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Sierra Space Provides Integration Services for New Nuclear Propulsion System as Part of DARPA’s DRACO Program

By Doug Messier
Parabolic Arc
June 26, 2021
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DRACO in orbit (Credit: Sierra Space)

LOUISVILLE, Colo., June 24, 2021 (Sierra Space PR) – Sierra Space, the new commercial space subsidiary of global aerospace and national security leader Sierra Nevada Corporation (SNC), will supply the propulsion components and integration services for a Nuclear Thermal Propulsion (NTP) system under a recent contract with General Atomics Electromagnetic Systems (GA-EMS). GA-EMS and Sierra Space will develop and demonstrate an on-orbit NTP system for a Defense Advanced Research Projects Agency (DARPA) program called Demonstration Rocket for Agile Cislunar Operations (DRACO).

While the primary mission of DRACO is to enable fast transit time between Earth and the moon, the development of nuclear powered spacecraft propulsion is also expected to open up deep space exploration to humans.

“This technology is an essential component of the new space economy,” said Tom Crabb, vice president of Sierra Space’s Propulsion & Environmental Systems group. “Faster, more fuel efficient propulsion and transportation systems support greater awareness of the cislunar space domain and broader exploration of our solar system. Theoretically we should be able to reach other planets nearly twice as fast with nuclear propulsion, placing less strain on the human body and the environmental systems needed for space travel.”

NTP uses a nuclear reactor to heat propellant to extreme temperatures before expelling the hot propellant through a nozzle to produce thrust. Compared to conventional space propulsion technologies, NTP offers a high thrust-to-weight ratio around 10,000 times greater than electric propulsion and two-to-five times greater specific propellant efficiency than chemical propulsion.

“We are really excited about the team dynamic with GA-EMS,” said Dr. Marty Chiaverini, director of Propulsion Systems at Sierra Space. “The GA-EMS reactor is smaller and more technologically advanced and Sierra Space brings extensive experience in developing and fielding mechanical, electrical and thermal conditioning systems that work reliably in space, as well as proven performance with liquid hydrogen-based rocket engines and liquid hydrogen turbomachinery.”

The NTP design will utilize a liquid hydrogen propellant heated by a nuclear fission reactor to provide two times the amount of energy than the most advanced liquid propellant rocket engine. Over the next 18 months, the team will define the system requirements such as power, weight, interfaces and control, and perform some subsystem risk reduction. Follow-on phases are anticipated to complete the demonstration system, leading to a flight test in 2025.

About Sierra Space

Sierra Space is a new independent commercial space company, created from the space capabilities of Sierra Nevada Corporation (SNC). Leveraging breakthrough technologies including the Dream Chaser® spaceplane and expandable LIFE™ habitat, Sierra Space builds and delivers the future of space transportation, destinations and infrastructure for LEO commercialization. Its turnkey, space-as-a-service solutions are modular, scalable and reusable, opening space to new participants globally. With 30+ years of proven spaceflight heritage, Sierra Space has provided more than 4,000 systems, subsystems and components to customers worldwide, and participated in more than 500 missions to space, including to Mars. Sierra Space is a subsidiary of global aerospace and national security leader Sierra Nevada Corporation.

About Sierra Nevada Corporation (SNC)

Owned by Chairwoman and President Eren Ozmen and CEO Fatih Ozmen, SNC is a trusted leader in engineering answers to the world’s toughest challenges, through customer-focused technologies and best-of-breed integrations in aerospace and defense and national security space. For nearly 60 years, SNC technology has delivered state-of-the-art civil, military and commercial solutions. SNC has received numerous awards and distinctions innovation, customer satisfaction and leadership including being named a US Best Managed Company for two consecutive years. In spring 2021, SNC announced the transition of its Space Systems business area to an independent commercial space company, Sierra Space.

About General Atomics Electromagnetic Systems

General Atomics Electromagnetic Systems (GA-EMS) Group is a global leader in the research, design, and manufacture of first-of-a-kind electromagnetic and electric power generation systems. GA-EMS’ history of research, development, and technology innovation has led to an expanding portfolio of specialized products and integrated system solutions supporting aviation, space systems and satellites, missile defense, power and energy, and processing and monitoring applications for critical defense, industrial, and commercial customers worldwide. For further information, visit

5 responses to “Sierra Space Provides Integration Services for New Nuclear Propulsion System as Part of DARPA’s DRACO Program”

  1. duheagle says:

    Good to see Sierra Space ever more solidly in the mainstream.

    That said, NTP is a tar-baby technology no one should be eager to punch. Sure, it has 2.5 or 3 times the vacuum Isp of methalox. But it gives all that, and more, back in crummy T/W ratio.

    • redneck says:

      Not to mention the anti-nuke political problems. And the problems inherent in hydrogen storage and use when long voyages are contemplated.

      • gunsandrockets says:

        Triple-point-phase slush-hydrogen storage? And my favorite for go-home propellant, liquid ammonia.

        SLS delenda est

        • duheagle says:

          Liquid ammonia eliminates a lot of specifically hydrogen-related engineering problems with the vehicle and is also manufacturable on Mars. But that isn’t enough, overall, to make nuclear thermal rockets a good idea.

  2. gunsandrockets says:

    Yay! More concrete information than the earlier press release teases about DRACO. So with that plus the yummy new Sierra Space artwork, I have playspace for fun guestimates about DRACO.

    That DRACO forebody looks like the Shooting Star module of the Dream Chaser CRS spacecraft. So the DRACO hydrogen propellant tank is probably about 3.5 meters in diameter and 7 meters long, which means about 5 metric tons of liquid propellant and a tank structure mass of roughly 1,750 kg.

    Reasonably assuming the DRACO NTR engine is related in size to an RL-10, I guess it generates 7,500 lbf thrust at an ISP of 900 seconds. That means the NTR engine masses about 850 kg, based upon typical NTR T/W ratios of 4/1.

    A ‘Shooting Star’ maximum mass is about 6,500 kg including 4,500 kg of ‘payload’, then the total mass of the DRACO could be about 14,000 kg which easily fits within the LEO payload limits of an Atlas V 531 launch. From a LEO parking orbit, a 14 ton DRACO would have plenty of propellant for a trans-lunar-injection burn.

    There are some critical variables at question here. How much ‘payload’ of the ‘Shooting Star’ is conventional rocket propellant? What if some novel technologies are incorporated into the DRACO? Perhaps slush-hydrogen storage, which would increase the NTR propellant load by 20%. Perhaps a bi-modal NTR engine able to produce electric power. Perhaps a low-pressure NTR engine with a significantly higher ISP.

    Good luck to them.

    SLS delenda est

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