SLS aims to launch a week after rollout – ML rolls back to Park Site

by Chris Bergin

The recently produced Concept of Operations (Con Ops) documentation has revealed the Space Launch System (SLS) will be ready to launch within a week of rollout, around a third of the average pad flow time required for the Space Shuttle. Meanwhile, the SLS Mobile Launcher (ML) has been transported back off Pad 39B following numerous tests.

SLS ML Testing:

The huge Mobile Launcher (ML) – originally designed for the Ares I launch vehicle, prior to changing call signs to the SLSrolled out to what is now a clean pad structure at Complex 39B on November 16.

The original test manifest called for four key elements to be evaluated, relating to the structural response of the ML during rollout, structural clearance, HVAC (Air Conditioning) pressurization, and Tower Fire Suppression testing – all while ML was powered up via the pad’s power supplies for the first time.

One of the the highlights was to be the Fire Suppression deluge test on November 28, which would have seen the structure and tower carrying out a test which would have mirrored the Apollo ML water deluge test in March, 1966. However, this pre-planned test was removed from the ML events due to the lack of a required pump.

“The deluge test was talked about in the beginning as (part of the) possible tests we could do, but after checking there was a pump needed for the test that was not ready yet,” KSC PAO Amber Philman told

Once returned back to the park site, the schedule shows the ML will receive a new coating of paint – required to protect the structure from the space coast’s corrosive salty air – a process which is due to begin in mid-December.

The two rolls will also provide vital engineering data on the Crawler Transporter (CT) trips both to and from Pad 39B, another key element of the ML’s move. For example, during the rollback to the Park Site, engineers were heard talking – via the KSC scanner – about increasing the CT’s speed to a pacey 1.1mph, in order to carry out an emergency stop test.

The current plan is to upgrade the existing CTs to be able to transport the ML and the SLS from the Vehicle Assembly Building (VAB) to the pad, with this extensive work outlined in the L2 SLS section – with a future article planned to overview the status.

All current work relating to what is currently a 2017 debut of the Space Launch System (SLS) – for an uncrewed mission around the Moon – is being conducted under the 21st Century Ground Systems Program (21CGSP), as the Kennedy Space Center (KSC) transitions from a sole government launch complex, into one which can host both the new NASA flagship and the upcoming commercial fleet.

For SLS/HLV Articles, click here:

SLS Con Ops – Pad Flow:

Following from the overview of integration and stacking operations inside the Vehicle Assembly Building (VAB) through to rollout, the expansive SLS Concept of Operations (Con Ops) presentation also provides the expected pad flow for the new Heavy Lift Launch Vehicle (HLV).

One of the most interesting notes is found at the start of the pad flow section, which notes SLS will be ready to launch within a week of rollout – as much as such claims can be found in similar early documentation, even for the Saturn V, before the pad flow was extended in reality.

“Once at the pad, the ML is connected to the pad interfaces to re-establish services to SLS, Orion-MPCV, and/or payload. A health check and status (HC&S) is performed at the pad. After rollout, the SLS will be ready to launch within a week to minimize the need for limited life items and consumable servicing during pad operations,” noted the Con Ops presentation, available on L2.

Key elements that can only be processed at the pad include the preflight checkout of the vehicle elements and facility systems (end-to-end tests), along with testing the SLS and ground systems data paths and fluid connections – that could not previously be verified – such as interface verifications that can only be done at the pad. Cryptographic devices will be used to load the keys.

For a mission flow, the launch countdown operations start once the stack begins to make its move down the crawlerway, hooking up the vehicle’s health status – to the Launch Control Center (LCC) it will pass in the opening hour of the rollout – continuously through the flow to launch.

“21CGSP conducts launch countdown operations through first motion in the LCC at KSC,” added the document. “The SLS and Orion-MPCV and/or payload provide health and status and caution and warning (C&W) data to support failure detection and isolation performed by the ground systems; the SLS also provides onboard command history.

“The SLS health and status is monitored and communicated to 21CGSP and mission operations to provide insight into anomalies that might initiate an abort, launch hold, scrub turnaround, or flight and ground crew emergency egress. Payload health and status data will be routed through the ground system to the payload customer.”

It is also noted that once at the launch pad, no internal access to the SLS is provided above the ML zero deck, meaning the stack would have to return to the VAB in the event of a required hardware replacement out of the reach of platforms on the ML deck.

However, as was the case with Shuttle, the core stage engines – RS-25s – can be replaced while the vehicle is at the pad.

“For contingency operations that require access above the ML zero deck – (e.g., LRUs (Line Replacement Units) that need to be removed and/or repaired) – the integrated stack will be rolled back to the VAB. GSE (Ground Support Equipment) required to remove and replace LRUs will be designed to be portable,” added the presentation.

“All propellant replenishing access provided at the ML zero deck includes the ability to remove core stage engine covers and closures. 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.”

With propellent servicing complete, including tanking operations which will follow a similar routine to that seen with the Space Shuttle on launch day, access to the payload or the Orion will both be provided by the crew access arm – an ability gained through most of the pad flow.

“For Orion-MPCV missions, the crew boards the vehicle via the access arm late in the countdown, to limit suited wait time. For all mission types – Orion-MPCV, Orion-MPCV + iCPS, or Payload – a common umbilical interface is used so that 21CGSP services each mission with a single umbilical arm/interface location/height”, continued the highlights of the expansive overview.

“Physical access to the payload (including iCPS) will be available. For cargo only missions, the crew access arm may also be used for physical access to the payload.”

Following the known – and trusted – heritage of pre-launch operations, SLS will be ruled by Launch Commit Criteria (LCC) flight rules, as determined by controllers, the Launch Director and the Mission Management Team (MMT). SLS will communicate with the crew via their Orion spacecraft’s displays, while taking commands and communicating with controllers in the Firing Room.

“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. Final configuration, checkout, and monitoring of the launch vehicle and spacecraft are performed remotely to minimize the need for pad access,” the presentation continued.

“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 Update, orbit insertion targets, mass properties, etc.), via hard-line to the integrated vehicle through ground systems and verified prior to launch.

“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.”

With all systems showing a good configuration for launch, the RS-25’s will be powered up, prior to the SLS commanding the twin Solid Rocket Boosters (SRB) – in what would be the initial configuration prior to the potential switch to liquid boosters – to fire on command at T-0.

“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.”

Further articles based on the fascinating Con Ops presentation will be published during December.

(Images: Via L2 content, driven by L2′s fast exapanding SLS specific L2 section, which includes, presentations, videos, graphics and internal updates on the SLS and HLV, available on no other site. Other images via NASA.)

(L2 is – as it has been for the past several years – providing full exclusive SLS coverage, available no where else on the internet. To join L2, click here:

Related Articles