1. On the direction of the TSB flight
The first investigators of the Tunguska meteorite (L.A.Kulik, E.L.Krinov, and I.S.Astapovich [1; 2; 3 ]) who analyzed comparatively fresh evidences of the flight of the TSB on the Angara river did not doubt that it had moved generally from the south to the north, though there were three versions of its trajectory (the southern one, proposed by L.A.Kulik, the south-eastern by E.L.Krinov and the south-western by I.S.Astapovich). By the early 60-s it was Krinov's trajectory, namely 135° east of the true meridian, that was considered the most realistic.
Later however, as more information was accumulated on the vector structure of the fallen forest field [9; 17; 59], a "corridor" of axially symmetric deviations of the vectors of the forest falling from the dominating radial pattern was revealed, and this deviation was interpreted as the track of the ballistic wave. The direction of, the "corridor" which was initially estimated as 111° E from N (114° east of the true meridian) [17] was later found to be 95° E from N (99° east of the true meridian) [10], which roughly coincides with the axis of symmetry of the radiant burn area [19]. In this period of time, V. G.Konenkin [60] and later other investigators [61-63] questioned old residents of the area who had lived in the upper reaches of the Nizhnyaya (Lower) Tunguska in 1908 (where there was no questioning in the 20-s and 30-s). This resulted in the conclusion that TSB had been observed in the said area as well, the analysis of the data suggesting that the body moved from the ESE to the WNW, i.e. by the path coinciding with the projection of that of the TSB, as found on the basis of analysis of the vector picture of the fallen forest area. This coincidence caused revision of the notion of the TSB path, and since the year 1965 the ESE-WNW (in fact, even E-W) version has been accepted in literature. For some years it was assumed to be finally true.
A grave disadvantage of the calculations of TSB path before the mid-80-s was that there were analyzed only some separate groups of eye-witnesses' accounts obtained by different researchers, in different periods of time, and not the whole body of evidence. Publication of the catalogue of eye-witnesses information [4] enabled analysis of the whole event. This was done in Ref.[56] and corroborated the considerations expressed earlier in Ref. [58] and also by I.S.Astapovich [64]. Two fundamental facts were established in particular:
1. The total combination of evidence given by "eye-witnesses of the Tunguska fall" contains in fact information on at least two (most likely more) large day-time bolides. It is important that the "images" of the "Angara" and the "Nizhnyaya Tunguska" bolides are quite different and everything seems to indicate that they belong to different objects.
2. The trajectory calculated on the basis of evidences of witnesses of the "Angara" phenomenon and corresponding most likely to its version proposed by E.L.Krinov [1] deviates considerably from that determined by analyzing of the vector structure of the forest fall area and the radiant burn area [9; 19]. Indeed, evidences of the Angara eye-witnesses, including the report of a district police officer, strongly suggest that the bolide flew "high in the sky", which is hardly consistent with the path 99° E of the true meridian. On the contrary, the data obtained on the Nizhnyaya Tunguska river, though agreeing with the configuration of the destruction area, are in contrast with the Angara observations.
An extra complication is that Nizhnyaya Tunguska data suggest virtually unambiguously that bolide's flight took place in the afternoon, unlike those of the Angara which refer to the early morning.
Attempts to resolve the conflict between the data face with considerable problems. If the Angara and Nizhnyaya Tunguska observations are due to different bolides, which is most probably so, — then with which of them the destruction area originally explored by L.A.Kulik is associated? Judging by the destruction area configuration, the most probable candidate is the eastern (Nizhnyaya Tunguska) bolide. However none of TSB investigators doubts that the explosion at the distance of 70 km from Vanavara occurred in the early hours of the day, not past midday [56]. Moreover, there is no direct proof that the Nizhnyaya Tunguska bolide was observed in the year 1908, inasmuch as this event was not recorded in any official documents, unlike the Angara bolide.
