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DLR research aircraft at ILA 2010

HALO Gulfstream G 550

28 May 2010

 HALO during its landing approach
zum Bild HALO during its landing approach

The new HALO (High Altitude and Long Range Research Aircraft) research aircraft heralds a new chapter in the history of German atmospheric research and Earth observation. HALO is based on a Gulfstream G 550 ultra-long range business jet. The combination of range, cruising altitude, payload and comprehensive instrumentation make the aircraft a globally unique research platform.

In almost all important parameters, HALO exceeds the performance of research aircraft operating worldwide until now: with a cruising altitude of more than 15 kilometres, a payload of up to three tonnes and a range of more than 8 000 kilometres, for the first time measurements can now be carried out on a continental scale, at all latitudes, from the tropics to the poles, and at altitudes as high as the lower stratosphere. As a result, it will be possible to answer scientific questions relating to areas that were inaccessible to previous research aircraft, especially the Falcon operated by the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR).

The HALO research aircraft was delivered on 21 January 2009 and landed at Oberpfaffenhofen after a non-stop transatlantic flight from Savannah, USA. It is now available to both DLR – as the keeper of the aircraft – other research centres in the Helmholtz Association (Helmholtz-Gemeinschaft; HGF), universities, institutes of the Max Planck Society (Max-Planck-Gesellschaft; MPG) and other scientific establishments for investigations in the field of atmospheric research.

31 research institutes participating in HALO project

The HALO project was made possible by the Max Planck Society, members of the Helmholtz Association of German Research Centres (Helmholtz-Gemeinschaft Deutscher Forschungszentren) and a number of other scientific institutes from the field of atmospheric research. In total, 32 research institutes are participating in the project. With a contribution of 47.5 million euros, the German Federal Ministry of Education and Research (Bundesministeriums für Bildung und Forschung; BMBF) is covering 70 per cent of the total costs for HALO. The remaining costs are shared between the Helmholtz Association of German Research Centres and the Max Planck Society. The Free State of Bavaria is contributing 1.8 million euros.


HALO is undergoing a number of modifications such as additional optical windows, apertures for air inlets and outlets, a special power supply and numerous devices for installing various instruments in the cabin and under the fuselage and wings.

Maximum altitude, range and payload represent significant advantages for the HALO compared with research aircraft in operation until now. In the service of science, HALO is equipped with a series of racks to accept instruments. So, with around 15 racks, HALO will be able to accommodate more than twice as many scientific instruments on board as the Falcon 20-E research aircraft that has been in use for DLR since 1976 and is now approaching its 'age limit'. Even before the aircraft is commissioned, more than 100 instrument proposals have been put to DLR for use on HALO. Amongst others, these include: in-situ detectors for evidence of trace gases and particles, remote sensing instruments such as LIDAR and infrared spectrometers, and instruments for investigating geophysical parameters.

 Extensive modifications in the interior of the HALO research aircraft
zum Bild Extensive modifications in the interior of the HALO research aircraft

The following modifications differentiate HALO from the standard G 550 ultra-long range business jet:

  • Apertures in the fuselage for trace substance inlets, as sample collectors and for meteorological measurement sensors. Temperature, pressure and humidity and wind speed will be measured.
  • Special side view ports for remote measurements .
  • Special view ports on the top and underside of the fuselage that enable the use of cameras and LIDAR (Light Detection and Ranging) systems for distance and speed measurement and for remote measurement of atmospheric properties. A LIDAR transmits a laser pulse and receives the signal back-scattered by the atmosphere. The concentration profiles of water vapour, ozone or aerosol particles above or below the flying altitude can be derived from this.
  • Payload hardpoints on the fuselage and under the wings for scientific instruments.
  • Nose boom with built-in flow sensors for wind measurements.
  • Mounting rails in the cabin for up to 15 racks and 5 seats.
  • Power supply rated up to 40 kW for scientific instruments.

Missions - research focus

HALO will offer a previously unattained quality of measurements, particularly in the high-altitude layers of the atmosphere so significant for life on earth. This will also make a significant contribution towards an understanding of the ozone problem and the exchange of air pollutants between the stratosphere and the troposphere. HALO is primarily intended for making measurements in the troposphere and lower stratosphere and for earth observations.

