Centaur launched 17 interplanetary missions during LeRC’s tenure. Every planet in the solar system was visited by a Centaur from a LeRC-led launch with the exception of Pluto.VIII Further, all first encounters with each planet
VII
The similar-to-GTO CRRES mission is included in this tally for convenience VIII
A Pluto flyby of a Centaur-launched (in January 2006) spacecraft will take place in July 2015, long after LeRC
were made by a Centaur-launched mission with the exception of Venus. In fact, with the exception of Mariners 2 & 4, every successful US interplanetary mission until the late 1980’s was launched on Centaur. Interplanetary missions were the second largest group (21%) of missions based on destination (see Fig. 21). But unlike the GEO missions, they were anything but routine trajectories. Though their final targets in DUKSUP were always hyperbolic orbital energy (C3) and declination, their values were significantly different depending on their planetary targets, and even between the launch opportunities for the same mission. Figure 23 illustrates the hyperbolic flight path of the spacecraft following Centaur injection burn. 21 Also shown are the declination (δ) and right ascension (α) of the outgoing asymptote of the hyperbola. Like the Surveyors, the interplanetary missions were high change in velocity ( ΔV) and usually two burn (though some were single burn). The duration of three phases of flight were optimized: the Centaur burns and the intervening parking orbit coast. Relatively speaking, even though the hyperbolic targets changed due to the relative motion of the planets, these missions were simpler to model than GEO missions.
Interplanetary missions in the late 1960’s (Mariners 6-9 and Pioneers 10-11) were launched by LeRC on Atlas/Centaur, but these were not initially analyzed with DUKSUP. Beginning in the 1970’s, there were various interplanetary missions following NASA’s decision to integrate the Centaur with the USAF’s Titan IIIE booster and continue the Atlas/Centaur even though the Space Shuttle decision was looming in the near future. DUKSUP was then modified to support Titan. After the single test flight, all of the six Titan IIIE/Centaur missions were interplanetary: two launches of the Viking orbiter/lander mission to Mars (targeted for landing in 1976 --- two hundred years after the Declaration of Independence), two launches of Helios for the Germans into heliocentric orbit, and two Voyager missions to Jupiter and Saturn (and later on to Uranus & Neptune). Other Atlas/Centaur missions such as Mariner 10, the two Pioneer Venus, and SOHO launches followed and were supported by DUKSUP. (see Fig. 22). The last interplanetary mission for LeRC-led Centaur was the Cassini mission to Saturn --- the largest launch vehicle and largest spacecraft ever launched by LeRC. Of the 17 missions, 16 were successful.IX
There were other interplanetary missions which were within only four months of launch, yet never flew on their intended launch vehicle. They were manifested on the new Shuttle/Centaur vehicle. The Galileo mission to Jupiter and solar polar Ulysses mission were to use Shuttle/Centaur to place these high C3/heavy payloads on “fast” trajectories to Jupiter (Ulysses used it for gravity assist out of the ecliptic plane). In addition, the Mars mission Magellan was also slated to fly on the smaller version of the Shuttle/Centaur. (see Section VI.C.).
IX
The failure of the sole test flight of the Titan IIIE/Centaur is tallied under “R&D”.
Unlike most Earth-orbital missions, the use of the Shuttle introduced a new variable: which orbit the Centaur and payload could be separated from the Orbiter (multi-revolution deployment). Since the Shuttle was in a low Earth orbit, the node was constantly regressing, significantly altering the initial state vector for the analysis. The optimum right ascension of the ascending node had to be first calculated, then fixed for the targeted deployment revolution. For the escape missions, Shuttle launch time and azimuth took on added importance. This was accommodated by numerically integrating the Shuttle coast orbit and optimizing the burn time of the Centaur stage. To obtain a launch window, the injection right ascension was varied around the optimum to assess the penalties for launch windows. Delayed deployment meant a misalignment of the right ascension of the ascending node (RAAN) of the outbound hyperbolic asymptote. This drove the DUKSUP analysis for the first time to multiple launch window analysis, where inertial targets had to be updated for each run and RAAN had to be modeled to generate the launch windows.
After the Challenger accident of January 28, 1986 (about four months prior to the planned launch date for the first missions: Galileo & Ulysses), it was clear that any reduction in Shuttle lift capability due to the accident would preclude doing any of the missions planned for the Shuttle/Centaur combination. On June 19, 1986, the Shuttle/Centaur project was cancelled. All missions were re-assigned to other vehicles.
Finally, one aspect of the interplanetary missions (and some of the Earth orbital missions as well) was that LeRC management usually provided a guarantee of performance to the spacecraft project office at other Centers (JPL in the case of the Mariner missions and Ames in case of the Pioneer missions). The LeRC Center Director signed a letter to the spacecraft project guaranteeing the payload weight to a specified target such that the spacecraft project could proceed with spacecraft development. The implication of these letters could be immense: they fundamentally drove major decisions on spacecraft valued in the multi-$100’s M range (and a launch vehicle of comparable cost). DUKSUP was the analytic tool used to calculate that guarantee. Around this way of doing business evolved a culture at LeRC of how performance analysis should be done, how various margins should be accounted for, that analysis ground rules be explicitly specified, the way nominal vs. dispersed values should be handled, and that performance guarantees should be made with “3σ” confidence. These engineering design philosophies were consistent with similar USAF methods, and as the commercial launch world developed they were continued.