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NASA'S HIGH FLIERS

In the last six years NASA has invested more than $ 110 million in the ERAST (Environmental Research and Sensor Technology) Program. The time has now come for the UAVs to leave their experimental status behind and to be used as research tools. "We are ready for business", was the message given at a conference on 13 October at the Dryden Flight Research Center on Edwards AFB (California), during which the possibilities of the Altus II, Helios Prototype, Perseus B and Proteus were being shown.

There was no lack of ideas of how these unusual flying apparatus could be deployed. They could be used to collect air samples, for chemical measurements in the stratosphere as well as for damage control after natural catastrophes. They could also be used as relay stations in the telecommunications market.

There is, however, still a sizeable gap between theory and practise, because the market is obviously harder to break into than was anticipated. In the scientific area the drones have to compete with existing aircraft like the Lockheed ER-2 (U-2). The use of the latter alledgedly being subsidised.

Despite this, one is still confident at Dryden. After all the ERAST program has been tailored to scientists' wishes for cost saving high flying platforms, which can be deployed for long periods of time. Three typical mission profiles were defined as follows:

• Deployments at an altitude of up to 30km with a small payload of 90kg,
• flights at around an altitude of 26km, lasting over 4hrs, carrying a payload of 150kg,
• continuous operation of over four days at altitudes of about 20km.

It was also important that a flight hour did not cost more than $ 5,000.

Four companies took up the challenge and joined the so-called ERAST Alliance. Various NASA research centres and universities belong to this alliance as well. A committee is steering the developments. The aim is not only the development of the UAVs but also the miniaturisation of sensors. The various projects are in need of various amounts of money. While Altus II is a modified Predator drone, the Helios Prototype needs a far greater level of funding. The solar cells alone cost several million US-Dollars.

The progress of the four devices is as different as is their design, (cp individual notes). According to NASA ERAST Manager John Sharkey Altus II, Perseus and Proteus have already proved their aptitude for operational scientific missions.

This is why it has been decided to concentrate most work in the future on the Helios Prototype. The development of fuel cells is the biggest problem here. Only if solar energy can be stored successfully for night flight, long flights will be made possible. This will take at least another four years.

AeroVironment Helios Prototype

The so-called Helios Prototype is the largest version of a super light wing by AeroVironment. At 75,3 meters it has a bigger wing span than a Jumbo Jet. When compared with the first Pathfinder, the wing was extended two and a half times, keeping the same depth. The structure stayed in principle the same. A round spar made of carbon fibres covered with Kevlar is used. It is combined with CFC ribs and a Mylar covering. The L-shaped structure of the "fuselages" also consists of composite materials.

14 electric engines, which are distributed over the wing span, propel the aircraft. They are powered by numerous lithium battery packs, which have to be exchanged after each flight. The wing will be fitted with solar cells for future high altitude flights. However, the special thin and powerful models are very expensive. Until now one was only able to purchase enough materials for one section.

A further problem awaiting solution is energy storage at night during high altitude flights, which will last several months. Special fuel cells will have to be developed especially.

Up to now the Helios Prototype can only be deployed on short flights. The maiden flight was successfully completed on 8 September. It handled satisfactorily, although the unexpected triggering of the rescue parachute caused the aircraft to land prematurely after 1:15hrs.

AeroVironment proved last year that the advance into high altitudes with solar powered aircraft is not just a dream. On 15 August 1998 an altitude of 24,445 meters was reached during a 15hr flight above Hawaii with the Parthfinder Plus (wing span 36.88 meters).

Aurora Flight Sciences Perseus B

The history of the Perseus Drone started as early as in 1989, which is a long time before the start of the ERAST program. Even at that time the aim was the research of the stratosphere at high altitudes. Over the years several ptototypes were developed. Perseus A for instance has a closed propulsion system with an on-board oxygen supply for the piston engine. This model took to the air for the first time in 1993.

The more conventional Perseus B with Rotax engine and three-stage turbocharger followed in October 1994. Unfortunately this aircraft was damaged in 1996 and was modified as a result of this. On 27 June 1998 Perseus B reached a height of 18,373 meters - a record for a single engine propeller aircraft. After this further improvements were carried out. External tanks have now doubled fuel capacity and the engine output has been increased by 20 per cent. The avionics have been enhanced by the addition of a second GPS and a laser INS. However, new flight tests ended on 1 October with a crash landing near Barstow, in which the aircraft sustained some damage.

General Atomics Altus II

Altus II is based on Predator, the reconnaissance drone used by the US Air Force. It has, however, got a much bigger wing span. The nose is designed to carry 150kg of scientific instruments. Altus II carried out her maiden flight on 1 May 1996, and was used for a radiation study of the Sandia National Laboratory in Oklahoma in October. A thorough overhaul was to follow, e.g. the installation of a two-stage turbocharger. With it an altitude of 16,765 meters was reached for four hours on 23 July. Altus II has flown above Hawaii several times. It was recently used as part of a programme for measuring cirrus clouds in April/May.

Scaled Composites Proteus

Proteus, which was designed by Burt Rutan, does not really fit into the ERAST program since it is a manned aircraft. This is why NASA mainly supports the development of an intricate autopilot, with which Proteus can be deployed unmanned. Apart from this, trials are being carried out with a Satcom System, which will make it possible to control the aircraft beyond the radar horizon.

Since its June 1998 first flight, Proteus has mainly flown from Mojave. Until the middle of September about 50 flights had been carried out, among them the first ones in which a big antenna pod was carried. This will house an aerial, with which Proteus will be able to operate as a flying relay station. Angel Technologies in connection with Raytheon are carrying out this project.

From page 90 of FLUG REVUE 12/99