Blue Origin’s recent successful launch, recovery, and re-flight of their suborbital RLV New Shepard got me thinking about an idea that I came up with back in late November shortly after their first flight.
In an article written shortly after the first successful flight and recovery, Erika Wagner of Blue Origin mentioned an intriguing suggestion for a potential mission upgrade for future customers:
Down the road, Wagner said Blue Origin would offer a number of upgrades for research, including quick access to payloads shortly before launch and after landing, as well as hand-on control of experiments once the vehicle starts carrying people, something she later said was still a couple of years away. Blue Origin would even be open to replacing the entire crew capsule with a research payload. “If you have something that weighs 8,000 pounds and needs to get up to 100 kilometers, come talk to me,” she said.
This got me thinking about the possibility of replacing the capsule with an orbital payload and small upper-stage, and flying a Pop-up TSTO trajectory. Basically, the New Shepard booster would follow a similar trajectory to its current operations, but shortly after main engine shutdown, the upper stage would separate, and fire horizontally to accelerate to orbital velocity. So long as the upper stage had a sufficient T/W ratio, this would mean that the first stage will have covered all or almost all of the gravity/drag losses, meaning that the upper stage would only have to deliver ~7400m/s of delta-V to reach orbit.
While that’s a lot for a single stage, the stage would be operating entirely in vacuum. For a LOX/Kerosene stage with a conservative 320s vacuum Isp, that would require a pmf of ~92% to deliver a 100lb payload to LEO. For a LOX/LH2 stage with a conservative 440s vacuum Isp, you’d need about an 83% pmf. Both of those seem reasonably achievable for small pump-fed stages (possibly using electro-pumps such as those under development by Ventions or RocketLabs). With slightly more aggressive pmf/Isp assumptions (85% pmf and 450s Isp for the LOX/LH2, and 94% pmf/340s Isp for the LOX/Kero), you can get closer to 300lb payload. And if you don’t care about the added complexity of going to a 3STO system, with two expendable stages lofted by New Shepard, my numbers suggest you could probably push up into the 500-800lb paylaod range, assuming similar pmfs and Isps to the single expendable stage–though how you would exactly configure a 3STO to fit in anywhere near the same payload volume as the capsule is an open question.
Volume-wise, even the LOX/LH2 stage would likely fit within close to the same volume as the existing capsule–at typical O/F ratios, you would need about 10m^3 for the LOX/LH2 tankage, compared to 15m^3 of internal volume in the existing New Shepard capsule, with the LOX/Kerosene upper stage being even smaller. You might want to stretch the volume a little bit to provide more length for putting a payload on top, and you’d likely have some sort of fairing to surround the upper stage and payload on the way up, but neither of those seem like show-stoppers.
It would be interesting to see how the economics of such a NLV compared with others in its class. Blue Origin didn’t give a price for replacing the capsule, but if they have six paying passengers at $200k each (comparable prices to what VG has been claiming for a while), that would imply a price per flight of <$1M for the first stage, possibly as low as $500-600k.
I wonder if Blue Origin is already thinking about something like this themselves, or if they aren’t personally interested, if they’d be willing to partner with another company to do something like this. Food for thought.