NASA has modified a contract with SpaceX to allow the company to launch the international Surface Water and Ocean Topography (SWOT) mission on a flight-proven Falcon 9 booster.
NASA announced its original decision more than half a decade ago. The agency awarded SpaceX an unusually expensive $112 million contract in November 2016 to launch SWOT on a Falcon 9 rocket in April 2021. SWOT is expected to weigh less than two tons (~4400 lb) and is headed to a simple low Earth orbit (LEO), meaning that the launch won’t be particularly challenging or performance-intensive for SpaceX or Falcon 9. Most importantly, the company will almost certainly be able to recover the mission’s Falcon 9 booster and may be able to perform a return-to-launch-site landing for even greater cost-efficiency.
SWOT’s launch should be almost identical to Sentinel 6A, a similarly light spacecraft that SpaceX successfully delivered to a similar orbit from the same launch pad in November 2020. In fact, both SWOT and Sentinel 6A are essentially flying altimeters designed to use radar to measure the surface height of Earth’s oceans and other bodies of water. Both also carry microwave-based instruments to determine the amount of water vapor present in Earth’s atmosphere. While Sentinel 6A was largely built by France’s CNES space agency, SWOT is a bit more collaborative, with NASA’s Jet Propulsion laboratory providing the main altimeter instrument and completing a significant amount of preliminary integration work.
Nonetheless, SWOT’s parts are sent to CNES facilities in France for final integration. Currently scheduled to launch no earlier than November 2022 after a roughly 1.5-year delay, SWOT will need to be delivered from France to California at least a month or two prior to liftoff in order to begin final launch preparations. It remains to be seen if the mission will avoid additional delays in the interim. Prior to most of the mission’s recent delays, NASA’s Office of the Inspector General (OIG) estimated [PDF] that SWOT would cost its partners around $1.15 billion over the spacecraft’s lifetime. Sentinel 6A’s total cost is also expected to be around $1.1 billion.
Once launched, SWOT will operate in a circular ~890-kilometer (~550 mi) orbit with an inclination of around 78 degrees, allowing the spacecraft to singlehandedly observe 86% of Earth’s surface. Sentinel 6A operates in a slightly higher 1336-kilometer (830 mi) orbit at a 66-degree inclination and will eventually be joined by a second spacecraft to enable full global coverage.