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The Advantages of a Maneuverable, Long Duration, High Altitude Astrophysics Platform

The Advantages of a Maneuverable, Long Duration, High Altitude Astrophysics Platform. R.A. Fesen Dartmouth College Department of Physics and Astronomy. The Main Point A high-altitude, balloon-borne optical telescope could generate high resolution images on a par with HST.

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The Advantages of a Maneuverable, Long Duration, High Altitude Astrophysics Platform

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  1. The Advantages of a Maneuverable, Long Duration, High Altitude Astrophysics Platform R.A. Fesen Dartmouth College Department of Physics and Astronomy

  2. The Main Point A high-altitude, balloon-borne optical telescope could generate high resolution images on a par with HST. But do it at a tiny fraction of the cost.

  3. The Hubble Space Telescope

  4. The Hubble Space Telescope’s high angular resolution at optical wavelengths has made it a extraordinarily powerful research tool in many sub-fields of Astronomy.

  5. HST is NASA’s best known spacecraft with its images seen worldwide. But Hubble is a relatively small telescope.

  6. What makes Hubble so great? There are much larger telescopes in the world.

  7. The primary mirror of Keck I. Thirty-six hexagonal segments are joined to form the 10-m mirror. (Notice the person on the crane in front of the mirror to set the scale.) The twin Keck I and II telescopes are the largest optical telescopes in the world.

  8. 11.8m (2 x 8.4m) LBT (05) 10.4m GTC LaPalma (05) 2 x 10.0m Keck I and II 10.0m SALT (05) 9.2m HET 8.3m Subaru 4 x 8.2m VLT (ESO) 8.1m Gemini North (40%) 8.1m Gemini South (40%) 6.5m MMT 2 x 6.5m Magellan 6.0m BTA 5.0m Hale 4.2m WHT 4.2m SOAR (30%) 4.0m CTIO (100%) 3.9m AAT 3.8m UKIRT 3.8m KPNO (100%) 3.6m ESO 3.6m CFHT 3.6m Telescopio Galileo 3.5m WYIN (40%) 3.5m ARC 3.5m NTT The Hubble Space Telescope doesn’t rank among the World’s 25 largest telescopes 2.4m Hubble

  9. Hubble’s Main Advantages: • High resolution optical imaging: FWHM = 0.03-0.05’’ • UV/Optical spectra at sub-arcsec angular resolution • UV sensitivity: 1160 – 3000 Angstroms • Low background in the near IR (1.0 – 2.5 microns)

  10. Hubble’s Main Advantages: • High resolution optical imaging: FWHM = 0.03-0.05’’ • UV/Optical spectra at sub-arcsec angular resolution • UV sensitivity: 1160 – 3000 Angstroms • Low background in the near IR (1.0 – 2.5 microns)

  11. The value of High Angular Resolution is obvious.

  12. The value of High Angular Resolution is obvious. 14,000 ft 250 miles

  13. We place telescopes on high mountains. But wouldn’t it better better from an airplane? A picture taken from 51,000 ft aboard the Concorde

  14. Stratospheric Unmanned Aircraft: UAVs. There’s currently considerable interest in UAVs in the military and in the general aerospace community, mostly in aircraft-type vehicles like Predator and Global Hawk. But these platforms are poorly suited for most science missions. They are expensive, not very stable, and have short flight times. Predator B (Altair) Global Hawk

  15. Just how high up do you have to go to avoid all clouds and stormy weather and start having space-like astronomical observing conditions?

  16. A photo taken from the window of a TR-1 (U2) aircraft from an altitude of around 75,000 ft.

  17. Lake Tahoe, CA

  18. View of Oregon from a U2 flying at 70,000 ft. The cloud deck is more than 30,000 ft below. There is simply noweather above 60 kft. And the sky gets very dark.

  19. Stratospheric Winds vs Altitude Nearly all HAPs are designed to operate in the 60-70 kft altitude range where wind speeds tend to be the lowest. National Weather Service

  20. The sweet spot in altitude for an airship serving as an astronomical observing platform is 65 - 85 kft. Altitude Pressure Density Temperature 0 km 0 ft 1013 mbars 1.2 kg/m3 +15 C +60 F 4.4 km 14,000 ft 620 mbars 0.82 kg/m3 -11 C +10 F 12.2 km 40,000 ft 185 mbars 0.31 kg/m3 -57 C -71 F 15.2 km 50,000 ft 115 mbars 0.19 kg/m3 -56 C -69 F 18.3 km 60,000 ft 70 mbars 0.12 kg/m3 -56 C -69 F 19.8 km 65,000 ft 55 mbars 0.088 kg/m3 -56 C -69 F 21.3 km 70,000 ft 45 mbars 0.075 kg/m3 -56 C -69 F 24.4 km 80,000 ft 28 mbars 0.042 kg/m3 -52 C -62 F 25.9 km 85,000 ft 22 mbars 0.034 kg/m3 -51 C -60 F 27.4 km 90,000 ft 17 mbars 0.027 kg/m3 -49 C -56 F

