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New systems for extending the useful float duration of standard zero-pressure balloon flights
Adv.Spac~ .~es.Vo1.3,No.6,pp.29—32,l983 Printed in Great Britain.Al1 rights reserved.
0273—1177/83 $0.00 + .50 Copyright © COSPAR
NEW SYSTEMS FOR EXTENDING THE USEFUL FLOAT DURATION OF STANDARD ZERO-PRESSURE BALLOON FLIGHTS S. Holder and D. Ramsden Department of Physics, University of Southampton, Southampton, England
ABSTRACT A model payload to test our proposals for a cryogenic gas replenishment system is described. The details of a telecommunications relay capable of receiving the complex video signal transmitted at L—band from a scientific balloon at a range of 1200 km are also presented. INTRODUCTION In many branches of science there is a strong demand for longer balloon flights than are normally available from existing launch facilities. For example, the power of some new hard Xray telescopes is such that the number and variety of objects that are now in reach of observation are at such a level that the scientific returns from a balloon flight is only limited by the length of time that the balloon can be maintained at a good altitude and within telemetry range. Even when careful efforts are made to select the most promising wind conditions at turn-around, it is rare for balloon flights to extend beyond 24 hours. If flights lasting a few days could be achieved routinely, not only would the scientific returns on the effort expended be greatly improvedbut the cost-effectiveness of the research programme would also be significantly enhanced. The problems associated with the achievement of long duration balloon flights fall into tw~ general categories (a)
The development of a balloon system capable of maintaining a good stable float altitude following sunset. (b) The development of techniques that will enable a good telemetry and telecommand link to be maintained between the experimenter and his scientific payload once it has crossed the radio horizon. In view of our own scientific interest in achieving both of these goals for X- and ~y-rayastronomy we have undertaken two new technological developments which will hopefully go some way to fulfilling our needs and may also be of value to our colleagues as well. This paper describes a new cryogenic gas replenishment system which is due to have its first test flight within a few weeks and a comprehensive telecommunications relay payload which was first tested in April 1981. CRYOGENIC GAS REPLENISH~NTSYSTEM A number of different balloon systems have been proposed which are designed to achieve the goal of long duration flights. The status of those developments which depend upon the particular features of super—pressure balloons to preserve a stable float altitude, either when used alone or in combination with a zero—pressure balloon, was to have been a subject of a separate review at this meeting. These important developments have necessitated the production of new materials, new balloon designs, and new launch methods. Hopefully, the NSBF Sky Anchor System will soon be routinely available for scientific groups needing long duration flights. Our approach is to use established zero—pressure balloon designs and technology and to maintain float altitude at night by adjusting the rate of addition of helium to the balloon from a liquid helium dewar. Whilst this idea, in principle, dates back to the early work carried out during the 1950’s in Minneapolis, the concept of cryogenic gas replenishment was re-evaluated by Ramsden and Baker (1) and Carten (2,3). Following our experience with three conventionally ballasted balloon flights across the Atlantic we concluded that a too small a fraction of the balloon payload could be made available for the scientific payload if one wants to ensure that the balloon floats reliably for at least five days. The advantage offered by the cryogenic system is illustrated in Fig.1. It ~hou1d be noted that this graph is based on the predicted performance of a hypothetical but hopefully realistic, 2000 litre liquid helium dewar design. Whilst, for some experiments, 10 day flights with scientific payloads weighing 500 kgare a very degirable objective, the cryogenic system could also be used to keep a larger, or heav29
30
S. Holder and 0. Ramsden
Boo
ier flight at float altitude for longer than is currently possible.
7~
We received funding to build a model cryogenic system with the object of discovering,
I
I
a) ~ 600
0/
10 ~ b) 8°
What, if any, are the problems in building a microprocessor control system to dispense helium at the right rate in order to neutrause the loss in buoyancy during, and after Sunset. How serious are the problems of devising ways of injecting the cold helium into the balloon in such a way as not to damage the polythene.
