I started with a ship full of max-level veterans, and I'm just a complete noob.

Jiang Ming pushed open the door to the Institute of Mechanics' office and first saw three well-worn copies of the Journal of Applied Mechanics on the coffee table, with calculation papers tucked between the pages and several formulas repeatedly revised with red and blue pencils.

Qian Xuesen stood by the window with a teacup in his hand. On the center of the table was a document on the thermal protection of a warhead reentry phase, with a top-secret seal on the cover. Next to it was the Fifth Academy's work schedule for that evening.

"You've come at the perfect time."

Qian Xuesen pushed the documents to the edge of the table, gesturing for Jiang Ming to sit down.

"The reentry material estimation needs to be re-evaluated. Comrade Guo Yonghuai has just arrived in Beijing, and his top-secret mission is related to this line. You should clarify the boundary conditions first."

With his trench coat draped over the back of the chair, Guo Yonghuai sat on the other side of the coffee table, revising a page of derivation draft with a pencil. The pencil tip moved from the heat flux density to the ablation interface, the movement always fluid.

Jiang Ming had only seen his name in the documents before. The scholar who had returned to China was even thinner than in the photos. The fatigue from the long journey was still there, but every change on the draft pointed directly to the skeleton of the equation.

Guo Yonghuai looked up at Jiang Ming, then at the file bag he had brought.

"Have you been in charge of unsteady heat transfer in variable cross-section throats?"

"We have done research on the promotion of temperature potential and are also working on the coupling terms between thermal shock and structural damping."

Guo Yonghuai placed the pencil next to the drawing, signaling him to continue.

The information he had at the moment came from Qian Xuesen's brief introduction. He only knew that Jiang Ming had participated in the recalculation of high-temperature furnace control and guidance, and he still held a critical attitude towards the depth of its theoretical derivation.

Jiang Ming walked to the blackboard, first drew the variable cross-section throat, and then wrote the wall heat flow, material thermal conductivity and structural vibration into the same set of coordinates.

"During the ignition and shutdown phases, changes in the throat cross-section alter the local heat flux peak, and the temperature gradient, in turn, affects the material's elastic modulus. If the damping remains constant, the thermal stress wave will be underestimated at the variable cross-section."

He formulated an integral equation for unsteady heat conduction, incorporated the temperature-dependent thermal conductivity coefficient into the new temperature potential variable, and then derived the energy conservation condition on the moving boundary.

Guo Yonghuai got up and walked to the blackboard. He looked at the first line and then at the end boundary term. He twirled the pencil in his hand and then placed it on the position where the non-axisymmetric perturbation was omitted.

He drew a heavy question mark on that item.

"In axisymmetric throats, this transformation can be used. When a reentry warhead has an angle of attack, the stagnation point shift will cause the circumferential heat flow distribution to lose symmetry. If you write the boundary temperature as a single-valued function, once lateral ablation occurs, the solution will degenerate along the wrong normal."

The sounds of discussion from the office carried into the corridor. Several researchers carrying documents slowed their pace and looked at the blackboard from the half-open doorway.

Jiang Ming had already appeared at the Fifth Academy's demonstration meeting, but many people only knew that he was good at engineering control. Now that they saw him discussing three-dimensional ablation boundaries directly with Guo Yonghuai, who had just returned from abroad, they couldn't move their feet.

An overseas-returned staff officer walked in with Soviet re-entry documents, attempting to reconcile the opinions of both sides within the existing framework.

"The Soviet calculations also adopted equivalent axisymmetric treatment. In engineering, the heat flux at the angle of attack can be converted into a correction coefficient to protect the nodes first, and then refine it later."

Guo Yonghuai opened the aerodynamic heating curves he brought, displaying the ablation rates under two sets of angle-of-attack conditions.

"Correction factors can only be applied to the results. Once the material surface undergoes non-uniform shrinkage along the circumference, the normal, curvature, and heat flow direction will change. If the old boundary is continued to be used, the error will enter the thickness estimation."

The staff officer looked at the curves for a few lines, but the Soviet formula he had prepared could not cover lateral ablation, so he had to put the data back on the table.

Jiang Ming stared at the question mark on the blackboard. The temperature potential scheme that he had originally prepared to write in von Kármán's reply was stuck at the same gap. If this gap could not be filled, the throat method would be difficult to safely extend to the re-entry stage.

He erased the single-valued boundary function and used local surface coordinates to describe the ablation interface, expanding the temperature potential along the normal, tangential, and circumferential directions respectively.

