Menu
Home
People
Places
Arts
History
Plants & Animals
Science
Life & Culture
Technology
Reference.org
Cryogenic rocket engine
open-in-new
<h2 id="cryogenic-propellants">Cryogenic propellants</h2> <p>Rocket engines need high <a href="/facts/Mass_flow_rate/v2DrbGvq">mass flow rates</a> of both oxidizer and fuel to generate useful thrust. Oxygen, the simplest and most common oxidizer, is in the <a href="/facts/Gas_phase/NkHXDdN3">gas phase</a> at <a href="/facts/Standard_temperature_and_pressure/JhJv9KFJ">standard temperature and pressure</a>, as is hydrogen, the simplest fuel. While it is possible to store propellants as pressurized gases, this would require large, heavy tanks that would make achieving <a href="/facts/Orbital_spaceflight/xdzKmkvt">orbital spaceflight</a> difficult if not impossible. On the other hand, if the propellants are cooled sufficiently, they <a href="/facts/Phase_diagram/rcemFgW0">exist</a> in the <a href="/facts/Liquid_phase/t9GkLWzt">liquid phase</a> at higher density and lower pressure, simplifying tankage. These <a href="/facts/Cryogenic/cw7dHAkp">cryogenic</a> temperatures vary depending on the propellant, with <a href="/facts/Liquid_oxygen/qnI0KDTb">liquid oxygen</a> existing below −183 °C (−297.4 °F; 90.1 K) and <a href="/facts/Liquid_hydrogen/Vpk3Gb8P">liquid hydrogen</a> below −253 °C (−423.4 °F; 20.1 K). Since one or more of the propellants is in the liquid phase, all cryogenic rocket engines are by definition <a href="/facts/Liquid-propellant_rocket/TAonrVDn">liquid-propellant rocket engines</a>.<a class="footnote-ref" id="fnref:3" href="#fn:3"><sup>3</sup></a> </p><p>Various cryogenic fuel-oxidizer combinations have been tried, but the combination of liquid hydrogen (<a href="/facts/LH2/Vpk3Gb8P">LH2</a>) fuel and the liquid oxygen (<a href="/facts/LOX/qnI0KDTb">LOX</a>) oxidizer is one of the most widely used.<a class="footnote-ref" id="fnref:4" href="#fn:4"><sup>4</sup></a><a class="footnote-ref" id="fnref:5" href="#fn:5"><sup>5</sup></a> Both components are easily and cheaply available, and when burned have one of the highest <a href="/facts/Enthalpy/bBou8lCE">enthalpy</a> releases in <a href="/facts/Combustion/ohQoWj8z">combustion</a>,<a class="footnote-ref" id="fnref:6" href="#fn:6"><sup>6</sup></a> producing a <a href="/facts/Specific_impulse/JKGgw2I4">specific impulse</a> of up to 450 s at an <a href="/facts/Effective_exhaust_velocity/JKGgw2I4">effective exhaust velocity</a> of 4.4 kilometres per second (2.7 mi/s; Mach 13). </p> <h2 id="components-and-combustion-cycles">Components and combustion cycles</h2> <p>The major components of a cryogenic rocket engine are the <a href="/facts/Combustion_chamber/FNqjDrN8">combustion chamber</a>, <a href="/facts/Pyrotechnic_initiator/BfUDd0PM">pyrotechnic initiator</a>, fuel injector, fuel and oxidizer <a href="/facts/Turbopump/D6L2o2Yk">turbopumps</a>, cryo valves, regulators, the