Firefly pulls out of second launch attempt due to weather -

Firefly pulls out of second launch attempt due to weather –

In a bid to successfully reach 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 Vandenberg Space Force Base in California, the vehicle is now expected to lift off no earlier than September 19 in a window from 3:00 p.m. to 7:00 p.m. PDT (10:00 p.m. to 2:00 a.m. UTC).

A Sunday launch attempt was called off after dropping out less than a minute before the window opened and subsequent delays throughout the window. The teams then pulled out of another opportunity on Monday due to weather.

FLTA002 will attempt to place several small satellites into a 300 km circular Low Earth Orbit (LEO) with an inclination of 137 degrees.

Firefly’s first orbital launch attempt ended during the first stage burnout on September 3, 2021, following an engine failure 14 seconds after launch. Despite this engine shutdown, the vehicle was able to maintain control for nearly two and a half minutes, before tumbling, causing ground operators to activate the flight arrest system.

Firefly was able to salvage the engine assembly downstream, which allowed them to figure out that the engine had shut down early due to failed pins in the main engine valve feed line, causing them to close and to stop the engine. This failure mode was supported by data received from the vehicle, which indicated a current drop on the fuel rail and the valve closed.

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

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

Alpha’s first stage is powered by four Reaver 1 engines, which run on RP-1 kerosene and liquid oxygen (LOX). Notably, Reaver uses the bypass engine cycle, meaning that instead of having a separate gas generator to spin the turbines, pressure from the main combustion chamber is used. However, since the exhaust gases used to spin the turbine are always 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 space vacuum. For rocket engines, the specific impulse of the engine is directly proportional to the velocity of the exhaust gases; for Reaver, the maximum average escape velocity is about 2900 m/s.

Alpha’s first and second stages are both constructed from carbon fiber composites that form ultra-lightweight, linerless propellant reservoirs. 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 supply LOX to the engines.

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

The second stage features a single Lightning 1 motor, which is also a bypass motor cycle capable of producing 70 N of thrust.

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

NASA’s TES-15 3U CubeSat also flies on FLTA002, which features a deployable exo-brake that will be used to validate center-of-mass systems for future re-entries. This payload is part of NASA Technological educational satellites program, which gives students the opportunity to work on satellites.

The final payload will be the Libre Space Foundation’s PicoBus, which will deploy six picosatellites. All these satellites are technological demonstrators for communication, remote sensing, etc.

Eight hours before launch, teams will begin performing final pad checks. 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 charged with helium, which is used to pressurize and refill the tanks as they empty during the ascent.

At T-5 hours and 15 minutes, the vehicle will begin to be charged with RP-1. 45 minutes later, the pad will clear, giving way to the start of the LOX charge at T-3 hours and 40 minutes. Propellant loading will last up to 20 minutes before launch when the vehicle enters terminal count. At this point, the rocket will be fully fueled (both with RP-1 and LOX) and will be continuously refilled with both boosters.

The four first-stage Reaver 1 engines will ignite at T-1.8 seconds using TEA-TEB, a pyrophoric compound, meaning it burns on 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 detach from the base of the vehicle, letting it take off.

At T+1:13 the vehicle will pass through the maximum aerodynamic pressure. At T+2:37, all four engines of the first stage 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 deployed. The second stage will then burn for another four minutes, before stopping at T+7:40. However, at this point the mission is not complete, as the stage will roll to T+53:57 when the engine fires a second time, this time for two seconds. This will raise the initial elliptical orbit to a 300 km circular orbit.

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

If the mission is successful, Firefly hopes to launch FLTA003 in late 2022, which will likely be the ELaNa 43 mission for NASA.

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

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