SLS launch to Orion separation – sequence outlined by NASA

by Chris Bergin

The NASA teams working on the Space Launch System (SLS) and Orion spacecraft are continuing to build a huge collection of documentation that will provide the tools to launch and flight controllers tasked with sending the US monster rocket and its Orion passenger into space.

SLS Launch To Orion Sep:

The huge Space Launch System is scheduled to make its debut flight at the end of 2017, lofting Orion into orbit ahead of its journey to the Moon on Exploration Mission -1 (EM-1).

The Block 1 70mT capable vehicle will actually be the smallest version of the Heavy Lift Launch Vehicle (HLV), but still far more powerful than a Space Shuttle.

This will be noticeable to the hundreds of thousands of spectators that are likely to be in attendance, many of whom were last at the Kennedy Space Center (KSC) to witness a Shuttle making her majestic rise into the heavens.

SSME RS-25Ds heading to their new life with SLSWith two larger five segment Solid Rocket Boosters (SRBs) and four Pratt & Whitney Rocketdyne RS-25D (Space Shuttle Main Engines) powering SLS off the pad, the uncrewed EM-1 launch will be accompanied by the intense light show and impressive rumble the Shuttle used to provide, as it rises into the Florida sky.

Some finite details and timings are still being worked out, per the pre-launch sequence that is likely to mirror large amounts of the business end of a Shuttle countdown, not least the powering up of the RS-25Ds seconds prior to T-0.

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Although there won’t be the “twang” – caused by the Shuttle’s configuration as the stack rocked back and forth on the pad during SSME ignition and power up – the RS-25Ds will need to reach full thrust and confirm their health prior to the launch commit stage of the Hold Down Posts (HDPs) releasing and SRB ignition.

SLS RS-25 IgnitionWith the boosters firing into life, SLS will rise off the Mobile Launcher at Pad 39B – a structure that will have its own sequence of umbilical connection retractions. As with Shuttle, the control of the mission will pass over from the Launch Control Center (LCC) at Kennedy to the Flight Control Room (FCR) in Houston.

“The SLS Launch Operations Support Team (KSC) will transition control of the launch vehicle to the SLS Flight Operations Support Team (JSC) after liftoff and supports the mission through ascent and disposal,” noted the Spacecraft and Payload Integration Office (SPIO) Integrated Spacecraft & Payload Element (ISPE) Concept of Operations (Con Ops) Document, acquired by L2.

See previous SPIO Con Ops Article:

Inside the LCCThe document also notes that the handover between KSC and JSC will have overlapping support on both sides of T-0

“The SPIO will support both launch operations and flight operations, for ISPE events, from a consolidated operations center.

“The SLS Engineering Support Center (SESC) located at the Huntsville Operations Support Center (HOSC) will support the Launch Operations conducted at Launch Control Center (LCC) and flight operations conducted at the Mission Control Center (MCC).

“The SLS Engineering Support Function will provide a consolidated team supporting operations from start of countdown through disposal of the Interim Cyrogenic Propulsion Stage (ICPS) per the Lunar DRM (Design Reference Mission) objectives.”

Information on the health of the vehicle as it lifts off will be provided by the brains of the operation, the Orion spacecraft, which will be collating the information provided by the integrated elements of the vehicle, from the RS-25Ds upwards.

SLS' first stage flightThe ICPS will also have its own downlink ability, although documentation cites Orion will be the “go to” element of the stack for providing the downlink of data via the ascent.

With SLS heading downrange as it pitches during first stage flight, the RS-25Ds will have the capability of throttling down as the vehicle enters the area of maximum dynamic pressure, or MaxQ.

Known as “in the bucket” on the Shuttle – due to the shape that would be drawn on a graph showing the change of thrust level profile – no decision has been documented on what requirements will be placed on SLS’ engines for this stage of flight at this time.

However, like Shuttle, a major milestone will be reached shortly after 120 seconds of ascent uphill, as SLS conducts staging by releasing its two near-expended boosters, which will depart from the stack via their Booster Separation Motors (BSMs). The two boosters will not be recoverable from the Atlantic.

