THE YE-6 LUNAR LANDER SERIES: 1963-1965

Campaign objectives:

After having focused for several years on Mars and Venus, the Moon reasserted itself as a priority in concert with the progress of the manned space flight program. The 1959 Soviet plan to send cosmonauts on circumlunar flights had also envisaged robotic orbiters and landers. An early proposal for a Yc-5 lunar orbiter to respond to the first American attempts at small lunar orbiters was canceled along wdth its three-stage 8K73 launcher in favor of launching Ye-6 landers and Ye-7 orbiters using the four-stage 8K78 ‘Molniya* developed for planetary missions. These new spacecraft were also to exploit the design and flight experience of the second generation Mars and Venus spacecraft launched in 1962. The 2MV was a modular spacecraft with a common flight module and a mission-specific flyby or entry probe payload module. Unlike the earlier Luna spacecraft, which were launched directly towards the Moon, the Ye-6 series and all subsequent lunar missions were placed in Earth orbit for later injection onto a lunar trajectory by the restart able fourth stage.

Spacecraft launched First spacecraft: Mission Type: Country; Builder: Launch Vehicle: Launch Date! Time: Outcome:	Ye-6 No.2 [Sputnik 25] Lunar Lander USSR OKB-1 Molniya January 4, 1963 at 08:49:00 UT (Baikonur) Failed to leave Earth orbit.
Second spacecraft: Mission Type: Countryj Builder: Launch Vehicle: Launch Date ‘: 7 "une: Outcome:	Ye-6 No.3 Lunar Lander USSR OKB-1 Molniya February 3, 1963 at 09:29:14 UT (Baikonur) Launch vehicle veered off course.
Third spacecraft: Mission type: Coun try j Builder: Launch Vehicle: Launch Date: Time: Encoun ter Dale і 17me: Mission End: Outcome:	Luna 4 (Yc-6 No.4) Lunar Lander USSR OKB-1 Molniya April 2, 1963 at 08:16:37 UT (Baikonur) April 5, 1963 April 6, 1963 Navigation failed in transit, missed Moon.
Fourth spacecraft: Mission Type: Conn try і Builder: Launch Vehicle: Launch Date: Time: Outcome:	Ye-6 No.6 Lunar Lander USSR OKB-1 Molniya-M March 21, 1964 at 08:15:35 UT (Baikonur) Upper stage failure. Did not reach orbit.
Fifth spacecraft: Mission Type: Country; Builder: Launch Vehicle: Launch Date! Time: Outcome:	Ye-6 No.5 Lunar Lander USSR OKB-1 Molniya-M April 20, 1964 at 08:08:28 UT (Baikonur) Upper stage failure. Fourth stage failed to fire.
Sixth spacecraft: Mission Type: Country; Builder: Launch Vehicle:	Ye-6 No.9 (Cosmos 60) Lunar Lander USSR OKB-1 Molniya

Launch Dale ‘: 7 ‘line: Outcome:	March 12, 1965 at 09:30:00 UT (Baikonur) Failed to leave Earth orbit.
Seventh spacecraft: Mission type: Country; Builder: Launch Vehicle: Launch Date: Time: Outcome:	Ye-6 No.8 Lunar Lander USSR OKB-1 Molniya April 10. 1965 (Baikonur) Upper stage failure. Did not reach orbit.
Eighth spacecraft: Mission Type: Country і Builder: Launch Vehicle: Launch Dale/ Time: Em ounter Da tei Time: Outcome:	Luna 5 (Ye-6 No.10) Lunar Lander USSR OKB-1 Molniya-M May 9, 1965 at 07:49:37 UT (Baikonur) May 12, 1965 at 19:10 UT Crashed.
Ninth spacecraft: Mission Type: Country; Builder: Launch Vehicle: Launch Dale ‘: 7 ime: Em’ounter Da tei Time: Outcome:	Luna 6 (Ye-6 No. 7) Lunar Lander USSR OKB-1 Molniya-M June 8, 1965 at 07:40:00 UT (Baikonur) June 11, 1965 Midcourse maneuver failed, missed moon.
Tenth spacecraft: Mission Type: Country і Builder: Launch Vehicle: Launch Dale ‘: 7 ime: Encounter Date; 7 7me: Outcome:	Luna 7 (Ye-6 No.11) Lunar Lander USSR OKB-1 Molniya October 4, 1965 at 07:56:40 UT (Baikonur) October 7, 1965 at 22:08:24 UT Crashed.
Eleventh spacecraft: Mission Type: Country і Builder: Launch Vehicle: Launch Date: Time: Encounter Date; 7 ime: Outcome:	Luna 8 (Ye-6 No. 12) Lunar Lander USSR OKB-1 Molniya December 3, 1965 at 10:46:14 UT (Baikonur) December 6. 1965 at 21:51:30 UT Crashed.

