How to calculate specific impulse Isp rocket engine (EN) classical rocket propulsion formula + base aerospace + base NASA JPL Pasadena + base NASA Marshall Huntsville Alabama + base NASA Kennedy Cape Canaveral + base NASA Glenn Cleveland + base NASA Johnson Houston Texas + base NASA Stennis Mississippi + base SpaceX Hawthorne California 13000 + base Blue Origin Kent Washington 11000 + base ULA United Launch Alliance Centennial Colorado 4000 + base Boeing Defense Space Saint Louis Missouri 145000 + base Lockheed Martin Bethesda Maryland 122000 + base Northrop Grumman Falls Church Virginia 95000 + base Aerojet Rocketdyne Sacramento California + base Sierra Space Louisville Colorado + base Rocket Lab Long Beach California + base Astranis San Francisco + base Relativity Space Long Beach + base Stoke Space Kent Washington + base Firefly Aerospace Cedar Park Texas + base Phantom Space Tucson Arizona + base ABL Space Systems El Segundo California + base AIAA American Institute Aeronautics Astronautics Reston Virginia + base ASE American Society Engineers + base AFRL Air Force Research Lab Wright-Patterson + base SwRI San Antonio Texas + base CEESI Colorado: Isp = v_e / g_0 = F / (m_dot * g_0) seconds + v_e effective exhaust velocity m/s + g_0 = 9.80665 m/s^2 + F thrust N + m_dot mass flow rate kg/s + classical reference world-leading.

Tsiolkovsky rocket equation: Delta_v = Isp*g_0*ln(m_0/m_f) + classical reference world-leading.

Propellant types Isp: solid SRB 240-280 s + RP-1/LOX 280-311 s Falcon 9 Merlin + LH2/LOX 410-460 s Saturn V SSME Vulcain + hypergolic UDMH/N2O4 280-340 s + LCH4/LOX 350-380 s SpaceX Raptor Blue Origin BE-4 + ion xenon 1500-10000 s GOCE Dawn + Hall 1500-2500 s + NTR 900 s + classical reference world-leading.

History: Konstantin Tsiolkovsky Russia 1903 Kaluga rocket equation 1903 + Encyclopedia Britannica + Russian classic centenario + classical reference world-leading; Robert Goddard USA 1919 Worcester Massachusetts first liquid rocket + American classic centenario + classical reference; Hermann Oberth Germany 1923 Munich Die Rakete zu den Planetenraumen + German classic centenario; Wernher von Braun Germany-USA 1942-1969 Peenemunde Huntsville V-2 + Saturn V Apollo 11 1969 + classical reference world-leading + classical American classic centenario; Sergei Korolev USSR 1957 Moscow Sputnik 1957 + Vostok Yuri Gagarin 1961.

USA aerospace research: NASA JPL Pasadena 6000 + NASA Marshall Huntsville + Saturn V Apollo + classical reference world-leading USA centenario; NASA Kennedy + Glenn + Johnson + Stennis; STScI Baltimore + SETI + Johns Hopkins APL; AFRL Wright-Patterson + Air Force propulsion; SwRI San Antonio + CEESI Colorado; MIT + Caltech + Stanford + UC Berkeley + Princeton + Cornell + Yale + Carnegie Mellon + Georgia Tech + Purdue + Penn State + Texas A&M + USC + UMich + UIUC; AIAA American Institute Aeronautics Astronautics Reston Virginia + classical reference world-leading USA centenario American classic.

