Comparing SpaceX's Dragon and Boeing's Starliner

Boeing's CST-100 Starliner docked with the International Space Station (ISS) Friday night at 8:28 p.m. EDT about 22 hours after lifting off from Cape Canaveral. Starliner joins two other American vehicles (Crew Dragon and a Cygnus-17 cargo craft) and three Russian vehicles (a pair of Progress cargo craft and a Soyuz crew capsule).

This second Orbital Flight Test (OFT-2) comes after the first attempt on December 19 which failed to dock after a series of software problems left the spacecraft in too low of an orbit forcing the Boeing to re-fly the test mission to certify it to carry astronauts to the ISS.

OFT-2 was to launch last summer but prelaunch checks found problems with valves in the propulsion system which required an additional eight months to find and correct.

With the shuttle program ending, NASA knew it needed a way to to the ISS from U.S. soil. Like the many redundant technical systems aboard these vehicles, it wanted two different spacecraft capable of ferrying astronauts.

Sierra Nevada Corporation, Blue Origin, SpaceX, and Boeing to began developing vehicles. Ultimately SpaceX and Boeing won contracts for six flights each.

Both also had significant technical challenges to overcome before getting the okay to launch humans.

This week's OFT-2 comes after the first attempt in December 19 where Starliner failed to dock after a series of software problems left the spacecraft in too low of an orbit forcing the Boeing to re-fly the test mission to certify it to carry astronauts to the ISS. Prelaunch checks last summer found issues with valves in the propulsion system which required eight months to find and correct.

Starliner experienced issues with two of the twelve thrusters used to maneuver in space. These problems were not unlike those SpaceX experienced in 2013 with their similarly new Dragon capsule during the CRS-2 mission when three of the four thrusters failed forcing docking with the ISS to be delayed by 24 hours.

Both companies saw thruster problems on the ground as well.

In 2018 malfunctioning valves caused fuel leaks and a fire which damaged part of the test capsule during a launch abort test. A year later a SpaceX Crew Dragon capsule was destroyed in an explosion following a hot-fire test of thrusters used in the event of an abort on the launch pad.

When SpaceX changed its initial plan from propulsively landing on dry land to focus to splashdown in the Gulf of Mexico, the four lightweight parachutes needed to be redesigned. This required another 15 ground tests which uncovered more problems.

Boeing also experienced problems when one of the three parachutes failed to open during a Starliner pad abort test in 2019. The problem was traced back to a simple pin that was overlooked by the close-out crew.

While both capsules were originally conceived as landing on land with ocean splashdown as an emergency backup option.

SpaceX originally envisioned landing legs extending through the heat shield in a propulsive landing but as work moved forward updating the Dragon capsule to human rating, that proved to be and complex modification. While each water landings is more expensive and salt water adds some complexity to refurbishing the capsule for reuse, this decision avoided a lot of costs in designing and certifying this new capability.

Boeing stuck with plans for their new spacecraft to land on dry land and successfully touched down in the New Mexico desert following the December 2019 flight which failed to reach the ISS.  Additional landing locations in Utah, Arizona, and California are also available.

The final crucial test of the OFT-2 mission is the led undocking and landing in White Sands, New Mexico on Wednesday, May 25.

Boeing also included some commemorative items including mission patches, pins, challenge coins, American flags and items from 14 historically Black colleges and universities (HCBUs). These items will be presented to organizations that contributed to the commercial crew program and returned to the HCBUs including NC A&T.

This mission also carried the same mix of seeds astronaut Stu Roose carried aboard Apollo-14. "Moon trees" grown from those seeds can be seen today Cradle of Forestry in North Carolina's Pisgah National Forest and  another in the Asheville, Botanical Gardens.  A descendent of one of the moon trees was planted several years ago near the walking path as it crosses the island.

The first crewed Starliner flight is scheduled for later this year with another five flights contracted through 2026. Boeing plans to service the contract alternating between a pair of spacecraft. A third was retired following its use in a pad abort test.