. Exploring the Moon surface

Apollo 13: Houston, We've Got a Problem

Apollo 13: Houston, We've Got a Problem - National Archives and Records Administration - ARC Identifier 1155023 / Local Identifier 255-HQa-200 - National Aeronautics and Space Administration. (10/01/1958 - ). This film depicts attempts to return the crewmen of the Apollo 13 mission safely to earth following an explosion on-board the service module. The film emphasizes the Mission Control and spacecraft teamwork that overcame the life-or-death problems of Apollo 13, as well as the worldwide reaction to the crisis.


By the Space Policy Directive-1 (SPD-1) signed by the President Donald J. Trump, in December 2017, NASA have to lead an innovative and sustainable program of exploration. With commercial and international partners, this program will enable human expansion across the solar system and bring back new knowledge and opportunities. Then, the United States will lead the return of humans to the Moon for long-term exploration and utilization, followed by human missions to Mars and other destinations.

The Lunar Orbital Platform, "Gateway", or LOP-G

As reflected in the NASA's Exploration Campaign, the next step in the human spaceflight is the establishment of U.S. pre-eminence in the cislunar space through the operations and the deployment of a U.S.-led Lunar Orbital Platform, “Gateway,” (LOP-G).

To respond at this request and at the Human Exploration Roadmap (NASA Transition Authorization Act of 2017-P.L. 115-10), NASA have laid out the National Space Exploration Campaign. This Campaign addresses five core national drivers, such as the Scientific Knowledge, the Global Engagement, the Economic Development, the Societal Improvement and, the Leadership and Inspiration.



Opening a New Era

Today, the American leadership and the commercial innovation, provided in part by the International Space Station, give a new economic arena. This is why, an action is necessary to drive new commercial enterprises and to provide a regulatory and security environment that enables and protects this emerging economy.

Also, recently, countries like China, India, Russia, Japan, South Korea, Israel and multiple European nations have all announced plans or initiated missions to send spacecraft into lunar orbit and to the surface of the Moon. The momentum is there.

The “Lunar Orbital Platform – Gateway” (LOP-G) is planned to orbit high above the poles of the Moon in support of crew visits and science experiments.

NASA seeks leadership in space science and exploration through excellence in long-duration spaceflight, in-space manufacturing, in-situ resource utilization (ISRU), long-term cryogenic fuel storage and management, and advanced spacecraft power and propulsion capabilities.

The LOP-G can evolve depending on mission needs. Basically, the initial functionality will include four main elements, such as a Power and Propulsion Element (PPE), a habitation element, a airlock element to enable docking and Extra-Vehicular Activities (EVA), and a logistics element for cargo delivery, science utilization, exploration technology demonstrations, and potential commercial utilization.

Credit: Nathan Kaga for NASAspaceflight.com

Gateway Initial Elements

The spacecraft “Gateway” will serve as a reusable command module for the lunar vicinity and the surface exploration. It will evolve to serve as a way station for the development of refueling depots, servicing platforms, and a sample return facility from the surface of the Moon and other bodies in support of science and commerce.

The Gateway will be constructed in orbit, incrementally, with the uses of the American-built Orion spacecraft and the Space Launch System (SLS), as well as commercial launch vehicles.

In fact, NASA plans to build the Gateway with just five or six rocket launches, compared to the 34 launches it took to build the space station. Large parts will be set up by automatic assembly, mean robotically.

The Power and Propulsion Element (PPE)

The PPE is the core element of the Gateway. It will provide transportation of the LOP-G between cislunar orbits, with the option to perform any needed orbital maintenance. So, it will provide attitude control in multiple configurations, communication to and from Earth, space-to-space communication, space-to-lunar communication, and in support of astronaut EVA.

The PPE will also deliver systems necessary for the deep space navigation, docking, and refueling. The High-level PPE for the spacecraft is it needs to have a 15-year on-orbit operational lifetime, beginning at separation from the launch vehicle. At the end of the LOP-G operational life, PPE will move the integrated LOP-G stack to a disposal orbit.

Artist concept of PPE in lunar orbit. Credit: NASA.

The main technology development to be integrated into the spacecraft is a Solar Electric Propulsion (SEP) system. The requirements will be a capability to operate over a thrust-to-power ratio range of at least 43 – 52 mN/kW (millinewtons per kilowatt). The PPE will include SEP and chemical propulsion systems based on monopropellants hydrazine.

