Apollo 10

LMP Eugene Cernan has entered the docked LM Snoopy, alone, to perform housekeeping chores, power transfer from the CSM to the LM batteries, power up the communications systems and perform S-band and VHF voice checks with MCC-H.

On entering Snoopy, Cernan encountered a mild snowstorm of Mylar insulation that, during the pressurization of the LM, had blown through the LM dump valve and into the LM. The hatch was inspected immediately and it was found that there were many pieces of insulation stuck all over the semi-greasy seal. The dump valve was also inspected and pieces were found stuck in the seal of the dump valve; pieces that had to be pulled out and picked out. The hatch was cleaned and wiped, and the dump valve was blown out by Cernan using his own breath.

He encountered no problems reorienting himself to the new LM cabin environment. The LM was found it to be exactly in the configuration it was left in at lift-off. Power was transferred from the CSM fuel-cell source to the LM internal batteries. Cernan described the issues he encountered in the cabin atmosphere once he entered the LM's cabin in the Technical Crew Debrief:

Cernan, from the 1969 Technical debrief: "...the problem then that was encountered after a little bit of work and switch verification in the LM was that the insulation was still floating around in zero-g. The circulation down in the LM was very poor. The insulation was irritating; it also became warm. You could feel yourself tending to breathe this stuff. What we did was pull a Command Module/LM Pilot hoses (of course, we had the screen on the exhaust hose all the time) and drop them all the way down into the LM and they just laid there and floated freely. This blew fresh air around in the LM and from that point on, although there was still a lot of Mylar floating around (and some of it going back into the Command Module), the comfort level working in shirtsleeves was adequate, and the ventilation was adequate."

The initial transfer of equipment from the CM to LM took place. Cernan described this process in the Technical Crew Debrief:

Cernan, from the 1969 Technical debrief: "This equipment was listed in the checklist, or in the Flight Plan, which we highly advocate. It was labeled on the transfer bag, such as 16-mm film packs. While the LM Pilot was in the LM making a switch verification, the commander was gathering the gear together (in the CM) and sending it on down (the tunnel). As he sent it, it was stowed immediately where it should be without any difficulty. A piece of cake."

This manoeuvre will be made with the Manual Attitude Pitch switch on panel 1 in the Accel Command position. In this position RCS control by the CMC or SCS is disabled.

Young, from the 1969 Technical debrief: "The systems used for the landmark updates, which is the map update, LOS 150 degrees west, and AOS, sunrise and sunset times, is excellent. It's recommended that they be used as standard procedures in future Flight Plans. The landmark-update format for defining the times at which the landmark appeared at the zero-degree line, and the 35 degree elevation line to start the pitch down rate for LM or landmark tracking was adequate. Landmark tracking of the first site, F-1, was done with the sextant by tracking a small crater on the left corner of the landmark F-1. The location of F-1 through the Auto Optics mode was about 5 or 6 degrees away from where F-1 actually is located, and this happened on every case. We ran five sets of five marks on F-1 and it was always wrong. It is believed, but I am not certain, that on the first attempt with B-1 with the LM Auto Optics acquisitioning, an erroneous landmark was tracked. It is highly recommended that, if landmark tracking is to be continued, more thought be given to selecting landmarks, the position of which is known prior to the mission and the acquisition of which can be easily performed with the LM attached. Landmark tracking per se conducted with the telescope or the sextant was easy and was a coordinated effort with the commander flying the vehicle and CMP tracking to locate mark intervals. It was noted by the ground that we commenced making our marks to early, and after we delayed them 20 to 30 seconds, the system seemed to work properly. There is no way for the crew to tell what is the proper time to start making marks. The geometry of the situation does not lend itself to an onboard determination of what this proper time should be, in my opinion."

Stafford is controlling the spacecraft attitude in pitch to enable Young to make the sightings on the landmarks with the CM optics.

T-2 is the time when the CDR begins manoeuvring the spacecraft at orbital rate to keep it pitched down 45° from the local horizon.

Cernan is asking Stafford to check his audio settings in the CM on panel 6. The Suit Power switch has two positions - Power which applies power to left and right hand microphone preamplifier and the suit biomed preamplifier associated with audio control, or Off.

The Power switch, also on panel 6 has three positions. Audio/Tone provides primary power to audio centre module and enable audible crew alarm signal to be heard at this astronaut position. Off removes all power to audio centre module and disables audible crew alarm for this astronaut station. Audio Provides primary power to audio centre module but leaves audible crew alarm circuit disabled at this station.

