With the Kennedy Space Center (KSC) falling silent after the retirement of the Space Shuttle, it’ll be at least five years before the public will see the iconic sight of NASA’s follow-on vehicle rising off the launch pad. Interestingly, the Space Launch System (SLS) will follow some of the Shuttle’s heritage of “Flight Operations” – as outlined in the Concept of Operations (Con Ops) presentation.
How SLS Will Launch – Pre Launch:
The new Space Launch System (SLS) is targeting a debut launch on December 17, 2017 – sending an uncrewed Orion (Multi-Purpose Crew Vehicle) on a mission around the Moon.
This maiden voyage will test out the SLS’ systems during the launch phase, prior to sending Orion on a Beyond Earth Orbit (BEO) mission – marking the historic return to deep space, last seen during the Apollo program – and ultimately allowing for the certification of the hardware ahead of sending astronauts on a similar mission a few years later (pending an official manifest).
The SLS Con Ops presentation provides an early knowledge base of operations, ranging from the fabrication of the hardware, its transportation for integration, rollout and pad operations, through to flight operations and the Design Reference Missions (DRMs) the spacecraft may undertake.
As covered in a previous articles in the Con Ops series, rolling out to the pad after stacking in the Vehicle Assembly Building (VAB) – potentially a week prior to launch – will allow the vehicle, via its Mobile Launcher (ML), to be hooked up to the pad’s vast array of connections and interfaces during its pad flow.
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Around this time, a similar set of procedures to a Shuttle launch will take place at the main NASA centers, as managers and teams verify the mission is read to launch via the Flight Readiness Reviews (FRRs) – with the final Agency-level review taking place at the Kennedy Space Center (KSC).
It is also understood that the mission will match Shuttle pre-launch operations from the standpoint of a Mission Management Team (MMT), as the procedures head into the launch day activities – with the mission already into the countdown. The count will also have the Built In Holds (BIH) to allow teams extra time to troubleshoot any problems ahead of launch.
“The SLS health and status is monitored and communicated to 21CGSP (21st Century Ground Systems Program) and mission operations to provide insight into anomalies that might initiate an abort, launch hold, scrub turnaround, or flight and ground crew emergency egress,” noted the expansive SLS Con Ops Presentation (available on L2 – link to presentation).
“Payload health and status data will be routed through the ground system to the payload customer. Liquid engine propellants (e.g., cryogenic propellants) are loaded. All propellant replenishing and/or pressurization activities are completed. The SLS has the capability to accommodate holds to minimize the chances for the launch to have to be scrubbed and minimize the impact to battery depletion.”
While SLS-1 will be launching without a crew, the nominal routine will call for astronauts to board Orion roughly at the same time as a Shuttle crew would have, known as “limited suited wait time”.
As noted by the Con Ops, SLS and Orion will be doing most of the talking between each other and controllers in the Firing Room, before and after the crew ingress, providing vital data on the vehicle’s health during propellant loading and final checkouts.
“The SLS provides to Orion-MPCV the health and status information the crew and Orion-MPCV need to determine the need for an emergency egress or pad abort,” added the Con Ops. “Final configuration, checkout, and monitoring of the launch vehicle and spacecraft are performed remotely to minimize the need for pad access.”
Again mirroring a countdown for the Shuttle, a handover to SLS’ onboard computers will occur late in the count – although it is not known if this will also be at the T-31 second mark – with flight rules and Launch Commit Criteria (LCC) providing the acceptable parameters for the vehicle to launch. Pad abort options will also be available for an emergency late in the count.
“The SLS switches to internal power and then autonomous handover to the launch vehicle occurs. The SLS accepts ground-computed mission parameters (DOLILU – Day of Launch I-Load Updates, orbit insertion targets, mass properties, etc.), via hard-line to the integrated vehicle through ground systems and verified prior to launch,” continued the Con Ops.
“The launch commit criteria (LCC) are monitored. Launch control and mission management makes a go/no-go launch decision based on their evaluation of compliance with all LCC, flight rules, and range safety rules. Prior to launch commit, remaining final configuration and automated verification of systems is completed and the integrated stack is ready for launch.
