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Webb’s fate hinges on high-risk sunshade, mirror deployments




If you want to see the faint, stretched-out light from the first stars and galaxies that began shining at the end of the cosmic dark ages a few hundred million years after the Big Bang, you’re going to need a big telescope. But not just any big telescope.

You’re going to need to put it in space where it will have to operate at a few degrees above absolute zero to register the exceedingly faint infrared traces of that bygone era, detecting light that has been stretched out by the expansion of space itself over nearly 14 billion years.

To do that, you’ll have to equip the observatory with a tennis court-size kite-shaped sunshade, made up of five membranes the thickness of a human hair separated and pulled taught by scores of motor-driven stainless steel cables routed through dozens of pulleys.

You’ll need to choose materials for the observatory’s structure that will retain their shape and size across enormous temperature gradients.

Then you’ll have to fold it all up so it can be crammed into the nosecone of a rocket and fired a million miles into space, hoping the vibrations and ear-splitting sounds of launch don’t dislodge a critical component so it can unfold itself, align its optics to nanometer precision and bring that feeble light to a razor-sharp focus.

That’s the Christmas holiday challenge facing the $9.8 billion James Webb Space Telescope, the successor to the 31-year-old Hubble. It is by far the most sensitive, technologically challenging — and expensive — science satellite ever built.

The spacecraft, encapsulated inside a protective nose cone atop a European Space Agency-provided Ariane 5 rocket, was rolled to the launch pad in Kourou, French Guiana, Thursday. Launch is targeted for 7:20 a.m. EST Christmas Day, weather permitting.

Once on its way, it will take a full month for the telescope to unfold like a high-tech origami, deploying its solar array, antennas, radiators, its segmented primary mirror, its secondary mirror and the complex, fragile sunshade that is so essential to success.

Another two months beyond that will be needed to carefully align the optics while the telescope continues a slow cool down to near absolute zero and then another three months or so to check out and calibrate Webb’s instruments.

And then, more than 20 years after it was first proposed, years behind schedule and billions over budget, JWST will finally be ready to take center stage on the high frontier, carrying the hopes and dreams of thousands of engineers and astronomers around the world.

“This is a high-risk and a very high-payoff program,” said NASA Deputy Administrator Pam Melroy, a former space shuttle commander. “We’ve done everything we can think of to make Webb successful. And now we just need to go do it.”


Unlike Hubble, which was placed in low-Earth orbit where space shuttle astronauts could make service calls, JWST is headed for Lagrange Point 2 on the other side of the Moon where the gravity of Sun, Earth and Moon are in balance, allowing the telescope to remain in place with a minimum of propellant.

Well beyond the reach of spacewalking repairmen, L2 offers an ideal place for Webb to chill out for its epic quest to peer back in time to the end of the so-called dark ages, when the the blazing light of the first stars burned off the hydrogen fog of creation to travel freely through space.

“It’s an infrared telescope,” said Paul Geithner, JWST’s technical project manager. “The main reason it was conceived in the first place was to see the end of the cosmic dark ages. And if you want to see objects from that epoch, the ultraviolet and the visible light they emitted so long ago has been red shifted all the way into the infrared spectrum.

“Infrared light is heat radiation. So if you want an infrared telescope to be exquisitely sensitive, first you put in space (and) besides putting in space, you need it to be super cold so that it’s not blinded by its own thermal emissions.”

Operating at L2, JWST will be less affected by the infrared background close to Earth and the scattered and re-emitted infrared light from dust in the equatorial plane of the solar system. “We need to be colder than 60 Kelvin so that we’re not limited by our own temperature,” Geithner said.

The hot side of JWST – the spacecraft bus and the bottom layer of the sunshade – will experience temperatures of nearly 230 degrees Fahrenheit. On the dark side, just beyond the fifth and uppermost layer of the sunshade, the temperature will be close to minus 390 degrees.

“That’s a huge, huge temperature differential, driven totally by these five layers on the sunshield (and) each layer is about the thickness of a human hair,” project manager Bill Ochs said in an interview.

