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Origin of the PTK landing system A defining feature of Russia's new-generation PPTS spacecraft would be its landing system. Due to the political requirement to land future manned missions in Russia, while the spacecraft would barely overfly the south of the country, a lot of maneuverability would be required from the descent module. At the same time, tough deadlines imposed on the development of the vehicle and limited funds, left little room for radical solutions.
Landing profile As envisioned in 2008, during its three-hour trip back to Earth, the ACTS/PTK spacecraft would conduct a deorbiting engine burn to slow itself down by 130 meters per second. The service compartment would then be jettisoned to burn up in the atmosphere, while the crew module would conduct a 40-minute reentry and touchdown with the help of solid-propellant soft-landing engines. (300) Combined with retractable landing legs and a reusable thermal protection system, 12 solid-propellant landing rockets promised to enable not only safe return to Earth, but also the possibility of multiple space missions of the same crew capsule. According to the presentation made by Nikolai Bryukhanov, the leading designer at RKK Energia, at the 26th International Symposium on Space Technology and Science in Hamamatsu, Japan, in the summer of 2008, the spacecraft would fire its engines at an altitude of just 600-800 meters, as the capsule was streaking toward Earth after reentering the atmosphere at the end of its mission. After a vertical descent, precision landing would be initiated at an altitude of 30 meters above the surface. Russian engineers arrived at this unusual design of the future spacecraft via a long and arduous path of conflicting requirements and compromises. In 2007, the Russian government made the momentous decision to build a new launch site in the nation’s Far East, hoping to end Russia’s dependency on the spaceport in Baikonur, located in the former Soviet republic of Kazakhstan. The future site would be located almost as far south as Baikonur, an important orbital mechanics factor, determining the cargo capacity of rockets. However, the very same decision left only a narrow strip of land in the European part of Russia, near the city of Orenburg, for returning space capsules to land if they followed their traditional inflexible path of reentry. Within the available territory of southern Russia considerable areas had to be eliminated due to tough requirements for the nature of the soil, wind speed and the absence of any man-made structures. (357) Not surprisingly, Russian engineers found themselves under political pressure to improve the maneuverability of the future spacecraft, so it could guide itself into a circular landing area with a radius of only two kilometers, instead of being at the mercy of winds, when landing under a parachute in the endless flatlands of Kazakhstan. Radical solutions like aircraft shapes and "transformers" with deployable wings were deemed too expensive and technically risky, given the concurrent requirement of the Russian government to have the new spacecraft ready for a first manned mission in 2018. Eventually, a capsule with rocket-assisted landing emerged as a winning combination, promising to keep the predicted touchdown to a piece of land of only two by five kilometers. As of March 2009, in its official requirements for the PPTS system, Roskosmos "relaxed" its requirements for the accuracy of the PPTS touchdown to 10 kilometers, while still directing the industry to continue studying various alternative modes of high-precision landing. In any case, the crew capsule had to have a capability to conduct an emergency return to Earth either from orbit, or during a powered flight to orbit, with the ability to touch down in any season on any unprepared piece of land or at sea, the agency's requirements said. Emergency escape and landing capabilities were mandated for every phase of the mission and had to provide the survivability of the crew until the arrival of the rescue and recovery teams. Thrust control for solid-propellant motors
Click play button to watch the animation of the nominal landing considered for the PPTS spacecraft as of 2009. QuickTime version of this video can viewed here. Copyright © 2009 Anatoly Zak On April 12, 2009, RIA Novosti quoted an unnamed space official as saying that the new spacecraft would land under rocket power, using environmentally clean engines, possibly burning alcohol. Although it probably reflected alternative proposals floating in development circles, solid motors were still likely considered as the most feasible landing system for the PPTS spacecraft. (As it transpired later, that source likely referred to attitude control thrusters using alcohol, rather than soft-landing engines.) In the meantime, reports surfaced about a new configuration of the solid-propellant landing engines favored for the PPTS system. Instead of 12 independent engines each with an individual nozzle, which had been mulled during 2008, solid-propellant charges now carried multiple nozzles, apparently to enable thrust control during descent. A steering (gimbal) mechanism attached to the nozzles would allow adjusting the thrust vector of the engine, while the solid motor itself would remain in a fixed position relative to the main body of the