NASA weighing the risks of the SLS Green Run versus EM-1 program –

NASA is still officially deciding whether or not to take the time to perform the large integrated test of its Main Stage of the Space Launching System (SLS). "That's why we tested" is a very cited philosophy in this phase of development of a new system; In order to keep alive the hopes of a first launch within the calendar year 2020, the agency reviewed whether to continue applying that philosophy to SLS or not.

Until recently, the "Green Run" or acceptance test of the stage was considered a critical development step in the program for the newer and more complicated part of the launch vehicle, but the test campaign is expected to take many months. months to complete and join. if time is lost during Core Stage badembly, it is likely that the launch of Exploration Mission-1 (EM-1) will begin in 2021. The Stage Green Run will culminate in the unique and planned hot fire test of a Core Stage before of EM-1.

The delivery of the first Core Stage by the main contractor Boeing has been delayed several times, and NASA hoped to catch up and speed up plans for a lunar landing with an American crew in 2024. The agency conducted a 45-day study that concluded in the middle of – Before looking again for any possible means to recover some of the lost time and try to maintain the objective of the release date of the EM-1 within 2020.

According to reports, NASA is leaning towards the maintenance of the test, which an external security panel strongly recommends, but no final decision has been announced. Although the mission is unmanned, it is crucial for SLS to make its first EM-1 launch because most of Orion's moon flight test objectives on its first solo flight depend on it.

Green Run is for the rookie stage, not for the veteran engines.

"Green Run" in this case is the abbreviation for Core Stage Green Run and the test campaign focuses on testing the scenario, not the engines. A Green Run is an acceptance test of new hardware and testing of liquid propulsion systems at the Stennis Space Center in Mississippi, the term can be applied to everything from acceptance tests of new components to new engine constructions to new stages of rockets like the SLS Core Stage.

Aerojet Rocketdyne RS-25 engines are one of the only Core Stage systems that are ready to fly today because they finished their tests a long time ago. The four flight engines (Engines 2045, 2056, 2058 and 2060) that will be installed in the first Core Stage have demonstrated safe performance in multiple launches of the Space Shuttle when they were named Space Shuttle Main Engines (SSME).

Credit: Aerojet Rocketdyne.

(Photo caption: the four RS-25 flight engines badigned to EM-1 as "delivered at the scene" in October 2017, at the Aerojet Rocketdyne facility in Stennis).

Two motors of "development" only on land (Motors 0525 and 0528) carried out numerous development tests that showed that the design of the Shuttle is adapted to the SLS in both nominal and non-nominal conditions. The hot development tests of the "adaptation" configuration RS-25 that will fly in the first four SLS launches concluded eighteen months ago.

Single-engine tests from 2015 to 2017 rated the design of the Shuttle to fly under the operating conditions of SLS, including its new engine control units (ECU). The single engine tests on stand A-1 in Stennis generally use development engines instead of flight hardware to test them at the edges and corners of their operating envelope.

The use of development engines avoids both the general wear and tear of the flight engines from additional operating cycles and the additional demands of margin tests on the engine hardware; however, two RS-25 flight engines that did not fly during the Ferry Program were independent tests of engine operation. Those acceptance tests further demonstrated the safe operation of the RS-25 flight hardware for the SLS requirements.

A third flight engine was turned on during the development tests in a calibration test of booth A-1.

In addition to the RS-25 engines, the SLS Boosters and the upper stage of the Interim Cryogenic Propulsion Stage (ICPS) also have an extensive history of ground testing, a flight history or both.

Credit: NASA.

(Photo caption: SLS Core Stage and its elements – Although they are designed around the main engines of the space shuttle and use other main propulsion system hardware (MPS) from the Shuttle, many of those components have been modified or redesigned. rest of the scenario is New, including the layout of your systems.)

In contrast to the other SLS elements that are tested in flight or on the ground, the Core Stage is the new piece of the launch vehicle. It began to develop behind the designs and hardware already evolved Space Shuttle or the canceled Constellation program and has not yet tested any version that works.

When it is finally completed, Core Stage-1 will not only be the first flight item, but also the first article of the program's work stage. The Green Run of this first unit of work is the only opportunity planned to demonstrate a full-length test run of a Core Stage before the first launch of the program.

For the integrated hot fire test, the RS-25 engines are essentially test support equipment to badess how well the new Core Stage meets the requirements to run four of them at the same time for more than eight minutes. In addition to meeting the demands of the engine group during the main stage, the new SLS flight software will also see its first full use.

The flight software that is executed in the new flight computers of the stage is in charge of the cycle of general control of the management of the vehicle, the state of the monitoring systems and the control of the scenario through the sequences of test of Green Run through a new avionics system.

NASA and Boeing are qualifying the different Core Stage subsystems individually and are testing some of them together in pairs and in small groups, but the tests during the Stage Green Run will be the first time all the Stage systems are operated.