fuel tanks, and <a href="/facts/Rocket_engine_nozzle/K4kHCmFX">rocket engine nozzle</a>. In terms of feeding propellants to the combustion chamber, cryogenic rocket engines are almost exclusively <a href="/facts/Pump-fed_engine/TAonrVDn">pump-fed</a>. Pump-fed engines work in a <a href="/facts/Gas-generator_cycle_(rocket)/TxVnVPuV">gas-generator cycle</a>, a <a href="/facts/Staged_combustion_cycle_(rocket)/eINPGPr5">staged-combustion cycle</a>, or an <a href="/facts/Expander_cycle/vUu8MYyj">expander cycle</a>. Gas-generator engines tend to be used on booster engines due to their lower efficiency, staged-combustion engines can fill both roles at the cost of greater complexity, and expander engines are exclusively used on upper stages due to their low thrust. </p> <h2 id="loxlh2-rocket-engines-by-country">LOX+LH2 rocket engines by country</h2> <p>Currently, six countries have successfully developed and deployed cryogenic rocket engines: </p> <table><tbody><tr><th>Country</th><th>Engine</th><th>Cycle</th><th>Use</th><th>Status</th></tr><tr><td rowspan="7"> <a href="/facts/United_States/P0sCdLe5">United States</a></td><td><a href="/facts/RL-10/xNrFPF99">RL-10</a></td><td><a href="/facts/Expander_cycle/vUu8MYyj">Expander</a></td><td>Upper stage</td><td>Active</td></tr><tr><td><a href="/facts/Rocketdyne_J-2/oNtBBUD7">J-2</a></td><td><a href="/facts/Gas-generator_cycle/TxVnVPuV">Gas-generator</a></td><td>lower stage</td><td>Retired</td></tr><tr><td><a href="/facts/Space_Shuttle_main_engine/vGkj6Vxm">SSME (aka RS-25)</a></td><td><a href="/facts/Staged_combustion_cycle/eINPGPr5">Staged combustion</a></td><td>Booster</td><td>Active</td></tr><tr><td><a href="/facts/RS-68/Y56hGjG8">RS-68</a></td><td><a href="/facts/Gas-generator_cycle/TxVnVPuV">Gas-generator</a></td><td>Booster</td><td>Retired</td></tr><tr><td><a href="/facts/BE-3/m4yJN4ma">BE-3</a></td><td><a href="/facts/Combustion_tap-off_cycle/tm8UUHvx">Combustion tap-off</a></td><td><a href="/facts/New_Shepard/QpzbYepM">New Shepard</a></td><td>Active</td></tr><tr><td><a href="/facts/BE-7/CxFvEmDr">BE-7</a></td><td><a href="/facts/Expander_cycle/vUu8MYyj">Dual Expander</a></td><td><a href="/facts/Blue_Moon_(spacecraft)/7eHatV7v">Blue Moon (spacecraft)</a></td><td>Active</td></tr><tr><td><a href="/facts/J-2X/JoWwCTkg">J-2X</a></td><td><a href="/facts/Gas-generator_cycle/TxVnVPuV">Gas-generator</a></td><td>Upper stage</td><td>Developmental</td></tr><tr><td rowspan="3"> <a href="/facts/Russia/jfkCwyxn">Russia</a></td><td><a href="/facts/RD-0120/J9WTame7">RD-0120</a></td><td><a href="/facts/Staged_combustion_cycle/eINPGPr5">Staged combustion</a></td><td>Booster</td><td>Retired</td></tr><tr><td><a href="/facts/KVD-1/76eMRN7K">KVD-1</a></td><td><a href="/facts/Staged_combustion_cycle/eINPGPr5">Staged combustion</a></td><td>Upper stage</td><td>Retired</td></tr><tr><td><a href="/facts/RD-0146/tLuke2sa">RD-0146</a></td><td><a