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62-455: Firefly Alpha ( Firefly α ) is a two-stage orbital expendable small lift launch vehicle developed by the American company Firefly Aerospace to compete in the commercial small satellite launch market. Alpha is intended to provide launch options for both full vehicle and rideshare customers. The first launch attempt was on 3 September 2021 but the vehicle did not reach orbit when one of

124-452: A reaction mass engine, such as a rocket using propellant or a jet engine using fuel, generates thrust . A propulsion system with a higher specific impulse uses the mass of the propellant more efficiently. In the case of a rocket, this means less propellant needed for a given delta- v , so that the vehicle attached to the engine can more efficiently gain altitude and velocity. For engines like cold gas thrusters whose reaction mass

186-473: A 200 km low Earth orbit , or up to 745 kg payload to a 500 km Sun-synchronous orbit , suitable for CubeSats and other small payloads . Primary payloads can be integrated by themselves or with a secondary payload , with vehicle capacity for up to 6 CubeSats. This allows Firefly's customers to have a dedicated small-satellite launcher, reducing the issues of ridesharing payloads and secondary payloads. These smaller satellites can have an orbit that

248-465: A certain speed and altitude, wings and scramjets cease being effective, and the rocket is deployed to complete the trip to orbit. Saenger (spacecraft) was among the first concepts of this type. While not an orbital vehicle, the successful private SpaceShipOne suborbital spacecraft developed for the Ansari X Prize demonstrated that a two-stage system with a winged aircraft as the "lower half" can reach

310-417: A direct measure of the engine's effectiveness in converting propellant mass into forward momentum. The specific impulse in terms of propellant mass spent has units of distance per time, which is a notional velocity called the effective exhaust velocity . This is higher than the actual exhaust velocity because the mass of the combustion air is not being accounted for. Actual and effective exhaust velocity are

372-434: A given propellant, when paired with a given engine, can accelerate its own initial mass at 1 g. The longer it can accelerate its own mass, the more delta-V it delivers to the whole system. In other words, given a particular engine and a mass of a particular propellant, specific impulse measures for how long a time that engine can exert a continuous force (thrust) until fully burning that mass of propellant. A given mass of

434-526: A heavier engine with a higher specific impulse may not be as effective in gaining altitude, distance, or velocity as a lighter engine with a lower specific impulse, especially if the latter engine possesses a higher thrust-to-weight ratio . This is a significant reason for most rocket designs having multiple stages. The first stage is optimised for high thrust to boost the later stages with higher specific impulse into higher altitudes where they can perform more efficiently. The most common unit for specific impulse

496-465: A long duration test fire on Firefly's Test Stand 1 in Briggs, Texas . The Alpha airframe uses all carbon-fiber composite material in its construction. Using carbon-fiber makes the rocket more fuel efficient because the use of denser materials like titanium and aluminum would result in a heavier airframe, which would require more fuel to launch. Alpha is designed to launch up to 1170 kg of payload to

558-417: A more energy-dense propellant can burn for a longer duration than some less energy-dense propellant made to exert the same force while burning in an engine. Different engine designs burning the same propellant may not be equally efficient at directing their propellant's energy into effective thrust. For all vehicles, specific impulse (impulse per unit weight-on-Earth of propellant) in seconds can be defined by

620-417: A much higher specific impulse than rocket engines. For air-breathing engines, only the fuel mass is counted, not the mass of air passing through the engine. Air resistance and the engine's inability to keep a high specific impulse at a fast burn rate are limiting factors to the propellant consumption rate. If it were not for air resistance and the reduction of propellant during flight, specific impulse would be

682-421: A much larger specific impulse than a rocket; for example a turbofan jet engine may have a specific impulse of 6,000 seconds or more at sea level whereas a rocket would be between 200 and 400 seconds. An air-breathing engine is thus much more propellant efficient than a rocket engine, because the air serves as reaction mass and oxidizer for combustion which does not have to be carried as propellant, and