Nothing official like ASAP makes recommendations.

As part of the efforts to shore up the EM-1 schedule, NASA began an internal 45-day study in early March in search of other possible ways to shorten the schedule to launch the preparation. The final badembly of Core Stage-1 remains the critical path, and recently a revised plan was implemented to rearrange the order in which the remaining three pieces were joined and make both positions horizontal.

The hope is that this will buy again a few months and that the badembly of the stage will be completed by the end of the year; however, according to the previous programming, a release would still be in danger before the end of 2020. The 45-day study looked for more programming options and Stage Green Run would be highlighted by anyone who watched the content to cut.

The study was to be presented on April 15 and after a review that week at NASA headquarters in Washington, DC, the SLS program held a meeting of all participants on April 22, where it was reported that the test remained in the program. Ars Technica also reported on an internal memo that the Associate Administrator of NASA's Directorate of Operations and Human Exploration (HEOMD), Bill Gerstenmaier, sent on the same day.

NASA says that nothing has been decided yet. "A final review of the badessment is still underway and no decisions have been made," NASA spokesman Mike Curie wrote in an email after the news of the All-Hands meeting.

Credit: NASA / Jude Guidry.

(Photo caption: The section of the attached Core Stage-1 engine and the tail of the boat are introduced into the final badembly area in a newly furnished tool at the Michoud Assembly Facility (MAF) on April 1. The integration and the payment of the duo was moved to this area and the final badembly sequence was reworked to advance the completion date of the entire stage, perhaps before the end of the year.)

The Aerospace Safety Advisory Panel (ASAP) emphasized its recommendation on the Green Run test in a public statement made on April 25 at the conclusion of its meeting at the Marshall Space Flight Center in Huntsville, Alabama. "There is no other test approach that collects the critical, large-scale, integrated operational data from the propulsion system necessary to ensure safe operations," said Dr. Patricia Sanders, ASAP President, during the public meeting.

"Shooting of shorter-duration engines on the launch pad will not achieve an understanding of operating margins and could have serious consequences if done in a much less controlled environment than Stennis and if margins are exceeded. I can not emphasize more than we advise NASA to withhold this test. "

The Core Stage production schedule has been a critical concern for a long time and there were reports until early summer of 2018 of studies to consider the replacement of a brief Flight Readiness (FRF) / static fire on Launchpad 39B at the Kennedy Space Center instead of the Green Race with the hope of regaining some of the lost time. Although static fire tests at the launch site have often been conducted before the first flight of a new program or new vehicle, they were generally preceded by more thorough acceptance tests.

The Space Shuttle Program ran twenty-second long FRFs on new Orbiter vehicles before its first flight, but not before pbading a Main Propulsion Test Item (MPTA) through several ground test shots at the end of the years 70 and early 80's in the B-2 Test Bench. SpaceX still performs stage flight acceptance tests in Texas before the static launch of the first pre-launch stage on its launch platforms in Florida.

The Delta 4 program used the same Stennis B-2 support to warm-shoot a Common Booster Core (CBC) first stage before the first launch of the program and a FRF prior to launch. The Saturn program also conducted flight duration acceptance tests of its scenarios at sites across the country in the 1960s, including what is now called the Stennis Space Center.

Credit: NASA.

(Photo caption: The main propulsion test article of the space shuttle was used to test shots of the long-duration integrated propulsion system in Stennis.) The image on the left shows the orbiter aft fuselage built and integrated for that the MPTA is lifted on the B-2 platform 1977. The aft fuselage, badogous to the engine section of the SLS Core Stage, was paired with a truss structure to be able to attach it to an external Shuttle tank The figure on the right shows the integrated MPTA test configuration, for SLS, these same basic elements were merged into a larger, online design.)

An FRF on the pad in KSC would be limited. The water supply for the sound suppression and flooding of the flame trench and launch platform at KSC are designed and dimensioned so that the vehicle can take off and clear the area relatively quickly. It will run after only a few seconds of engine running time.

As with Shuttle, SLS does not accelerate to the maximum until after takeoff; While the Stennis test plan is to accelerate the engines to 109 percent of the rated power level (RPL) and try to replicate an acceleration profile similar to that of a flight, it is not clear if KSC can withstand full power for a while. Hypothetical FRF.

During the April 25 public meeting of ASAP to summarize their private conversations with NASA earlier this week, Dr. Sandra Magnus could have alluded to the "understanding of operating margins" that Dr. Sanders stated in her comments. initials.

In a summary of the ASAP review of the state of the Commercial Crew Program (CCP) of NASA, Dr. Magnus, a former shuttle astronaut who flew on the final flight of the program, noted that before committing to flights with crew, CCP requires sufficient test data "to ensure that we understand the margins, that we are controlling those margins and that we are operating in the environment that those margins require."

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