Wind Tunnel testing conducted on SLS configurations, including Block 1B

by Chris Bergin

With the Space Launch System (SLS) family heading towards the Preliminary Design Review (PDR) phase, engineers at two NASA centers have conducted wind tunnel testing on scales models of the Heavy Lift Launch Vehicle (HLV). These models include the SLS Block 1B, a new configuration that may become the vehicle of choice throughout the 2020s.

NASA’s Space Launch System has successfully transitioned from the joint System Requirements Review (SRR) and System Definition Review (SDR) to the key PDR stage of development, with the focus on further maturing the “Block” design variants that will provide the evolving capability of the Heavy Lift Launch Vehicle (HLV).

Achieved in less than a year since the Program’s inception, the move to the PDR stage for the SLS continues to keep the vehicle well within the schedule for its 2017 debut, with a good amount of margin for unforeseen future challenges.

“This is a pivotal moment for this program and for NASA,” SLS Program Manager Todd May noted in a recent NASA announcement. “This has been a whirlwind experience from a design standpoint.

“Reaching this key development point in such a short period of time, while following the strict protocol and design standards set by NASA for human spaceflight is a testament to the team’s commitment to delivering the nation’s next heavy-lift launch vehicle.”

The 2017 debut will involve the Block 1 SLS, a “70mt” rocket that will loft Orion on an uncrewed flight around the Moon, known as Exploration Mission -1 (EM-1). This vehicle is also tasked with the same mission, this time crewed, for its second flight.

However, with only the 2017 mission firmly scheduled – along with the continued uncertainty surrounding the Exploration Roadmap, one that will likely remain undefined until after the outcome of the Presidential elections – the SLS teams are having to create a flexible approach to the launch vehicle’s capabilities.

Technically, the law calls for the 70mt SLS to evolve into a 130mt-capable HLV, the latter being the target capability for crewed missions to Mars. However, such missions are highly unlikely to occur prior to the mid-2030s.

With only the vague reference to missions to a Near Earth Asteroid (NEA) into the mid 2025s, the teams tasked with building the hardware – that will provide the foundations to such missions – are desperately lacking direction from their politically-aligned leadership at NASA HQ.

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Thankfully, SLS managers are thinking ahead, with their Block system approach capable of providing the required options for an array of mission requirements throughout the 2020s – an approach that is mindful of the fact the 130mt monster vehicle may never actually fly, not least due to the uncertainties of the future political appetite for major multi-billion dollar deep space missions to Mars – or its Moons – in the 2030s.

As it stands, SLS will evolve in two stages from its initial 70mt capability, with the Block 1A providing an interim 105mt capability, prior to the Block 2.

However, following source information from SLS team members, it has now been documented that there is a Block 1B version of the SLS, a vehicle that further mitigates against major – and potentially costly – changes the the key hardware of the Block 1.

Coming in both the Cargo and Crew versions, the Block 1B would continue to use Solid Rocket Boosters, would sport an 8.4m core with four RS-25D/E engines, an 8.4m Cryogenic Propulsion Stage with four RL10A-4-2 engines, and either an Orion MPCV or a payload under a 8.4m fairing.

This vehicle would also be aiming to launch 105mt to LEO. However, the new stage can perform part of the ascent as well as TLI (Trans Lunar Injection).

Source information also notes there are enough RS-25D engines in stock to support four missions – prior to requiring the RS-25Es to be available – and enough RSRMV material (casings, etc.) to support 10 missions.

Selecting the SLS Block 1B over the Block 1A would result in delaying the advanced boosters until the 2030s, depending on the flight rate that is to be determined by the currently undefined Exploration Roadmap.

While SLS is being designed to work with either solids or liquids, the main focus of the “competition” relating to the “advanced boosters” is with the Block 2 in mind, as opposed to any critical requirement of the other SLS configurations. Delaying the debut of the advanced boosters would not be critical to SLS’ interim role.

However, the main consideration for the Block 1B is from an engineering standpoint, given analysis with the Block 1A – sporting advanced boosters – shows it to be a “high-acceleration” launch vehicle. As such, it has been noted the environments (vibration, loads, etc.) caused by the high acceleration may be higher than Orion will allow.

With this consideration in mind, the SLS teams want to take the Block 1B design to the same maturity as the Block 1A, then make a decision on which way to proceed.

Vehicle configurations with advanced boosters and J-2X based upper stages – Block 1A and Block 2 – will continue be studied by the Advanced Concepts Office to a System Design Review (SDR) level of fidelity, but are not the primary focus of the vehicle development at this time.

The first view of the Block 1B came via its small scale model, as the SLS configurations were put through wind tunnel testing at the Marshall Space Flight Center (MSFC) in Alabama.

“The Block 1B cargo only (SLS-27000) and crewed (SLS-28000) configurations Force and Moment Test Program in the MSFC 14” Trisonic Wind Tunnel has been completed,” notes on SLS’s Rolling Update L2 Section added.

“The vehicle configurations were tested for multiple roll angles and total angles of attack between around 10 degrees for Mach numbers ranging from 0.3 to 5. A total of 909 runs were obtained.”

Testing has also been carried out at the Langley Research Facility (LaRC) on the Block 1B, and other configurations, via what is described as Structures and Environments (STE) Aerodynamic Force and Moment Testing.

“The LaRC Aerodynamics Team has completed high Mach number testing of numerous SLS configurations, including the SLS-27000 and SLS-28000 (Block IBs) using 0.8 percent scale wind tunnel models”, added L2’s LaRC SLS testing section.

“The data, which will include protuberance data, will be compared to the MSFC Tri-Sonic Wind Tunnel data, and merged with data from the transonic test to be conducted at the Boeing PolySonic Wind Tunnel (PSWT) in September.

“These tests represent the largest scale force and moment testing to be conducted during the SLS program to date. Data for the non-Design Analysis Cycle-2 (DAC-2) configurations will be provided to the MSFC Advanced Concepts Office for refinement of SLS architecture studies.

Sadly, these tests proved to be the final role for the LaRC Unitary Plan Wind Tunnel (UPWT), which is now scheduled for closure.

(Images: Via 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. Other image via NASA)

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