Acts
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ACTS (Advanced Crew Transportation System) is a crew transportation system which is jointly studied by the European Space Agency (ESA) and the Russian Space Agency (Roskosmos) with the objective to design a spacecraft for LEO operations such as servicing the International Space Station but also capable of exploration of the Moon and beyond. ESA officials have stated that this study is a response to NASA's Vision for Space Exploration and the Crew Exploration Vehicle which NASA wants to develop without participation of international partners. According to press releases that are available at the moment, JAXA could join the cooperation as well. ACTS is currently in an initial study phase, which shall last for two years from 2006 to 2008. The outcome of the study is planned to be presented to the ESA full memberstate conference in 2008.
Background
ACTS as answer to the CEV
In 2004 George W. Bush announced the Vision for Space Exploration, a program that includes the United States return to the Moon by 2020 and a manned mission to Mars by 2030. For these purposes the Crew Exploration Vehicle is currently being developed. ESA officials have formally asked NASA to be part of this program for exploration, however received a negative response. Jean-Jacques Dordain, ESA's General Director stated with regard to this rejection by NASA: "I have been told by Mike Griffin and Marburger that the CEV is not for international cooperation. But if Europe is not involved in the next-generation transportation systems, we will stay forever a second-class partner."http://www.planetary.org/news/2006/0628_Europe_and_Russia_Join_Forces_to_Study.html
If the CEV could not be developed or used in cooperation with ESA, ESA would face a major obstacle for continuation of its manned spaceflight program with the end of the Space Shuttle program by 2010 and the contemplated end of the International Space Station program by 2015/2016.
Cooperation with Russia
Since 2004, ESA has been in talks with Roskosmos on a cooperation for the development of Kliper, the Russian successor project to the Soyuz spacecraft which has been in service for nearly 40 years. While ESA's management was enthusiastic about this cooperation, ESA memberstates turned down funding for a design and collaboration study in December 2005, mainly because certain memberstates did feel that ESA would just be a minor industrial contributor to the program, while Russia would actually develop and design the Kliper spacecraft.
After the December 2005 rejection of Kliper by ESA, Jean-Jacques Dordain emphasized that a collaboration with Russia on a new spacecraft could still be decided in June 2006. On June 13, 2006 the press reported that the winged Kliper project has been replaced by a study to develop a capsule under the Advanced Crew Transportation System program that ESA is funding.http://www.flightglobal.com/Articles/2006/06/13/Navigation/177/207228/Kliper+dropped+for+lunar+capsule.html It is however necessary to understand that Kliper was a Russian program that might still be funded entirely by Roskosmos - this is however unlikely to happen if Russia and Europe really go forward with ACTS together. Reasons for going with ACTS include that it gives Europe the possibility to be a full partner in a Russian-European program, because the modular structure (see below) allows to divide responsibilities for design to each partner (for instance Russia could be in charge of the overall design of the reentry capsule, while ESA works on the habitation module etc.)
About €15 million have been currently pledged for the ACTS program on ESA's regular meeting on June 21 and June 22, 2006. Further funding of the study will be asked for at the next ESA meeting in July. Both partners, Russia and ESA, will bear their own costs in the first 2 years of the program. "We are now entering a phase of working with the Russians where we will establish a preliminary design of the vehicle, establish all the legal framework for the operation, delineate the work share for the parties, and outline the aspects of development," said Manuel Valls, head of Policy and Plans Department in ESA's Directorate of Human Spaceflight, Microgravity, and Exploration Program.
On July 4, 2006 Russian media reported that the head of the Russian Space Agency Anatoly Perminov has met with Jean-Jacques Dordain to discuss the ACTS proposal, however no agreement was signed between the Russians and Europeans after that meeting.http://www.mosnews.com/news/2006/07/04/russianasaiss.shtml
Overall Design
Three module design
The Soyuz three module design will be followed by ACTS as well
ACTS, designed for exploration missions, will feature as re-entry vehicle an improved, Soyuz-type capsule, having increased resources for extended missions duration, improved thermal protection system for reentry into Earth's atmosphere with a higher velocity than just from LEO, new interplanetary navigation systems and possibly an increased size to accommodate a larger crew of 4 members. It will also include a habitation module (like the orbital module on the Soyuz) large enough to accommodate the necessary equipment and resources, as well as to provide the necessary living space to the crew for the longer duration missions. A service module, including attitude control thrusters, oxygen tanks, TCS, Motion Control Systems data handling and distribution, command system, telemetry and feedback the main propulsion system and other subsystems, including solar arrays, electrical power control system, etc. http://www.flightglobal.com/Articles/2006/06/13/207228/Kliper+dropped+for+lunar+capsule.html
The three-part design of ACTS is similar to the one used on Soyuz. The advantages of using such a system instead of the two-part CEV structure (only a crew module that is also used as re-entry module and one service module), is that the re-entry module can be stripped down to a minimum size and weight, as it is not necessary for the crew to stay in the re-entry module for the whole mission duration but the crew can use the habitation module as well. Because the habitation module is discarded before reentry into Earth's atmosphere, it can be made out of light-weigh material that does not need to withstand the forces of a re-entry. This approach reduces overall weigh of the spacecraft.
