CSTS

CSTS (Crew Space Transportation System)
ACTS (Advanced Crew Transportation System)

Proposed CSTS design (spring 2008)
Manufacturer	Korolev/RKK Energia, EADS Astrium (original proposal) EADS Astrium (later proposal)
Country of origin	ESA member states, Russia (original proposal) ESA member states (later proposal)
Operator	Russian Federal Space Agency, European Space Agency (original proposal) European Space Agency (later proposal)
Applications	Carry cosmonauts and astronauts to orbit and back (main goal) possible future improvements for beyond-LEO missions (additional goal)
Specifications
Regime	Low Earth orbit (main operations) circumlunar spaceflight (proposed beyond-LEO operations)
Production
Status	study phase, original proposal cancelled
Related spacecraft
Derived from	original version of PPTS (older proposal) Automated Transfer Vehicle evolution variant (later proposal)
Derivatives	PPTS (after Russian departure from the project)

CSTS (Crew Space Transportation System) or ACTS (Advanced Crew Transportation System) is a human spaceflight system proposal. It was originally a joint project between the European Space Agency (ESA) and the Russian Space Agency (FKA), but is now solely an ESA project. It aims to design a spacecraft for low Earth orbit operations such as servicing the International Space Station but also capable of exploration of the Moon and beyond. This study was conceived as a basic strategic plan to keep a viable European human space program alive because NASA officials had announced that NASA's Vision for Space Exploration Orion spacecraft, subsequently cancelled, would be developed without participation of international partners.

CSTS had completed an initial study phase, which lasted for 18 months from September 2006 to spring 2008, before the project was shut down before an ESA member state conference in November 2008. However, the head of the ESA denies that the ATV evolution plan is an alternative and talks are still ongoing as to whether or not to continue funding the ACTS plan. As of late November 2008, the project funding has been limited to a feasibility study with a launch of an actual vehicle possible no earlier than 2017.

In 2009 Russia decided it would go with a version of the original design of the CSTS and renamed it the "PPTS" or Prospective Piloted Transport System. ESA decided to go with an ACTS (Advanced Crew Transportation System), an evolution of the CSTS craft that would be an upgraded manned version of the ATV spacecraft. In mid-2009 EADS Astrium was awarded a €21 million study into designing a manned variation of the European ATV vehicle which is believed to now be the basis of the ACTS design. Since early 2013, ESA and NASA have begun cooperation on developing the Orion service module for the current version of the Orion spacecraft. This has cast previous ESA efforts concerning a manned derivative of the ATV spacecraft into uncertainty. As of summer 2015, no known new developments on the CSTS/ACTS project have been disclosed to the public.