The PPE is the initial element of the LOP-G, and it will be placed around the Moon by 2022, through a competitive commercial launch contract with U.S. commercial companies. At that time, the contractor will demonstrate more powerful solar-electric power (SEP) and propulsion bus systems that will support both NASA and commercial applications. 

PPE works with U.S. industry to utilize deliverables from STMD (which will be part of the new Exploration Research & Technology [ER&T] organization) in Advanced Electric Propulsion Systems (AEPS). It will demonstrate an advanced SEP system, including ER&T- developed 12.5 kW AEPS thrusters and power processing units, and advanced high power solar array systems. PPE will use SEP technology to insert itself into cislunar orbit and provide overall station-keeping for the LOP-G and will move the LOP-G into different low gravity lunar orbits depending on mission requirements and will provide high-bandwidth communications. PPE has a targeted launch readiness of 2022.

The PPE is intended to supply power and propulsion for additional elements and systems on the LOP-G as well as communication to and from Earth, space-to-space, space-to-lunar, and in support of astronaut EVA.  Refuellable, the PPE needs to support cislunar operations for more than a decade.

Once the PPE, habitation, airlock capabilities and sufficient logistics have been delivered to cislunar space, a crew of four - launched on Orion - will visit the LOP-G on missions initially lasting 30 days. As additional habitation capabilities are incorporated (e.g., volume, life support systems, and logistics resupply), crew visits may increase in duration.

NASA transitioned away from the Asteroid Redirect Mission (ARM) and all relevant work previously conducted on power and propulsion was continued to advance toward a demonstration of that capability in deep space. Activities transitioned from ARM include low-thrust mission design, advanced SEP-based spacecraft bus requirements development, industry spacecraft design studies, and human/robotic mission integration. These activities provide important ground work for the LOP-G PPE and other future deep space exploration objectives.

PPE selected five proposals for further industry study from the inputs received in FY 2017. Other progress includes developing PPE requirements and planning for acquisition and partnership approaches in coordination with the Space Technology Mission Directorate (STMD). PPE will award a contract for PPE spacecraft development in FY 2018 and mature design with industry to baseline the preliminary design in early 2019. Critical to this selection process is therealization of a deep space operational power and propulsion capability that is directly applicable to wide range of commercial, robotic, and human spaceflight missions.

PPE award(s) next year if funding approved

The final Broad Agency Announcement (BAA) solicitation for the PPE, “Spacecraft Demonstration of a Power and Propulsion Element,” was released by NASA on September 6. Originally released for comments in draft form in July, the solicitation defines a set of NASA unique requirements that the spacecraft must meet, but the BAA is intended to allow bidders to use as much off the shelf technology as possible. Basically, it is possible to use a commercial satellite bus augmented by an electric propulsion.

The final BAA set a deadline for bidders to submit proposals of November 15. “NASA and its PPE partner(s) will begin the project upon contract award, which is targeted for March 2019 (TBD), and conclude 24 months after the successful spaceflight demonstration if all of the options are executed,” the final BAA adds.

So, we don’t need a unique spacecraft design, we don’t need a unique bus, we believe what’s available in industry can be used with augmentation of the solar electric propulsion, and that’s what we’ll find out with this BAA activity

The PPE Flight System shall utilize the Ion Propulsion System for orbit insertion into the Near Rectilinear Halo Orbit,” the final BAA requirements say. “Chemical propulsion may be used in combination with SEP.”

“In looking at different orbits to put the Gateway in, there’s been a lot of discussion of low lunar orbits, distant retrograde orbits, halo orbits of different families — L1, L2-type orbits,” Crusan said. “The orbit that we’re putting Gateway nominally in to begin with is what we call a near rectilinear halo orbit, likely optimized for the South Pole.”

Presentation slide to the NAC HEO committee outlining the PPE. Credit: NASA.

L1 and L2 refer to two of the Lagrangian points in the Earth-Moon system. L1 bias or an L2 bias and you can do a North and South version of those as well. We are optimizing for the South because we believe that’s a more target rich areas for surface activities as well.”

The PPE is required to be in the NRHO chosen for Gateway one year after launch. Its fuel load is sized to meet requirements based on overall operating expectations over its lifetime.

“We have enough propellant in the Power Prop Element to handle orbital maintenance for fifteen years and two large maneuvers, the most pressing case maneuvers of the entire Gateway stack back and forth, we have that all in the Power Prop Element,” Crusan noted. “The ESPRIT capability will actually increase our overall propellant capacity and could be as high as doubling that before we need our first refuel; but we will be able to refuel if we wanted to move it around more often.”