And finally the S-band switch again on panel 6 is a three position switch. T/R enables, by circuit closure, headset to transmit and receive over S-band equipment operating in Voice mode. Off selects no mode. RCV enables, by circuit closure, headset to receive (only) output of S-band equipment operating in Voice mode.

The LMP S-band T/R switch is on panel 12 in the LM and has 3 positions.

• S-band T/R (Transmit/Receive) - Enables routing received S-band audio to the headset amplifier, and microphone amplifier outputs to the PMP (Premodulation Processor) for S-band transmission.
• Off - Inhibits routing S-band transmitter and receiver outputs through the LMP's audio centre.
• S-band RCV - Enables routing received S-band audio to the headset amplifier.

The LMP VHF A switch is on panel 12 in the LM and has 3 positions.

• T/R (Transmit/Receive) - Enables routing the received VHF A audio to the headset amplifier, and microphone amplifier outputs to the VHF A transmitter for transmission. VOX keying voltage is routed to VHF A transmitter.
• Off - Inhibits routing VHF A transmitter and receiver outputs through LM Pilot's audio centre.
• RCV - Enables routing received VHF A audio to headset amplifier.

The LMP VHF B switch is also on panel 12 in the LM and has 3 positions:

• T/R (TRANSMIT/Receive) - Enables routing the received VHF B audio to the headset amplifier, and microphone amplifier outputs to the VHF A transmitter for transmission. VOX keying voltage is routed to VHF A transmitter.
• Off - Inhibits routing VHF B transmitter and receiver outputs through LM Pilot's audio center.
• RCV - Enables routing received VHF B audio to headset amplifier.

All of the communications switches Engle is now reading out to Cernan are on LM panel 12.

The Power Ampl switch, has 3 positions - Prim/Off/Sec permits the selection of either of two redundant power amplifiers for use with the S-Band equipment. When activated, the amplifier requires a 72-watt power input; however during certain phases of the lunar stay, S-Band transmissions are possible in a low power mode, with the power amplifier turned off. This switch is enabled only if the Transmitter/Receiver switch is in the Prim or Sec position, thus preventing operation of either power amplifier without a driving signal. Engle is instructing setting this switch to Prim.

The Voice Function switch, has 3 positions - Voice/Off/Dn Voice BU (Down Voice Backup) permits the selection of either normal voice or backup voice for transmission via the S-band equipment. In the Voice position, the voice output is modulated onto a 1.25 MHz subcarrier within the PMP (Premodulation Processor) and routed to the S-band PM transmitter for transmission to Earth. If the FM transmitter is selected, and the Range Function switch is in the Off/Reset position, the voice is routed to the FM transmitter for modulation directly on the carrier (used during lunar stay). In the Dn Voice BU position, the PM (Phase Modulation) section of the S-band transmitter is automatically selected (regardless of the position of the Modulate switch) to transmit voice directly on the carrier, bypassing the PMP. In this position the system is permitted to transmit low bit rate PCM (Pulse Code Modulation) data on a 1.024 MHz subcarrier if the PCM position is selected on the PCM/Key Function switch and either of the hardline biomeds are selected on Biomedical switch. (Additionally, in the Dn Voice BU position, the ranging or television function of the Range Function switch is interrupted if either has been selected). In the Off position, all S-band voice transmission capability is interrupted. Engle is instructing setting this switch to Dn Voice BU.

The PCM/Key Function switch, has 3 positions - PCM/Off/Key. It permits the selection of either the telemetry or the emergency keying function for transmission via the S-Band equipment. In the PCM position, telemetry data is routed to the PMP for transmission to earth via the S-Band. (This function is used in conjunction with the PCM Rate switch). In the Off position no data is transmitted, nor is the subcarrier transmitted. In the Key position all other selected S-Band Function switches (Range Function, Biomed, Modulate, and Voice) are interrupted and the PM section of the selected S-Band transmitter is enabled; DC power is applied to the PMP emergency key gating circuitry, and the PTT/Keyer switches (PTT (Push To Talk), PTT/Keyer) located on the ACA's (Attitude Controller Assembly) and ECS (Environmental Control Subsystem) suit umbilicals , are enabled to serve as Morse code keyers for emergency transmissions. Engle is instructing setting this switch to PCM.