Besides, even assuming the area of the leveled forest, discovered by L.A.Kulik, to be due to the Nizhnyaya Tunguska bolide, it remains unclear where the Angara bolide fell, then. Throughout the Tunguska "meteorite" study there was no doubt the latter had in fact exploded in the Vanavara region...
But if the forest leveling was caused by the Angara bolide, how does it fit the direction of the "corridor" impressed in the area of the fallen forest by the TSB ballistic wave?
In the search of way out of this maze, more than one approach has been tried. Some researchers, preferring direct physical evidence, practically ignored eye-witnesses' testimonies as an unreliable subjective material. This approach could be agreed with to some extent, if it were amatterof a few inconsistent testimonies, not many hundreds of independent reports. Besides — what is very important — the testimonies of the year 1908 include official documents of the time, whose authors were responsible to the authorities for their trustworthiness. For this reason, the eye-witnesses' reports should be regarded as a material equal to other data sets or at any rate not to be ignored, even if they do not conform to some speculative arguments.
Other investigators tried their best to combine the Angara evidence, the Nizhnyaya Tunguska data and the geometry of the destruction area [65]. The results were rather dubious, strained, and quite different in this from the sufficiently unambiguous and clear picture which is provided when the two groups of eye-witnesses' reports are analyzed separately.
Then, F.Yu.Zigel [58] introduced the concept of a "manoeuvre" made by the TSB, assuming it to have moved initially in a path close to that calculated by E.L.Krinov [1] and then, describing an arc, entered the space over the interfluve of the Nizhnyaya and Podkamennaya Tunguskas and took an eastern path which led it to the "explosion".
These contradictions have not been reconciled. It seems probable that the eastern group of eye-witnesses' evidence is not directly related to the Tunguska bolide and that the latter moved in a trajectory-close to that calculated by E.L.Krinov [1]. The cause of the incompatibility of the bolide path projection with the data of the Angara eye-witnesses' group remains unclear. Yet it should be borne in mind that the identity of the axis of symmetry of the observed forest destruction pattern with the projection of the bolide path that appears almost self-evident to the Tunguska meteorite investigators is only an assumption of high probability, rather than an established truth. Theaxially symmetric "corridor" is the trace of the ballistic wave where it touched the earth surface', it remains essentially an open question what its initial space position was and whether it could change for some reason or other.
However, the problems associated with the TSB path parameters are not only these. Most of the authors who studied this question conclude that the slope of the TSB path was relatively small (some 15°) [1; 66; 67]. Still, modeling experiments [68; 69], as well as results of mathematical simulation of the Tunguska explosion parameters [70; 71] evidence that the slope of the final path section was most probably 40°. The transition of the TSB from the comparatively flat path to the steep one ("the peck") seems to have taken place as the bolide approached the spot of the explosion: it might be due, as is held in Refs. [72; 73], to avalanche breaking of the "meteorite", enlargement of its frontal surface and increasing resistance of the air.
Especially embarrassing is the fact that the "corridor", this impression of the ballistic wave on the forest, is observed, as has been recently shown, even beyond the epicenter of the explosion, as if roughly-continuing the direction of the TSB flight [74]. The most reasonable explanation is assumption of a ricochet of the TSB part which survived the explosion and continued its flight, maintaining, to some degree, the same trajectory. The question however arises if this assumption satisfies the requirements of the theory of the strength of materials.
As was mentioned above, the TNT equivalent of the Tunguska explosion is estimated as 10-40 megatons, the temperature of the center of the fire ball measuring at least tens of thousands of degrees Kelvin [75]. What must have been the characteristics of the TSB substance to withstand this "fiery font" and retain compactness and ability to ricochet? And how does it go with the above concept of the TSB consisting of comet ice or a silicate material, suggested by the first group of hypotheses to account for the Tunguska phenomenon?
Thus, analysis of materials characterizing the TSB path suggests its rather complex nature. It is not improbable that the Tunguska object moved in a non-ballistic trajectory.