Apollo 10 Complete Guide

Introduction

Apollo 10 played a pivotal role in the history of lunar exploration, serving as the critical dress rehearsal for the historic Apollo 11 Moon landing. Launched in May 1969, this mission tested every component and procedure needed for a successful lunar landing without actually touching down on the Moon’s surface. From the meticulous preparation and hardware testing to the groundbreaking achievements and unique hardware dispositions, Apollo 10’s contributions were instrumental in paving the way for humankind’s first steps on the Moon. This comprehensive guide delves into the mission highlights, hardware fate, and the enduring legacy of Apollo 10, showcasing its significant impact on space exploration.

The Essential Details of Apollo 10: A Critical Pre-Moon Landing Mission

Apollo 10, which took place from May 18 to May 26, 1969, was a pivotal mission in the Apollo space program. It was the fourth crewed flight and the second to orbit the Moon, setting the stage for the historic Apollo 11 landing just two months later.

NASA referred to Apollo 10 as a “dress rehearsal” for the Moon landing. This mission was essential in testing all spacecraft systems and procedures without actually landing on the Moon. The operation verified the performance and reliability of the equipment and the preparedness of the crew, ensuring the success of subsequent lunar missions.

Key Achievements of Apollo 10’s Lunar Orbit

After reaching lunar orbit, astronaut John Young stayed in the Command and Service Module (CSM). Meanwhile, astronauts Thomas Stafford and Gene Cernan piloted the Apollo Lunar Module (LM) to within 14.4 kilometers (7.8 nautical miles) of the Moon’s surface. This distance marked the point where the descent for a landing would start on an actual Moon mission.

Successful Rejoining and Safe Return

After completing four orbits, Stafford and Cernan rejoined Young in the CSM. The CSM then completed its 31st orbit of the Moon before the crew safely returned to Earth.

The Decision for a Practice Flight

While NASA had considered attempting the first crewed lunar landing with Apollo 10, mission planners ultimately decided it would be wise to conduct a practice flight to perfect the necessary procedures and techniques. This cautious approach allowed the crew to address potential issues in a controlled environment.

Challenges Faced During Apollo 10

The crew encountered several challenges during the mission, including pogo oscillations during the launch phase and a brief, uncontrolled tumble of the LM ascent stage in lunar orbit. Despite these issues, the mission successfully achieved its primary objectives.

Observations and Achievements

Stafford and Cernan conducted important observations and photographed the planned Apollo 11 landing site in the Sea of Tranquility. Apollo 10 spent 61 hours and 37 minutes orbiting the Moon, with Stafford and Cernan piloting the LM separately from Young in the CSM for about eight hours. The entire mission lasted approximately eight days in space. Additionally, Apollo 10 set a record for the highest speed attained by a crewed vehicle, reaching 39,897 km/h (24,791 mph) on May 26, 1969, during their return from the Moon.

Apollo 10’s Unique Call Signs

The mission’s call signs were inspired by the Peanuts characters: Charlie Brown for the CSM and Snoopy for the LM. These characters became the semi-official mascots of Apollo 10, and Peanuts creator Charles Schulz even contributed mission-related artwork for NASA.

Mission Types and the Path to the Moon Landing

By 1967, NASA had outlined a series of mission types, designated by letters, to be completed before attempting a lunar landing, known as the “G” mission. Early uncrewed flights were labeled “A” or “B” missions. Apollo 7, the crewed test of the Command and Service Module (CSM), was the “C” mission. The first crewed orbital test of the Lunar Module (LM) was Apollo 9, the “D” mission. Apollo 8, which orbited the Moon without an LM, was a “C-prime” mission. Its success allowed NASA to skip the “E” mission, which would have tested the full Apollo spacecraft in medium or high Earth orbit. Apollo 10, the dress rehearsal for the lunar landing, was designated as the “F” mission.

Debating the First Lunar Landing Attempt

There was internal debate within NASA about skipping the “F” mission and attempting the first lunar landing with Apollo 10. Some argued it was inefficient to bring astronauts so close to the lunar surface only to turn back. Although the lunar module intended for Apollo 10 was too heavy for a landing, the one planned for Apollo 11 could have been used by delaying Apollo 10 by a month. George Mueller, known for his ambitious approach, favored this idea.

The Decision for a Dress Rehearsal

However, others, including Director of Flight Operations Christopher C. Kraft, opposed this. They believed new procedures were needed for a rendezvous in lunar orbit and that there was insufficient information about the Moon’s mass concentrations, which could affect the spacecraft’s trajectory. After considering arguments from both sides, Lieutenant General Sam Phillips, the Apollo Program Manager, decided that a dress rehearsal was essential, leading to the final decision to proceed with Apollo 10 as planned.

Announcing the Apollo 10 Crew

On November 13, 1968, NASA introduced the crew members of Apollo 10.

