On February 9th NASA announced that a Falcon Heavy rocket built by SpaceX will be used to launch the first two elements of the Lunar Gateway. These elements are the Power and Propulsion Element (PPE) and the Habitation and Logistics Outpost (HALO).
The PPE is a solar electric propulsion spacecraft that will provide power, communications, and attitude control (spacecraft pointing), as well as the propulsion system necessary to alter the outpost’s orbit around the Moon. Solar electric propulsion will provide the gateway with far more maneuvering capability than the ISS has. Although solar electric propulsion systems outputs much lower thrust than traditional chemical rockets, they have a far greater specific impulse; essentially, the fuel efficiency of the engine. This will allow the Gateway will be able to significantly change its orbit if desired.
The HALO will be the pressurized living quarters for astronauts visiting the gateway and will also serve as a work space for these astronauts. Within the HALO will be the command and control center for the Gateway. It will also have the capability of docking with other crewed spacecraft including those on their way to the lunar surface.
These two pieces were originally planned to be launched separately, however NASA has decided to launch them together to save money. The contract cost will be approximately $332 million. It is likely that this budgeting move was in response to a smaller than anticipated amount of funding in the latest House Appropriations bill. This decision to do a two for one launch may also be a move to save time. There are concerns budget restrictions, caused by the nations COVID response, will impact the proposed timed table. Although the launch is now more complex, this move will save NASA the effort of having to rendezvous the two elements in orbit.
The Falcon Heavy will likely utilize a new extended payload fairing to accommodate the size of both of these Gateway elements. Given the combined weight of the PPE and HALO, the boosters may end up not being reusable. Instead they could be required to expend all their fuel to get to lunar orbit thus having none left for boost back and landing burns. The launch is slated to take place no earlier than May 2024, however, it will be worth the wait to see this massive rocket fly again.