How do these funds operate and maintain fixed value?
https://investor.vanguard.com/investment-products/mutual-funds/profile/vusxx"Vanguard Treasury Money Market Fund, which invests primarily in U.S. Treasury securities, seeks to provide current income and preserve shareholders’ principal investment by maintaining a share price of $1. This fund at a minimum invests 80% of the assets in debt issued directly by the government in the form of Treasury bills and may invest in other securities including, but not limited to debt issued by federal agencies that are sponsored, guaranteed, or owned by the federal government. As a government money market fund, this fund is required to invest at least 99.5% of its total assets in cash, U.S. government securities, and/or repurchase agreements that are collateralized solely by U.S. government securities or cash (collectively, government securities)."
https://investor.vanguard.com/investment-products/mutual-funds/profile/vmfxx"Vanguard Federal Money Market Fund’s investment objective is to seek to provide current income while maintaining liquidity and a stable share price of $1. The fund invests at least 99.5% of its total assets in cash, U.S. government securities, and/or repurchase agreements that are collateralized solely by U.S. government securities or cash (collectively, government securities)."