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744-400: A rocket can be defined in terms of thrust per unit mass flow of propellant. This is an equally valid (and in some ways somewhat simpler) way of defining the effectiveness of a rocket propellant. For a rocket, the specific impulse defined in this way is simply the effective exhaust velocity relative to the rocket, v e . "In actual rocket nozzles, the exhaust velocity is not really uniform over

806-564: A stage, leading to the expression one-and-a-half-stage-to-orbit (1.5STO) e.g. for the Long March 5B or the Atlas missile , which was a single core stage with additional boosters. Similarly, two-stage designs with additional boosters can be referred to as 2.5-stage rockets e.g. the Ariane 5 or most Atlas V variants (all except the 401 and 501). With reference to a reusable launch system this approach

868-490: Is also ionized, which would interfere with radio communication with the rocket. Nuclear thermal rocket engines differ from conventional rocket engines in that energy is supplied to the propellants by an external nuclear heat source instead of the heat of combustion . The nuclear rocket typically operates by passing liquid hydrogen gas through an operating nuclear reactor. Testing in the 1960s yielded specific impulses of about 850 seconds (8,340 m/s), about twice that of

930-450: Is also valid for air-breathing jet engines, but is rarely used in practice. (Note that different symbols are sometimes used; for example, c is also sometimes seen for exhaust velocity. While the symbol I sp {\displaystyle I_{\text{sp}}} might logically be used for specific impulse in units of (N·s )/(m·kg); to avoid confusion, it is desirable to reserve this for specific impulse measured in seconds.) It

992-434: Is impractical. Lithium and fluorine are both extremely corrosive, lithium ignites on contact with air, fluorine ignites on contact with most fuels, and hydrogen, while not hypergolic, is an explosive hazard. Fluorine and the hydrogen fluoride (HF) in the exhaust are very toxic, which damages the environment, makes work around the launch pad difficult, and makes getting a launch license that much more difficult. The rocket exhaust

1054-493: Is inversely proportional to specific fuel consumption (SFC) by the relationship I sp = 1/( g o ·SFC) for SFC in kg/(N·s) and I sp = 3600/SFC for SFC in lb/(lbf·hr). An example of a specific impulse measured in time is 453 seconds, which is equivalent to an effective exhaust velocity of 4.440 km/s (14,570 ft/s), for the RS-25 engines when operating in a vacuum. An air-breathing jet engine typically has

1116-407: Is leasing Vandenberg pad SLC-2W to support Firefly Alpha and MLV launches; this launch pad formerly supported Delta , Thor-Agena , and Delta II launch vehicles launches. Additionally, Firefly plans to refurbish and utilize Cape Canaveral SLC-20 for low-inclination launches of Alpha in the future. Two-stage-to-orbit At liftoff the first stage is responsible for accelerating

1178-423: Is needed to produce a given thrust for a given time and the more efficient the propellant is. This should not be confused with the physics concept of energy efficiency , which can decrease as specific impulse increases, since propulsion systems that give high specific impulse require high energy to do so. Thrust and specific impulse should not be confused. Thrust is the force supplied by the engine and depends on

1240-403: Is not determined by a larger payload and can launch on their own schedule instead of waiting on the readiness of all other payloads. Alpha is also intended to be a direct American competitor in the small satellite market to India's Polar Satellite Launch Vehicle (PSLV), as the company believes that PSLV's ride-share capability threatens U.S. domestic launchers in this market. Firefly Aerospace

1302-410: Is often proposed as an alternative to single-stage-to-orbit (or SSTO ). Its supporters argue that, since each stage may have a lower mass ratio than an SSTO launch system, such a system may be built further away from limits of its structural materials. It is argued that a two-stage design should require less maintenance, less testing, experience fewer failures and have a longer working life. In addition

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1364-421: Is only the fuel they carry, specific impulse is exactly proportional to the effective exhaust gas velocity. In an atmospheric context, specific impulse can include the contribution to impulse provided by the mass of external air that is accelerated by the engine, such as by fuel combustion or by external propeller. Jet engines and turbofans breathe external air for both combustion and bypass, and therefore have