Thirty minutes after liftoff, JWST will separate from the Ariane 5’s upper stage. Moments later, the observatory’s solar array will deploy to begin recharging on-board batteries and 12 hours after that, a thruster firing is planned to fine-tune the trajectory to L2.

Passing the moon’s orbit the day after Christmas, JWST will deploy its high-gain antenna and aim it toward Earth, giving flight controllers a high-speed data link.

Three days after launch, the two pallets holding the stowed sunshade membranes will unfold, dropping into place on either side of the Optical Telescope Element-Integrated Science Instrument Module, or OTIS. The OTIS is the actual telescope, its mirrors and instruments mounted in a carbon composite framework.

To achieve the required operating temperature, a telescoping “deployable tower assembly” will move the OTIS 48 inches away from the spacecraft’s support section, or bus, which houses relatively warm communications, thermal control and computer gear, along with the observatory’s propulsion and electrical power systems.


With the DTA extended, the stage will be set for the make-or-break deployment of the sunshade’s five Kapton membranes.

“The solar array deploying, the high gain antenna gimbal deploying and working are kind of standard stuff on a spacecraft and not that uncommon,” Geithner said. “And we’ve got to deploy that tower to separate the telescope from the bus to isolate it mechanically and thermally. That’s a little new, but it’s a fairly straightforward ball-screw mechanism.

“But yeah, the sun shield is where so much of the deployment risk exists because that’s where so many of the single point failures exist. And it’s just complicated.”

With the sunshade pallets already deployed fore and aft of the extended optics assembly, launch restraints will be released and protective covers rolled back to either side of the folded sunshade membranes. Two mid booms at right angles to the pallets then will extend and motor-driven cables will pull the stowed membranes out into a kite-like shape.

The five-layer sunshield is tensioned on the James Webb Space Telescope during ground testing at a Northrop Grumman factory in California. Credit: NASA/Chris Gunn

As the cables tighten, the layers will be separated and tensioned as required to ensure a slight gap between each taut layer. Near the center of the shade, the gap is as small as one inch to five inches while at the outboard corners, the separation is about a foot to facilitate heat flow. Fully deployed, the sunshade will measure 69.5-by-46.5 feet.

“The sunshield alone has 90 cables in it, that if you strung them end to end would be almost a quarter mile in length,” Geithner said. “And that’s for pulling out the membranes and tensioning them. … And, of course, we have 107 little non-explosive actuator devices, membrane release devices, that basically pin the membranes down and the covers over them for launch.”

Except for the booms, the sun shield is made up of “floppy things, and they’ll just float around in zero G and you’ll get a tangled mess if you don’t deterministically control them as much as possible,” he said.

“And so we have many little devices to constrain and ensure that all these cables and membranes and such don’t just flop around randomly and snag on something. That’s just where so much of the deployment risk is because it’s a lot of parts. They’re simple mechanisms, but there are a lot of them, and they all have to work.”

Ochs said the sunshade deploy sequence was designed to be “slow and deliberate” to give engineers time to evaluate each step in the procedure. While NASA can’t send an astronaut repair crew to the telescope, engineers have developed contingency plans to coax open jammed mechanisms.

“Whereas the mechanisms themselves are not redundant, the electronics that drive those mechanisms have redundant sides, we can go to the redundant side if there was a problem there to try to deploy it,” he said. “And then if we get to a situation where let’s say something stuck, we can shake the spacecraft using its attitude control system. We call it the ‘shimmy,’ where you can go back and forth at various frequencies and cause it to kind of shake something loose.”

Another procedure, known as the “twirl,” was developed to spin the observatory at various speeds, again to “shake something loose.”

“You can also back things up and have them start again,” Ochs said. “So if you need  to back it up and give it another shot, you can do that. We’ve exercised many of these things in some of our rehearsals already, so we have these tools to help us along as we go through all these deployments.”

But what happens if there’s a serious snag, layers remain in contact with each other or membranes are torn?

