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Acta Astronautica

Acta Astronautica 70 (2012) 112–121

0094-57

doi:10.1

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Technol

journal homepage: www.elsevier.com/locate/actaastro

Balloon-borne air traffic management (ATM) as a precursor tospace-based ATM$

Yuval Brodsky n, Richard Rieber, Tom Nordheim

International Space University, 1 rue Jean-Dominique Cassini, 67400 Illkirch-Grafenstaden, France

a r t i c l e i n f o

Article history:

Received 26 February 2011

Received in revised form

22 June 2011

Accepted 24 June 2011Available online 13 September 2011

Keywords:

Air traffic management

ADS-B

Balloon-satellite

Aviation

SESAR

NextGen

65/$ - see front matter & 2011 Elsevier Ltd. A

016/j.actaastro.2011.06.013

s paper was presented during the 61st IAC in

espondence to: 10-8707, Dufferin St., Suite 368

L4J 0A6. Tel.: þ1 905 334 5374; fax: þ416 63

ail addresses: yuval.brodsky@gmail.com (Y. B

gmail.com (R. Rieber), tom.nordheim@gmail.

BATE: International Space University—Balloo

ogy Experiment.

a b s t r a c t

The International Space University—Balloon Air traffic control Technology Experiment

(I-BATE1) has flown on board two stratospheric balloons and has tracked nearby aircraft

by receiving their Automatic Dependent Surveillance-Broadcast (ADS-B) transmissions.

Air traffic worldwide is facing increasing congestion. It is predicted that daily European

flight volumes will more than double by 2030 compared to 2009 volumes. ADS-B is an

air traffic management system being used to mitigate air traffic congestion. Each

aircraft is equipped with both a GPS receiver and an ADS-B transponder. The

transponder transmits an equipped aircraft’s unique identifier, position, heading, and

velocity once per second. The ADS-B transmissions can then be received by ground

stations for use in traditional air traffic management. Airspace not monitored by these

ground stations or other traditional means remains uncontrolled and poorly monitored.

A constellation of space-based ADS-B receivers could close these gaps and provide

global air traffic monitoring. By flying an ADS-B receiver on a stratospheric balloon,

I-BATE has served as a precursor to a constellation of ADS-B-equipped Earth-orbiting

satellites. From the �30 km balloon altitude, I-BATE tracked aircraft ranging up to

850 km. The experiment has served as a proof of concept for space-based air traffic

management and supports a technology readiness level 6 of space-based ADS-B

reception.

& 2011 Elsevier Ltd. All rights reserved.

1. Introduction

There are numerous major issues facing current airtraffic management (ATM) schemes, two of which willworsen significantly if not addressed in the near future:(1) current ATM infrastructure is incapable of handlingprojected flight volumes [1] and (2) the increased riskposed by increasing air traffic and climate change totrans-oceanic and polar flights [2–4].

ll rights reserved.

Prague.

, Vaughan, Ontario,

8 5634.

rodsky),

com (T. Nordheim).

n Air traffic control

The aforementioned issues, along with numerous others,have catalyzed the development of several programs acrossthe globe aiming to solve the challenges facing the globalaviation industry. Among the more notable programs arethe US Federal Aviation Administration’s (FAA) NextGenprogram, and the European Union’s (EU) Single EuropeanSky (SES) and its ATM Research program—SESAR [1,5].

Automatic Dependent Surveillance-Broadcast (ADS-B)has been identified as a key technological enabler withinNextGen and SESAR. Both programs seek to build uplimited terrestrial ADS-B infrastructure [1,5]. Each aircraftusing this technology is equipped with a GPS receiver andan ADS-B transponder. The transponder broadcasts theaircraft’s unique identifier, position, heading, and velocityonce per second. Traditionally, these ADS-B transmissionsare received by ground stations and are used to monitorthe location of aircraft.

Fig. 1. Commercial aviation in Europe. Number (in millions) of annual

commercial flights in Europe between 2006 and 2030. Adapted from [16].

