The NASA Pathfinder and NASA Pathfinder Plus were the first two aircraft developed as part of an evolutionary series of solar- and fuel-cell-system-powered unmanned aerial vehicles (UAVs). AeroVironment, Inc. developed the vehicles under NASA's Environmental Research Aircraft and Sensor Technology (ERAST) program. They were built to develop the technologies that would allow long-term, high-altitude aircraft to serve as atmospheric satellites, to perform atmospheric research tasks as well as serve as communications platforms. They were developed further into the NASA Centurion and NASA Helios aircraft.

Pathfinder

AeroVironment initiated its development of full-scale solar-powered aircraft with the Gossamer Penguin and Solar Challenger vehicles in the late 1970s and early 1980s, following the pioneering work of Robert Boucher, who built the first solar-powered flying models in 1974. As part of the ERAST program, AeroVironment built four generations of long endurance unmanned aerial vehicles (UAVs) under the leadership of Ray Morgan, the first of which was the Pathfinder.

Development

In 1983, AeroVironment obtained funding from an unspecified US government agency to secretly investigate a UAV concept designated "High Altitude Solar" or HALSOL. The HALSOL prototype first flew in June 1983. Nine HALSOL flights took place at Groom Lake in Nevada. The flights were conducted using radio control and battery power, as the aircraft had not been fitted with solar cells. HALSOL's aerodynamics were validated, but the investigation led to the conclusion that neither photovoltaic cell nor energy storage technology were mature enough to make the idea practical for the time being, and so HALSOL was put into storage.

In 1993, after ten years in storage, the aircraft was brought back to flight status for a brief mission by the Ballistic Missile Defense Organization (BMDO). With the addition of small solar arrays, five low-altitude checkout flights were flown under the BMDO program at NASA Dryden in the fall of 1993 and early 1994 on a combination of solar and battery power. A series of flights were planned to demonstrate that an extremely light and fragile aircraft structure with a very high aspect ratio (the ratio between the wingspan and the wing chord) can successfully take-off and land from an airport and can be flown to extremely high altitudes (between and ) propelled by the power of the sun. In addition, the ERAST Project also wanted to determine the feasibility of such a UAV for carrying instruments used in a variety of scientific studies.

On October 21, 1995, the aircraft's fragility was aptly demonstrated when it was severely damaged in a hangar accident, but was subsequently rebuilt.

Atmospheric satellite tests

In July 2002, Pathfinder-Plus carried commercial communications relay equipment developed by Skytower, Inc., a subsidiary of AeroVironment, in a test of using the aircraft as a broadcast platform. Skytower, in partnership with NASA and the Japan Ministry of Telecommunications, tested the concept of an "atmospheric satellite" by successfully using the aircraft to transmit both an HDTV signal as well as an IMT-2000 wireless communications signal from , giving the aircraft the equivalence of a tall transmitter tower. Because of the aircraft's high lookdown angle, the transmission utilized only one watt of power, or 1/10,000 of the power required by a terrestrial tower to provide the same signal. According to Stuart Hindle, Vice President of Strategy & Business Development for SkyTower, "SkyTower platforms are basically geostationary satellites without the time delay." Further, Hindle said that such platforms flying in the stratosphere, as opposed to actual satellites, can achieve much higher levels of frequency use. "A single SkyTower platform can provide over 1,000 times the fixed broadband local access capacity of a geostationary satellite using the same frequency band, on a bytes per second per square mile basis."

Ray Morgan, president of AeroVironment, has described the concept as, "What we're trying to do is create what we call an 'atmospheric satellite,' which operates and performs many of the functions as a satellite would do in space, but does it very close in, in the atmosphere"

Specifications

thumb|Pathfinder Plus (left) and Helios Prototype (right) on the Dryden ramp

thumb|Solar Aircraft Evolution through the ERAST Program

{| class="wikitable" style="text-align:center;"

|+ Specifications

!   !! Pathfinder !! Pathfinder-Plus !! Centurion !! Helios HP01 !! Helios HP03

|-

| Length ft(m) || 12 (3.6) || 12 (3.6) || 12 (3.6) || 12 (3.6) || 16.5 (5.0)

|-

| Chord ft(m) || colspan="5" | 8 (2.4)

|-

| Wingspan ft(m) || 98.4 (29.5) || 121 (36.3) || 206 (61.8) || colspan="2" | 247 (75.3)

|-

| Aspect ratio || 12 to 1 || 15 to 1 || 26 to 1 || colspan="2" | 30.9 to 1

|-

| Glide ratio || 18 to 1 || 21 to 1 || ? || ? || ?

|-

| Airspeed kts(km/h) || || || 15–18 (27–33) || 16.5–23.5 (30.6–43.5) || ?

|-

| Max altitude ft(m) || 71,530 (21,802) || 80,201 (24,445) || n/a || 96,863 (29,523) || 65,000 (19,812)

|-

| Empty Wt lb(kg) || ? || ? || ? || 1,322 (600) || ?

|-

| Max. weight lb(kg) || 560 (252) || 700 (315) || ±1,900 (±862) || 2,048 (929) || 2,320 (1,052)

|-

| Payload lb(kg) || 100 (45) || 150 (67,5) || 100–600 (45–270) || 726 (329) || ?

|-

| Engines || colspan="5" | electric, 2 hp (1.5 kW) each

|-

| No. of engines || 6 || 8 || 14 || 14 || 10

|-

| Solar pwr output (kW) || 7.5 || 12.5 || 31 || 35 || 18.5

|-

| Supplemental power || batteries || batteries || batteries || Li batteries || Li batteries, fuel cell

|}

See also

  • Electric aircraft
  • History of unmanned aerial vehicles
  • Regenerative fuel cell
  • NASA Centurion (First flight 10 November 1998)
  • NASA/AeroVironment Helios Prototype (First flight 8 September 1999)
  • QinetiQ/Airbus Zephyr (First flight in 2008)
  • Facebook Aquila (First flight 28 June 2016)
  • SoftBank/AeroVironment HAPSMobile (First flight 11 September 2019)
  • BAE Systems PHASA-35 (First flight 17 February 2020)

References

This article contains material that originally came from the web article by Greg Goebel, which exists in the Public Domain.

  • "Photovoltaic Finesse: Better Solar Cells—with Wires Where the Sun Don't Shine", an article by Daniel Cho on page thirty-three of the September, 2003 issue of Scientific American
  • NASA's Helios Project
  • Helios for kids
  • Helios model by DesignsbyALX .
  • "3G Tested at in the stratosphere" 3G news release July 23, 2002
  • Science Daily article on Pathfinder Plus altitude record
  • Telecom relay achievements at Airport International
  • Space.com article
  • History of solar powered UAVs at The Future of Things
  • Pathfinder Plus at NASM
  • NASA-AeroVironment contract for followon projects
  • Helios record attempt article
  • NASA image collections:
  • NASA Pathfinder
  • NASA Pathfinder Plus
  • NASA Centurion
  • NASA Helios Prototype