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

Astrophysics PlatformAstrophysics Platform

R.A. Fesen R.A. Fesen Dartmouth CollegeDartmouth College

Department of Physics and AstronomyDepartment of Physics and Astronomy

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.

The Hubble Space Telescope

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.

HST is NASA’s best known spacecraft with its images seen worldwide.

But Hubble is a relatively small telescope.

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

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.

The Hubble Space Telescope doesn’t rank among the World’s 25 largest

telescopes 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

2.4m Hubble

Hubble’s Main Advantages:

1. High resolution optical imaging: FWHM = 0.03-0.05’’

2. UV/Optical spectra at sub-arcsec angular resolution

3. UV sensitivity: 1160 – 3000 Angstroms

4. Low background in the near IR (1.0 – 2.5 microns)

Hubble’s Main Advantages:

1. 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)

The value of High Angular Resolution is obvious.

The value of High Angular Resolution is obvious.

14,000 ft 250 miles

A picture taken from 51,000 ft aboard the Concorde

We place telescopes on high mountains. But wouldn’t it better better from an

airplane?

Stratospheric Unmanned Aircraft: UAVs.Stratospheric Unmanned Aircraft: UAVs.

There’s currently considerable interest in UAVs in the There’s currently considerable interest in UAVs in the military and in the general aerospace community, mostly military and in the general aerospace community, mostly in aircraft-type vehicles like Predator and Global Hawk.in aircraft-type vehicles like Predator and Global Hawk.

But these platforms are poorly suited for most science But these platforms are poorly suited for most science missions. They are expensive, not very stable, and have missions. They are expensive, not very stable, and have short flight times. short flight times.

Global HawkGlobal HawkPredator B Predator B (Altair)(Altair)

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

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

Lake Tahoe, CALake Tahoe, CA

View of Oregon from View of Oregon from a U2 flying at 70,000 a U2 flying at 70,000 ft.ft.

The cloud deck is The cloud deck is more than more than 30,000 ft 30,000 ft belowbelow..

There is simply noThere is simply no weather above 60 weather above 60 kft.kft.

And the sky gets And the sky gets very dark.very dark.

National Weather Service

Nearly all HAPs are designed to operate in the 60-70 kft altitude range where wind speeds tend to be the lowest.

Stratospheric Winds vs Altitude

The sweet spot in altitude for an airship The sweet spot in altitude for an airship serving as an astronomical observing serving as an astronomical observing platform is 65 - 85 kft.platform is 65 - 85 kft.

Altitude Pressure Density Altitude Pressure Density TemperatureTemperature

0 km 0 ft 1013 mbars 1.2 kg/m3 +15 C 0 km 0 ft 1013 mbars 1.2 kg/m3 +15 C +60 F+60 F

4.4 km 14,000 ft 620 mbars 0.82 kg/m3 -11 C +10 4.4 km 14,000 ft 620 mbars 0.82 kg/m3 -11 C +10 FF

12.2 km 40,000 ft 185 mbars 0.31 kg/m3 -57 C -71 12.2 km 40,000 ft 185 mbars 0.31 kg/m3 -57 C -71 F F

15.2 km 50,000 ft 115 mbars 0.19 kg/m3 -56 C -69 15.2 km 50,000 ft 115 mbars 0.19 kg/m3 -56 C -69 F F

18.3 km 60,000 ft 70 mbars 0.12 kg/m3 -56 C -69 18.3 km 60,000 ft 70 mbars 0.12 kg/m3 -56 C -69 FF

19.8 km 65,000 ft 55 mbars 0.088 kg/m3 -56 C -69 19.8 km 65,000 ft 55 mbars 0.088 kg/m3 -56 C -69 FF

21.3 km 70,000 ft 45 mbars 0.075 kg/m3 -56 C -69 21.3 km 70,000 ft 45 mbars 0.075 kg/m3 -56 C -69 F F

24.4 km 80,000 ft 28 mbars 0.042 kg/m3 -52 C -62 24.4 km 80,000 ft 28 mbars 0.042 kg/m3 -52 C -62 FF

25.9 km 85,000 ft 22 mbars 0.034 kg/m3 -51 C -60 25.9 km 85,000 ft 22 mbars 0.034 kg/m3 -51 C -60 FF

27.4 km 90,000 ft 17 mbars 0.027 kg/m3 -49 C -56 27.4 km 90,000 ft 17 mbars 0.027 kg/m3 -49 C -56 FF

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 hrsDevelopment/Construction Cost: $482M ? Est. Operations costs per year: ~$50M small; $2-3M

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.

MaunaMauna KeaKea

SOFIASOFIA

AirshiAirshipp

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.

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 any ground-

based facilities.

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

Built by AeroVironment

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.

