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Webb closes in on destination with critical mirror alignment on tap
STORY WRITTEN FOR CBS NEWS & USED WITH PERMISSION
Thirty days outbound from Earth, the James Webb Space Telescope will slip into its parking orbit a million miles away Monday, an ideal spot to scan the heavens in search of faint infrared light from the first generation of stars and galaxies.
But getting there — and successfully deploying a giant sunshade, mirrors and other appendages along the way — was just half the fun.
Scientists and engineers now have to turn the $10 billion Webb into a functioning telescope, precisely aligning its 18 primary mirror segments so they work together as a single 21.3-foot-wide mirror, by far the largest ever launched.
Earlier this week, the mission operations team remotely completed a multi-day process to raise each segment, and the telescope’s 2.4-foot-wide secondary mirror, a half inch out of the launch locks that held them firmly in place during the observatory’s Christmas Day climb to space atop a European Ariane 5 rocket.
Now fully deployed, the 18 segments currently are aligned to within about a millimeter or so. For the telescope to achieve a razor-sharp focus, that alignment must be fined tuned to within 1/10,000th of the width of a human hair using multiple actuators to tilt and even change a segment’s shape if required.
“Our primary mirror is segmented, and those segments need to be aligned to a fraction of a wavelength of light,” said Lee Feinberg, optical telescope element manager at NASA’s Goddard Space Flight Center. “We’re not talking microns, we’re talking a fraction of a wavelength. That’s what’s tricky about Webb.”
Once aligned and its instruments calibrated, Webb will be 100 times more powerful than Hubble, NASA says, so sensitive to infrared light that it could detect the faint heat of a bumblebee as far away as the moon.
Each mirror segment was ground to a prescription that takes into account the deforming effects of gravity during their manufacture on Earth and their expected shrinkage in the ultra-low-temperatures of space. They were so precisely figured that if one was blown up to the size of the United States, the 14,000-foot-high Rocky Mountains would be less than 2 inches tall.
But if Webb was aimed at a bright star today, the result would be 18 separate images “and they’re going to look terrible, they’re going to be very blurry,” Feinberg said in an interview, “because the primary mirror segments aren’t aligned yet.”
That’s the next major hurdle for the Webb team, mapping out and then tilting each segment in tiny increments, merging those 18 images to form a single exactly focused point of light. It’s an iterative, multi-step process expected to take several months to complete.
But first, the telescope must get into orbit around Lagrange Point 2, 930,000 miles from Earth where the gravity of Sun and Earth combine to form a pocket of stability that allows spacecraft to remain in place with a minimum expenditure of fuel.
It’s also a point where Webb’s tennis court-size sunshade can work to maximum advantage, blocking out heat from the sun, Earth, moon and even warm interplanetary dust that otherwise would swamp the telescope’s sensitive infrared detectors.
As of Saturday, the mirror segments had cooled down to around minus 340 Fahrenheit, well on the way to an operational temperature of around minus 390, or slightly less than 40 degrees above absolute zero.
While the cool-down process continues, a 4-minute 58-second course correction thruster firing is planned Monday at 2 p.m. EST to change the spacecraft’s velocity by a slight 3.4 mph, just enough to put it in a distant orbit around Lagrange Point 2.
If all goes well, the telescope will remain in that six-month orbit for the rest of its operational life, firing its station-keeping thruster periodically to remain on station.
With the orbit insertion burn behind them, engineers will press ahead with mirror alignment, one of the most complex aspects of Webb’s already complicated deployment.
Each 4.3-foot-wide hexagonal primary mirror segment features six mechanical actuators in a “hexapod” arrangement on the back side, allowing movement in six directions. A seventh actuator can push or pull on the center of a segment to ever so slightly distort its curvature if needed.
After Webb’s Near Infrared Camera, or NIRCam, cools down to its operating temperature, Webb will be aimed at a bright star so the instrument can map out the reflections from all 18 segments, creating a mosaic showing their relative size and position.
The mirror segments then will be adjusted one at a time, using one actuator then another, to properly aim each one. Additional mosaics will be made as the process continues and depending on the results, the alignment process may have to be repeated.
“The big thing is getting the 18 primary mirror segments pointing in a similar way so that their images are about the same size,” Feinberg said. “Some of them might be very defocused and so you might get a big spot (blurred star image) on segment 5 and a small spot on segment 3.”
The goal is to tilt the segments as required to minimize the size of the defocused images and then to move the multiple reflections to the same point at the center of the telescope’s optical axis, all of them stacked on top of each other to produce a single beam of sharply focused light.
