Every orbital launch to date has used either solid rockets (which are super simple but can't be throttled, turned off, or relit), or liquid rockets (which can do all of those things and are generally safer but at the cost of significantly increased complexity).
Hybrid propellant rockets can theoretically combine many of the advantages of both systems by using (typically) a liquid oxidiser that runs through a solid fuel grain, allowing for the control and safety of a liquid rocket with much of the simplicity of solid rockets.
Presently they're a popular choice for sounding rockets and other sub-orbital or amateur rocketry, but no one's ever successfully reached orbit with one due to difficulties with scaling them up (particularly thanks to the fuel regression rate, and the issue of how to provide pressure for the liquid propellant).
However there are a number of companies and organisations working on doing just that, and it's only a matter of time before someone succeeds. This question therefore asks which hybrid rocket* will reach orbit** first.
*For the rocket to count: its first stage must use a combination of a solid propellant and a fluid propellant (either liquid or gas) as its primary method of propulsion. If air-launched, the first rocket stage is the one that counts.
**For it to count as reaching orbit: either a stage of the rocket or something deployed by the rocket must complete at least one full orbit around the Earth with an apogee of ≥150km
Variants of rockets count under the one answer so long as they share the name and reasonable flight heritage (eg if Gilmour Space gave up on the Eris and started work on an Eris block 2 that had a different upper stage and modified first stage that would still count for "Eris (Gilmour Space)".
The organisation's name is included in the answers for readability but is not required for resolution (eg if Rocket Lab bought out Gilmour Space and started operating Eris I would simply rename the Eris option to "Eris (Rocket Lab)"
If no launches that have met the criterion have occurred by the end of 2035, will resolve to None; otherwise, please feel free to add new companies and organisations working on orbital hybrids if they pop up.
This market includes launches that occurred prior to market creation so if I'm wrong and you know of a hybrid propellant rocket that has already made it to orbit (as per the criterion), feel free to bet and let me know!
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Hybrid propellant rockets can theoretically combine many of the advantages of both systems by using (typically) a liquid oxidiser that runs through a solid fuel grain, allowing for the control and safety of a liquid rocket with much of the simplicity of solid rockets.
Lol. There are reasons they haven't been used for orbital launches. In practice, they combine the complexities of both with the advantages of neither. And they add in O:F ratio shift problems and (in some applications) weird CG behavior.
You get the pressure-fed performance of a high pressure casing like a solid. You have to deal with valves and igniters suitable for liquids. You need a pressurization (or self-press) system. You lose all the convenient pump cycles.
Where's the option for "none of the above"? Or "All of the listed companies either go bankrupt, get acquired, or successfully launch a non-hybrid vehicle to orbit before a hybrid"?
@EvanDaniel That said, there are applications where they're great. Those basically amount to medium-sized nitrous hybrids on an amateur scale where burn rates are tractable without weird additives and you aren't super picky about mass fractions. I'd much rather hear someone talk about their college hybrid project that flew than their liquid that didn't in an interview.
@EvanDaniel I don't entirely disagree btw - the number of companies who were working on orbital hybrids that have either gone bankrupt, pivoted away from orbital, pivoted away from launches entirely, or swapped to liquid propulsion is kind of ridiculous; like at least 3/4 of the organisations I looked at have given up or gone bankrupt.
That said, while they do introduce a ton of new technical problems and therefore maybe aren't worth it, I think the primary reason none have been successful yet is more a result of lack of R&D invested into them - and with that investment and those problems solved they would be reasonably viable.
Of course whether that R&D investment is worth it is another question, maybe if you're doing that much work you should just develop a liquid rocket (it's sort of the same argument applied to developing aerospikes and it's a valid one) but regardless companies are making that investment so I personally do feel like it is inevitable that someone will succeed eventually.
@Nat Yeah, the basic argument is kinda... if you're doing the work on a solid, just do solids. And if you're doing the work on a liquid, just do a liquid. The second fluid circuit is easier than the first, etc.