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Hydrogen is NASA's fuel of choice for Artemis I, but it's also hard to manage – Florida Today



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Artemis I NASA’s plans to travel beyond the moon

Artemis 1 will be the first integrated test of NASA’s deep space exploration systems: the Orion spacecraft, Space Launch System (SLS) rocket and the ground systems at Kennedy Space Center.


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As NASA pushes toward a third attempt at launching the Artemis I mission later this month, the agency’s use of a popular rocket propellant – supercooled liquid hydrogen – has become the center of attention due to its finicky nature.

Now set for liftoff no earlier than 6:47 a.m. EDT Friday, Sept. 23, the 322-foot Space Launch System rocket’s ground support equipment is under repair at Kennedy Space Center. Two previous attempts at launching an uncrewed Orion capsule to the moon were scrubbed due to hydrogen-related cooling and fueling issues.

Teams at pad 39B are currently investigating what caused a serious hydrogen leak during the fueling process on Sept. 3. The massive rocket’s liquid oxygen tank reached 100% filled, but hydrogen only hit 11% during the countdown, forcing teams to scrub and investigate the issue contained to a quick-disconnect, or QD.

Frequent issues with hydrogen, many of which trace back to the space shuttle program, are common. That it requires more cooling – liquid hydrogen must be stored at minus 423 degrees Fahrenheit – compared to other propellants ultimately means embrittlement, or the weakening of components like metal storage tanks, tends to be the primary driver of hardware issues. It also must be pumped in at high pressures, easily exposing even the smallest leaks.

On the plus side, though, hydrogen provides more performance than other rocket fuels.

More: NASA retargets late September for Artemis I launch as teams work hardware

NASA’s huge Artemis launch: It’s going to be loud, but how loud? That depends

“Certainly there’s no question that hydrogen is a challenging molecule, but it’s worth it,” John Blevins, NASA’s chief SLS engineer, said during a post-scrub briefing this week. “Hydrogen is the highest-performance molecule and if you look at the mission we’re doing, it begs the use of this fuel.”

“It wants that sustained, high performance that you get out of what is really the most high-performing rocket engine on the planet: that is the (four RS-25 main engines),” Blevins said.

Artemis I is part of NASA’s overall program to take astronauts back to the moon. If everything goes well with this uncrewed test flight, astronauts are expected to fly a similar there-and-back mission known as Artemis II sometime after 2024. NASA hopes to put two people on the surface before 2030, then establish a permanent presence before moving on to Mars.

FLORIDA TODAY spoke with Jim Brenner, an associate professor of chemical engineering at Florida Tech with extensive experience in hydrogen, about rocket propellants and how they compare.

Note: This Q&A has been edited for length and clarity.

FLORIDA TODAY: Kerosene, methane, and hydrogen are some of the most popular rocket propellants today. Can you offer a brief overview on how they rank?

Brenner: Kerosene has a lower density – that’s probably the best way to put it – than methane, and hydrogen has the highest of the three.

But as you go from kerosene to methane to hydrogen, the boiling point is going to go down considerably. That means to keep it as a liquid, and you need to do that to minimize the amount of space taken up on the rocket, you’ve got to go much, much colder. And the colder you go, the more likely you are to embrittle the container that you’re putting it in.

Differences in temperature

FT: At that point, you’re probably also contending with fluctuations in temperature, right? Like the difference in temperatures between these cryogenic propellants, hardware that’s been warmed up by the warm Florida air, and so on?

Brenner: That is a factor. Certainly temperature variations both within the day and between when a tank is full versus when it’s not, do have their effects. 

Going back to the first two space shuttle disasters, both of those were caused by thermal expansion-related problems. For the second space shuttle disaster (Columbia in 2003), the conclusion from one of the dissertations that I was part of here was that the polymer foam on the outside of the space shuttle should have been replaced … and it ultimately caused the second disaster. That really is probably the best example that the general public would be able to remember of what I call cryogenic embrittlement. When you get down to a sufficiently low temperature, even metal is going to become brittle. 