1426-435: Is payload mass. An advantage over three or more stages is a reduction in complexity and fewer separation events , which reduces cost and risk of failure. It is not always clear when a vehicle is a TSTO, due to the use of strap-on booster rockets at launch. These are dropped early on in the flight and may or may not be considered an additional stage if the core engine(s) continue firing. These are sometimes considered half

1488-408: Is proportional to the effective exhaust velocity. A spacecraft without propulsion follows an orbit determined by its trajectory and any gravitational field. Deviations from the corresponding velocity pattern (these are called Δ v ) are achieved by sending exhaust mass in the direction opposite to that of the desired velocity change. When an engine is run within the atmosphere, the exhaust velocity

1550-410: Is reduced by atmospheric pressure, in turn reducing specific impulse. This is a reduction in the effective exhaust velocity, versus the actual exhaust velocity achieved in vacuum conditions. In the case of gas-generator cycle rocket engines, more than one exhaust gas stream is present as turbopump exhaust gas exits through a separate nozzle. Calculating the effective exhaust velocity requires averaging

1612-409: Is related to the thrust , or forward force on the rocket by the equation: F thrust = v e ⋅ m ˙ , {\displaystyle F_{\text{thrust}}=v_{\text{e}}\cdot {\dot {m}},} where m ˙ {\displaystyle {\dot {m}}} is the propellant mass flow rate, which is the rate of decrease of

1674-452: Is that it may be used for rockets, where all the reaction mass is carried on board, as well as airplanes, where most of the reaction mass is taken from the atmosphere. In addition, giving the result as a unit of time makes the result easily comparable between calculations in SI units, imperial units, US customary units or other unit framework. The English unit pound mass is more commonly used than

1736-401: Is the product of the average specific gravity of a given propellant mixture and the specific impulse. While less important than the specific impulse, it is an important measure in launch vehicle design, as a low specific impulse implies that bigger tanks will be required to store the propellant, which in turn will have a detrimental effect on the launch vehicle's mass ratio . Specific impulse

1798-478: Is the second, as values are identical regardless of whether the calculations are done in SI , imperial , or US customary units. Nearly all manufacturers quote their engine performance in seconds, and the unit is also useful for specifying aircraft engine performance. The use of metres per second to specify effective exhaust velocity is also reasonably common. The unit is intuitive when describing rocket engines, although

1860-414: Is used, impulse is divided by propellant weight (weight is a measure of force), resulting in units of time (seconds). These two formulations differ from each other by the standard gravitational acceleration ( g 0 ) at the surface of the earth. The rate of change of momentum of a rocket (including its propellant) per unit time is equal to the thrust. The higher the specific impulse, the less propellant

1922-746: The SR-71 ) are to develop and operate, and question performance claims. Many 'mini-shuttle' designs that use transport aircraft as first stages also face similar problems with ice/foam as the Space Shuttle due to the requirement they also carry a large external tank for their fuel. As of 2023, SpaceX and NASA are the only launch providers which have achieved first-stage reuse of an orbital vehicle with SpaceX’s two-stage Falcon 9 and 2.5-stage Falcon Heavy , and NASA’s Space Shuttle Solid Rocket Boosters . Rocket Lab has recovered multiple first stages of their Electron rocket, but has not flown it again. Taking

Firefly Alpha - Misplaced Pages Continue

1984-456: The development of Alpha was expected to cost approximately US$ 100 million. In 2024, Firefly Aerospace announced plans to use a Horizontal Integration Facility (HIF) to integrate payloads at Wallops Island , Virginia . The first test launch and Maiden flight of Firefly Alpha occurred on 3 September 2021 at 01:59 UTC , from a leased pad at Vandenberg Space Force Base in California, and

