Altius was excited to be selected yesterday by NASA for an SBIR Phase II contract to develop a cryogenic propellant transfer coupling for in-space refueling1. This is a follow-on to one of the three SBIR Phase I contracts Altius was awarded last April, and completed during the second half of 2016. While Altius has won a few SBIR Phase I contracts in the past, this is our first SBIR Phase II contract, and to give you an idea of how competitive this process is, Altius was one of only 133 Phase II awardees–out of a total of 399 Phase I contracts this cycle, which were selected from 1278 Phase I proposals. Since I didn’t have the chance to explain what we were doing for this project back when we won the Phase I effort, I wanted to spend some more time and give some background on what we’re doing and where we’re trying to take this after Phase II.
What is a Cryogenic Propellant Coupling?
A cryogenic propellant coupling is a device that allows you to temporarily connect two tanks together in a way that allows you to transfer super-cold liquids or gases between the two tanks. This is similar to how you use a gasoline nozzle and the fill receptacle on your car to transfer gasoline from a storage tank at the gas station into your vehicle, except you’re now dealing with super cold pressurized liquids or gases2. For rockets, cryogenic couplings are used for filling the stages prior to launch, but can also be used for refilling a stage in-space, similar to how military aircraft are sometimes refueled in-flight, enabling them to complete longer-range, and much more complicated missions without having to land to be refueled.
Traditionally, rockets are designed with a break-away coupling that is used to fill the rocket tanks with cryogenic propellants prior to launch, and to drain the tanks in the case of a last-second abort. If the flight is scrubbed at the last second, you don’t want to have to have someone climb up the support tower to reconnect fluid lines before you can drain the tank as part of safing the stage. So these couplings are designed to stay attached to the vehicle until the absolute last possible second3–after main engines have been lit, and as the rocket is just starting to leave the pad, at which point the coupling is yanked away from the vehicle so the rocket exhaust doesn’t melt it as the vehicle climbs off the pad.
The problem is that most of these couplings were only designed for fueling a vehicle on the pad. In order to not leak at cryogenic temperatures, cryogenic seals are used which typically take a significant amount of force to make the initial connection and provide seal “preload”. This means that these couplings are typically bolted onto the vehicle with frangible or explosive bolts that are actuated to remove the coupling–not exactly something that would be easy to reconnect on orbit for refueling! So, if you want to refuel a launch vehicle upper stage in space, say to do a Distributed Launch mission like ULA has proposed or like SpaceX has proposed for its Mars colonization plans, you have one of two choices–either you go with two separate fill/drain ports–one designed for ground T-0 disconnect operations and another one for easy in-space connection (likely robotically), or you could develop a single vehicle-side coupling design that could be used for both T-0 disconnect operations and reused for in-space robotic refueling.
That second option is what Altius is developing in this Phase II effort. Our thinking is that you need a fill/drain coupling anyway, so if you can design it for easy alignment and low-force connection/separation, you can kill two birds with one stone by having the same coupling do double-duty. This also has the benefit of providing a nearer-term market for these couplings than depots or distributed lift, since many companies are currently designing new upper stages, and all of them will need lightweight cryogenic propellant couplings.
Our Overall Plan for Phase II
Our Phase II plan includes doing some work to refine our unique cryogenic sealing architecture, which enables the super low connection/extraction forces, and then wrapping that into a full flight coupling design. Since we wanted to design and build a flight-like prototype in Phase II anyway, we decided it was best to tie it to a real-world application, so we could make sure we were designing something that could actually be used after Phase II is over. So, during Phase I, we reached out to several launch vehicle companies that are actively developing upper stages that use at least one cryogenic fluid, and found a few who would like to work with us to provide design requirements and design feedback as we develop the coupling. I won’t go into the details of who we’re working with yet, as I haven’t verified with the customers that I have permission to discuss their applications, but we’ve found at least one customer who needs a LOX coupler, in a size that’s convenient to work with in Phase II, and which could potentially get us a flight opportunity for the coupler very soon after the end of Phase II. We’ll be working with them to size the system, define requirements, flesh-out the design, and ultimately put it through qualification testing to qualify it for flight. Most of the Phase II design/testing effort will be focused on the T-0 fill/drain disconnect configuration of the coupling, but we’ll also build a slightly less flight-like in-space refueling coupling half, and practice robotic insertion/extraction operations (using our UR-3 robot arm or potentially one of our STEM Arms), and then simulated in-space fill/drain operations in our Thermal-Vacuum chamber. This will take us to a flight-ready T-0 disconnect design ready to integrate into the customer’s vehicle, and will also raise the TRL of the in-space refueling version of the coupler to TRL 6, where it could be integrated into a future in-space refueling demo.
