RocketAgent: A Long-Horizon Engineering Agent for Multidisciplinary Design of Liquid-Rocket Thrust Chambers

Junxiang He; Runze Mao; Kun He; Teng Zhang; Liming Zheng; Ke Xiao; Zhi X. Chen

cs.AIOct 5, 2026

RocketAgent: A Long-Horizon Engineering Agent for Multidisciplinary Design of Liquid-Rocket Thrust Chambers

Authors: Junxiang He, Runze Mao, Kun He, Teng Zhang, Liming Zheng, Ke Xiao, Zhi X. Chen

Organizations: State Key Laboratory of Turbulence and Complex Systems, School of Mechanics and Engineering Science, Peking University, Beijing, 100871, China · College of Engineering, Peking University, Beijing, 100871, China · Legendspace Intelligence Technology Co., Ltd., Beijing, 100080, China · AI for Science Institute (AISI), Beijing, 100084, China

Abstract

Liquid-rocket thrust-chamber design involves interdependent analyses in which downstream constraints can require earlier design decisions to be revisited. Managing these dependencies across heterogeneous tools requires consistent design information and coordinated updates throughout the workflow. We present RocketAgent, a long-horizon engineering agent for multidisciplinary preliminary design of liquid-rocket thrust chambers. A single plan-owning Coding Agent coordinates engineering skills for performance sizing, subsystem optimization, geometry generation, and multiphysics assessment. A provenance-aware knowledge graph supports method selection, while a typed Design Intermediate Representation maintains shared parameters, artifacts, and decisions. Revision-aware checks invalidate affected results and block superseded inputs, with consequential changes subject to engineering approval. In a representative simulation-based design, RocketAgent continued from an infeasible cooling search through an engineer-authorized operating-point revision, identified feasible subsystem designs, and coordinated subsequent geometry generation and multiphysics assessment to support final configuration selection. Separate module tests assessed surrogate predictions and nozzle adaptation. A two-configuration comparison across three controlled scenarios verified the expected dependency invalidations and superseded-input blocking before solver execution. The representative case demonstrates sustained coordination across a multidisciplinary design workflow, while the controlled tests establish the behavior of the revision mechanisms supporting that execution.

Figures & tables

Figure 1: RocketAgent architecture: (a) natural-language design intent; (b) the plan-owning Coding Agent and its Think–Act–Observe–Improve cycle; (c) an illustrative thrust-chamber representation; (d) the engineering KG; and (e) specialist calculation, geometry, simulation, and optimization capabilities.

Figure 2: Conceptual workflow of RocketAgent across Conceptual Design, Embodiment Design, and Verification, coordinated by a plan-owning Coding Agent with revision-aware feedback.

Figure 3: KG semantic schema: (A) requirement semantics, (B) engineering objects, (C) cases and source-linked evidence, and (D) methods and agents. The four relation groups connect design intent to an accepted concept and numerical inputs.

Figure 4: Embodiment-design tasks linked to the thrust-chamber regions: performance, geometry, and thermal refinement (left); GA-based cooling-channel search and trade-off selection (center); and GPR-assisted NSGA-II injector optimization (right). The Pareto and surrogate plots are schematic.

Figure 5: Selected four-element thrust-chamber geometry: (a) exterior view showing the igniter port and separate oxidizer and fuel inlets; (b) longitudinal section showing the injectors, combustion chamber, nozzle, and regenerative-cooling channels; (c) enlarged injector-head cutaway showing the liquid collection chambers and internal injector passages.

Figure 6: Representative engineering workflow for the 500 N LOX/RP-1 thrust chamber. Conceptual Design defines the requirements and KG-grounded concept. Embodiment Design realizes the chamber contour, cooling-channel layout, and four- and five-element injector alternatives. Geometry realization then feeds injector VOF, chamber-combustion, and coupled thermal–structural assessments. The evidence cards summarize spray angle/pressure drop, thrust/chamber pressure, and stress/margin checks; passing evidence advances to the selected design shown at right.

Figure 7: Cooling-channel trade-off after the governed rich-side redesign. The axes show coolant pressure loss

\Delta p

and maximum wall temperature

T_{\mathrm{w,max}}

. Hollow markers fail at least one hard gate, whereas green markers are fully feasible. The blue square marks the selected balanced design and the red triangle a temperature-priority alternative.

Figure 8: Water-reference injector-module surrogate and search evidence. (a) Held-out VOF–surrogate parity for spray-cone angle ( $n=118$ ). (b) Held-out parity for Fuel- and Ox-side pressure drops. (c) Standardized residuals $z=(y-\mu)/\sigma$ for 140 independent, search-conditioned post-selection VOF evaluations; dashed lines at $z=\pm 2$ mark nominal two-standard-deviation limits, whose empirical coverage is reported in Table 1 . (d) NSGA-II nondominated objective set, colored by the Ox-pressure-drop objective, with the selected module-validation knee point highlighted.

Response	$C(1)$ (%)	$C(2)$ (%)	Mean $z$	SD $z$	NLPD
Spray-cone angle	50.71	80.71	0.750	1.175	3.565
$\Delta p_{\mathrm{w},\mathrm{Fuel}}$	92.86	100.00	$-0.007$	0.540	11.762
$\Delta p_{\mathrm{w},\mathrm{Ox}}$	64.29	93.57	$-0.430$	0.945	10.680

Table 1: Uncertainty assessment on 140 independent, search-conditioned post-selection water-reference VOF evaluations. Gaussian reference coverage is 68.27% at

\pm 1\sigma

and 95.45% at

\pm 2\sigma

. NLPD uses degrees for angle and Pa for pressure; its values are unit-dependent and are not compared across outputs.