Thomas P. Stafford: Mission Commander

Thomas P. Stafford, the mission commander, was 38 years old during the Apollo 10 mission. A 1952 graduate of the Naval Academy, Stafford was commissioned in the Air Force. Selected in 1962 for the second group of astronauts, he flew as pilot of Gemini 6A in 1965 and command pilot of Gemini 9A in 1966.

John Young: Command Module Pilot

John Young, the command module pilot, was also 38 years old at the time. A 1952 graduate of Georgia Tech, Young entered the Navy after graduation and became a test pilot in 1959. Selected as a Group 2 astronaut alongside Stafford, he flew in Gemini 3 with Gus Grissom in 1965, becoming the first American outside the Mercury Seven to fly in space. He later commanded Gemini 10 in 1966, flying with Michael Collins.

Eugene Cernan: Lunar Module Pilot

Eugene Cernan, the lunar module pilot, was 35 years old and a commander in the Navy during Apollo 10. A 1952 graduate of Purdue University, Cernan entered the Navy after graduation and was selected for the third group of astronauts in 1963. He flew with Stafford on Gemini 9A before his assignment to Apollo 10.

A Highly Experienced Crew

With five prior flights among them, the Apollo 10 crew was the most experienced to reach space until the Space Shuttle era. This mission was also the first American space mission where all crew members were spaceflight veterans.

The Backup Crew for Apollo 10

The backup crew for Apollo 10 consisted of L. Gordon Cooper Jr. as commander, Donn F. Eisele as command module pilot, and Edgar D. Mitchell as lunar module pilot. According to the normal crew rotation, Cooper, Eisele, and Mitchell were initially slated to fly on Apollo 13. However, circumstances prevented this from happening.

Changes in Crew Assignments

Deke Slayton, the Director of Flight Crew Operations, felt that Cooper did not train as diligently as he should have. Eisele was sidelined due to conflicts during Apollo 7 and personal issues, including a messy divorce. Slayton only assigned them as backups due to a lack of available veteran astronauts at the time.

Replacements and Training Needs

Cooper and Eisele were replaced by Alan Shepard and Stuart Roosa. George Mueller, wanting to ensure thorough preparation, felt the new crew needed more training time. As a result, Shepard and his crew were switched from Apollo 13 to Apollo 14. Ultimately, Alan Shepard and Edgar Mitchell successfully walked on the Moon during Apollo 14.

The Role of Support Crews in Apollo Missions

For the Mercury and Gemini projects, only prime and backup crews were designated. However, Apollo introduced a third group known as the support crew. Deke Slayton established the support crews early in the Apollo program based on advice from Jim McDivitt, who would lead Apollo 9. McDivitt pointed out that with preparation occurring at various facilities across the U.S., key meetings requiring a flight crew member could be missed.

Duties of the Support Crew

Support crew members, usually lower in seniority, were tasked with assisting the mission commander as needed. They were responsible for assembling, updating, and maintaining the mission’s rules, flight plan, and checklists. For Apollo 10, the support crew consisted of Joe Engle, James Irwin, and Charles Duke.

Key Personnel in Apollo 10

Flight Directors:

• Gerry Griffin
• Glynn Lunney
• Milt Windler
• Pete Frank

Flight directors during the Apollo missions had a succinct job description: “The flight director may take any actions necessary for crew safety and mission success.”

CAPCOMs (Capsule Communicators):

• Charles Duke
• Joe Engle
• Jack Lousma
• Bruce McCandless II

Call Signs and Mission Insignia

The call signs for Apollo 10’s spacecraft were “Charlie Brown” for the command module and “Snoopy” for the lunar module, named after characters from the comic strip “Peanuts.” These names were chosen by the astronauts with the approval of the strip’s creator, Charles Schulz. Initially, Schulz was unsure about the idea since Charlie Brown was often portrayed as a failure. However, the names gained widespread popularity and became a public relations success.

Popular Reception and NASA’s Reaction

While some at NASA found the names undignified, particularly in light of Apollo 9’s “Gumdrop” and “Spider,” the public embraced them. Public relations chief Julian Scheer suggested a change for the lunar landing mission, but for Apollo 10, the public’s love for Charlie Brown and Snoopy prevailed. Eugene Cernan noted that the P.R. team at NASA “lost this one big-time,” as the names were well-received worldwide.

Significance of Snoopy and Charlie Brown

The choice of “Snoopy” for the lunar module was fitting because it was meant to “snoop” around the landing site. “Charlie Brown” for the command module complemented this as Snoopy’s loyal companion. Snoopy had been associated with the space program for some time, with exceptional workers being awarded silver “Snoopy pins,” and posters featuring Snoopy in a space helmet were common at NASA facilities.