“At the very top level, think of it as 18 separate telescopes aligned to about the same level,” Feinberg said. “And then we will overlap 18 spots on top of each other. We call that image stacking. It is a process of tilting the primary mirror segments so that the images fall on top of each other.”
The key, he said, is “you really need very good control of those actuators, very precise tilts, because we need these 18 spots to overlap each other very well.”
Any given segment can lose one of its six tilt actuators with no impact. Even the loss of a center actuator can be compensated for to some extent by moving the segment up or down slightly.
But exhaustive testing on the ground showed the high-tech actuators are extremely reliable. The procedures were tested before launch using a sub-scale model of the telescope and Feinberg said he’s confident the alignment process will work as planned.
“When will we have an image of a star that’s phased (properly stacked and focused)? I think that’s going to be sometime in March, maybe late March,” he said.
“But then the next question is, when will we have the telescope fully aligned, including the secondary mirror, optimized for all the four instruments? The original plan had us achieving that a full four months into the mission. So that would be like the end of April.”
That still won’t be enough for science observations to commence.
Once the optical system is aligned, the team will focus on testing and calibrating NIRCam, a combination camera and spectrograph, and the telescope’s three other spectrographic instruments, one of which includes the fine guidance sensor needed to keep Webb locked on target.
That process will take another two months or so to complete. Only then will focused “first light” images be released to the public.
“We want to make sure that the first images that the world sees, that humanity see, do justice to this $10 billion telescope and are not those of, you know, hey look, a star,” said Jane Rigby, Webb operations project scientist at Goddard.
“So we are planning a series of ‘wow’ images to be released at the end of commissioning when we start normal science operations that are designed to showcase what this telescope can do … and to really knock everybody’s socks off.”
Atlas 5 rocket delivers two military inspector satellites to high-altitude orbit
Two satellites for a once-classified U.S. military program to track and inspect other spacecraft in orbit — a mission the Space Force’s top general equates to a “neighborhood watch” — lifted off from Cape Canaveral Friday on top of a United Launch Alliance Atlas 5 rocket.
Bound for an orbit thousands of miles above Earth, the satellites rode side by side in the Atlas 5 rocket’s payload compartment for the climb into space. The two satellites are the fifth and sixth spacecraft to join the Space Force’s Geosynchronous Space Situational Awareness Program.
The GSSAP satellites lurk near the ring of geosynchronous satellites that fly around Earth at the same speed of the planet’s rotation, allowing craft to remain over a fixed geographic location at an altitude of more than 22,000 miles (nearly 36,000 kilometers). Commercial companies and defense agencies use the orbit for communications, missile warning and signals intelligence missions.
Not only can the surveillance platforms help the Space Force track objects in geosynchronous orbit — a capability needed to manage traffic and avoid collisions — the GSSAP spacecraft can adjust their orbits to approach and image other satellites using sharp-eyed optical cameras.
The GSSAP satellites’ ability to maneuver around other spacecraft gives military officials data on the location, orbit and size of other objects in geosynchronous orbit, according to the Space Force, “enabling characterization for anomaly resolution and enhanced surveillance, while maintaining flight safety.”
“Data from GSSAP uniquely contributes to timely and accurate orbital predictions, enhancing our knowledge of the geosynchronous orbit environment, and further enabling space flight safety to include satellite collision avoidance,” officials wrote in the Space Force’s official GSSAP fact sheet.
The new GSSAP satellites launched Friday join four others deployed into orbit by Delta 4 rockets in 2014 and 2016.
ULA’s launch team at Cape Canaveral loaded the 196-foot-tall (59.7-meter) Atlas 5 rocket with liquid propellants during a trouble-free countdown Friday, culminating in startup of the first stage’s Russian-made RD-180 engine and ignition of a single strap-on solid-fueled booster at 2 p.m. EST (1900 GMT).
Liftoff of the Atlas 5 rocket with two satellites to join the US Space Force’s fleet of surveillance satellites tracking objects in geosynchronous orbit. https://t.co/YkxrNrSD8F pic.twitter.com/2X0XfOPUfo
— Spaceflight Now (@SpaceflightNow) January 21, 2022
The two powerplants combined to produce about 1.2 million pounds of thrust, five times the thrust of a Boeing 747 jumbo jet at full throttle, to propel the Atlas 5 rocket through a thin overcast cloud layer and downrange east from Cape Canaveral.