The requirements indicate maintenance of the NRHO chosen for the Gateway are relatively low: “The PPE Flight System shall conduct orbit maintenance maneuvers in the Near Rectilinear Halo Orbit with a maximum magnitude of less than 10 m/s of delta-v per year.”

Following the demonstration period when NASA would exercise the option to assume ownership of the spacecraft, the PPE mass is required not to exceed 8000 kg, including a minimum of 1050 kg of Xenon for SEP and 800 kg of hydrazine for the Reaction Control System (RCS). The Xenon tank in the PPE is required to have a minimum capacity of 2000 kg, and both the Xenon and hydrazine propellant tanks will have the capability to be refueled.

Logistic Elements

NASA is currently assessing specific configurations and strategy for unpressurized logistics delivery, refueling, commercial launch vehicle pressurized logistics, and the Space Launch System (SLS) pressurized logistics. All potential concepts deliver cargo to the LOP-G to enable extended crew mission durations, science utilization, exploration technology demonstrations, potential commercial utilization, and other supplies.

NASA's Astronaut Akihiko Hoshide near the airlock in the Kibo lab in the International Space Station. Credit: NASA

The Logistics Module must deliver pressurized and/or unpressurized cargo to the Lunar Gateway located in a Near Rectilinear Halo Orbit (NRHO), beginning no earlier than 2024 (dependent on development and/or launch of other Gateway modules). It is expected that the initial requirement will be for three missions, with a single mission expected to deliver up to 5 metric tons of pressurized cargo and 2.6 metric tons of unpressurized cargo. The first Logistics Module may be required to transport a Robotic Arm as unpressurized cargo. The Logistics Module must include guidance and navigation, power generation, and propulsion to enable autonomous docking to a port on the Utilization Module or Habitat Modules via an International Docking System Standard (IDSS) compliant docking port.

Once docked, the module will be used by crew primarily for stowage volume, trash stowage, and trash disposal. In addition, the module will depart the Gateway and perform self-disposal without assistance after a period of no more than three years of cislunar space operations.

It is anticipated that the first two logistics missions will launch the Logistics Module using commercial launch vehicles, but after Gateway assembly, the Space Launch System (SLS) may be available for co-manifested logistics delivery.

Airlock Elements

The airlock element provides the LOP-G with the capability to enable astronaut EVAs as well as the potential to accommodate docking additional elements, observation ports, or a science utilization airlock.

Multiple concepts are currently being assessed and feasibility studies have identified several different approaches ranging from small, single chamber airlocks to large, dual chamber airlocks with inflatable crew locks.

Above: Astronaut ingresses the Airlock-hatch of the Quest Module on the ISS. Right: View of the Quest exterior. Credit: NASA

Credit: Reference: NASA Leading Human Space Exploration, August 2018, Mack McElroy, PhD

The Space Launch System (SLS) Evolution

SLS is designed for deep space missions and will send Orion or other cargo to the Moon, which is nearly 1,000 times farther than where the space station resides in low-Earth orbit. The rocket will provide the power to help Orion reach a speed of at least 24,500 mph needed to break out of low-Earth orbit and travel to the Moon. That is about 7,000 mph faster than the space station travels around Earth.

Every SLS configuration uses the core stage with four RS-25 engines. The first SLS vehicle, called Block 1, can send more than 26 metric tons (t) or 57,000 pounds (lbs.) to orbits beyond the Moon. It will be powered by twin five-segment solid rocket boosters and four RS-25 liquid propellant engines. After reaching space, the Interim Cryogenic Propulsion Stage (ICPS) sends Orion on to the Moon.

The next planned evolution of the SLS, the Block 1B crew vehicle, will use a new, more powerful Exploration Upper Stage (EUS) to enable more ambitious missions. The Block 1B vehicle can, in a single launch, carry the Orion crew vehicle along with exploration systems like a deep space habitat module.

The Block 1B crew vehicle can send approximately 37 t (81,571 lbs.) to deep space including Orion and its crew. Launching with cargo only, SLS has a large volume payload fairing to send larger exploration systems or science spacecraft on solar system exploration missions.

The next SLS configuration, Block 2, will provide 11.9 million lbs. of thrust and will be the workhorse vehicle for sending cargo to the Moon, Mars and other deep space destinations. SLS Block 2 will be designed to lift more than 45 t (99,000 lbs.) to deep space. An evolvable design provides the nation with a rocket able to pioneer new human spaceflight missions.