Thomas Stafford highlighted that choosing Snoopy as a call sign acknowledged the contributions of the thousands of people involved in the mission. Additionally, in the comic strip, Snoopy had journeyed to the Moon the year before, humorously besting the Americans, Russians, and even “that stupid cat next door,” as Schulz put it.

Apollo 11’s Call Signs

For the subsequent Apollo 11 mission, the call signs were “Columbia” for the command module and “Eagle” for the lunar module, reflecting a more serious and dignified approach suitable for the first lunar landing.

The Mission Insignia of Apollo 10

The shield-shaped insignia of Apollo 10 prominently features a large, three-dimensional Roman numeral X on the Moon’s surface. This symbol, as Thomas Stafford described, signifies that the mission left its mark on the lunar surface, even though it did not involve a landing. The numeral’s prominence underscores the significant contributions Apollo 10 made to the overall Apollo program.

Design Elements of the Patch

The insignia also includes a Command and Service Module (CSM) orbiting the Moon, while the Lunar Module (LM) ascent stage ascends from a low pass over the lunar surface, its engine visibly firing. In the background, Earth is visible, emphasizing the mission’s connection to both the Moon and home.

Details and Symbolism

The mission patch features a wide, light blue border with the word “APOLLO” at the top and the crew members’ names around the bottom. The patch is elegantly trimmed in gold, adding a touch of distinction. Designed by Allen Stevens of Rockwell International, the insignia encapsulates the spirit and achievements of Apollo 10, symbolizing its crucial role in the journey toward the first Moon landing.

Training and Preparation for Apollo 10

Apollo 10, designated as the “F” mission, served as a dress rehearsal for the first lunar landing. Its primary objectives were to demonstrate the performance of the crew, the space vehicle, and mission support facilities during a crewed mission to lunar orbit and to evaluate the lunar module’s performance in that environment. Additionally, the mission aimed to photograph Apollo Landing Site 2 (ALS-2) in the Sea of Tranquillity, the intended landing site for Apollo 11.

Objectives and Operations

According to Thomas Stafford, Apollo 10’s mission involved taking the lunar module to the Moon, descending to within about ten miles above the lunar surface, mapping the terrain, and identifying potential landing sites. The mission also included conducting the first lunar rendezvous around the Moon and returning to Earth.

Adherence to Apollo 11 Plans

Apollo 10 followed plans closely aligned with those of Apollo 11, including the trajectory to and from lunar orbit, the timeline of mission events, and the angle of the Sun at ALS-2. However, no landing was attempted. ALS-1, located further east in the Sea of Tranquillity, had been extensively photographed by Apollo 8. Scientist-astronaut Harrison Schmitt suggested delaying Apollo 10’s launch by a day to ensure ALS-2 was photographed under optimal conditions. ALS-2 was ultimately chosen for Apollo 11’s landing due to its relatively smooth terrain and scientific interest, while ALS-1 was considered too far east.

Launch Date Adjustments

Originally scheduled for May 1, 1969, Apollo 10’s launch date was shifted to May 17 to allow for a better view of ALS-2. On March 17, 1969, the launch was postponed until May 18 to facilitate better observation of ALS-3, located west of ALS-2.

Additional Time in Lunar Orbit

A key difference from Apollo 11’s mission plan was that Apollo 10 spent an extra day in lunar orbit after the Command and Service Module (CSM) and Lunar Module (LM) rendezvoused. This extension allowed for additional testing of the LM’s systems and provided more time for photographing potential future Apollo landing sites.

Intensive Training and Preparation for Apollo 10

The Apollo 10 astronauts dedicated extensive time to training, with five hours of formal training for every hour of the mission’s eight-day duration. This rigorous preparation was in addition to standard mission activities such as technical briefings, pilot meetings, and individual studies.

Hands-On Testing and Briefings

The crew participated in the testing of the Command and Service Module (CSM) at North American Rockwell’s facility in Downey, California, and the Lunar Module (LM) at Grumman’s facility in Bethpage, New York. They also traveled to Cambridge, Massachusetts, for detailed briefings on the Apollo Guidance Computer at the Massachusetts Institute of Technology Instrumentation Laboratory.

Simulator Sessions and Centrifuge Training

Each astronaut logged over 300 hours in simulators for the CM or LM at both the Manned Spacecraft Center (MSC) in Houston and the Kennedy Space Center (KSC) in Florida. To prepare for the intense acceleration during re-entry into Earth’s atmosphere, they underwent centrifuge training at MSC, simulating the high G-forces they would encounter.

Lunar Landing Capability of Apollo 10

While Apollo 10 meticulously followed the procedures of a lunar landing mission up to the point of powered descent, its Lunar Module (LM) was not designed for an actual landing and subsequent return to lunar orbit. The ascent stage of the LM was loaded with only the amount of fuel and oxidizer it would have had remaining if it had lifted off from the lunar surface, reaching the altitude at which Apollo 10’s ascent stage fired. This was approximately half the total amount required for a full lift-off and rendezvous with the Command and Service Module (CSM).