This illustration shows the major elements of the James Webb Space Telescope. As the name might suggest, the Integrated Science Instrument Module, or ISIM, contains the mission’s four science instruments. Credit: NASA

Depending on the degree of thermal degradation, JWST’s three passively-cooled near-infrared instruments — the Near-Infrared Camera, or NIRCam; the Near-Infrared Spectrograph, or NIRSpec; and the Near InfraRed imager and Slitless Spectrograph/Fine Guidance Sensor, or NIRISS/FGS — should still be able to collect valuable data.

All three use 4-megapixel mercury-cadmium-telluride detectors to register infrared wavelengths between 0.6 and 5 microns. All three are designed to operate best at temperatures just below 40 Kelvin (degrees above absolute zero), but they would still work if slightly warmer.

JWST’s fourth instrument, the Mid-Infrared Instrument, or MIRI, uses 1-megapixel arsenic-doped silicon detectors to pull in wavelengths between 5 and 28 microns. It is designed to operate below 7 Kelvin, relying on a sophisticated cryocooler to pump cold helium gas from the spacecraft bus to the MIRI’s detectors.

The instrument has built-in margin, but “the real question is will the heat load on the Mid-Infrared Instrument be so high that the cryo cooler can’t overcome it? I think we’re still okay,” Geithner said. “Worst case, maybe we wouldn’t have a mid-infrared instrument. But you’d still be able to do some near-infrared science. You’d still have a mission, but it would be degraded.”

Ochs is confident the sunshade will deploy as designed based on years of testing and analysis.

“We have found things, and we’ve gone back and corrected them,” he said. “You don’t want to test it too much because the sunshield is so fragile, but we did three or four deployments and the last one, we were fully successful, we felt really good about it. It only has to work one more time. And that’s in orbit.”


Assuming the sunshade does, in fact, deploy normally, the next major challenge will be unfolding JWST’s mirrors starting about 10 days after launch.

The Hubble Space Telescope is a Ritchey-Chrétien Cassegrain, with a 91.5-inch primary mirror and a secondary bringing the light to a sharp focus just behind the main mirror. From there, pick-off mirrors feed the light to the telescope’s instruments.

JWST is what astronomers call a three-mirror anastigmat. Light first hits the 21.3-foot primary mirror, bounces up to the convex secondary and then down, slightly off axis, to a third elliptical mirror just behind the primary. The elliptical mirror corrects for astigmatism and widens the field of view, bouncing the light back up to a flat “steering mirror” that reflects it back down to the instruments.

The steering mirror can tip and tilt “very slightly at up to 100 cycles a second,” Geithner said, to exactly counteract any residual mechanical jitter in the system due to spinning reaction wheels and cryocooler pumps in the spacecraft bus.

Because a one-piece primary mirror would be too heavy and would not fit into an existing nose cone fairing, the observatory was designed around a segmented beryllium primary made up of 18 hexagonal sub-mirrors, each one 4.3 feet in diameter and coated with a thin layer of gold to maximise reflectivity.

Six of those segments, three on each side, were designed to be folded away for launch as was the telescope’s 2.4-foot secondary mirror. About 10 days after launch, after the sunshade is fully deployed and tensioned, Webb’s secondary mirror will be erected at the apex of three articulating booms.

Two of JWST’s primary mirror segments. Credit: Stephen Clark / Spaceflight Now

The two side panels of the primary, each with three mirror segments, then will be rotated into position to either side of the central 12 segments.

“The aperture (width) had to be at least six-and-a-half meters (21.3 feet) to gather enough light and have the same resolution at near infrared wavelengths that Hubble has at visible wavelengths,” Geithner said.

Ultra-precise optical alignment of the 18 primary mirror segments is critical. To achieve that, each segment features six mechanical actuators allowing movement in six directions. A seventh actuator can push or pull on the center of a segment to ever so slightly distort its shape if needed.

Each segment was so precisely ground and polished 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 high.