Updated launch sequence

The Exploration Mission 1 (EM-1) is an uncrewed mission to test Orion’s capabilities in deep space. EM-1 is the first flight of the European Service Module (ESM) and also Orion’s first flight on the new SLS. During the mission, the Crew Module guidance navigation and control system will command the ESM propulsion system to place the spacecraft into a Distant Retrograde Orbit around the moon. The nominal mission duration is 25 days, but will be adjusted between 21 and 43 days in order to ensure a landing under daylight conditions.

The above presentations show that the Exploration Mission-1 (EM-1) is to be launching in 2020. This first mission will fly without crew in a Distant Retrograde Orbit (DRO).   For the Exploration Mission-2 (EM-2) in 2022, the Orion spacecraft will take the first astronauts on a lunar flyby, as showing below. 

The Exploration Mission 2 (EM-2) is the first crewed mission for the Orion spacecraft. This mission will be historical for the Europe because the European Service Module 2 (ESM-2) will be the first European spacecraft to be part of a human transportation system beyond the low Earth orbit. After the launch, the SLS and the Interim Cryogenic Propulsion Stage (ICPS) will place the Orion spacecraft into a high Earth orbit, where the astronauts will remain for 24 hours to check out the spacecraft’s systems. When Mission Control gives the approval to initiate trans-lunar injection, the ESM-2’s Orion Orbital Manoeuvring System (OMS) will fire and send the spacecraft on a free-return trajectory out toward and around the Moon. The ESM-2’s Auxiliary (AUX) thrusters will be used to make any needed trajectory corrections along the way.

NASA and Lockheed Martin will conduct the EM-2 Critical Design Review (CDR) in late 2018. In 2015, NASA and LM completed the Orion CDR evaluating the common aspects of the spacecraft for EM-1 and the spacecraft for EM-2. The EM-2 CDR will confirm that the EM-2 unique systems also meet the necessary requirements and that the upgrades to the ESM design from ESM-1 to ESM-2 are appropriately integrated into the overall spacecraft design.

The SLS Block 1 cargo variant will be capable of delivering Orion beyond LEO in an Trans-Lunar Injection (TLI). The evolved Block 1B will be capable of delivering 9-10 metric tons to TLI, co-manifested with Orion. These SLS/Orion missions will demonstrate the capability to operate safely and productively around the Moon.

Altogether the first three SLS launches would fly on the Block 1 vehicle, the two Orion test mission launches and the launch of the Europa Clipper probe directly to Jupiter.

The SLS co-manifested payloads are delivered with the Orion through the Trans-Lunar Injection (TLI) burn by the Exploration Upper Stage (EUS). With the payload still attached to the EUS, the Universal Stage Adapter (USA-2) fairing is jettisoned and the Orion rotates to dock with the payload. After docking, the EUS releases the payload and the Orion Service Module delivers the payload to the Lunar DRO destination

By its volume, the SLS' large module provides a significant mass savings per unit and, has enough space for consumable payload to accommodate long duration missions. Also, it can be lifted in one shot by SLS without the need of on-orbit assembly. Learn more @ Space Habitat
SLS Co-Manifested And Dedicated Payload Configurations. Two co-manifested elements and one of three large habitats complete the configuration planned for the lunar DRO.
Credit: Habitation Concepts For Human Missions Beyond Low- Earth-Orbit / David V. Smitherman* NASA Marshall Space Flight Center, Huntsville, Alabama, 35802

The European System Providing Refuelling, Infrastructure and Telecommunications (ESPRIT) and the American-provided Utilization Module would then fly with the Orion and crew on the third Exploration Mission (EM-3) in 2024. This latter trip would be the debut of ML-2 and the SLS Block 1B vehicle with the larger Exploration Upper Stage (EUS). Although NASA indicated there weren’t any notional masses for the modules, the initial SLS Block 1B launch is expected to be able to place both the 25-metric ton Orion spacecraft and several metric tons of secondary, “co-manifested” payloads on a trans lunar injection (TLI) trajectory. The habitation modules would then follow one at a time on EM-4 and EM-5.

The Gateway is also now expected to need two habitation modules rather than one, as the earlier minimum of 55 cubic meters of habitable volume wouldn’t meet the requirements developed between NASA and several of its international partners working on the International Space Station (ISS).

NASA will work with U.S. companies to build a small living and working area for the Gateway called a habitation module.