  21. SOFIA HA Airship Altitude: 41 kft 80 kft Primary Mirror Diameter: 2.5 m (~ HST ) 0.5 m Image quality: ~ 3” @ 5 microns ~2.5” @ 5 microns Diffraction image quality: > 15 microns > 0.3 micron Wavelength regime: 0.3 – 1600 microns 0.3 -1.0 microns Number of observing hrs per yr: 960 hrs (~ 8 hrs per night) ~3000 hrs Development/Construction Cost: $482M ? Est. Operations costs per year: ~$50M small; $2-3M

  22. Even at an altitude of 14 km (46 kft), nearly a mile above where NASA’s SOFIA 747SP will fly, there are still many strong atmospheric absorption features between 5 – 10 microns. And these can vary with time. But nearly all these features go away when flying at 28 km (90 kft), with little gained by flying higher than this. Airship SOFIA MaunaKea

  23. A 70 kft High-Altitude, Station-Keeping LTA Platform • Advantages: • Offers spacecraft-like optical imaging capabilities. • No ground-site to purchase or develop. • No LDB/ULDB “no-fly” zone worries. • No weather interference; robust target scheduling. • Little atmospheric extinction; superb photometric conditions. • Locations near the Equator offers both N & S hemisphere target viewing. • True horizon-to-horizon observing is possible. • Little scattering of moonlight; i.e., largely darktime observing. • Simple line-of-sight 24/7 communications to platform.

  24. Several commercial telecommunication firms together with a well funded US military project are aiming at making autonomous, high-altitude, lighter-than-air (LTA) vehicles which can maneuver and station-keep for weeks to months. Such platforms may be a reality in a few years. A 0.5 m (20-inch) telescope mounted on such a high-altitude platform could generate high-resolution optical images superior to anyground-based facilities.

  25. HELIOS is a solar powered, propeller-driven, ultralightweight aircraft reached an altitude of 96,800 ft in August 2001. Built by AeroVironment

  26. DoD is spending $40M just on a 9 month PDR study for a design of a long-duration, station-keeping airship. It must fly unmanned autonomously at 70,000 feet for 1 – 6 months. Payload weight: 2 tons with 10 – 15 kWatts of power available to the payload. Fly at mid-latitudes. NORAD and MDA liked Lockheed-Martin’s design, an wanted to spend $50M on a 2-yr CDR program, followed by $9M for construction of a full-scale prototype.

  27. The telescope could be mounted in between the two airships, allowing for nearly unobstructed viewing.

  28. A 70 kft High-Altitude, Station-Keeping LTA Platform • Engineering Obstacles • Platform engine and payload power requirements; “Sprint & Drift” mode. • LTA envelope fabric strength and UV + ozone durability. • Launch and recovery procedures. • Lightweight telescope + precise pointing and tracking system. • Ability to slew telescope quickly without re-positioning the airship.

  29. One could go even higher than 70 kft, but… • The higher up one goes, the larger the LTA vehicle needed. • The heavier the payload, the larger the LTA vehicle needed. • And the bigger the airship, the harder it will be to fly/push • against the stratospheric winds in order to station-keep.

  30. A High-Altitude Astronomical Observatory would be basically a “Hubble-Junior” We know that if we go up to 100 kft, the image quality will be space-like. However, it is unlikely in the near future to build a high altitude science platform that can station-keep at these altitudes. So: Can we do excellent science at 65-75 kft? Can we make optical observations during the day? That is, could we operate 24/7 ? How dark is the sky at 65 kft at night and day?

  31. A High-Altitude Astronomical Observatory • Sky brightness measurements • How does the sky brightness overhead change with altitude • Is it possible to observe during the day? Is the sky dark enough? Can one image stars during the daytime at 65+ kft ? • Payload stability.

  32. Station Keeping: Sprint and Drift station - desired position over ground upwind position - nav algorithm attempts to maintain this position Rd - drift radius, determined by wind/speed equation Rc - control radius for navigation control algorithm wind Rc upwind position Rd station Vehicle V drives for station until within distance Rd, then upwind position becomes new target. V continues at desired ground speed to upwind position until within Rc then desired ground speed becomes zero. V

  33. Now Flying: A small prototype (but science-sized!) is already flying. South Korea’s Station-Keeping HA Airship Program by the Korean Aerospace Research Institute & Worldwide Aero Corp. Size: 50 m x 12 m

  34. The telescope could be mounted in between the two airships, allowing for nearly unobstructed viewing.

  35. Summary: • A High-Altitude Astronomical Airship Platform • Besides space-like optical imaging capabilities, an Astro-HAP offers: • No ground-site to purchase or develop. • No weather interference; robust target scheduling • Little atmospheric extinction; superb photometric conditions • True horizon-to-horizon observing is possible. • Little scattering of moonlight; i.e., longer darktime observing runs • Simple line-of-sight communications 24/7 • Locations near the Equator offer both N & S hemisphere target viewing • Engineering Obstacles • Platform engine and payload power requirements; “Sprint & Drift” mode • LTA envelope fabric strength and UV + ozone durability • Launch and recovery procedures • Lightweight telescope + precise pointing and tracking system • Ability to slew telescope quickly without re-positioning the airship

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