A moment nearly ten years in the making. After receiving a formal development award on 18 April 2011 for their CST-100 crew capsule, Boeing sent its Starliner spacecraft on its inaugural flight, albeit one that will be cut short.
The uncrewed test, known as the Orbital Flight Test — or OFT — launched on a modified United Launch Alliance Atlas V rocket from the Cape Canaveral Air Force Station, Florida, at 06:36:43 EST (11:36:43 UTC) on Friday, 20 December 2019.
However, the mission to the ISS – set for docking 25 hours after launch – was placed into doubt after Starliner suffered an orbital insertion issue. It was later confirmed that an issue with the Mission Elapsed Clock timing for the orbital insertion burn has forced the decision to return Starliner to White Sands, as opposed to docking with the ISS, by Sunday.
Starliner: Boeing’s answer to NASA’s call to move the launch of humans from the government to the commercial sector; a capsule that builds from the heritage of the U.S.’s past human spaceflight systems.
Under the terms of the international agreements, Starliner will always ferry a NASA astronaut and a Russian cosmonaut on each crew rotation flight. The remaining two seats will either be taken by NASA astronauts, a European astronaut, a Japanese astronaut, a Canadian astronaut, or some combination thereof.
A complement of four will be the normal crew rotation number, with Boeing having the option to sell a fifth seat to a private astronaut.
In total, Starliner is capable of launching and landing seven people at the same time. This is largely driven by NASA’s desire for a full seven-person Station crew to pile into Starliner to quickly evacuate the Station if all crew happen to be on the U.S. side of the outpost if an emergency occurs.
At present, there are no plans to fly more than five people at a time on Starliner.
To accommodate this NASA requirement, Starliner has an internal pressurized volume of 11 cubic meters (390 cubic feet) for crew and cargo.
For OFT, Starliner will carry 270 kg of cargo – mainly food, clothing, and crew supplies. During operational flights, Starliner can launch and land 163 kg of cargo and science experiments in addition to crew.
On OFT, the capsule will also carry Rosie, an Anthropometric Test Device, that will measure the stresses, pressures, and G forces that will be imparted onto a crew during launch.
Starliner itself is composed of two separate vehicles: the Crew Module and the Service Module.
The Crew Module is equipped with 12 Reaction Control System (RCS) thrusters that can produce 100 lbf of thrust each.
Those will primarily be used after Service Module separation and during reentry and landing to maintain the Crew Module’s proper angle of attack to the atmosphere.
The Service Module is where all of the RCS and other engines reside for the majority of on-orbit maneuvering.
The Service Module contains 28 RCS thrusters that produce 85 lbf thrust each and 20 Orbital Maneuvering and Attitude Control (OMAC) engines.
The OMACs produce 1,500 lbf thrust each.
The Service Module’s OMAC engines will be used to perform the Orbit Insertion Burn after launch, all major on-orbit maneuvers, and the critical deorbit burn at the end of the mission.
As Starliner approaches the Station for docking, it will switch from its OMAC engines to its RCS thrusters for Station proximity ops.
Additionally, the bottom of the Service Module contains the four Launch Abort Engines and all of the solar panels for power.
For OFT, the Launch Abort Engines will be disabled.
Each Starliner is capable of being used up to 10 times.
The veteran Atlas V, flying for the 81st time, was the rocket tasked with doing almost all – but not the entirety – of the process of bringing Starliner to orbit.
Nominal Atlas V launch profiles involve the first stage – the Atlas V booster – bringing the Centaur upper stage and payload to a high altitude in just 3.5 minutes.
But for Starliner missions – especially those with a crew – that trajectory would not permit survivable aborts in the event of a launch vehicle failure.
If the Atlas V were to fly its normal profile and Starliner had to abort, the angle of reentry would be such that Starliner would either skip off the atmosphere – resulting in a Loss Of Crew and Vehicle situation – or experience G-forces during reentry that would kill the crew.
To avoid this – and permit Starliner to safely abort during all phases of launch, something mandated by NASA’s Commercial Crew Program – the Atlas V had to fly a much more shallow and lower flight trajectory.
Moreover, the Atlas V booster had to throttle its Russian-made RD-180 main engine down a lot more than it does for satellite missions to maintain no more than 3 Gs of acceleration for crew safety.
These two changes to how the Atlas V booster flew with Starliner result in a significant loss of efficiency and performance of the Atlas V and mandates the use of a Dual Engine Centaur upper stage – which needs greater thrust to overcome the shortfall in the Atlas V performance for Starliner launch trajectories.
The Dual Engine Centaur is not new. It has flown 166 times to date (not counting OFT/Starliner) — 143 times on an Atlas and 23 times on a Titan rocket. However, this is the first time the Dual Engine Centaur is flying with the Atlas V rocket.
