推进·可行性审查

AdMerk 无火箭航天飞机的推进选项

AdMerk Spaceship 团队的贡献——五种推进方法，按近期可行性排名，完全来自公共研究。

底线

A "rocket-free" spaceplane is an audacious goal that likely requires combining several of these technologies rather than relying on one. Air-breathing precooled engines offer the best near-term chance to reach high altitude and speed efficiently, while a transition to a moderate chemical rocket or a nuclear thermal stage remains the only realistic way to reach orbit or beyond in the next decade. Plasma and electric propulsion, while revolutionary in efficiency, are best treated as supporting players for in-space maneuvers rather than primary launch systems, and beamed-energy propulsion — while promising for eliminating onboard fuel — remains further in the future. The most practical near-term path is a combined-cycle vehicle: air-breathing engines used to the fullest extent possible, AI-assisted control to optimize the transition points between propulsion modes, and a design that stays upgradable as nuclear or beamed power options mature.

按近期可行性排名

#1预冷空气-呼吸+火箭(组合-循环)

e.g. SABRE (Synergetic Air-Breathing Rocket Engine)

预冷空气呼吸引擎如SABRE在较低高度和速度下摄入大气氧气,然后在薄空气中切换到机上氧化剂. 预冷器热交换器在约0.01秒内将进入的空气从约1000°C降低到-150°C,允许用液氢进行轻量级压缩和高压燃烧——在空气呼吸模式下产生远超常规火箭的有效特定冲动.

SABRE的设计是,在空气呼吸推力~28公里时,将单级飞行器推进到大约Mach 5+,然后向封闭循环火箭模式过渡,用于轨道插入. 这使得SABRE动力飞行器到达了有效载荷分数高于纯火箭的轨道,尽管它仍然需要火箭相位来关闭剩余的速度差距到轨道.

目前还没有联合循环空气呼吸发动机飞向超音速,但关键部件在地面上得到证明:2019年在Mach 3.3+摄入条件下测试了一台全尺寸的预冷器,一台SABRE核心显示器在2022年通过了地面射击测试. 美国航天局和欧空局的研究确认了这一概念的可行性,同时注意到将重热交换器和低温处理器并入轨道器的复杂性。

比冲量: ~3,000–3,600 s air-breathing mode; ~450 s in rocket mode
推力重量比: ~14–20 (engine); high total thrust
准备状态（TRL）: ~4 (key components demonstrated; full system not yet flown)

优点

+High efficiency in atmosphere — draws oxidizer from ambient air, saving propellant mass
+High thrust across the flight regime (0 to Mach 5+), enough to lift a heavy vehicle
+Enables single-stage reuse — no staging, runway-style operations

缺点

–Complex, heavy engine — the precooler and compressor add mass
–Air-breathing mode alone is limited to ~Mach 5 / 25 km; needs a rocket phase beyond that
–Development cost is high; the lead developer (Reaction Engines Ltd) filed for bankruptcy in 2024

#2核热火箭(NTR)

solid-core, using liquid hydrogen propellant

核热推进利用裂变反应堆超热推进剂(典型的液态氢),并通过喷嘴将其驱逐——用裂变热取代化学燃烧. 在非常高的温度下运行反应堆大约比同一推进剂的化学发动机增加了一倍

美国的NERVA计划(1960年代)对十多个反应堆进行了地面测试,并证明核发动机可以可靠地重启和节流,在1973年被取消之前达到大约6-7的技术准备水平. NASA和DARPA的DRACO计划旨在2027年前在地球轨道上飞行演示一个核热级.

对于航天飞机来说,核发动机实际上只会在大气层之上点燃——例如,在呼吸空气的第一阶段达到Mach 5和~30公里之后——既是为了安全,也因为固体核心发动机无法产生足够的推力对重量,无法无助地从地面升起.

比冲量: ~900 s (solid-core, flight heritage); 1,500–2,000+ s theorized for advanced designs
推力重量比: ~5–7 (solid-core engine); up to ~10+ projected
准备状态（TRL）: ~5–6 (ground-tested extensively in the 1960s; never flown)

优点

+High Isp — roughly double chemical rockets, cutting propellant needs for orbit by about half
+High thrust (10⁴–10⁵ N class) — can perform quick orbital insertions, unlike electric propulsion
+Established ground-test heritage (NERVA program) plus active modern development (NASA/DARPA)

缺点

–Radiation and safety concerns — regulatory and political hurdles around igniting a reactor near Earth
–Reactor mass and shielding reduce net performance; not viable for lift-off from the ground
–Not operational yet — requires new development and a flight demonstration (possibly ~2030)

#3电波-能源推进

laser or microwave thermal rockets

贝梅德-能量推进器通过激光或微波束向外输送动力,因此飞行器不携带重型的机载电源或氧化剂——例如,激光热火箭可以聚焦一个束,为推力加热氢推进剂.

