Sierra Nevada’s 5-year partnership with NASA – Progress on Dream Chaser

by Chris Gebhardt

Five years after joining forces with NASA’s Langley Research Center, the Sierra Nevada Corporation continues to narrow its focus on their Dream Chaser spaceplane – a NASA Commercial Crew Development-funded vehicle that will one day transport astronauts to Low Earth Orbit destinations including but not limited to the International Space Station.

NASA Langley and Sierra Nevada’s 5-year partnership – From HL-20 to Dream Chaser:

Engineers at NASA’s Langley Research Center (LRC) have marked five years of collaboration with Sierra Nevada Corporation (SNC) as partners in the design and development of the Dream Chaser spaceplane and systems.

Birthed from the HL-20 lifting body vehicle, LRC and SNC’s five year partnership has focused on the evolution and substantiation of the Dream Chaser orbital crew vehicle.

“We’re thrilled to see our HL-20 design being advanced by Sierra Nevada and glad to have the chance to work with the company on the further development of its Dream Chaser,” said Robbie Kerns, manager of the Commercial Space Projects Office at NASA Langley.

Added by Mark Sirangelo, Corporate Vice President and head of Sierra Nevada Space Systems, “NASA Langley has been an engaged and supportive partner since the beginning of our Dream Chaser Program. The Dream Chaser was born at NASA through the great work of the Langley Center. We would not be where we are without the talented NASA people, past and present, who have enabled our Dream Chaser vehicle to start its operational flight testing.”

Signaling the beginning of a new phase of Dream Chaser’s development, the LRC-SNC team recently partnered with engineers at United Launch Alliance, operators of Dream Chaser’s preferred launch vehicle, the Atlas V, for buffet tests on the launch vehicle/orbital crew vehicle stack.

These buffet tests supplied Dream Chaser engineers with data on pressure fluctuations the launch vehicle stack may experience during its ascent to Low Earth Orbit (LEO) from the Atlas V’s LC-41 launch pad at the Cape Canaveral Air Force Station – the world’s premiere spaceport facility in Central Florida.

But understanding the launch environment that will be induced onto Dream Chaser during its liftoff on the Atlas V is only one of the considerations under analysis by Sierra Nevada Corp.

As related to in an interview with Lee Jay Fingersh, Mark Sirangelo stated that the Atlas V rocket, in its never-before flown 402 configuration, is the desired launch vehicle at this time.

This configuration of the Atlas V – as with all Atlas V rocket numerical designations – is representative of the payload fairing size, number of solid rocket motors, and number of engines on the Centaur upper stage.

The never-before-flown 402 vehicle configuration for Dream Chaser, would technically consist of a 4-meter payload fairing (though no evidence exists to support the use of a payload fairing for Dream Chaser missions, with the Dream Chaser itself not requiring the aerodynamic protection offered by a payload fairing), no solid rocket motors, and a dual-engine Centaur upper stage.

In fact, the only element that makes this Atlas V configuration unflown is the dual-engine Centaur.

Regardless, United Launch Alliance has committed itself to completing all work on man-rating the Atlas V 402 vehicle by 2014 by completing work on and integration of the Atlas V’s new Emergency Detection System (EDS).

This EDS would be crucial in detecting potentially mission-ending anomalies with the Atlas V and relaying those issues to the crew inside Dream Chaser. 

As related by Mark Sirangelo, “We picked Atlas because it’s known, it’s reliable, and [the astronauts] really don’t have to worry about [the Atlas].  They just need an Emergency Detection System so they know when to get off the vehicle.”

The EDS would be especially critical to the Dream Chaser and its crew during the final four-minute terminal count for the Atlas V through orbital insertion and separation from the Centaur upper stage.

While it is obviously hoped that the EDS will never be needed, especially given the Atlas V’s impressive 100 percent success rate (as defined by the launch vehicle’s customers), a launch abort scenario is under examination by Sierra Nevada.

In the event of an EDS-triggered launch abort, Dream Chaser would use the Atlas V’s thrust termination (cutoff of all propulsive elements) abort style to its advantage.

Classed as being able to provide “moderate acceleration” when coupled with the Atlas V’s thrust termination, the hybrid engines on Dream Chaser would be able to separate and clear the spaceplane from the destructing Atlas V and begin a return trajectory to any nearby airport – either commercial or government controlled.

But aside from the addition of the EDS to the Atlas V, no other modifications would be needed – or are planned – for the Atlas V/Dream Chaser stack.

Even more impressive is the seeming lack of modifications needed to the Atlas V’s ground equipment currently in use by United Launch Alliance. In fact, Sierra Nevada indicates that only an adaptor to the current launch tower would be needed for vehicle access – both for the crews of Dream Chaser and support personnel who would assist astronauts with entry into the vehicle and final preparations for launch.

Moreover, on the other side of mission operations, Dream Chaser will hold the capability of returning to Earth (from the International Space Station or any point along the ISS’s orbit – aka, a 51.6 degree inclined orbit) within six (6) hours of the declaration of any emergency or immediate End Of Mission termination notice/decision.

This capability is based in large part on the spaceplane’s 1,500 kilometer cross-range capability, its ability to be flown entirely in a manual or automated mode, and its ability to land on any conventional runway at any commercial airport.

The ability to land safely at any commercial airport is something that, while not technically new to the arena of spaceplane operations (the Space Shuttle orbiters carried the ability to land at any commercial airport with a runway long enough and sturdy enough to accommodate their weight, landing speed, and roll out/stopping distance), is greatly improved by Dream Chaser.

This is primarily due to Dream Chaser’s use of non-toxic, non-explosive ethanol-based reactants for its Reaction Control System thrusters – a rather significant departure from the monomethyl hydrazine reactant used by the Space Shuttle orbiter fleet, a substance that was explosively volatile and required extreme ground-handling precautions/care for a just-landed Space Shuttle.

For Dream Chaser’s ethanol-based RCS propellant, ground crews will be able to approach the spaceplane immediately after landing – giving significant advantage to a scenario where Dream Chaser could be called upon to bring a sick astronaut home from the ISS for immediate medical care.

But regardless of the nature of Dream Chaser’s landing, Sierra Nevada is currently looking at a two-month turn-around of the vehicle between flights to LEO.

In those two months, large-scale sections of the spaceplane’s Thermal Protection System tiles would be replaced if needed – with whole tiles being replaced (even if just for a scratch) instead of repaired, as was the case with Shuttle.

Moreover, the vehicle’s docking adapter will be removed and replaced after each mission instead of being reused.

According to Mark Sirangelo, “The economics work out that it’s not really advantageous to reuse it.” This goes toward an explanation for why there is no body flap on the back of Dream Chaser, like there was on Shuttle, to protect Dream Chaser’s docking adaptor.

Finally, while current operations are scheduled to begin in 2017, Sierra Nevada is confident that Dream Chaser could be ready to go sooner than that, as long as there is consistent funding provided by NASA.

(Images via L2 – via the new DC section, *L2 members click here* – with additional images via NASA and SNC)

(With the shuttle fleet retired, NSF and L2 are providing full transition level coverage, available no where else on the internet, from Orion and SLS to ISS and COTS/CRS/CCDEV, to European and Russian vehicles. 

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