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NuSTAR Blazes Into Space On The Wings Of Pegasus

Diagram shows NuSTAR in its 33 ft. long fully deployed configuration. The mast will be commanded up in about a week. Image Credit: NASA, JPL, CalTech

An exotic new space telescope with owl eyed X-ray vision  is poised to see right through blocking gas and dust to reveal undiscovered black holes in the Milky Way and more distant cosmos.

The NASA’s  NuSTAR Nuclear Spectroscopic Telescope Array is undergoing checkout in space after launch June 13 by a  three-stage winged Pegasus XL rocket,  dropped from the Orbital Sciences “Stargazer” L-1011 aircraft flying in darkness near Kwajalein atoll in the Pacific.

The night launch of the Pegasus XL  viewed from the cockpit of Stargazer was a stunning sight based on my own unique experience of participating in a Pegasus launch on board the same L-1011. Launching a Pegasus is like unleashing a flaming hypersonic freight train just outside your windows.

Both the Pegasus and the 772 lb. spacecraft were built by a consortium of contractors led by Orbital Sciences Corp. The launch placed NuSTAR into a  393 x 389 mi. equatorial orbit. The observatory will have 100 times better sensitivity than its predecessors, and 10 times sharper resolution.

Television sequence looking forward from the Pegasus tail and first stage motor nozzle was taken by a camera mounted on the belly of the L-1011. As the Pegasus drops away its 22 ft. dia wing comes into view. The ignition plume obliterated the picture immediately after the last image. Image Credit: Orbital Sciences

“NuSTAR will help us find the most elusive and energetic black holes, to help us understand the structure of the universe,” said Fiona Harrison, the mission’s principal investigator at the California Institute of Technology in Pasadena, Calif.

The Jet Propulsion Laboratory spacecraft will spend at least two years observing high-energy X-rays more closely, and in higher resolution, than any space telescope before it. On the electromagnetic spectrum, high-energy X-rays are beyond the scope of visible light and are challenging to detect.

NuSTAR’s advanced design uses two sets of 133 thin, nested  canisters of mirrors to capture X-rays as they bounce off the reflecting surfaces at glancing angles. The expected result is an orbiting observatory that enables astronomers to see the universe in an additional band of light, advancing our understanding of how galaxies form and evolve.

Specially coated grazing incidence mirrors are shown edge on (left) and as an optical unit prior to integration with spacecraft. Photo Credit: NASA, JPL, CalTech

NuSTAR’s primary science objectives include:

  • Conducting a census for black holes on all scales using wide-field surveys of extragalactic fields and the Galactic center.
  • Mapping radioactive material in young supernova remnants; Studying the birth of elements and understand how stars explode.
  • Observing powerful jets of gas millions of miles long found in the most extreme active galaxies,  to understand what powers the giant cosmic accelerators that create them.

To achieve these goals  NuSTAR uses a novel design. Powerful X-ray detectors are located on the spacecraft bus, along with a single 5 panel solar array.

The telescope’s optics however are located in an optical section that will be separated from the bus by a 33 ft. long self assembling truss,  like the truss structures used to deploy solar arrays on the International Space Station.

Graphic illustrates the current X-ray imaging capability for deep space black holes (upper left) compared with the lower right depiction of how black holes and other X-ray sources should appear with NuSTAR resolution. Image Credit: NASA. JPL. CalTech

On NuSTAR the truss will be used to separate the optics from the detectors to achieve a proper focus. About a week after launch,  ground controller’s will command the truss to extend the optical section away from the detectors.

The mirrors are equally divided with 133 mirrors between each of two cylindrical mirror shells that have apertures that resemble two giant owl eyes when viewed head on. The mirrors are arranged in this way in order to focus as much X-ray light as possible back down on the detectors.

X-rays don’t behave like visible light. Instead of easily bouncing off surfaces, they tend to be absorbed. However, if an incoming X-ray grazes a surface at a very small, glancing angle, it will be reflected. By nesting mirrors of different sizes and angles to form grazing incidence reflectors more X-rays can be reflected and focused onto the same spot down at the detector end of the spacecraft.

A Pegasus launch from the L-1011 Stargazer  is a far more dynamic and spectacular operation than it might seem on television which can not convey the impressive sights and sounds of the event.

Winged Pegasus XL is mounted to belly of Lockheed L-1011 “Stargazer” Orbital Sciences drop aircraft.  Photo Credit: NASA, JPL, CalTech

My flight in 2003 as a senior editor for Aviation Week & Space Technology was to launch the Sorce solar monitoring spacecraft, a satellite that is still operational.

Except for the Boeing 747/shuttle Enterprise separation flights in the 1970s the Pegasus XL winged booster is largest, heaviest air launched vehicle ever dropped by another aircraft

As an example,  a Pegasus XL with payload is 9 tons heavier than was the  X-15 rocket plane dropped from a B-52.

Pilot Bill Weaver and copilot Ebb Harris flew  Wednesday’s  NuSTAR launch from Kwajalein, the same crew that piloted the  Sorce mission I was on. Weaver is one of the most notable pilots in the U. S.  with about 25,000 flight hours. As a Lockheed test pilot Weaver survived being ripped from his disintegrating  SR-71 at Mach 3 and 78,000 ft.

There is a large two seat computer panel in what was the first class section of the L-1011.  The controller for Pegasus systems sits on the left while the controller for spacecraft systems is on the right. They begin a countdown checklist in the aircraft 4 hr. before launch.

After takeoff  exactly  1 hr. before launch,  they work through a 70 item checklist. In the last hour of the countdown the L-1011 climbs to 39,000 ft. and is  piloted around a racetrack course precisely plotted with GPS waypoints to achieve launch at the right moment pointed in the correct direction as the aircraft enters a 10 x 40 naut. mi. “launch box” .  The drop and ignition as I saw it from the cockpit is described in the following excerpts from my story in the Aug. 25, 2003 Aviation Week. I was the first and only journalist to ever fly on a Pegasus launch.

Pegasus launch panel in L-1011 has launcher controller on left and NuSTAR spacecraft controller in foreground. Photo Credit: Orbital Sciences

“The Launch Conductor confirmed ‘Go’ for launch. Drop on my mark 3, 2, 1 drop. The copilot pushed a button on his side of the center console opening five large retention hooks, and the Pegasus fell away.

“The instant loss of 52,000 lb.—17% of the aircraft’s weight—had a dramatic affect on the L-1011. A loud bang and a tremendous shudder in the airframe made it feel like the aircraft had just made an extremely hard landing.”

Freed of the Pegasus weight, we quickly shot up, as if the aircraft was hooked to a giant bungee cord on the uptake.

The pilots quickly made a 10 deg. left heading change to avoid flying through the Pegasus plume or flying debris and to put at least 1,000 ft. between us and the rocket.

“Inside a jet aircraft you can almost never hear things outside, but not so with the Pegasus ignition. Five seconds after release the 163,000 lb. thrust first stage ignited with a roar clearly audible in the cockpit”.

Looking down from the right cockpit windows we could see the wings of the Pegasus flash below us trailing an unexpectedly vivid orange rocket plume as the Pegasus quickly accelerated to Mach 2. In an instant it surged ahead then pulled up hard into a 35 deg. climb directly in front of the L-1011.

At 39,000 ft. the sky above is already getting dark and to see the vivid orange plume of the Pegasus up close climbing to space against that dark sky was an unforgettable sight.

The Sorce solar monitoring satellite Pegasus launch I participated with in 2003 had excellent NASA T-38 photo chase coverage showing a Pegasus launch sequence like occurred with NuSTAR in darkness. Photo Credit: NASA

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