The re-entry module
Soyuz uses a bell-shaped re-entry module that has space for three cosmonauts. Its weight is approximately 2.8 metric tons. The ACTS study will have to decide whether they are using the same bell-shaped form for the 4 crew re-entry module or which other configuration the re-entry module will take (cone-shaped such as the Apollo spacecraft or the CEV). What is clear today is that the re-entry module will be a capsule and not a lifting body, which reduces complexity of the system. While the CEV crew module is currently designed to weigh over 9 metric tons, the ACTS re-entry capsule will probably weigh much less, as living space for the whole spacecraft is divided into the re-entry module and habitation module.The habitation module
ATV - heritage to be used for ACTS
For spaceflights beyond LEO, it is necessary to accommodate certain equipment and appliances (toilet etc.) in a spacecraft. This habitation module could be derived from hardware that has already been developed by ESA, that is the Automated Transfer Vehicle or the Columbus Orbital Laboratory.
The service module
Power and propulsion needs to be provided by another module. Heritage for this module may come from both the Soyuz spacecraft or the Automated Transfer Vehicle. In light of a mission beyond LEO this module will however be by far the largest of the three modules the spacecraft consists of (see below).Missions beyond LEO
Launchers
To understand the ACTS mission parameters it is first important to understand what limitations ACTS will have to deal with. Manuel Valls, head of Policy and Plans Department in ESA's Directorate of Human Spaceflight, Microgravity, and Exploration Program noted on the question of available launch vehicles for the ACTS spacecraft that "although nothing at this stage is definitive, [...] both the Russians and we think that it is only prudent, and most efficient and effective, to go with 2 stages and not one. The 1-stage has been done already with Saturn V and Apollo. To do that now would entail the development of quite a new launcher and that will take time and money like hell, if I may say. Going with two stages is far more effective [...] because we could use – and this is our intention – existing launch vehicles or launch vehicles with minimal development." This means that ACTS will have a tight mass budget, as only launchers with a maximum payload capacity in the class of Ariane 5, Proton or Angara will be available for a launch. With '2 stages' and LEO docking that means that ACTS together with an Earth Departure Stage will not be able to weigh more than about 45 to 50 metric tons in LEO (note however that this is just for the lunar spacecraft, a lunar lander is not integrated in this calculation).
An ESA presentation from June 13, 2006 however presents a lunar orbital mission of the ACTS spacecraft with 3 launches, of that 2 are propulsion modules to propel the spacecraft to a trans-lunar trajectory. Such a scenario, while more complicated than the 2-stage approach mentioned by Manuel Valls, gives more leeway in terms of the ACTS' mass budget.
Scaling the ACTS for a lunar mission
lunar orbit insertation architecture with 3 launches (note that the lunar lander in this picture is only for illustration purposes and is not included in the 3 launches scenario and has to be deployed to the moon separately)
With the limitations on launch vehicles in mind, the size and weight restrictions of the ACTS spacecraft allows to give a good sense of how large the spacecraft may actually be. A two launcher scenario would bring an Earth Departure Stage (EDS) to LEO with one launcher and the ACTS spacecraft with the other launcher. One LEO docking would be needed after that the ACTS spacecraft would be propelled to a trans-lunar injectory (TLI). Assuming that the partners would develop a 25 ton EDS such as an enhanced Block-D or KVRB, the ACTS spacecraft would be limited to a 16-17 metric ton mass at the outmost if only the EDS would do the TLI burn - in this scenario the ACTS spacecraft could be launched by a Soyuz-3 that is currently contemplated to be developed and would be able to carry up to 16-17 tons into LEO http://russianspaceweb.com/soyuz3_lv.html, while the EDS would be launched either by Ariane 5, Proton or Angara. However it is a possibility that the ACTS spacecraft does part of the TLI burn with its own service module, in this case it could be scaled up to the max payload of Ariane, Proton or Angara.
In any event, to reach (Lunar orbit injection (LOI)) and leave (Trans-earth injection (TEI)) lunar orbit after TLI the minimum required delta-v is about 2.5 km/s. With storable propellant (isp 360 sec) at least 50% of the spacecraft mass needs to consist of propellant. A 17 ton spacecraft would thus need to consist of at least a 10-12 tons service module (8.5-9 ton of propellant and the rest structure and power supply). This leaves about 5-6 tons for both the re-entry and the habitation module together (note that the Soyuz re-entry capsule and orbital module already weighes 4.2 tons while only being used for short LEO mission with 3 crew members). The Soyuz re-entry capsule weighs 2.8 tons, enlarging it to accommodate 4 crewmembers and enhancing the heatshield for rentry from TEI (higher velocity) will at a minimum require it to weigh 3.5 tons. That leaves 2-2.5 tons for the habitation module, compared to the 1.3 tons of the Soyuz orbital module an increase that could work for a lunar mission.