Differences in LM Specifications

The LM for Apollo 10 weighed 13,941 kilograms (30,735 lbs), compared to 15,095 kilograms (33,278 lbs) for the Apollo 11 LM, which successfully completed the first lunar landing. Additionally, the software necessary to guide the LM to a landing was not yet available during Apollo 10.

Preventive Measures to Avoid an Unauthorized Landing

In his book Rocket Men, Craig Nelson highlighted NASA’s precautionary measures to ensure astronauts Thomas Stafford and Eugene Cernan would not attempt an unauthorized landing. Nelson quoted Cernan: “A lot of people thought about the kind of people we were: ‘Don’t give those guys an opportunity to land, ’cause they might!’ So, the ascent module, the part we lifted off the lunar surface with, was short-fueled. The fuel tanks weren’t full. So had we literally tried to land on the Moon, we couldn’t have gotten off.”

Design and Intent

George Mueller, NASA’s Associate Administrator for Manned Space Flight, emphasized that it was impossible for the Apollo 10 crew to land due to the LM’s design. He stated, “There had been some speculation about whether or not the crew might have landed, having gotten so close. They might have wanted to, but it was impossible for that lunar module to land. It was an early design that was too heavy for a lunar landing, or, to be more precise, too heavy to be able to complete the ascent back to the command module. It was a test module for the dress rehearsal only, and that was the way it was used.”

This careful planning and strict adherence to the mission’s objectives ensured that Apollo 10 achieved its goals without jeopardizing future lunar landing missions.

Equipment and Assembly of Apollo 10

The descent stage of Apollo 10’s Lunar Module (LM) arrived at Kennedy Space Center (KSC) on October 11, 1968, followed by the ascent stage on October 16. The two stages were mated on November 2. The Service Module (SM) and Command Module (CM) were delivered on November 24 and mated two days later. Portions of the Saturn V launch vehicle arrived in November and December 1968, and the complete vehicle was assembled in the Vehicle Assembly Building (VAB) by December 30. After undergoing testing in an altitude chamber, the Command and Service Module (CSM) was placed atop the launch vehicle on February 6, 1969.

Launch Preparations

The fully assembled space vehicle was rolled out to Launch Complex 39B on March 11, 1969. Assembled in the VAB’s High Bay 2 for the first time, the crawler had to exit the rear of the VAB, loop around the building, and join the main crawlerway to reach the launch pad. This rollout, using Mobile Launch Platform-3 (MLP-3), occurred eight days after Apollo 9’s launch while that mission was still in orbit.

The Saturn V Launch Vehicle

Apollo 10’s launch vehicle, designated AS-505, was the fifth flight-ready Saturn V and the third to carry astronauts to orbit. This Saturn V had a lower dry weight in its first two stages compared to Apollo 9’s, with a significant reduction in the interstage joining them. Despite the S-IVB third stage being slightly heavier, all three stages could carry more propellant, and the S-II second stage generated more thrust than its Apollo 9 counterpart.

Spacecraft Composition

The Apollo spacecraft for the mission included:

• Command Module 106 (CM-106)
• Service Module 106 (SM-106) (together with the CM known as CSM-106)
• Lunar Module 4 (LM-4)
• Spacecraft-Lunar Module Adapter (SLA-13A)
• Launch Escape System (LES)

The SLA was a mating structure joining the Instrument Unit on the S-IVB stage of the Saturn V and the CSM, housing the LM. The LES contained rockets to propel the CM to safety in case of an aborted launch. Weighing approximately 76.99 metric tons, Apollo 10 was the heaviest spacecraft to reach orbit at that time.

Mission Highlights: Launch and Outbound Trip

Launch from Kennedy Space Center

Apollo 10 launched from Kennedy Space Center (KSC) on May 18, 1969, at 12:49:00 EDT (16:49:00 UT), at the start of a 4.5-hour launch window. The timing was set to ensure optimal lighting conditions at Apollo Landing Site 2 during the Lunar Module’s (LM) closest approach days later. The launch countdown began at 21:00:00 EDT on May 16 (01:00:00 UT on May 17). Unlike other Apollo missions, Apollo 10 launched from Pad 39B, making it the only Apollo flight to do so and the only one to be controlled from Firing Room 3. This distinction was due to Apollo 11 preparations already underway at Pad 39A.

Countdown and Launch Challenges

Any issues that arose during the countdown were resolved during the built-in holds, ensuring the mission was launched on time. The day before the launch, astronaut Eugene Cernan experienced a minor complication. While returning from a final visit with his wife and child, Cernan was stopped for speeding. Without identification and under orders to maintain secrecy about his identity, Cernan feared arrest. However, launch pad leader Gunther Wendt, who had pulled over nearby, explained the situation to the police officer. Despite skepticism, the officer released Cernan after Wendt’s intervention.