DoD is spending $40M just on a 9 month PDR study for a design of a long-duration, station-keeping airship.

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

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.

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.

A High-Altitude Astronomical Observatorywould 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:

1. Can we do excellent science at 65-75 kft?

2.Can we make optical observations during the day? That is, could we operate 24/7 ?

3.How dark is the sky at 65 kft at night and day?

A High-Altitude Astronomical Observatory

1. Sky brightness measurements

2. How does the sky brightness overhead change with altitude

3. Is it possible to observe during the day? Is the sky dark enough? Can one image stars during the daytime at 65+ kft ?

4. Payload stability.

Station Keeping: Sprint and Drift

windwind

stationstation

upwind positionupwind position

RRdd

RRccstation - desired position over groundstation - desired position over groundupwind position - nav algorithmupwind position - nav algorithm attempts to maintain this positionattempts to maintain this positionRd - drift radius, determined byRd - drift radius, determined by wind/speed equationwind/speed equationRc - control radius for navigationRc - control radius for navigation control algorithmcontrol algorithm

VV

Vehicle V drives for station until withinVehicle V drives for station until withindistance Rdistance Rdd, then upwind position becomes, then upwind position becomesnew target. V continues at desired groundnew target. V continues at desired groundspeed to upwind position until within Rspeed to upwind position until within Rccthen desired ground speed becomes zero. then desired ground speed becomes zero.

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

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

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

A High-Altitude, Astronomical Platform

• Advantages:• 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 running 24/7.

• Engineering and Environment Obstacles• Platform engine and payload power requirements• LTA envelope fabric strength and UV + ozone durability• Night-time battery, fuel-cell capacity• Launch and recovery procedures• Lightweight telescope + precise pointing/tracking system• Ability to slew telescope without re-positioning the airship

SOFIA: Stratospheric Observatory For Infrared Astronomy Altitude: 41 kft Primary Mirror Diameter: 2.5 m (~ HST ) Image quality: ~ 3” @ 5 microns Diffraction image quality: > 15 microns Wavelength regime: 0.3 – 1600 microns Number of observing hrs per yr: 960 hrs (~ 8 hrs per night) Development/Construction Cost: $482M Est. Operations costs per year: ~$40M

How high up do you have to fly?

A photo taken from the window of a TR-1 (U2) aircraft

from an altitude of around 75,000 ft.

SOFIA: Stratospheric Observatory For Infrared Astronomy Altitude: 41 kft Primary Mirror Diameter: 2.5 m (~ HST ) Image quality: ~ 3” @ 5 microns Diffraction image quality: > 15 microns Wavelength regime: 0.3 – 1600 microns Number of observing hrs per yr: 960 hrs (~ 8 hrs per night) Development/Construction Cost: $482M Est. Operations costs per year: ~$40M

Platform Communications Corp.

Instead of a balloon gondola arrangement which blocks out part of the sky, a high-altitude scientific airship platform might employ a double-hulled catamaran design.

A solar powered, super-pressure Airship platform

But…

The higher up one goes, the larger the LTA vehicle needed.

The bigger the payload mass, the larger the LTA vehicle needed. And the bigger the airship, the harder it will be to fly/push against the stratospheric winds.

So…

How high do you have to get to get Hubble-like images?Can a LTA vehicle be maneuverable (i.e. station-keeping) and have a long duration flight time?Can a lightweight, moderate-size telescope be built to fly on a LTA Airship and be stable enough for precise pointing and image tracking over much of the sky?

Many technology challenges have been solved. A Hybrid Airship concept leverages many prior NASA projects: e.g., ULDB balloon fabrics, HA airship designs (SWRI), HA solar powered aircraft (AeroVironment), thin-film solar arrays (ITN Energy Systems), & “Blind Pointer” (NASA/AMES).

DoD has fast-tracked $90M (PDR/CDR) for a similar but far larger & much more powerful airship design for use by NORAD and Missile Defense Agency being developed by Lockheed-Martin. Military Reqs: 4000 lb payload & 10-15 kilowattts of payload power; to be located at mid-latitudes with flight durations of at least 6 months up to 5 yrs.

Now: How do you do this?

…leverage prior & current UAV Research.

Can one really build a HA Airship for astronomy?

• The platform must: • Be stable enough for subarcsec resolution images• Be able to view most if not much of the sky• Carry a relatively large, lightweight telescope• Require no expendables (e.g., LN2)

Telescope and Optical Imaging Camera:• Ball Aerospace’s 1.3m Beryllium AMSD mirrors (10.3 kg/m^2) or a silicate graphite mirror• CCD camera + thermal electric cooler (no dewar; no LN2). Ambient air temperature ( -55 C)

• An array of four 8128 x 8128 CCD with 0.1’’/pixel would provide a FOV of nearly 30 arcmin square. But no dewar needed! If scale was set at 0.2”/pixel, image would be 1 degree square.• Telescope + CCD camera + filter wheels: <100 kg.

