Explanation of geodetic target error from the ICBM in relating launch and target points on different continents
CIA-RDP63-00314R000200160042-9
OCAOCT
Approved For Release 2001/08: CIA-RDP63-00314R000200160042-9
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Introduction
US ICBM tests have demonstrated a capability of impacting nosecones within less than 2 n. miles of the designated target. This achievement not only exceeded expectations of American engineering, but in so doing it must be noted that a significant factor contributing to this accuracy—and its calibration—was the accurate geodetic positional relationship of the launch and target points to an error of about ±500 feet.
Unfortunately, such geodetic accuracies are currently attainable by the US only for European USSR. This paper explains, in brief and non-technical terms, the nature of the geodetic problem and efforts to improve current inadequate geodetic accuracies.
A. Intercontinental Geodetic Inaccuracies
The problem of intercontinental geodetic inaccuracies arises from the diversity of geodetic systems and difficulties of interconnections across the oceans:
- Continental systems of geodetic control end abruptly at coasts.
- Gaps in control over ocean areas create uncertainty in positioning of the continents.
- The large geodetic nets of the world are based upon different datums.*
- The US uses the North American Datum, adopted 1927; the USSR uses the Pulkovo 1942 Datum, adopted in 1946.
*See the Annex for explanation of the basic elements of the geodetic system.
- Datum differences give rise to errors in computing distances and directions between widely separated launch and target points.
- Ultimate target accuracies depend on availability of identifiable geodetic points to which targets must be related.
B. Causes of Geodetic Errors
Geodetic errors develop because the Earth is not a true sphere but an irregular figure flattened at the poles and having a bulge near the equator:
- Size and shape of the Earth – Estimates of semi-major axis and polar flattening have varied widely, causing differing discrepancies in the fitting of an ellipsoid to the geoid (generalized undulating sea-level Earth surface).
- Orientation of ellipsoids – Ellipsoid axes do not coincide with the Earth’s axis of rotation, making positions of different geodetic systems not directly comparable for geodetic computations.
- Errors due to deflections of the vertical – Result from angular differences between observations that are vertical to the geoid and computed as perpendicular to a displaced ellipsoid.
C. Insufficiency of Soviet Geodetic Data
The insufficiency of Soviet geodetic data and large-scale maps causes a significant US disadvantage in accurate location of targets:
- Systematic geodetic data on USSR are unavailable east of Leningrad–Gorkiy–Novosibirsk, preventing production of accurate maps or use of aerial photography for computing target locations.
- Modern large-scale maps are lacking for vast areas east of Gorkiy and the Caspian.
- Map error is determined by the scale of available maps. Negligible if scales are 1:100,000 or larger, but significant, particularly for locating Soviet ICBM sites, in areas covered at scales of 1:1,000,000 or smaller.
- Gravity anomalies have an effect on missiles during flight.
D. Comparative Estimates of US-Soviet Geodetic Target Error
Over a 5,500 n. mile range:
| Error Type | US Against USSR | USSR Against US |
|---|---|---|
| Uncertainties in size, shape of ellipsoid, target uncertainty | 1,000 feet or less to 2 miles | 1,000 to 2,000 feet |
| Map error (varies with scale) | 200 to 2,000 feet | 100 to 500 feet |
| Gravity error | 500 to 2,500 feet | 500 to 2,000 feet |
Estimated Overall Geodetic Error
- Average instance: 0.3 to 0.6 n. mile
- For 90% of European USSR targets: Within 1,000 feet
- For remainder of USSR:
- 50% certainty: 2,000 feet to 1 n. mile
- 90% certainty: 4,000 feet to 2 n. mile
*Simplified rounding of representative estimates provided by Army and USAF sources.
**Differences between US and USSR based on Soviet advantage of withholding geodetic capabilities.
E. US Programs to Improve Geodetic Accuracies
Improving geodetic accuracies is necessary for greatly enhancing future weapons systems. Present geodetic requirements are ±1,000 feet; current projections are ±500 feet (1965), and ±250 feet (1970).
Planned or Current Scientific Programs:
a. Different national geodetic systems on different ellipsoids, connected since World War II into continental systems (European, Tokyo, North American), have been reconciled into a single Defense World Geodetic System. This represents a first approximation; further refinement and verification are required.
b. IGY lunar photography program; results expected in 1 to 2 years.
c. HIRAN (high-precision Shoran) for intercontinental ties; reduced uncertainty of Europe–North America connections to ~240 feet; uncertainty persists due to Canadian geodetic weaknesses.
d. World gravity survey; under consideration for oceanic survey. Surface-ship and airborne instrumentation being tested; will reduce cost and speed up survey completion.
e. Earth satellite observations and orbit analysis; ties with ±100 feet accuracy expected by ~1965.
f. High-altitude rocket flashes for determining 3D coordinates between continents, positions free of deflection-of-vertical errors; programs in planning.
g. Reconnaissance satellite photography may yield the most direct and accurate checks on intercontinental positions and provide geodetic positions in the USSR where none exist.
Collection of Soviet Maps and Geodetic Data:
- Essential for accurate positioning of targets, especially in the Urals and Siberia.
- Soviet maps (1:100,000; 1:50,000; 1:25,000) and geodetic data sought since WWII; collection now a top priority. Yield to date: 13 East German sheets (1:25,000); 102 additional sheets obtained through chance events.
- Efforts at international scientific meetings to secure data: no success.
F. Comparison of US and USSR
- Competence of geodesists – Generally comparable; Soviets possibly superior in theoretical gravity and number of trained personnel.
- USSR has a vastly greater number of trained geodesists for missile operations.
- Soviets have geodetic targeting advantage due to:
a. Withholding of topographic maps from the West. Large-scale maps very tightly held; available maps are pre-1940 and limited, especially for Siberia.
b. Withholding of gravity and geodetic data. Revision of Soviet geodetic system in 1946. Available data mostly Pulkovo 1932; no USSR data on Pulkovo 1942 system.
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