Outbound Trip to the Moon

After a smooth launch, Apollo 10 embarked on its outbound trip to the Moon. The journey involved precise navigation and multiple system checks to ensure everything functioned correctly for the upcoming critical maneuvers in lunar orbit. The primary objectives of this phase were to demonstrate the crew, spacecraft, and mission support facilities’ performance during a crewed mission to lunar orbit and to evaluate the Lunar Module’s performance in lunar orbit conditions.

Apollo 10’s trajectory to the Moon closely mirrored that planned for Apollo 11, including the timeline of mission events and even the angle of the Sun at the target landing site, ALS-2 in the Sea of Tranquility. This careful replication was essential for testing all components and procedures in a real mission environment, short of an actual lunar landing.

The Journey to Orbit and Trans-Lunar Injection

Rough Ride to Orbit

During the ascent to orbit, the Apollo 10 crew experienced significant pogo oscillations, leading to a somewhat rough ride. Despite this, about 12 minutes after liftoff, the spacecraft successfully entered a low Earth orbit, reaching a high point of 185.79 kilometers (100.32 nautical miles) and a low point of 184.66 kilometers (99.71 nautical miles).

Systems Check and Trans-Lunar Injection (TLI)

Once in orbit, a thorough systems review confirmed all systems were functioning normally. The crew then restarted the S-IVB third stage to achieve trans-lunar injection (TLI), propelling them towards the Moon. During the TLI burn, the vehicle shook again, causing concern for Eugene Cernan that an abort might be necessary. However, the burn was completed without incident, setting Apollo 10 on its course to the Moon.

Docking Maneuver and Televised Coverage

John Young performed the transposition, docking, and extraction maneuver. This involved separating the Command and Service Module (CSM) from the S-IVB stage, turning it around, docking the nose to the top of the Lunar Module (LM), and then separating it from the S-IVB. Apollo 10 was the first mission to carry a color television camera inside the spacecraft, allowing mission controllers in Houston and a large television audience to watch the maneuver and enjoy color views of Earth.

Issues Encountered

One issue encountered was that the mylar cover of the CM’s hatch pulled loose, causing fiberglass insulation to spill into the tunnel and subsequently into both the CM and LM. Despite this, the mission continued smoothly. The S-IVB stage, after separation, was fired by ground command and sent into a solar orbit with a period of 344.88 days.

This phase of the mission demonstrated the crew’s ability to handle challenges effectively and maintain the mission’s trajectory towards its lunar objectives.

Settling In for the Voyage to the Moon

The Apollo 10 crew settled into their routine for the journey to the Moon with a relatively light workload. They spent much of their time studying the flight plan or sleeping. During the trip, they made five more television broadcasts back to Earth, and it was reported that over a billion people watched some part of their activities. In June 1969, the crew accepted a special Emmy Award on behalf of the first four Apollo crews for their television broadcasts from space.

Course Correction and Minor Issues

A slight course correction was necessary during the journey, which occurred 26 hours, 32 minutes, and 56.8 seconds into the mission and lasted 7.1 seconds. This adjustment aligned Apollo 10 with the trajectory that Apollo 11 was expected to follow.

One issue the crew encountered was with the food. Due to an apparent double dose of chlorine in their drinking water, used to rehydrate their food, the meals tasted unpleasant. Despite this minor inconvenience, the crew remained focused on their mission objectives.

This phase of the mission demonstrated the crew’s ability to manage both their workload and unforeseen issues effectively, maintaining the mission’s alignment with its planned course and ensuring continued engagement with audiences back on Earth.

Lunar Orbit: Arrival and Initial Operations

Entering Lunar Orbit

At 75 hours, 55 minutes, and 54 seconds into the mission, the Command and Service Module’s (CSM) service propulsion system (SPS) engine fired for 356.1 seconds. This maneuver executed 176.1 kilometers (95.1 nautical miles) above the far side of the Moon, slowed the spacecraft into an initial lunar orbit of 314.8 by 111.5 kilometers (170.0 by 60.2 nautical miles). After completing two orbits, the SPS fired again for 13.9 seconds at 80 hours, 25 minutes, and 8.1 seconds into the mission. This burn circularized the orbit to 113.0 by 109.6 kilometers (61.0 by 59.2 nautical miles).

Observations and Photography

Within the first few hours after the initial lunar orbit insertion burn and the subsequent circularization burn, the crew began tracking planned landmarks on the lunar surface. They recorded observations and took photographs of key features. In addition to Apollo Landing Sites (ALS) 1, 2, and 3, the crew observed and photographed various features on both the near and far sides of the Moon, including the craters Coriolis, King, and Papaleksi.