The Range Function switch, has 3 positions - Range/Off-Reset/TV CWEA Enable. It permits the selection of the ranging function for transmission via the S-Band equipment. In the Range position, the received ranging signal is re-transmitted back to earth via the phase modulated S-Band transmitter (Modulate switch in the PM position). The TV CWEA Enable position enables the CWEA logic which feeds the annunciator light S-bd Rcvr (S-bd Rcvr Failure Caution Light). This light and the Master Alarm light and warning tone will be activated, if for any reason, the received signal is interrupted. This position disables the range gate, thereby interrupting the re-transmission of the ranging signal to Earth. This position is not wired into the TV circuitry. If the Range Function switch is in the Off-Reset position, the range gate is disabled. This position also provides a reset to the CWEA (Caution and Warning Electronics Assembly) logic which feeds the annunciator light S-bd Rcvr (S-bd Rcvr Failure Caution light). A reset will extinguish the light, if on, or inhibit from illuminating if not on. Engle is instructing setting this switch to Off/Reset.

The Biomed switch, has 3 positions - Left/Off/Right. It selects which crew station hardline biomedical data will be sent to Earth via the S-Band. In the Left or Right positions, inputs are fed from the Commander's or LM pilots stations respectively. With this switch in the Off position, and with the Voice switch in the Dn Voice BU position, the transmission of hardline biomed and EMU data is interrupted, and additional speech processing of the voice signal transmitted to Earth is accomplished. Engle is instructing setting this switch to Off.

The PCM RATE switch, has 2 positions-HI / LO. It selects the high or low bit rate telemetry to be transmitted via PCM to Earth on S-band. Some information is sent in high bit rate telemetry only, including AGS (Abort Guidance System) and PGNS (Primary Guidance and Navigation System) downlink, and AGS State Vector update via PGNS downlink. Additionally, with this switch in the 1.0 position, and with the VHF B Transmitter switch in the DATA position, PCM telemetry data is transmitted to the CSM and recorded there for eventual re-transmission to earth. (Used when LM is behind the moon and when CSM is in LOS.) Engle is instructing setting this switch to LO.

The VHF A Transmitter switch on LM panel 12 has 3 positions, Voice/Rng/Off/Voice. It enables simultaneous voice transmission & range capability via the VHF A XMTR when in the Voice/Rng position. In the Voice position it enables voice transmission only. All power from the VHF A XMTR is removed in the Off position.

The VHF B Receiver switch has 2 positions, On/Off. It controls primary power to the VHF B receiver (259.7 MHz) respectively. In the On position, electrical power is applied to the B receiver assembly and in the Off position power to the assembly is interrupted.

The S-band Antenna is a 4 position rotary switch, Fwd/Aft/Slew/Lunar Stay. It provides selection of any of the four S-band antennas for communication with Earth. The Fwd and Aft positions select #1 and #2 omni-directional antennas respectively, for use in the event of S-band steerable antenna failure. The Slew position selects the 1 steerable antenna, and the LUNAR STAY position selects the S-band erectable antenna for use during lunar stay. A lock mechanism is incorporated in this rotary knob to prevent inadvertent selection of the Lunar Stay position in the absence of an antenna load at the S-band erectable antenna connector.

Engle is confirming with Cernan the LM communications switch settings in an attempt to pinpoint the problem that is preventing MCC-H hearing Cernan's transmissions from the LM apart from over the CSM comms.

Gas is circulated through the pressure suit circuit by two centrifugal compressors, which are controlled by individual switches on panel 4. Normally only one of the compressors is operated at a time; however, the individual switches provide a means for connecting either or both of the compressors to either a-c bus.

Secchi is a small lunar (diameter approximately 25km) crater formation on the northwest edge of Mare Fecunditatis. To the northeast is the crater Taruntius.

Flight Plan page 3-45.

MCC-H is advising Cernan to configure for the S-band Voice tests using the Omni antenna.

With the Voice switch on LM panel 12 in the DN Voice BU position, comms tests continue using the PM (Phase Modulation) section of the S-band transmitter which is automatically selected (regardless of the position of the Modulate switch) to transmit voice directly on the carrier.

Break in DSE CM recording.

The voice PM checks now continue using the LM steerable antenna. The pointing angles are provided by MCC-H for this test.

Comm break.

The H₂ tank heater switches on CM panel 2, when placed in the Auto position enables automatic pressure switches to control DC power in either of the two H₂ tanks heater elements. In the Off position, all DC power is disconnected from the heater elements.