Y. Brodsky et al. / Acta Astronautica 70 (2012) 112–121 113

Described herein is the I-BATE experiment (InternationalSpace University—Balloon Air traffic control TechnologyExperiment), which was performed by three Masters stu-dents at the International Space University in Strasbourg,France. I-BATE tracked aircraft by equipping a high-altitudescientific balloon with an ADS-B receiver. It has served as avaluable precursor to space-based ADS-B, and supports theincrease in technology readiness level of space-based ADS-Bto 6 [6,7]. I-BATE flew twice from the Esrange Space Centerlocated near Kiruna, Sweden. The experiment was super-vised by the Balloon EXperiments for University Studentsprogram (BEXUS), which is a joint program between theGerman Space Agency (DLR), the Swedish National SpaceBoard (SNSB) in collaboration with the European SpaceAgency (ESA).

2. Background

2.1. Current air traffic management

Generally, controlled airspace exists over continentalregions, and may extend up to 200 NM out to sea from agiven country’s shoreline. Not all nations control theirairspace, and the ones that do control their airspace do soto varying degrees.

The primary tool used by most Air Navigation ServiceProviders (ANSPs) to monitor a nation’s airspace is anetwork of terrestrial radar stations [3], which are limitedin range to approximately 200 NM [8–11]. As such,aircraft flying outside of controlled airspace (includingtrans-oceanic and trans-polar flights) are often tracked ormonitored using Automatic Dependent Surveillance-Con-tract (ADS-C) position reports. These are sent by theaircraft every 14, 27, or 32 min [3].

Using such a system for aircraft in uncontrolled air-space, it is plausible that the most recent reported posi-tion for a given flight could be as old as 31 min. At normalcruise velocity, a commercial aircraft can travel nearly475 km during these 31 min. In the event of a catastrophe,rescue crews could be required to search an area as largeas 710 000 km2, which is larger than the area of France.Air France flight 447 from Rio de Janeiro to Paris wentdown over the Atlantic Ocean on 01 June 2009. The lastknown position of the aircraft was known with littleaccuracy as a result of the inadequate communicationand tracking infrastructure. As such, search and rescuecrews were unable to find the wreckage until 06 June,2009, by which time crews were unable to locate theflight data recorders, which were already submerged to adepth of 3980 meters and would only be recovered inMay 2011 [12–14].

2.2. Predicted air traffic volumes

EUROCONTROL estimates that as many as 30 000commercial flights take to the skies daily within Europeanairspace, and this figure is expected to increase by a factoras high as 2.2 by 2030 compared to 2009 values [15]. Thegrowth rate of air traffic will continue into the latter halfof this century. Fig. 1 shows the forecasted increase inannual commercial flights from 2006 to 2030 in Europe.

This growth trend is not limited to Europe, but is global innature. The FAA predicts that by 2030 US air traffic willhave increased by at least a factor of two compared with2009 values [16].

2.3. Aviation and climate change

The International Civil Aviation Organization (ICAO)states that approximately 20% of all aviation accidentsand 8% of all fatal aviation incidents are weather related[2]. It has been shown that in the coming decades, thefrequency and intensity of meteorological events (such ashurricanes, thunderstorms, high winds, convective/turbu-lent air, and intense precipitation) is likely to increasesignificantly [4]. These events are the most commoncauses of weather related aviation accidents [17]. As such,it can be assumed that even if the IntergovernmentalPanel on Climate Change’s (IPCC) most conservativeclimate change predictions are accurate, there will likelybe an increase in weather-related aviation accidents inthe future, particularly on trans-oceanic routes whereweather is often most extreme [2,4,16]. Coupled withincreasing flight volumes, it can be expected that thenumber of aviation accidents, disasters, and fatalities willincrease in the coming years [4,18].

2.4. Future air traffic management

As a partial solution to the aforementioned problems,ADS-B is currently being implemented in many regionsworld-wide, including the USA (through NextGen) [5],Europe (through SESAR) [1], Canada [19,20], Sweden [21],Australia [22], China [23], Singapore [24] and the UAE [25].The intention is that each aircraft will be fitted with botha GPS receiver and an ADS-B transponder (or transceiverin some cases), which will broadcast the aircraft’s uniqueidentifier, flight number, GPS-WGS84 latitude, longitude, andaltitude, velocity, and intention. These transmissions willoccur automatically at regular, pre-defined intervals (usuallyonce per second) [1,3,5]. At the time of this paper’s publica-tion, not all commercial aircraft carry ADS-B transponders.

