RANGE AND GUIDANCE ACCURACY CAPABILITY OF THE ATLAS MISSILE SYSTEM

REPORT NO. ZW-7-366

DATE 6 JUNE 1960

(EXCERPTED HERE. FULL PDF IS LINKED HERE.)

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Page i – FOREWORD

An estimate of the accuracy of the two guidance systems used by the Atlas missile system is presented in this report. An approximate indication of the size of the pay load that can be delivered to ranges from 4700 n. miles to 8700 n. miles is also given.

Pages 1 to 3

SUMMARY

This report has attempted to answer two questions; first, the range to which various size payloads can be sent and second, the accuracy to which these payloads can be delivered by the guidance systems now available.

A typical D series missile configuration was selected for the purposes of this study. A nominal launch weight of 265,190 lbs. was used and the Rocketdyne MA-2 engines were assumed to produce nominal thrust and specific impulse. The missile that was simulated was launched due north from Vandenberg AFB. The accuracies of two different guidance systems, the G.E, Mod. III radio-inertial and the ARMA Lot IV all-inertial, have been studied and the results included in the text of this report.

Four burnout weights were used to establish the ranges at which the guidance system accuracies were determined. Those trajectories were flown with a constant missile inertial attitude of 23.4° during sustainer stage. The following table summarizes these results.

Burnout Weight (lbs)

Payload (lbs)

Range (Approx.)
(nautical miles)

C.E.P. (nautical miles)

G. E. Mod III System

ARMA System

13,642

6000

1750

0.61

1.08

12,642

5000

5500

0.44

1.25

11,142

3500

6900

1.05

1.57

9,642

2000

8700

2.63

1.97

It was found that the C.E.P.'s could be made smaller by pitching the missile during sustainer stage. The payloads associated with the minimum error trajectories were changed to allow the same range to be reached. These results are listed in the following table. It is obvious from the table that the decrease in error results in lower payload capability.

Range (Approx.)

Payload, lbs

C.E.P., n. miles

G.E. Mod III

ARMA

G.E. Mod III

ARMA

4750

5325

5700

0.34

1.03

5500

4850

4550

0.43

1.20

6900

3600

3C00

1.03

1.51

8700

1150

1500

2.23

1.86

It was also found that the maximum payload that can be sent to the 6900 and 8700 n. mile ranges were 3800 and 3000 lbs. As shown in the following table, this is at the expense of an increase in the C.E.P.. The location of the rate antenna would have to be changed if the G.E. System were used. The look angle requirements are not satisfied in the maximum payload trajectories.

Range (Approx.)
(n. miles)

Payload
(lbs)

C.E.P., (n. miles)

G.E. Mod III

ARMA

6900

3800

0.85

2.55

8700

3000

3.87

3.70

The values of the C.E.P.'s given in this report will be optimistic due to omission of various sources of impact dispersions for which the guidance system cannot predict or correct. The dispersions caused by the effects of geophysical, atmospheric re-entry, and cutoff uncertainties will be of the order of 0.5 n, miles; so the cases which indicate a guidance system C.E.P. of this magnitude will be affected significantly.

Pages 4 to 5

INTRODUCTION

This report deals with the range capability of the D series missile for various payloads and the guidance accuracies of both the radio-inertial (RIG) and all-inertial (AIG) guidance systems. The ranges considered were 4750 n. miles, 5500 n. miles, 6900 n. miles, and 8700 n. miles. Although the range capability may change for later series missiles due to changes or design improvements, (i.e., such as the change to MA-3 engines), the guidance error partials at the ranges considered In this study should not be affected greatly.

All of the cases presented herein use the same missile configuration; the only variables are the sustainer and vernier burnout weights and the second stage tilt program. The data for the report was obtained by using a missile trajectory simulation, as described in detail in Reference 1, and radio-inertial and inertial guidance error programs.

Two different guidance systems have been considered, the General Electric Mod. III radio-inertial and the ARMA all-Inertial systems. Errors in these systems lead to target misses, the size of the miss being dependent upon the magnitude of the error, the trajectory, and the distance to the target. The errors used to obtain the misses are the 1 sigma values as quoted by G.E. and ARMA. The target errors can be minimized by pitching during sustainer stage, as is shown later in the report. Target misses also result from sources other than the guidance system but these errors have not been considered in this report (e.g., re-entry winds, geophysical uncertainties, vernier cutoff errors, and atmospheric density variations).

