Meanwhile Venera 5 was launched from its parking orbit towards Venus to obtain atmospheric data. The spacecraft was very similar to Venera 4 although it was of a stronger design. When the atmosphere of Venus was approached, a capsule weighing 405 kg and containing scientific instruments was jettisoned from the main spacecraft. During satellite descent towards the surface of Venus, a parachute opened to slow the rate of descent. For 53 min on May 16, 1969, while the capsule was suspended from the parachute, data from the Venusian atmosphere were returned. The spacecraft also carried a medallion bearing the coat of arms of the U.S.S.R. and a bas-relief of V.I. Lenin to the night side of Venus. References: 2, 6, 64, 296, 367.

Rocketdyne and Pratt & Whitney were selected for the Phase A, advanced study phase of the competition. The same basic engine (combustion chamber and turbomachinery) was to be used in both stages of the planned two-stage fully-recoverable shuttle. The orbiter would be equipped with a two-position deployable nozzle, with expansion ratios of 58:1 for the low altitude portion of the ascent, and 120:1 with the extension deployed for the vacuum portion of the flight to orbit. The engine was to have a thrust of 270,000 kgf in vacuum, 235,000 kgf at sea level, and be throttleable from 73% to 100% of the rated thrust. The engine for the booster was to use a 5:1 ratio expansion nozzle, producing 227,000 kgf at sea level. Pratt & Whitney seemed to have a clear lead in this portion of the competition, having produced the XLR-129-P-1, a prototype high-pressure Lox/LH2 engine under USAF contract. This produced 188,000 kgf using a smaller fixed nozzle. Most of the shuttle bidders proposed use of this engine in their Phase A vehicle designs.

The Space Task Group put together to run the shuttle design process was composed of various agencies of the federal government. Each group favoured differing basic configurations for the shuttle, reflecting controversies extending back over ten years to the time of DynaSoar development. Faget at NASA Houston favoured a straight-wing orbiter, the bottom surface being essentially a cross shape cut out of the spherical section of one of the Apollo or Mercury heat shields he had designed. This had minimal cross range, but was supposed to have the advantages of minimum weight and good subsonic glide performance. NASA Langley and Edwards AFB favoured a lifting body, based on the HL-10 shape under test there. This had supposed weight advantages over a winged vehicle, more cross range than Faget's straight wing, but less cross range than a delta wing. USAF Flight Dynamics Laboratory and Draper Laboratories favoured a swept delta wing spaceplane, like the Dynasoar, for maximum cross range on re-entry.

Faget favoured a small net payload to orbit (6800 kg) while the other government centres favoured heavier payloads, at least 11,300 kg, and up to 29,500 kg. As in the case of earlier USAF ILRV studies, the Space Task Group had initially considered three categories of launch solutions. Class I used an existing expendable launch vehicle (the Titan 3MV or Saturn IB) and a reusable orbiter. Class II were 1.5 stage to orbit designs, using an orbiter vehicle and a drop tank. Class III were fully reusable two-stage-to-orbit designs. In contrast to the USAF studies, which favoured immediate development of a Class I vehicle, followed by a Class II vehicle, Task Group's preferred solution was to proceed immediately with a Class III vehicle. References: 44.

• Apollo 9 - February 28, SA-504, CSM 104, LM-3; manned orbital; up to 10 days' duration; Atlantic recovery.
• Apollo 10 - May 17, SA-505, CSM 106, LM-4; manned lunar mission, Pacific recovery.
• Apollo 11 - SA-506, CSM 107, LM-5; manned lunar mission; up to 11 days' duration; Pacific recovery.
• Apollo 12 - SA-507, CSM 108, LM-6; manned lunar mission; up to 11 days; Pacific recovery.
• Apollo 13 - SA-508, CSM 109, LM-7; manned lunar mission; up to 11 days' duration; Pacific recovery.

• At a funding level of $8 to $ 10 billion a year indefinitely, NASA could do it all - a manned expedition to Mars, permanent manned space bases in lunar orbit and the lunar surface, a 50-person space station in earth orbit, and a reusable space shuttle to support all of these projects on an economical basis
• All of the objectives could be achieved, but the funding level kept at $ 8 billion per year, by deleting the manned lunar orbit station
• At $ 5 billion per year, a program consisting of just the earth orbit station and the space shuttle could be funded - but no further manned exploration of the moon or planets

Nixon rejected all of the alternatives and wanted something even cheaper.

The Mariner 6 spacecraft was removed, put on another Atlas/Centaur, and launched on schedule. The main booster was jettisoned 4 min. 38 sec. after launch, followed by a 7.5 minute Centaur burn to inject the spacecraft into Mars direct trajectory. After Mariner 6 separated from the Centaur the solar panels were deployed. A midcourse correction involving a 5.35 second burn of the hydrazine rocket occurred on 1 March 1969. A few days later explosive valves were deployed to unlatch the scan platform. Some bright particles released during the explosion distracted the Canopus sensor, and attitude lock was lost temporarily. It was decided to place the spacecraft on inertial guidance for the Mars flyby to prevent a similar occurrence.

On 29 July, 50 hours before closest approach, the scan platform was pointed to Mars and the scientific instruments turned on. Imaging of Mars began 2 hours later. For the next 41 hours, 49 approach images (plus a 50th fractional image) of Mars were taken through the narrow-angle camera. At 05:03 UT on 31 July the near-encounter phase began, including collection of 26 close-up images. Due to a cooling system failure, channel 1 of the IR spectrometer did not cool sufficiently to allow measurements from 6 to 14 micrometers so no infrared data were obtained over this range. Closest approach occurred at 05:19:07 UT at a distance of 3431 km from the martian surface. Eleven minutes later Mariner 6 passed behind Mars and reappeared after 25 minutes. X-band occultation data were taken during the entrance and exit phases. Science and imaging data were played back and transmitted over the next few days. The spacecraft was then returned to cruise mode which included engineering and communications tests, star photography TV tests, and UV scans of the Milky Way and an area containing comet 1969-B. Periodic tracking of the spacecraft in its heliocentric orbit was also done.

Science Results

Mariner 6 returned 49 far encounter and 26 near encounter images of Mars. Close-ups from the near encounter phases covered 20% of the surface. The spacecraft instruments measured UV and IR emissions and radio refractivity of the Martian atmosphere. Images showed the surface of Mars to be very different from that of the Moon, in some contrast to the results from Mariner 4. The south polar cap was identified as being composed p