“Nominal terminal countdown results in launch of the vehicle at Time Zero (T-0) when the SRB Fire Signal is received by the SLS Flight Computer, the vehicle is released from hold downs, the T-0 umbilicals are disconnected, and the integrated stack lifts off from the launch pad. The SLS launches.”
The moment SLS rises off the launch pad, the mission moves into the Flight Operations Phase.
As with Shuttle, controllers in the Mission Control Center (MCC) Flight Control Room (FCR) will take over the primary responsibility of the vehicle – led by the the Mission Operations Directorate (MOD) team in Houston.
“The Flight Operations phase for SLS begins at first motion (hardware lifts off the pad) and ends with the disposal of the stages. Flight Operations includes a disposal of the boosters, stages, fairing, spacers, and adapters,” the Con Ops presentation outlined.
“At first motion, when the integrated stack lifts off from the launch pad, primary authority transitions from 21CGSP to MCC and the launch vehicle performs the necessary functions to transport the payload and/or Orion-MPCV safely to the ascent target.
“Prior to first motion, the primary responsibility rests with the Launch Control Team. At first motion, the SLS ground-based system monitoring responsibility transfers to the Mission Control Team. The Mission Operations Directorate conducts ascent and flight operations with support as required from SLS, Orion-MPCV, and/or payload engineering organizations.”
The SLS will provide automated and autonomous flight operations on board during launch and ascent to both the controllers on the ground – and in case of a crewed mission – to the astronauts. Notably, human rating rules requires that the integrated vehicle complete each mission with full automated and autonomous capability in case of loss of communication.
Rising uphill in what will be an impressive sight, the SLS will fly to the ascent target by managing the “states and modes” of the integrated vehicle systems, managing failures, providing power to all the integrated subsystems and elements, performing guidance, navigation, and control (GN&C), and providing propulsion to the integrated stack.
These are all primary roles of a launch vehicle, as it manages the health monitoring of its systems and provides feedback to the MCC and any astronauts onboard. Abort modes will be built into the programming, although “remote sources” – such as Range Safety – can provide the back up in the event of a serious emergency.
“The SLS monitors vehicle health and status and controls the integrated vehicle trajectory. SLS will provide attitude control (maintain attitude and perform attitude positioning) of the stack during ascent operations for all missions. However, in an off-nominal situation, the SLS can be commanded to terminate thrust (after solid booster separation) on the SLS from remote sources, such as the Orion-MPCV or Range Safety on the ground,” added the Con Ops.
“The SLS supports Communications & Tracking (C&T) and contains a flight safety system for range safety operations. The SLS downlinks/transmits telemetry (i.e., health and status data, performance data, and imagery) to the ground real-time during the ascent phase through Orion-MPCV or payload separation.
“The SLS can accept commands from the Orion-MPCV and Range Safety in off-nominal situations. The MCC can send commands to the SLS through the Orion-MPCV interface. The SLS will provide a Range Safety command RF interface for all missions. The SLS performance engineering data is transmitted from the SLS and then recorded, reduced, and archived on the ground for future reference and analysis.
“The SLS will have physically and functionally-separate mission-critical and non-mission critical avionics. Data will be collected, prioritized based on budget and bandwidth constraints, for engineering analysis via the available flight instrumentation during vehicle ascent. This includes collecting data from the flight operations, engineering, and flight-specific instrumentation.
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“The MCC will receive telemetry in real time. The MCC monitors the vehicle using space-based telemetry. The United States Air Force (USAF) Mission Flight Control Officer (MFCO) in the Morrell Operations Center (MOC) monitors vehicle trajectory and performance using ground-based telemetry and tracking data.”
SLS will have its own dedicated Fault Management (FM) system, which will allow the launch vehicle to inform Orion and controllers on the ground of a problem – such as a redline issue with an engine.
A critical issue, as determined by the vehicle’s “abort decision logic” would result in Orion being pulled free from the SLS via the Launch Abort System (LAS). However, the Con Ops noted that some issues during a cargo mission – such as an engine out during second stage flight – would result in SLS “seeking mission accomplishment until propellant is depleted.”
