Wind Tunnel tests evaluating environmental conditions for SLS

by Chris Bergin

The various configurations of the Space Launch System (SLS) are continuing their wind tunnel testing at various locations around the United States. One team is focusing on how the Heavy Lift Launch Vehicle (HLV) will react to environmental forces during liftoff, while another team evaluates potential design changes to the booster nose cones.

SLS Wind Tunnel Testing:

With the Outer Mold Line (OML) of the SLS now confirmed via the successful Preliminary Design Review (PDR) phase of the vehicle’s development, wind tunnel testing allows engineers to ensure the performance of the design will ably cope with the expected conditions during launch and ascent.

Working alongside powerful computational tools, engineers have built several scaled models of the new HLV, models that provide a real-world knowledge base that will be further refined when SLS launches for real at the end of 2017.

Z417Testing has been ongoing for some time, with all of SLS’ configurations – designated by their Vehicle Configuration Reference (VCR) numbers – receiving a level of evaluation.

Known as SLS Block 1, the VCR 10000 vehicle consists of two five segment Solid Rocket Boosters (SRBs) and a core stage powered by four RS-25D engines re purposed from their role with the Space Shuttle Program (SSP). The vehicle will also include an ICPS (Interim Cryo Propulsion Stage), with the Orion (MPCV) spacecraft completing the stack.

There are four SLS Block 1A configurations on the table, all based around the 105mT requirement, with a crew version and a cargo version of the vehicle, each with either a solid or liquid booster option.

However, the 105mT SLS may become known as the Block 1B, 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 can endure.

The impact of the booster decision will also relate to the 130mT fully evolved version of the SLS, known as the Block 2. However, this vehicle is not expected to come on line until the 2030s, if at all.

Z321The first view of the Block 1B (L2) came via a photo of its small scale model, as the SLS configurations were put through wind tunnel testing at the Marshall Space Flight Center (MSFC) in Alabama last year.

Testing was also 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.

Boeing’s PolySonic Wind Tunnel (PSWT) and NASA AMES have also been utilized during the evaluations into the various SLS models.

“The Space Launch System (SLS) Aero-acoustic Wind Tunnel Test, which is being led by the Aerosciences Branch (EV33), completed testing as planned after the third week of operations on September 5, 2013,” noted L2’s SLS Update Section.

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“This test was conducted in the transonic and supersonic test sections of the Ames Research Center Unitary Plan Wind Tunnel. Testing in the transonic tunnel section was completed on August 29, 2013. Transition to the supersonic tunnel section finished on August 30, 2013, with data collection on the 2.5 SLS-10003 (Block 1) model.”

Z452The AMES testing is responsible of checking into a potential design change with the SLS booster nose cone, relating to an aeroacoustic loading issue – in the transonic flight region – impacting on the booster/core attach points, per evaluations.

If implemented, SLS’ boosters will have the appearance more akin to the Ariane 5’s boosters. ATK – who are supplying the solids for the opening SLS missions and competing for the Advanced Booster contract – were already looking into this new nose cone design for their ACB option.

“Supersonic testing of the 2.5 percent SLS-10003 configuration concluded on September 3, 2013. It included the “best” buffet mitigation option based on preliminary results from the transonic testing and one NASA Engineering and Safety Center booster nose cone concept,” added the notes.

Meanwhile, back at LaRC, NASA engineers and contractors recently completed liftoff transition testing of a 67.5-inch model of the SLS in a 14-by-22-foot subsonic wind tunnel at the facility.

Z8“In a typical wind tunnel test, we point the model into the flow field,” noted John Blevins, lead engineer for aerodynamics and acoustics in the Spacecraft & Vehicle Systems Department at MSFC. “For the liftoff test, that’s not the case. The wind is actually traversing across the model at much higher angles – simulating a liftoff environment.

Engineers used a technique for studying airflow streamlines called smoke flow visualization. Smoke is put into the wind flow and can be seen during testing, allowing engineers to see how the wind flow hits the surface of the model.

Z7“The test data is key to ensure vehicle control as we lift off and pass the ground tower,” added Mr. Blevins. “At supersonic speeds, engineers can more easily compute the forces and moments, but that’s more challenging at low speeds. This test is low speed, with winds in the tunnel only reaching up to 160 miles per hour.”

Engineers will use the data from this test to run flight simulations on the actual SLS vehicle and assess its performance, evaluating moments, or torque, that act like a twisting force on the vehicle, in turn helping the teams understand the flow pattens.

The models will gain their largest database of information when SLS launches for real, during its EM-1 test flight in 2017.

(Images: Via L2 content from L2’s SLS specific 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 images via NASA)

(L2 is – as it has been for the past several years – providing full exclusive SLS and Exploration Planning coverage.  To join L2, click here:

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