The most, often utilized method of thermal design verification for past and current types of spacecraft has been by Solar Thermal Vacuum (STV) tests at system level. This approach, however, will require fundamental modifications for future large and complex spacecraft, three types of which are defined; a large communication satellite, a modular earth observation satellite and a large infrared telescope, all exceeding the capabilities of existing STV test facilities. A trade-off is made between analysis only and analysis plus test, considering the influence of temperature limits, analysis uncertainty and correlation of analysis and test, as well as indicating the ways in which it affects the thermal design verification. Alternative test methods - STV testing in parts, infrared radiation tests, thermal canister method, skin heater application - are also discussed with regard to their advantages and disadvantages of applying them to the large types of spacecraft. The thermal design considerations to be regarded and the critical parameters to be verified by test are highlighted, in order to enable the alternative verification test concept at an acceptable level of confidence. The test concepts for the large spacecraft are described briefly.