Y. Brodsky et al. / Acta Astronautica 70 (2012) 112–121114

ADS-B messages transmitted from aircraft are receivedby ADS-B ground stations, which are slated to be fullyoperational by 2020 for many of the regions discussedpreviously [1,5,19–25]. ADS-B ground stations provideincreased accuracy and timeliness over radar-based airtraffic monitoring and provide coverage where radar isimpractical, such as the Gulf of Mexico and the HudsonBay. It does not however, solve the issue of monitoringaircraft that are outside of controlled airspace.

Implementing terrestrial radar or ADS-B ground stationsalong every global flight path would be cost-prohibitive. Analternative solution to monitoring all airspace is space-based ADS-B reception. A global constellation of satellitescarrying ADS-B receivers as hosted payloads would providethe capacity for receiving ADS-B transmissions from aircraftanywhere in the world. I-BATE serves as a precursorexperiment that should be successfully accomplished priorto the deployment of ADS-B-receiving spacecraft.

3. Experiment objectives and description

3.1. Objective

I-BATE’s primary objective was to conceptually provethe technical viability of space-based ADS-B reception.A key challenge of receiving ADS-B messages from highaltitudes and in space is that the receiver’s field of view isso large that the risk of message corruption from simul-taneous aircraft transmission within the field of viewgrows to an unacceptable level. This message corruptionis termed False Replies Un-synchronized In Time (FRUIT)and is discussed in more detail in [26].

3.2. Technical description

The primary component of the I-BATE payload was theEmbedded Radar Module (ERM), an ADS-B receiver pro-vided by Kinetic Avionic Products Ltd. All other compo-nents of the payload, as seen in Fig. 2, were designed to

Fig. 2. Computer drawing of I-BATE with sides and t

support proper operation of the ERM and provide data tooperators on the ground.

The ERM is about the size of a small matchbox with asensitivity of –94 dBm. It received signals from the 27 cm(1-wave), 5 dB gain (without a ground plane) dipoleantenna, and sent the data to the Gumstix Overo Earthmicrocomputer. The microcomputer then stored all pro-cessed data in onboard solid-state memory, and relayed asubset of the data in real-time to the balloon’s telemetrysystem. This data was displayed in real-time at the I-BATEground station. A 90 Wh Celltech LiFePO4 battery pro-vided power to the experiment. Power was regulated by acustom-designed power distribution and thermal controlunit, which also regulated the internal temperature of I-BATE through a series of heaters. With the exception ofthe antenna, all components were housed in a stainlesssteel box that provided both physical protection and radiofrequency shielding. The box was lined with polyethylenefoam for insulation, which was covered in carbon-impreg-nated polyolefin (Velostat) to minimize the risk of elec-trostatic discharge. The antenna hung below the balloonand had an unobstructed field of view below the balloonand to all sides.

3.3. Predicted range

In order to determine the theoretical maximum dis-tance at which aircraft could be detected by I-BATE, theline of sight range and the detector noise-limited rangewere both calculated. The theoretical maximum range ofthe experiment would be the lesser of the two aforemen-tioned ranges.

The line of sight range was a slant range calculatedassuming a balloon altitude of 30 km and an aircraftcruising altitude of 10 km. Based on these values, the lineof sight range was 977 km.

The noise-limited range was calculated from a basiclink budget. A number of assumptions have been madeand are shown in Table 1.

op removed to show the internal components.

Y. Brodsky et al. / Acta Astronautica 70 (2012) 112–121 115

Based on the link budget, the noise-limited range ofthe system would be 691 km. The noise-limited range isless than the line of sight range, and is therefore the

Table 1I-BATE link budget.

Parameter Value Origin

Transmitter power 250 W ADS-B transponder

Transmitter power 24.0 dBW Calculated

Transmitter antenna gain 3 dBi ADS-B transponder

Transmitter line loss 3 dB Assumed

Frequency 1090 MHz ADS-B signal

Wavelength 27.5 cm Calculated

Bit rate 1.04 Mbit/s ADS-B signal

Receiver antenna gain 5 dBi Known value

Receiver sensitivity �94 dBm Known value

System noise temperature 650 K Assumed

EIRP 24 dBW Calculated

Received power �124 dBW Calculated

Path loss 150 dB Calculated

Range 691 km Calculated

Table 2Flight parameters for BEXUS-10 and BEXUS-11.