Credit: Cislunar and Gateway Overview, William Gerstenmaier, HEOMD AA / Jason Crusan, AES Director and Gateway Formulation Lead, NASA HQ
The NextSTEP Phase 2 Habitation contracts, funded in Exploration Advanced Systems (EAS), to develop prototype deep space habitats are directly applicable to the Lunar Orbital Transport - Gateway. NASA is formulating the LOP-G by defining system requirements, developing design and interoperability standards, establishing program and system-level control boards, developing strategy and execution mechanisms to acquire a PPE, and developing an integrated ground test plan for prototype habitats.
At the end of NextSTEP Phase 2 study contracts, the industry partners will provide the functional habitat ground prototype units to NASA for testing. The intended outcome of these activities is a complete set of long-duration deep space architecture designs (including standards, common interfaces, and testing approaches) from the awarded contractors as well as development and test of full-size ground prototypes.
The LOP-G habitation element provides a livable section and short-duration life support functions for the crew in cislunar space. The docking ports allow for attachment to the PPE, other elements and visiting vehicles. The habitat also provides attach points for external robotics, external payloads or rendezvous sensors; thermal radiators provide heat rejection and micro-meteoroid protection; and additional habitat systems provide accommodations for crew exercise, science/utilization and stowage. Some functions may be outfitted via future logistics flights.

“One of the things in our analysis, both with our U.S. industry and our international partners, the Hab volume that we had originally…didn’t quite meet what we needed to get there as far as the crew health and other accommodations we have there. So we expanded that to the two Habs in concert providing that overall function; this also increased the internal space for biological-type research that folks would like to do there.”

The two Hab modules, one provided by the United States and one provided internationally, would now provide at least 125 cubic meters of habitable volume. Those would be launched with Orion on separate SLS flights following the ESPRIT and Utilization modules on EM-3.

Even without crew present, cutting-edge robotics and computers will operate experiments inside and outside the spaceship, automatically returning data back to Earth.

Click on it to see bigger

Slide from one of the presentations to the NAC HEO committee showing currently defined Gateway modules. The SLS launch date for the Early Operational Capability was said in the meeting to be 2024. Credit: NASA.

Orion Launch date: June 2020


Astrobotic is contracting payloads to Trans-Lunar Insertion (TLI), Lunar Orbit, and Surface on the Moon at Lacus Mortis for theirFirst Mission . 


Already very prolific launcher of payloads in space with its Atlas and Delta families, United Launch Alliance (ULA) wants the Moon more accessible for every one. It will be not easy, but very, very possible because its determination and skills are there.

The cis-lunar econosphere is a territory that includes trade routes of business between LEO and GEO orbits, Lunar orbit, Earth/Moon Lagrange Points, and near Earth objects (NEO). 

New Vulcan. Credit: ULA

ISPACE - Expand our planet. Expand our future.

Japan-based lunar exploration company ispace, inc. raises $90.2 million to be used for development of lunar lander and two lunar missions by 2020.

ISPACE has already started the development of its small, agile and modular lunar lander. The main goal is to provide a regular transportation service to the Moon.

ROSCOMOS gives OK to LUNA-25

The Russian Luna-Glob mission, currently scheduled for launch in the mid-2020s, will study the physical conditions and composition of the regolith near the lunar south pole, as well as test new soft-landing technologies. The engineering constraints for the mission require that potential landing sites lie between 70-85°S and 0-60°E, and Boguslawsky crater fits the bill and was selected as the primary target.


Private space companies are on the starting line to develop the Moon's resources. Some such as Shackleton Energy Company, have big and precise plans to do it.

To establish fuel stations in orbit, many problems must first be solved. It is necessary to have orbital corridors clear of space junks, efficient satellites robotic servicing, many orbital and lunar hotels and Research labs. To be more independent from the Earth, we also have to be able to manufacture materials and built structures in gravity, and mine asteroids.

Shackleton Energy Fuel Depot. Credits: Boeing and Shackleton Energy


Because all missions of Moon Express start in Low-Earth Orbit (LEO), its MX spacecrafts have to be launched there by rockets. In order to reach this orbit, the company has signed a contract for 5 launches with Rocket Lab USA, scheduled to start in 2018.

The China Chang'e-4 mission to the Moon will be Historical!

For the first time a country will land a spacecraft on the far side of the Moon! Chang'e-4 will be the fourth mission in its series named after the Chinese moon goddess.

The two-part missions of Chang'e-4 will focusing on the low-frequency astronomy and the investigation of the subsurface, the topography and the mineralogical composition of the lunar far side.