Hydrogen is also different from some materials in that it will make the metal brittle independent of the temperature (a well-documented phenomenon caused by metals absorbing hydrogen). So you can have embrittlement issues at any temperature with hydrogen, but they’re obviously much worse at lower temperatures.

Hydrogen’s performance

FT: When it comes to Artemis I and the Space Launch System, NASA officials say hydrogen is needed for performance. So of the three popular propellants mentioned, hydrogen has the highest performance once it’s in use?

Brenner: That is correct. And that’s why hydrogen has always been the preferred fuel for that.

If you are not interested in reusability (like SLS since it will be expended after launch), then it probably is the best choice. But if you’re going to reuse things, then you have to make sure after each fill and empty that the cryogenic embrittlement and cyclic fatigue associated with repeated use isn’t going to cause a cumulative effect that makes problems similar to what they’re experiencing with Artemis.

There are only so many times you can cool things down to that low of a temperature before you are eventually going to have problems. While Artemis has had problems like this, it’s far from the first time the space business has had this problem. They’ve had problems with liquid hydrogen and liquid oxygen for a long time.

Kerosene’s popularity in reusability

FT: So looking at something like SpaceX’s Falcon 9 rocket, is the difference between kerosene and hydrogen so great that SpaceX is able to fly over and over again without as many issues?

Brenner: That certainly is the working premise. I couldn’t tell you how many cycles it’s going to be able to last, but that is why they’re going that route.

Because it’s not getting as cold, you’re not going to have as many problems as you would with liquid hydrogen. Their premise is a reasonable one.

Hydrogen as the most abundant element

More: Artemis I spectators swarm Space Coast but launch attempt scrubbed

FT: When discussing hydrogen as fuel, you’re bound to hear about how it must be a logical choice since it’s the most abundant element in the universe – and how it could someday be produced on the moon before missions to Mars. Is there any practical truth to that?

Brenner: You can’t mine hydrogen on the moon. If we’re going to have a space vehicle come back from either the moon or Mars, we’re either going to have to send a vehicle up with the fuel to come back – economically, that’s a loser – or we’re going to have to mine the necessary resources for a propellant to get us back.

There are plenty of people who are looking at mining aluminum from the moon or Mars, forming that into nanoparticles, and using that as a propellant. That’s frankly quite dangerous because you’re quite literally trying to store an explosive.

Hydrogen also isn’t at a high enough concentration to be able to practically do much with it. Yes, it’s the most abundant thing in the universe, but it’s not in a form that you can easily use. Water here on Earth is pretty easy to use because it’s in a liquid form, but trying to concentrate something that’s in the gas phase so that it’s easy to store makes a big difference.

That’s why kerosene, or gasoline or diesel for that matter, are better for terrestrial vehicles than natural gas or hydrogen. Yes, you can run vehicles off natural gas or hydrogen here on Earth, too. But when you do that, you’ve either got to cool them down to a very low temperature or you’ve got to pressurize them to a very high pressure – and often both. That’s just not as easy to do as it sounds on paper.

SpaceX using methane for Starship


Artemis | Five facts about the Space Launch System rocket

Five facts you should know about the Space Launch System rocket.

Rob Landers, Florida Today

FT: How does SpaceX’s Starship system – also massive in size and being developed for deep space – and its use of methane fit into this?

Brenner: Methane is kind of in between kerosene and hydrogen. It’s not as dense of an energy source, but you don’t have to cool it down as much as hydrogen, so you’re not going to have as many problems with reusability as you would with hydrogen.

A lack of materials data

FT: You mentioned that one of the reasons we’re seeing these issues is the lack of data and experience. Can you expand on that?

Brenner: There’s really not that much data out in the public domain on the reliability of materials at the kinds of conditions that we abuse our materials at in East Central Florida. No place in the world abuses our materials like we do here.

