Rocket Crafters notes safety of hybrid rockets after SpaceX disaster
Image Credit: Mike Wagner / USLaunchReport
SpaceFlight Insider spoke with former NASA astronaut and current Rocket Crafters CEO and Chairman Sid Gutierrez about the potential of hybrid rockets in the wake of the Sept. 1, 2016, explosion that consumed a SpaceX Falcon 9, its Amos-6 satellite, and damaged the launch site at Cape Canaveral’s SLC-40.
According to Gutierrez, the propellants used couldn’t be safer. Nitrous oxide (N2O – more commonly known as laughing gas) and acrylonitrile butadiene styrene (ABS) – the same material that Lego bricks are made from. He noted that ABS is transportable on commercial aircraft, a far cry from cryogenic fuels.
SpaceX’s Falcon 9 rocket is fueled by a mixture of RP-1 (highly refined rocket-grade kerosene) and liquid oxygen. The volatile nature of this mixture was made apparent with this month’s accident at SLC-40.
Gutierrez rode fire to orbit twice: first as the pilot of STS-40 on the Space Shuttle Columbia in 1991 and then as the commander of Space Shuttle Endeavour on STS-59 in 1994.
The veteran astronaut noted that safety is one of the foremost rationales behind his company’s use of hybrid rocket engines.
“I wish I could have flown on a hybrid [fueled rocket] instead,” Gutierrez said. “I think that’s the reason that Virgin Galactic selected a hybrid rocket motor for their spaceship.”
For simplicity, Gutierrez broke the main types of rocket motors into three groups – liquid, solid, and hybrid. With liquid-fueled engines, two liquid propellants are combined under high pressure. The fuel and oxidizer within solid-fueled motors are mixed and combined well before the actual launch date. As noted, Rocket Crafters’ Intrepid rocket uses ABS and nitrous oxide.
“Nitrous oxide is much safer and easier to work with than liquid oxygen, and it is much more forgiving in terms of, you know, the temperatures you keep it at and how it operates,” Gutierrez told SpaceFlight Insider.
Gutierrez went on to note that since the fuel was in a solid form whereas the oxidizer is in a liquid form, this makes it more difficult for the two to mix and, therefore, means that an accident is less likely.
“You can, literally, pour the nitrous oxide down the center of the fuel grain and, unless you ignite it, unless you have some source of heat? Nothing will happen,” Gutierrez told SpaceFlight Insider. “The nitrous oxide would pool out the other side and you’d be left with, essentially, a wet Lego brick sitting there.”
According to Gutierrez, in the interest of having their launch vehicle operate as precisely as possible and being able to maintain a high degree of control, the Titusville, Florida-based company uses helium as its header gas on their nitrous oxide system as it is a self-pressurizing gas. Using helium should ensure that the pressure from this system is constant.
Hybrid Rocket Engine illustration. Image Credit: Rocket Crafters, Inc.
Some 30 tests of this design have already been completed (these were carried out in Utah). Since moving to Florida, Rocket Crafters has partnered with the Florida Institute of Technology on the construction of a test stand. This stand will be used to test the 400 lbf (1,880 N) version of the engine that Rocket Crafters is currently working on. If everything goes according to how the company plans, these tests should begin within the next few weeks. There are plans underway to develop a 5,000 lbf (22.2 kN) capable engine.
Although Rocket Crafters has plans to build larger motors, the company has its eyes fixed on the burgeoning CubeSat market. With the first launches of Intrepid currently scheduled to begin in the 2018–2019 time frame.
While there are a number of launch sites at Cape Canaveral that are available, the possibility remains that recently dubbed Launch Complex 39C (a portion of Kennedy Space Center’s historic Launch Complex 39B) might be used to launch Intrepid from.
“We are considering 39C, we walked around there at the pad and noted that there’s this giant hydrogen tank. So, we think that there’s too much around there,” Gutierrez said. “Launches from that site would be driven by the activity of other launch vehicles – and we’re looking at other launch sites due to that.”
Intrepid is roughly on the same scale of Firefly Alpha or Rocket Lab’s Electron rocket. Rocket Crafter’s business model has them eventually launching at the rate of about once per week.
“These smallsat operators want to launch on their schedule on the orbits that they want to go to,” Gutierrez told SpaceFlight Insider. “They want to be able to accomplish this at a reasonable price – and you can’t do that with a large launch vehicle like a Falcon 9.”