For these tests a standard stainless steel 350 litre dewar is being used and no attempt has been made to combine a scientific payload with 5m3 technological balloon is todevelopment be used forflight. this first this A small, 10 flight so that the payload should float at an 200 I 10 altitude close to 5 mb. In order to avoid over0 2 4 6 8 reacting to short—term altitude fluctuations, FUGHT DURATION (days) changes in the mean altitude (Aj) of the balloon are computed every 15 minutes and the amount of Fig.l. Estimated scientific payload weight gas that should be fed into the balloon is comavailable as a function of flight duration forPuted according to the following expression, a) conventional ballast and b) a cryogenic — system (based on data for a 7x105m3). Q k(A~ - A 1) - C 10%
where k is a constant of the proportionality which is defined by the size and weight of the balloon system and the degree of altitude stability required. The constant C sets a threshold value which must be exceeded before any helium is dispensed. This enables one to safeguard against continual small bursts of helium being demanded. Previous experience Showed that such an automatically controlled ballast system will make demands regularly during the afternoon period whilst its major demand will, of course, occur within about 40 minutes of sunset. at 6 litres peratminute full—scale version. These considerations indicated5m3 theflight need and to vaporise helium a ratefor of the about 1 litre of liquAid 40per watt heater close to the bottom of the dewar and heat is applied in one second minute for isthelocated model 10 bursts until ‘the pressure in the dewar exceedea pre—set lower threshold. The electromagnetic valve in the balloon line is them opened and gas starts to flow. The dewar pressure is monitored continuously and the heater sequence is interrupted if the pressure should exceed a second threshold. A second electromagnetic valve discharges helium gas to waste if, for some reason, the pressure should continue to rise. This is itself backed up by a mechanical relief valve and a bursting disc in order to ensure the safety of the system. A superconducting dipstick and a software integral of the energy deposited in the devar provide independent checks on the quantity of liquid vaporised. Whilst the amount of energy required to vaporise liquid helium at the correct rate is very small, as much as 2 kW would be required in order to warm the gas before its injection into the balloon at ambient temperature. The possibility of using an external heat-exchanger was explored but the heat input available from the ambient atmosphere at an altitude of 40 km was so low as to make it impracticable. An alternative approach has been followed to ensure that cold helium gas does not come into contact with the fabric of the balloon. A series of laboratory tests using liquid nitrogen were conducted in order to study the possibility’ of stimulating vigorous turbulent mixing between the incoming cold gas and the gas within the balloon. A supersonic jet of cold gas was produced from the dewar and the temperature at points along the axis of the jet was measured as a function of ambient pressure Fig 2. These tests indicated that the temperature of the jet increased rapidly as a result of turbulent mixing. Extrapolation to 5 mb of the data obtained in a 1 metre cube environmental chamber down to pressures of the order of 50 mb indicated that the gas jet would warm by 200 K within a distance of less than 1 metre. We have therefore designed a simple stainless steel tubular fitting for the base of the balloon which will raise the injection nozzle to a height of about 2 metres above the base fitting. This probe is sheathed in ethaform to avoid abrasion during handling prior to launch. Gas will only be injected when the balloon is near fullyinflated. The vertical motion of the jet will stimulate some circulation of the gas within the balloon with the result that the cool mixture will be in contact with a very large heat exchanger
Standard zero—pressure balloon flights
31
provided by the base of the balloon itself. It is difficult to be precise about the dimensions of the circulation cell but the estimated surface area the will balloon which is likely be in 2. of This be warmed both by theto rather contact with the cool gas will be in excess of 100 m inefficient convective heat transfer process and also by radiation. Thermistors have been placed along one of the gores in order to measure the fabric temperature in the lower part of the balloon. Other temperature sensors are located in the bottom—end fitting of the balloon and in the gas injection tube. The temperature of the helium gas at two points on the vertical axis will also be recorded during the flight. The dewar itself is mounted in a tubular crash protection frame and is close coupled to the bottom end fitting of the balloon by a flexible stainless steel tube. The model dewar system is scheduled for its first flight in June 1982 and, provided that no fundamental snags are encountered we inhope to have a full scale version ready for testing 1983. We are cur-
60
rently studying ways of combining this cryogenic systern with a satellite data communications terminal so as to provide a complete service to scientific users who are interested in flights lasting 8/10 days with data rates at the level of 2—4 kilobit per seconds.
