Space Sunday: Starliner’s first orbital flight

Ignition: the United Launch Alliance Atlas V topped by an uncrewed Boeing CST-100 Starliner vehicle lifts-off from Space Launch Complex 41 at Canaveral Air Force Station on its uncrewed Orbital Flight Test mission. Credit: ULA / Boeing

On Friday, December 20th, 2019, NASA and Boeing, together with launch partner United Launch Alliance (ULA), attempted to undertake the first flight of the Boeing CST-100 Starliner commercial crew transportation system to the International Space Station (ISS).

I say “attempted” because while the first part of the mission went precisely to plan and the Starliner successfully reached orbit, a software issue left it unable to reach the ISS. However, while this prevented a core mission objective from being met – that of rendezvousing and docking with the ISS – it did not leave the mission a failure: the ascent to orbit was successful, with a lot of data gathered on the vehicle’s performance, and further data could be gathered while on-orbit and during the vehicle’s return to Earth – also a critical part of the test.

The vehicle was uncrewed for this test flight, but is carrying a range of cargo – including Christmas gifts for the ISS crew; tree seeds that will be planted on Earth after the mission to mark it; a mannequin fitted with a host of sensors to measure the stress placed on a human body during the flight to orbit (the mannequin is called “Rosie the Rocketeer” in reflection of “Rosie the Riveter”, the iconic role model for U.S. women working in factories and on production lines in WWII, and a Snoopy soft toy “zero gee indicator” – Snoopy is the mascot for NASA’s Artemis programme to return humans to the Moon.

The Atlas V, dual Centaur and CST-100 vehicle stack. Credit: ULA

Things started off well enough: following a near-perfect count down, the core booster of the Atlas V and its two strap-on  solid rocket motors ignited precisely on time at 11:36:43 UT (06:36:43EST) on the launch pad of Space Launch Complex 41 at Cape Canaveral Air Force Station, and the vehicle lifted off smoothly into the still-dark early morning sky.

Due to the need to keep the vehicle within a 3.5 G limit during ascent, the Atlas V rose into a “flat” trajectory during its climb, the two solid rocket boosters being  jettisoned some 2 minutes into the flight, the core stage motors continuing to burn for almost three more minutes before BECO – Booster Engine Cut-Off – was called. Shortly after, the core stage of the Atlas V separated from the Centaur upper stage, allowing it to fire its twin RL-10A motors – marking the first time a twin-engined Centaur had been used with the Atlas V booster. Again, the additional power provided by the additional motor was required to push Starliner toward orbit, running for seven minutes in the process.

It was after the Starliner has separated from the Centaur upper stage that the major problem occurred. At this point, the vehicle was supposed to orient itself and then fire the main engine on the service module to push itself into an initial orbit that would allow it to complete further engine burns to both raise its orbit and circularise it, allowing the Starliner to catch-up and rendezvous with the ISS.

However, that initial burn failed to occur on time. Instead the vehicle continued to fire its attitude control thrusters while ignoring commands from Earth to fire the the service module’s motor. Some seven minutes passed before the engine was ignited, allowing Starliner to achieve its initial orbit – but by that time its was “off course” in relation to where it needed to be in order to catch up with the ISS, and had used too much attitude control system fuel to be able to make necessary course corrections and achieve any form of rendezvous with the ISS.

The Boeing Starliner space vehicle experienced an off-nominal insertion. The spacecraft currently is in a safe and stable configuration. Flight controllers have completed a successful initial burn and are assessing next steps. Boeing and NASA are working together to review options for the test and mission opportunities available while the Starliner remains in orbit.

– Kelly Kaplan, Boeing’s spokesperson, after the planned automated engine burn failed

According to initial investigations, it is believed that the mission clock aboard Starliner overseeing all of the vehicle’s automated flight operations – including triggering the engine burn – had incorrect data, causing it to believe the service motor had fired, and thus triggering the use of the attitude control system.  While the issue left Starliner unable to reach the ISS, mission controllers were able to order the vehicle to complete two additional engine burns to put it into a near-circular 250km high orbit, where a range of tests on the vehicle have been made, and from which it could complete its planned EDL – entry, descent and landing.