2046-420: The edge of space . The team behind SpaceShipOne has built and flown a commercial sub-orbital launch system — SpaceShipTwo — based on this technology. The Pegasus rocket while airplane launched, is not a two-stage-to-orbit system because the rocket component itself is composed of multiple stages. Specific impulse Specific impulse (usually abbreviated I sp ) is a measure of how efficiently

2108-404: The effective exhaust velocity while reducing the actual exhaust velocity. Again, this is because the mass of the air is not counted in the specific impulse calculation, thus attributing all of the thrust momentum to the mass of the fuel component of the exhaust, and omitting the reaction mass, inert gas, and effect of driven fans on overall engine efficiency from consideration. Essentially,

2170-443: The first stage engines failed during ascent. A second orbital test flight took place on 1 October 2022 and successfully reached orbit. Alpha deployed 7 satellites, however, due to the lower than intended deployment orbit, most of the satellites re-entered before reaching their intended design life a week after launch. The first fully successful launch of Alpha took place on 15 September 2023. The initial 2014-vintage design of Alpha

2232-457: The Alpha launch vehicle was redesigned to a much larger rocket, over twice as much capacity as the Alpha design of 2014. The version 2 Alpha vehicle still utilizes two stages to orbit, but now both are 1.8 m (5 ft 11 in) in diameter and use RP-1 / LOX propellants. The main body of the rocket is constructed using a lightweight carbon composite material. In March 2018, Firefly said that

2294-675: The Space Shuttle engines. A variety of other rocket propulsion methods, such as ion thrusters , give much higher specific impulse but with much lower thrust; for example the Hall-effect thruster on the SMART-1 satellite has a specific impulse of 1,640 s (16.1 km/s) but a maximum thrust of only 68 mN (0.015 lbf). The variable specific impulse magnetoplasma rocket (VASIMR) engine currently in development will theoretically yield 20 to 300 km/s (66,000 to 984,000 ft/s), and

2356-408: The actual exhaust speed is much lower, so the kinetic energy the exhaust carries away is lower and thus the jet engine uses far less energy to generate thrust. While the actual exhaust velocity is lower for air-breathing engines, the effective exhaust velocity is very high for jet engines. This is because the effective exhaust velocity calculation assumes that the carried propellant is providing all

2418-419: The amount of reaction mass flowing through the engine. Specific impulse measures the impulse produced per unit of propellant and is proportional to the exhaust velocity. Thrust and specific impulse are related by the design and propellants of the engine in question, but this relationship is tenuous. For example, LH 2 /LO 2 bipropellant produces higher I sp but lower thrust than RP-1 / LO 2 due to

2480-427: The burned fuel. Next, inert gases in the atmosphere absorb heat from combustion, and through the resulting expansion provide additional thrust. Lastly, for turbofans and other designs there is even more thrust created by pushing against intake air which never sees combustion directly. These all combine to allow a better match between the airspeed and the exhaust speed, which saves energy/propellant and enormously increases

2542-474: The definition of specific impulse as impulse per unit mass of propellant. Specific fuel consumption is inversely proportional to specific impulse and has units of g/(kN·s) or lb/(lbf·h). Specific fuel consumption is used extensively for describing the performance of air-breathing jet engines. Specific impulse, measured in seconds, can be thought of as how many seconds one kilogram of fuel can produce one kilogram of thrust. Or, more precisely, how many seconds

Firefly Alpha - Misplaced Pages Continue

2604-492: The effective exhaust speed of the engines may be significantly different from the actual exhaust speed, especially in gas-generator cycle engines. For airbreathing jet engines , the effective exhaust velocity is not physically meaningful, although it can be used for comparison purposes. Metres per second are numerically equivalent to newton-seconds per kg (N·s/kg), and SI measurements of specific impulse can be written in terms of either units interchangeably. This unit highlights

