Firefly aims for orbit on second demonstration flight

With the goal of successfully reaching orbit, Firefly is set to launch FLTA002 – its second demonstration flight of the Alpha launch vehicle – on the mission dubbed “To The Black.” Launching from Space Launch Complex 2 West (SLC-2W) at the Vandenberg Space Force Base in California, the vehicle is scheduled to lift off on Sunday, Sept. 11 at 3:00 PM PDT (22:00 UTC). In the event of a delay, the launch window extends to 7:00 PM PDT (02:00 UTC on Sept. 12).

FLTA002 will attempt to place several small satellites into a 300 km circular low-Earth orbit (LEO) with a 137-degree inclination.

Firefly’s first orbital launch attempt was terminated during the first stage burn on Sept. 3, 2021, following an engine failure 14 seconds into launch. Despite this engine shutdown, the vehicle was able to maintain control for nearly two and a half minutes, before tumbling, leading ground operators to activate the flight termination system.

Firefly was able to recover the engine assembly downrange, allowing them to figure out that the engine shut down early due to pins failing in the power line to the main engine valves, causing them to close and shut the engine down. This failure mode was backed up with data received from the vehicle, which reported a drop in current on the power rail and the closure of the valve.

Firefly founder Tom Markusic noted that the engines on flight 1 were “rougher” than newer engines and therefore produced more vibrations during flight. However, to be safe, teams moved the electrical conductor further up on the vehicle where vibrations are less intense, ensuring the failure mode will not repeat itself.

Alpha is a two-stage small-lift launch vehicle built and developed by Firefly Aerospace. With an eventual goal of being able to place 1,170 kg of payload into LEO, the meters vehicle stands at 29.48 tall. Alpha has a significantly higher mass-to-orbit than other small satellite launchers, such as Rocket Lab’s Electron or Astra’s Rocket 3, which have put placing up to 300 kg and 25 kg into LEO, respectively.

The first stage of Alpha is equipped with four Reaver 1 engines, which run on RP-1 kerosene and liquid oxygen (LOX). Notably, Reaver utilizes the tap-off engine cycle, meaning that instead of having a separate gas generator to spin the turbines, pressure from the main combustion chamber is used. However, as the exhaust gas used to spin the turbine is still exhausted, this is still considered an open-cycle engine.

Each Reaver engine produces a maximum thrust of 200 kN and achieves a specific impulse of 296 seconds in the vacuum of space. For rocket engines, the engine’s specific impulse is directly proportional to the velocity of the exhausting gas; for Reaver, the maximum average exhaust velocity is ~2,900 m/s.

Alpha’s first and second stages are both built from carbon-fiber composites that form ultra-light linerless propellant tanks. Similar to the Falcon 9, both stages have their RP-1 tanks on the bottom with the LOX tank on top, with a transfer tube to deliver LOX to the engines.

FLTA002 vertical at SLC-2W before launch. (Credit: Michael Baylor for NSF)

The second stage is equipped with a single Lightning 1 engine, which is also a tap-off engine cycle capable of producing 70 N of thrust.

On top of the second stage lies the carbon-composite payload fairing. For “To The Black,” there are a number of small payloads inside. Firstly, Teachers in Space will launch the Serenity 3U CubeSat, which will collect flight data during its mission and make it available to the educational community.

Also flying on FLTA002 is NASA’s TES-15 3U CubeSat, which has a deployable exo-brake that will be used to validate center of mass systems for future reentries. This payload is part of NASA’s Technology Educational Satellites program, which gives students the opportunity to work on satellites.

The final payload will be Libre Space Foundation’s PicoBus, which will deploy six picosatellites. All of these satellites are technology participants for communication, remote sensing, and more.

Eight hours before launch, teams will begin final pad checkouts. During this time, the Alpha vehicle will be powered up and perform sensor checks, which should be completed by T-6 hours. At this point, the vehicle will begin to be loaded with helium, which is used to pressurize and backfill the tanks as they are empty during ascent.

At T-5 hours and 15 minutes, the vehicle will begin being loaded with RP-1. 45 minutes later, the pad will clear, giving way to the start of LOX load at T-3 hours and 40 minutes. Propelant loading will last until 20 minutes before launch when the vehicle will enter terminal count. At this point, the rocket will be fully fueled (both with RP-1 and LOX), and will continually be topped off with both propellants.

The four Reaver 1 engines on the first stage will ignite at T-1.8 seconds utilizing TEA-TEB–a pyrophoric compound, meaning it combusts upon contact with oxygen. This combustion will be bright green and will signal the start of the engines. Assuming all four engines and the vehicle are nominal, the launch clamps will release from the base of the vehicle, letting it lift off.

At T+1:13 the vehicle will pass through maximum aerodynamic pressure. At T+2:37, the four first-stage engines will shut down, in an event called main engine cutoff (MECO), before the stages separate and the second stage ignites its engine.

Less than a minute later, at T+3:25, the fairing will be. The second stage will then burn for another four minutes, before shutting down at T+7:40. However, at this point the mission is not over, as the stage will coast until T+53:57 when the engine will ignite for a second time, this time for two seconds. This will raise the initial elliptical orbit into a circular 300 km orbit.

Alpha will then deploy all three payloads, finishing its mission at T+1:01:57.

In the event of mission success, Firefly is hoping to launch FLTA003 in late 2022, which will likely be the ELaNa 43 mission for NASA.

(Lead photo: FLTA002 on the pad before launch. Credit: Jack Beyer for NSF)

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