The early Ye-6 series, built at OKB-1, was designed to accomplish the first lunar soft landing. Unfortunately, it suffered eleven straight failures between January 1963 and December 1965. Four spacecraft were lost to booster failures, two were stranded in Earth orbit by fourth-stage failures, two failed in transit and missed the Moon, and three failed at the target by crashing.

The years 1962-65 were dismal for Soviet robotic lunar and planetary exploration. The early sueecsses of Luna 1, 2, and 3. and the encouraging but ultimately fruitless flights of Venera 1 and Mars 1. had built expectations for more success. But by the end of 1962 the Molniya launcher had failed in all but one of ten launches and the truncated flight of Mars 1 had revealed the shortcomings of the 2MV series. These problems were addressed with the 3MV series, essentially the same spacecraft with advanced engines and avionics, and these advances were incorporated into the first Ye-6 series. Nevertheless by the end of 1965 three 2MV Mars missions, three 2MV Venus missions, two test and one 3MV Mars missions, one test and five 3MV Venus missions, and eleven Ye-6 lunar missions – a total of twenty-six missions had been lost without a single success at the assigned targets. Ironically, in the midst of this awful record, one of the test 3MV Mars spacecraft did achieve a measure of success at the Moon, when Zond 3 provided far-side photography of better quality than that from Luna 3. It was the only lunar accomplishment in this period. Such a long string of failures could well have shut down an American program, so vulnerable to public criticism, but in the Soviet Union it led to the determination to succeed, although not without a great deal of internal criticism by the government and outright threats of punishment.

Spacecraft:

The Ye-6 spacecraft consisted of three sections totaling 2.7 meters in height. The first section consisted of the Isayev mideourse correction and descent engine, which produced a thrust of 4.64 tons using hypergolic nitric acid/amine propellants. Four smaller 245 N thrusters mounted on outriggers were used for attitude control during the descent. The main pressurized cylindrical compartment containing avionics and communication equipment was mounted above the engine. Л pair of cruise modules were attached to the central cylinder. One held both attitude control thrusters for the translunar flight and a radar altimeter to trigger the landing sequence, and the other contained avionics sensors for attitude reference and control during the cruise. Both were discarded after the altimeter triggered the landing sequence. The lander capsule was strapped to the top of this stack. Unlike their planetary cousins, these spacecraft carried no solar panels because the flight time for the carrier module and the time on the surface for the lander were sufficiently short that the batteries would not require a recharge.

A new autonomous control system, the 1-100. was made for the Ye-6 which not only controlled the spacecraft but also the attitude and firings of both the third and fourth stages of the launcher. This approach deviated from usual practice but saved a great deal of w eight by eliminating the third and fourth stage controllers with their associated cabling and connectors. However, this had never been tried before, and w ould be the cause of further problems for a launcher that had already failed in nine out of ten attempts.

The lander capsule comprised a 105 kg hermetically sealed 58 cm sphere encased in tw’o hemispherical airbags sewn together. It carried communications equipment, a program timer, heat control systems, batteries, and scientific instruments including a television system. Once the lander was on the surface, it would deploy four petals to

Lunar lander

Gas ttjnks for astroorientalion

Control system

Astroorientalion system

Radio

Oxygen lank Fuel tank

M

Radioaltimeter

engine

Radioaltimeter antenna

Main engine

Figure 9.1 Ye-6 lunar soft-lander spacecraft.

Figure 9.2 Drawings of the Ye-6 spacecraft and lander.

expose its upper hemisphere and raise four 75 an antennas. The batteries were to supply power for a total of 5 hours over a period of 4 days, with its activities being driven either by timer or by command from Earth. The mass distribution was biased towards the bottom to assist the lander in turning upright on the surface when the petals were opened. The ideas of using air bags for impact and articulating petals to ensure a final upright stance on the surface were both quite clever, but not patented, and so the Americans adapted them for the pyramidal lander of the Mars Pathfinder mission in 1996.

