May 1980:Soviet reentry tests

Readers will be aware that the Soviet Union has conducted three mysterious one-orbit flights, Cosmos 881/882, 997/998 and 1100/1101 over the past three years. These missions have generally been assumed to be man-related and connected in some way with the Soviet space shuttle programme, but this has never been proved: nor have observers been in agreement about the tests carried out. It is the object of this article to present strong evidence showing that these flights were in fact re-entry tests of a winged vehicle,and to give a brief outline of the probable mission profile.

Mission Profile

In summary, the three flights each consisted of two spacecraft being launched by a Proton launch vehicle into an approximately 210 km circular orbit of inclination 51.6 °. Launch times were within about two hours of midnight GMT in each case, and the spacecraft were deorbited (assumed recovered) within one revolution. The very short flight durations strongly suggest that re-entry and/or landing tests were the primary mission objectives,as the ground-track of the 51.6° inclination orbit flown only passes over Kazakhstan on the first three revolutions of each day. Thus, if the vehicle tested is not equipped to survive a flight of as long as one day (as would be the case for a re-entry vehicle), recovery must be attempted on the first few passes.

Furthermore, these launches all occurred at night, a fact which is hard to attribute to chance alone. It is therefore almost certain that these missions had some sort of launch window constraint. In addition, the December flight had the latest launch time and the May flight the earliest one, leading to the possibility that each launch took place at a fixed interval before dawn at some northern latitude. Indeed, it can be shown that certain latitudes satisfy this condition, and that they lie in the very narrow range from 40.0°N to 40.6°N. (These calculations are based on the times of launch given by the Royal Aircraft Establishment). Sunrise at the meridian of Greenwich for these latitudes occurs 0.237-0.238 days (5 hr,41-43 min.) after launch for all three missions considered here.

This result is interesting for three main reasons. Firstly, it obviously allows the time of launch for any further flights of this type to be calculated for a given launch date. For example,if the supposed Proton launch failure of 4 August 1977 was intended to be such a mission, launch would be expected at about 0.971-0.972 GMT.

Secondly, only certain launch times from the original RAE ranges satisfy the requirement that dawn (at 40.0-40.6°N) follow them by a fixed interval. This allows refined estimates of the actual launch times to be made.

Thirdly, and most importantly, this connection with dawn at the latitudes mentioned can be used to gain some insight into the mission profile flown. In particular, if we assume a Proton launch phase lasting 11 minutes and covering a range of 2500 km (typical values for a launch vehicle), the spacecraft crosses the 40.3°N line at about 87 min. Ground Elapsed Time (GET) and at a longitude of 29.6 °E. Combining this with the delay estimated above places the crossings at about 136-138 minutes before local dawn, well before any appreciable daylight. We are thus faced with an apparent paradox, in that these flights are clearly keyed to dawn at certain latitudes and yet cross these same latitudes in darkness. The only way to solve this problem is to assume that the spacecraft have some means of travelling far to the east of their original ground-track, i.e. towards dawn. To achieve this in practice requires considerable cross-range manoeuvring during re-entry, probably of up to about 1000 km. This is well above the capability (less than 100 km) of offset centre-of-gravity re-entry vehicles such as Apollo and Soyuz, but less than the performance quoted for winged and lifting-body vehicles (e.g., 2040 km for the US Space Shuttle and 2060 km for the Aerospatiale Hermes design study). It is therefore highly probable that the spacecraft flown on these Cosmos missions are lifting-bodies or winged, and so are almost certainly prototypes of the Soviet shuttle vehicle whose drop tests were revealed by Aviation Week & Space Technology.

Recovery Zone

As noted previously, the short lengths of these flights point towards their being re-entry tests. This identification is supported by the connection with dawn established above, as such timing causes the early entry to be in darkness (enabling flames, ionization plume, etc., to be clearly visible) and the later part in daylight so that the spacecraft can be photographed in flight. Such lighting is roughly ideal for a re-entry test flight. It is unlikely that a landing at Tyuratam would be attempted on these early development flights, due to the danger involved if anything were to go wrong: in any  case, the new shuttle runway there was reported as being still under construction in early 1979. Some other suitable recovery zone must therefore be chosen: this should preferably be relatively flat and sparsely populated, should yield a re-entry path as much over Soviet territory as possible (to facilitate tracking), and should of course be reachable with the cross-range capability assumed. One such area is located at about 44°N and 73°E in Peski Muyunkum, a small sandy desert lying south-west of Lake Balkhash in eastern Kazakhstan.

In order to complete this analysis we shall have to make two further working assumptions: these are that the re-entry trajectory flown follows a Great Circle route from Entry Interface (EI) to landing (probably a fairly good first approximation), and that the total range covered is between 6950 km and 9050 km (as compared with the US Space Shuttle range of 8150 km on its first flight). On the basis of these, the spacecraft cross the 40.3 °N latitude line at a longitude of from 46.2 °E to 50.8° E and at about 89 to 91 min GET, probably shortly before the end of radio blackout. Combining this with the delay between launch and dawn obtained above gives a crossing at 48 to 67 minutes before local sunrise, approximately at the time of first appreciable daylight.

Conclusions

In summary, the three Cosmos flights investigated were almost certainly re-entry tests of a lifting-body or winged vehicle,probably the reusable Soviet shuttle speculated on elsewhere. Aircraft-type horizontal landings are not thought to have been included on these tests, as the most probable recovery zone (a desert in eastern Kazakhstan) is unlikely to be equipped with a suitable runway. Future unmanned flights culminating in landings at Tyuratam should be expected: note that such flights will not have launch times governed by the relationship outlined above.