A couple of important points to highlight here is that had the vehicle been carrying a crew, they would not have been in any danger – in fact, they would likely have been able to correct the initial burn failure, allowing the rendezvous with the ISS to take place.

The stages of a Starliner’s return to Earth. Credit: Boeing

With the issue understood – if not the cause known – the decision was taken to complete the planned orbital tests and then bring the Starliner back to Earth  and a landing at the White Sands Missile Range, New Mexico on Sunday, December 22nd. These orbital test included testing the navigation systems and the vehicle’s flight handling, and communications (including establishing a link with the ISS).

Landing commenced with Starliner turning itself around and using the service module’s motor in a de-orbit burn. This took place at 12:23 UT (06:23 CST at the White Sands landing ground) on December 22nd, slowing the vehicle sufficiently for it to start a decent into the denser part of the Earth’s atmosphere. Three minutes after this, the service module was detached and left to burn-up in the upper atmosphere.

The capsule, protected by a double heat shield system – referred to as the forward heat shield (protecting the upper part of the vehicle: the airlock and the landing system parachutes) and the base heat shield (at the base of the capsule and designed to protect it from the full heat of atmospheric entry) and covered in a thermal protection system – reached “entry interface” some 20 minutes later. This is the point where the atmosphere becomes dense enough to generate friction around the vehicle, both heating up and slowing the vehicle down. At this point, Starliner was some 15 minutes away from landing.

The first direct view of the OFT CST-100 Starliner as it travels 33km above the surface of Earth. It is captured in infra-red by a NASA high-altitude WB-57 observation aircraft. Credit: NASA

This interface also marks the start of a period of communications black-out with a craft entering the atmosphere, due to the intense “bubble” of ionised, super-heated air that forms around it. However, mobile tracking stations at the White Sands landing area reported tracking the Starliner through atmospheric entry, and a NASA WB-57 observation  aircraft – one of only two types of aircraft capable of flying at altitudes in excess of 15 km (50,000 ft), captured the Starliner via an infra-red camera when the vehicle still some 33 km above the ground over New Mexico.

Following a successful entry into the denser atmosphere, the forward heat shield was detached at 12:52 UT, allowing the drogue chutes to deploy. These helped slow the vehicle to sub-sonic speeds (causing Starliner to generate a sonic boom) and to adjust its descent trajectory to an almost vertical descent.

After this things happened in rapid succession:

  • 12:54 UT – the three main parachutes deployed.
  • 12:55 UT – base heat shield jettisoned.
  • 12:56 UT – the six landing airbags deployed and inflated.
  • 12:58 UT – Starliner touched down at the landing zone and main parachutes detached.
Two of the first true-colour images of the Starliner, both captured from the ground at the White Sands landing ground, showing the main parachutes deployed (l) and the detached base heat shield falling away (r). Credit: NASA

Touch-down occurred more-or-less on time, and at a speed of around 24 km/h (15 mph). The six airbags designed to to absorb the impact, venting gas as the vehicle landed. At this point the Landing and Recovery Team (LRT) – split into a number of sub-teams – moved in to commence a complex series of operations:

  • Gold Team – a hazmat team, assigned with “sniffing” Starliner to ensure there no residual hydrazine fuel (used by the attitude control systems and a highly toxic substance) was present on the vehicle’s hull or leaking from its attitude control systems.
  • Sliver Team – the second team in, discharged any static electricity that may have built up on the vehicle as a result of entry into the atmosphere and generally “safe” it ready for post-landing operations.
  • Green Team – responsible for deflating the landing airbags and enclosing the vehicle in a protect shroud. As each Starliner is designed to be re-used up to 10 times, it is essential it is protected from the elements after landing, and from risk of accidental damage (particularly to the outer thermal protection system). This team also places the vehicle on ground-based electrical power.
  • Red Team – the group responsible for checking and unsealing the hatch and extracting the crew from the vehicle.
The Starliner capsule captured a few seconds after touch down at12:58 UT, and prior to the main chutes being detached. Credit: NASA / Boeing

At the same time as these teams went about their work, additional teams were dispatched to recover the main parachutes – these detached on touch-down so they would drift clear of the vehicle and not foul it – and the base heat shield, which will be subject to extensive examination to confirm its performance, although the Starliner heat shields are not intended to be re-used.