22rrv~~ Nozzle Ftow~0.67ttr/mw~
30 20
io
1.Onyn
~
TELECOMMUNICATIONS RELAY
Flo,,oCtO8ttr/mifl At the COSPAR Scientific Balloon Symposium in Inns____________________________________ bruck a proposal for the development for a balloonU borne telecommunications relay was presented (4). A A~E similar system was also described by Nishimura (5).
The objective of the proposal was the development of an autonomous balloon system that could relay the Fig.2. Distance from nozzle to the complex signal radiated by the standard NSBF balloon point at which gas has warmed to zero instrumentation package. This provides a combination centigrade. of FM/FM and PCM/FM telemetry systems for scientific and operational use. It was envisaged that the relay system should be constructed in such a way that it should be transparent to the user that the data he receives is no longer coming directly from his payload but via the relay. Similarly, it was planned that the relay should offer the ability to receive, and retransmit from high altitude, command signals compatible with the NSBF standard. The distance to the radio horizon as a function of the altitude of the transmitting and receiving antennae may be determined from the nomogram shown in Fig.3. From this it is clear 2000 that if a small balloon carrying a telemetry tr1700ansponder were flown at an altitude in excess of —50 . 50 about 27 km, data could be retrieved from a scientific balloon,at a range of at least 1200 km. 1500If the balloon relay were to drift towards a rad—40 40— io horizon in the same general direction as a E scientific balloon then useful ranges of up to E -1500 1800 km from the ground station would be achieved—30 . —. 30 ~.The technical feasibility of such a relay system was demonstrated in a test flight conducted in March 1981. If flights launched, for example, ~ ~ H 20from Alice Springs in Australia were allowed to continue until they reached the east or western _,ooot~ 15 coastal zones, then flights in excess of 50 hours should be attainable throughout a period of eight ~ 40— weeks. At times within this launch window much ~ longer flights should be achievable. - . ~ The telecommunications relay payload is shown in
5
o
500—
-
1 0.5
300 200 100
.
.400 303 .
.
~oo
~
1
. .
o~
103 —
Fig.4 and consists of three main items.
.
~oo-
.
Fig.3. Nomogram for determining the dis tance to the radio horizon as a function of the altitudes of the transmitting and receiving antennae,
I—
Firstly
a light weight dish antenna which has a gain of 26 dE at not 1.5 GHz, packagetranspondwhich contains only an the electronics L-band telemetry er hut also the microprocessor which controls the payload, and an azimuth control motor and reaction wheel. A radiated power of more than 1.5 watt from the scientific payload should ensure an adequate signal—to-noise ratio at the receiver when the distance to the relay is 1200 km. The signal from the antennae passes through two multistage filters and a wide band preamplifier before being detected by the receiver. In addition to provi-
32
S. Holder and D. Ramsden ding the base—band signal in a form that can be mixed again with a locally generated sub—carrier and re— transmitted, the receiver also provides an indication of the received signal strength which is useful in the antenna control system. The antenna must be pointed with a precision of ±10 in order to receive a good signal at maximum range. loop required to mainREACTION The tam control stabilisation is generated by MOTOR software. The angle derived from
)~MIXER~NSMI~J’
__________
M~GNETOMETERrL....... —~ I DIGITAL I
PR~’~1AZIM~J____
QUAD I/p
____________
4
QUAD 0/P
TX~R
~ BALLAST HOPPER
______
___
TIMER BALLAST (SThTSOT. DATA TN’T’PR5A(~
MOTOR
cinwrROT. ADC POWER SUPPLY
‘
the digital azimuth system, based on flux gate magnetometers, is com— pared with the required ta,rget az— imuth and the error signal proportional to the difference is output from a DAC to the reaction motor. Various methods of azimuth control are available including an ‘auto— seek and acquire’ facility.