Cernan has set the S-band steerable antenna in Track Mode-Auto using the switch on LM panel 12. In this mode AC and DC power is applied to the steerable antenna electronics. The antenna is enabled to track the received MSFN signal automatically. The strength of the received signal is indicated on the Signal Strength gauge also on LM panel 12.

Engle has instructed Cernan to leave the Modulate switch on LM panel 12 in the FM position rather than switching back to the PM position. With the switch in the FM position, the FM control circuit and disables the phase modulator and range gate amplifier in the S-band transmitter.

Comm break.

MCC-H are requesting that the CSM terminates the CSM Relay mode.

Cernan, from the 1969 Technical Debrief - "The MSFN/CSM/LM relay comm tests were effectively not performed at the direction of MSFN. We did the LM comm checks; we proved out the adequacy of the LM comm system. We proved out the anomalies that we expected; although we had time prior to the upcoming LOS, we were directed to forget about the MSFN/LM/CSM relay mode test."

The Glycol Temp gauge on LM panel 2, displays the glycol temperature (in Fahrenheit) of the primary or secondary coolant loop. A water-glycol solution circulates through each loop. The primary loop provides temperature control for batteries, electronic equipment that require active thermal control, and for the oxygen that circulates through the cabin and pressure suits. Heat is removed by absorption as the solution through cold plates and cold rails to which the electronic equipment is attached. The heat absorbed is rejected to space by sublimation. When necessary, the primary loop is also a source of heat for the cabin atmosphere.

The Deadband switch on LM panel 3, has two positions, Max/Min. In the Max position it allows a large amplitude limit cycle for attitude control system, to conserve RCS fuel during coasting flight. In the Min position a narrow deadband for periods during which accurate manual attitude control is required.

The Disp/Eng Ovrd/Logic circuit breaker on LM panel 16 to the left of the LMP's station, Applies DC power to the Main Propulsion Temp and Press indicators, Ascent and Descent He Reg talkbacks, and Descent Propulsion Vent talkbacks. It also supplies redundant power to ascent engine firing circuit.

The 3 position Prplnt Temp/Press Mon switch on LM panel 1 selects inputs to propellant temperature and pressure indicating devices from ascent or descent propellant tanks. In the ASC position it connects the output of temperature and pressure sensors in ascent propellant tanks to Temp and Press gauges.

MCC-H continue to give tips to the crew on cleaning up the Mylar hatch insulation particles, especially the tunnel hatch seal, which is manufactured from RTV-room temperature vulcanized rubber.

Now that Stafford has joined Cernan onboard the LM 'Snoopy', they are checking out the OPS (Oxygen Purge System). The OPS would be required if the final docking between CSM 'Charlie Brown' and LM 'Snoopy' failed to occur. The two LM crew members would have to transfer between the two spacecraft by performing an EVA, wearing the OPS to provide life support.

Cernan, from the 1969 Technical debrief: "The OPS check was left until the end of that day after all the communications procedures and everything was checked out. One OPS was taken out and handed to the Commander, and he effectively was halfway through the tunnel and was checking it out while the LM Pilot was fully in the LM, checking the other OPS out. The checks went normally with the exception of one item. On the OPS that was labeled Stafford, the heater lights failed to light during the press to test, indicating that the heater was not operating. Neither light operated. However, the other OPS checked out satisfactory. Pressures were good and as far as we are concerned, we still had two good OPSs except for the heaters in the one. They restowed with very little difficulty. Once I understood that you've got to push that one oxygen supply hose out of the way to get the pins in, I had no trouble at all."

Break in transcription.

The LM Power switch on panel 2 has three positions:

• Off - Disconnect power to LM. In this position the it does not open controlling relay in the LM.
• CSM - Energizes relay in the LM to connect CSM power and CSM dc negative to the LM through two umbilicals and disconnect LM power from it's heater circuits.
• RESET - Placing the switch momentarily in this position opens relays in the LM to disable CSM circuits and connect LM power to it's heater circuits.

Two electrical umbilicals are installed in the LM tunnel at launch. One end is attached to the LM connectors, the other end routed and attached to stowage connectors on the LM tunnel wall. These stowage connectors are physically clear of the drogue supports and probe supports and pitch arms. The connectors are accessible from the CM tunnel between the drogue periphery and the LM tunnel wall. In this manner CM connections can be accomplished after transposition and docking, without requiring probe or drogue removal.

Flight Plan page 3-46.

Young is still concerned about particles coming into the CM from the LM.

The adhesive tape will be used to capture some of the Mylar tunnel hatch insulation.

About now, Apollo 10 begins its fifth lunar orbit.