Normally, the LRT would aim to have a returning Starliner safed, the hatch open and the crew extracted within an hour of touch-down. However, as this first flight was uncrewed, and the team wanted to ensure everything was handled correctly and cautiously, the hatch was not opened until around an hour and 35 minutes after landing.

What was most evident after landing was the condition of the capsule: the exterior of the craft show little sign of wear and tear; there were no residual heat streaks generated as a result of the intense heating of the atmosphere close to the hull, indicating the base heat shield had performed more than perfectly. With the hatch opened, the Red Team were able to examine the cargo packages and “Rosie the Rocketeer”, confirming everything appeared to have survived the entry, descent and landing without mishap (data from “Rosie” throughout the flight indicates Starliner is more than capable of doing its job and keeping astronauts aboard it safe).

A member of the LRT Red Team checks the CST-100 capsule for possible hydrazine leaks following touch-down. Note the also pristine condition of the capsule hull. Credit: NASA / Boeing

The capsule will be transferred from White Sands to Boeing’s facilities, where it will be comprehensively examined, together with all the data gathered from the flight. After this it will refurbished in readiness for its second flight into orbit in what is planned to be the first “operational” flight for a Starliner vehicle. Designated USCV-2 by NASA (CTS-1 by Boeing), this flight will carry mission commander Sunita Williams, NASA astronaut Josh Cassada (making his first flight into space) and ESA astronaut Thomas Pesquet to the ISS.

Given she would be flying in this capsule the next time it is launched, Sunita Williams was at the landing zone to inspect it first-hand. During an interview at the landing site, and in keeping with a long tradition dating all the way back to the first Mercury flights wherein astronauts get to name the capsules they fly in, she revealed that this particular capsule will be named Calypso.

A little homage to other explorers and the ships that they rode on, I think we’re going to call her Calypso … [for] Jacques Cousteau. I love the ocean, and what the ocean means to this planet … there’s so much to discover in the ocean and so much to discover in space, it just seemed like a natural marriage.

– NASA astronaut and USCV-2 commander Sunita Williams

A member of the LRT Red Team in a hazmat suit liaises with a Green Team member in front of the Starliner capsule, while behind the capsule, two more Green Team members prepare the environmental shroud they will place around it

A core part of the post-flight review of both the vehicle and the data gathered throughout the flight will be to try to determine why the on-board mission clock system came to have incorrect information that led to the initial orbital burn mishap; a lot of pre-launch integration checks between the Starliner and the Centaur and Atlas (from which the initial data for the clock is generated) failed to reveal any potential issue. The outcome of these investigations are likely to inform NASA and Boeing on whether a further uncrewed test flight is required ahead of the first planned crewed flight.

Currently, the first crewed flight for a Starliner vehicle is scheduled for the first half of 2020 using the second flight-ready vehicle. This will carry astronauts Christopher Ferguson, Mike Fincke and Nicole Mann and possibly a 4th individual to the ISS. Although classified a test flight and originally intended to last just 2 weeks, the flight has been extended to a full crew rotation flight in order to compensate for delays in bringing both the CST-100 and the SpaceX Crew Dragon to operational status. As such, it will remain at the ISS for some 6 months.

In all, NASA has awarded some US $8 billion in total to Boeing and SpaceX  for ferrying crews to and from the ISS between 2020 and 2024, with the majority of the funding going to Boeing – some US 4.8 billion – going the Boeing, which actually means the cost per seat of Starliner is higher than the fees NASA pays to Roscosmos for Soyuz spacecraft seats to fly US and partner-nation astronauts to the space station.