BE

Date 09

Launch time (UTC (local)) 01

Cut-down time (UTC (local)) 05

Time to cut-down (h) 4.7

Float altitude (km) 25

Float direction to loss of signal (1) 12

Float distance to loss of signal (km) 21

Launch coordinates 67

Cut-down coordinates 66

Fig. 3. BEXUS-10 trajectory. BEXUS-10 balloon trajectory (top) and elevation pr

is 217 km, maximum altitude is 25 km.

theoretical maximum range at which I-BATE should beable to detect aircraft.

3.4. Description of balloon flight

I-BATE flew as one of several experiments managed bythe BEXUS program. Although originally slated for a singleflight on board the BEXUS-10 balloon, I-BATE was able tofly on the BEXUS-11 balloon as well. Both balloonslaunched from the Esrange Space Center near Kiruna,Sweden located at 681N, 211E.

BEXUS-10 launched on 09 October 2010 and BEXUS-11launched on 23 November 2010. Table 2 gives key para-meters for both flights. Fig. 3 and 4 illustrate the flighttrajectories for both BEXUS-10 and -11, respectively.Cut-down (Table 1) refers to the separation of the payloadfrom the stratospheric balloon. This occurs in order toterminate the flight and return the payload to earth viaparachute.

XUS-10 BEXUS-11

October 2010 23 November 2010

:00 (03:00) 08:20 (09:20)

:45 (07:45) 11:35 (12:35)

5 3.25

33.5

0 117

7 441

.531N, 21.051E 67.531N, 21.051E

.961N, 25.551E 64.831N, 27.191E

ofile (bottom) from the Esrange Space Center into Finland. Float distance

Fig. 4. BEXUS-11 trajectory. BEXUS-11 balloon trajectory (top) and elevation profile (bottom), from the Esrange Space Center into Finland. Float distance

is 441 km, maximum altitude is 34 km.

Y. Brodsky et al. / Acta Astronautica 70 (2012) 112–121116

Fig. 5 shows the area covered by I-BATE along theballoon’s flight path using the known 691 km maximumrange described in Section 3.3.

4. Results

The BEXUS-10 balloon launched on 09 October 2010at 01:00 UTC (03:00 local time) and was cut down at05:45 UTC (07:45 local time). There are few aircraftaloft during these early morning hours over the Scandina-vian Arctic. Despite successful operation, I-BATE was unableto achieve its primary objective due to the low number ofaircraft tracked. I-BATE was fortunate to be given theopportunity to fly on board BEXUS-11 several weeks laterwith the hopes of seeing more aircraft.

4.1. BEXUS-10

Some key details about the aircraft tracked duringBEXUS-10 can be seen in Table 3. Over 8000 ADS-Bmessages were received during the 4.75-h flight. TheADS-B position message received at the longest rangewas 885 km away. This is beyond the noise-limited rangepreviously described. This is further described later in thepaper. A map of different aircraft tracked during theBEXUS-10 flight can be seen in Fig. 6 along with the balloontrack and an overlay of the 691 km noise-limited range.

Fig. 7 shows a histogram representing the number ofADS-B position messages received by I-BATE at variousranges. The ranges are calculated assuming a straight linefrom the balloon position to the aircraft position, and donot take altitude into account. There are several types ofADS-B messages sent by aircraft; however, only positionmessages can be used for range calculations. As such, thesummation of the total number of messages displayed inFig. 7 does not equate to the total number of messages

received (Table 3). I-BATE received the most positionmessages (1191) in the 90–110 km range, comprisingover 27% of the total ADS-B position messages receivedduring the BEXUS-10 flight. I-BATE received 742 (17%)ADS-B position messages in the 150–170 km range. Over50% of all position messages received during this flightwere within the 170 km range, and 95% of the positionmessages received were within 350 km of the payload asseen in Table 3.

The temporal distribution of ADS-B transmissionsreceived during the BEXUS-10 flight is shown in Fig. 8.The payload was operational on the balloon launch padbeginning at approximately 19:00 UTC on 08 October 2010,and received several ADS-B messages prior to the balloonlaunch. Following the 01:00 UTC launch of the BEXUS-10balloon, the number of flights tracked increased signifi-cantly. The majority of transmissions received occurred after03:00 UTC (05:00 local). The overall number of ADS-Btransmissions received during this flight (N¼8178) is quitelow, due to the nighttime flight. Note that no messages werereceived after the 05:45 UTC (07:45 local) cut-down. It isbelieved that the experiment continued to operate afterlanding, but the data was not collected.