The constraints outlined above are lower if the ACTS spacecraft does part of the TLI burn, in this case the mass of the ACTS spacecraft could be about 20 tons after completed TLI-burn. In this scenario about 6.5-7 tons of the spacecraft could be allocated to the re-entry capsule and habitation module. http://www.mars-lunar.net/Lunar%20Mission%20models/lunar.orbit.and.back.pdf Spreadsheet for lunar orbit mission delta-v and mass of spacecraft (pdf)
Another scenario would be a three launch mission involving the Soyuz-2 vehicle in a further developed stadium (a Soyuz 2-3 with a LEO payload mass of 12.7 t from Kourou is currently in development and scheduled to be ready in 2010 ). In a 3-launch scenario, the crew would be launched on the ACTS spacecraft on the Soyuz and two EDS (launched by Ariane 5, Proton or Angara) would be utilized for the TLI burn and LOI burn. One of the unmanned launches would carry both an EDS and a TEI stage. The advantage of this strategy would be that the manned spacecraft could be launched by the Soyuz (although enhanced, the Soyuz 2-3 would still have the same dimensions as the current Soyuz), which has a 40 year track record of human flight.
Scenario
Mass in LEO
Maximum mass of ACTS Crew Module + Habitation Module
Delta-v provided by EDS for TLI burn
Delta-v provided by ACTS Service Module for TLI burn
Mass after TLI burn
Mass after LOI burn
Mass after TEI burn, propellant used for plane changes and dockings in LLO
Soyuz-3 and Ariane 5/Angara 5 class option
40 ton (ACTS spacecraft = 16 tons)
5.5 tons
3.2 km/s
0 km/s
16 tons (with dry EDS 19.5 tons)
12.5 tons
8-9 tons
2×Ariane 5/Angara 5 class option
50 ton (ACTS spacecraft = 25 tons)
7 tons
2.4 km/s
0.8 km/s
20 tons (dry EDS jettonised before second burn)
16 tons
10-11 tons
Soyuz-2-3 and 2×Ariane 5/Angara 5 class option
62 ton (ACTS spacecraft = 12.5 tons)
9-9.5 tons
3.2 km/s (1.9 km/s by EDS-1, 1.3 km/s by EDS-2)
0 km/s
27 tons
20 tons (dry EDS-2 jettonised - EDS-2 does LOI)
12 tons (dry TEI-stage jettonised after TEI)
A lunar lander (LM)
The Apollo LM weighed about 15 tons and was designed for a max. 3 day mission for 2 crew members
Press coverage of the ACTS study up to now only talks of the ACTS spacecraft itself, not of any other equipment and vehicles needed for a lunar mission (apart from just a lunar flyby or lunar orbital mission). If the ACTS spacecraft is launched as outlined above, the best possible solution for a lunar landing is to rendezvous the ACTS spacecraft with a Lunar Lander Module in Lower Lunar Orbit (LLO). Otherwise three or more dockings would be required in LEO which leads to a far too complicated mission. With the LLO approach the overall dockings with by the ACTS spacecraft would be two, in LEO with the EDS and in LLO with the LM. The advantages of this approach are that the ACTS spacecraft is independent of the actual design of an LM. That leaves the design of the LM flexible and even allows for the use of different LM vehicles for different missions.
A heavy variant of the LM could be deployed to lunar orbit in the same way that the ACTS spacecraft is. One launcher would bring the LM into LEO and another launcher the EDS (the same hardware used for the ACTS spacecraft). The LM does part of TLI (like the ACTS spacecraft) and all of LOI. Assuming the LM weights about 20-25 tons in LEO and assuming a KVRB-EDS of the same mass is used, the LM in lunar orbit could still weigh about 14-15tons. This is the same mass that the Apollo LM weighed. However today the isp for storable propellant is higher than the 311 sec isp the Apollo LM engines could provide. This leaves a higher cargo and crew capacity to lunar surface with this LM, which would allow lunar landings of 3 or 4 astronauts/cosmonauts or landings with 2 crewmembers with a longer mission duration.
In a light variant an LM could be directly launched to LOI (the most capable Ariane 5 (ECA) today could launch 10.5 tons to GTO, from where this LM would do the rest of TLI and LOI and would end up with about 6tons in LLO). Designed as an open-cap lunar lander, this vehicle could be used to bring astronauts or cosmonauts to a predeployed lunar base in a more cost-effective way, as the total mission scenario would only use 3 launchers instead of 4 as outlined above.
Launch Sites
Both the ESA's launch site at French Guiana and the Russian spaceports at Baikonour and Plesetsk are discussed to be utilized for ACTS.See also
References
External links
- [ESA presentation on ACTS dated June 13, 2005 (pdf)]
- [Europe and Russia Join Forces to Study Advanced Crew Transportation System]
- [ESA, Russia to Collaborate on New Spacecraft Design]
- [ESA to finalise manned capsule contributions at July meeting]
- [Kliper dropped for lunar capsule]
- http://www.mars-lunar.net/Lunar%20Mission%20models/lunar.orbit.and.back.pdf Spreadsheet for lunar orbit mission delta-v and mass of spacecraft (pdf)
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All text is available under the terms of the GNU Free Documentation License See Wikipedia Copyrights for details.