DISCUSSION

Basic Trajectory Information

The trajectories simulated for this report are those of a nominal D series miscile launched due north from Vandenberg AFB. Every trajectory was based or a missile launch weight of 265,190 lbs., a booster jettison weight of 7,197 lbs., nominal thrust and specific impulse (i.e., booster and sustainer engines specific impulses were 251 seconds and 219.3 seconds), and a staging time of 135 seconds. In addition, the D series tilt program was attenuated by a factor of 0.97. The tracker simulated for the radio-inertial guidance (hereafter referred to as RIG) portion of the error study was for the G.E. Mod. III guidance system with the "q" baseline oriented directly downrange and the "p" crossrange.

Four trajectories were flown to establish the ranges at which the error studies were made. These four trajectories were simulated with a constant missile inertial attitude of 23.4° during sustainer stage. The only differences between the trajectories were the sustainer burnout weights, which were taken to be 13,642 lbs., 12,642 lbs., 11,142 lbs., and 9,642 lbs. These burnout weights apply to a D-R&D vehicle and correspond approximately to payloads of 6000 lbs., 5000 lbs., 3500 lbs., and 2000 lbs., respectively. A D-IOC missile is capable of carrying about 1100 lbs. more payload for comparable sustainer burnout weights.

An oblate (Clarke's spheroid of 1866), rotating earth model was assumed in the simulation. The ICA0 standard atmosphere was used during both powered flight and nose cone re-entry. To conserve computer time, a spherical earth and vacuum re-entry were assumed in finding the error partials. These approximations will cause little change in the partials since the errors are relative quantities.

PAGE 10

RESULTS

Range and Payload Capabilities

The maximum range of a missile carrying a payload of 6000 ,lbs., 5000 lbs., 3500 lbs., or 2000 lbs. was found to be 4766 n. miles, 5478 n. miles, 6889 n. miles, or 8724 n. miles respectively for missile trajectories in which a constant missile inertial attitude of 23.4° was maintained during sustainer stage. The RIG and AIG error studies were made at these ranges although, for the sake of brevity, the ranges are referred to as 4.750 n. miles, 5500 n. miles, 6900 n. miles, and 8700 n. miles.

PAGE 12

Comparison of RIG and AIG Systems

The constant attitude trajectories that were used for the RIG error study correspond exactly to the AIG trajectories in which a missile attitude of 23.4° was maintained. Comparison of the C.E.P.'s for these cases shows that the RIG system gives the smallest values, except at the extreme range of 8700 n. miles. The following table gives a concise summary of these result!.

Range

C.E.P.

RIG System

AIG System

4750

0.61

1.08

5500

0.44

1.25

6900

1.05

1.57

8700

2.63

1.97

PAGE 14

TABLE I
C.E.P, FOR RADIO-INERTIAL GUIDANCE SYSTEM

RANGE
NAUTICAL MILES

TILT RATE
DEG/SEC

C.E.P.
NAUTICAL MILES

4750

-0.10

0.34

4750

-0.05

0.43

4750

0.00

0.61

4750

+ 0.05

0.91

4750

+ 0.10

1.45

5500

-0.10

0.55

5500

-0.05

0.43

5500

0.00

0.44

5500

+ 0.05

0.64

5500

+ 0.10

1.10

6900

-0.10

1.11

6900

-0.05

1.09

6900

0.00

1.05

6900

-0.05

0.98

6900

+ 0.10

0.89

8700

-0.10

1.91

3700

-0.05

2.23

8700

0.00

2.63

8700

+0.05

3.08

8700

+0.10

3.89

PAGE 15

TABLE II
C.E.P. FOR ALL-INERTIAL GUIDANCE SYSTEM

RANGE
NAUTICAL MILES

ATT ITUDE
DEGREES

C.E.P.
NAUTICAL MILES

4750

31.1

1.03

4750

23.4

1.08

4750

15.8

1.19

5500

31.1

1.20

5500

23.4

1.25

5500

15.8

1.41

6900

31.1

1.51

6900

23.4

1.57

6900

15.8

1.83

6900

9.9

2.27

6700

31.1

1.91

8700

2 3.4

1.97

6700

15.8

2.37

8700

8.0

3.23