The experiment also experienced a memory leak duringthe flight. It is believed that the memory leak preventeddata from being both saved to on board storage and frombeing transmitted to the ground. In order to clear thememory leak, the experiment was rebooted at 02:43:39UTC. After the boot was complete (approximately twominutes later), the rate of data collection increased fromfour messages received in 40 min to 123 messages receivedin 15 min. This may be due to the fact that more aircraft areoperating between 04:45 and 05:00 local time thanbetween 04:00 and 04:40 local time—however, such alarge, immediate increase seems unlikely. This indicatesthat perhaps all ADS-B messages received by the ERM

Table 3Aircraft tracking data from BEXUS-10.

Total aircraft tracked 24

Total number of ADS-B transmissions 8178

Maximum number of aircraft tracked in 1 s 5

Maximum aircraft tracking range (km) 885

Mean aircraft tracking range (km) 190

Third quartile range (km) 241

95th Percentile range (km) 349

Fig. 6. Aircraft tracked during BEXUS-10 flight on 09 October 2010,

displayed with the theoretical range of the experiment (shaded circular

area) and the balloon’s trajectory (thin black line crossing the Sweden-

Finland border from NW to SE). Note the aircraft at the extreme

southern portion of the map that are beyond the theoretical range of

I-BATE.

Fig. 5. I-BATE ranges. I-BATE’s theoretical experiment range (691 km)

for BEXUS-10 (A) and BEXUS-11 (B) flight profiles (shaded circular

areas). Balloon tracks are denoted by black lines (starting in the north-

west and floating southeast in both images).

Y. Brodsky et al. / Acta Astronautica 70 (2012) 112–121 117

may not have been relayed to the Gumstix microcomputerfor storage and/or real-time transmission and thus, are notincluded in the dataset previously described. This discre-pancy is not believed to affect the validity of the dataset.

4.2. BEXUS-11

Key details about the aircraft tracked during BEXUS-11can be seen in Table 4. Over 38 000 ADS-B messages werereceived during the 3.25-h flight, despite the shorter flight

time compared to BEXUS-10. The BEXUS-11 balloon flewat an altitude of 33.5 km—approximately 8 km higherthan BEXUS-10. This provided a greater line of sight range,but had little effect since the experiment’s range remainednoise-limited. The balloon launched at 08:20 UTC (09:20local), which was a significantly more favorable time asmore aircraft were aloft during these daytime hours. TheADS-B position message received at the longest range was740 km away. This is beyond the noise-limited range pre-viously described and is further discussed later in the paper.A map of the different aircraft tracked during the BEXUS-11flight can be seen in Fig. 9, along with the balloon track andan overlay of the 691 km noise-limited range.

Fig. 10 shows a histogram of the range distribution ofADS-B position messages for BEXUS-11. Nearly 50% of theposition messages received during this flight originatedfrom within 110 km of the balloon. The most positionmessages were received from the 90 to 110 km range(3890 transmissions, 20.4%) and in the 70–90 km range(2700 transmissions, 14.1%). Three quarters of the ADS-Bposition messages received during this balloon flight werewithin a range of 210 km, and 95% of the transmissionswere within 334 km, as seen in Table 4. Please note thatthe total number of messages presented in Fig. 10 do notsum to the total number of ADS-B messages received, asonly ADS-B messages containing the aircraft’s positioncan be used to calculate range. Other ADS-B messagesinclude flight number, velocity, and heading messages.

The local daytime launch of BEXUS-11 was favorableto I-BATE, as more aircraft were aloft than during thenighttime flight of BEXUS-10. As with BEXUS-10, theexperiment began operating several hours prior to launchand received some ADS-B messages prior to launch. It isworth noting that unlike BEXUS-10, the data from afterlanding was recovered and included in the BEXUS-11dataset. Cut-down occurred at 11:35 UTC and one canreadily see in Fig. 11 that most data were received afterthat time. This large post-landing dataset is likely a result

Fig. 7. BEXUS-10 range histogram. A histogram displaying range between I-BATE and tracked aircraft during the BEXUS-10 flight. Vertical bars (and

accompanying numerical labels) represent the number of ADS-B position messages received at a given range, the solid line represents percent of total

ADS-B position messages received, and the dashed line represents cumulative percent of total ADS-B position messages received.