Two minutes after liftoff, the Atlas 5 shed its single Northrop Grumman-built strap-on booster. Three-and-a-half minutes into the mission, the Atlas 5’s payload fairing jettisoned to reveal the mission’s two U.S. Space Force satellites after climbing above the atmosphere.
The RD-180 first stage engine shut down nearly four-and-a-half minutes after liftoff, and the single-use bronze-colored booster stage separated to fall into the Atlantic Ocean. A Centaur upper stage, powered by an Aerojet Rocketdyne RL10C-1 engine, ignited a burn lasting more than eight minutes to reach the required velocity to enter orbit around Earth.
The Centaur stage fired two more times — at T+plus 1 hour, 9 minutes, and at T+plus 6 hours, 30 minutes — to maneuver the GSSAP satellites into their targeted deployment orbit at an altitude of 22,440 miles (36,113 kilometers) over the equator.
The satellites separated from the Centaur upper stage one at a time, and ULA confirmed the final spacecraft separation event at 8:45 p.m. EST Friday (0145 GMT Saturday).
The GSSAP satellites, built by Northrop Grumman, were expected to open their solar panels soon after separating from the Centaur upper stage. Friday’s mission, officially designated USSF 8, was the first launch by ULA this year, and the 91st flight of an Atlas 5 rocket since its inaugural launch in August 2002.
“ULA continues to launch national security assets into highly complex orbits,” said Gary Wentz, ULA’s vice president of government and commercial programs. “The USSF 8 mission was successfully delivered to near-geosynchronous orbit after a nearly 7-hour mission.”
The GSSAP program, which was classified until 2014, produces data that helps military and other government satellites “navigate freely and safely” in geosynchronous orbit, according to the Space Force’s Space Systems Command.
“The first four GSSAP satellites have performed remarkably well,” said Lt. Gen. Stephen Whiting, commander of Space Operations Command. “These next two satellites will add to that capability and enable us to understand more completely things that occur in the geosynchronous orbit. It’s a key piece in the puzzle for space domain awareness.”
The new GSSAP satellites will become sensors in the Space Force’s Space Surveillance Network, which tracks more than 27,000 satellites, derelict rockets, and other pieces of space junk circling Earth.
“The way I describe it is a neighborhood watch capability,” said Gen. John “Jay’ Raymond, the chief of space operations and the highest-ranking officer in the Space Force. “It allows us to better understand what’s going on in the domain, especially in a really critical orbit like geosynchronous orbit.”
Before the establishment of the Space Force, the Air Force sent one of the GSSAP satellites to the aid of a crippled U.S. Navy communications satellite in 2016. The Navy’s fifth MUOS relay satellite ran into propulsion trouble after launch, forcing it to use backup thrusters to climb into its perch in geosynchronous orbit.
The GSSAP satellite changed course to capture imagery of the MUOS 5 spacecraft to give engineers insight into its status and condition, the Air Force said at the time.
“Historically, the way we have surveilled or had awareness of the domain is we’ve taken observations from radars or optical capabilities, and we’ve come up with an address in space, if you will, of objects,” Raymond said Tuesday in a virtual discussion hosted by the Mitchell Institute.
Cataloguing satellites and space debris has been the a chief goal of the military’s space-related efforts for decades. But with countries like China and Russia fielding increasingly sophisticated military spacecraft, including anti-satellite capabilities, the Space Force needs the GSSAP satellites to add a new dimension in its tracking of objects in orbit.
“We’ve been worried about making sure two things don’t collide, that we can keep that domain safe for all, which is critical. But it’s not sufficient,” Raymond said. “If you move into a war fighting domain, you have to have more knowledge than just where something is. You have to have some insights into what those capabilities are, and this neighborhood watch capability has provided us a fuller look at what’s in space, specifically in the geosynchronous domain.”
The fifth and six satellites will provide “additional capacity” for the GSSAP network to better cover the large volume of space in the geosynchronous belt, Raymond said in response to questions from Spaceflight Now.
The rocket used to launch the fifth and sixth GSSAP satellites debuted a new configuration of ULA’s workhorse Atlas 5. The variant combined a single solid-fueled booster with a a 5.4-meter (17.7-foot) diameter payload fairing provided by RUAG Space, and a single RL10 engine on the Centaur upper stage.
This version of the Atlas 5 is known as the “511” configuration, with the first number denoting the size of the payload fairing, the second number representing the number of solid rocket booster, and the third digit the number of engines on the Centaur stage.