The rocket business is a very unforgiving environment. We take materials up to very high temperatures and to very low temperatures and there just isn’t a lot of materials reliability data under the conditions that we’re talking about.

Until somebody develops a database that is in the public domain on materials reliability under these sorts of conditions, you’re going to have problems like what Artemis is having. You can’t look that sort of stuff up on the internet – it’s just not there.

We can’t afford to have another space disaster. If somebody has a problem with a materials reliability issue and it was an FIT person responsible, I was probably the person who taught that student. It’s important that I make sure they’re doing things as safely as reasonable.

It’s not very easy because we don’t really have the appropriate data at this point to be able to predict these things as well as we ought to.

Contact Emre Kelly at or 321-242-3715. Follow him on Twitter, Facebook and Instagram at @EmreKelly.

Current Launch Windows for Artemis I

Friday, September 23:

  • Launch time: 6:47 a.m. EDT
  • Launch window: 120 minutes
  • Orion splashdown: Oct. 18

Tuesday, September 27:

  • Launch time: 11:37 a.m. EDT
  • Launch window: 70 minutes
  • Orion splashdown: Nov. 5

Visit three hours before each window opening for live video and real-time updates.

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Squirrels, volcanoes, and ancient DNA – – Town and Country TODAY



ATHABASCA — What does the research into ground squirrels dating back 50,000 years have to do with ancient DNA or volcanoes? 

Those are some of the fascinating details Scott Cocker, a paleoecologist and PhD student at the University of Alberta (U of A), will be discussing in a Zoom presentation hosted by Science Outreach – Athabasca Sept. 27 at 7 p.m. 

“I’m interested in the ground squirrels themselves because we jokingly refer to them as furry botanists,” Cocker said in a Sept. 15 interview. “They were grabbing plants; they were grabbing whatever they could grab before they went into hibernation. So, they would store all this stuff in their nest and then the nest is what we find 40,000 years later or whatever have you … frozen in the permafrost with all those seeds or with bones of other animals. They are basically like little archives of the Ice Age and Yukon.” 

Cocker realized while everyone was distracted by larger creatures like woolly mammoths and woolly rhinos, they didn’t offer as much information on life at the time as ground squirrel nests could. 

“The ecosystem and the environment, we call that the mammoth steppe and for a long time that’s what everyone referred to; the mammoth steppe this, the mammoth steppe that, and it’s just because the mammoths are big and charismatic,” he said. “But my whole thesis is that if you really want to understand the mammoth steppe and the environment that they were living in, you actually have to look to things like the ground squirrels because they tell us way more about the environment than the mammoths do.” 

Throw in some new sequencing of DNA which allows scientists to accurately identify a species from just small pieces of DNA. 

“In the last 20 years, it’s something that’s been developed,” he said. “We can work with modern DNA really easily because stranded DNA are in the count of millions … but once that organism dies and sits around for a while, then the DNA starts to degrade, and it breaks down over time and so we end up with these really short little pieces of DNA.” 

Then mix in the aftermath of a volcanic eruption in southern Alaska 25,000 years ago which covered the area with up to a metre of ash and it changes how all fauna lived and you have the basics of Cocker’s presentation. 

“How did that impact the animals and plants at the time of the eruption? Because it definitely was one of the largest in the last million years in this part of the world,” Cocker said. “It completely covered the plants. Think about (the) ground squirrels or the voles and mice and stuff that … rely on foraging and you’re half the size of the ash fall, you’re gonna struggle.” 

The link to the presentation can be found on the Science Outreach – Athabasca website and social media and will start at 7 p.m. Sept. 27. 

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Why is NASA crashing a spacecraft into a harmless asteroid at 14,000mph? – Sky News



A harmless asteroid millions of miles away is about to be rammed by a NASA spacecraft at 14,000mph. Why? The fate of the human race could one day depend on doing the same.

It has been 66 million years since an asteroid crashing into the Earth brought an end to the reign of the dinosaurs, scientists say, and they are keen to avoid a similar ending for humanity.

