With Dragon now returned to flight and safely berthed to the ISS, time is ticking closer to the start of commercial crew transportation services to the station. In line with this, NASA’s plans for future crew rotations are solidifying, as opportunities have emerged to increase NASA’s crew count earlier than planned.
Commercial crew schedule:
The future schedule currently planned for commercial crew vehicles was detailed in the latest Flight Planning Integration Panel (FPIP) long term manifest presentation in L2, a notional planning document used by the ISS Program to track future launches and crew rotations through into the 2020s.
Regarding demonstration flights, the SpX-Demo1 flight, which will be a two-week un-crewed test of the Dragon crew vehicle, will occur from 11 to 25 November 2017.
This will be followed by a month-long crewed test of Dragon on the SpX-Demo2 flight throughout May 2018.
Following hot on the heels, the Boe-OFT flight, which will be an uncrewed test of the Boeing CST-100 spacecraft, will then occur throughout June 2018.
A roughly two-week crewed test flight of CST-100 will then occur in August 2018, ready for the start of limited operational commercial crew flights starting in late September 2018.
The ISS was originally designed to support a crew of seven – three on the Russian Segment (RS), and four on the United States Orbital Segment (USOS).
This would have been achieved via the use of two Soyuzes, carrying six crewmembers between them, with the seventh rotating via the US Space Shuttle, and the Crew Return Vehicle (CRV) serving as a lifeboat for all seven crewmembers.
However, with the Space Shuttle’s retirement and the cancellation of the CRV, leaving Soyuz as the only method of crew transportation to and from the station, the ISS crew has been limited to six crewmembers – typically three Russian cosmonauts, and three NASA/ESA/JAXA astronauts.
But with the new generation of US commercial crew vehicles, which can accommodate four astronauts, it will finally become possible to increase the station’s crew size to its originally conceived number of seven, including four USOS crewmembers.
The first two operational commercial crew flights, however, will only fly with two crewmembers each, with the other two seats reserved for cargo. These flights will be US Crew Vehicle-1 (USCV-1), which will occur from September to November 2018, and USCV-2, which will occur from December 2018 to June 2019.
However, since two Soyuz spacecraft will continue to fly to the station during this period, carrying six crew in total, including three USOS crewmembers, the total station crew during the period from September 2018 to June 2019 will actually increase to eight, including five USOS crewmembers.
Beginning in May 2019, USCV-3 will launch to the ISS carrying four USOS crewmembers, establishing the norm for all subsequent commercial crew vehicles, which will then continue to launch at a cadence of once every six months.
Also in May 2019, Roscosmos will reduce its amount of Soyuz flights to the ISS, in line with the reduced requirement for seats since NASA will no longer be transporting its astronauts via Soyuz.
This will occur when Soyuz MS-11/57S returns to Earth in mid-May, and is replaced two weeks later by a USCV, rather than another Soyuz. Typically, four Soyuz flights to the ISS are performed every year. However, once the USCVs begin flying, at a rate of two per year, only two Soyuz flights per year will be required.
With two Soyuzes per year each flying with three crewmembers, and two USCVs per year each flying with four crewmembers, this will allow for a seven-crew ISS, and four-crew USOS. This in turn will allow for a large increase in the amount of crew time available for science operations aboard the station.
Interestingly, as detailed in the FPIP chart (L2), NASA are now planning to move to a “direct handover” model for the USCVs, as opposed to the “indirect handover” model that was previously planned to be used.
In an indirect handover – the model which is currently utilized for Soyuz transfers – one vehicle returns to Earth with its crew, before another vehicle launches in its place. This means that the two vehicles and their crew never meet each other on-orbit.
This also leads to a temporary crew reduction on station during the roughly two-week periods in-between one vehicle landing and another vehicle launching, which is inefficient for science operations on ISS.
In direct handovers, however, one vehicle arrives at the ISS with is crew before the vehicle it is replacing departs. This means that the crew of both vehicles are temporarily aboard the ISS at the same time.
While historically the plan for commercial crew had been to perform indirect handovers, the latest FPIP now confirms that NASA is instead planning to conduct direct handovers with the USCVs, beginning in May 2019 with USCV-3.
This means every six months there will be a roughly ten-day handover period where the ISS crew will surge to 11 in total – three crewmembers from a single Soyuz, and eight crewmembers from two USCVs.
