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เครื่องยนต์จรวด
| ชนิด | รายละเอียด | ข้อดี | ข้อเสีย |
|---|---|---|---|
| จรวดขวดน้ำ (water rocket) | ใช้กำลังขับดันจากแรงดันก๊าซที่ถูกอัดตัวอยู่ภายในภาชนะบรรจุ เช่น ก๊าซคาร์บอนไดออกไซด์ที่เกิดจากเครื่องดื่มน้ำอัดลมและควบคุมทิศทางการเคลื่อนที่ของตัวจรวดด้วยครีบหางและจมูกถ่วงน้ำหนัก (Partially filled pressurised carbonated drinks container with tail and nose weighting) | ง่ายต่อการสร้างมาก (Very simple to build) | ระยะความสูงจากการยิงปล่อยมักจะจำกัดอยู่เพียงแค่ไม่กี่ร้อยฟุตหรือมากกว่านั้นนิดหน่อย (บันทึกสถิติโลกคือ 623 เมตร หรือ 2,044 ฟุต) (Altitude typically limited to a few hundred feet or so (world record is 623 meters/2044 feet)) |
| จรวดขับดันแบบก๊าซเย็น (cold gas thruster) | จะไม่มีการสันดาปหรือเผาไหม้ของเชื้อเพลิงในเครื่องยนต์จรวดเกิดขึ้นเลย, ใช้สำหรับเครื่องยนต์จรวดแบบเวอร์เนียร์ทรัสเตอร์ (A non combusting form, used for vernier thrusters) | ไม่มีมลพิษจากการเผาไหม้ของเชื้อเพลิงในเครื่องยนต์จรวด (Non contaminating exhaust) | มีประสิทธิภาพการทำงานในระดับที่ต่ำมาก (Extremely low performance) |
| Type | Description | Advantages | Disadvantages |
|---|---|---|---|
| จรวดเชื้อเพลิงแข็ง | Ignitable, self-sustaining solid fuel/oxidiser mixture ("grain") with central hole and nozzle | Simple, often no moving parts, reasonably good mass fraction, reasonable Isp. A thrust schedule can be designed into the grain. | Throttling, burn termination, and reignition require special designs. Handling issues from ignitable mixture. Lower performance than liquid rockets. If grain cracks it can block nozzle with disastrous results. Grain cracks burn and widen during burn. Refueling harder than simply filling tanks. |
| Hybrid rocket | Separate oxidiser/fuel; typically the oxidiser is liquid and kept in a tank and the fuel is solid. | Quite simple, solid fuel is essentially inert without oxidiser, safer; cracks do not escalate, throttleable and easy to switch off. | Some oxidisers are monopropellants, can explode in own right; mechanical failure of solid propellant can block nozzle (very rare with rubberised propellant), central hole widens over burn and negatively affects mixture ratio. |
| Monopropellant rocket | Propellant (such as hydrazine, hydrogen peroxide or nitrous oxide) flows over a catalyst and exothermically decomposes; hot gases are emitted through nozzle. | Simple in concept, throttleable, low temperatures in combustion chamber | catalysts can be easily contaminated, monopropellants can detonate if contaminated or provoked, Isp is perhaps 1/3 of best liquids |
| Bipropellant rocket | Two fluid (typically liquid) propellants are introduced through injectors into combustion chamber and burnt | Up to ~99% efficient combustion with excellent mixture control, throttleable, can be used with turbopumps which permits incredibly lightweight tanks, can be safe with extreme care | Pumps needed for high performance are expensive to design, huge thermal fluxes across combustion chamber wall can impact reuse, failure modes include major explosions, a lot of plumbing is needed. |
| Dual mode propulsion rocket | Rocket takes off as a bipropellant rocket, then turns to using just one propellant as a monopropellant | Simplicity and ease of control | Lower performance than bipropellants |
| Tripropellant rocket | Three different propellants (usually hydrogen, hydrocarbon and liquid oxygen) are introduced into a combustion chamber in variable mixture ratios, or multiple engines are used with fixed propellant mixture ratios and throttled or shut down | Reduces take-off weight, since hydrogen is lighter; combines good thrust to weight with high average Isp, improves payload for launching from Earth by a sizeable percentage | Similar issues to bipropellant, but with more plumbing, more research and development |
| Air-augmented rocket | Essentially a ramjet where intake air is compressed and burnt with the exhaust from a rocket | Mach 0 to Mach 4.5+ (can also run exoatmospheric), good efficiency at Mach 2 to 4 | Similar efficiency to rockets at low speed or exoatmospheric, inlet difficulties, a relatively undeveloped and unexplored type, cooling difficulties, very noisy, thrust/weight ratio is similar to ramjets. |
| Turborocket | A combined cycle turbojet/rocket where an additional oxidiser such as oxygen is added to the airstream to increase maximum altitude | Very close to existing designs, operates in very high altitude, wide range of altitude and airspeed | Atmospheric airspeed limited to same range as turbojet engine, carrying oxidiser like LOX can be dangerous. Much heavier than simple rockets. |
| Precooled jet engine / LACE (combined cycle with rocket) | Intake air is chilled to very low temperatures at inlet before passing through a ramjet or turbojet engine. Can be combined with a rocket engine for orbital insertion. | Easily tested on ground. High thrust/weight ratios are possible (~14) together with good fuel efficiency over a wide range of airspeeds, mach 0-5.5+; this combination of efficiencies may permit launching to orbit, single stage, or very rapid intercontinental travel. | Exists only at the lab prototyping stage. Examples include RB545, SABRE, ATREX |
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