All valid coi~ands received by the conmiand relay module are issued to QUAD I/P the microprocessor system. The MICROPROCESSOR SYSTEM software then decodes them to decide if any local action is necessFig.4. Block diagram of rei.ay system. ary. A total of 64 discrete commands are available, of which commands 0 to 20 octal are used by the relay and should therefore be avoided by the experimenter. After a small delay the transceiver is switched into transit mode and the FSK signal is relayed to the experimenters balloon using a 6 watt output. It should be noted that when both balloons are within range of the ground installation the experimenter will receive the same command twice. Because of this delay imposed by the relay, commands may be sent at a maximum rate of once every six seconds. SBC
LATCH/ECHO
CONCLUSION By using a combination of the techniques described above we look forward to achieving longer flights with heavy scientific payloads. Of launched from a cnidcontinental location close to turn-around, a full telecommunications link through the relay should provide a wide bandwidth data link and command capability for the entire flight. Alternatively, the cryogenic system should enable experiments weighing typically 500 kg to be maintained above 3mb for 8/10 days. REFERENCES 1. 2. 3. 4. 5.
,
D. Ramsden, R.E. Baker, Scientific Ballooning (COSPAR) W. Riedler Ed. Pergaznon Press 1979. A.S. Carten Jr., C.F. Sindt. AFGL-TR-79—0278 (1979) A.S. Carten Jr., C.F. Sindt. Paper 1.2.2. Workshop on Instrumentation and Technology for Scientific Ballooning. COSPAR, Ottawa(1982). D. Ramsden, R.E. Baker, R.W. King. Scientific Ballooning (cOSPAR). W.Riedler Ed. Pergamon Press (1979). U. Hirosawa, J. Nishimura. Scientific Ballooning (COSPAR). W.Riedler Ed. Pergamon Press (1979).
0273—1177/83 $0.00 + .50 Copyright © COSPAR
NEW SYSTEMS FOR EXTENDING THE USEFUL FLOAT DURATION OF STANDARD ZERO-PRESSURE BALLOON FLIGHTS S. Holder and D. Ramsden Department of Physics, University of Southampton, Southampton, England
ABSTRACT A model payload to test our proposals for a cryogenic gas replenishment system is described. The details of a telecommunications relay capable of receiving the complex video signal transmitted at L—band from a scientific balloon at a range of 1200 km are also presented. INTRODUCTION In many branches of science there is a strong demand for longer balloon flights than are normally available from existing launch facilities. For example, the power of some new hard Xray telescopes is such that the number and variety of objects that are now in reach of observation are at such a level that the scientific returns from a balloon flight is only limited by the length of time that the balloon can be maintained at a good altitude and within telemetry range. Even when careful efforts are made to select the most promising wind conditions at turn-around, it is rare for balloon flights to extend beyond 24 hours. If flights lasting a few days could be achieved routinely, not only would the scientific returns on the effort expended be greatly improvedbut the cost-effectiveness of the research programme would also be significantly enhanced. The problems associated with the achievement of long duration balloon flights fall into tw~ general categories (a)
The development of a balloon system capable of maintaining a good stable float altitude following sunset. (b) The development of techniques that will enable a good telemetry and telecommand link to be maintained between the experimenter and his scientific payload once it has crossed the radio horizon. In view of our own scientific interest in achieving both of these goals for X- and ~y-rayastronomy we have undertaken two new technological developments which will hopefully go some way to fulfilling our needs and may also be of value to our colleagues as well. This paper describes a new cryogenic gas replenishment system which is due to have its first test flight within a few weeks and a comprehensive telecommunications relay payload which was first tested in April 1981. CRYOGENIC GAS REPLENISH~NTSYSTEM A number of different balloon systems have been proposed which are designed to achieve the goal of long duration flights. The status of those developments which depend upon the particular features of super—pressure balloons to preserve a stable float altitude, either when used alone or in combination with a zero—pressure balloon, was to have been a subject of a separate review at this meeting. These important developments have necessitated the production of new materials, new balloon designs, and new launch methods. Hopefully, the NSBF Sky Anchor System will soon be routinely