Planning for a clean touchdown on Mars

A U.S. mission to land astronauts on the floor of Mars might be not like every other extraterrestrial touchdown ever undertaken by NASA.

Though the area company has efficiently landed 9 robotic missions on Mars since its first floor missions in 1976 with the Viking Challenge, safely bringing people to Mars would require new applied sciences for flight via the Martian environment. However these applied sciences and programs cannot be comprehensively examined on Earth beforehand.

Since 2019, a workforce of NASA scientists and their companions have been utilizing NASA’s FUN3D software program on supercomputers situated on the Division of Power’s Oak Ridge Management Computing Facility, or OLCF, to conduct computational fluid dynamics, or CFD, simulations of a human-scale Mars lander. The OLCF is a DOE Workplace of Science person facility situated at DOE’s Oak Ridge Nationwide Laboratory.

The workforce’s ongoing analysis challenge is a primary step in figuring out how you can safely land a automobile with people onboard onto the floor of Mars.

“By its very nature, we do not have validation information for this. We are able to do priceless however restricted assessments in floor amenities like a wind tunnel or on a ballistic vary, however such approaches can not absolutely seize the physics that might be encountered on Mars. We will not flight-test within the precise Martian atmosphere—it is all or nothing after we get there. That is why supercomputing is so critically essential,” mentioned Eric Nielsen, a senior analysis scientist at NASA’s Langley Analysis Heart and principal investigator for the five-year effort on the OLCF.

In contrast to in latest Mars missions, parachutes aren’t a part of the operation. As a substitute, the main candidate for touchdown people on Mars is retropropulsion—firing forward-facing rockets constructed into the craft’s warmth defend to decelerate.

“We have by no means flown something like this earlier than. The elemental query from the outset was, “Are we going to have the ability to safely management this automobile?'” Nielsen mentioned.

The rationale that NASA is investigating retropropulsion fairly than standard parachutes is a matter of physics. Previous Mars landers have weighed about 1 ton; a automobile carrying astronauts and all their life-support programs will weigh 20 to 50 occasions extra, or concerning the measurement of a two-story home. Mars’ skinny environment—about 100 occasions much less dense than Earth’s—will not assist a parachute touchdown for such a big craft.

“With a traditional automobile, we fly via a really clear, predictable atmosphere. All of that goes out the window with this idea, the place we might be touring via a particularly dynamic atmosphere consisting of high-energy rocket exhaust,” mentioned NASA workforce member and CFD professional Gabriel Nastac.

With steering from NASA mission planners, the workforce formulated a multiyear plan consisting of more and more subtle simulations aimed on the key query of controllability.

In 2019, the workforce carried out CFD simulations on the Summit supercomputer at resolutions as much as 10 billion components to characterize static automobile aerodynamics at anticipated throttle settings and flight speeds starting from Mach 2.5 right down to Mach 0.8, circumstances wherein the automobile’s rocket engines might be required for preliminary deceleration.

All through 2020, an intense code growth effort targeted on porting FUN3D’s common reacting-gas capabilities to Summit’s graphics processing unit, or GPU, accelerators.

“Realizing environment friendly efficiency of an unstructured-grid CFD solver within the face of complicated physics-laden kernels is a gigantic problem in a GPU-based computing atmosphere. However we had been in the end capable of restructure essential segments of code to ship the efficiency we had been after,” mentioned NASA analysis pc scientist Aaron Walden, who leads the workforce’s multi-architecture software program growth.

The work set the stage for an essential 2021 marketing campaign that enabled the workforce to handle the complicated interactions of the liquid oxygen/methane rocket engines with the Martian environment, which consists of primarily carbon dioxide and nitrogen. A petabyte (equal to 1,000 terabytes) of output information for every simulation carried out utilizing 15,000–20,000 GPUs on Summit yielded key insights into essential variations in automobile aerodynamics versus these noticed utilizing the prior simulation’s perfect-gas assumption.

For the 2022 marketing campaign, the workforce took a serious step ahead by incorporating the state-of-the-art NASA flight mechanics software program referred to as the Program to Optimize Simulated Trajectories II, or POST2, into the workflow. Shifting past simulations that assume a static flight situation, the workforce now sought to “fly” the automobile within the digital supercomputing atmosphere. This take a look at would symbolize a primary try to quantify and tackle essential unsteady dynamics that may be encountered throughout an precise powered descent to the Martian floor.

The workforce enlisted key specialists from Georgia Tech’s Aerospace Methods Design Laboratory; this group was led by Brad Robertson. These specialists had already spent a number of years creating a coupling algorithm to exchange the low-order aerodynamic fashions inside POST2 with real-time, physics-based FUN3D simulations to in the end understand high-fidelity trajectory simulations that leverage subtle flight management algorithms.

“Coupling FUN3D and POST2 was fairly a problem. We needed to juggle 5 – 6 reference frames and the info transformations between them. However the reward was having the ability to undertake all of the onerous work achieved by different NASA engineers on detailed steering, navigation, management and propulsion fashions and to deliver all of them right into a single, unified, multiphysics simulation,” mentioned workforce member Zach Ernst, a Georgia Tech doctoral scholar on the time, who labored with NASA graduate intern Hayden Dean on the trouble.

Incorporating POST2 introduced a further problem. As a result of POST2 is topic to extra restrictive export-control rules than FUN3D, workforce member Kevin Jacobson was tasked with creating a distant coupling paradigm wherein POST2 would execute on a NASA facility whereas speaking in real-time with FUN3D working at management scale on the OLCF.

Establishing and sustaining this connection whereas accounting for firewalls, community interruptions and job schedulers introduced quite a few challenges. This work required a couple of 12 months of planning and coordination with cybersecurity personnel and system directors at each amenities.

The extra effort paid off when the workforce achieved their long-term objective of flying a considerable portion of the descent section within the digital atmosphere.

The arrival of OLCF’s Frontier supercomputer couldn’t have come at a greater time for the challenge. With exascale computing energy (a quintillion or extra calculations per second) now a actuality, the workforce may afford to reintroduce the specified bodily modeling and different classes realized over the lifetime of the challenge.

In 2023, the workforce targeted on the final word simulation they’d hoped for years earlier: a very autonomous, closed-loop take a look at flight leveraging the world’s strongest supercomputing system.

Whereas the eight most important engines are used to manage pitch (up-and-down rotation) and yaw (side-to-side rotation) because the steering system goals for the designated touchdown zone, POST2 additionally points instructions to instruct FUN3D to periodically fireplace 4 response management system, or RCS, modules organized circumferentially across the bottom of the lander to carry out roll corrections in flight.

“These capabilities might be essential for assessing the controllability of future automobiles,” mentioned Georgia Tech’s Alex Hickey, who led growth of the RCS modeling.

The workforce’s long-term objective grew to become a actuality in late 2023, as OLCF workers assisted in coordinating a cautious sequence of high-priority jobs over a two-week interval at scale on Frontier.

“For the primary time, we had been capable of return to the unique query of safely controlling this sort of automobile in autonomous flight,” Nielsen mentioned. “In a typical aerospace CFD simulation, one may compute a second or two of bodily time. Right here, Frontier enabled us to efficiently fly 35 seconds of managed flight, descending from 8 kilometers (about 5 miles) altitude to about 1 kilometer (0.6 miles) because the automobile approached its touchdown section.

“The decision, bodily modeling and temporal period are past something we may try on a traditional high-performance computing system,” Nielsen added “The sheer pace of the GPUs applied at management scale is actually enabling, and we’re deeply grateful for the various alternatives and world-class experience that the OLCF has supplied.”