spacecraft. Thus, steering of the descent module into a precise landing site would become possible. The design was reportedly based on existing Russian hardware (possibly from the field of ballistic missiles), thus ensuring low-risk and low-cost development of the landing system. During 2009, RKK Energia sources were apparently reluctant to disclose the developer of the prospective rocket-assisted landing system, probably hinting at the involvement of a military contractor. If successful, the creation of the rocket-assisted landing system would benefit the future development of lunar and martian landers, Russian officials said. (357) Alternatives to rocket landing As an alternative solution, RKK Energia representatives reportedly considered a nominal splashdown of the new spacecraft into the Pacific Ocean, instead of the traditional land-based landing practiced by the Russian manned space program since its inception. Water landings would be supported by rescue and recovery ships, which would have to be deployed in the Pacific anyway to provide emergency services to the crew in case of an accident during launch from Vostochny. However such a proposal apparently would still fail to eliminate the requirement for a powered, high-precision landing, since during the initial phase of its flight from Vostochny, the spacecraft would overfly the evergreen forests of the Russian Far East, and in case of emergency, would have to be able to steer itself into a limited size landing area. A compromise of rockets and a parachute As yet another option, a parachute was proposed for use in case of emergency. However, due to weight restrictions on the parachute landing, it was necessary to separate the reentry vehicle into a 4.5-ton crew module and a bottom propulsion section. The landing hardware kit, known by the Russian abbreviation KSP, including the parachute, was expected to weigh around 250 kilograms. In case of problems with the soft-landing engine, the propulsion section would be jettisoned and the crew module would land under the parachute. This method apparently became a favorite by April 2009. Still, skeptics of rocket-powered landing claimed that developers would eventually return to traditional parachute landing. With the official start of the PTK NP project in the spring of 2009, the President of RKK Energia Vitaly Lopota said that despite a superficial resemblance to the US Orion spacecraft, the Russian vehicle would have distinct features, reflecting Russia's specifics. It was a clear hint about the rocket-powered landing without the use of a parachute, which was considered for the new spacecraft. In a previous interview to Rossiskaya Gazeta, Lopota stressed that the provision of launching and landing the spacecraft on the Russian territory would be decisive in determining its design. (330) Parachute gets a role in nominal landing On June 2, 2010, RKK Energia released a vague statement, which contained a rather typical reaction to recent coverage of the PTK NP project in the Russian press, especially, doubts expressed by observers about the rocket-powered landing. While providing little information on the current state of the project, the press release dismissed unnamed press reports as "authors' speculations based on previous phases of the spacecraft development." The document went on saying that the company and its contractors had come to the conclusion that a "parachute-reactive" landing would be the most suitable for the reentry capsule, known as VA. It hinted that some sort of combination of a multi-cupola parachute system, rocket engines and retractable landing legs would be employed to control vertical and horizontal motions of the capsule during landing. However, as it transpired, the approved preliminary design of the PTK NP still called for nominal landing under sole power of rocket engines, while parachutes would be employed in an emergency only. Therefore, the basic concept of the rocket-powered landing, as it was envisioned in 2008-2009 had not changed, as the June 2 statement implied. The RKK Energia statement also said that an effective, quick-disconnect and expendable thermal shielding had been developed, apparently referring to a jettisonable heat shield protecting the landing gear. The architecture of the spacecraft was updated and new progressive technologies were proposed with a spin-off potential for aviation and other industries, RKK Energia said. During the 61st International Astronautical Congress, in September 2010, Aleksandr Krasnov, the head of the manned space flight directorate at Roskosmos, told the editor of this web site that the ship’s nominal landing profile would use a combination of parachutes and rocket engines. According to sources at RKK Energia, the prime developer of the next-generation spacecraft, the debate on the exact design of the landing system of the future spacecraft still continued. Few weeks later, Vitaly Lopota, president of RKK Energia, confirmed that a combination of rockets and parachutes would be used for landing. The accuracy of landing was still cited at two kilometers and the primary location of landing remained in the vicinity of the Vostochny launch site. However, no detailed technical information on the landing system and its functioning during nominal and emergency flight modes had yet been released at the time.
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