Because the mirror segments will change shape slightly as the telescope cools down in space, “we basically had to build this thing perfectly wrong at room temperature so that it will be precisely correct at an operating temperature below 60 Kelvin,” Geithner said. “That’s the over-arching big challenge.”

Before alignment, the 18 segments will produce 18 separate images. Using the NIRCam instrument, engineers will map the alignment of each segment and send commands to adjust the orientation and curvature as required to produce a single, sharply-focused image.

“You’ve got to get these 18 mirrors to act as one mirror,” Ochs said. “So when we get on orbit, we go through what we call a wavefront sensing process, but really it’s the focusing process. When you start out, if you’re looking at one star, you’re going to have 18 images and you need to get that down to one.

“So we use the actuators on the back of the mirror, there are motors on the back of each mirror that allow you to move the mirrors up and down, back and forth, in and out as well as change shape slightly.”


The Hubble Space Telescope was launched in 1990 with a famously flawed primary mirror, the result of a testing error on the ground that led to spherical aberration and blurred pictures. Shuttle astronauts were able to repair the telescope by installing instruments with built-in corrective optics.

With that lesson in mind, JWST managers opted for detailed pre-launch testing to ensure Webb’s optical system will work as planned. Along with exhaustive testing of each primary mirror segment, the entire telescope was sent to the Johnson Space Center in Houston and tested inside an Apollo-era vacuum chamber that duplicated the space environment.

“We made artificial stars with light coming from the end of fibre optics and we passed light all the way through the system and we know we can line it up and make it work,” Geithner said.

And what if an actuator fails or some other problem crops up and one of the primary mirror segments cannot be properly aligned?

“We can meet all our most fundamental requirements with 17 segments,” he said. “We can try to compensate with the other segments and the secondary, it depends on if it’s within a certain range. But if it’s a bad segment, we can just tilt it completely out of the way with the remaining actuators. That’s not great … but we could still meet our level-one requirements.”

Source: Space


Webb closes in on destination with critical mirror alignment on tap




The James Webb Space Telescope with its five-layer sunshade and optical elements fully deployed. Credit: NASA

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.

Credit: On Monday, Webb will slip into orbit around Lagrange Point 2 nearly a million miles away where the gravity of the sun and Earth combine to form a pocket of stability where spacecraft can remain in place with minimal amounts of fuel. Credit: NASA

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.

Webb’s primary mirror is made up of 18 hexagonal gold-coated beryllium segments that must be aligned to within a tiny fraction of the width of a human hair to achieve a sharp focus. This photo shows the mirror during pre-launch preparations with the telescope’s secondary mirror folded away for flight. Credit: NASA

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.”

Source: Space

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Atlas 5 rocket delivers two military inspector satellites to high-altitude orbit



An Atlas 5 rocket, boosted by an RD-180 main engine and one strap-on solid rocket motor, lifts off from pad 41 at Cape Canaveral Space Force Station with a pair of U.S. Space Force tracking satellites. Credit: Alex Polimeni / Spaceflight Now

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).

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.

Artist’s concept of two GSSAP spacecraft in orbit. Credit: U.S. Space Force

“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 Atlas 5 rocket’s single solid rocket booster and RD-180 main engine power the launcher into an overcast sky Saturday over Cape Canaveral. Credit: Michael Cain / Spaceflight Now / Coldlife Photography

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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Source: Space

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Science mission begins for NASA’s new eye on the X-ray universe



Artist’s concept of the Imaging X-ray Polarimetry Explorer. Credit: NASA

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.

This image from NASA’s Chandra X-ray Observatory shows Cassiopeia A, the remnants of a star the exploded in a violent supernova event around 350 years ago. NASA’s IXPE mission is observing Cassiopeia A as its first scientific target. Credit: NASA/CXC/SAO

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.

Nine Merlin main engines power SpaceX’s Falcon 9 rocket off pad 39A on Dec. 9 with NASA’s IXPE mission. Credit: Michael Cain / Spaceflight Now / Coldlife Photography

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.

Source: Space

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