Television Broadcast

Shortly after the circularization burn, the crew conducted a scheduled half-hour color-television broadcast. They provided descriptions and video transmissions of the lunar surface below, sharing their observations and the breathtaking views with audiences back on Earth.

This phase of the mission showcased the crew’s ability to execute precise maneuvers and conduct detailed observations, contributing valuable data and imagery for future lunar missions.

Entering the Lunar Module and Handling Issues

Initial LM Check and Cleanup

About an hour after the second burn, astronauts Thomas Stafford and Eugene Cernan entered the Lunar Module (LM) to check its systems. They encountered a flurry of fiberglass particles, remnants of the earlier mylar cover problem. Using a vacuum cleaner, they cleaned up the debris as best they could. Stafford even helped Cernan remove smaller bits from his hair and eyebrows. Stafford humorously noted that Cernan looked like he had just come out of a chicken coop. The particles caused itching and infiltrated the air conditioning system, leading them to scrape debris off the filter screens for the remainder of the mission.

Impact on Docking Ring

While the fiberglass particles were mainly an annoyance, there was concern that they might have affected the docking ring joining the CSM and LM, potentially causing a slight misalignment. However, Mission Control determined that the misalignment was within safe limits, allowing the mission to proceed without major issues.

This phase underscored the crew’s ability to handle unexpected challenges and maintain the integrity of the mission’s objectives. Despite the inconvenience, the crew successfully managed the situation, ensuring the mission remained on track.

The Flight of Snoopy

Preparing for the Descent

After checking out the Lunar Module (LM) “Snoopy,” astronauts Thomas Stafford and Eugene Cernan returned to the Command and Service Module (CSM) “Charlie Brown” for a rest. They later re-entered Snoopy and undocked it from the CSM at 98:29:20 into the mission. Meanwhile, John Young, remaining in the CSM, became the first person to fly solo in lunar orbit.

Inspecting and Separating the LM

Once undocked, Stafford and Cernan deployed the LM’s landing gear and inspected its systems. The CSM, piloted by Young, performed an 8.3-second burn with its Reaction Control System (RCS) thrusters, creating a separation of about 30 feet from the LM. Young then visually inspected the LM from the CSM. A subsequent separation burn increased the distance between the two spacecraft to approximately 3.7 kilometers (2 nautical miles).

Descent Orbit Insertion and Low Passes

Stafford and Cernan performed the descent orbit insertion maneuver by firing the LM’s descent engine for 27.4 seconds at 99:46:01.6. They tested the landing radar as they descended to 15,000 meters (50,000 feet), the altitude where Apollo 11 would begin its powered descent to the Moon. During these maneuvers, Young monitored the LM’s location and status, ready to assist if needed.

The LM crew conducted a detailed survey of Apollo Landing Site 2 (ALS-2). On their first pass, they came within 15.6 kilometers (8.4 nautical miles) of the lunar surface, 15 degrees east of the site. A phasing burn at 100:58:25.93, lasting just under 40 seconds, positioned them for a second pass, during which they approached within 14.4 kilometers (7.8 nautical miles) of the Moon, their closest approach.

Observations and Confirmation of Landing Site

Stafford reported that ALS-2 appeared smoother than expected, likening its appearance to the desert around Blythe, California. However, he cautioned that Apollo 11 might encounter rougher terrain if it approached off-target. The detailed observations from Apollo 10’s low passes gave NASA mission planners the confidence to confirm ALS-2 as the target site for Apollo 11’s historic landing.

The flight of Snoopy allowed critical testing and observations that were pivotal for the success of subsequent missions. The careful maneuvers and thorough inspections conducted by Stafford and Cernan, coupled with Young’s vigilant monitoring, ensured that Apollo 10 met its objectives and provided invaluable data for the first lunar landing.

Critical Maneuvers and a Close Call

Preparing for Ascent and Separation

The next critical step for the Apollo 10 crew was to separate the Lunar Module’s (LM) ascent stage from the descent stage, jettison the descent stage, and fire the Ascent Propulsion System to bring the ascent stage back towards the Command and Service Module (CSM), “Charlie Brown.” As Thomas Stafford and Eugene Cernan prepared for this maneuver, the LM began to gyrate uncontrollably.

In-Flight Emergency

Alarmed by the sudden instability, Cernan exclaimed, “Son of a bitch!” into a live broadcast microphone, which, along with other strong language used by the crew during the mission, drew some complaints from Earth. Stafford jettisoned the descent stage about five seconds after the tumbling began and fought to regain control manually, suspecting a stuck thruster might be causing the problem. He managed to stabilize the LM in time to reorient the spacecraft for rejoining “Charlie Brown.”