Providing the mission is following a nominal flight profile with nominal performance, staging of the twin five-segment Solid Rocket Boosters (SRBs) – the initial boosters of choice for SLS – will occur just over two minutes into flight. These boosters will not be recovered and will sink to the bottom of the Atlantic Ocean after impacting downrange.
“The SLS will command a boosters-level vehicle attitude prior to SRB separation that will be ‘heads-down’ for Orion-MPCV missions. After SRB separation, the core stage continues to burn until orbit is achieved and cutoff is internally commanded. During core stage burn, the vehicle can control attitude in the event of one core stage engine shutdown. After impact in the Atlantic Ocean, the boosters will sink.”
Fairing jettison will occur shortly after staging, revealing the Orion-MPCV or payload – depending on the mission – as the core stage continues to burn its Pratt & Whitney Rocketdyne RS-25 engines, providing orbital insertion for the passenger spacecraft.
“At the appropriate time, the fairing is jettisoned for payload missions. Fairing debris is expected to land in the Atlantic Ocean. After impact, all fairing debris sinks. For Orion-MPCV missions, Orion-MPCV SM fairings jettison will be compatible with SLS flight profiles,” the presentation added.
“The SLS inserts the Orion-MPCV, Orion-MPCV + ICPS (Interim Cryogenic Propulsion Stage), or payload into the ascent target. The ascent trajectory and SLS separation conditions are designed to ensure safe separation.
“SLS provides Orion-MPCV, Orion-MPCV + ICPS, or the propulsive payload element with insertion burn responsibility with main engine cutoff (MECO) confirmation, after which the Orion-MPCV or Orion-MPCV + ICPS initiates separation from the SLS when safe separation conditions are achieved.”
A slightly different approach is adopted for cargo missions, with the sequence including the Cargo Payload Adaptor (CPA) between the SLS and the passenger. For this mission scenario, the SLS is able to initiate separation from the CPA and the CPA itself performs separation for the payload. The CPA stays attached to the core stage (or upper stage for SLS Block II) and is disposed of with the stage.
However, for the variants of SLS used during an Orion mission, the spacecraft controls both the separation of the ICPS – if used – from the LVSA (Launch Vehicle Stage Adaptor), in tandem with its responsibility to separate itself from Orion-MPCV Stage Adaptor or launch stack spacer, after the SLS sends the ‘go-for-separation’ notification or flag to Orion.
This critical element of the flight also requires the staging vehicles to avoid recontact, mitigation which will be built into the flight profiles trajectory.
“After Orion-MPCV or payload separation, the SLS will follow the designed trajectory to avoid collision with the Orion-MPCV after MECO to assure safe separation conditions. The nominal ascent trajectory is designed to ensure safe disposal of the stage in the ocean. Actual mission trajectories are dependent on the day of launch atmospheric conditions and target orbit,” noted the Con Ops.
“The stage, or its debris, impacts in the ocean; either aerothermal, aerodynamic forces, or splashdown force will cause the stage to break up. It sinks after impact. The MCC will track all vehicle elements during powered flight and ensure that all jettisoned elements or vehicle elements on a sub-orbital trajectory will impact in uninhabited areas of the ocean.”
With SLS’ role complete, Orion will will begin preparations for the trip to its destination – with SLS 1 involving a Trans-Lunar Injection (TLI) burn to send it on a path towards the Moon.
“For BEO missions, after the SLS inserts the Orion-MPCV + ICPS into orbit, the ICPS performs all post-MECO maneuvers. At the time for the TLI burn, the ICPS performs a burn to place the Orion-MPCV on a lunar trajectory, and the Orion-MPCV separates from the ICPS with no recontact, after which the ICPS performs any necessary maneuvers for safe disposal.
“Orion-MPCV SM fairings jettison will be compatible with SLS flight profiles.”
Several contingency scenarios are also outlined in the presentation – such as Late Abort Modes, using the Service Module engine, or even the ICPS. These will be outlined in a future article.
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