The placement of just one strap-on booster on the side of the Atlas 5’s first stage will give the rocket asymmetrical thrust as it climbs off the pad. Atlas 5 missions have flown with a single solid rocket booster before, but those flights used the smaller 4-meter-wide payload fairing option.
The Atlas 5-511 rocket will take off with 1.2 million pounds of thrust from the single solid-fueled booster and the first stage’s kerosene-fueled RD-180 main engine. According to ULA, the Atlas 5-511 can carry up to 11,570 pounds (5,250 kilograms) to an elliptical geostationary transfer orbit. Its capacity to low Earth orbit is roughly 24,250 pounds (11,000 kilograms), according to ULA performance data.
Tory Bruno, ULA’s CEO, calls the “511” version of the Atlas 5 the “Big Slider” because the asymmetrical thrust causes the rocket to “power slide off the pad.”
The launch Friday was the only planned flight of the Atlas 5-511 configuration as the Atlas 5 family nears retirement.
“That nozzle (of the solid rocket booster) is canted to pass through the average center of gravity, and the RD-180 has tremendous control authority with its thrust vector system, and it can overcome that and compensate for it, and this is just the right amount of energy to carry these two payloads to their very cool mission of space surveillance,” Bruno said.
The Atlas 5 rocket was designed by Lockheed Martin to fly in up to 20 different configurations, giving engineers the ability to “dial” the rocket’s power and payload volume to meet the needs of each specific mission. Mission planners have the option of flying a four-meter or five-meter diameter payload fairing, and can fly the Atlas 5 with up to five strap-on solid boosters, or none if the mission doesn’t need them.
The Atlas 5’s Centaur upper stage can fly with one or two RL10 engines, depending on mission requirements. So far, all but one Atlas 5 launch has flown with the single-engine Centaur upper stage.
The exception is on launches with Boeing’s Starliner capsule, which launches with a dual-engine Centaur stage. There are no other missions on the Atlas 5 launch schedule confirmed to use the dual-engine Centaur stage.
The addition of the unique Atlas 5 configuration for Starliner missions and the lack of use of other dual-engine Centaur variants effectively leaves 11 Atlas 5 versions that will have flown at least once before the rocket’s retirement.
Lockheed Martin merged its Atlas rocket program with Boeing’s Delta family in 2006 to create United Launch Alliance.
The most-used version of the Atlas 5 to date is the “401” variant with a four-meter fairing and no solid boosters. The Atlas 5-401 has flown 40 times, including the first Atlas flight in 2002.
There have been six flights of the Atlas 5-411 configuration with a sole solid booster.
With asymmetrical thrust countered by steering from the Atlas 5’s RD-180 main engine, the Atlas 5-511 and -411 configurations are unique among launchers currently in service. The ability to add a single booster allows customers to pay for just enough capacity for their payloads, rather than buying a more larger, more expensive Atlas 5 variant.
ULA is developing the upgraded Vulcan Centaur rocket to replace the Atlas and Delta rocket families.
There are 25 more Atlas 5 rockets remaining in ULA’s inventory, following the launch Friday afternoon. All have been allocated to future missions for the Space Force, NASA, and Amazon’s Kuiper internet satellite constellation.
There are just three Delta rockets left to fly, and all are assigned to carry classified cargo into orbit for the National Reconnaissance Office, the U.S. government’s spy satellite agency.
ULA’s next mission is set for liftoff March 1, when another Atlas 5 will carry a weather satellite into orbit from Cape Canaveral for the National Oceanic and Atmospheric Administration, or NOAA.
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Follow Stephen Clark on Twitter: @StephenClark1.
Science mission begins for NASA’s new eye on the X-ray universe
A NASA astronomy satellite that launched Dec. 9 from Kennedy Space Center on a SpaceX rocket has started observing the X-ray universe, beginning a mission to study the nature of black holes and the super-dense skeletons left behind by exploded stars.
The Imaging X-ray Polarimetry Explorer, or IXPE, mission launched Dec. 9 aboard a SpaceX Falcon 9 rocket, which delivered the satellite to a unique equatorial orbit at an altitude of about 373 miles (600 kilometers).
After separating from the Falcon 9 launcher, the 727-pound (330-kilogram) IXPE spacecraft unfurled its solar panels and sailed through a series of tests. On Dec. 15, less than a week after launch, IXPE extended an origami-like boom holding the satellite’s three X-ray telescopes, giving the satellite a length of about 17 feet (5.2 meters) end-to-end.