Lightweight Telescope and Pointing/Guiding System

Stability and Precise pointing:• NASA Ames “Blind Pointer” – 10 arcminute accuracy• NASA/Univ. Wisconsin Starfinder: ~2 arcsec accuracy• Commerical image stabilization platforms/software• Tip/tilt secondary mirror for fine guiding and image control

Lightweight Telescope and Pointing/Guiding System

A High Altitude Science Platform would leverage several technological developments from prior NASA and DoD

projects

• LTA Vehicle (Balloon) fabrics:• ULTRA Long Duration Balloon Project (NASA/Wallops)

• Airship design/hardware, and command and control software

• Army’s Sounder project (SWRI/DoD)• High Altitude propulsion: (lightweight motors and efficient props)

• Pathfinder and Helios (AeroVironment and NASA/ERAST)• Lightweight Photovoltaic cells (Solar Cells)

• Pathfinder and Helios (AeroVironment and NASA/ERAST)• Lockheed-Martin’s DoD high altitude airship (e.g., United Solar Ovonic’s ultra-light, amorphous, thin-film triple junction PV modules)

There has long been interest in building such a vehicle from various governmental agencies and the telecom industry.The first real attempt was made by Raven Industries in the late 60’s with a project called High Platform II. This solar powered 20 knot, 136 lb aerostat had control surfaces attached to its Mylar hull and was capable of operating for more than 6 months at 70,000 ft.

This experimental solar powered airship was flown successfully at 70,000 ft. Note the solar cell array on the nose.

The gondola provided the support for the mechanical components of the propulsion system.

Summary:

1.1. Optical imaging would greatly raise the visibility of NASA’s balloon Optical imaging would greatly raise the visibility of NASA’s balloon program with the public and in the science communities.program with the public and in the science communities.

2.2. A HA airship with a 1-2 meter astronomical telescope would A HA airship with a 1-2 meter astronomical telescope would generate space quality data and could be built by leveraging generate space quality data and could be built by leveraging many technology developments from previous NASA and on-many technology developments from previous NASA and on-going DoD programs. going DoD programs.

3.3. Development costs could be rather modest relative to the potential Development costs could be rather modest relative to the potential science impact.science impact.

4.4. A maneuverable, long duration, high altitude platform has A maneuverable, long duration, high altitude platform has applications outside of Astronomy, e.g., Earth Science, applications outside of Astronomy, e.g., Earth Science, Atmospheric Science.Atmospheric Science.

Supplemental slides

Large, ultra lightweight mirrors are now available

The VLT 1.1 meter secondary mirrors are Beryllium mirrors. Each has a total weight 51 kg with mirror assembly.The 0.9 m SIRTF mirror is also made of Beryllium. The whole Ritchey-Chretien design telescope weights less than 50 kg.

SIRTF

VLT

The high cost of spacecraft development, deployment, and operations have kept current

UV/Optical/IR space observatories down to just a handful.

• 2.40 m Hubble Space Telescope (end ~2007)• 0.85 m SIRTF/Spitzer Space Telescope (end before 2009)• 0.75 m (4 x 0.35 m) FUSE (end ~2006)• 0.50 m Galex (end ~2006)

Q2) Can one build a maneuverable, long-duration LTA science platform suitable for astronomical imaging?

2001 NASA Study:

Cross Enterprise Technology Development Program

A high Altitude, Station-Keepping Platfor for Astronomy

Winds areslowest aroundaltitudes near 16 - 20 km.

StratSat is being built by ATG and is intended to remain airborne for up to five years at 60,000 ft, undertaking narrow and broadband communications as part of a much larger global communications and surveillance network. It will have a solar array and a 450 hp diesel engine as a propulsion unit. Overall length is 656 ft (200m). Completion of the first vehicle is expected in 2004/2005.

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

Built by AeroVironment

HA Airships are also being looked at as HA Airships are also being looked at as communication platformscommunication platforms

The cost of building, launching, and establishing The cost of building, launching, and establishing communication links for conventional communication links for conventional communication satellites, plus the expenses communication satellites, plus the expenses and environmental issues with numerous cell and environmental issues with numerous cell phone towers have lead some phone towers have lead some telecommunication companies to look closer to telecommunication companies to look closer to Earth for cheaper solutions. Earth for cheaper solutions.

Company Country Platform Name Company Country Platform Name SkyStation USA Sky Station SkyStation USA Sky Station ATG UK StratSatATG UK StratSatWireless ISG Japan Stratospheric PSWireless ISG Japan Stratospheric PSPlatform Wireless USA Airborne Relay Platform Wireless USA Airborne Relay Comm Comm