The Chinese  Chang'e-5 mission will return samples from the Moon

Since the Apollo's missions, China will be the first to return to Earth, samples from the near side of the Moon. That will be the mission of Chang'e-5, scheduled for November 2019, near Mons Rümker in Oceanus Procellarum, a large area of lunar mare in the northwest region of the Moon.

Chang’e-5 is China’s first lunar sample return mission and the most ambitious endeavor in the country’s lunar program, aiming to introduce new technologies and techniques such as a fully-automated rendezvous in lunar orbit and sample transfers in between different spacecraft modules. 

Scientists work on China's Chang'e-5 landing and ascent vehicles. Credit: Framegrab/CCTV

The Indian Chandrayan-2 spacecraft is ready for the Moon

Chandrayaan-2 is an Indian Space Research Organization (ISRO) trivia mission including an orbiter, a soft lander and a rover. Previously scheduled for April 2018, the lift off has been delayed to October 2018 aboard the ISRO's rocket GSLV Mark 2, or equivalent.

Its primary mission objective is to do a soft-land on the lunar surface at the South Polar region, situated between the 65° and 90° latitudes, and operate a robotic rover.


Pit crater/lava tubes - 33.22°E, 8.336°N - Mare Tranquillitatis

Lunar pit craters are small, steep-walled collapse features that suggest subsurface voids. Over 200 pit craters are located in impact melt and are relatively shallow, at about 10 m. However, 10 pits are located in mare highland units and are much deeper, in a range of about 10 to 40 m. These pits may have lava tubes of unknown lateral extent. For those in non-mare impact melt, they may have networks of sub-lunar tubes. 

Five of many LROC Narrow Angle Cameras (NACs) showhigh resolution views of the increasingly famous "Mare Pit Crater" in the Sea of Tranquillitatis.

The Aristarchus plateau - 50°W, 25°N

Aristarchus crater is located on the edge of the Aristarchus Plateau, one of the most geologically interesting regions of the Moon. It is a complex crater of 40 km wide, 3.5 km deep, that has been formed about 175 millions years ago. The impact straddled the boundary of the plateau and the surrounding mare, thus excavating both very different rock types, as well as underlying crustal rocks.

West wall of Aristarchus crater seen obliquely by the LROC NACs from an altitude of only 26 km. Scene is about 12 km wide at the base. Image NAC M175569775. Credit: NASA/GSFC/Arizona State University.

The Orientale basin - 95°W, 20°S

The Orientale multi-ring basin is the largest lunar impact structure

In fact, it is the most prominent and best preserved. Located on the western limb of the nearside, Orientale contains at least four ring structures encompassing a diameter of 930 km making it one of the largest lunar impact structures. Relative ageing suggests Orientale is the youngest basin with an estimated age of 3.82 Ga (Wilhelms, 1987).

At the right,an oblique view of the interior of the Orientale basin. NAC images M1124173129L & R, image centered at 24.23°S, 264.30°E, scene width is approximately 16 km and the cliff at center is 1.7 km high Credit:[NASA/GSFC/Arizona State University].

The Schrödinger basin - 135°E, 75°S

Second youngest large basin on the Moon, the Schrödinger impact basin include variety of geologic features available that could be interesting for future exploration. Often, boulders in Schrödinger come from regions that are not easily accessible by robotic equipment or humans. The above image highlights a distribution of boulders near the base of a part of the central peak ring, located at 77.196°S and 133.178°E.

Located near the South Pole on the lunar far side, it is the second youngest impact basin (after Orientale) and, thus, remains well exposed for scientific study. Schrödinger intersects the pre-Nectarian Amundsen-Gainswindt basin (AG), as well as the inner rings of the South Pole-Aitken (SPA) basin.

Dozens of boulders, ranging from 10 m to more than 30 m in diameter, are distributed within an ejecta ray close to the crater rim (lower right). These boulders represent the deepest material excavated during crater formation. LROC NAC M159013302LR, image width is ~850 m [NASA/GSFC/Arizona State University].

Tycho crater is one of the most visible and important craters on the Moon due to its extensive, bright ray system.

Other Moon landing sites considered


. South Pole - Aitken Basin - 170°W, 53°S

. Gruithuisen Domes - 36.5°N, 40.2°W

. Moscoviense - 147°E, 26°N

. Rima Bode - 3.5°W, 12°N

. The potential for volatiles in the Intercrater Highlands of the lunar North Pole