Space Physics Analysis Network. This important research tool of the NASA scientific community links space researchers from over 50 institutions throughout the United States. The SPAN system is growing within the United States, and it also is expanding to connect NASA scientists with European and Japanese space research institutions.The SPAN system serves many functions. Its paramount purpose is to provide scientists with a tool that improves their productivity. SPAN has traditionally been used to exchange mail messages, to send data back and forth for scientific papers and analysis workshops, and to share scientific software. SPAN has played a crucial role by disseminating spacecraft data in near‐real time during several recent NASA and ESA program successes, such as the International Cometary Explorer (ICE) spacecraft encounter with Comet Giacobini‐Zinner (see “Behind the Scenes During a Comet Encounter” by J.L. Green and J.H. King, Eos, March 4, 1986, p. 105), the Voyager 2 encounter with Uranus, and the Giotto spacecraft encounter with Comet Halley (see “Networking Ground‐Based Images of Comet Halley during the Giotto Encounter” by D. Rees et al., Eos, December 16, 1986, p. 1385). Of course, SPAN has served a variety of broader purposes. It has provided (and will continue to provide) an excellent testing ground for trying new technologies and for evaluating ideas about processing, storing, and transferring various kinds of information. Until the recent availability of computers sponsored by the National Science Foundation, the SPAN network provided one of the few opportunities for NASA researchers to have ready access to the supercomputers needed for large‐scale numerical simulation of magnetospheric and ionospheric plasma systems. SPAN has also increased its usefulness substantially by the addition of the National Space Science Data Center (NSSDC) as a data node on the system. The network, which was originally based on a starshaped configuration, has been redesigned over the last year to take advantage of NASA's new Program Support Communications Network (PSCN).

ESA plans new missions

The tragic explosion of the space shuttle Challenger has caused a delay of at least 13 months to the European Space Agency/National Aeronautics and Space Administration (ESA/NASA) cooperative mission Ulysses, previously known as the Solar Polar Mission. Ulysses was scheduled for launch in May 1986. The launch of the Hubble Space Telescope, in which ESA is a cooperative partner, is certain to be delayed beyond the October 1986 launch date.As Eos went to press, the Giotto spacecraft, which has been on its way to Comet Halley since July 1985, was performing well, according to ESA. All investigator groups participated in operation rehearsals at the European Space Operations Centre in Darmstadt, Federal Republic of Germany, in preparation for the cometary encounter, which occurred near midnight (UT) on March 13, 1986.

Behind the scenes during a comet encounter

Personnel at the National Space Science Data Center (NSSDC) and the Space Physics Analysis Network (SPAN) had the privilege of participating in an exciting adventure, namely the September 11, 1985, rendezvous of the International Cometary Explorer (ICE) spacecraft with Comet Giacobini‐Zinner (G‐Z). An incredible number of details must be worked out to ensure the success of an encounter mission, and extraordinary efforts on the part of many individuals become the norm rather than the exception. Tracking, communications, and a seemingly endless array of analysis computers must all function well together to provide near—real‐time data to the scientists, who are then asked to do near‐real‐time data analysis.There is much praise to be given to many organizations and individuals who participated in the various aspects of the encounter. However, in this report, we will concentrate only on the contributions of NSSDC and SPAN, both of which are bringing about a new space data systems environment, and both of which are being vastly improved for use by the space and earth science communities. The purpose of NSSDC is to serve as a centralized archive and distribution center for data obtained from National Aeronautics and Space Administration (NASA) space and earth science flight investigations and to perform a variety of services to enhance the scientific return from the initial NASA investment in these missions. SPAN is a mission‐independent computer‐to‐computer network that is used as a tool to gain electronic access to NASA facilities (such as NSSDC), coinvestigators, and data for several thousand scientists.