Identifying the Cause

The issue was traced to a switch controlling the abort guidance system mode. Both Stafford and Cernan had switched it, inadvertently returning it to its original position. This misstep could have resulted in firing the LM in the wrong direction, potentially missing the rendezvous with “Charlie Brown” or even crashing into the Moon.

Regaining Control and Continuing the Mission

Stafford regained control of the LM ascent stage within about eight seconds. The pair then fired the ascent engine at the lowest point of the LM’s orbit, simulating the orbital insertion maneuver that would be used after launch from the lunar surface in a future landing mission. “Snoopy” coasted on this trajectory for about an hour before firing the engine once more to fine-tune its approach to “Charlie Brown.”

This incident underscored the importance of precise procedures and quick thinking under pressure. The crew’s ability to recover from this potentially dangerous situation demonstrated their skill and preparedness, contributing valuable experience for future lunar missions.

Successful Rendezvous and Final Maneuvers

Rejoining Charlie Brown

“Snoopy” successfully rendezvoused and re-docked with “Charlie Brown” at 106:22:02, just under eight hours after undocking. The docking was broadcast live in color from the Command and Service Module (CSM), providing viewers with a real-time look at the critical maneuver. After Thomas Stafford and Eugene Cernan re-entered “Charlie Brown,” they sealed off “Snoopy” and separated it from the CSM.

Disposal of Snoopy’s Ascent Stage

The remaining fuel in the ascent-stage engine was burned to send “Snoopy” on a trajectory past the Moon and into a heliocentric orbit, making it the only Apollo Lunar Module (LM) to be sent into such an orbit.

Comparison with Other Apollo Missions

Unlike “Snoopy,” the Apollo 11 ascent stage was left in lunar orbit to eventually crash on the Moon. Post-Apollo 11 missions typically steered their ascent stages into the Moon to gather seismometer readings from instruments placed on the surface. There were two exceptions: Apollo 13’s ascent stage, which was used as a “lifeboat” to bring the crew safely back to Earth before it burned up in Earth’s atmosphere, and Apollo 16’s ascent stage, which NASA lost control of after jettison.

Key Takeaways

The successful rendezvous and final disposal of “Snoopy” marked the completion of Apollo 10’s objectives, providing critical data and experience for future lunar missions. The mission’s unique handling of the LM ascent stage set a precedent and offered valuable lessons for subsequent Apollo flights.

Return to Earth

Ejecting the LM Ascent Stage and Preparing for Return

After ejecting the Lunar Module (LM) ascent stage, the Apollo 10 crew conducted photography and observations of the lunar surface from orbit. They identified 18 landmarks and took numerous photographs of surface features. However, crew fatigue led to the cancellation of two scheduled television broadcasts.

The main Service Propulsion System (SPS) engine of the Command and Service Module (CSM) reignited for about 2.5 minutes, setting Apollo 10 on a trajectory back to Earth at 137:39:13.7 into the mission. As Apollo 10 departed lunar orbit, it had orbited the Moon 31 times over approximately 61 hours and 37 minutes.

Journey Back to Earth

During the return trip, the crew engaged in observational activities, including star-Earth horizon sightings for navigation. They tested the reflectivity of the CSM’s high-gain antenna and broadcasted six television transmissions, showcasing views inside the spacecraft and of the Earth and Moon from their perspective. Eugene Cernan later reported that he and his crewmates became the first to “successfully shave in space” using a safety razor and thick shaving gel, items previously considered a safety hazard.

The crew performed a mid-course correction burn at 188:49:58, lasting about 6.7 seconds, a few hours before separating the Command Module (CM) from the Service Module (SM). As they approached Earth on the final day, Apollo 10 traveled faster than any humans before or since, relative to Earth, at 39,897 km/h (11.08 km/s or 24,791 mph). This rapid return was designed to take only 42 hours, compared to the usual 56 hours. Additionally, the Apollo 10 crew traveled farther from their Houston homes than any humans before or since, at 408,950 kilometers (220,820 nautical miles).

Reentry and Splashdown

At 191:33:26, the CM separated from the SM in preparation for reentry, which occurred about 15 minutes later at 191:48:54.5. The CM splashed down in the Pacific Ocean approximately 740 kilometers (400 nautical miles) east of American Samoa on May 26, 1969, at 16:52:23 UTC, with a mission elapsed time of 192:03:23.

The astronauts were recovered by USS Princeton and spent about four hours aboard, during which they received a congratulatory phone call from President Richard Nixon. Since they did not make contact with the lunar surface, the Apollo 10 crew was not required to undergo quarantine like the first landing crews. They were flown to Pago Pago International Airport in Tafuna for a reception before boarding a C-141 cargo plane to Ellington Air Force Base near Houston.

Conclusion

Apollo 10’s successful mission provided crucial data and experience that paved the way for Apollo 11’s historic lunar landing. The crew’s ability to manage unexpected challenges and perform critical maneuvers underscored their skill and preparedness, making significant contributions to the success of the Apollo program.