"The boundary temperature is changed to a field quantity on the curved surface, the moving speed is given by the local energy balance, the stagnation point offset caused by the angle of attack is entered into the circumferential heat flow term, and the material stress is updated with the interface normal."

Guo Yonghuai took the chalk and added the shear component next to the three-dimensional thermal stress tensor, and wrote the effect of curvature change on local heat flow accumulation into the shrinkage rate.

"Structural response is still lacking. After the thermal layer is thinned, the external load transfer path also changes."

Jiang Ming extracted the temperature-dependent modulus term from the derivation of throat damping coupling, substituted the material thickness as a time-varying parameter into the structural equation, and then closed the thermal stress tensor with the ablation rate.

One person guarded the flow and ablation, while the other completed the unsteady heat transfer and structural damping. The equations on the blackboard were gradually connected into a computable path.

More and more researchers gathered in the corridor, but Qian Xuesen remained standing by the table, only noting down a few symbols when the two of them discussed the overall interface.

After completing the last boundary condition, Guo Yonghuai returned to the coffee table and used a slide rule to input the typical re-entry heat flow from the data.

Jiang Ming used the existing material thickness for the first round of estimation. The ablation margin was exhausted in advance under non-axisymmetric conditions, and the structural safety factor dropped to near the overall red line.

Guo Yonghuai used another set of angle of attack data, and the results still pointed to the same gap, and the working condition with a larger stationary point offset was more dangerous.

"The original estimate was that it needed to be thickened."

He pushed the slide rule to Jiang Ming.

Jiang Ming recalculated based on three sets of material parameters, taking into account processing tolerances, peak heat flux, and shrinkage rate, and determined that the thickness increase ratio was between 18% and 22%.

"The engineering quota will be increased by 20%, with additional space reserved for testing and correction."

Qian Xuesen wrote this conclusion on the task list and then assigned the access permissions for the materials group, structure group, and ballistics group to the same column.

Previously, Jiang Ming could only access data related to guidance and temperature control, but now the heat flow data, material curves, and structural interfaces of the reentry thermal protection system are also open to him.

The phone on the table rang repeatedly. The senior executives of the Fifth Academy first asked about the final draft timeline, and then urged the overall team to submit the changes in the weight of the materials before the meeting the next day.

After hearing the request, Qian Xuesen only offered one night.

"Tonight we will complete the recalculation of three operating conditions. The impact of the thickened center of gravity and ballistics will be handled by the overall team simultaneously, and a signed draft will be completed tomorrow morning."

Jiang Ming gathered up the draft, the fatigue from working on multiple fronts weighing on his eyes, but the question marks on the blackboard had been replaced by the three-dimensional boundary conditions. This exchange had actually made his thinking much clearer.

Guo Yonghuai walked over to him and patted him on the shoulder.

"Your temperature potential transformation grasps the essence of physics, and you're willing to dismantle and rebuild when you encounter three-dimensional boundaries. This kind of intuition is more useful than memorizing a whole set of formulas."

The researchers who had been peering out dispersed, their previous scrutiny turning into discussion as the closed equation on the blackboard came into focus. Several people went directly to retrieve materials and data, preparing to join the nighttime recalculation.

Jiang Ming re-inserted the throat problem from von Kármán's third letter into the draft, and Guo Yonghuai's pointing out of the non-axial symmetry gap also provided a more solid direction for that reply.

Qian Xuesen handed the top-secret mission envelope to Guo Yonghuai, and then handed the resource allocation form to Jiang Ming.

"You can directly access the high-temperature materials records and overall assembly time summary from the Institute of Physics. The office will complete the formalities, but each document must be recycled as a Class A item."

Jiang Ming took the call order, and a temporary authorization stamp appeared next to the signature column, which meant that he had gained greater scheduling space between basic theory and engineering interface.

As Guo Yonghuai put away the derivation draft on the table and prepared to go to the materials group, his gaze fell on another Soviet meteorological parameter assessment sheet stamped with a red seal.

He opened the first page and saw the low Mach lateral deflection coefficient and the Jiuquan monsoon input. His pencil stopped beside the unusually smooth curve.

Who handled this line?

Qian Xuesen turned the evaluation sheet to him, and Guo Yonghuai read page by page to the end, the lines between his brows growing deeper and deeper. Finally, he pressed the pencil he had just drawn a question mark on heavily onto the revision date of the Soviet matrix.