available for scientific groups needing long duration flights. Our approach is to use established zero—pressure balloon designs and technology and to maintain float altitude at night by adjusting the rate of addition of helium to the balloon from a liquid helium dewar. Whilst this idea, in principle, dates back to the early work carried out during the 1950’s in Minneapolis, the concept of cryogenic gas replenishment was re-evaluated by Ramsden and Baker (1) and Carten (2,3). Following our experience with three conventionally ballasted balloon flights across the Atlantic we concluded that a too small a fraction of the balloon payload could be made available for the scientific payload if one wants to ensure that the balloon floats reliably for at least five days. The advantage offered by the cryogenic system is illustrated in Fig.1. It ~hou1d be noted that this graph is based on the predicted performance of a hypothetical but hopefully realistic, 2000 litre liquid helium dewar design. Whilst, for some experiments, 10 day flights with scientific payloads weighing 500 kgare a very degirable objective, the cryogenic system could also be used to keep a larger, or heav29
30
S. Holder and 0. Ramsden
Boo
ier flight at float altitude for longer than is currently possible.
7~
We received funding to build a model cryogenic system with the object of discovering,
I
I
a) ~ 600
0/
10 ~ b) 8°
What, if any, are the problems in building a microprocessor control system to dispense helium at the right rate in order to neutrause the loss in buoyancy during, and after Sunset. How serious are the problems of devising ways of injecting the cold helium into the balloon in such a way as not to damage the polythene.
For these tests a standard stainless steel 350 litre dewar is being used and no attempt has been made to combine a scientific payload with 5m3 technological balloon is todevelopment be used forflight. this first this A small, 10 flight so that the payload should float at an 200 I 10 altitude close to 5 mb. In order to avoid over0 2 4 6 8 reacting to short—term altitude fluctuations, FUGHT DURATION (days) changes in the mean altitude (Aj) of the balloon are computed every 15 minutes and the amount of Fig.l. Estimated scientific payload weight gas that should be fed into the balloon is comavailable as a function of flight duration forPuted according to the following expression, a) conventional ballast and b) a cryogenic — system (based on data for a 7x105m3). Q k(A~ - A 1) - C 10%
where k is a constant of the proportionality which is defined by the size and weight of the balloon system and the degree of altitude stability required. The constant C sets a threshold value which must be exceeded before any helium is dispensed. This enables one to safeguard against continual small bursts of helium being demanded. Previous experience Showed that such an automatically controlled ballast system will make demands regularly during the afternoon period whilst its major demand will, of course, occur within about 40 minutes of sunset. at 6 litres peratminute full—scale version. These considerations indicated5m3 theflight need and to vaporise helium a ratefor of the about 1 litre of liquAid 40per watt heater close to the bottom of the dewar and heat is applied in one second minute for isthelocated model 10 bursts until ‘the pressure in the dewar exceedea pre—set lower threshold. The electromagnetic valve in the balloon line is them opened and gas starts to flow. The dewar pressure is monitored continuously and the heater sequence is interrupted if the pressure should exceed a second threshold. A second electromagnetic valve discharges helium gas to waste if, for some reason, the pressure should continue to rise. This is itself backed up by a mechanical relief valve and a bursting disc in order to ensure the safety of the system. A superconducting dipstick and a software integral of the energy deposited in the devar provide independent checks on the quantity of liquid vaporised. Whilst the amount of energy required to vaporise liquid helium at the correct rate is very small, as much as 2 kW would be required in order to warm the gas before its injection into the balloon at ambient temperature. The possibility of using an external heat-exchanger was explored but the heat input available from the ambient atmosphere at an altitude of 40 km was so low as to make it impracticable. An alternative approach has been followed to ensure that cold helium gas does not come into contact with the fabric of the balloon. A series of laboratory tests using liquid nitrogen were conducted in order to study the possibility’ of stimulating vigorous