After a direct approach to the target site on the Moon, the landing sequence was initiated at an altitude of 8,300 km. The attitude thrusters stabilized any roll that the spacecraft might possess and aligned the vehicle to the lunar vertical. At about 70 to 75 km altitude the radar altimeter was triggered, sending a signal to jettison the two cruise modules, inflate the airbags to 1 bar and ignite the main engine. At this time its speed relative to the Moon was about 2.630 m/s. The engine was to be shut off at an altitude of 250 to 265 meters and the four outriggers ignited for terminal descent. When a 5 meter long boom made first contact with the surface, the capsule would be ejected vertically to reduce its velocity to 15 m/s. The impact would be absorbed by the airbags. Four minutes after landing, the airbag cover would be severed along the joining seam and discarded. One minute later the lander would right itself by opening the four spring-loaded petals that formed its upper hemisphere, then raise its antennas.

The sites that could be reached by this type of mission were severely constrained, because the final approach of the translunar trajectory had to be perpendicular to the surface to direct the entire thrust of the retro-rocket straight downward. The control system of the vehicle was incapable of dealing with lateral velocity components. In practice, this limited the targets to western longitudes at latitudes that varied with the time of the year.

Luna 4 launch mass:	1.422 kg
Luna 5 launch mass:	1.476 kg
Luna 6 launch mass:	1.442 kg
Luna 7 launch mass:	1.506 kg
Lima 8 launch mass:	1.552 kg

Lander payload:

1. Panoramic camera

2. Radiation detector

The camera weighed 3.6 kg and drew 15 W. It was a single photometer directed at the zenith inside a pressurized glass cylinder and used a nodding and rotating mirror to scan the scene both horizontally and vertically. It could expose a full 360 degree panorama in an hour with a resolution of 5.5 mm at a distance of 1.5 meters. Three small dihedral mirrors on deployable poles facilitated 3-dimensional view s of small strips of the surface. Calibration targets were dangled from the four whip antennas.

which also provided a measurement of the lander’s tilt on the surface. The radiation detector was a miniature gas discharge Geiger counter.

Mission description:

Six of the first eleven Ye-6 spacecraft were lost to launch vehicle failures, and none of those that flew to the Moon achieved a soft landing.

The first spacecraft to launch, Ye-6 No.2, was stranded in Earth orbit on January 4, 1963, when the failure of the PT-500 transformer in the power supply of the new I-100 controller prevented the fourth stage from reigniting. This was the sixth failure for the fourth stage out of eight attempts to use it. The object was designated Sputnik 25 by the Americans but was not acknowledged by the Soviets, and it re-entered the following day. The second attempt with Ye-6 No.3 on February 3. 1963, failed even to reach orbit because the 1-100 provided an improper pitch angle to the trajectory control system after the separation of the core stage. The third stage did not fire and the remaining stack fell into the Pacific near Hawaii – although this was commented upon by the American press no explanation was forthcoming from the USSR.

With the I-100 control unit fixed, Ye-6 No.4 was successfully sent towards the Moon on April 2, 1963, as Luna 4. The Soviet press announced the launch, saying that scientists were w’orking on the task of landing on the Moon, and pontificated on the possibility of human flights. But the mood soon changed. By the next day it was clear that the navigation system had malfunctioned and that it would not be possible to make the planned mideourse correction. Luna 4 missed the Moon by 8.336 km at 13:25 UT on April 5, and a miffed Soviet press claimed that a flyby was all that had been intended. The spacecraft ceased to transmit on April 6. The Soviet Academy of Sciences undertook a review7 of the program, but could not determine precisely why Luna 4’s navigation system had failed. However, some issues were identified, and it W’-as apparent that the rushed program was suffering quality control problems. It was decided to add a backup radio direction finding system, but this took time and it was a year before the next launch.

Unfortunately Ye-6 No.6 failed to reach orbit on March 21, 1964, when the third stage had an oxygen valve problem, failed to deliver full thrust, and cut off early. An upper stage failure also caused the loss of Ye-6 No.5 on April 20, 1964. when the command to fire the fourth stage failed. Suspicion fell on either the PT-500 current converter or the 1-100 controller, and extensive new testing began on these devices. It took almost a year to complete testing and modifications. The sixth attempt with Ye – 6 No.9 on March 12. 1965, was lost w7hen the fourth stage did not ignite due to a failed transformer in the power system. Unlike the ease for the first Ye-6 launch, the spacecraft was acknowledged by the Soviets and designated Cosmos 60, but it was obviously a failed lunar mission. After so many problems, the entire guidance and control system for the upper stages was reworked using a new three-phase converter, and separate guidance systems installed on the third and fourth stages. This change did not even get a test when the seventh attempt on April 10, 1965. failed because a

Figure 9.3 Ye-6 flight profile (from Space Travel Encyclopedia)’. 1. Launch; 2. Parking orbit; 3. Translunar injection; 4. Fourth stage separation; 5. Telemetry for trajectory determination; 6. Trajectory correction; 7. Original trajectory; 8. Corrected trajectory; 9. Landing sequence initiation; 10. Determine lunar vertical; 11. Orient to lunar vertical; 12. Radar altimeter activated; 13. Altimeter fires retrorocket system; 14. Retrorocket burn:l 5. Landing.