Under the operational responsibility of DLR, as keeper of the aircraft, HALO will primarily be used for the following foci of atmospheric research:

  • Chemistry and transport of trace substances in the troposphere and lower stratosphere.
  • Ozone destruction in the stratosphere.
  • Integrated investigations of the interactions between chemistry, climate, biosphere and humanity.
  • Transport characteristics and chemical conversions in convective and turbulent systems.
  • Investigations of the distribution of sea ice in the context of polar research.
  • Research into the effects of air traffic on the tropopause region.
  • Earth and remote sensing with particular focus on the carbon cycle.

By now, German environmental and climate researchers have developed numerous mission proposals that can only be realised with HALO. Concrete planning for the first demonstration mission with HALO - which should already take place in 2009 - has already started. A few of the research foci from these proposals are:

Climate change and extreme weather events

 Modifications for HALO: From business jet to research aircraft
zum Bild Modifications for HALO: From business jet to research aircraft
In a changing climate, associated with the increasing concentration of greenhouse gases, precipitation is increasing in many areas, as more water is evaporated from the warmer Earth's surface. Linked to a changed vertical temperature profile, the precipitation rate in thunderstorms and large-scale weather systems is increasing. This leads to increased upward movement of air masses (convection) up to the highest layers of the troposphere (boundary layer of the earth's atmosphere). This intensive upward movement must be compensated by downward movement in other areas, which become drier as a result. HALO measurements will cover the entire altitude range influenced by high-reaching convection. Moisture transport and precipitation formation will be investigated in detail in this work.

Aerosols, clouds and the water cycle

Aerosols - finely distributed, microscopically-small particles in the air - not only influence air quality, but also reduce the amount of sunlight reaching the earth's surface. As a result, the air on the ground becomes less warm.

In addition, they affect the radiation characteristics and lifetimes of clouds. These microphysical interactions between aerosols and clouds, and their influence on the atmospheric energy balance and the water cycle, can only be accurately determined by measurements in the atmosphere. This can be achieved by comparative measurements in different regions of the atmosphere: relatively clean maritime regions, the atmosphere over the rain forest, or in air masses polluted by industry or forest fires.

Self-cleaning capacity of the atmosphere

The lifetime of pollutants and various greenhouse gases in the atmosphere is controlled by oxidation processes stimulated by hydroxyl radicals. These radicals limit the increase in concentration of many gases by removing them from the atmosphere before they reach toxic concentrations or enter the stratosphere, where they contribute to ozone destruction. It will be of particular interest to measure the rapidly increasing pollutant emissions in the principal source regions - Europe, North America and Asia - and to determine their effect on the oxidation ability of the atmosphere. Many of the relevant trace gases, including the radicals, will be measured with HALO. This is necessary for an understanding of atmospheric chemical processes and to verify existing atmosphere models.

Tropopause chemistry and dynamics

In terms of measurement techniques, the transition region between troposphere and stratosphere, up to an altitude of 16 kilometres, is difficult to explore. However, this region influences the atmospheric energy balance, the oxidation capability and the vertical transport of momentum and trace gases quite significantly. Moreover, the influence of high-altitude ice clouds (cirrus clouds) on climate disturbances is of enormous importance. The climate effect can be increased or reduced as a result. The rapidly expanding fleet of commercial aircraft operating at these altitudes further influences the cirrus clouds through vapour trails and aerosols, with thus far unknown consequences. HALO will be used to carry out the measurements necessary to quantify these critical factors.

Technical data

HALO Gulfstream G550

Length: 31 metres (incl. 1.6 metre nose boom)
Length: 7.9 metres
Wingspan: 28.5 metres
Cabin length: 11 metres
Cabin width: 2.24 metres
Cabin height: 1.88 metres
Seats: 19 (normally three crew members and five to eight scientists and engineers, depending on the instrumentation)
Empty mass: 22.23 tonnes
Total mass: 41.28 tonnes max.
Engines: two Rolls-Royce BR 710 engines
Thrust: two x 68.4 kilonewton
Range: approximately 8 000 kilometres
Flight altitude: 15.5 kilometres max. (51 000 feet)
Speed: 1 054 kilometres per hour max.
Fuel tank capacity: 18.73 tonnes
Original use: Business jet, military use
DLR flight facility: Oberpfaffenhofen

Dr.rer.nat. Monika Krautstrunk
German Aerospace Center

Flight Operations
, Flight Facility Oberpfaffenhofen
Tel.: +49 8153 28-2981, -2986

Fax: +49 8153 28-1347

Last update: 05/06/2009 15:34:11