Proteus Completes Pacific, Polar Mission

Aviation Week—April 23, 2001:

Scaled Composites’ Proteus high-altitude aircraft has completed a five-week government science mission throughout the Pacific Rim, capped by atmospheric measurements taken over the North Pole at 48,000 ft.

For some missions, Proteus may serve as an alternative to NASA’s ER-2 research aircraft, which are converted Lockheed U-2 reconnaissance aircraft. The trip demonstrated the reliability and cost of the one-of-a-kind Proteus over an extended period and a range of conditions.

Scientists are pleased with the flexibility of dealing with Scaled Composites’ operation. They can be adjusting instruments almost until engine start and make mission changes quickly, something that is not possible with the elaborate procedures of the ER-2s, flown by pilots in cumbersome pressure suits.

Proteus was carrying a large belly pod containing two atmospheric sounding instruments—NAST-I, which uses infrared interferometry, and NAST-M, which measures microwave emissions ( AW&ST Nov. 20, 2000, p. 34). These may be used in next-generation Earth observation satellites, and NASA’s Langley Research Center was funding the flights to support this effort. The payload weighed about 1,300 lb., and the total pod weight was around 1,700 lb., said Michael W. Melvill, Scaled vice president and general manager.

The aircraft took off from Scaled’s Mojave, Calif., base on Feb. 19 and flew to Honolulu, Majuro Island in the Marshall Islands, Guam, Kadena AB on Okinawa, Yokota AB near Tokyo, Eielson AFB, Alaska, and returned to Mojave on Mar. 26. It made an 11.6-hr. flight on Mar. 23 from Eielson AFB to the North Pole, the longest of the journey.

Total flight time was 123 hr. with no significant problems, and the aircraft was always within a day of its planned schedule. The flight started six weeks after contract approval. The active Scaled crew was two pilots and two ground crewmen, and the mission was tracked at Mojave via Inmarsat satellite telephone voice and data link, which worked below 78 deg. Lat. The mission operated under a $680,000-fixed-price contract, good for up to 160 hr., or an average of $4,250/hr. This covered all expenses, including airfare and hotel bills for ground support. Estimated from NASA budget figures, the basic cost for an ER-2 is about $20,000/hr., or five times higher.

Proteus has a fore and aft wing configuration and is powered by two Williams-Rolls FJ44-2A turbofan engines modified to operate at up to 65,000 ft. It set a sustained altitude record of 61,919 ft. for its weight class in October, with the instrument pod removed. Pilots Melville and Michael T.
Alsbury have enough confidence in the composite structure and pressurization systems that they wear flight suits instead of pressure suits in the room-temperature cockpit. Though designed for 10 psi., it is operated at 7 psi., which requires supplemental oxygen at higher altitudes.

In the tropics, ceiling can be limited by very cold temperatures instead of performance, Melville said. The tropopause there is higher than at the upper latitudes, so the temperature continues to lapse down to lower levels. Cold temperatures, e.g. -125F, let nitrogen pressure leak past landing gear seals.

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