Rocket Crafters is looking at placing roughly 550 lbs (250 kg) to a 466 mile (750 km) orbit. While this is a far cry from the Falcon 9’s listed capabilities of some 50,265 lbs (22,800 kg) to low-Earth orbit, Rocket Crafters has stated that it is looking into bigger rockets and scaling their technology up.
Video Courtesy of Rocket Crafters, Inc.
Jason Rhian
Jason Rhian spent several years honing his skills with internships at NASA, the National Space Society and other organizations. He has provided content for outlets such as: Aviation Week & Space Technology, Space.com, The Mars Society and Universe Today.
I don’t think hybrid rocket safety is worthy against efficiency. Liquid fueled rocket was more dangerous but i don’t think that in the future someone would launch a comm sat with hybrid fueled rocket. It’s in a different class.
We fundamentally disagree. At Rocket Crafters we believe that the additional protocols required to work with dangerous or explosive materials makes those rockets less efficient. The loss of a pad makes the operation less efficient. Therefore safety is very important. Reliability is also important. The failure to launch on time or reach orbit is part of efficiency. And unless launch becomes more affordable, space will be too expensive for many applications. Therefore cost is also a factor. When the primary requirement driving rocket technology was the delivery of nuclear weapons, these factors may have been less important. But with commercial space driving the future of launch vehicles, we believe it is time to pay attention to them. At Rocket Crafters we have designed a vehicle around them. Finally, we believe our technology will enable hybrids to compete favorably with carbon based liquid bi-propellants. Our consistent, smooth burning 3D printed hybrid rocket engines will change the game. I believe you will see a com sat fly into space on a hybrid and it will be on a Rocket Crafters Intrepid 1.
Gutierrez should be ashamed for spewing such nonsense, as he certainly ought to know better. He didn’t ride on hybrids because hybrids couldn’t have done the job. They simply don’t have the performance of liquid fueled rockets, and they have major problems with scaling up. Nor are they as safe as claimed. Why compare the ABS fuel to the oxidizer used in the liquid fueled rocket? The fuel in the Falcon 9 is comparable to a high-grade jet fuel, which obviously is acceptable on aircraft. Liquid or high pressure nitrous oxide, on the other hand, is no more acceptable than liquid oxygen.
““Nitrous oxide is much safer and easier to work with than liquid oxygen, and it is much more forgiving in terms of, you know, the temperatures you keep it at and how it operates,” Gutierrez told SpaceFlight Insider.”
Actually, unlike liquid oxygen, nitrous oxide can detonate without any fuel present (like so many nitrogen compounds, it’s prone to explosive decomposition), and Virgin Galactic has already had a nitrous oxide explosion that resulted in three deaths. It also mixes well with greases and oils, or even hydrocarbon materials in plastics and composites, forming highly explosive mixtures. The scenario of a liquid nitrous oxide spill is much the same as for a liquid oxygen spill: you don’t do anything that might cause an explosion while you wait for it to evaporate.
http://www.knightsarrow.com/rockets/scaled-composites-accident/
Scaled Composites had an explosion when they were operating in the Mojave when the temperature was 105 degrees Fahrenheit where Nitrous Oxide goes critical at 97.7 Fahrenheit degrees. If you cool your tank then you don’t have to worry about it going critical and it is safer than LOX.
Several points relative to my desire to have flown on a hybrid rather than solids or liquid bi-propellants. The Challenger Accident was attributed to a burn through in one of the solid rocket motors. Once that occurred, the crew had no survivable options. They could not shut the solid rocket motors down like hybrids. After the accident NASA did look at replacing the solids with hybrids. But the technology was not there at that time. We believe our patented and patent pending manufacturing processes and fuel choices have changed the equation. .
The Columbia Accident was attributed to a piece of insulating foam from the external tank hitting the leading edge of the left wing. The damage ultimately resulted in loss of the vehicle and crew during reentry. Insulating foam was used because the external tank contains cryogenics – requiring special handling and presenting special hazards. When I was a test pilot in the Air Force I flew some of the early tests of an onboard oxygen generation system. The Air Force created a system to generate oxygen on the aircraft to eliminate the procedures and hazards associated with loading and carrying liquid oxygen on the vehicle. I agree Nitrous Oxide requires care and expertise in the design and operation of the system. We have studied the accident you reference at Virgin Galactic and believe we have addressed the issues in our design. We will do extensive testing to verify this. But all things considered, we have elected to use Nitrous Oxide because we believe it is safer. We would actually enjoy a significant boast to ISP if we used liquid oxygen, but safety is our top priority at Rocket Crafters.