Eric Ralph · June 18th, 2019
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Although the company quietly teased the concept for the first time several months ago, Firefly has released a detailed update on its Orbital Transfer Vehicle (OTV), an ambitious spacecraft meant to complement its Alpha and Beta launch vehicles. If Firefly can deliver on the independent spacecraft’s technical promises, the combination of Alpha (~$15M) and OTV could help usher in a new era of small, high-performance satellites launched on small, high-performance rockets.
In fact, Rocket Lab – currently the world’s only truly commercial smallsat launch provider – has already demonstrated the power of this new paradigm, albeit on a smaller scale. After just one failed attempt, the first successful orbital launch of the company’s Electron rocket also marked the surprise debut of a tiny third stage used to circularize the payload’s orbit. After five successful uses in orbit, Rocket Lab has taken its third stage a step further, adding redundant avionics, solar arrays, and more to effectively create an independent spacecraft/satellite bus called Photon. By all appearances, Firefly’s OTV is much larger than Photon but is functionally quite similar. By taking advantage of Alpha’s significant performance benefits compared to Electron, Firefly has designed a third stage/spacecraft capable of delivering hundreds of kilograms to geostationary orbit, the Moon, and (perhaps) beyond.
Changing the delta V game
- Generally speaking, OTV is quite small. According to Firefly’s Payload User’s Guide, the spacecraft will weigh just 130 kg (285 lb) dry and will carry perhaps 30-70 kg of xenon fuel for its electric ion thrusters. This is a critical differentiator relative to Rocket Lab’s Photon and kick stage, which rely on the inefficient (but simple and reliable) Curie chemical rocket engine.
- According to Firefly, Alpha is designed to launch a max of 1000 kg (2200 lb) to a 200 km (125 mi) low Earth orbit (LEO). Given OTV’s ~200 kg wet mass, Alpha + OTV offer some incredible capabilities relative to the rocket’s size and design.
- Powerful electric thrusters undeniably add a lot of complexity to any spacecraft that chooses to use them but that pain is often deemed worth it for the benefits they can offer. Most notably, ion propulsion is extremely efficient.
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| This graph demonstrates the potential performance benefits of Alpha + OTV relative to Alpha on its own. (Firefly) |
- Thanks to OTV’s efficient electric thrusters and light carbon composite structure, the potential benefits of Alpha + OTV are hard to believe for a rocket as (relatively) small as Alpha.
- On its own, Alpha can only deliver a meaningful payload (~100 kg) to perhaps 4000 km (2500 mi). With OTV, Alpha can suddenly deliver ~600 kg to a circular geostationary orbit (~36,000 km, 22,300 mi) and upwards of 400-500 kg into orbit around the Moon.
- For reference, despite weighing around 10% of Falcon 9, Alpha and OTV would offer perhaps 10-15% the performance of Falcon 9 to trans lunar injection (TLI). This utterly defies the general rule of thumb that as a rocket gets significantly smaller, its performance (particularly to higher-energy orbits) deteriorates disproportionately.
- With OTV, Alpha – nominally a ~$15M launch vehicle relegated to LEO payloads – becomes an incredibly intriguing option for small geostationary communications satellites and small-scale public and private exploration of the Moon, near Earth asteroids, and maybe even Mars/Venus.
- According to a senior Firefly investor and board member, Firefly hopes to have OTV ready for its orbital debut on Alpha’s third launch, tentatively scheduled no earlier than mid-2020.
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Alpha readies for launch
- Of course, OTV is a bird without wings without Firefly’s Alpha launch vehicle. Weighing 54,000 kg (120,000 lb) fully-fueled, Alpha is a two-stage rocket that will stand 1.8m (6ft) wide and 29m (95ft) tall. Powered by four Reaver engines, the first stage will produce ~740 kN (166,000 lbf), approximately 85% of one of Falcon 9’s nine Merlin 1D engines.
- Firefly is working relentlessly towards an ambitious December 2019 Alpha launch debut, a target that will probably slip into early 2020 due to the inherent complexity of the task at hand. Critically, though, Firefly has made a huge amount of progress towards that goal.
- Notably, Firefly’s second stage – powered by one vacuum-optimized Lightning engine – has already been qualified for launch with full-duration static fires at the company’s Texas facilities. Firefly is in the midst of preparing for an identical series of qualification tests for its more powerful first stage, shown above in the form of one Reaver engine attached to an Alpha S1 thrust structure.
- As early as July, a full set of four Reaver engines will be installed on the same thrust structure to perform static fire testing, much like SpaceX gradually added Merlin 1D engines during Falcon 9 development testing.
- If all goes as planned, Firefly will have completed its first Alpha rocket – first stage, second stage, and payload fairing – by October or November 2019. Expect plenty of new photos and updates as Alpha nears its inaugural launch.
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– Eric |