Sky News takes a look at NASA’s latest experiment – a $325m (£301m) planetary defence test – and answers some key questions about how it could prove useful down the line.

What is the Dart spacecraft?

Dart – a snappier nickname than Double Asteroid Redirection Test – is essentially a battering ram the size of a small vending machine.

It faces certain destruction in the fulfilment of its goal.

Dart weighs 570kg and has a single instrument: a camera used for navigating, targeting and chronicling its final demise.

More on Nasa

Where is the spacecraft going?

Dart is headed for a pair of asteroids about seven million miles from Earth. Its target is called Dimorphos, which is the smaller offspring of Didymos (that’s Greek for twin).

Dimorphos is roughly 525 feet (160 metres) across and it orbits the much larger Didymos at a distance of less than a mile (1.2km).

NASA insists there’s a zero chance either asteroid will threaten Earth – now or in the future. That’s why the pair was picked.

The spacecraft’s navigation is designed to distinguish between the two asteroids and, in the final 50 minutes, target the smaller one.

What happens on impact?

“This really is about asteroid deflection, not disruption,” said Nancy Chabot, a planetary scientist and mission team leader at Johns Hopkins University, which is managing the effort.

“This isn’t going to blow up the asteroid. It isn’t going to put it into lots of pieces.”

Instead, the impact will dig out a crater metres in size and hurl some two million pounds of rocks and dirt into space.

Why are scientists doing this?

The impact should be just enough to nudge the asteroid into a slightly tighter orbit around its companion space rock – demonstrating that if a killer asteroid ever heads our way, we’d stand a fighting chance of diverting it.

Cameras and telescopes will watch the crash, but it will take months to find out if it actually changed the orbit.

Observatories will track the pair of asteroids as they circle the sun, to see if Dart altered Dimorphos’ orbit.

In 2024, a European spacecraft named Hera will retrace Dart’s journey to measure the impact results.

Although the intended nudge should change the moonlet’s position only slightly, that will add up to a major shift over time, according to Ms Chabot.

“So if you were going to do this for planetary defence, you would do it five, 10, 15, 20 years in advance in order for this technique to work,” she said.

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Last West Coast Delta IV Heavy to launch with NROL-91 – –



United Launch Alliance’s (ULA) Delta IV Heavy rocket made its last West Coast launch on Saturday, carrying out a mission for the National Reconnaissance Office, as it moves one flight closer to retirement. Liftoff of the NRO Launch 91 (NROL-91) mission from Space Launch Complex 6 — at the Vandenberg Space Force Base in California — took place at 3:25 PM PDT (22:25 UTC).

Delta IV Heavy is the most powerful version of the Delta IV, one of two rockets developed under the US Air Force’s Evolved Expendable Launch Vehicle (EELV) program to meet the US Government’s launch needs in the early 21st century. Delta IV, alongside its former competitor-turned-stablemate Atlas V, is now being phased out as a new generation of launchers prepare to take their place.

One of the first steps in that transition was winding down Delta IV operations, with the last Delta IV Medium+ launch taking place in 2019. Delta IV Heavy, with its significantly higher payload capacity, has been kept in service to carry out a handful of national security launches that cannot be performed by Atlas V.

Saturday’s mission, NROL-91, is the final Delta IV launch from California’s Vandenberg Space Force Base, with the rocket’s remaining missions to be executed from the East Coast at Cape Canaveral.

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While the National Reconnaissance Office (NRO) keeps details of its satellites classified, the use of a Delta IV Heavy and the fact the launch is taking place from Vandenberg speak volumes. Delta IV Heavy missions carry satellites that have too great a mass for the most powerful Atlas V configurations to place into their destined orbits, indicating the satellite is very heavy, bound for a high orbit, or both. From its location on the West Coast, Vandenberg is an ideal launch site for low Earth orbit (LEO) reconnaissance satellites operating in polar and near-polar orbits, as well as some signals intelligence satellites in elliptical orbits.