This will eliminate the need to temporarily reduce the station’s crew to three during handover periods. Whilst the crew increase during handover periods will place additional strains on the station’s life support systems, during the Shuttle era the ISS routinely supported up to 13 crewmembers at a time.
The direct handover model also opens up the possibility for additional astronauts to conduct short-term visits to the ISS, as the commercial crew vehicles are being designed to seat more than the required number of four astronauts.
For instance, maintenance crews could be flown to conduct ten days of intense EVA activity, or researchers to conduct specific experiments during the ten-day period. At this time, however, this is not planned for.
Under the indirect handover model which was previously planned, one US crewmember would have needed to continue to fly on the Soyuz, in order to maintain at least one US crewmember on the ISS during the handover period where no USCV would have been present at the station.
However, despite the move to USCV direct handovers, it will still be necessary for one NASA astronaut to continue to fly on the Soyuz, since one Russian cosmonaut will be required to fly on the USCVs in order to maintain a Russian presence on the ISS during Soyuz handover periods, which are still planned to use the indirect handover model.
The use of the indirect handover model for Soyuz means that, if no Russian crewmember were to fly on the USCVs, then the two-week period between when one Soyuz leaves the ISS and another arrives would see no Russian presence aboard the station.
Therefore, since one Russian must fly on the USCVs, taking up one of the four seats, one US astronaut must continue to fly aboard the Soyuz.
However, as Roscosmos will go down to flying just two Soyuz per year in May 2019, as opposed to the usual four, this will open up the possibility for the Soyuz to move to the direct handover model as well. This is because, with only one Soyuz docked to the ISS as opposed to two, a Russian docking port will be freed up.
Currently, one Soyuz must depart before another arrives, in order to vacate a docking port for the new Soyuz, as all other ports on the Russian Segment are occupied by the additional Soyuz and two Progress vehicles.
However, with just one Soyuz docked to the ISS due to the reduction in Soyuz flights, a port would be free on the RS for one Soyuz to arrive before the other departs.
Under this model, there would be no need to fly a cosmonaut on the USCVs, since Roscosmos would launch one Soyuz every six months with three Russian crewmembers aboard, and NASA would launch one USCV every six months with four USOS crewmembers aboard.
However, at this time the FPIP still shows that Russia is planning to continue the indirect model for Soyuz rotations after the USCVs begin flying, meaning one Russian crewmember will need to fly on the USCVs, and thus one NASA astronaut on Soyuz.
ISS crew size to increase early:
It was originally planned that the USOS crew would increase to four once the commercial crew vehicles start flying, currently planned for September 2018.
However, an opportunity has recently arisen for NASA to increase the size of its crew earlier than anticipated, as a result of a Russian decision to decrease their own crew from three to two. This decision was taken as a cost-saving measure, as reducing the Russian crew from three to two allows for the reduction of one Progress flight per year.
The rationale for the crew decrease is that three Russian crewmembers cannot be justified until the Multipurpose Laboratory Module (MLM) arrives at the ISS, bringing with it extra research facilities to occupy a third crewmember’s time.
The process to reduce the Russian Segment to two crewmembers will begin in mid-April, when Soyuz MS-02/48S returns to Earth, leaving two USOS and one Russian crewmembers aboard the station.
However, when Soyuz MS-04/50S launches ten days later, only one Russian crewmember will be aboard instead of the usual two, as well as one US crewmember, and one empty seat.
Each subsequent Soyuz will then continue to launch with just one Russian crewmember until the MLM arrives at the ISS.
While the six-monthly Soyuz flights that contain an international partner astronaut (ESA/JAXA) will continue to have all three of their seats filled, it is the intervening flights with empty seats that have afforded NASA the opportunity to increase their own crew from three to four earlier than planned, although the total station crew will remain at six due to the loss of one Russian crewmember.
NASA will be increasing the US crew to four from September 2017, a full year earlier than planned, via empty seats on two Soyuz flights resulting from the reduction in Russian crewmembers.
In a recent announcement, NASA confirmed that they would be purchasing two spare Soyuz seats from Boeing, who in turn have acquired the seats from RSC Energia. One of these seats will be in the “fall of 2017” and one will be in the “spring of 2018”. These correspond to Soyuz MS-06/52S in September 2017, and Soyuz MS-08/54S in March 2018.