The LM Cabin Repress valve control is situated on the oxygen control module controls.

The three positions of this valve are: Manual/Auto/Close.

In the Manual position, there is an unregulated flow of oxygen into the cabin from the oxygen manifold. The Auto position enables the valve to respond to inputs from the cabin pressure switch and the low suit circuit pressure sensor. The valve opens fully whenever cabin pressure drops below 3.70-4.45 psia, and closes as cabin pressure rises above 4.40-5.00 psia, It is also opened when suit circuit pressure falls to 2.9-3.4 psia with the cabin pressure switch closed, and closes when the pressure increases to 3.0-3.5 psia, If both the Atmosphere Revitalization Section Pressure Regulator A and B are in either the Egress or Close position the automatic activation of Cabin Repress valve by the cabin pressure switch is disabled, unless the suit pressure falls to 2.9 - 3.4 psia, The Close position prevents oxygen flow into the cabin from the oxygen manifold.

The crew are now reinstalling the docking drogue and probe.

Young, from the 1969 Technical debrief: "It was originally thought that we would keep the probe and drogue and the hatch under the couches, but it was noticed that they took up so much room that it didn't seem to be a very nice way to operate, so we reinstalled them. It was more difficult to get the drogue in and out of the tunnel than any other piece of equipment, although this had been anticipated and it was no problem. We reinstalled the probe and unloaded it, and reinstalled the hatch. The total time for this reinstallation was somewhat less than 15 minutes."

With the LM Tunnel vent switch in the LM PRESS position the LM cabin atmospheric pressure will be maintained by the CSM environmental control system.

The cryogenic contents of the H₂ & O₂ tanks are circulated by internal fans. The Flight Plan calls for the fans to be cycled prior to the sleep period to reduce the probability of stratification in the tanks. By doing so the chance of an alarm sounding during the upcoming sleep period is reduced.

The Flight Plan calls for the LMP to give a series of consumable onboard readouts to MCC-H prior to the sleep period. The breakdown of the above readouts are:

• The LM went off CSM electrical power onto it's own internal battery source at 082:29:20.
• The LM went back onto CSM electrical power at 084:32:00.
• CSM onboard battery readouts: Battery C, 37V; pyrotechnic battery A & B, 37V.
• SM RCS propellant levels (per cent): Alpha, 81; Bravo, 87; Charlie, 84; Delta, 84.
• The H₂ and O₂ cryogenic tank fans have been cycled.

Cernan has also initiated the charging of CSM battery B from the SM fuel cells.

The roll CAL angle measures the roll angle between the optimum docked alignment of the CM and LM to the actual. It is measured in degrees on a scale scribed on the CM docking ring. An initial reading is taken following the transposition and docking and further readings are taken when crewmembers transfer between the two vehicles to monitor for any change in the alignment.

Radiation level.

Using the Power/Temp Mon rotary selector switch on LM panel 14, enables the voltage and current of the 4 descent stage and 2 ascent stage batteries to be displayed on the voltage and current displays, also on LM panel 14. The range of the voltage indicator is from 20 to 40 volts DC and 62.5 to 125 volts AC. Cernan is referring to the voltage readings he took for the 4 descent stage batteries as he deactivated the LM systems. The readings had changed significantly from the first readings he took. The 4 descent stage batteries are connected to their Low Voltage taps after they are disconnected from the ground support equipment prior to launch. This is due to the inherent initial high voltage of the batteries and allows for them to discharge slightly prior to power up. This is the configuration Cernan would have found when he began the power up for the subsystems checks. He changed to the Hi Voltage setting as he powered up the LM's subsystems.

The primary Glycol Temp is indicated in Fahrenheit on a strip meter on LM panel 2 when the ECS Glycol Pump 1 & 2 circuit breaker on LM panel 11 is pressed in.

The Delta-P is the pressure differential between the CM cabin and the LM tunnel as read off the gauge on CM panel 12.

Comm break.

ROT Contr Pwr, Direct-2 Off switch on panel 1, removes 28 VDC from the direct switches on rotation controller 2.

The O₂ Flow Hi warning light on panel 2 indicates when total ECS oxygen flow reaches 1 lb per hr for a period of time exceeding 16.5 seconds. The red warning light illuminates at critical flow rates which, if continuous, indicates cabin leakage or oxygen subsystem leakage. The continuous O₂ flow rate is displayed on the O₂ flow indicator, also on panel 2. The cause of the warning light is the restriction of the flow by the inflow valve be clogged by the airborne Mylar insulation from the CM forward tunnel.

