Thursday, January 20, 2022

New Rocket Company Aiming for a Holy Grail of Spaceflight

A Washington State company that had been working under the radar and in relative anonymity has decided to go public and announce they're working in pursuit of one of the holy grails of spaceflight: a Single Stage To Orbit (SSTO) space plane.     

Radian Aerospace concept rendering. 

Radian Aerospace said it is deep into the design of an airplane-like vehicle that could take off from a runway, ignite its rocket engines, spend time in orbit, and then return to Earth and land on a runway.

"We all understand how difficult this is," said Livingston Holder, Radian’s co-founder, chief technology officer, and former head of the Future Space Transportation and X-33 program at Boeing.

If the X-33 program isn't familiar to you, that was a NASA program in the late 1990s that was short lived and never actually flew.  It was envisioned to take off "like a rocket" and land like an airplane, a big difference from Radian's goal.  The X-33 seemed to conceptually be a child of the McDonnell Douglass DC-X, or Delta Clipper- Experimental, a vehicle that achieved flight a few times between 1993 and 1996.  What flew was a 1/3 size scale model and didn't fly to orbit, but did launch, translate (move sideways) and land under power, said to be the first rocket ever to achieve that goal.  Today, the DC-X is referred to as The Rocket That Beat SpaceX by 20 Years - at least there at Amusing Planet. 

Radian's announcement came as the company revealed they had just secured $27.5 million in funding to help them get started, but that won't get anything flying.  Ars Technica reports the company has raised $32 million but didn't specifically say "not including this $27.5" so I'm going to assume it does include it.  The company has 18 employees is Renton, WA.  

During an interview with Ars, Holder and Radian CEO Richard Humphrey explained that they realized it would require significantly more funding to build such an ambitious orbital space plane. Funding will pace their development efforts. For that reason, Humphrey said he was not comfortable putting a date on the company's first test flights but said that Radian was aiming to have an operational capability well before the end of the 2020s.

The current design of Radian One calls for taking up to five people and 5,000 pounds of cargo into orbit. The vehicle would have a down-mass capability of about 10,000 pounds and be powered by three liquid-fueled engines. The idea would be to get as close to airline operations as possible, by flying, landing, re-fueling, and flying again.

It's almost a cliche to say "space is hard" or "orbit is hard."  Neither of those adequately addresses how much harder SSTO is.  The "three liquid-fueled engines" they mention in that second paragraph are reported to exist and I assume that's as at least one full scale prototype, which is claimed to produce 200,000 pounds of thrust.  By comparison, SpaceX's Raptor 2 engine seems to be emerging into production at closer to 500,000 lbs of thrust.  We have heard of individual engines producing 540,000 lbs of thrust during tests. 

The question has come up of whether Starship and its six Raptor engines could achieve orbit without the Super Heavy booster several times on the Lab Padre comment sections.  It has been said the answer is "just barely" but not with enough cargo capability to be worthwhile (and I read "profitable" for that word).   

The article at Ars is worth reading.  All of the principal people at Radian say they understand the difficulties of the road ahead and the backgrounds they list add some believability to the claim.  As I was saying before, the $32 million they've raised so far isn't going to fund a program this ambitious until "well before the end of the 2020s."  I doubt that's a tenth of what they'll need; multiply that $32 million by 30 or more.  Final words to Eric Berger at Ars Technica.

"A long time has passed since the last true attempt at this," Holder said. "The technology has moved forward, and people are willing to fund projects like this."

If Radian can succeed technologically, large markets would likely open. A vehicle like Radian One would be well suited to fly people to commercial space stations in low Earth orbit, which NASA seeks to foster development of by 2030. These planes could also perform Earth observation work and play a role in bringing back space-manufactured goods. There is also the potential for point-to-point travel on Earth.




  1. Rocket thrust is not the most important thing, "thrust efficiency" or specific impulse (Isp) is. Think of it as driving up a very long, steep mountain - you need enough horsepower to get you climbing the mountain, but you have to be able to carry enough fuel (at a specific MPG) to get to the top. If the mountain is long enough, it may be impractical to carry enough fuel - your vehicle will need to be a tanker truck (there are no gas stations on the way). Staged rockets allow you to drop no longer needed mass along the way to increase your efficiency (no longer need to carry the extra weight) as you move up the mountain.

    Not that I have done the math* for many years, but IIRC SSTO (with any significant payload) is not practical without Isp's significantly higher (more than 2x?) than current liquid rocket engines/liquid fuels. Isp determines what mass fraction of the vehicle needs to be propellant. To achieve orbit current rockets require ~90% fuel mass at launch (that is 90% propellant, 10% structural mass and payload).

    What new technologies are they exploiting? Ramjet (or similar using atmospheric oxygen to reduce the oxidizer needed, but it increases complexity and mass)? Maybe enhanced with an ejectable external fuel tank? Or nuclear** (may be feasible, and it adds a large amount of non-fuel mass to the spacecraft)?

    *See: If you are interested in the math, propellant mass fraction (they call it propellant mass ratio) is addressed in the last several equations near the end of the page. And I cannot resist adding this:

    ** Example: current DARPA DRACO program


  2. What Art said. Either significantly lighter material and/or much more powerful fuel and efficiency is required for SSTO.

    Unless the company has found a way around chemistry and physics.

  3. Falcon Heavy has the lowest price to date to low orbit, at $681.82/lb ($1500/kg).

    That puts the ticket price for a 200# human at only $136,364.

    Or, only 9½ times the price of a round trip first class non-stop ticket from L.A. to Dubai, and only 2½ times the entire average annual income of anyone in the US ($55.1K/yr), which has the highest median income in the world. (But anyone could skip food and shelter for 2 1/2 years, amirite?)

    Sh'yeah, this will happen when monkeys fly outta my butt.

    Someone call Popular Science or Popular Mechanics, theyy could get a cover article smoking that much malarkey, hopeium, and crack cocaine.

    We'll have flying cars and jetpacks for the masses first.

    But it's always fun to dream.

  4. Things get interesting the closer one gets to CDR (Critical design Review). THAT is when you find out all the things you missed earlier in your design process. And how their weight adds up.

  5. Did they talk to anyone who worked on x-33. If I recall correctly the killer was the use of composite cryogenic tanks with the ensuing microcracking problem.

    1. The real killer for Venturestar was negative payload capability to orbit. Mass fraction is hell for single stage to orbit.

    2. The only thing the article mentioned that's relevant to the mass fraction issue was that carbon fiber was an exotic material in 1995, not so much now. They never touched the topic of the Specific Impulse of the engines.

      The whole idea of a useful SSTO vehicle being based on a single technology like a carbon fiber vehicle seems like a lot of metaphorical eggs in one basket.

      Casey Handmer has a very deep series of articles on misconceptions about space travel. I believe that was the first place where I encountered the idea that if Earth was a bit bigger, we couldn't make orbit with any known rocket technology.

  6. And how many carbon credits is this going to cost?


  7. Yes, Anonymous, a composite cryogenic tank failure was the reason X-33 was cancelled. I was working that program when the failure happened and X-33 was cancelled immediately after that failure. The subscale X-33 vehicle was the demonstration program which was supposed to lead to the development of a full-scale vehicle called the Venture Star. Realizing a true SSTO vehicle is going to need a heavy dose of unobtainium.

    1. I believe you will find that the reason the Venture Star was cancelled was NOT because of the cryo tank failure.