Soyuz MS-04 was a Soyuz spaceflight that launched on 20 April 2017 to the ISS. It transported two members of the Expedition 52 crew to the International Space Station. MS-04 was the 133rd flight of a Soyuz spacecraft. The crew consisted of a Russian commander and an American flight engineer. It was the first of the Soyuz MS series to rendezvous with the Station in approximately 6 hours, instead of the 2 day orbital rendezvous used for the previous launches. It was also the first Soyuz to launch with only 2 crew members since Soyuz TMA-2.

The Roscosmos State Corporation for Space Activities, better known as Roscosmos, is only sending two people inside the Soyuz instead of three. This was a result of a decision by the Russia to reduce the size of its station crew size from three per expedition to two in order to save money to launch a new module to the ISS – the decade-delayed Nauka science module.

The extra seat will afford already-in-space Whitson a three-month extension to her space stay. She will return to Earth with the Soyuz MS-04 crew in early September 2017, instead of early June, with Pesquet and Novitskiy in Soyuz MS-03.

Not long after jettisoning the LES, the four strap-on boosters consumed their supply of highly refined kerosene (RP-1) and liquid oxygen (LOX) propellant and separated from the still-firing core stage.

The four boosters, now independent from the rest of the launch vehicle, appeared to form a cross as they performed a flipping and tumbling maneuver during their free-fall to the ground below. This aerial display is called the Korolev Cross in homage to Sergei Korolev, the inventor of the R-7 rocket – a precursor to the Soyuz booster.

HOT STAGING
At an altitude of 48 miles (78 kilometers) and above most of the atmosphere, the protective aerodynamic shroud covering the Soyuz spacecraft was no longer needed. Splitting in half along its length, the fairing separated from the launch vehicle and exposed the spacecraft to the harsh near-space environment.

The core stage’s RD-108A engine continued to fire, pushing the rocket and its crewed payload to an altitude of 95 miles (153 kilometers) and a velocity of 8,500 mph (13,600 km/h).

The Soyuz’s second stage (or third, depending on how the boosters are classified) began to fire its RD-0110 while still attached to the core stage – an operation known as “hot staging” – and separated approximately 4 minutes, 45 seconds into flight.

Hot staging negates the need for separation motors in the core stage, thus decreasing the complexity of the staging process. It has been a mainstay of much of the Russian spaceflight industry for 60 years.

The upper stage’s RD-0110 burned for approximately four minutes, placing the Soyuz MS-04 spacecraft on a trajectory to reach the ISS a scant six hours after leaving Kazakhstan. In the past, Soyuz spacecraft have taken upward of two days to reach the orbiting laboratory.

Shortening the rendezvous profile to six hours – just four orbits around Earth – not only offers the benefit of getting a crew to the station more quickly but also helps conserve the spacecraft’s limited supply of consumables, such as fuel and oxygen.

With only a four-day supply of those consumables aboard the spacecraft, the expedited rendezvous and docking process gives extra margin in the event of an emergency.

For Yurchikhin, this marks his fifth launch to space, having logged a total of 537 days on one space shuttle mission in 2002 and three long duration missions on the International Space Station in 2007, 2010 and 2013. When he lands on Earth at the end of this flight, Yurchikhin will rank seventh in the world for time in space, just ahead of Whitson.