With SLS into second stage flight, the RS-25’s will gimbal to correct any transients caused by staging and to ensure the vehicle continues to be on its correct trajectory towards Main Engine Cut Off (MECO).

Staging Profile (Contray to the Con Ops)While videos have shown various ascent profile simulations, the accuracy can only be found in documentation, with the Con Ops overview providing the current plan.

“After SRB separation, but prior to ICPS separation, Orion will jettison the LAS (Launch Abort System) and SM (Service Module) panels,” the document notes, as opposed to this sequence occurring after Orion and the ICPS have separated from the Launch Vehicle Stage Adaptor (LVSA) on the SLS core.

Orion with SM and ICPSWith Orion and the ICPS coasting, the Service Module will deploy its solar arrays. Due to the recent deal with the European Space Agency (ESA), the SM on EM-1 and EM-2 will be mainly ATV hardware, meaning the vehicle will deploy four “X Wing” style arrays, as opposed to the previous arrangement of two circular arrays.

“After separation from the LVSA, ICPS will coast towards apogee and prepare for the first scheduled ICPS maneuver. During this period Orion will deploy the solar arrays and jettison the star tracker covers,” the document continued.

TLI BurnThe vehicle will then move towards the role of sending Orion on its path to the Moon, enabled by the Trans Lunar Injection (TLI) burn(s) conducted by the ICPS.

“The flight crew (EM-2 onwards) or the ground (EM-1) will provide the Authority To Proceed (ATP) for the chill-down and perigee raise maneuver. At or near apogee, the ICPS will perform this maneuver,” adds the Con Ops.

“After appropriate vehicle checkouts and orbital trajectory confirmation, the ground or crew will provide the ATP for the TLI (Trans Lunar Injection) maneuver. At or near LEO perigee, the ICPS will perform this maneuver. The ICPS maintains attitude control within the required thermal profile.

ISPE GraphicAlthough the ICPS avionics will be responsible for ICPS operations, the Orion will also have external commanding and/or inhibit capability to ICPS for mission execution during contingency operations. Telemetry for both the ICPS and Orion will be routed through Orion and transmitted to the ground operations team via the Tracking and Data Relay Satellite System (TDRSS) and/or the Near Earth Network (NEN).

Orion-commanded ISPE functions that are planned include burn ATP and engine shutdown.

Other functions under consideration include ICPS free drift, manual steering (attitude control), burn target designation, as well as real-time orbit/trajectory state vector target and ICPS disposal maneuver updates during contingency operations.

The ICPS will be disposed off after separation occurs, allowing Orion and its SM to head towards the Moon.

ICPS/Orion Sep“The Orion is responsible for initiating and performing separation from the ICPS. The Orion separation plane is located at the Orion Spacecraft Adapter (SA) to Service Module (SM) interface. Hence, the SA will fall away with the MSA/ICPS as an assembly upon Orion separation,” the Con Ops presentation noted.

“After engine cut-off, the ICPS will maintain 3-axis stabilization in preparation for Orion separation. When commanded by Orion, the ICPS will go to free-drift to prevent Attitude Control System (ACS) firing during the separation sequence and then Orion will execute separation at the Orion SA interface.

Upon confirmation that Orion has separated, ICPS will initiate the disposal sequence.

“The ICPS disposal sequence will be pre-loaded and autonomously executed after completion of Orion separation. This sequence will include a time delay to ensure that Orion has achieved a safe distance from ICPS before execution of the disposal maneuver to avoid re-contact.”

After confirmation that Orion has separated, presumably through the separation loopbacks, the ICPS disposal operation will be enabled. Per the automated disposal sequence, ICPS will utilize its attitude control system and venting of on-board propellants to perform a maneuver to place the ICPS in the required disposal orbit/trajectory.

Orion, in the meantime, will be racing on a path towards its meeting with the Moon.

(Images: Via NASA and L2 content from L2′s SLS specific L2 section, which includes, presentations, videos, graphics and internal – interactive with actual SLS engineers – updates on the SLS and HLV, available on no other site.)

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