Fig. 8. BEXUS-10 time histogram. Temporal distribution of ADS-B transmissions received by I-BATE during the BEXUS-10 flight. Vertical bars (and

accompanying numerical labels) represent the number of ADS-B messages received at a given 30 min timeslot, the solid line represents percent of total

ADS-B messages received, and the dashed line represents cumulative percent of total ADS-B messages received. Along the x-axis, times start on 08

October 2010 and continue into 09 October 2010. The star represents the balloon launch time.

Table 4Aircraft tracking data from BEXUS-11.

Total aircraft tracked 77

Total number of ADS-B transmissions 38,176

Maximum number of aircraft tracked in 1 s 12

Maximum aircraft tracking range (km) 740

Mean aircraft tracking range (km) 151

Third quartile range (km) 202

95th Percentile range (km) 334

Y. Brodsky et al. / Acta Astronautica 70 (2012) 112–121118

of landing near Oulu, Finland, and between several heav-ily traveled air traffic routes as seen in Fig. 9. It is worthnoting that the number of transmissions received duringthis flight (N¼38,176) is significantly greater than that ofthe BEXUS-10 flight.

As with the BEXUS-10 flight, the BEXUS-11 flightsuffered a similar memory leak. This memory leak pre-vented ADS-B messages from being both saved to diskand transmitted to the ground for real-time display.The experiment began indicating memory leak issues as

Y. Brodsky et al. / Acta Astronautica 70 (2012) 112–121 119

early as twelve minutes after the launch (08:30 UTC) andcontinued until the experiment was rebooted at 09:31:10UTC via ground command. The same symptom occurredagain after landing at 13:08:53 UTC and persisted untilanother reboot at 20:28:28 UTC when the watchdog timerexpired. The result is that the only timeframe that mayaccurately reflect the flight volume is between 09:30 UTCand 13:00 UTC.

5. Discussion

I-BATE was unable to meet its primary experimentobjectives during BEXUS-10 as there were too few aircrafttransmitting ADS-B messages during the balloon flight.However, the BEXUS-11 balloon flight allowed I-BATE to

Fig. 9. Aircraft tracked during BEXUS-11 flight on 23 November 2010,

displayed with the theoretical range of the experiment (shaded circular

area) and the balloon’s trajectory (thin black line crossing the Sweden-

Finland border from NW to SE). Note the aircraft at the extreme southern

portion of the map that are beyond the theoretical range of I-BATE.

Fig. 10. Histogram displaying range between I-BATE and tracked aircraft during

represent the number of ADS-B position messages received at a given range, the

and the dashed line represents cumulative percent of total ADS-B position me

satisfy its primary objective as there was a significantincrease in both the quantity and density of ADS-Bmessages received.

Due to the pre-dawn launch time of BEXUS-10 and thelow commercial flight volumes, only 24 aircraft weretracked despite the maximum range of up to 885 km. Itis important to note that reception at this range was notcommon, and the vast majority of position messagesreceived were within a range of 450 km.

The total number of flights tracked during BEXUS-11increased by more than a factor of 3 and the total number ofADS-B messages received increased by a factor of 5 despitethe shorter flight duration of BEXUS-11. These increases areattributed to the daytime flight of BEXUS-11 compared tothe nighttime flight of BEXUS-10. It is believed that therewas no significant difference in the experiment’s perfor-mance between the two balloon flights. The data receivedmay not be fully representative of the system’s capabilities,given that results are dependent on the distribution ofADS-B-transmitting aircraft during the balloon flights.

Both the mean range and maximum range of ADS-Bposition messages received by I-BATE on BEXUS-11decreased slightly compared to the BEXUS-10 values.However, these decreases are likely attributed to thedifferent distributions of airborne aircraft during bothflights and the actual balloon track. BEXUS-11 flew moresoutherly, towards Oulu, Finland, and BEXUS-10 flewfarther north, in a more remote region of Finland.

A most interesting observation is that some ADS-Bposition messages indicated that the transmitting aircraftwas beyond line of sight from the experiment, effectivelyover the horizon. 1090 MHz, the frequency used for thisexperiment, is too high to reflect off of the ionosphere.It is believed that signals reaching the top of theatmosphere are both refracted back towards earth andtransmitted into space. This phenomenon is of utmostimportance to future designers of a space-based ADS-B

the BEXUS-11 flight. Vertical bars (and accompanying numerical labels)

solid line represents percent of total ADS-B position messages received,

ssages received.