turbulent mixing between the incoming cold gas and the gas within the balloon. A supersonic jet of cold gas was produced from the dewar and the temperature at points along the axis of the jet was measured as a function of ambient pressure Fig 2. These tests indicated that the temperature of the jet increased rapidly as a result of turbulent mixing. Extrapolation to 5 mb of the data obtained in a 1 metre cube environmental chamber down to pressures of the order of 50 mb indicated that the gas jet would warm by 200 K within a distance of less than 1 metre. We have therefore designed a simple stainless steel tubular fitting for the base of the balloon which will raise the injection nozzle to a height of about 2 metres above the base fitting. This probe is sheathed in ethaform to avoid abrasion during handling prior to launch. Gas will only be injected when the balloon is near fullyinflated. The vertical motion of the jet will stimulate some circulation of the gas within the balloon with the result that the cool mixture will be in contact with a very large heat exchanger
Standard zero—pressure balloon flights
31
provided by the base of the balloon itself. It is difficult to be precise about the dimensions of the circulation cell but the estimated surface area the will balloon which is likely be in 2. of This be warmed both by theto rather contact with the cool gas will be in excess of 100 m inefficient convective heat transfer process and also by radiation. Thermistors have been placed along one of the gores in order to measure the fabric temperature in the lower part of the balloon. Other temperature sensors are located in the bottom—end fitting of the balloon and in the gas injection tube. The temperature of the helium gas at two points on the vertical axis will also be recorded during the flight. The dewar itself is mounted in a tubular crash protection frame and is close coupled to the bottom end fitting of the balloon by a flexible stainless steel tube. The model dewar system is scheduled for its first flight in June 1982 and, provided that no fundamental snags are encountered we inhope to have a full scale version ready for testing 1983. We are cur-
60
rently studying ways of combining this cryogenic systern with a satellite data communications terminal so as to provide a complete service to scientific users who are interested in flights lasting 8/10 days with data rates at the level of 2—4 kilobit per seconds.
22rrv~~ Nozzle Ftow~0.67ttr/mw~
30 20
io
1.Onyn
~
TELECOMMUNICATIONS RELAY
Flo,,oCtO8ttr/mifl At the COSPAR Scientific Balloon Symposium in Inns____________________________________ bruck a proposal for the development for a balloonU borne telecommunications relay was presented (4). A A~E similar system was also described by Nishimura (5).
The objective of the proposal was the development of an autonomous balloon system that could relay the Fig.2. Distance from nozzle to the complex signal radiated by the standard NSBF balloon point at which gas has warmed to zero instrumentation package. This provides a combination centigrade. of FM/FM and PCM/FM telemetry systems for scientific and operational use. It was envisaged that the relay system should be constructed in such a way that it should be transparent to the user that the data he receives is no longer coming directly from his payload but via the relay. Similarly, it was planned that the relay should offer the ability to receive, and retransmit from high altitude, command signals compatible with the NSBF standard. The distance to the radio horizon as a function of the altitude of the transmitting and receiving antennae may be determined from the nomogram shown in Fig.3. From this it is clear 2000 that if a small balloon carrying a telemetry tr1700ansponder were flown at an altitude in excess of —50 . 50 about 27 km, data could be retrieved from a scientific balloon,at a range of at least 1200 km. 1500If the balloon relay were to drift towards a rad—40 40— io horizon in the same general direction as a E scientific balloon then useful ranges of up to E -1500 1800 km from the ground station would be achieved—30 . —. 30 ~.The technical feasibility of such a relay system was demonstrated in a test flight conducted in March 1981. If flights launched, for example, ~ ~ H 20from Alice Springs in Australia were allowed to continue until they reached the east or western _,ooot~ 15 coastal zones, then flights in excess of 50 hours should be attainable throughout a period of eight ~ 40— weeks. At times within this launch window much ~ longer flights should be achievable. - . ~ The telecommunications relay payload is shown in
5
o
500—
-
1 0.5
300 200 100
.