Figure 9.4 Ye-6 soft landing profile (from Space Travel Encyclopedia): 1. Balloons inflated, encapsulated lander ejected at 14 m/s; 2. Impact with several bounces to final complete stop; 3. Balloon hemispheres separated by firing stitches around circumference 4. Petals are deployed from upper hemisphere to insure lander rests upright.

failed oxidizer pressurization system prevented the third stage engine from igniting, and the spacecraft. Ye-6 No.8. never reached orbit.

But Ye-6 No.10 was successfully dispatched towards the Moon on May 9. 1965. and announced as Luna 5. During the mideourse maneuver attempt on May 10. the gyroscopes in the I-100 guidance system were not given sufficient time to warm up and the spacecraft began to spin around its longitudinal axis. Engineers brought the spacecraft back under control and attempted the maneuver a second time, but sent it an incorrect command. By the time this was diagnosed it was too late to perform the maneuver. With the spacecraft on course to hit the Moon, albeit obliquely, it was decided to attempt to initiate the terminal maneuvers to exercise the system, but the guidance failed again and the engine did not fire. On May 12, the spacecraft hit the Moon at 1.6 S 25"W instead of the planned site at 31’S 8°W. becoming the second Soviet spacecraft to do so. Moscow, without portraying the mission as a failure, said a lot of information had been obtained ‘for the further development of a system for a soft landing on the Moon’s surface’’.

Ye-6 No.7 was launched on June 8. 1965, and successfully sent toward the Moon as Luna 6. The mideourse correction on June 9 began well, but a command error prevented the engine from cutting off, and it fired until the fuel was exhausted. This deflected the trajectory to such an extent that the spacecraft missed the Moon by 160,935 km on June 11, 1965. However, the engineers successfully put it through all of its landing sequence events.

An attempt to launch Ye-6 No. l 1 was canceled on September 4. 1965. when the core stage avionics failed in pre-flight testing. The vehicle was returned to the barn for major repairs to its control system. A month later, on October 4, this same rocket successfully dispatched Luna 7. This time the mideourse maneuver was performed successfully, making this the first Ye-6 in ten launches to be given the opportunity actually to attempt a lunar landing. However, in making its approach it lost attitude control, which prevented the retro-rocket from firing, and it crashed in the Ocean of Storms at 22:08:24 UT on October 7, at 9.8 N 47.8 W, west of the crater Kepler. An optical sensor had been set at the wrong angle and had lost sight of Earth during the attitude control maneuver immediately prior to starting the retro-rocket. As Moscow reported in its first admission of a failure. "Certain operations were not performed in accordance with the program and require additional optimization.”

Leonid Brezhnev, who had ousted Khrushchev the previous year, called Korolev to Moscow7 to account for the long string of failures. Korolev’s political charm stood him in good stead as he explained the difficulties and promised success with the next mission, due to launch in December. Although he did not deliver on this promise, he never had to face the new7 leadership again because he died during colon surgery on January 14. 1966. After the Moscow summons. Boris Chertok. a deputy at OKB-1. investigated the reliability and testing of spacecraft subsystems, and identified a lack of integrated testing of some subsystems during spacecraft assembly as a particular problem. Although corrective action was taken for the next launch, this was not in itself sufficient.

On December 4. 1965. Yc-6 No. l2 was launched into a lower inclination parking

orbit than its predecessors, at 51.6 degrees instead of 65 degrees. This allowed for a mass increase beyond 1.500 kg. The fourth stage then sent the spacecraft towards to Moon as Luna 8. The midcourse maneuver went well the following day, but alas the second Ye-8 to be presented with an opportunity to make a lunar landing failed. Just prior to retro-rocket ignition, the two airbags were inflated, as planned, but one was pierced by an improperly manufactured mounting bracket on a lander petal and the thrust of the escaping gas caused the spacecraft to spin. As a result, the retro-rocket cut off after just 9 of the required 42 seconds. The spacecraft crashed in the Ocean of Storms at 21:51:30 UT on December 6, at 9.ГК 63.3 W. to the west of the crater Kepler. The bracket problem was fixed, and on future missions the airbags would be inflated only after the retro-rocket had completed its burn.

Luna 8 was the eleventh straight failure in the Ye-8 program and the last before NPO-Lavochkin took over management of the Soviet lunar and planetary programs.

Results:

None.