2000年,"Lightcraft"实验使用脉冲CO2激光将50克的飞行器发射到71米高度. 一项由美国航天局资助的2012年研究结论束能发射在技术上原则上是可行的,但需要新技术和长期的大量投资。

亚轨道示范比完全的轨道插入更近似,因为光束必须不断跟踪和为飞行器提供动力——轨道使用需要多个地面站或空间中继,因为车辆曲线脱离了直视线。

比冲量: ~1,000–1,500 s (laser thermal); up to ~2,000 s best-case
推力重量比: N/A — power source is off-board; thrust ~50–500 N per megawatt beamed
准备状态（TRL）: ~2–3 (small-scale lab demonstrations only)

优点

+No onboard oxidizer needed — huge potential mass savings on the vehicle itself
+Scalable energy: one ground facility could in principle support many launches
+Vehicle can be lighter since external power replaces heavy onboard generators

缺点

–Extremely high infrastructure cost — multi-megawatt lasers or large phased microwave arrays
–Line-of-sight and atmospheric limits (clouds, diffraction) constrain continuous thrust
–Very low technology readiness — test flights have only reached about 0.1 km altitude so far

#4高功率等离子体推力器

e.g. VASIMR, magnetoplasmadynamic (MPD) thrusters

等离子推进器通过电场和磁场加速推进剂—— x,rg,和类似推进剂,产生高速度的等离子体排气. 它们提供了非常高的特异性冲动,但以低推力和大量电源要求为代价,因此它们无法从地球表面发射.

VASIMR原型已显示可捕性特定冲动,可达约5000秒,利用RF能量在磁喷嘴中加热等离子体,但其VX-200试验物品在200千瓦输入时仅产生约5N的推力——大致相当于一束纸的重量.

对于航天飞机来说,等离子推进器最适合轨道操纵——微调轨道或长期站台维护——而不是主要升力推进,至少在5至10年内。

比冲量: ~3,000–5,000 s typical (argon/xenon); up to ~10,000 s possible
推力重量比: Very low — roughly 5 N of thrust per 200 kW of input power
准备状态（TRL）: ~4–5 (lab-tested prototypes; no in-space use at scale)

优点

+Very high specific impulse — 5–10× chemical rockets, excellent fuel economy for a given delta-V
+Variable thrust/Isp trade-off (VASIMR can trade exhaust velocity for thrust)
+Ideal for in-space missions — cargo tugs, deep space — achieving high delta-V with minimal propellant

缺点

–Insufficient thrust for launch or orbital insertion on its own — requires long, continuous burns
–Requires massive electrical power (hundreds of kW to megawatts) plus significant cooling
–Engine hardware (magnets, power units) is heavy, reducing net acceleration; unproven in flight

#5离子/霍尔效应电推器

conventional electric propulsion used on satellites and probes

离子和霍尔效应推进器是几十年来在卫星和探测器上使用的更小,经过充分证明的电动推进装置——例如,深空1号和黎明探测器在一段时间内使用离子推进进行大型三角洲-V操纵,美国航天局的NEXT离子推进器在地面试验中运行了超过48000小时.

尽管燃油效率非常高,推力还是很小——即使是迄今为止测试过的最强大的电动推进器(一台100千瓦级的巢式霍尔推进器),在实验室中只生产了约5.4N,这是场内的记录,但对于发射目的来说仍然微不足道.

对于一个空间飞机来说,电动推进器最好被作为轨道修饰器的辅助系统,一旦在空间中已经存在,而不是一种主要上升方法。它们的技术准备状态是本文审查的任何备选方案中最高的,但它们对发射的适用性是最低的。

比冲量: ~1,500–4,000 s (Hall/ion); up to ~8,000 s for some ion designs
推力重量比: Extremely low — e.g. 5 N of thrust for a 230 kg thruster (X3 Hall thruster)
准备状态（TRL）: 9 (widely flight-proven on satellites; high-power versions ~6)

优点

+The most fuel-efficient option in practice — flight-proven on many spacecraft
+Reliable and long-lived — some thrusters have run continuously for years
+Good for precision maneuvers, station-keeping, and augmenting mission flexibility once in orbit

缺点

–Ultra-low thrust (millinewtons to a few newtons) — useless for overcoming Earth's gravity quickly
–Orbital insertion would take days to weeks of continuous thrust — not feasible for a crewed launch
–Power demands exceed current spaceplane capability; limited to vacuum operation only

来源

这篇评论综合了公开的研究——这里没有任何内容受到限制或保密。

未决问题

?Is a combined-cycle approach actually the right near-term bet, or is there a stronger case for skipping straight to a simpler two-stage design?
?Which of these five options deserves the most additional research funding first?
?What would change this ranking if cost, not near-term feasibility, were the primary criterion?

同行评审，公开