According to Caleb Weiss, Atlas V/Starliner Mission Manager at United Launch Alliance, “The nice thing about the Dual Engine Centaur is that it gets all the heritage from the Dual Engine Centaur that last flew 15 years ago, but it gets all the improvements of the last 15 years on the Single Engine Centaur — the avionics and material upgrades.”
But even with the Dual Engine Centaur upper stage, the rocket didn’t quite take Starliner all the way to orbit.
This is not a shortfall of Atlas V performance. Atlas V and the Dual Engine Centaur can get Starliner all the way into orbit. Rather, the suborbital trajectory is deliberate and at the request of Boeing.
At Dual Engine Centaur engine cutoff, the craft was at a velocity of just over 7,800 meters per second, resulting in an initial suborbital trajectory of Starliner – just a few meters per second shy of orbital velocity.
This suborbital trajectory was requested by Boeing so that under normal conditions, Starliner can then burn most of its unused launch abort fuel (via the Orbit Insertion Burn) to lighten its mass before it boosts its orbit to phase up to the Station.
In this way, a suborbital injection by Atlas V with Starliner finishing the orbit insertion is the most efficient use of the system and something designed into the profile from the beginning.
Moreover, the Atlas V rocket was heavily modified for its role as Starliner’s launch vehicle.
The two most obvious and visual changes to the rocket are:
- No payload fairing
- The addition of an aeroskirt below where Starliner attaches to the top of the Atlas V.
For Starliner missions, the Atlas V cannot fly with a payload fairing because Starliner needs to be able to abort away from the rocket within milliseconds if a critical failure should occur with the launcher.
The aeroskirt, on the other hand, is to prevent a critical failure from occurring.
After Boeing selected the Atlas V rocket as Starliner’s launch vehicle, ULA engineers discovered that Starliner’s 5 meter diameter created an unstable and dynamic airflow around the rocket – an instability that could lead to the loss of the rocket during flight.
With the aeroskirt below Starliner, the airflow down the Atlas V is back within stable parameters to permit a smooth launch.
Hidden by Starliner and the aeroskirt is another major structural change to the Atlas V – the Launch Vehicle Adaptor.
“The Launch Vehicle Adaptor is also new,” related Mr. Weiss. “It’s very integrated with the aeroskirt and adapts from the Centaur diameter out to the 5 meter diameter of Starliner’s Service Module.”
The aeroskirt is attached to the Launch Vehicle Adaptor, and this is also where the Centaur upper stage’s Gaseous Hydrogen vent systems are routed through for Starliner Atlas V configurations.
In addition to the exterior and visually obvious changes, the rocket’s internal systems flew with a new computer program called the Emergency Detection System – which carefully monitored the Atlas V and Centaur upper stage systems.
The Emergency Detection System looked for anomalies or issues that would indicate a critical failure and need for Starliner to abort off the top of the rocket.
For OFT, the Emergency Detection System will do everything it will on future crew missions except trigger a Pad or In Flight Abort if there is an issue.
The reason for this is to ensure that the Emergency Detection System functions as programmed and talks to Starliner as intended.
For OFT, Boeing and ULA did not want a miscalibration of the Emergency Detection System or a “miscommunication” between the system and Starliner to accidentally trigger an abort when nothing is actually wrong with the rocket.
Starliner’s Launch Abort Engines were also disabled for OFT to prevent an accidental abort.
Wondering when and where you may see the historic maiden launch of #AtlasV #Starliner? This visibility map shows when and where your best chances are to see the rocket! Launch is scheduled for tomorrow at 6:36amEST from @45thspacewing at Cape Canaveral. https://t.co/1zR8TnX3Ww pic.twitter.com/FAtZ86neCz
— ULA (@ulalaunch) December 19, 2019
The trade off is – of course – that should an actual anomaly occur on the Atlas V during OFT, the rocket and Starliner would both be lost as Starliner will not have the ability to abort away to safety.
The pre-launch and launch profile of the Atlas V rocket was quite different from all 80 Atlas V missions that have flown to date.
A full 24 hours before launch, ULA and Boeing conducted a weather and systems briefing to ensure all was ready to proceed to launch.
Atlas V and Starliner’s communication systems were then activated 19 hours 55 minutes before launch and put through a series of checkouts.