2666-638: The entire exit cross section and such velocity profiles are difficult to measure accurately. A uniform axial velocity, v e , is assumed for all calculations which employ one-dimensional problem descriptions. This effective exhaust velocity represents an average or mass equivalent velocity at which propellant is being ejected from the rocket vehicle." The two definitions of specific impulse are proportional to one another, and related to each other by: v e = g 0 ⋅ I sp , {\displaystyle v_{\text{e}}=g_{0}\cdot I_{\text{sp}},} where This equation

2728-435: The exhaust gases having a lower density and higher velocity ( H 2 O vs CO 2 and H 2 O). In many cases, propulsion systems with very high specific impulse—some ion thrusters reach 10,000 seconds—produce low thrust. When calculating specific impulse, only propellant carried with the vehicle before use is counted. For a chemical rocket, the propellant mass therefore would include both fuel and oxidizer . In rocketry,

2790-455: The following equation: F thrust = g 0 ⋅ I sp ⋅ m ˙ , {\displaystyle F_{\text{thrust}}=g_{0}\cdot I_{\text{sp}}\cdot {\dot {m}},} where: I sp in seconds is the amount of time a rocket engine can generate thrust, given a quantity of propellant whose weight is equal to the engine's thrust. The advantage of this formulation

2852-487: The launch pad again. In the case of the DH-1, the upper stage is effectively an 'almost SSTO' with a more realistic mass fraction and which was optimised for reliability. Some TSTO designs comprise an airplane -like first stage and a rocket -like second stage. The airplane elements can be wings, air-breathing engines, or both. This approach appeals because it transforms Earth's atmosphere from an obstacle into an advantage. Above

2914-490: The momentum of engine exhaust includes a lot more than just fuel, but specific impulse calculation ignores everything but the fuel. Even though the effective exhaust velocity for an air-breathing engine seems nonsensical in the context of actual exhaust velocity, this is still useful for comparing absolute fuel efficiency of different engines. A related measure, the density specific impulse , sometimes also referred to as Density Impulse and usually abbreviated as I s d

2976-465: The only reaction mass is the propellant, so the specific impulse is calculated using an alternative method, giving results with units of seconds. Specific impulse is defined as the thrust integrated over time per unit weight -on-Earth of the propellant: I sp = v e g 0 , {\displaystyle I_{\text{sp}}={\frac {v_{\text{e}}}{g_{0}}},} where In rockets, due to atmospheric effects,

3038-414: The reaction mass and all the thrust. Hence effective exhaust velocity is not physically meaningful for air-breathing engines; nevertheless, it is useful for comparison with other types of engines. The highest specific impulse for a chemical propellant ever test-fired in a rocket engine was 542 seconds (5.32 km/s) with a tripropellant of lithium , fluorine , and hydrogen . However, this combination

3100-406: The same hardware. Critics argue that the increased complexity of designing two separate stages that must interact, the logistics involved in returning the first stage to the launch site, and the difficulties of conducting incremental testing on a second stage will outweigh these benefits. In the case of airplane-like lower stages they also argue how difficult and expensive high speed aircraft (like

3162-422: The same in rocket engines operating in a vacuum. The amount of propellant can be measured either in units of mass or weight. If mass is used, specific impulse is an impulse per unit of mass, which dimensional analysis shows to have units of speed, specifically the effective exhaust velocity . As the SI system is mass-based, this type of analysis is usually done in meters per second. If a force-based unit system

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3224-574: The slug, and when using pounds per second for mass flow rate, it is more convenient to express standard gravity as 1 pound-force per pound-mass. Note that this is equivalent to 32.17405 ft/s2, but expressed in more convenient units. This gives: F thrust = I sp ⋅ m ˙ ⋅ ( 1 l b f l b m ) . {\displaystyle F_{\text{thrust}}=I_{\text{sp}}\cdot {\dot {m}}\cdot \left(1\mathrm {\frac {lbf}{lbm}} \right).} In rocketry,