href="/facts/Expander_cycle/vUu8MYyj">Expander</a></td><td>Upper stage</td><td>Developmental</td></tr><tr><td rowspan="3"> <a href="/facts/France/CxIeIKM3">France</a></td><td><a href="/facts/Vulcain_(rocket_engine)/pe01NawI">Vulcain</a></td><td><a href="/facts/Gas-generator_cycle/TxVnVPuV">Gas-generator</a></td><td>Booster</td><td>Active</td></tr><tr><td><a href="/facts/HM7B/LhcJ3f3y">HM7B</a></td><td><a href="/facts/Gas-generator_cycle/TxVnVPuV">Gas-generator</a></td><td>Upper stage</td><td>Retired</td></tr><tr><td><a href="/facts/Vinci_(rocket_engine)/619Pf33Q">Vinci</a></td><td><a href="/facts/Expander_cycle/vUu8MYyj">Expander</a></td><td>Upper stage</td><td>Active</td></tr><tr><td rowspan="2"> <a href="/facts/India/1kKHcnxM">India</a></td><td><a href="/facts/CE-7.5/BhNXKT7y">CE-7.5</a></td><td><a href="/facts/Staged_combustion_cycle/eINPGPr5">Staged combustion</a></td><td>Upper stage</td><td>Active</td></tr><tr><td><a href="/facts/CE-20/Im5eoenA">CE-20</a></td><td><a href="/facts/Gas-generator_cycle/TxVnVPuV">Gas-generator</a></td><td>Upper stage</td><td>Active</td></tr><tr><td rowspan="4"> <a href="/facts/China/lTjIXY5p">China</a></td><td><a href="/facts/YF-73/TyE0UFLI">YF-73</a></td><td><a href="/facts/Gas-generator_cycle/TxVnVPuV">Gas-generator</a></td><td>Upper stage</td><td>Retired</td></tr><tr><td><a href="/facts/YF-75/5qTGIWoG">YF-75</a></td><td><a href="/facts/Gas-generator_cycle/TxVnVPuV">Gas-generator</a></td><td>Upper stage</td><td>Active</td></tr><tr><td><a href="/facts/YF-75D/C9WkYyhI">YF-75D</a></td><td><a href="/facts/Expander_cycle/vUu8MYyj">Expander cycle</a></td><td>Upper stage</td><td>Active</td></tr><tr><td><a href="/facts/YF-77/T5n0YJf5">YF-77</a></td><td><a href="/facts/Gas-generator_cycle/TxVnVPuV">Gas-generator</a></td><td>Booster</td><td>Active</td></tr><tr><td rowspan="3"> <a href="/facts/Japan/U5mz0SRT">Japan</a></td><td><a href="/facts/LE-7/xuLBI2Hn">LE-7 / 7A</a><a class="footnote-ref" id="fnref:7" href="#fn:7"><sup>7</sup></a></td><td><a href="/facts/Staged_combustion_cycle/eINPGPr5">Staged combustion</a></td><td>Booster</td><td>Active</td></tr><tr><td><a href="/facts/LE-5/CmIB1NHS">LE-5 / 5A / 5B</a><a class="footnote-ref" id="fnref:8" href="#fn:8"><sup>8</sup></a></td><td><a href="/facts/Gas-generator_cycle/TxVnVPuV">Gas-generator</a>(LE-5)<a href="/facts/Expander_cycle/vUu8MYyj">Expander bleed</a>(5A/5B)</td><td>Upper stage</td><td>Active</td></tr><tr><td><a href="/facts/LE-9/UhDX2T0e">LE-9</a><a class="footnote-ref" id="fnref:9" href="#fn:9"><sup>9</sup></a></td><td><a href="/facts/Expander_cycle/vUu8MYyj">Expander bleed</a></td><td>Booster</td><td>Active</td></tr></tbody></table> <h2 id="comparison-of-first-stage-cryogenic-rocket-engines">Comparison of first stage cryogenic rocket engines</h2> <table><tbody><tr><th>model</th><th><a href="/facts/Space_Shuttle_main_engine/vGkj6Vxm">SSME/RS-25</a></th><th><a