21.04.2013 Views

ETTC'2003 - SEE

ETTC'2003 - SEE

ETTC'2003 - SEE

SHOW MORE
SHOW LESS

You also want an ePaper? Increase the reach of your titles

YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.

BACK<br />

STUDY OF 3∆t PASSIVE LOCATING SYSTEM<br />

Xie Nan and Chen Da-Hai<br />

Electronic Engineering Institute of China Academy of Engineering Physics<br />

P.O.BOX 919-517, Mianyang, Sichuan, P.R.China<br />

Zip Code: 621900 Tel: +86 816 2487524 Fax: +86 816 2487594 E-mail:xienanlx@hotmail.com<br />

ABSTRACT<br />

The reentry low altitude vehicle locating technology based on 3∆t passive locating principles is<br />

discussed in this paper. At first its basic principle is introduced, and we discuss the sources of errors in<br />

the existing telemetry system and corresponding precision. Some methods, which are used to improve<br />

the precision, are proposed at the end of this paper.<br />

KEY WORDS<br />

Reentry, Telemetry System, 3∆t Passive Locating, Error<br />

INTRODUCTION<br />

In the reentry measurement, one of our missions is to measure the track and the point of fall of the<br />

reentry vehicle. It can be named reentry-locating technology. In general, radar can be used to locate the<br />

track and the point of fall of aircraft. It locates the position of aircraft by measuring the azimuth, the<br />

elevation and the distance. The optical measurement is also used sometimes. The precision and the<br />

accuracy of these methods are satisfying. In the reentry-locating measurement, the reentry vehicle is<br />

different from any other aircrafts. During the reentry, it will pass the blackout area. The<br />

telecommunication will be interrupted in this area. After the vehicle going out of the area, the speed of it<br />

is very high and the altitude is very low. So above-mentioned systems can’t capture the target before it<br />

fell to the ground. These systems are not suitable for the reentry vehicle track measurement.<br />

Another system, which is called 3R-locating system, can be used in the track measurement of reentry<br />

vehicle. It needs at least three ground stations A, B, C and locates the position of vehicle by measuring<br />

the distance between the vehicle and each of the respective stations. The stations sent query signals to<br />

reentry vehicle and received the responses. The time of propagation from each of the respective stations<br />

to the vehicle, i.e., the time to travel the distances, , and r , are computed. The distance<br />

r C r is<br />

rA B<br />

given by r = τ ⋅ c , where c is the velocity of light. Then the position can be located. This system<br />

works in active mode. The result of test is not satisfying. So we need a useful system to realize the<br />

locating of reentry vehicle.<br />

In this paper, the 3∆t passive locating system is introduced. It needs at least four ground stations. In this<br />

system, the ground stations don’t send any signals; they receive the common telemetry signal, for<br />

example the frame synchronization signal, from the reentry vehicle and record the time of arrival.<br />

Because the time when the signal was sent is unknown, one more station is needed in 3∆t system than in<br />

3R system. Three time differences are given by ∆ ti = ti<br />

− ti+<br />

1 , ( i = 1,<br />

2,<br />

3)<br />

, where ti<br />

is the time of

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!