Aftermath of Apollo 10

Paving the Way for Apollo 11

The orbital operations and solo maneuvering of the Lunar Module (LM) during Apollo 10 were critical in paving the way for the successful Apollo 11 lunar landing. Apollo 10 demonstrated the capabilities of the mission hardware and systems, proving that the LM checkout procedures, initial descent, and rendezvous could be accomplished within the allotted time. The mission confirmed the sufficiency of the LM’s communication systems, the operability of the rendezvous and landing radars in lunar orbit, and the ability of Earth-based personnel to adequately monitor the two spacecraft. Additionally, the precision of lunar orbital navigation improved significantly, and combined with data from Apollo 8, NASA achieved a level of precision sufficient for executing the first crewed lunar landing.

Clearance for Apollo 11

After about two weeks of analyzing Apollo 10 data, a NASA flight readiness team cleared Apollo 11 to proceed with its scheduled July 1969 flight. On July 16, 1969, the next Saturn V launched Apollo 11 astronauts Neil Armstrong, Buzz Aldrin, and Michael Collins. On July 20, Armstrong and Aldrin landed on the Moon, and four days later, the three astronauts returned to Earth, fulfilling President John F. Kennedy’s challenge to land astronauts on the Moon and return them safely by the end of the 1960s.

Careers of Apollo 10 Astronauts

Thomas Stafford

In July 1969, Thomas Stafford replaced Alan Shepard as Chief Astronaut and became the deputy director of Flight Crew Operations under Deke Slayton. In his memoirs, Stafford noted that while he could have rejoined the flight rotation, he sought managerial experience. In 1972, Stafford was promoted to brigadier general and assigned to command the American portion of the Apollo-Soyuz Test Project, which flew in July 1975. He later commanded the Air Force Flight Test Center at Edwards Air Force Base in California and retired in November 1979 as a lieutenant general.

John Young

John Young went on to command the Apollo 16 lunar landing mission in April 1972. From 1974 to 1987, Young served as Chief Astronaut. He commanded two Space Shuttle missions: STS-1 in April 1981 and STS-9 in November 1983. Young retired from NASA’s Astronaut Corps in 2004.

Eugene Cernan

Eugene Cernan commanded the final Apollo lunar mission, Apollo 17, in December 1972. Cernan retired from NASA and the Navy as a captain in 1976.

Legacy

Apollo 10’s success was a critical step toward the historic Apollo 11 mission, validating the systems and procedures necessary for a safe lunar landing and return. The experience and data gathered from Apollo 10 significantly contributed to the precision and confidence with which NASA approached the first crewed Moon landing, marking a pivotal moment in space exploration history.

Hardware Disposition of Apollo 10

Command Module Charlie Brown

Since 1970, the Smithsonian Institution has been responsible for the command module “Charlie Brown.” The spacecraft was displayed in various countries before being loaned to the London Science Museum in 1978. The Service Module (SM) of Charlie Brown was jettisoned just before re-entry and subsequently burned up in Earth’s atmosphere, with its remnants scattering in the Pacific Ocean.

Saturn V’s S-IVB Third Stage

After achieving translunar injection, the Saturn V’s S-IVB third stage accelerated past Earth escape velocity and became space debris. As of 2020, it remains in a heliocentric orbit.

Lunar Module Snoopy

Ascent Stage: The ascent stage of the Lunar Module “Snoopy” was jettisoned into a heliocentric orbit. After 1969, its orbit was not tracked, and its location remained unknown. In 2011, a group of amateur astronomers in the UK initiated a project to search for it. In June 2019, the Royal Astronomical Society announced a possible rediscovery of Snoopy, identifying the small Earth-crossing asteroid 2018 AV2 as likely being the spacecraft with “98%” certainty. Snoopy’s ascent stage is the only once-crewed spacecraft known to still be in outer space without a crew.

Descent Stage: The descent stage of Snoopy was jettisoned in lunar orbit. Its exact location is unknown, though it likely crashed into the Moon due to orbital decay. Planetary scientist Phil Stooke noted that the descent stage “crashed at an unknown location,” while other sources suggest it eventually impacted within a few degrees of the equator on the near side of the Moon. Richard Orloff and David M. Harland, in their Apollo sourcebook, stated that the descent stage was left in low lunar orbit, and perturbations by lunar mass concentrations (“mascons”) would have caused its orbit to decay, leading to a crash on the lunar surface.

Legacy of Apollo 10 Hardware

Apollo 10’s hardware disposition highlights the journey and ultimate fate of the mission’s components. The continued existence of Snoopy’s ascent stage in a heliocentric orbit adds a unique chapter to the history of human space exploration, while the analysis of crash sites on the Moon provides valuable data for understanding the behavior of spacecraft in lunar orbit.