Russia to Introduce Two-Orbit Express Rendezvous with International Space Station
Russia plans to speed up the rendezvous of the country’s Soyuz and Progress spacecraft to bring crews and cargo to the International Space Station faster than with the current six-hour flight profile that has been in use for the last five years. The upcoming Progress MS-07 cargo resupply mission will debut a new two-orbit rendezvous profile, taking only three and a half hours from liftoff to docking with crewed missions inaugurating the new rendezvous technique once proven by Progress.
To realize a two-orbit launch-to-docking profile, one would either have to deal with a very narrow phase angle range or take a different approach to find a compromise between planar and phase angle constraints. The method chosen by the Russian flight dynamics team is referred to as a Quasi-Coplanar Insertion and will broaden the planar launch window and so allow the chaser to be launched into an orbit with optimized phase angle while keeping the planar separation within a manageable range.
4-Orbit Profile – Image: RSC Energia
The second important trick that comes into play is a change in orbital inclination which can be varied in order to reduce the angle at which the orbit of the Space Station and the chaser intersect and so reduce the change in velocity required by the chaser to accomplish the plane change into the ISS orbit. Without this exploitation of orbital mechanics, the two-orbit profile was found to come with excessive propellant consumption and would not have been practical.
Two-Orbit Rendezvous Profile – Image: RSC Energia/TSNIIMASH “Cosmonautics & Rocket Engineering”
If accepting a 0.65° angular separation in RAAN (Right Ascension of Ascending Node), the planar launch window will broaden by ±2.5 minutes, allowing some leeway in the setup of the phase angle by the Space Station. But as consequence, the angle at which the ISS orbit and that of Progress/Soyuz intersect will be 0.51° and it would cost the spacecraft over 66m/s of delta-v to accomplish the plane change. Varying the orbital inclination by ±0.18° will allow Soyuz to accomplish the plane change at a much more manageable delta-v of 25m/s.
Setting the Inter-Orbit Angle via Inclination Modification – Image: RSC Energia/TSNIIMASH “Cosmonautics & Rocket Engineering”
Widening the planar window to ±5 minutes (corresponding to phase angles of 20°) will require an inclination change of ±0.35° and a delta-v of 50m/s for the plane change, still manageable for the Soyuz/Progress vehicle within its typical propellant margin.
Source:
Spaceflight101.com