Imaging experiment on board the NERVA-1 rocket vehicle.
Rugescu, Dragos Radu Dan ; Simion, Ionel ; Dobre, Daniel 等
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'