In parallel with this SBIR-funded effort for developing a LOX version of the coupling, we’ll also be working with other groups to test the coupling and cryogenic sealing architecture for other fluids such as cryogenic hydrocarbons like Liquid Methane, super-cold Liquid Hydrogen and maybe even Liquid Helium.
Post Phase II In-Space Demonstration Ideas
After the Phase II effort, we have a few ideas for how to affordably demonstrate the in-space refueling version of this coupling. One option that we haven’t started discussing with Goddard yet would be to make a version of our coupling that could be tested on a future Robotic Refueling Mission on ISS. The Satellite Servicing Program Office at Goddard has been developing testbeds for testing various satellite servicing and refueling-related tools using the Dextre robot arm on ISS. One of their demos on the next RRM mission will in fact include demonstrating a Methane coupling they’ve developed in-house. We could work with them to see if we could adapt our system for an ISS demonstration transferring some sort of cryogenic fluid on-orbit.
We also have some affordable, higher-fidelity “distributed-lift” demo ideas we could potentially perform after we’ve developed our upper stage rendezvous/capture technology. One option that’s particularly intriguing could involve refueling a small launch vehicle upper stage using leftover LOX on a Centaur, and Kerosene/Helium brought up in additional tanks as a secondary payload. That would allow the smallsat launcher to launch with a payload, rendezvous with the Centaur, be captured, refueled, and then reignite to send its payload to some destination beyond LEO. Most of the small launch vehicle upper stages I’ve run the numbers for could send their full LEO payload to almost anywhere in the solar system if fully refueled in LEO4.
I don’t know if there’s a market for dedicated small-sat launch to MEO, GEO, or Deep Space, but if there is, this demo would provide a way to start doing initial missions for on the order of half to two-thirds of the price of a dedicated reused Falcon 9 flight5. If you can get a rideshare slot to your interplanetary destination, obviously that’ll be cheaper, but if you’re trying to go to some place that doesn’t have other regular passengers, something like this could be an intriguing option.
As we work on the Phase II LOX coupling, we’re going to reach out to as many launch vehicle developers that have cryogenic upper stages as we can, both commercial (ULA, Blue Origin, SpaceX, Virgin Orbit, Generation Orbit, Ventions, RocketLabs, Masten, etc), government (SLS/EUS), and foreign (Arianespace, MHI, etc), especially focusing on those that are developing new upper stages. Our goal is to see if we can get enough customers that we can start creating a few standard sizes (maybe one for ACES/New Glenn/Falcon 9/EUS sized vehicles, one for Centaur/Ariane class vehicles, and one for smallsat launch vehicles like LauncherOne, Electron, etc) for fuel and oxidizer, to start making it easier for companies to transition to either refuel their upper stages on-orbit, or also to provide fuel-delivery on-orbit. These vehicles need a fill/drain valve anyway, and if we can keep ours simple, light, and affordable, we hope to be able to land several customers, especially for anyone who is designing a new upper stage so who may require a new coupling design anyway. By going with a few standard sizes, you get to an ideal like what people deal with at the gas station–you know when you drive up to a gas station, in any state, that the gas nozzle is going to fit into your car. If we can do that for upper stages, I think we’ll be well on our way to a future where on-orbit refueling becomes commonplace.
Sorry this initial post was deliberately light on both pictures and technical details. I usually like being pretty open about what we’re doing, but since these couplings are used for rocket vehicles, they may fall under ITAR, and some of the technical elements are probably patentable–especially the low connection force cryogenic sealing architecture. Once we’ve had a chance to file some patent protection and talk with our export control lawyers, we’ll see what we can say going forward. We’ll make sure we find some way of sharing more information and progress updates as we go along. In the meantime, if you’re a US company or research group that is interested in this technology, please reach out to us and we can give you more information off-line6.
- The Phase II proposal abstract can be found at https://sbir.nasa.gov/SBIR/abstracts/16/sbir/phase2/SBIR-16-2-H2.04-8454.html
- Liquid Oxygen (LOX) is only a liquid at temperatures below -180C, and Liquid Hydrogen (LH2) is a liquid only below about -250C, both of which are really, really cold
- This is why this style of coupling is often called a T-0 fill/drain disconnect, because it doesn’t disconnect until literally at the point the vehicle transitions from countdown to flight
- Most of them can send at least some useful payload literally anywhere humanity has sent other space probes if they’re willing to live with a smaller spacecraft than the maximum LEO capacity of the launcher
- Using the currently proposed $50M price SpaceX is offering for flights on a F9 with reused first stage
- My contact info can be found in the abstract linked-to here