Fig. 11. Temporal distribution of ADS-B messages received by I-BATE during the BEXUS-11 flight. Vertical bars (and accompanying numerical labels)

represent the number of ADS-B messages received at a given 30 min timeslot, the solid line represents percent of total ADS-B messages received, and the

dashed line represents cumulative percent of total ADS-B messages received. Along the x-axis, times start on 23 November 2010 and continue into 24

November 2010. The star represents the balloon launch time.

Y. Brodsky et al. / Acta Astronautica 70 (2012) 112–121120

receiving system. The signal strength in space of atmo-spherically refracted ADS-B messages may not be power-ful enough to be detected by the satellite system. This willrender the satellite blind to aircraft in this particulargeometry. However, the speed at which the satellite-aircraft geometry is changing ensures that this specificgeometric configuration is momentary such that only a fewADS-B messages may be lost. Regardless, this phenomenonrequires additional study.

6. Conclusion

The I-BATE experiment was designed to operate anADS-B receiver from the high vantage point of a near-spaceenvironment. I-BATE flew on board two high-altitudeballoons and successfully received ADS-B messages fromnearby aircraft.

The high-altitude and large field of view from whichI-BATE received ADS-B messages served as a near-spaceanalog for space-based ADS-B reception. More steps need tobe taken to further develop the technology. It is recom-mended that ADS-B receivers be operated near dense airtraffic areas such as London or New York to better under-stand the effects that large flight volumes will have on theADS-B receiver. This may be accomplished by deploying anADS-B-equipped Earth-orbiting platform.

Space-based ADS-B reception can provide global airtraffic monitoring and can make skies safer for air trave-lers. The authors believe that I-BATE’s successful experi-ment supports an increase in the technology readinesslevel of space-based ADS-B reception from 5 to 6.

7. Addendum

In March 2011, it came to the attention of the authorsthat Iridium is considering deployment of ADS-B receiverson its constellation of 66 low-Earth orbiting communications

satellites, which is planned to be fully operational by 2017[27]. Furthermore, in July 2011 it was announced thatGlobalstar Inc. and ADS-B Technologies LLC are ‘‘almosthalfway’’ to providing global space-based ADS-B coverage,after the July 2011 launch of six new ADS-B-equippedGlobalstar satellites [28].

If successfully deployed, these systems will provide along-anticipated global air traffic monitoring solution.

Acknowledgments

The authors would like to thank Dr. Angie Bukley forher support in the execution of this project. They wouldalso like to thank the REXUS/BEXUS program and KineticAvionic Products Ltd.; without whose support this projectwould not have been possible. The authors also thank thefollowing sponsors and partners: OSEO, Celltech, WindRiver, La TechniSoudure, ESA, DLR, SNSB, SSC, EuroLaunch,ISU, Mr. Paulo Esteves, Mr. Raphael Garcia, Barbara andPeter Wood, Shandy Asturias, Andrew Browne, and oneanonymous donor from the ISU Board of Trustees.

The BEXUS program (www.rexusbexus.net) is realizedunder a bilateral Agency Agreement between the GermanAerospace Center (DLR) and the Swedish National SpaceBoard (SNSB). The Swedish share of the payload has beenmade available to students from other European countriesthrough a collaboration with the European Space Agency(ESA).

References

[1] European Commission, SESAR JU, EUROCONTROL, European AirTraffic Management Master Plan, Brussels, 2009.

[2] European Union, European Civil Aviation Conference, EUROCON-TROL, Effects of climate change on aviation safety, in: Proceedingsof the ICAO High-level Safety Conference 2010, Montreal, ICAO,2010: pp. 1–3.

Y. Brodsky et al. / Acta Astronautica 70 (2012) 112–121 121

[3] International Air Transport Association, User Requirements for AirTraffic Services, Montreal, 2009.

[4] Intergovernmental Panel on Climate Change, Climate Change 2007:Synthesis Report, Valencia, 2007.

[5] Federal Aviation Administration—US Department of Transporta-tion, FAA’s NextGen Implementation Plan, 2010.