Those signals intelligence satellites are typically launched by smaller rockets, so the combination of rocket and launch site suggests that NROL-91 will deploy one of the agency’s large imaging satellites, part of a program identified in previously leaked documents as Crystal. The NRO does not acknowledge the names or types of satellites it operates; instead, they are assigned an NROL designation prior to launch and a numerical USA designation upon reaching orbit. The satellite launched by the NROL-91 mission is expected to take on the designation USA-337, the next available number in this sequence.

Crystal, also known as KH-11, is the successor to a long line of Keyhole reconnaissance satellites that the NRO has operated since the 1960s. Earlier members of this series used small capsules to return photographic film to Earth for development. When it was introduced in 1976, the KH-11 did away with these, instead downlinking images electronically. Since then, the satellites have undergone further upgrades, with several different blocks of spacecraft identified.

NROL-91 will be the nineteenth Crystal satellite to be launched, and the fifth to fly aboard a Delta IV. Previous satellites had flown aboard Titan rockets, initially the Titan III(23)D and Titan III(34)D, and later the Titan IV. The fourteenth KH-11, USA-186, was the payload for the final Titan IV launch and was at the time also expected to be the last Crystal satellite. Failures in the procurement of the successor Future Imagery Architecture (FIA) saw additional Crystal spacecraft constructed, with the first bearing a conspicuous phoenix on its mission patch.

Declassified image taken by a KH-11 satellite, showing Iran’s Semnan launch site (Credit: NRO/US Government)

The Crystal satellites are believed to give the NRO its highest-resolution pictures of the Earth’s surface. They are rumored to resemble the Hubble Space Telescope but pointed toward the Earth, rather than out into space. Most have operated in a Sun-synchronous orbit (SSO) — a particular type of low, near-polar, orbit that allows them to cover most of the Earth’s surface, ensuring they pass over each point at the same local solar time every day, ensuring consistent lighting conditions.

Up until now, the only KH-11 not operated in Sun-synchronous orbit has been USA-290. Deployed by the NROL-71 mission in January 2019, it was the last-but-one KH-11 to launch prior to NROL-91. With an orbital inclination of 73.6 degrees, its orbit is lower than the other operational satellites, meaning that it does not pass as close to the Earth’s poles.

Hazard areas published ahead of the NROL-91 mission, to warn aviators and mariners to stay away from areas where debris from the launch is expected to fall, suggest that this mission is targeting the same inclination as USA-290, rather than the more typical SSO.

With Saturday’s launch marking the last Delta IV flight from Vandenberg, it is not clear whether this also means that NROL-91 was the final launch of a Crystal satellite. The now-abandoned optical element of the FIA program sought to develop a smaller, cheaper high-resolution imaging satellite using more modern technology. Future missions could follow this model, or alternatively, Crystal satellites could continue launching aboard a different rocket — such as Falcon Heavy or ULA’s next-generation vehicle, Vulcan.

Delta IV during rollout from the Horizontal Integration Facility to the launch pad ahead of the NROL-91 mission (Credit: United Launch Alliance)

The Delta IV Heavy is a two-stage expendable launch vehicle, with its first stage consisting of three Common Booster Cores (CBCs). A five-meter-diameter Delta Cryogenic Second Stage (DCSS) sits atop this, with the satellite housed within the payload fairing at the top of the rocket. Both stages of the rocket use cryogenic propellants: liquid hydrogen and liquid oxygen.

First flown in November 2002, Delta IV has made 42 flights prior to the NROL-91 mission, of which 13 have used the Heavy configuration. Other versions of the Delta IV have included the long-retired Delta IV Medium, which consisted of a single CBC, a four-meter DCSS, and several intermediate Medium+ configurations which augmented the Medium’s CBC with two or four solid rocket boosters and could fly with either version of the second stage.

Of the previous 42 missions, Delta IV has completed 41 successfully. Its only failure was the maiden flight of the Delta IV Heavy in 2004, during which all three CBCs shut down prematurely due to cavitation in the propellant lines. The rocket, which was carrying a mass simulator and a pair of small satellites, reached a lower orbit than had been planned.

