This was the ULA paper I read about 5 years ago : https://www.ulalaunch.com/docs/default-source/extended-duration/micro-gravity-cryogenic-experiment-opportunity

This was the ULA paper I read about 5 years ago : https://www.ulalaunch.com/docs/default-source/extended-duration/micro-gravity-cryogenic-experiment-opportunity.pdf https://www.ulalaunch.com/docs/default-source/extended-durat... There are a number of papers on the ULA site describing fairly innovative ways to keep the LOX from boiling away. As this stage would not have a "payload" in the traditional sense it could have a refrigerator attached :-)