I just asked Grok how we could get back to the Moon if SLS/Orion were canceled. Its response:

If the Space Launch System (SLS) and Orion spacecraft were to be canceled, alternative architectures for getting Americans back to the Moon would need to leverage existing or soon-to-be-developed technology from both NASA and the private sector. Here are several conceptual architectures:
1. SpaceX Starship Architecture:

• Launch Vehicle: Use SpaceX’s Starship, which is designed for full reusability and can carry significant payloads to the Moon.
  • Mission Profile: Direct to the Moon:
    • Starship would launch from Earth, perform a trans-lunar injection, and either land directly on the Moon or rendezvous with a lunar lander in lunar orbit.
    • For a direct landing, Starship would serve as both the orbiter and lander, potentially refueling in Earth orbit before departure or using in-situ resource utilization (ISRU) on the Moon for return fuel.
• Benefits:
  • High payload capacity.
  • Reusability could significantly reduce costs per mission.
  • Potential for rapid mission tempo due to the frequent availability of Starship.
• Challenges:
  • Development and operational risks associated with new technology.
  • Need for extensive on-orbit refueling capabilities.

2. NASA’s Commercial Lunar Payload Services (CLPS) with Crew:

• Concept: Adapt CLPS for crewed missions by integrating human-rated systems into existing or future lunar landers.
  • Launch: Use multiple launches with existing or new commercial rockets like Falcon Heavy, Vulcan Centaur, or New Glenn to assemble components in Low Earth Orbit (LEO) or directly send to the Moon.
  • Lander: Use landers developed by companies like Blue Origin (Blue Moon), Dynetics, or others that could be adapted for human missions.
• Benefits:
  • Leverages existing contracts and partnerships.
  • Encourages competition and innovation in the private sector.
• Challenges:
  • Integrating human safety protocols into primarily cargo-focused designs.
  • Coordination of multiple launches and in-space assembly.

3. Modular Approach with Gateway or Lunar Orbit:

• Gateway Station: Use a lunar Gateway as a staging point, which could be launched by existing or upcoming heavy-lift rockets.
  • Launch: Various rockets could lift parts of the Gateway, landers, and crew modules to LEO or directly to the Moon’s orbit.
  • Crew Transport: Crew could be sent to the Gateway via a human-rated commercial spacecraft (like Crew Dragon or Starliner), then transfer to a lunar lander for descent.
• Benefits:
  • Reduces the need for a single massive rocket by using multiple launches.
  • Provides a platform for testing technologies for Mars missions.
• Challenges:
  • Increased complexity with multiple vehicles and rendezvous operations in space.
  • Higher dependency on in-space assembly and refueling.

4. International Collaboration:

• Partnership: Collaborate with international partners like ESA, JAXA, or Roscosmos, utilizing their launch capabilities or spacecraft technology.
  • Launch: Use Ariane, H-IIA/H-IIB, or Soyuz rockets for components, with American rockets for the crew module.
  • Lander: Potentially use or co-develop a lunar lander with international partners.
• Benefits:
  • Shared costs and risks.
  • Enhanced international cooperation, potentially leading to broader space exploration initiatives.
• Challenges:
  • Political and diplomatic complexities.
  • Technical integration of different national spacecraft systems.

5. Hybrid Approach:

• Mixed Fleet: Use a combination of existing rockets for different mission segments. For instance, one rocket for the crew, another for the lander, and yet another for logistics.
  • Mission Profile: Crew could launch on a proven vehicle, dock with a lander in orbit (launched separately), and proceed to the Moon.
• Benefits:
  • Flexibility in mission planning.
  • Utilizes the strengths of various commercial rocket providers.
• Challenges:
  • Coordination and timing of multiple launches.
  • Increased operational complexity.

Each of these architectures would need to consider factors like cost, safety, timeline, and the strategic goals of returning to the Moon, such as establishing a sustainable presence, scientific research, or setting the stage for Mars missions. The choice would also depend on the evolution of technology and the political and budgetary environment at the time of decision-making.