[6] J.C. Mankins, Technology Readiness Levels (1995) 1–5.[7] US Department of Defense, Technology Readiness Levels, n.d.[8] Indra, Air route surveillance 3D radar, n.d.[9] Encyclopaedia Britannica, Radar. /http://www.uv.es/EBRIT/macro/

macro_5005_40_24.htmlS (accessed: 2011).[10] D.L. Clark, Early advances in radar technology for aircraft detection,

Lincoln Laboratory Journal 12 (2000) 167–180.[11] Jane’s, ARSR-4 (AN/FPS-130) Air Route Surveillance Radar (United

States), Land-based Air Defence Radars, Jane’s Radar and ElectronicWarfare Systems, 2010.

[12] Bureau d’enquetes et d’analyses pour la securite de l’aviation civile,Interim Report on the Accident on 1st June 2009 to the AirbusA330-203 Registered F-GZCP Operated by Air France Flight AF 447Rio de Janeiro–Paris, 2009.

[13] Bureau d’enquetes et d’analyses pour la securite de l’aviation civile,Interim Report #2 on the Accident on 1st June 2009 to the AirbusA330-203 Registered F-GZCP Operated by Air France Flight AF 447Rio de Janeiro–Paris, 2009.

[14] Bureau d’enquetes et d’analyses pour la securite de l’aviation civile,Interim Report #3 on the Accident on 1st June 2009 to the AirbusA330-203 Registered F-GZCP Operated by Air France Flight AF 447Rio de Janeiro–Paris, 2011.

[15] EUROCONTROL, EUROCONTROL Long-Term Forecast—Flight move-ments 2010–2030, 2009.

[16] Federal Aviation Administration—US Department of Transporta-tion, FAA aerospace forecast fiscal years 2010–2030, 2010.

[17] U. Wienert, Climate change and its possible impact on aviation, in:Proceedings of the International Air Safety & Climate ChangeConference, Cologne, Deutscher Wetterdienst, n.d., p. 23.

[18] X. Oh, Airports and Adaptation—Changing Climate and BusinessConditions, Montreal, 2010.

[19] NAV CANADA, NAV CANADA Announces the Acquisition of NewSurveillance Technology to Improve Air Traffic Safety and Customer

Efficiency. /http://www.navcanada.ca/NavCanada.asp?Language=en&Content=ContentDefinitionFiles%5CNewsroom%5CNewsReleases%5C2007%5Cnr0212.xmlS (accessed: 2011).

[20] NAV CANADA, New Air Traffic Surveillance Technology to beDeployed, Starting in the North. /http://www.tc.gc.ca/eng/civilavia

tion/publications/tp185-1-07-pre-flight-3009.htm#tphpS Trans-port Canada (accessed: 2011).

[21] Swedavia, Sweden announces plans for nationwide ADS-B network.

/http://www.airporttechnology.com/features/feature619/SAirport-technology.com (accessed: 2011).

[22] Airservices Australia, ADS-B Mandate Update. /http://www.airservicesaustralia.com/projectsservices/projects/adsb/mandate.aspS(accessed: 2011).

[23] Aviation Today, China to Conduct First ADS-B Commercial AviationTrials. /http://www.aviationtoday.com/regions/usa/17130.htmlSAir Safety Week (accessed: 2011).

[24] COMSOFT, COMSOFT has been Selected to Implement ADS-BGround Equipment in ingapore. /http://www.atc-network.com/

News/28810/-ADS-B-for-SingaporeS (accessed: 2011).[25] COMSOFT, COMSOFT Provides Three Additional ADS-B Ground

Stations to the General Civil Aviation Authority (GCAA) of the

UAE. /http://www.atcnetwork.com/News/29815/Further-ADS-B-Installations-in-Abu-Dhabi-through-COMSOFTS. Further ADS-B

Installations in Abu Dhabi Through COMSOFT (accessed: 2011).[26] R.R. Rieber, T. Nordheim, Y. Brodsky, I-BATE: a precursor to space-

based air traffic control, in: Proceedings of the 20th ESA Sympo-

sium on European Rocket & Balloon Programmes and RelatedResearch, Hyeres, France, ESA, 2011.

[27] G. Warwick, Iridium Plans to Monitor ADS-B from Space, AviationWeek, 2011.

[28] ADS-B technologies, ADS-B Technologies and Globalstar Connect to

Create Worldwide Air Traffic Network. /http://www.ads-b.com/news.htmS (accessed: 2011).