href="/facts/LE-7A/xuLBI2Hn">LE-7A</a></th><th><a href="/facts/RD-0120/J9WTame7">RD-0120</a></th><th><a href="/facts/Vulcain_(rocket_engine)/pe01NawI">Vulcain 2</a></th><th><a href="/facts/RS-68/Y56hGjG8">RS-68</a></th><th><a href="/facts/YF-77/T5n0YJf5">YF-77</a></th></tr><tr><th>Country of origin</th><td> <a href="/facts/United_States/P0sCdLe5">United States</a></td><td> <a href="/facts/Japan/U5mz0SRT">Japan</a></td><td> <a href="/facts/Soviet_Union/m7wWsPto">Soviet Union</a></td><td> <a href="/facts/France/CxIeIKM3">France</a></td><td> <a href="/facts/United_States/P0sCdLe5">United States</a></td><td> <a href="/facts/China/lTjIXY5p">China</a></td></tr><tr><th>Cycle</th><td><a href="/facts/Staged_combustion_cycle/eINPGPr5">Staged combustion</a></td><td><a href="/facts/Staged_combustion_cycle/eINPGPr5">Staged combustion</a></td><td><a href="/facts/Staged_combustion_cycle/eINPGPr5">Staged combustion</a></td><td><a href="/facts/Gas-generator_cycle/TxVnVPuV">Gas-generator</a></td><td><a href="/facts/Gas-generator_cycle/TxVnVPuV">Gas-generator</a></td><td><a href="/facts/Gas-generator_cycle/TxVnVPuV">Gas-generator</a></td></tr><tr><th>Length</th><td>4.24 m</td><td>3.7 m</td><td>4.55 m</td><td>3.00 m</td><td>5.20 m</td><td>2.6 m</td></tr><tr><th>Diameter</th><td>1.63 m</td><td>1.82 m</td><td>2.42 m</td><td>1.76 m</td><td>2.43 m</td><td>1.5 m</td></tr><tr><th>Dry weight</th><td>3,177 kg</td><td>1,832 kg</td><td>3,449 kg</td><td>1,686 kg</td><td>6,696 kg</td><td>1,054 kg</td></tr><tr><th>Propellant</th><td><a href="/facts/LOX/qnI0KDTb">LOX</a>/<a href="/facts/LH2/Vpk3Gb8P">LH2</a></td><td><a href="/facts/LOX/qnI0KDTb">LOX</a>/<a href="/facts/LH2/Vpk3Gb8P">LH2</a></td><td><a href="/facts/LOX/qnI0KDTb">LOX</a>/<a href="/facts/LH2/Vpk3Gb8P">LH2</a></td><td><a href="/facts/LOX/qnI0KDTb">LOX</a>/<a href="/facts/LH2/Vpk3Gb8P">LH2</a></td><td><a href="/facts/LOX/qnI0KDTb">LOX</a>/<a href="/facts/LH2/Vpk3Gb8P">LH2</a></td><td><a href="/facts/LOX/qnI0KDTb">LOX</a>/<a href="/facts/LH2/Vpk3Gb8P">LH2</a></td></tr><tr><th>Chamber pressure</th><td>18.9 MPa</td><td>12.0MPa</td><td>21.8 MPa</td><td>11.7 MPa</td><td>9.7 MPa</td><td>10.1 MPa</td></tr><tr><th>Isp (vac.)</th><td>453 sec</td><td>440 sec</td><td>454 sec</td><td>433 sec</td><td>409 sec</td><td>428 sec</td></tr><tr><th>Thrust (vac.)</th><td>2.278MN</td><td>1.098MN</td><td>1.961MN</td><td>1.120MN</td><td>3.37MN</td><td>0.7MN</td></tr><tr><th>Thrust (SL)</th><td>1.817MN</td><td>0.87MN</td><td>1.517MN</td><td>0.800MN</td><td>2.949MN</td><td>0.518MN</td></tr><tr><th>Used in</th><td><a href="/facts/Space_Shuttle/7BoyetEv">Space Shuttle</a><a href="/facts/Space_Launch_System/DbGCgH1W">Space Launch System</a></td><td><a href="/facts/H-IIA/W9Q48DHS">H-IIA</a><a href="/facts/H-IIB/k5CMQBXm">H-IIB</a></td><td><a href="/facts/Energia_(rocket)/snJSoyMA">Energia</a></td><td><a href="/facts/Ariane_5/H78wlLG4">Ariane 5</a></td><td><a