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Imaging experiment on board the NERVA-1 rocket vehicle.

1. INTRODUCTION

The NERVA-1 experiment was performed on June 15, 2010 and consisted in the real flight measurement of the six degree of freedom motion of a drone rocket vehicle built by Electromecanica S. A. Romania, the partner of the NERVA project consortium, through simple modification of the military Volkhov anti-aircraft missiles of the Romanian Air Force. The drone, currently called "RT-759M", is in fact a Volkhov vehicle where the second stage, the sustainer, is kept dry and this way not fired, with the first, booster stage as the only powering unit of the rocket (Fig. 1). A short flight trajectory within a range of 20 km is thus obtained, with an extension right enoughf to be used as a mobile target for the actual SA-2 missiles during annual training campaigns of the RAF at the Cape Midia NATO test range on the western Black Sea bank. A large payload is thus available in the fuselage of the second stage of the RT-759M rocket and a small, 200 grams payload consisting of the inertial platform, powering battery and TV camera were easily accomodated into this large space. The position of the TV set is on a 45 [degrees] direction of sight, bacward looking, towards the nozzle exit of the solid motor booster and at 45 [degrees] orientation between the transversal axes of the on-board referential. The basic observation is that the booster flight of the NERVA launcher (Rugescu 2008, Tache et al. 2009) and the mechanical loads are almost identical to those on RT-759M.

[FIGURE 1 OMITTED]

Worth mentioning that the NERVA-1 experiment is the first in-flight measurement and data telemetry ever performed in Romania and a tight plan of preparation was set-up in order to surpass the concernes regarding the reliability of the measuring equipment during this genuine test.

The paper is focused on presenting the results of the image processing for extracting the roll rate and the global attitude of the NERVA-1 vehicle during the powered and coast flight.

The nominal flight trajectory of the experiment extentded up to a maximal altitude of 7 km and with a total range of 18 km, into a launching vertical plane positioned at 112 [degrees] geographycal azimuth over the Black Sea.

2. THEORETICAL CONSIDERATIONS

The paper is devoted to applying the methods of descriptive geometry and presents a graphic solution for the problem of finding the angle of attack of the rocket vehicle corresponding to each location on the presumed flight trajectory of the rocket.

For this purpose we have to run through the following steps:

* to determine the coordinates [u.sub.i] and [h.sub.i] of the mass center at successive moments of time [t.sub.i] recorded by the digital camera placed on-board the rocket vehicle;

* to determine the ellipse resulted at the intersection of the visualizing cone with the horizontal-projecting plane (plane of zero quota-Fig. 2);

* to determine the angle [gamma] between the axis of the visualizing cone and the horizontal line;

* to determine the angle [alpha] between the longitudinal axis of the rocket during its descent through Earth atmosphere and a parallel to the Ox axis, in the current point on the trajectory.

A sample view from the onboard movie is given in Fig. 3.

[FIGURE 2 OMITTED]

[FIGURE 3 OMITTED]

The visualisation cone of the TV camera placed on the rocket determines in the horizontal-projecting plane:

* an ellipse when the plane intersects all the generatrices of the cone and yet is not perpendicular to the axis of the cone;

* a fragment of a hyperbola when the plane only intersects a few generatrices of the cone.

To build the horizontal projection of the ellipse a series of planes, perpendicular to the cone axis, are drawn, each of which intersects the cone along a circle and the horizontal-projecting plane in a horizontal perpendicular to the frontal plane. At the intersection of the horizontal projections of the horizontals with the horizontal projections of the corresponding circles, the current points of the ellipse are obtained.

The true size of the ellipse is given by the method of coincidence (Pare at al., 1997).

3. MEASUREMENTS AND RESULTS

Visual field of camera is a right circular cone with the tip angle of 60 [degrees]. By assumption, the roll axis of the rocket frame remains in the launching plane (Fig. 4). Images recorded by the camera during the flight revealed the following aspects (Fig. 5):

* the current position in respect to the launching site;

* time value at which this position is recorded;

* position of the cone axis (angle [gamma]), determined by the vertex of the cone (the current point on the trajectory) and the center of the rectangular image of the TV camera.

[FIGURE 4 OMITTED]

[FIGURE 5 OMITTED]

Equations that suply the inclination of the vehicle during its descent flight are:

tan [gamma] = h / [u.sub.B] - [u.sub.A] (1)

[gamma] [tan.sup.-1] h / [u.sub.B] - [u.sub.A] (2)

[alpha = 45 [degrees] - [gamma] (3)

The altitude and the corresponding angle of attack have been determined and entered in Table 1.

4. CONCLUSION

The direct geometrical method applied to compute the attitude angle (angle of attack) of the flying vehicle along the trajectory proves simple and reliable, involving a minimal number of computational steps. The method is simple and fast enough to be considered for implementation into an automatic, real time procedure of attitude snesing during the whole plight of the orbital launcher NERVA.

The only problem that remains to be futher investigated and solved is related to the transmission reliability of the radio chain in order to cover a much wider range of up to 2000 km in horizontal direction for real-time data telemetry.

5. ACKNOWLEDGEMENTS

The work was performed by University "Politehnica" of Bucharest, Romania with the financial support of the NERVA grant, financed by the Romanian Ministry of Education, Research, Youth and Sports, within the frames of Program P-4.

6. REFERENCES

Pare, E.G.; Loving, R.O. & Hill, I.L. (1997). Descriptive Geometry, 9th ed. Prentice-Hall, ISBN 0-02-391341-X, N.J.

Neelamani, Ramesh (2004), Inverse problems in image processing, PhD Thesis, Rice University, 135 p.

Alexander, G. R. (ed. 1998), Inverse Problems, Tomography and Image Processing, Plenum Press ISBN 0-306-45828-4. Niblack, W., An Introduction to Digital Image Processing, Prentice-Hall International (UK) Ltd, London, England, 1986.

Rugescu, R. D. (2008), NERVA Vehicles, Romania's Access to Space, Scientific Bulletin of U. P. B., Series D in Mechanics, 70, no. 3, p. 31-44.

Tache, F.; Bogoi, A. & Rugescu, R. D. (2009). Airflow study on the NERVA space launcher aileron, Proceedings of the 20th International DAAAM Symposium, Katalinic, B. (Ed.), pp. 0527-0528, ISSN 1726-9679, November 2009, Vienna.
Table 1. Results and measurements

t [s] [u.sub.B] [m] [u.sub.A] [m] h [m]

34.21 7550 2100 4800
34.32 7550 2050 4750
44.4 9070 670 3750
45.11 9270 570 3600
46.05 9380 600 3540
54.91 10080 620 2500

 [gamma] [alpha]
t [s] [[degrees]] [[degrees]]

34.21 41[degrees]20' 3[degrees]40'
34.32 40[degrees]45' 4[degrees]15'
44.4 24[degrees]5' 20[degrees]55'
45.11 22[degrees]25' 22[degrees]35'
46.05 22[degrees] 23[degrees]
54.91 13[degrees]10' 31[degrees]50'
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Article Details
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Author:Rugescu, Dragos Radu Dan; Simion, Ionel; Dobre, Daniel; Lorincz, Istvan
Publication:Annals of DAAAM & Proceedings
Article Type:Report
Geographic Code:4EXRO
Date:Jan 1, 2010
Words:1206
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