The extendable boom is the right length to allow the telescopes’ mirrors to focus X-ray light back on detectors inside the main body of the spacecraft, giving IXPE satellite the ability to register high-energy waves emitted from black holes, neutron stars, and X-ray sources invisible to telescopes tuned to observe in other wavelengths.
“The commissioning has been successfully completed,” said Martin Weisskopf, IXPE’s principal investigator from NASA’s Marshall Space Flight Center in Huntsville, Alabama. “The two most nerve-racking elements of the commissioning were the solar panels deploying and the boom deploying.”
With the boom extension complete, ground teams spent about three weeks checking the observatory’s maneuvering and pointing capabilities and aligning the telescopes, according to NASA.
“All spacecraft functions have been activated and verified during commissioning,” Weisskopf said in a Jan. 10 press briefing at an American Astronomical Society meeting.
IXPE is one of several X-ray astronomy missions in NASA’s portfolio, but it’s the first tuned to measure the polarization signal of X-ray light. Previous telescopes, which must in space to detect cosmic X-rays, have imaged X-ray sources in high angular resolution, measured their spectroscopy, or chemical fingerprints, and studied the time variation of X-ray signals.
“By doing this mission, we are adding two variables to the astrophysics toolkit to understand these sources,” Weisskopf said before IXPE’s launch. “That’s the degree of polarization, and the direction associated with polarization.”
The polarization of X-ray light a measurement of the direction of its electromagnetic field, a telltale signal that can inform astrophysicists about the extreme environments around black holes and supermassive objects, including the supermassive black hole at the center of the Milky Way galaxy.
Weisskopf said Jan. 10 that IXPE’s detectors, which are the first designed to measure X-ray polarization from space, observed bright calibration sources with known properties to help ground teams fine-tune the alignment of the missions’s telescopes.
IXPE’s three identical telescopes can measure the energy, position, time of arrival, and polarization of each X-ray photon they collect.
Satisfied that the IXPE mission is ready for its science campaign, NASA managers gave the green light for the spacecraft to begin the first of its regular astronomical observations Jan. 11.
IXPE’s first target is named Cassiopeia A, or Cas A, a giant debris cloud surrounding a super-dense neutron star around 11,000 light years away. Cassiopeia A formed around 350 years ago, when a star estimated to be five times more massive than the sun exploded in a violent supernova.
The explosion sent matter from the star’s interior out into space in all directions at nearly the speed of light, leaving behind the star’s collapsed core, a neutron star. IXPE’s observations will yield insights into the magnetic field surrounding the neutron star.
The observatory will observe Cassiopeia A for about three weeks. It’s the first of 33 planned science targets selected for the first year of IXPE’s mission, Weisskopf said.
Mission planners have also set aside observing time for IXPE to turn its telescopes toward “targets of opportunity,” such as features or objects that suddenly brighten in the sky, Weisskopf said. “So if something interesting comes up, we can go and look at it.”
The flight plan has time for observations of about 40 targets overall in IXPE’s first year of operations. IXPE will aim its telescopes at each targets for days or weeks at a time, collecting long X-ray exposures to allow scientists to sort out polarized signals from background noise.
NASA is funding IXPE for a two-year primary mission, which the agency says adds up to $214 million, including development, the launch, and operations. The spacecraft doesn’t need any rocket fuel for pointing or orbital maneuvers.
IXPE is a partnership between NASA and the Italian Space Agency, which provided the mission’s X-ray detectors and a ground station Kenya to receive science data from the satellite when it flies overhead.
According to Weisskopf, X-ray polarization can tell scientists about the spin of a black hole. Theoretical calculations show that the degree of polarization of an X-ray signal varies with the energy of the magnetic field at its source.
“Black holes don’t have many properties, but one of them is spin,” he said. “So this is a very fascinating use of the polarimetry to determine something about the nature of its source, and that story holds true in many other cases.”
Other targets for IXPE include the supermassive black hole at the center of our galaxy, known as Sagittarius A*. IXPE’s measurements may confirm whether the black hole was much brighter just a few hundred years ago, as some scientists believe.
IXPE will also look at more distant targets, such as blazers at the centers of other galaxies. Blazars have powerful jets of radiation that happen to be aimed directly at Earth.
The mission will also study the polarization of X-rays coming from magnetars, which have the strongest magnetic fields of any star, some one thousand trillion times more intense than Earth’s magnetic field.
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Follow Stephen Clark on Twitter: @StephenClark1.
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