href="/facts/Delta_IV/QWun0yHh">Delta IV</a></td><td><a href="/facts/Long_March_5/rzP8BRBA">Long March 5</a></td></tr></tbody></table> <h2 id="comparison-of-upper-stage-cryogenic-rocket-engines">Comparison of upper stage cryogenic rocket engines</h2> Specifications<table><tbody><tr><th> </th><th><a href="/facts/RL-10/xNrFPF99">RL-10</a></th><th><a href="/facts/HM7B/LhcJ3f3y">HM7B</a></th><th><a href="/facts/Vinci_(rocket_engine)/619Pf33Q">Vinci</a></th><th><a href="/facts/KVD-1/76eMRN7K">KVD-1</a></th><th><a href="/facts/CE-7.5/BhNXKT7y">CE-7.5</a></th><th><a href="/facts/CE-20/Im5eoenA">CE-20</a></th><th><a href="/facts/YF-73/TyE0UFLI">YF-73</a></th><th><a href="/facts/YF-75/5qTGIWoG">YF-75</a></th><th><a href="/facts/YF-75D/C9WkYyhI">YF-75D</a></th><th><a href="/facts/RD-0146/tLuke2sa">RD-0146</a></th><th>ES-702</th><th>ES-1001</th><th><a href="/facts/LE-5/CmIB1NHS">LE-5</a></th><th><a href="/facts/LE-5A/CmIB1NHS">LE-5A</a></th><th><a href="/facts/LE-5B/CmIB1NHS">LE-5B</a></th></tr><tr><th>Country of origin</th><td> <a href="/facts/United_States/P0sCdLe5">United States</a></td><td> <a href="/facts/France/CxIeIKM3">France</a></td><td> <a href="/facts/France/CxIeIKM3">France</a></td><td> <a href="/facts/Soviet_Union/m7wWsPto">Soviet Union</a></td><td> <a href="/facts/India/1kKHcnxM">India</a></td><td> <a href="/facts/India/1kKHcnxM">India</a></td><td> <a href="/facts/China/lTjIXY5p">China</a></td><td> <a href="/facts/China/lTjIXY5p">China</a></td><td> <a href="/facts/China/lTjIXY5p">China</a></td><td> <a href="/facts/Russia/jfkCwyxn">Russia</a></td><td> <a href="/facts/Japan/U5mz0SRT">Japan</a></td><td> <a href="/facts/Japan/U5mz0SRT">Japan</a></td><td> <a href="/facts/Japan/U5mz0SRT">Japan</a></td><td> <a href="/facts/Japan/U5mz0SRT">Japan</a></td><td> <a href="/facts/Japan/U5mz0SRT">Japan</a></td></tr><tr><th>Cycle</th><td><a href="/facts/Expander_cycle/vUu8MYyj">Expander</a></td><td><a href="/facts/Gas-generator_cycle/TxVnVPuV">Gas-generator</a></td><td><a href="/facts/Expander_cycle/vUu8MYyj">Expander</a></td><td><a href="/facts/Staged_combustion_cycle/eINPGPr5">Staged combustion</a></td><td><a href="/facts/Staged_combustion_cycle/eINPGPr5">Staged combustion</a></td><td><a href="/facts/Gas-generator_cycle/TxVnVPuV">Gas-generator</a></td><td><a href="/facts/Gas-generator_cycle/TxVnVPuV">Gas-generator</a></td><td><a href="/facts/Gas-generator_cycle/TxVnVPuV">Gas-generator</a></td><td><a href="/facts/Expander_cycle/vUu8MYyj">Expander</a></td><td><a href="/facts/Expander_cycle/vUu8MYyj">Expander</a></td><td><a href="/facts/Gas-generator_cycle/TxVnVPuV">Gas-generator</a></td><td><a href="/facts/Gas-generator_cycle/TxVnVPuV">Gas-generator</a></td><td><a href="/facts/Gas-generator_cycle/TxVnVPuV">Gas-generator</a></td><td><a href="/facts/Expander_cycle/vUu8MYyj">Expander bleed cycle</a>（Nozzle Expander）</td><td><a href="/facts/Expander_cycle/vUu8MYyj">Expander bleed cycle</a>（Chamber Expander）</td></tr><tr><th>Thrust (vac.)