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Above: PTK-Z spacecraft. Click arrow buttons to spin the vehicle.

Previous chapter: PPTS/PTK-NP development during 2010

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New Russian spacecraft might mimic classic Soyuz design

First published: 2010 Nov. 2

In October 2010, the Russian space agency, Roskosmos, published its requirements to the industry for the development of the Technical Project of the next-generation spacecraft, PTK NP. The document identified two versions of the spacecraft which would be a priority for the Technical Project in the next two years. The first of these two variants was the three-module PTK-Z spacecraft. It was designed for long-duration autonomous missions in Earth's orbit, while the two-module PTK-S variant was intended to service Earth-orbiting station, such as ISS.

PTK-Z spacecraft

According to Roskosmos, the PTK-Z spacecraft (where "Z" probably stands for "Zemnaya orbita" or Earth orbit) would fly scientific, application and experimental missions in Earth's orbit. As usual, the capabilities of the spacecraft were likely defined in coordination with RKK Energia, Russia's prime developer of manned spacecraft which would ultimately be responsible for the new generation of vehicles.

PTK-Z would have to be able to carry four people on a two-week mission, or provide for a reduced crew of two during an extended month-long flight. It would differ from the base version of the PTK NP spacecraft by a so-called Additional Pressurized Module, or "Dopolnitelny Germetichny Otsek, DGO," in Russian, which would be attached to the front of the cone-shaped crew capsule. Such a configuration would make the general arrangement of the spacecraft components very similar to those of the classic Soyuz spacecraft, with the returnable crew capsule in the center, the habitation module in front and the propulsion module in the back. However, unlike the Habitation Module of the Soyuz spacecraft, the DGO module would ride into orbit below the rest of the spacecraft. After reaching orbit and separating from the second stage of the launch vehicle, PTK-Z would turn around and dock to the DGO module mounted on the rocket stage. Only then would the completed three-module spacecraft separate from the empty rocket stage. Such a flight scenario was well familiar to Apollo astronauts. In each lunar expedition, the Apollo spacecraft, including the command and service modules, would have to turn around after separation from the upper stage of the Saturn rocket, in order to dock to the lunar module which during the launch was mounted on the rocket stage behind the manned portion of the spacecraft. Such an architecture was dictated primarily by the goal of having the crew capsule at the very top of the rocket during the ride to orbit, in order to simplify the escape system.

DGO module requirements

In the PTK-Z design, the DGO module would have to be capable of carrying no less than a ton of customized payloads and provide up to six cubic meters of volume for their accommodation. No less than 800 kilograms of instruments and equipment should be removable and returnable to Earth, the agency required.

The agency specifically requested the evaluation of the possibility of mounting external payloads on the DGO module with the help of "robotic means," a clear reference to the use of remotely controlled manipulator arms on the exterior of the spacecraft. The DGO module was also required to have at least two windows perpendicular to the axis of the spacecraft, probably intended for remote-sensing of the surface of the Earth, and astronomical observations of the sky. At least one window would have to be able to accommodate UV sensors.

Peculiarly, agency documents envisioned the dockings of the PTK-Z spacecraft to an orbital station, while carrying the DGO module or without it.

Roskosmos provided no specifications of the design of the DGO module and no visual references for this component had been officially released at the time. However as of 2010, it was widely believed that RKK Energia hoped to rely on the design of the ball-shaped Node Module proposed for the Russian segment of the International Space Station as a basis for the structure of the DGO. Unlike the station's Node Module, which was expected to carry six docking ports on its surface, the DGO module would only be equipped with two ports. One "passive" docking unit would be used for docking with the crew module of the PTK-Z spacecraft and one forward mechanism would be used to dock with the space station as necessary.

The design of the Russian Docking Compartment on the International Space Station was also rumored as a possible basis for the DGO module design. However due to the larger size and mass of the structure, it was considered a less likely candidate for the DGO design than the Node Module.

Other requirements

The PTK-Z spacecraft was expected to fly in regular orbits, which would be accessible from Vostochny launch site with an altitude of 200-500 kilometers and an inclination 51.7 degrees toward the Equator. Roskosmos asked the industry to additionally evaluate the possibility of bringing the ship into a radiation-prone altitude of 1,000 kilometers for as long as three days. Optional missions in higher inclination orbits would also be studied. As expected, the Rus-M rocket would be responsible for delivering the spacecraft into orbit.

In another peculiar development, the agency cited the accuracy of the landing radius for the PTK-Z spacecraft as five kilometers, which was a considerably "relaxed" target from the two-kilometer accuracy which Russian space officials and documents had quoted previously. This change likely reflected a recent decision to use parachutes during the nominal landing, instead of relying exclusively on rocket power.


Known PTK-Z specifications:

DGO module payload capacity no less than 1,000 kilograms
DGO module available payload volume no more than 6 cubic meters
Return to Earth payload capability no less than 800 kilograms
Power supply for payload in the DGO module no less than 2 kWatts
Standard operational orbit 200-500 kilometers; 51.7 degrees
Optional orbital inclination 63, 72, 83 and 98 degrees
Launch vehicle Rus-M

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Writing and illustrations by Anatoly Zak: Last update: March 25, 2011

Page editor: Alain Chabot; Last edit: March 25, 2011

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The PTK-Z spacecraft would use an additional pressurized module, DGO, based on the design of the Node Module, UM, of the International Space Station.

PTK with SO

A possible configuration of the PTK NP spacecraft with an additional pressurized module, DGO, which could be based on the Docking Compartment or the node module of the International Space Station. The head of the Russian space agency Anatoly Perminov first mentioned such an option in April 2010. Click to enlarge. Copyright © 2010 Anatoly Zak