Orbital propellant depot: Difference between revisions
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NASA administrator Mike Griffin commented at the 52nd AAS Annual Meeting in Houston, November 2005, that "...at a conservatively low government price of $10,000/kg in LEO, 250 MT of fuel for two missions per year is worth $2.5 B, at government rates."<ref>http://www.nasa.gov/pdf/138033main_griffin_aas1.pdf Remarks For AIAA Space 2005 Conference & Exhibition</ref> |
NASA administrator Mike Griffin commented at the 52nd AAS Annual Meeting in Houston, November 2005, that "...at a conservatively low government price of $10,000/kg in LEO, 250 MT of fuel for two missions per year is worth $2.5 B, at government rates."<ref>http://www.nasa.gov/pdf/138033main_griffin_aas1.pdf Remarks For AIAA Space 2005 Conference & Exhibition</ref> |
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== History and Plans == |
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The Air Force and United Launch Alliance performed an experimental demonstration of propellant settling on the DMSP launch[http://www.ulalaunch.com/site/docs/publications/SuccessfulFlightDemonstrationConductedbytheAirForceandUnitedLaunchAllianceWillEnhanceSpaceTransportation_.pdf]. The ULA is also currently planning the CRYOTE testbed for demonstrating a number of technologies needed for cryogenic propellant depots. |
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== Boil-off mitigation == |
== Boil-off mitigation == |
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Revision as of 04:23, 5 March 2010
An on-orbit propellant depot would allow spacecraft to be fueled in space. Launching a spacecraft separately from some of its propellant enables missions with more massive payloads. The spacecraft would conduct a space rendezvous with the depot and then transfer propellant used for subsequent orbital maneuvers.
Potential users of in-orbit refuelling and storage facilities include space agencies, defense ministries and communications satellite companies.
The depots are likely to be placed in low Earth orbit (LEO) and either on the way to the Moon at Earth-Moon Lagrange point 1 (EML1) or behind the Moon at EML2. Proposals also exist to place depots in lunar and Mars orbit.
Rockets using cryogenic fuels like liquid hydrogen and liquid oxygen (LOX) suffer from a problem called "boil off". The boil off from only a few days delay can result in the vehicle carrying insufficient fuel, potentially resulting in a mission abort. Since they are not mass critical, depots can protect their propellant with sun shields and refrigeration equipment. Methane normally does not need cooling in Earth orbit.
Propellants used by ion thrusters include xenon, bismuth and argon.
The upper stage of the SpaceX Falcon 9 chemical rockets use the Liquid rocket propellants LOX and the RP-1 version of kerosene. Other chemicals are used for in-space manoeuvring.[1]
The crew and passengers on reusable orbital transfer vehicles may purchase consumables like food, water and oxygen gas.
NASA administrator Mike Griffin commented at the 52nd AAS Annual Meeting in Houston, November 2005, that "...at a conservatively low government price of $10,000/kg in LEO, 250 MT of fuel for two missions per year is worth $2.5 B, at government rates."[2]
History and Plans
The Air Force and United Launch Alliance performed an experimental demonstration of propellant settling on the DMSP launch[1]. The ULA is also currently planning the CRYOTE testbed for demonstrating a number of technologies needed for cryogenic propellant depots.
Boil-off mitigation
For a propellant depot to effectively store cryogenic fluids, boil-off caused by heating from solar and other sources must be mitigated or eliminated.
Sun shields
United Launch Alliance (ULA) has proposed a depot which would use a conical sun shield to protect the cryogenic propellant from solar and Earth radiation. The open end of the cone allows residual heat to radiate to deep space.[3]
Propellant settling
Transfer of liquid propellants in microgravity is complicated by the uncertain distribution of liquid and gasses within a tank. Propellant settling at an in-space depot is thus more challenging than in even a slight gravity field. ULA plans to use the the DMSP-18 mission to flight-test centrifugal propellant settling as a cryogenic fuel management technique that might be used in future propellant depots.[4]
Propellant transfer
As part of the Orbital Express mission in 2007, hydrazine propellant was successfully transferred between a Boeing servicing spacecraft and a Ball Aerospace serviceable client spacecraft.[5] Since no crew were present on either spacecraft, this was reported as the first autonomous spacecraft-to-spacecraft fluid transfer.
Refilling
After propellant has been transferred to a customer the depot's tanks will need refilling. Organizing the construction and launch of the tanker rockets bearing the new fuel is the responsibility of the propellant depot's operator. Since space agencies like NASA hope to be purchasers rather than owners, possible operators include the aerospace company that constructed the depot, manufactures of the rockets, a specialist space depot company or an oil company that refines the propellant. By using several tanker rockets the tankers can be smaller than the depot and larger than the spacecraft they are intended to resupply.
Difficulties of propellant depots
Propellant depots are of little use when the depot is in a different orbital plane than the target orbit, except at very high altitudes, as the delta-v to change planes is typically extremely high.
Propellant depot's orbital planes are susceptible to perturbations; and over a long period can tend to precess (equatorial depots are more stable).
Depots in LEO are subject to airdrag and this can require propellant use to maintain the orbit, which can increase costs, or can impose timing constraint on launch timing that may be difficult to guarantee due to launch reliability.
See also
References
- ^ http://www.spacex.com/Falcon9UsersGuide_2009.pdf Falcon 9 User Guide
- ^ http://www.nasa.gov/pdf/138033main_griffin_aas1.pdf Remarks For AIAA Space 2005 Conference & Exhibition
- ^ Bernard F. Kutter; et al. (2008). "A Practical, Affordable Cryogenic Propellant Depot Based on ULA's Flight Experience" (PDF). AIAA.
{{cite web}}: Explicit use of et al. in:|author=(help) - ^ Jon Goff; et al. (2009). "Realistic Near-Term Propellant Depots" (PDF). American Institute of Aeronautics and Astronautics.
{{cite web}}: Explicit use of et al. in:|author=(help) - ^ "Boeing Orbital Express Conducts First Autonomous Spacecraft-to-Spacecraft Fluid and Component Transfer". Boeing. April 17, 2007.
- "Presentation of Boeing's proposed LEO Propellant Depot" (PDF). USRA.edu.