Use of a telephone data link in statospheric balloon flights

Adv. Space Res. Vol. 7, No. 7, pp. (7)95—(7)96, 1987 Printed in Great Britain. All rights reserved.

0273—1177/87 SO.OO+.50 Copyright © COSPAR

USE OF A TELEPHONE DATA LINK IN STATOSPHERIC BALLOON FLIGHTS C. Bannelier and A. Soubrier Division Ballons, Centre National d’Etudes Spatiales, 18, avenue E. Belin, 31055 Toulouse Cedex, France

A down—range telephone data and Command link has been used for the two years now in the Transmediterranean Flights. This paper presents the performances of the system and the results obtained on the occasion of actual Flights. Long duration Flights with drifting Stratospheric balloons imply the use of down—range telemetry stations in order to provide a permanent tracking of the balloon in flight. Although all the stations may be equally equiped and operated by an equal number of servants to insure the control of both the balloon and the gondola, an alternative solution may be set up, allowing substantial savings in staff and equipments, and resulting in a much larger efficiency Opposed to the problem in the metropolitan summer flights (2 stations) or in the trarismédi— terranean flights (3 stations), CNES has developped a system of data transmission thru a telephone link. Successfully tested in 1984 and 1985, this system is ready to be fully ope— rationnal for the 1986 Transmediterranean flights campaign, where it will be used between Spain and Sicily. It works as follows The “mother station” is linked to the down—range station thru a pair of dedicated telephone lines devoted to data transmission, with a capability of 9600 bits/sec each. The system operates in full duplex, allowing the mother station to receive the telemetry signals from the balloon, relayed by the down—range station, and send thru the same relay, commands to the balloon. The down—range equipment is set up and operated directly from the mother station. Prime advantage of the system, the scientist is able to control and operate his experiment from a single point, in which he may concentrate all his ground equipment. The transmission is performed according to a HDLC (High level Data Link Control) synchronous bit oriented protocole. Data are transmitted in a digital form transcoded in 8 bits words (or 8 bits multiples) and arranged in any array including 2048 words or less. The system includes six imput—output ports. Each one of these ports is able to handle messages up to a 40 kbits/sec rate, in a synchronous mode, and 20 kbits/sec in an asynchronous mode. If the total ted, without the data are performed in

input flow rate is less than the line capability, the data are fully transmitany change in rate or structure. If the input flow exceeds the line capability processed and the rate reduced to a compatible value. This reduction can be two ways

The first method, the simplest one, consists in transmitting only one out of n arrays. The structure remains unchanged, and the output flow appears to be the same. Only the rate i8 reduced to a ratio of 1 to n with respect to the input flow. The second method is more sophisticated. All the arrays are transmitted, only some words are omitted. On the reception end, the data are presented according to the same original array the untransmitted words are only replaced with blanks. The choice of the left—over data depends only upon the customer needs. They can be changed very easily, at any time, during the transmission. The only constraint is to keep the input flow rate, below the transmission capability of the telephone line. The transmission of commands towards the balloon suffers no restriction, as its bit rate is far below the limit. Besides the transmission of data in both directions, the system allows a dialogue between station operators. The messages are written in clear form, but their transmission is delayed, and authorized by the processor, only when the data flow is sufficiently low to remain urn— perturbed. (7)95

(7)96

C. Bannelier and A. Soubner

As it has been described, this system has been satisfactorily tested in 1985 between Spain and Italy. Its main limitations remains the flow rate which imposes in several cases a selection of the data transmitted with a high bit rate from the balloon. Even limited, however, this flow proved to be sufficient to control any experiment, even the most sophisticated. In any case, no lost occurs in the informations coming from the gondola, as the original signal is fully recorded in the station in sight of the balloon. This limitation results mainly from the modems introduced between the data processor and the telephone line. New modems however appeared recently which might sustantially improve the performances of the system in increasing by more than 50 % the maximum flow rate. They might be tested during the forthcoming campaign.

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