NASA’s Artemis rocket makers declare it’s a marathon • The Register

NASA’s Space Launch System may look like a mishmash of historic space shuttle parts, but it’s all new hardware, and the team that built the twin boosters and thrusters has spoken about the challenges of bringing designs from the 1970s into to bring a lunar future.

Northrop Grumman is the company behind the boosters used by the SLS. The work is overseen by NASA, but as the agency’s Bruce Tiller (the SLS Booster Manager) puts it, “it’s all a team”.

A team it may be, but as Tiller also admitted, “I have a small team on the government side, and they have a large team on the contractor side.” This is not surprising given that Northrop Grumman (like a number of other large aerospace and space companies) receives a significant amount of US taxpayer money and plays a key role in many aspects of the US space program.

The registry spoke to the teams on both the NASA and NG sides responsible for the two solid rocket boosters that, along with four RS-25 engines, are still sitting on the Florida launch pad after two scrubbed launch attempts.

Last weeks planned start was scrubbed after problems refueling, and a second try went south on Saturday after another fuel leak.

Booster Boosts

It’s hard to avoid thinking of a shuttle stack (just without the shuttle) when looking at the SLS, although the orange tank that sits between the boosters is a very different beast than the previous generation. However, the twin solid rocket boosters are very old parts. That means there are changes. “We did two big things,” NASA’s Tiller said, “and a lot of small things.”

The most visible of the big things is the addition of an additional booster segment: “That gives us another 20 percent more power on these boosters,” explained Tiller. “I like to joke with my engine friends, ‘You can light all four engines and go nowhere. Once you light those boosters, you’re gone!”

It’s not really a joke, although one manager responsible for the engines referred to the boosters as “sprinters”, while his units were more like “mile runners”.

The solid rocket boosters provide about three quarters of the SLS’s initial thrust at launch. Each consists of five segments whose case designs date back to the space shuttle era. “Two were on STS-135…I flew with them 11 years ago,” said Doug Hurley, senior director and pilot for the last Space Shuttle mission, Northrop Grumman.

However, unlike Hurley’s final Shuttle mission, these pods will not be parachuted back to Earth, nor will these RS-25 engines slide back on a Shuttle.

“It’s above all performance,” Tiller explained about the fate of the boosters and the cancellation of the parachutes – one of the big changes. “We saved eight flight sets… because we knew we were going to develop a more powerful booster [Northrop Grumman’s Booster Obsolescence and Life Extension (BOLE) boosters]”That, coupled with what is expected to be a low flight frequency compared to the Space Shuttle, means that the spent pods are falling into the ocean.

“The more you fly,” Tiller explained, “the more recovery makes sense. And it really saves you a lot of money. I wish we would fly that often,” he added ruefully, “but we’re not… that…”

The boosters are therefore dispensable. Or go out in a glow of glory. “It’s just great to see them being used in this way,” Hurley said, “when we get back to the moon.”

The show must go on

The same applies to the engines, formerly Space Shuttle Main Engines, which are now to be thrown into the ocean after one last hurray. Douglas Bradley, RS-25 associate program director at Aerojet Rocketdyne, who helped develop the units in the 1970s, said production would account for the loss. “We have a total of 16 engines from the shuttle program,” he explained, “so that we can get to Artemis IV.”

The SLS uses four engines per vehicle (compared to the three for the Shuttle) and operates at 109 percent of the Artemis I rated thrust. This was something that was possible in the Shuttle days, but as noted by Hurley and Northrop Grumman’s director of business development, Rick Mastracchio – also a former Shuttle ‘naut – it would only be done in an emergency.

With the thrust of the Artemis engine, there’s scope to push things further, and Aerojet Rocketdyne’s Bradley added, “We’ve raced 109s, 111s and 113s a lot of times, so we knew they were capable of that… “

Why so high? “We know sooner or later we’re going to run at 111, and so our process at Aerojet Rocketdyne has always been to go two percentage points above that… You usually have to run a little bit higher to make sure every part has seen that kind of strength.” .”

Those engines (14 of which were used on shuttle missions) have been paragons of reliability throughout the shuttle’s lifetime, he said, but admitted some mixed feelings, knowing the end was fast approaching. “We’ve been using them for so long, we’re getting to know them somehow. You know – this one runs a little warmer. This one runs a little more specific (ISP)… and so on one hand it’s sad, but it’s the coolest thing ever to have a couple of engines that I’ve been working on to get us back to the moon.”

As Northrop Grumman works on the BOLE project to replace the old SRB booster parts, Bradley outlined the challenges of resuming production of the ex-Space Shuttle engines. “Some of the things we made ourselves – but people have retired. Some of the suppliers we sourced our hardware from – they are no longer in business. So we had to relearn how to make the parts a bit.”

And cheaper too – Bradley told us that since the engines were intended to be dispensable, the expectation was that they would be less expensive without sacrificing reliability or performance. “In some cases,” he said, “we had changes that we wanted to make during the shuttle program, but we ran out of time.

In other cases, modern manufacturing techniques can be used to reduce costs — Bradley is a big fan of 3D printing rocket engine parts, something many other manufacturers use to reduce costs without sacrificing reliability.

As for other changes, the Aerojet engineer explained that an adjustment program was needed – for example, the Artemis stack is significantly taller than the Shuttle, and the engines are clustered at the base. This means that the operating pressures are higher and so on.

While the RS-25s spring to life seconds before the SRBs, like in the Shuttle days, their position means the familiar buzz of the Shuttle stack that would tilt slightly when fired is gone.

“The twang,” Bradley said, “was weird to see when I first saw it. It will be strange not to see it [happen].”

Arguments about retaining the reusability of the traditional Shuttle parts have been made somewhat moot due to the SLS’s lower flight cadence and the need to squeeze every last bit of power out of what lurks in the storerooms.

While the engineers and ex-Shuttle astronauts all confessed to mixed feelings about the use and disposal of the equipment, everyone was also visibly pleased that the hardware isn’t just gathering dust in a museum, but is coming one last time for a long-awaited return to the moon.

NASA said over the weekend that it had decided not to attempt another launch in early September and will have to Both the rocket and spacecraft will taxi back to the Vehicle Assembly Building after deciding whether work to replace a seal will be done on the pad itself, where it can be tested under cryogenic conditions, or in the Vehicle Assembly Building.

According to the information, the launch pad is required for a flight to the International Space Station in early October NASA Director Bill Nelson, it is likely that Artemis-1’s next launch attempt will not occur until the second launch window next month — anytime after mid-October. ®

https://www.theregister.com/2022/09/05/nasa_sls_northrop_grumman/ NASA’s Artemis rocket makers declare it’s a marathon • The Register

Laura Coffey

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