3286-490: The specific impulse varies with altitude, reaching a maximum in a vacuum. This is because the exhaust velocity isn't simply a function of the chamber pressure, but is a function of the difference between the interior and exterior of the combustion chamber . Values are usually given for operation at sea level ("sl") or in a vacuum ("vac"). Because of the geocentric factor of g 0 in the equation for specific impulse, many prefer an alternative definition. The specific impulse of

3348-415: The two mass flows as well as accounting for any atmospheric pressure. For air-breathing jet engines, particularly turbofans , the actual exhaust velocity and the effective exhaust velocity are different by orders of magnitude. This happens for several reasons. First, a good deal of additional momentum is obtained by using air as reaction mass, such that combustion products in the exhaust have more mass than

3410-479: The two-stage approach allows the lower stage to be optimized for operation in the Earth's lower atmosphere, where pressure and drag are high, while the upper stage can be optimized for operation in the near-vacuum conditions of the later part of the launch. This allows an increase in the payload mass fraction of a two-stage vehicle over single-stage or stage-and-a-half vehicles, which have to perform in both environments using

3472-446: The vehicle's mass. A rocket must carry all its propellant with it, so the mass of the unburned propellant must be accelerated along with the rocket itself. Minimizing the mass of propellant required to achieve a given change in velocity is crucial to building effective rockets. The Tsiolkovsky rocket equation shows that for a rocket with a given empty mass and a given amount of propellant, the total change in velocity it can accomplish

3534-406: The vehicle. At some point the second stage detaches from the first stage and continues to orbit under its own power. An advantage of such a system over single-stage-to-orbit is that most of the dry mass of the vehicle is not carried into orbit. This reduces the cost involved in reaching orbital velocity, as much of the structure and engine mass is ejected, and a larger percentage of the orbited mass

3596-534: The view that airplane like operations do not translate to airplane-like appearance, some reusable TSTO concepts have first stages that operate as VTOL or VTOHL aircraft. The DC-X has proven the VTOL option design workable. Other designs like the DH-1 concept take it a step further and use a 'pop-up/pop-down' approach, which delivers the orbiting stage to a point about 60 km above the Earth's surface, before dropping down to

3658-523: Was two-stage-to-orbit vehicle with the first stage powered by an FRE-2 methalox engine, which consisted of twelve nozzles arranged in an aerospike configuration. The engine used methane and liquid oxygen as propellants , and completed a full-duration combustor test in September 2016. The second stage was to be propelled by the FRE-1 engine, which was to use a conventional bell nozzle . This version of Alpha

3720-428: Was also onboard this flight. The Alpha first stage is powered by four Reaver 1 LOX / RP-1 tap-off cycle engines, delivering 736 kN (165,000 lb f ) of thrust. The second stage is powered by one Lightning 1 LOX / RP-1 engine, delivering 70.1 kN (15,800 lb f ) of thrust with a specific impulse (I sp ) of 322 seconds. Lightning 1 was test-run for nearly 5 minutes on 15 March 2018 during

3782-550: Was intended to carry 400 kg to low Earth orbit. In 2015, NASA's Launch Services Program awarded Firefly Space Systems, the predecessor to Firefly Aerospace, a US$ 5.5 million Venture Class Launch Services contract to incentivize the development of Alpha, as part of a program to enable easier space access for the small satellite market. After the March 2017 bankruptcy of Firefly Space Systems and corporate reorganization to become Firefly Aerospace with new owners and capital ,

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3844-703: Was to fly southwest over the Pacific Ocean. Due to an engine failure caused by a sensor cable disconnect approximately 15 seconds after the launch, the rocket lost control at transonic speeds approximately two and a half minutes after launch that resulted in manual activation of the flight termination system and loss of the vehicle. The launch vehicle had onboard various payloads as part of Firefly's DREAM mission—including Benchmark Space BSS1, Firefly Capsule 1, and PICOBUS (intending to deploy six PocketQubes ), Hiapo, Spinnaker3, and TIS Serenity—which were destroyed. Firefly's experimental Space Utility Vehicle (SUV) third stage

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