## 7 Challenges and Future Opportunities
The integration of more subsystems and the multidisciplinary nature of these methods contribute to their complexity. Therefore, future work should focus on enhancing their versatility and addressing time-related issues (e.g., computational time or simulation time) due to the increasing complexity of design. Based on the challenges and opportunities presented above, a summary list of requirements for future IPTMSs is as follows:  
1. Enhanced system integration: future IPTMSs could benefit from higher levels of integration, not only with TMS and PMS but also with other aircraft subsystems. 2. Improved system stability and safety: as the complexity of IPTMSs increase, the importance of system stability and safety may also increase. 3. Minimisation of system weight and volume: for military and civil aircraft, future IPTMS research should investigate methods to minimise the system weight and volume. 4. Minimisation of cooling power and ram air usage: future research should explore approaches to minimise the use of ram air and the power usage of TMS. 5. Optimised power management strategies: Future IPTMS should consider the trade-off study between propulsive power and the power usage of TMS. This could lead to the development of optimal battery power supply strategies across the aircraft flight mission. 6. Investigation of IPTMS optimisation domain: For different operating conditions and different propulsion requirements, the impacts of the TMS and the PMS would be different. Future IPTMSs should investigate at the system level whether the optimisation of the IPTMS should be in the thermal domain or the power domain. 7. Versatility and stability of methods and tools: The methods and tools developed for an IPTMS at the aircraft level should be versatile enough to accommodate different power conditions, flight conditions (e.g., subsonic/supersonic, normal/cold-day/hot-day conditions), and different aircraft platforms. At the same time, the methods and tools should ensure their stability through validation. 8. Addressing time-related issues: with the increasing complexity of design, future work should focus on addressing time-related issues, such as computational time or simulation time. For civil EPA, the electrified propulsion systems introduce more electrical components than those in military aircraft, thereby increasing the requirements for cooling and energy conservation. Although the IPTMS with energy recovery has the capability to handle cooling and power generation simultaneously, it is not suitable for civil EPA. This is due to this IPTMS typically using fuel as the coolant. While the fuel flow is sufficient for cooling the heat loads of military aircraft, it is inadequate for civil aircraft. Furthermore, the power generation of the IPTMS might not meet the power requirements of civil EPA, as they have more power consumers than military aircraft. In this case, the IPTMS with advanced EPS and TMS could be a feasible IPTMS solution for EPA. With an advanced EPS or TMS design, the thermal and power requirements can be reduced at the architecture level by minimising electric components and simplifying the TMS. Furthermore, an optimal battery power supply strategy can affect the capability of energy saving and the size of the battery, and the battery size then impacts thermal and power requirements. Additionally, the implementation of power management strategy can further optimise the IPTMS performance across the flight mission, reducing energy consumption. Therefore, a potential approach for an IPTMS to address the challenges of EPA is the combination of architecture design (IPTMS with advanced EPS and TMS) and power management optimisation. Typically, the iteration of civil aircraft models tends to be faster than that of military aircraft. This is because manufacturers need to update their models based on market conditions to meet customer demands and pursue higher profits. Therefore, it is necessary to develop IPTMS platforms with high versatility for civil EPA.