Each Common Booster Core is powered by an Aerojet Rocketdyne RS-68A engine, capable of providing 312 kilonewtons of thrust at sea level. The upper stage and payload are mounted above the center core, while the others are attached to the port and starboard sides of the vehicle.

While the CBCs provide an initial boost through Earth’s atmosphere, the DCSS is responsible for completing the insertion of the NROL-91 payload into orbit. It is powered by a single cryogenic engine from Aerojet Rocketdyne’s RL10 family.

The NROL-91 payload, encapsulated in its fairing, is installed atop the rocket (Credit: United Launch Alliance)

Although the Delta IV program is being wound down, Saturday’s launch marks the first flight of a new engine variant, the RL10C-2-1, which replaces the RL10B-2 used on previous Delta IV missions. The RL10C was developed to reduce production costs by increasing standardization between the RL10A engines used on Atlas and the RL10Bs used on Delta. The RL10C-2-1 is expected to be used on the remaining Delta IV launches, as well as future Space Launch System (SLS) missions with the Interim Cryogenic Propulsion Stage (ICPS), which is derived from DCSS.

For NROL-91, Delta IV flew with a bisector, or two-part, payload fairing made of composite materials. This is one of two fairings that can be flown on Delta IV Heavy and has been used on previous Crystal launches. Most other national security missions have used a trisector — three-part — design of metallic construction, derived from a fairing previously used on the Titan IV.

Delta IV launches from Vandenberg Space Force Base take place from Space Launch Complex 6 (SLC-6), and with Saturday’s launch marking the last Delta IV mission from Vandenberg, this is expected to be the last time the complex is used in its current configuration. With no launch providers having made public plans to use SLC-6 going forward, the complex will likely be decommissioned and mothballed in the immediate future, closing another chapter in the eventful history of this launch pad.

SLC-6 was originally built in the 1960s but did not see a launch until 1995, after the first two programs that were meant to use it were both canceled at late stages of development. The first of these was the Titan IIIM, an upgraded version of the Titan III rocket that was to have launched the Manned Orbiting Laboratory (MOL), a crewed reconnaissance platform developed by the US Air Force. Construction of the launch complex began in March 1966 and was nearing completion when MOL was abandoned in 1969.

After MOL’s cancellation, SLC-6 was selected as a launch site for Space Shuttle missions to polar orbit. Such orbits could not safely be reached from the Kennedy Space Center, so a launch pad on the West Coast was deemed necessary for planned military Shuttle missions. After the pad had undergone extensive modifications, the orbiter Enterprise was used for fit checks in early 1985, and the complex was accepted into service later that year.

Space Shuttle Enterprise at SLC-6 in February 1985 (Credit: US Air Force)

The loss of Challenger in 1986, and the reviews of the Space Shuttle program that followed, saw plans for polar orbit missions canceled. At the time of the accident, the first launch from SLC-6 had been a few months away, with Discovery slated to deploy an experimental reconnaissance satellite during the STS-62-A mission. With Shuttle launches restricted to the Kennedy Space Center, SLC-6 was again placed into mothballs.

It would not be until the 1990s, when Lockheed selected SLC-6 for its Lockheed Launch Vehicle (LLV) rocket, later named Athena, that SLC-6 would finally host a launch. Four missions, two using the Athena I configuration followed by two using the Athena II configuration, were flown between August 1995 and September 1999. These launches did little to help SLC-6’s cursed reputation: the first and third missions failed to achieve orbit, while the second successfully deployed NASA’s Lewis satellite only for the spacecraft to malfunction and lose power less than three days later.

In a strange twist of fate, NROL-91 lifted off 23 years to the day after the fourth and final Athena launch from SLC-6, which successfully deployed a commercial Ikonos imaging satellite.