From there, the countdown and sequence to launch unfolded as follows:
|Time to Launch||Event|
|Launch -6hrs (L-6hrs)||Fueling of the Atlas V and Centaur upper stage begins|
|L-4hrs 5mins||Fueling complete; Atlas V and Centaur in stable replenish|
|L-4hrs 4mins||T-4mins and HOLDING (Built In Hold)|
|L-3hrs||Crew Module/Starliner final launch preparations begin|
|L-1hr 25mins||Starliner hatch closed and locked for flight|
|L-1hr 15mins||Starliner Crew Module cabin leak checks complete|
|L-1hr 05mins||Starliner Crew Module pressurization for flight complete|
|L-22mins||Flight Director/NASA Johnson “Go/No Go” poll for Terminal Count|
|L-18mins||Starliner “Go/No Go” poll for Terminal Count|
|L-15mins||Starliner on internal power|
|L-10mins||Crew Access Arm retracted for launch|
|L-8mins||Launch Director “Go/No Go” poll for launch|
|L-4mins 45secs||Starliner configured for Terminal Count|
|T-4mins (Time to Launch)||Terminal Count begins / T-4mins and COUNTING|
|T-1min||Starliner configured for launch|
|T-2.7secs||Atlas V RD-180 engine ignition|
After liftoff, Atlas V rose vertically from SLC-41 before beginning a Pitch and Yaw maneuver at T+6.1 seconds to place the rocket onto the correct azimuth (heading) for flight to the International Space Station.
Once the Pitch and Yaw maneuver was complete, the Atlas V rolled to place Starliner in a “heads down” position (so crew – if there were crew – rides in a heads down position for flight). That roll began 12 seconds into flight.
The Atlas V’s Russian-built RD-180 engine then throttled down to maintain dynamic loads on Starliner, the new aeroskirt, and the Atlas V rocket overall at T+30 seconds.
The rocket reached Max-Q – the moment of maximum mechanical stress on the rocket – 41.8 seconds after T0.
Mach 1 – the speed of sound – will be reached 1 minute 05.8 seconds into flight, followed 1 second later by throttle up of the RD-180.
From there, the rest of the launch sequence, to Starliner deployment, unfolds as follows:
|Time since T0||Event|
|T+1min 35secs||Solid Rocket Booster burnout|
|T+2mins 40secs||Solid Rocket Booster separation|
|T+4mins 29secs||Atlas V Booster Engine Cutoff (BECO)|
|T+4mins 35secs||Atlas V booster separation|
|T+4mins 41secs||Starliner ascent cover (nose cone) jettison|
|T+4mins 45secs||Dual Engine Centaur RL-10-A engine ignition|
|T+5mins 05secs||Aeroskirt jettison|
|T+11mins 54.5secs||Dual Engine Centaur Main Engine Cutoff (MECO)|
|T+14mins 54.5secs||Starliner separation|
At this point, Starliner and the Dual Engine Centaur were in a suborbital trajectory of 72.7 x 181.4 km inclined 51.6° to the equator.
Both vehicles also climbing in altitude – coasting up to the suborbital trajectory’s apogee (highest point of trajectory above Earth sea level) of 181.4 km.
Twenty seconds before reaching apogee, four of Starliner’s 12 OMAC engines were to fire to begin the Orbit Insertion Burn. This burn was to last 40 seconds and will circularize Starliner’s trajectory and bring it into a full orbit of 181.4 km.
The initial suborbital trajectory was to allow the Dual Engine Centaur to passively reenter the atmosphere without Centaur reigniting its engines.
However, this is where the mission suffered an issue, when the Mission Elapsed Timer on the spacecraft suffered a fault, impacting on the orbital insertion burn.
Despite launching successfully on the United Launch Alliance Atlas V rocket from SLC-41, Boeing’s CST-100 Starliner is not in its planned orbit.
The spacecraft currently is in a stable configuration while flight controllers are troubleshooting. https://t.co/4sQ7H1lLSC
— NASA Commercial Crew (@Commercial_Crew) December 20, 2019
For Starliner, the Orbit Insertion Burn was to begin at T+31 minutes 00 seconds and complete at T+31 minutes 40 seconds — at which point Starliner would be in orbit.
This initial suborbital trajectory is quite familiar to NASA and Boeing. Every single one of the 134 Space Shuttle missions that reached orbit were initially dropped off in a suborbital trajectory – primarily to allow for disposal of the large External Tank.
The Shuttle Orbiter itself then performed the OMS-2 (Orbital Maneuvering System 2) burn to insert itself into orbit.
Per the planned schedule, after completing the Orbit Insertion Burn, Starliner was to immediately – within 20 seconds – begin its on-orbit testing and demonstration sequence.
It was set to autonomously rendezvous and dock to the International Space Station 25 hours 50 minutes after launch at 08:27 EST (13:27 UTC) on Saturday, 21 December. Instead, it will now return to White Sands on Sunday.