USA space industry: SpaceX Hawthorne California 13000 + Falcon 9 Heavy Starship Crew Dragon Starlink + Merlin RP-1/LOX Isp 282 + Raptor LCH4/LOX Isp 350 + classical reference world-leading + American classic centenario Vorreiter; Blue Origin Kent Washington 11000 + New Glenn New Shepard + BE-4 LCH4/LOX + classical reference; ULA Centennial Colorado 4000 + Atlas V Delta IV Vulcan Centaur + RD-180 RD-181 + classical reference; Boeing Defense Space Saint Louis 145000 + Starliner CST-100 + classical reference world-leading; Lockheed Martin Bethesda 122000 + Orion + Lunar Gateway + Space Launch System SLS + classical reference world-leading; Northrop Grumman 95000 + Cygnus ISS + Antares + Pegasus XL + Castor SRB + classical reference; Aerojet Rocketdyne Sacramento California 4500 + AR1 RS-25 RS-68 J-2X RL10 + classical reference world-leading + American classic centenario; Sierra Space Louisville Colorado + Dream Chaser; Rocket Lab Long Beach California 2000 + Electron + Neutron + Rutherford engine; Relativity Space Long Beach + Aeon engine 3D-printed; Stoke Space Kent Washington + reusable LH2/LOX; Firefly Aerospace Cedar Park Texas + Alpha Reaver; ABL Space Systems El Segundo + RS1 + E2 engine; Phantom Space Tucson Arizona;

Astra Space Alameda California; Astranis + Planet Labs + Maxar + Spire Global; Voyager Space + Axiom Space + Made In Space; NASA Artemis Lunar Gateway HLS 2026 classical reference world-leading USA centenario.

Isp 1903 Tsiolkovsky formula

Isp = v_e/g_0 = F/(m_dot*g_0) seconds. Tsiolkovsky equation Delta_v = Isp*g_0*ln(m_0/m_f). Isp typical: solid 240-280 + kerosene 280-311 Merlin + LH2/LOX 410-460 SSME + hypergolic 280-340 + methane 350-380 Raptor BE-4 + ion 1500-10000 + Hall 1500-2500 + NTR 900 classical reference world-leading.

History 1903 Tsiolkovsky + 1919 Goddard + 1923 Oberth + 1942 von Braun

Tsiolkovsky Russia 1903 Kaluga + Goddard USA 1919 Worcester American classic centenario + Oberth Germany 1923 Munich + von Braun Germany-USA 1942-1969 Peenemunde Huntsville Saturn V Apollo 11 1969 + Korolev USSR 1957 Sputnik Vostok Gagarin 1961 + Newton 1687 Principia third law action-reaction classical reference world-leading.

Rocket engine Isp table

5 Isp examples

Example 1 SpaceX Falcon 9 Merlin RP-1/LOX: F=854 kN sea level + Isp=282 s + v_e=2766 m/s + Hawthorne 13000 + Falcon Heavy 27 engines classical reference world-leading USA centenario.

Example 2 SpaceX Raptor LCH4/LOX: F=2300 kN sea level + Isp=350 s + v_e=3434 m/s + Starship Super Heavy classical reference world-leading USA centenario.

Example 3 ULA Vulcan Centaur RL10 LH2/LOX: F=110 kN + Isp=465 s vacuum + v_e=4561 m/s + Aerojet Rocketdyne Sacramento + classical reference world-leading USA.

Example 4 NASA Saturn V J-2 LH2/LOX: F=1033 kN + Isp=421 s + Apollo 11 1969 + von Braun Marshall Huntsville classical reference world-leading USA centenario American classic Vorreiter.

Example 5 NASA Dawn ion thruster Xenon: F=0.092 N + Isp=3000 s + 11 years mission Vesta Ceres + Aerojet Rocketdyne classical reference world-leading USA centenario.