Figure 9: Injector-scale VOF verification. (a) Water volume fraction $\alpha_{\mathrm{water}}$ and (b) velocity magnitude $|\mathbf{U}|$ in m/s on the centerline $x$ – $z$ plane at $t=0.1$ s.

Response	GPR $\mu\pm\sigma$	VOF mean	VOF–GPR	Relative deviation	$z$
Spray angle	$87.621\pm 5.523^{\circ}$	$84.674^{\circ}$	$-2.947^{\circ}$	$3.48\%$	$-0.53$
Fuel $\Delta p$	$311.266\pm 44.963$ kPa	$313.295$ kPa	$+2.029$ kPa	$0.65\%$	$+0.05$
Ox $\Delta p$	$253.004\pm 11.646$ kPa	$246.505$ kPa	$-6.498$ kPa	$2.64\%$	$-0.56$

Table 2: Independent endpoint comparison between the GPR prediction and the DeepFlame VOF window mean. Deviations are VOF minus GPR; the relative deviation uses the GPR mean, and

z

is the standardized residual.

Figure 10: Chamber-scale Fluent verification for the four-element configuration. (a) Three-dimensional static-temperature field on a 0–3400 K scale. (b) Corresponding velocity-magnitude field on a $0$ – $2200~\mathrm{m\,s^{-1}}$ scale. Both panels show sections at $z=20$ , 60, 100, and 140 mm and expose the injector-side entry, chamber, convergent section, and nozzle.

Metric	Design reference	Four elements	Relative error	Five elements	Relative error
$\overline{p}_{\mathrm{c}}$	$1.000$ MPa	$0.9441$ MPa	$-5.59\%$	$0.9303$ MPa	$-6.97\%$
$F$	$500$ N	$471.63$ N	$-5.67\%$	$460.53$ N	$-7.89\%$
$I_{\mathrm{sp}}$	$180.197$ s	$169.939$ s	$-5.69\%$	$165.940$ s	$-7.91\%$
$c^{*}$	$1403.5~\mathrm{m\,s^{-1}}$	$1362.1~\mathrm{m\,s^{-1}}$	$-2.95\%$	$1342.2~\mathrm{m\,s^{-1}}$	$-4.37\%$

Table 3: Integral chamber-performance comparison from the Fluent reacting-flow calculations. Relative errors are measured against the corresponding design or RocketCEA reference; the preliminary-design screening criterion is

|\delta|<10\%

for each listed response.

Figure 11: Coupled thermal–structural response of the selected four-element injector assembly: (a) steady nodal-temperature field obtained from the kerosene- and LOX-side film conditions; (b) von Mises stress field after transfer of the temperature field and application of the pressure loads; and (c) averaged nodal von Mises stress along the declared top-plate path. The path maximum is 254.00 MPa at $X=18.175~\mathrm{mm}$ , corresponding to a margin of 1.38 relative to the approximately 350 MPa aged-state yield reference and satisfying the minimum criterion of 1.2. The connecting line in panel (c) is for visualization only.

Figure 12: Oxidizer-side branch mass-flow distributions from CFD under the same prescribed Ox inlet flow. Each marker gives the percentage deviation

d_{\mathrm{Ox},i}=100(\dot{m}_{\mathrm{Ox},i}/\overline{\dot{m}}_{\mathrm{Ox}}-1)

; labels report the integrated Ox outlet flow in kg/s. (a) Four elements: total 0.14736 kg/s,

\mathrm{CV}_{\mathrm{Ox}}=1.92\%

, and

\delta_{\mathrm{Ox},\max}=3.11\%

. (b) Five elements: total 0.14664 kg/s,

\mathrm{CV}_{\mathrm{Ox}}=5.08\%

, and

\delta_{\mathrm{Ox},\max}=6.51\%

. Both layouts satisfy the flow-acceptance checks for the Ox circuit; the lower within-layout dispersion favors four elements.

Figure 13: Contour comparison after strict 0.1-mm simplification. (a) Chamber and convergent profiles from the injector face to the throat, plotted against

x

. (b) Divergent profiles from the throat to the exit, plotted against

x-x_{\mathrm{t}}

. Insets illustrate the coordinate definitions and are not to scale. Open markers denote retained profile points; maximum interpolation errors against the quantized source profiles are 0.1000 mm for TOC, 0.09828 mm for the

15^{\circ}

conical contour, and 0.1000 mm for the

30^{\circ}/10^{\circ}

parabolic bell.

Appendix figures & tables3 assets

Supplementary material from the paper’s appendix.

Appendix

Figure 14: Calibration diagnostic for the 140 independent post-selection water-reference VOF evaluations. The diagonal denotes equality between empirical and nominal central-interval coverage. Curves below it indicate under-coverage and curves above it indicate conservative intervals. The candidates are selected by optimization; the curves describe this search-conditioned population, not a random held-out test or a guarantee for real-propellant operation.

Figure 15: Shared Design IR record relationships. Boxes separate fields from usage checks; solid arrows indicate information links, and the dashed arrow denotes authorization of a parameter revision subject to the state-transition contract.

Figure 16: Contract-bound execution: capability selection, skill invocation, adapter/backend execution, and checked state commitment. Dashed arrows show accepted-state reads for subsequent planning and execution.

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