</th><td>66.7 kN (15,000 lbf)</td><td>62.7 kN</td><td>180 kN</td><td>69.6 kN</td><td>73 kN</td><td>186.36 kN</td><td>44.15 kN</td><td>83.585 kN</td><td>88.36 kN</td><td>98.1 kN (22,054 lbf)</td><td>68.6 kN (7.0 tf)<a class="footnote-ref" id="fnref:10" href="#fn:10"><sup>10</sup></a></td><td>98 kN (10.0 tf)<a class="footnote-ref" id="fnref:11" href="#fn:11"><sup>11</sup></a></td><td>102.9 kN (10.5 tf)</td><td>r121.5 kN (12.4 tf)</td><td>137.2 kN (14 tf)</td></tr><tr><th>Mixture ratio</th><td>5.5:1 or 5.88:1</td><td>5.0</td><td>5.8</td><td></td><td></td><td>5.05</td><td>5.0</td><td>5.2</td><td>6.0</td><td></td><td>5.2</td><td>6.0</td><td>5.5</td><td>5</td><td>5</td></tr><tr><th>Nozzle ratio</th><td>40</td><td>83.1</td><td></td><td></td><td></td><td>100</td><td>40</td><td>80</td><td>80</td><td></td><td>40</td><td>40</td><td>140</td><td>130</td><td>110</td></tr><tr><th><a href="/facts/Specific_impulse/JKGgw2I4">Isp</a> (vac.)</th><td>433</td><td>444.2</td><td>465</td><td>462</td><td>454</td><td>442</td><td>420</td><td>438</td><td>442.6</td><td>463</td><td>425<a class="footnote-ref" id="fnref:12" href="#fn:12"><sup>12</sup></a></td><td>425<a class="footnote-ref" id="fnref:13" href="#fn:13"><sup>13</sup></a></td><td>450</td><td>452</td><td>447</td></tr><tr><th>Chamber pressure :MPa</th><td>2.35</td><td>3.5</td><td>6.1</td><td>5.6</td><td>5.8</td><td>6.0</td><td>2.59</td><td>3.68</td><td>4.1</td><td>5.9</td><td>2.45</td><td>3.51</td><td>3.65</td><td>3.98</td><td>3.58</td></tr><tr><th>LH2 TP rpm</th><td></td><td></td><td>90,000</td><td></td><td></td><td></td><td></td><td>42,000</td><td>65,000</td><td>125,000</td><td>41,000</td><td>46,310</td><td>50,000</td><td>51,000</td><td>52,000</td></tr><tr><th>LOX TP rpm</th><td></td><td></td><td>18,000</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>16,680</td><td>21,080</td><td>16,000</td><td>17,000</td><td>18,000</td></tr><tr><th>Length m</th><td>1.73</td><td>1.8</td><td>2.2~4.2</td><td>2.14</td><td>2.14</td><td></td><td>1.44</td><td>2.8</td><td></td><td>2.2</td><td></td><td></td><td>2.68</td><td>2.69</td><td>2.79</td></tr><tr><th>Dry weight kg</th><td>135</td><td>165</td><td>550</td><td>282</td><td>435</td><td>558</td><td>236</td><td>245</td><td>265</td><td>242</td><td>255.8</td><td>259.4</td><td>255</td><td>248</td><td>285</td></tr></tbody></table> <h2 id="external-links">External links</h2> <ul><li><a href="https://web.archive.org/web/20120204144940/http://www.astronautix.com/engines/rl10b2.htm">USA's Cryogenic Rocket engine RL10B-2</a></li> <li><a href="http://www.lpre.de/energomash/RD-170/index.htm">Russian Cryogenic Rocket Engines</a></li> <li><a href="https://www.blueorigin.com/engines/be-7">[1]</a></li></ul> <h2 id="references">References</h2> <ol> <li id="fn:1"><p>Bilstein, Roger E. (1995). Stages to Saturn: A Technological History of the Apollo/Saturn