.400 303 .
.
~oo
~
1
. .
o~
103 —
Fig.4 and consists of three main items.
.
~oo-
.
Fig.3. Nomogram for determining the dis tance to the radio horizon as a function of the altitudes of the transmitting and receiving antennae,
I—
Firstly
a light weight dish antenna which has a gain of 26 dE at not 1.5 GHz, packagetranspondwhich contains only an the electronics L-band telemetry er hut also the microprocessor which controls the payload, and an azimuth control motor and reaction wheel. A radiated power of more than 1.5 watt from the scientific payload should ensure an adequate signal—to-noise ratio at the receiver when the distance to the relay is 1200 km. The signal from the antennae passes through two multistage filters and a wide band preamplifier before being detected by the receiver. In addition to provi-
32
S. Holder and D. Ramsden ding the base—band signal in a form that can be mixed again with a locally generated sub—carrier and re— transmitted, the receiver also provides an indication of the received signal strength which is useful in the antenna control system. The antenna must be pointed with a precision of ±10 in order to receive a good signal at maximum range. loop required to mainREACTION The tam control stabilisation is generated by MOTOR software. The angle derived from
)~MIXER~NSMI~J’
__________
M~GNETOMETERrL....... —~ I DIGITAL I
PR~’~1AZIM~J____
QUAD I/p
____________
4
QUAD 0/P
TX~R
~ BALLAST HOPPER
______
___
TIMER BALLAST (SThTSOT. DATA TN’T’PR5A(~
MOTOR
cinwrROT. ADC POWER SUPPLY
‘
the digital azimuth system, based on flux gate magnetometers, is com— pared with the required ta,rget az— imuth and the error signal proportional to the difference is output from a DAC to the reaction motor. Various methods of azimuth control are available including an ‘auto— seek and acquire’ facility.
All valid coi~ands received by the conmiand relay module are issued to QUAD I/P the microprocessor system. The MICROPROCESSOR SYSTEM software then decodes them to decide if any local action is necessFig.4. Block diagram of rei.ay system. ary. A total of 64 discrete commands are available, of which commands 0 to 20 octal are used by the relay and should therefore be avoided by the experimenter. After a small delay the transceiver is switched into transit mode and the FSK signal is relayed to the experimenters balloon using a 6 watt output. It should be noted that when both balloons are within range of the ground installation the experimenter will receive the same command twice. Because of this delay imposed by the relay, commands may be sent at a maximum rate of once every six seconds. SBC
LATCH/ECHO
CONCLUSION By using a combination of the techniques described above we look forward to achieving longer flights with heavy scientific payloads. Of launched from a cnidcontinental location close to turn-around, a full telecommunications link through the relay should provide a wide bandwidth data link and command capability for the entire flight. Alternatively, the cryogenic system should enable experiments weighing typically 500 kg to be maintained above 3mb for 8/10 days. REFERENCES 1. 2. 3. 4. 5.
,
D. Ramsden, R.E. Baker, Scientific Ballooning (COSPAR) W. Riedler Ed. Pergaznon Press 1979. A.S. Carten Jr., C.F. Sindt. AFGL-TR-79—0278 (1979) A.S. Carten Jr., C.F. Sindt. Paper 1.2.2. Workshop on Instrumentation and Technology for Scientific Ballooning. COSPAR, Ottawa(1982). D. Ramsden, R.E. Baker, R.W. King. Scientific Ballooning (cOSPAR). W.Riedler Ed. Pergamon Press (1979). U. Hirosawa, J. Nishimura. Scientific Ballooning (COSPAR). W.Riedler Ed. Pergamon Press (1979).