Comm break.

An interpretation of the PAD follows:

• Purpose: This PAD is for an early return to Earth at the end of the tenth lunar orbit in case an abort situation develops.
• System: The burn of the SPS would be under the control of the Guidance and Navigation System.
• Time of ignition, Tig (Noun 33): 96 hours, 02 minutes, 40.54 seconds GET. As with all the TEI PAD's, the burn is timed for when the spacecraft is over the far-side.
• Change in velocity (Noun 81), fps (m/s): x, +2996.6 (+913.4); y, -179.4 (-54.7), z: -160.5 (-48.9). The large positive x component shows that this burn would be prograde, i.e. with their orbital motion, increasing their velocity so that they escape the gravitational pull of the Moon. The y component indicates that the plane of their orbit would be changed.
• Spacecraft attitude: Roll, NA; Pitch, 54°; Yaw, NA.

Other items, such as the size of the orbit, on the standard form are not applicable (NA) to this PAD or will be taken from previous versions. All these values assume the CSM is no longer carrying the weight of the LM.

Flight Plan page 3-47.

The SCS-Electronics Power rotary switch on panel 7 has three positions, Off, ECA and GDC/ECA. In the ECA position, AC and DC power is supplied by all buses to the ECA (Electronics Control Assembly).

The ECA contains the electronics used for SCS automatic attitude hold, proportional rate, and minimum impulse capabilities. It also contains the attitude BMAGs uncage logic. It receives control inputs from the gyro assemblies and the rotational controller-transducers and breakout switches (MIN IMP). The ECA provides rotational control commands to the RCS logic in the Reaction Jet Electronic Control.

The Pot H₂O Htr switch on panel 2 has three positions, MnA, Off and MnB. The MnA or MnB positions provide 28VDC to the potable water tank heaters from the selected power bus. In the Off position this power is removed. The some potable water provided as a by-product by the fuel cells is chilled for drinking and food production, the remainder is heated for warm food production. As the crew is about to commence a rest period, MCC-H are instructing the crew to remove the power from the heaters whilst they sleep.

The G&N Optics Power switch on panel 100 has two positions. In the Off position removes DC operating power from the optics subsystem.

The HGA Track switch on panel 2 has 3 positions. In the Reacq position, the HGA will automatically point toward, MSFN stations, provided the MSFN stations are within + or - 60 degrees of the antenna boresight axis (Auto Track mode) and should it go beyond predetermined scan limits it will automatically switch to the Man mode. In the Man mode the antenna will point at the angles set on the Pitch and Yaw controls. Once a signal is again present the mode will automatically return to the Auto Track mode.

Using CMC routine R03 to configure and engage the Digital Auto Pilot (DAP), the crew will select to use RCS quadrants Bravo and Delta on opposing sides of the SM to control the spacecraft's roll attitude.

Engle is pointing out that Cernan has initiated a purge of fuel cell 2 instead of 1. He now corrects his mistake. The fuel cell O₂ purge is performed first. This takes 2 minutes. The H₂ purge is then commanded, taking 80 seconds. The purging opens the purge valve on the O₂ & H₂ sides respectively of the selected fuel cell to remove the impurities from the electrodes. The period between purges is dependent on the pre-launch purity tests and the load profile since the last purge. When purging the fuel cell, the Master Alarm and the relevant Fuel Cell caution and warning light to activate. This is due to an increase during the purge in the cryogenics flow rate. The O₂ and H₂ purge switches are both on panel 3.

Long comm break.

PRD-Personnel Radiation Dosimeter.

The guy on the left that Engle is referring to is the Flight Surgeon.

Landmark B1/10. Click on the region surrounding the landmark for a closeup view.

Long comm break.

The Auto RCS switches are situated at the top of panel 8 by window 1. The required SM RCS engines can be activated using power from the selected electrical bus, Main A or Main B.

When preparing the spacecraft for the crew rest period, the appropriate SM RCS are selected and the DAP is configured to provide automatic attitude control with the minimum of thruster activity during this period. There is some confusion in the forthcoming conversations between the crew and MCC-H as to the required RCS selections and DAP configuration. Apollo 10 being the first flight in lunar orbit of the joint CSM-LM combination, the DAP configuration is being tested to find the most appropriate settings whilst in the docked mode.

About now, Apollo 10 begins its sixth revolution.

End of DSE tape recording in the CM.

Comm break.