Isp model limits

Assumes complete combustion + optimal nozzle expansion + constant ambient pressure. Reality: nozzle expansion altitude-dependent + sea level vs vacuum 10-20% diff; combustion efficiency 95-99%; throat erosion SRB; specific heat ratio gamma; chamber pressure 50-300 bar; regenerative cooling Vulcain Merlin Raptor; film cooling; ablative SRB; staged combustion Raptor SSME RD-180; gas generator Merlin F-1; expander RL10; pressure-fed; aerospike plug; full-flow staged combustion Raptor SpaceX; throttle range 40-100%; multi-stage Saturn V 3 stages Falcon 9 stages; SRB strap-on; cryogenic LH2 -253 LOX -183 LCH4 -161 + Linde Cryogenics Air Products partner; storable hypergolic UDMH N2O4; green ASCENT AF-M315E HAN; Tsiolkovsky 1903 rocket equation; multi-stage advantage; Hohmann transfer Oberth effect Lagrange; missions Apollo 11 1969 Saturn V + Shuttle 1981-2011 + ISS + Falcon Heavy Crew Dragon Starship + Soyuz + Long March + Ariane 5 6 + Vega C + JAXA H3 + ISRO + DART NASA 2022 + Artemis NASA 2026 + JUICE 2031 ESA + Europa Clipper 2030 + Mars Sample Return 2030s classical reference world-leading USA centenario.

Common Isp errors

Confusing Isp seconds vs v_e m/s vs F N vs m_dot kg/s + Isp = v_e/g_0 NOT v_e*g_0 + g_0 = 9.80665 m/s^2 standard NOT local + sea level vs vacuum 10-20% diff + combustion efficiency 95-99% + SRB throat erosion + LH2/LOX cryogenic Linde Air Products + methane SpaceX Raptor BE-4 + hypergolic UDMH N2O4 storable + ion xenon GOCE Dawn + Hall Starlink + NTR NERVA DRACO + rocket equation Delta_v = Isp*g_0*ln(m_0/m_f) NOT Isp/g_0 + Tsiolkovsky 1903 + Goddard 1919 + Oberth 1923 + von Braun + Korolev + Newton 1687 third law + multi-stage mass ratio + Hohmann Oberth Lagrange + missions Apollo Shuttle ISS Falcon Crew Dragon Starship Soyuz Ariane Vega + units Isp s + v_e m/s + F N kN MN + m_dot kg/s + aerospike plug + staged combustion + gas generator + expander + regenerative film ablative + green propellant + launcher Falcon 9 Heavy Starship Super Heavy.

Isp applications USA

1. SpaceX Hawthorne 13000 Falcon 9 Heavy Starship Crew Dragon Starlink Merlin Raptor + Blue Origin Kent 11000 New Glenn New Shepard BE-4 + ULA Centennial 4000 Atlas Delta Vulcan Centaur + Aerojet Rocketdyne Sacramento 4500 AR1 RS-25 RS-68 J-2X RL10 classical reference world-leading USA centenario American classic Vorreiter
2. NASA JPL Pasadena 6000 + NASA Marshall Huntsville Saturn V Apollo + Kennedy Glenn Johnson Stennis + STScI Baltimore + SETI + Johns Hopkins APL + AFRL Wright-Patterson + SwRI CEESI classical reference world-leading USA centenario American classic
3. Boeing Defense Saint Louis 145000 Starliner CST-100 + Lockheed Martin Bethesda 122000 Orion Lunar Gateway SLS + Northrop Grumman 95000 Cygnus Antares Pegasus Castor SRB + Sierra Space Dream Chaser + Rocket Lab Electron Neutron Rutherford classical reference world-leading USA centenario
4. Relativity Space Aeon 3D-printed + Stoke Space reusable LH2/LOX + Firefly Aerospace Alpha Reaver + ABL Space RS1 E2 + Phantom Space + Astra Space + Astranis + Planet Labs + Maxar + Spire Global + Voyager Space + Axiom Space + Relativity classical reference world-leading USA centenario American classic Vorreiter Space Industry
5. NASA Artemis Lunar Gateway HLS 2026 + DART 2022 + Europa Clipper 2030 + Mars Sample Return 2030s + Lucy 2027 + Psyche 2029 + Voyager Cassini Galileo + AIAA Reston Virginia ASE + MIT Caltech Stanford Berkeley Princeton Harvard Cornell Yale Johns Hopkins Carnegie Mellon Georgia Tech Purdue Penn State Texas A&M USC UMich UIUC classical reference world-leading USA centenario American classic propulsion

Updated July 2026