Launch Vehicles (NASA SP-4206) (The NASA History Series). NASA History Office. pp. 89–91. ISBN 0-7881-8186-6. <a href="0-7881-8186-6" target="_blank">0-7881-8186-6</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li> <li id="fn:2"><p>Bilstein, Roger E. (1995). Stages to Saturn: A Technological History of the Apollo/Saturn Launch Vehicles (NASA SP-4206) (The NASA History Series). NASA History Office. pp. 89–91. ISBN 0-7881-8186-6. <a href="0-7881-8186-6" target="_blank">0-7881-8186-6</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li> <li id="fn:3"><p>Biblarz, Oscar; Sutton, George H. (2009). Rocket Propulsion Elements. New York: Wiley. p. 597. ISBN 978-0-470-08024-5. <a href="978-0-470-08024-5" target="_blank">978-0-470-08024-5</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li> <li id="fn:4"><p>Bilstein, Roger E. (1995). Stages to Saturn: A Technological History of the Apollo/Saturn Launch Vehicles (NASA SP-4206) (The NASA History Series). NASA History Office. pp. 89–91. ISBN 0-7881-8186-6. <a href="0-7881-8186-6" target="_blank">0-7881-8186-6</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li> <li id="fn:5"><p>The liquefaction temperature of oxygen is 89 kelvins, and at this temperature it has a density of 1.14 kg/L. For hydrogen it is 20 K, just above absolute zero, and has a density of 0.07 kg/L. <a href="/wiki/Kelvin" target="_blank">/wiki/Kelvin</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></p></li> <li id="fn:6"><p>Biswas, S. (2000). Cosmic perspectives in space physics. Bruxelles: Kluwer. p. 23. ISBN 0-7923-5813-9. "... [LH2+LOX] has almost the highest specific impulse." <a href="0-7923-5813-9" target="_blank">0-7923-5813-9</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></p></li> <li id="fn:7"><p>"Le-7A｜エンジン｜H-Iiaロケット｜ロケット｜Jaxa 宇宙輸送技術部門". <a href="https://www.rocket.jaxa.jp/rocket/engine/le7/" target="_blank">https://www.rocket.jaxa.jp/rocket/engine/le7/</a> <a href="#fnref:7" class="footnote-back-ref">↩</a></p></li> <li id="fn:8"><p>"Le-5B｜エンジン｜H-Iiaロケット｜ロケット｜Jaxa 宇宙輸送技術部門". <a href="https://www.rocket.jaxa.jp/rocket/engine/le5b/" target="_blank">https://www.rocket.jaxa.jp/rocket/engine/le5b/</a> <a href="#fnref:8" class="footnote-back-ref">↩</a></p></li> <li id="fn:9"><p>"Le-9｜エンジン｜H3ロケット｜ロケット｜Jaxa 宇宙輸送技術部門". <a href="https://www.rocket.jaxa.jp/rocket/engine/le9/" target="_blank">https://www.rocket.jaxa.jp/rocket/engine/le9/</a> <a href="#fnref:9" class="footnote-back-ref">↩</a></p></li> <li id="fn:10"><p>without nozzle 48.52kN (4.9 tf) <a href="#fnref:10" class="footnote-back-ref">↩</a></p></li> <li id="fn:11"><p>without nozzle 66.64kN (6.8 tf) <a href="#fnref:11" class="footnote-back-ref">↩</a></p></li> <li id="fn:12"><p>without nozzle 286.8 <a href="#fnref:12" class="footnote-back-ref">↩</a></p></li> <li id="fn:13"><p>without nozzle 291.6 <a href="#fnref:13" class="footnote-back-ref">↩</a></p></li> </ol>