The Russian crew will increase back to three crewmembers once MLM has arrived at the ISS, currently scheduled for early December 2017. However, it is rumored that the launch of MLM has slipped again, to early-to-mid 2018.
Thus, the fact that Soyuz 54S in March 2018 will only fly with one Russian crewmember is interesting, as it may be an indication that the MLM is not expected to have arrived at the ISS by that point.
Starting with Soyuz MS-10/56S in September 2018, by which time MLM should have arrived at the ISS, the Russian crew is planned to increase back to three once again.
However, with Soyuz MS-08/54S scheduled to return to Earth in September 2018, the same month that commercial crew vehicles are scheduled to begin flying, a seamless 4-crew USOS should be enabled, apart from the usual brief periods where the crew will reduce in-between Soyuz handovers.
While the plan is to have US commercial crew vehicles operational by September 2018, NASA also announced that they have the option to procure some extra Soyuz seats from Boeing in the “spring 2019 timeframe on two Soyuz spacecraft”.
These seats correspond to Soyuz MS-12/58S in March 2019, which is scheduled to launch with two Russian cosmonauts and one NASA astronaut, but would instead launch, if required, with one Russian cosmonaut and two NASA astronauts.
The other Soyuz flight, however, would be an additional Soyuz flight flown specifically on behalf of Boeing, in the May 2019 timeframe, and would launch with one Russian cosmonaut and two USOS crewmembers.
This is because, with Roscosmos planning to reduce its Soyuz flights to two per year starting in May 2019, an additional Soyuz will have to be flown in order to accommodate the two spring 2019 NASA slots, should they be required.
This extra Soyuz, when combined with the extra seat made available on the previous Soyuz (58S) in March 2019, will give NASA four seats in total, and allow for a four-crew USOS from March to September 2019, and three-crew USOS from October to December 2019.
This will give NASA a “buffer” against any potential commercial crew delays into 2019, although from 2020 onwards the USOS crew would be forced to go down to just one crewmember, who would rotate via Soyuz, if commercial crew is not online by that point.
NASA’s use of its 2019 backup slots would mean that the RS crew would be reduced to just two cosmonauts during the period March to October 2019, even though the MLM should be present at the ISS at this time.
In the event of a commercial crew vehicle delay, however, there would be a six-month gap in four-crew USOS coverage, since Soyuz MS-10/56S in September 2018 is planned to launch with two Russian cosmonauts and one NASA astronaut, rather than the other way around.
This means that for a six-month period from September 2018 to February 2019, there will be three Russian crewmembers and three USOS crewmembers aboard the ISS.
It is not yet known at this time whether Roscosmos would be willing to reduce its own crew by one, to make an extra seat available to Boeing/NASA on 56S should the USCVs be delayed, in order to allow NASA to maintain a 4-crew USOS from the end of its already planned extra slots in September 2018, through to the start of its backup slots in March 2019.
Additionally, an opportunity has recently arisen for NASA bring forward its four-crew USOS plans three months earlier than the already early date of September 2017.
This is due to the fact that Soyuz MS-03/49S is currently scheduled to return to Earth in mid-May, carrying NASA astronaut Peggy Whitson, ESA astronaut Thomas Pesquet, and Russian cosmonaut Oleg Novitsky.
However, since Soyuz MS-04/50S, which will have launched one month prior, will only contain two crewmembers, an opportunity exists for Whitson to extend her stay on station and return to Earth in the spare seat on 50S, rather than with her own crew on 49S. This will of course mean that 49S would return to Earth with one empty seat.
Although this would mean Whitson extending her stay on ISS for 3.5 months (for a total of 9.5 months) until mid-September, it is notable that Whitson was originally a candidate for the year-long ISS mission, which was ultimately flown by Scott Kelly.
This plan would allow for the increase of the USOS crew to four once Soyuz MS-05/51S arrives at the ISS in early June carrying NASA astronaut Randy Bresnik, ESA astronaut Paolo Nespoli, and cosmonaut Sergey Rayazinsky.
NASA are understood to be in the process of evaluating this proposal. However, at this time it remains unconfirmed.
(Images: NASA, Roscosmos and L2 ISS Section. Numerous renders by L2 Artist Nathan Koga. The full gallery of Nathan’s (SpaceX Dragon to MCT, SLS, Commercial Crew and more) L2 images can be *found here*))
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