Athena was far smaller than the rockets that SLC-6 had been designed to serve, but Boeing’s need to find a West Coast launch site for its Delta IV rocket would bring the pad a new lease of life. The first of 10 Delta IV flights from the pad — including the NROL-91 mission — took place in June 2006 when a Delta IV Medium+(4,2) flew the NROL-22 mission, deploying a signals intelligence satellite.

A Delta IV Medium+(5,2) launches from SLC-6 in 2012 (Credit: United Launch Alliance)

The Delta IV Medium and Medium+(4,2) each made a single flight from SLC-6, while the Medium+(5,2), with a five-meter upper stage, made three flights from the pad. Including Saturday’s launch, the Delta IV Heavy configuration has used the pad five times, with all of its launches deploying Crystal satellites.

Overall, NROL-91 is the fourteenth launch to take place from SLC-6. In keeping with previous Delta IV missions, the rocket has been assigned a flight number, or Delta number, which indicates its place in the history of the Delta series of rockets. These numbers have counted — with a handful of exceptions — up from the first Thor-Delta launch in 1960. While the Delta IV is a completely different rocket even compared to the Delta II that retired a few years ago, the tradition has been maintained, and the rocket that performed Saturday’s launch is be Delta 387.

Saturday’s countdown saw the Delta IV rocket filled with cryogenic propellants while critical systems are powered up and tested as the count proceeds toward liftoff. The ignition sequence for the three RS-68A engines began seven seconds before liftoff with the starboard booster before the port and center cores ignited two seconds later. This staggered start helps mitigate the effects of hydrogen build-up around the base of the vehicle, which has scorched the rocket or set fire to insulation on previous missions.

Liftoff occurred at T0. After Delta IV cleared the tower, it began a series of pitch and yaw maneuvers to attain its planned orbit, with the first of these beginning about 10 seconds after liftoff. Flying downrange, Delta 387 throttled down its center core to its partial thrust setting. It passed through the area of maximum dynamic pressure, or Max-Q, 89.6 seconds into the mission and reached Mach 1, the speed of sound, about 1.4 seconds later.

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With the side boosters firing at full thrust and the center core operating in partial thrust mode, the port and starboard cores depleted their propellant first. As they approached burnout, they began to throttle back before shutting down at the three-minute and 56.3-second mark in the mission. The spent boosters separated 2.2 seconds later, falling away from the center core as it throttled up to full thrust.

Booster Engine Cutoff (BECO), the end of first-stage flight, occurs five minutes and 37 seconds after liftoff. Six and a half seconds after BECO, the first stage separates and the DCSS begins preparations to ignite its RL10C-2-1 engine, including deployment of the extendible nozzle. RL10 ignition occurs under 13 seconds after stage separation. 10 seconds into the burn, Delta IV’s payload fairing separates, and the NROL-91 payload is exposed to space for the first time.

With fairing separation complete, NRO missions tend to enter a news blackout, with further mission details remaining classified other than a brief press release to confirm the successful deployment of the satellite. The DCSS can be expected to continue firing its engine for about 12 minutes as it inserts the satellite directly into orbit. Spacecraft separation will occur shortly afterward, before the DCSS restarts its engine for a deorbit burn.

With Delta 387’s mission complete, only two more Delta IV missions remain to be launched. These are both slated to fly from the Cape Canaveral Space Force Station, with the NROL-68 mission slated for liftoff early next year and NROL-70 to follow in the first months of 2024. The first flight of Vulcan, ULA’s replacement for both its Delta IV and Atlas V rockets, is also currently scheduled for the first half of next year.

While these milestone launches are still some months away, ULA will be back in action on Friday with an Atlas V slated to deploy a pair of communications satellites for commercial operator SES. This is one of three Atlas V launches currently slated for the tail end of 2022, with deployment of JPSS-2, a military weather satellite, slated for the start of November and the US Space Force 51 (USSF-51) mission tracking no earlier than December.

(Lead photo: Delta IV Heavy and NROL-91 ascend toward orbit. Credit: Jack Beyer for NSF)

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